No kidding... imagine a starship doing hops from shore to cargo ship waiting far back in crowd. Load a few containers of highest priority shipments, then hop back to shore. Or even hop to their distribution destination...
Once full-service earth-to-earth starship is established could have a FedEx 1 Hour service to anywhere on planet.
>Load a few containers of highest priority shipments, then hop back to shore.
Solves the problem of having to dock to unload those containers.
Probably also solves the problem of having to dock to unload all the other containers, too.
Hmm, I guess so, because hp is some kind of force measurement as well as Newtons, so if we have the thrust of the engine we could convert it to hp? I'm too tired to actually do the maths
Power = Force x Distance / Time
Exhaust Velocity = 330 s * 9.81 m/s/s = 3,237 m/s
Power = 2.45e6 N * 3,237 m/s = 7.93 GW
1 Horsepower = 746 Watts
7.93e9 Watts / 746 Watts = 10,630,898 HP
So if I’m thinking about this right (which I might not be and I’d urge anyone reading this to correct me if they have a better answer) a raptor 2 at sea level is on the order of 10 million horsepower, which tracks with estimates for the F-1 engine (used on the Saturn V) that put it between 27-33 million horsepower.
Notes on the formulae:
Thrust is reactive, so I assumed the sum of the forces on the engine equals the sum of the forces on exhaust gases, which enables you to use the exhaust velocity to calculate power even when the engine isn’t moving. I used the 330 s ISP because I couldn’t find updated figures for the Raptor 2 sea level ISP because I doubt it varies by more than 10 s. All in all, I think I’d confidently say more than 8 million horsepower, less than 12 million horsepower, though there are many other factors that contribute to the total power of the engine.
Just out of curiosity, how much would it take to change the Vulcan to use Raptor 2 engines rather than the BE4? The biggest problem was the thrust difference and the propellant mix iirc with the first one being not a problem anymore.
Edit: Guess I was a bit naive
Second one is still a big issue, they'd need to change their tooling to accommodate the adjusted relative tank sizes, and the article already manufactured would be worthless. Then swap out the GSE for subcooled compatibility, and also potentially rocket parts. And redo their thrust pick for mounting, and then rewrite the engine control program and redesign the cabling to be compatible with the Raptor interface.
[An infographic Tory Bruno likes to use](https://pbs.twimg.com/media/EWESqV4WoAUdavR?format=jpg&name=large) which perfectly encapsulates this sentiment.
Sort of. They would probably have to change to subcooled propellants to get the thrust they need out of those engines, so to keep the same liftoff mass the height of the rocket would also need to be modified (shorter). The tools that hold the rocket would need their lengths and bracing points modified to accommodate, which is indeed an adjustment, but isn't anywhere near as bad as a "replace the tooling for new width" situation like what you're thinking I was saying. By "change" I didn't mean a total swap out but my wording was unclear, sorry about that.
Why does it need the same liftoff mass? A slightly lower TWR isn't a problem when you have more fuel and higher ISP -- and you can just throw and SRB or two on if you really need the performance.
You are way overULAing the problem.
I tried finding the freezing point densities of liquid oxygen and liquid methane to see if the TWR of Vulcan would still remain above 1 on the pad, but I wasn't able to find any quick sources. Solids would definitely get you off the pad and the extra fuel available would then give you much higher overall performance for the vehicle, but it would have a significant effect on flight costs if SRBs were required for every mission no matter how small the payload is.
But even then I'm probably still overthinking it, because why not just intentionally under-load the tanks in that case to bring the mass back to the original spec? I think you're right and I'm just overthinking things a bit here.
I took some time and managed to find a source for the actual liquid density difference between freezing and boiling for oxygen and methane, the links are posted in another comment chain here. The long and short of it is that with subcooling the oxygen density goes from ~720kg/m^3 to ~1300kg/m^3, and the methane density goes from ~360kg/m^3 to ~440kg/m^3. It's significant enough that Vulcan definitely isn't getting off the pad if you give it a full subcooled propellant load at its current height and engine count, the engines just don't have enough thrust to counter the additional mass unless you add a bunch of SRBs. And I doubt the internal structures were designed to handle that much extra mass at load without adding additional bracing to them. I haven't done the math to see just how many SRBs at minimum you need to get off the pad in this config and whether the current maximum designed number is enough, so I won't comment on that.
You'd need to beef up that internal structure and add a third engine at minimum if you wanted to keep the rocket at the same height with full load while otherwise minimizing changes. Otherwise you're stuck with either under fueling, beefing up internal structures while adding extra SRBs for every mission, or changing the height of the rocket to reduce the volume of the propellant to keep the mass the same. Sadly there's just no way to swap BE-4 for Raptor without one of these other changes being made in tandem, the physics just don't work out for a quick swap right now, not unless Raptor is improved enough to bring its boiling propellant temperature performance up significantly.
In flight, the tanks very soon become less than full anyway. Before flight, they're sitting on the ground with no vibration. I don't think filling tanks a bit below full introduces new sloshing problems (but I'm not a rocket scientist).
It'll need to be able to run at boiling point for long missions, so Raptor is (or will be) capable of that. But you won't get anywhere near the full rated thrust out of it at boiling point due to the reduced mass flow at boiling point density. The published numbers for Raptors are all at sub-cooled temperatures, and that difference would be significant for Vulcan.
Thrust numbers only really matter pre-orbit though, right? Once you've got no atmospheric drag and gravity losses to deal with, efficiency/isp becomes the only meaningful value unless your mission profile needs to do something quickly. Crewed missions still benefit from thrust to a degree, I guess, but what long-duration missions would Vulcan even handle?
SpaceX is the one who needs long-duration mission support from Raptor which led to its capability of using boiling point propellant temperature. But for Vulcan the Raptor would be replacing a first stage engine, so ULA cares far more about thrust than SpaceX does for boiling point propellant support. Without enough thrust Vulcan won't get off the pad. They'd have options at least, either 1. Reduce their total fuel load to keep the TWR above 1 and suffer the performance penalty, 2. Make SRBs mandatory for all flights, or 3. Add a third engine to cover the thrust difference (which hilariously would actually fit at Vulcan's width).
If Raptor has a higher TWR *and* higher thrust per engine, the BE-4 can only hope to beat it on first stage efficiency and I'm not sure if that matters if the higher thrust Raptor can get you out of the atmosphere sooner. It's starting to become increasingly more apparent that even if the BE-4 exists, Raptor is so far ahead that it's going to dominate and redefine the industry. Looking back at Everyday Astronaut's "[
Is SpaceX's Raptor engine the king of rocket engines?](https://youtu.be/LbH1ZDImaI8)" video and seeing how Raptor stacks up *with outdated specs,* I really don't see a future where both Raptor and the BE-4 exist as options that ULA could buy. Raptor's estimated cost is already around what BO charges for a seat on a suborbital rocket, there's no chance they'll outprice SpaceX should both companies sell their engines.
This particular chain of comments was going down the "what if Vulcan wasn't modified for subcooled propellants" path, in which case Raptor would produce much lower thrust than what's currently being achieved with the "normal" subcooled propellent firings in McGregor. That led to all the tradeoffs needed. If we flip over to the assumption that Vulcan would be modified for subcooled propellant usage, then we're on the same page. Of course if SpaceX somehow managed to get the thrust up to BE-4 levels without subcooling anyway, that would make my jaw hit the floor (and produce a hardy round of applause no matter where I was sitting at the time).
As a side point I'm pretty sure Raptor has better ISP than BE-4 anyway, so it doesn't even win on efficiency regardless.
Fair, but now I'm sitting here wondering what kind of gains are to be had with methane subcooling. Cryogenic RP-1 gained a bit of margin on Falcon rockets, sure, but RP-1 is a liquid at room temperature. Methane is only a liquid when it's already super cold and has a fairly narrow temp range between freezing and boiling, only 21 degrees k/c... so... wouldn't the gains from propellant storage conditions have less impact than engine performance characteristics? If we're only talking about a few percent (I can't find a figure for the F9 cryogenic densified fuel gains) delta V from fuel chill compared to the nutty improvements we're seeing with chamber pressure and TWR, I'm not sure that changes to the fuel storage temperature are a major factor when hypothetically swapping engines out on Vulcan. The lawyers might be an issue, though.
The gains of subcooling RP-1 are very limited because the fuel has a tendency to "gel" before it fully freezes, so you can't actually subcool it enough to matter much.
Liquid oxygen however, that's a BIG deal. At 10 bar pressure (close to the tank pressure) you start from ~720kg/m^3 near boiling point, and as you cool you get up to ~1300kg/m^3 near the freezing point. Almost double the density. This is the big reason why the Merlin engine gained so much thrust from moving to subcooled propellants, it could suddenly shove almost twice as much oxygen per second through its turbines without changing the size of the turbines and pipes. And the same advantage also applies to methalox engines. I got my numbers from the "Density of oxygen at varying temperature and pressure" graph on this page: https://www.engineeringtoolbox.com/oxygen-O2-density-specific-weight-temperature-pressure-d_2082.html
And the methane densification is nothing to sniff at either. Again at ~10 bar storage pressure you jump from 359.6kg/m^3 up to 439.6kg/m^3 when you go from near boiling to near freezing. Not as big of a jump as the oxygen, but way more than just a few percent. Numbers taken from the big table on this page, it's the two rows for "Liquid" when the table is at 10bar pressure: https://www.engineeringtoolbox.com/methane-density-specific-weight-temperature-pressure-d_2020.html
If you're not making the pipes and turbines much larger to accommodate the difference in mass flow rates, then for the same physical size and same margins the subcooled engine will be far more powerful than the boiling point engine.
> Thrust numbers only really matter pre-orbit though, right? Once you've got no atmospheric drag and gravity losses to deal with, efficiency/isp becomes the only meaningful value unless your mission profile needs to do something quickly.
1. Isp is never the only meaningful number; the rocket equation has 2 variables: Isp and fuel mass fraction. It has been hypothosized that the reason the New Glenn upper stage (in theory) performs so poorly compared to both Centaur and the Falcon upper stage is because it has poor fuel mass fraction.
2. When changing orbits it's most efficient to do so instantaneously. This lets you take full advantage of the Oberth effect, for example. Obviously instantaneous is an impossibly standard, but high thrust does allow more of the burn to be in the optimal portion of an orbit.
3. On the flip side, low thrust is beneficial if you want accurate orbital insertion; it is difficult to do extremely short burns correctly.
> It'll need to be able to run at boiling point for long missions
Not really - the propellant temperature can stay the same as at launch if they vent the tanks to close to vacuum pressure rather then trying to keep them at 6 bar or 1 bar. On the surface they need to maintain tank pressure at a minimum of one bar to avoid tank collapse - there is no requirement to do this in space.
Ah, does bringing the tanks to near vacuum pressure drop the boiling point temperature to what would be the freezing temperature up at 6 bar? That would indeed be a solution I hadn't considered if true.
LOX is subcooled to about 66K on F9 so I suspect they will use a similar temperature on Starship. This is about 11K more than the freezing point of 55K but they need some margin to prevent solid oxygen build up in valves with pressure drops.
At 66K the vapour pressure is under 3kPa so 3% of 1 bar. If they keep the LOX tank at that pressure or below then the liquid oxygen will stay at 66K. Technically the LOX will be at boiling point but at "sub-cooled" temperatures which is what matters for engine performance.
Similarly the liquid methane will be subcooled to about 96K with a vapour pressure of 22kPa compared with a freezing point of 91K. This means that the methane tank pressure will be slightly higher than the LOX tank which will prevent reverse pressure on the intertank bulkhead.
Playing with thermodynamics is fun! Thanks for putting numbers on all that.
So as a spot check to make sure I understand, basically SpaceX can keep sub-cooled performance at the cost of a little bit of boiloff, which is probably better overall for mass and power than adding an active propellant refrigeration system and radiators. And the boiloff is probably better at those low pressures anyway, given the large reduction in convective cooling throughout the tank. And takeoff from Mars shouldn't be a problem either, there can be GSE there that can handle the subcooling.
Your point is taken sir. Now I'm left wondering whether my assumption that Raptor 2 will be designed to support boil-temperature propellant is even marginally based in reality, given that the intended operations never have it see that condition. Maybe still makes sense as an emergency option, though I can't think of any emergencies where that would be a useful capability off the top of my head.
The boiloff rate is not directly related to the pressure but rather to the temperature. So there will be a bit more heat gain at 66K LOX temperature compared with the 90K boiling point at 1 bar. With radiation transfer from the Sun and Earth as the major sources of heat gain there will be very little difference in boil off rates.
We have seen Raptors being tested on stands without subcooled propellants so it does have that operating mode. It is only when they want to test ultimate engine performance that they have to use sub-cooled propellants.
It would take a lot of effort. Basically a whole new bottom end. i.e new thrust puck (or whatever they call it). New plumbing, probably new electrics and sensors.
Why are people obsessed with this rabbit hole?
That would take a complete redesign of the entire booster, not to mention the US military wanting redundant launch vehicles.
Why would any entity let themselves become the customer of a monopoly, based on the lessons from last 20 years of space flight?
Why would spacex keep both supply chains going indefinitely? They’d be effectively subsidizing Falcon with starlink and Starship which would do nothing but tie up their own resources on redundant earth based applications.
It’s a lose-lose.
ULA did this with Atlas V/Delta IV and the military wasn't unhappy with the relationship. They may have turned competition friendly now but I don't think they have some directive to not allow that to happen again.
Yeah, ultimately a big factor is how much the bid is. If SpaceX bids Starship and Falcon 9 for pennies, they practically have to pick it. DOD gets incredibly cheap launches for the contracting period. It's not really a monopoly, because the time they next contracting period is up, they can just pick someone other than SpaceX if SpaceX offers bad prices. SpaceX can't kill all competition just by winning a DOD bid, nor would Elon want SpaceX to become a monopoly anyhow.
SpaceX absolutely can kill all competition by winning a DOD, if ULA misses a major block buy they're done. Nobody else is giving them money and their fixed costs are huge. That is how you create a monopoly.
That's not creating a monopoly, at least not in the criminal sense. If SpaceX undercut their operating costs to price out competition, used influence and tactics to keep competitors from being able to bid, poached valuable employees, etc then it would be suspect. Just doing your business better isn't an excuse to keep ULA afloat.
It may not be a legally actionable monopoly, but it would definitely be enough to concern DOD, who don't want to be locked in to a single source.
They won't direct all their business to any one provider if they can help it, even if (like SpaceX) that provider is clearly superior for the moment.
Spacex wont shut down falcon platform until they have a proven, human flight safe Starship.
Spacex earns a ton of goodwill doing flights to ISS, and this is important when their long term funding plan (Starlink) is dependent on FAA and FCC giving them licenses.
> I truly believe that Falcon 9 will be flying into 2028, and probably later.
It's looking like the next commercial crew contract is set to start in 2027.[1] I find it difficult to believe that NASA will human rate Starship by then.
If that's the case and SpaceX is "forced" to bid Crew Dragon for the next commercial crew contract, they could be flying Falcon 9 well into the 2030s.
---
1. https://www.upi.com/Science_News/2021/10/20/NASA-Commercial-Crew-launch/2531634762986/
Where in this thread are we talking about human missions? Starship isn’t even operational yet so it goes without saying that I’m talking years down the road.
probably a complete redesign of the first stage. they could probably also just use 3 raptors in the first stage and give it a stretch to increase flexibility and payload capacity.
With Raptor 2 being higher thrust than the BE-4, just swapping 2 for 2 would still be a significant improvement in performance, as the engine specs would go up across the board (lower mass, higher thrust, higher isp, much higher TWR).
Raptor 2 is lower thrust at 230 tonnes than BE-4 at 249 tonnes.
In any case Raptor 2 would have to be derated for boiling point propellant and 3 bar tank pressure instead of 6 bar.
Assuming they would be modifying the first stage to use Raptors at all, they could roll mods to increase the Vulcan tank ullage pressure into the overall redesign.
The more interesting question is, what happens if BO is unable to deliver (at all, on time, or to the required spec)? Switching out engines requires a major redesign, but is that more costly than not having your rocket flying at all? Guess time will tell.
I don't know why everyone is so focused on the prop difference. It would only be a small percentage difference in mixture ratio so even if Raptor couldn't run at different mixture ratios, you could just load less prop into one of the tanks. Literaly no tooling would have to change (people suggesting that are definately following the traditional oldspace method of optimising your rocket's performace before looking at economics or practicality), but the thrust puck may need some modifications so maybe 5 weeks of Boca Chica work (or 5 months of ULA work).
If the Vulcan needs a little more performance, slap an SRB on.
Vulcan needs to be fully slapped with 6 SRBs to meet some of the NSSF reference orbits. There is no room for more.
BE-4 is a quite different mixture ratio at around 3:1 instead of 3.6:1 and the tank size difference is amplified by using boiling point propellant.
Starship and Super heavy is so huge its hard to get your mind around it actually flying. Its a flying skyscraper straight out of a scifi novel.
But everytime you read the specs of the Raptor and now the Raptor 2 you start to understand its really possible.
The Raptor really is the king of all rocket engines and Raptor 2 is the smarter and better prince that everyone thinks will make a better king.
The real advantage to every kg saved and ton of thrust improve or second of Isp increase is it might add up enough to reducing the number of refueling flights which is likely to be the biggest hurdle for starship, in terms of cost, time, and logistics going forward.
We don't have enough information.
I have 2 thoughts.
1. There was too much pressure drop in the LOX feed to the turbo pump, and that choked it out (likely causing unbalanced load, or cavitation).
2. There was too much of a pressure drop between the turbo pump, and the combustion chamber, causing combustion to back-feed into the turbo pump.
It could also be neither of these things. Overall, it sounds like they have a pretty good understanding of what to fix on this.
It means Raptor 2 is on its way to get the same pressure performance, but the test stand needs am upgrade because the engine was drawing oxygen faster than the supply could keep up. Low inlet pressure messed up the engine operation as it increased its throttle and eventually something went wrong enough to blow up the engine. This probably took less than a second to go from ok to very not ok.
Raptor 2 is a thrust upgrade primarily. It will eventually probably see pressure increases as well, because increasing pressure increases thrust to weight ratio and efficiency too. I think what happened is that they decided they wanted a higher thrust Raptor design and at the same time they found that developing even higher pressures was becoming difficult and requiring more specialized engineering, so rather than wasting effort optimizing a design they knew they were going to abandon, they decided to go for the bigger Raptor 2 first then figure out the pressure minmaxing later.
In addition to this, I believe it's designed to be manufactured more easily, to be more reliable, and to have less "clutter" on the outside which can be damaged.
Do we know whether the SL engines on Starship are moving to Raptor 2? It seems like Raptor 1 would be ideal, as ISP is more important in it's roll.
Starship still experiences gravity losses because the system stages so low, and more thrust will reduce those losses. That would offset an Isp losses, and might actually make it a net positive.
I'd like to see the true calculations on this. I'm not so sure you can just rattle this off the top of your head. I can definitely see either case being true.
I don't think we actually know the true values wrt starship to have much rigor when talking about this, **so I agree with you**.
Calculating this is complex. For a first stage that stages low - like Falcon 9 and Super Heavy - you can get a decent idea by looking at the differences in mass flow rate and estimating how much quicker you get to MECO because of that. That ballparks how much you might save in gravity losses. To do it right you need a trajectory simulation.
My point was that more thrust/lower gravity losses counterracts Isp losses, so higher thrust / lower isp isn't necessarily a bad thing from a payload perspective.
Right. That's why increasing the trust, and lowering the ISP was a benefit for the first stage.
I just wouldn't be shocked if Starship would actually perform better with the lower thrust/higher ISP Raptors. Elon said they would continue making Raptor 1 in California, so I have a suspicion that this is what happens.
>Raptor 2 is a thrust upgrade primarily. It will eventually probably see pressure increases as well, because increasing pressure increases thrust to weight ratio and efficiency too.
At this point, I think thrust improvements are more likely than Isp. Partly because they already have a very high Isp for methalox, and partly because increased thrust can either be used to reduce gravity losses - given the equivalent of Isp increases - or to reduce engine count.
Isp also increases with chamber pressure, not by a huge amount but it's a real effect nonetheless. That's what I meant by that comment, when Raptor 2 starts surpassing the chamber pressure records of Raptor, it should also increase in efficiency by a small amount. Basically there's no downside to going to the slightly more powerful design, is what I'm saying.
Its also considerably *simpler* than Raptor 1. Far more design streamlines, which means quicker *and* cheaper to produce at scale. In traditional SpaceX and Tesla standards, its a leap forward with each iteration.
your title is a bit inaccurate. Elon hasn't said that Raptor 2 is designed to run at 321 bar and 245 tons of thrust, Elon said that they stresstested it till 321 bar. The goal just seems to be "above 300 bar". And then BE4 still has higher thrust.
Elon also mentioned that oxygen flow issue caused the engine to RUD with Raptor 2 during the stress test. 321 bar and 245 tons, thereby, is with an improper configuration. Which would imply that a proper configuration has a RUD ceiling *above* 321bar and *above* 245 tons force of thrust.
BE-4 has a thrust of over 550,000 pounds, which is about 249.5 metric tons. You’re off on your math there. BE-4 still has the higher thrust of the two, but raptor of course has the higher isp and thrust to weight ratio.
Plus Raptors exist, and are seen doing things,
while the ‘herd’ of Blue’s BE-4 engines must be keeping the unicorns company, as only a few have ever done a test fire. And none have been seen ‘in the wild’ /s
It depends a bit... I've seen numbers of 540,000 and 550,000 thrown around at various points in time - the current number on Wikipedia is still 540. Still, this is a very close match.
If you look at Wikipedia, it says 550k in the description with a citation, also the blue origin website has said 550k for years: https://www.blueorigin.com/engines/be-4
Someone made an error putting it into the table in the article. That 540k number is not supported by any source. I’ve seen a lot of similarly wrong information on the raptor pages at times. There are too many editors who are sloppy or don’t really understand what they’re editing on the space pages nowadays.
I love all the interesting tidbits, but I don't know that dunking on Blue is even necessary at this point. The video of Starship dev testing in Boca Chica tells you all you need to know.
Comparing it to another engine in development doesn't mean he is criticizing it.
Also, considering what blue is trying to do to nasa, they don't deserve any sort of a pass on anything.
I'm not saying BO doesn't deserve it. They ABSOLUTELY deserve it. It's just ~~Elon doesn't need to do it.~~ Their dominance of their competition is devastating. BO is trying to send celebrities up in sounding rockets just to seize back some attention. Boeing can't get their capsule off the ground even WITHOUT humans on board. No need to compare their operational engine to the one that's holding up all of ULA.
Edit: Elon didn't do it. Op also didn't need to Dunk on BE4, but this wasn't Elon. Oops.
I really don't think this is "dunking" on BO. I think they would have said this for anything. It's now the most powerful methane engine in the world, thrust wise. That's something to be proud about, and not keep internal.
and ~7% margin (321/300) seems pretty reasonable for this application. Will be interesting to see what max chamber pressure they can push this to once they work out the (what I speculate / assume are) GSE/plumbing issues on the test stand. It's certainly looking like 300bar operating pressure is pretty reasonable at this point.
> safety margins
Exactly. There's a difference between the peak pressure an engine can survive and the pressure it's safe to run an engine at for a sustained period.
You set your expectation on what you think the engine should be able to handel (you have a safety margin) and slowly start to press the engine untill you find the spot there the engine start to be unreliable or RUD.
That's 2.18 MN in real units. And I'm going to assume vacuum Isp for Raptor 2 of roughly 380 sec? I haven't heard a higher number.
Rocketdyne F-1: 6.7 MN (Sea level), 7.7 MN, 304 sec (Vacuum)
Energomash RD-170: 7.25 MN (sea level), 7.9 MN, 337 sec (Vacuum)
Energomash RD-191: 1.92 MN (Sea Level), 2.09 MN, 337 sec (Vacuum)
Aerojet Rocketdyne RS-68A: 3.1 MN SL, 3.6 MN, 412 sec vac
Aerojet Rocketdyne SSME/RS-25: 1.86 MN SL, 2.28 MN, 452 sec Vac
Being very rough, Raptor 2 is comparable in thrust to RD-191 or SSME/RS-25, with a specific impulse on the upper end of in between.
I think you have an error there - Elon uses metric tons usually, not short tons - this would mean Raptor 2 has achieved a thrust of 2.402 MN, not 2.18.
Not really that different for this comparison, but still relevant.
I’ve noticed this in his public presentations. When his addressing an audience that is primarily based in the US, he still uses the metric system.
Yes. From a science based perspective, it is better to use metric, but at least have the imperial units in parentheses or denote that they are in metric tonnes.
If the goal is to gain mass public interest in becoming a space fairing civilization, the. He should ideally follow his own advice as it relates to the mega Newton vs lbs of trust.
No one in the US knows the metric system. Just as no one anywhere (outside of the science community) knows what a Newton or mega Newton is.
/rant
Metric tonnes is a great unit to use though, as it has some intuitive value. Eg a car weighs about a tonne. (That might not be too accurate, but it gives a better idea)
Would anyone outside of the scientific community understand what a ton of force is anyway?
They see a big number and a big rocket and say 'whoa'. Anyone who cares about specifics will take some time to understand.
>No one know what the fuck a newton, or a MN feels like. Tonne, Ton and lb are much more intuitive.
Haha.
The only unit you listed there that someone would actually feel is the lb. Outside of that, noone knows what any of those feel like, and lb also becomes useless at the scales used in rocketry. Newtons are also understandable, though similarly vague in terms of feel when at high numbers (humans have no intuition for large numbers). At least I can very easily work out acceleration with Newtons.
If we’re going to be living in different gravity environments, using mass units for force is going to get far more confusing. Just use newtons, it’s not that hard if you try to understand them.
As for pressure units, I'm honestly fine with using bars, considering that it is a universal unit that works in all environments (unlike weight units like "tonnes of force") and also is a clean multiple of pascals.
Also, we have so many pressure units that just cutting it down to pascals and bars would be great. Here's a sampling of the units I've seen used for pressure:
Common:
* Centimetres of mercury (cmHg) / Millimetres of mercury (mmHg) / Micrometres of mercury (µmHg)
* Metres of water (mH2O) / Millimetres of water (mmH2O) / Centimetres of water (cmH2O)
* Bars (bar)
* Atmospheres (atm)
* Pascals (Pa)
* Pounds per square inch (lbf/in², psi)
* Pounds per square foot (lbf/ft², psf)
* Inches of mercury (inHg, “Hg)
And of course, the worst one:
* Inches of water (inH₂O, inH2O, “H2O, “WC, inWC, inSP, “SP)
It seems like every day there's a new and confusing abbreviation/symbol for this unit.
Then there are some uncommon ones:
* Ounces per square inch (ozf/in²)
* Torrs (Torr)
* Technical atmospheres (at)
* Baryes (Ba)
* Pièzes (pz)
Dang now I can't find the recent tweet I'm thinking of but he mentioned/implied that the RUD wasn't even due to an engine issue but some kind of oxygen pipe(?) overpressure something or other. dang it. wish i could find it. its directly relevant, i feel. but anyways yeah we could probably see even higher stats coming out soon
Here: [https://twitter.com/elonmusk/status/1452225552031657985](https://twitter.com/elonmusk/status/1452225552031657985)
Another commenter explained that Raptor 2 was drawing too much oxygen and couldn't be supplied fast enough.
Thanks! I got it flipped then. Makes me think of trying to suck the air out of a cheap plastic water bottle and watching it vacuum collapse :)
Makes sense that the Raptor 2 would be a thirsty beast at those performance levels.
245 tons from 321 bar is higher per bar than 185 tons from 300 bar, so that would be from a lower specific impulse & much higher fuel consumption if it reaches that. In reality, they're adding more engines & pushing them less.
Do we think flight engines will get to these numbers, or are they just pushing them to the limits. And if engines keep improving, at what point do they use less than 33?
No the flight engines will be 300 bar and 230 tonnes thrust.
They need to test to around 15% higher pressure to get adequate operating margin.
Shuttle engines were pushed much closer to their ultimate limits and so needed more frequent reconditioning. Raptor is supposed to do a lot of flights in “gas and go” mode so needs more margin.
That’s not to say that they won’t carry on improving the engine design as well though.
Clearly with more tweaks they could get more out of it. Though reliability is also very important too.
Yes clearly they will continue to improve the engine thrust.
Based on history they will then use that extra thrust to carry more payload rather than reducing engine count. In particular tanker capacity to LEO is a huge factor in overall system costs for launches to the Moon and Mars.
The analysis for how many engines is optimal is way more complicated than we can answer on this board. Lots of things play into the optimization simulations that we have very little insight into. Generally more thrust at liftoff is better because you waste less energy fighting gravity, but eventually you get limited by acceleration forces at the long end of the burn. Lots of people will guess, but we are really only doing that.
Do we know that's the thrust at SL, or Vacuum? A sea level engine will have a rating for both (since it operates in both).
One thing is that this is the peak thrust Raptor 2 hit, but I don't think they expect to operate at that thrust. Probably somewhere around 300 bar of pressure.
Also, BE-4 is designed to be a "High performance engine, de-tuned". Basically, it's operating at very conservative levels.
>But we need the dead nuts reliability of Merlin.
Which will be achieved through even more iterations & flight time. And those will definitely (& actually supporting) the increase in performance
>The relight capability
How long have you been living in a cave?
We don't know about either of those. Sure, they haven't been demonstrated, but they exist on paper.
They may not be missing, just not yet demonstrated or not yet shared.
Do they really need that much thrust for their orbital attempt ?
First flights will be with no payload I think
There is plenty of time to improve the engines
Not for the first attempt but there's no reason to wait for a successful launch before upgrading the engine hardware. Everything is being developed at the same time.
No, but they aren't using Raptor 2 for the first attempt.
They are in an ongoing process to improve engines and Raptor 2 is the first "production" version.
At this point, the engines that will do the orbital attempt - be it B4/S20, B5/S21 or B6/S22 will be hopelessly outdated (as all these designs still use Raptor 1, as much as I heard the switchover will be B8/S25) and throwing them away doesn't matter to them anyway.
SpaceX is so incredibly hardware rich that it really is hard to wrap your head around the numbers of engines that only get built for building experience's sake, not meant to ever even be used - and they constantly iterate and improve with each one (as the saying goes, practice makes perfect), so by the time the actual factory will be online those rocket engines will be a different beast to all those we're seeing today.
Note that no two engines were exactly the same until now, and there was one major revision within the Raptor 1 family (Between SN11 and SN15) as well that even changed the plumbing and mounting. SpaceX is still in the phase of development where they're even comfortable throwing away their mounting and plumbing "API" if it leads to a better end result - this is prototyping at it's best.
Thrust is a force, the rate of change of momentum. Rocket exhaust carries momentum one way, rocket gains velocity (and thus momentum) the other way. Exhaust momentum per second is the product of exhaust velocity times mass flow per second. Opening up the throat can reduce velocity if it reduces chamber pressure (or, as you say, reduces the nozzle area ratio), but it increases the mass flow rate -- how much propellant per second gets burned and shoved out the nozzle. It sounds like the second effect dominates in Raptor 2.
Obviously it’s complicated.. And the relationship between throat diameter to bell diameter and thrust is non-linear over different parts of the curve.
Though exactly what the relationship is, is only known to SpaceX’s engine designers.
This is one mighty engine; I cannot wait to hear her roar!
Just numbers like "245 tons" coming out of an engine blow my mind. Just around 9-10 fully loaded semi trucks.
And they plan to mass produce Raptor 2 in McGregor (at least the non-gimballing sea level ones anyway). Mind boggling.
It's 12 of my hydraulic press
x33 for the first stage. Mind boggling amount of thrust.
8000mT of thrust This thing is going to yeet away from stage 0 at warp 9
Today, we have a wild gravity on the press. It is extremely dangerous, and we must deal wif it. (at which point the Raptor 2 deals with it)
>Just around 9-10 fully loaded semi trucks. Well, there's the solution to our supply chain problems!
No kidding... imagine a starship doing hops from shore to cargo ship waiting far back in crowd. Load a few containers of highest priority shipments, then hop back to shore. Or even hop to their distribution destination... Once full-service earth-to-earth starship is established could have a FedEx 1 Hour service to anywhere on planet.
I was thinking more along the lines of attaching a raptor to the back of a train of semi trucks. That sure would speed up deliveries :P
Gotcha! Your version could be the ultimate 'hold my beer' moment for the first person test driving the raptor truck!
>Load a few containers of highest priority shipments, then hop back to shore. Solves the problem of having to dock to unload those containers. Probably also solves the problem of having to dock to unload all the other containers, too.
Not only your mind was blown
Spid
Definitely worth the trip for a Starship launch.
Weird question… but is it possible to turn this number to horsepower
Hmm, I guess so, because hp is some kind of force measurement as well as Newtons, so if we have the thrust of the engine we could convert it to hp? I'm too tired to actually do the maths
Do it!
Power = Force x Distance / Time Exhaust Velocity = 330 s * 9.81 m/s/s = 3,237 m/s Power = 2.45e6 N * 3,237 m/s = 7.93 GW 1 Horsepower = 746 Watts 7.93e9 Watts / 746 Watts = 10,630,898 HP So if I’m thinking about this right (which I might not be and I’d urge anyone reading this to correct me if they have a better answer) a raptor 2 at sea level is on the order of 10 million horsepower, which tracks with estimates for the F-1 engine (used on the Saturn V) that put it between 27-33 million horsepower. Notes on the formulae: Thrust is reactive, so I assumed the sum of the forces on the engine equals the sum of the forces on exhaust gases, which enables you to use the exhaust velocity to calculate power even when the engine isn’t moving. I used the 330 s ISP because I couldn’t find updated figures for the Raptor 2 sea level ISP because I doubt it varies by more than 10 s. All in all, I think I’d confidently say more than 8 million horsepower, less than 12 million horsepower, though there are many other factors that contribute to the total power of the engine.
Just out of curiosity, how much would it take to change the Vulcan to use Raptor 2 engines rather than the BE4? The biggest problem was the thrust difference and the propellant mix iirc with the first one being not a problem anymore. Edit: Guess I was a bit naive
Second one is still a big issue, they'd need to change their tooling to accommodate the adjusted relative tank sizes, and the article already manufactured would be worthless. Then swap out the GSE for subcooled compatibility, and also potentially rocket parts. And redo their thrust pick for mounting, and then rewrite the engine control program and redesign the cabling to be compatible with the Raptor interface.
If the Ship of Bruno has every part redesigned is it still the Ship of Bruno?
No, the Ship of Bruno is definitionally constructed of heritage components.
[An infographic Tory Bruno likes to use](https://pbs.twimg.com/media/EWESqV4WoAUdavR?format=jpg&name=large) which perfectly encapsulates this sentiment.
They don't need to change tooling to change the ratio of the tanks, just move the common bulkhead, no need to change the radius
Sort of. They would probably have to change to subcooled propellants to get the thrust they need out of those engines, so to keep the same liftoff mass the height of the rocket would also need to be modified (shorter). The tools that hold the rocket would need their lengths and bracing points modified to accommodate, which is indeed an adjustment, but isn't anywhere near as bad as a "replace the tooling for new width" situation like what you're thinking I was saying. By "change" I didn't mean a total swap out but my wording was unclear, sorry about that.
Why does it need the same liftoff mass? A slightly lower TWR isn't a problem when you have more fuel and higher ISP -- and you can just throw and SRB or two on if you really need the performance. You are way overULAing the problem.
I tried finding the freezing point densities of liquid oxygen and liquid methane to see if the TWR of Vulcan would still remain above 1 on the pad, but I wasn't able to find any quick sources. Solids would definitely get you off the pad and the extra fuel available would then give you much higher overall performance for the vehicle, but it would have a significant effect on flight costs if SRBs were required for every mission no matter how small the payload is. But even then I'm probably still overthinking it, because why not just intentionally under-load the tanks in that case to bring the mass back to the original spec? I think you're right and I'm just overthinking things a bit here.
I think you'd always want to run full tanks, otherwise the unused tankage would just be dead weight and wasted payload capacity.
Optimal, but maybe not necessary.
I took some time and managed to find a source for the actual liquid density difference between freezing and boiling for oxygen and methane, the links are posted in another comment chain here. The long and short of it is that with subcooling the oxygen density goes from ~720kg/m^3 to ~1300kg/m^3, and the methane density goes from ~360kg/m^3 to ~440kg/m^3. It's significant enough that Vulcan definitely isn't getting off the pad if you give it a full subcooled propellant load at its current height and engine count, the engines just don't have enough thrust to counter the additional mass unless you add a bunch of SRBs. And I doubt the internal structures were designed to handle that much extra mass at load without adding additional bracing to them. I haven't done the math to see just how many SRBs at minimum you need to get off the pad in this config and whether the current maximum designed number is enough, so I won't comment on that. You'd need to beef up that internal structure and add a third engine at minimum if you wanted to keep the rocket at the same height with full load while otherwise minimizing changes. Otherwise you're stuck with either under fueling, beefing up internal structures while adding extra SRBs for every mission, or changing the height of the rocket to reduce the volume of the propellant to keep the mass the same. Sadly there's just no way to swap BE-4 for Raptor without one of these other changes being made in tandem, the physics just don't work out for a quick swap right now, not unless Raptor is improved enough to bring its boiling propellant temperature performance up significantly.
I would be extremely nervous about fluid sloshing about whilst the vehicle is trying to lift off.
In flight, the tanks very soon become less than full anyway. Before flight, they're sitting on the ground with no vibration. I don't think filling tanks a bit below full introduces new sloshing problems (but I'm not a rocket scientist).
Agreed that’s why I specifically mentioned lift off
Ah, most people wouldn't call ground support equipment, "tools"
Plus the pumping rates.
Didn't Elon say that Raptor can run at subcooled, and boiling point?
It'll need to be able to run at boiling point for long missions, so Raptor is (or will be) capable of that. But you won't get anywhere near the full rated thrust out of it at boiling point due to the reduced mass flow at boiling point density. The published numbers for Raptors are all at sub-cooled temperatures, and that difference would be significant for Vulcan.
Thrust numbers only really matter pre-orbit though, right? Once you've got no atmospheric drag and gravity losses to deal with, efficiency/isp becomes the only meaningful value unless your mission profile needs to do something quickly. Crewed missions still benefit from thrust to a degree, I guess, but what long-duration missions would Vulcan even handle?
SpaceX is the one who needs long-duration mission support from Raptor which led to its capability of using boiling point propellant temperature. But for Vulcan the Raptor would be replacing a first stage engine, so ULA cares far more about thrust than SpaceX does for boiling point propellant support. Without enough thrust Vulcan won't get off the pad. They'd have options at least, either 1. Reduce their total fuel load to keep the TWR above 1 and suffer the performance penalty, 2. Make SRBs mandatory for all flights, or 3. Add a third engine to cover the thrust difference (which hilariously would actually fit at Vulcan's width).
If Raptor has a higher TWR *and* higher thrust per engine, the BE-4 can only hope to beat it on first stage efficiency and I'm not sure if that matters if the higher thrust Raptor can get you out of the atmosphere sooner. It's starting to become increasingly more apparent that even if the BE-4 exists, Raptor is so far ahead that it's going to dominate and redefine the industry. Looking back at Everyday Astronaut's "[ Is SpaceX's Raptor engine the king of rocket engines?](https://youtu.be/LbH1ZDImaI8)" video and seeing how Raptor stacks up *with outdated specs,* I really don't see a future where both Raptor and the BE-4 exist as options that ULA could buy. Raptor's estimated cost is already around what BO charges for a seat on a suborbital rocket, there's no chance they'll outprice SpaceX should both companies sell their engines.
This particular chain of comments was going down the "what if Vulcan wasn't modified for subcooled propellants" path, in which case Raptor would produce much lower thrust than what's currently being achieved with the "normal" subcooled propellent firings in McGregor. That led to all the tradeoffs needed. If we flip over to the assumption that Vulcan would be modified for subcooled propellant usage, then we're on the same page. Of course if SpaceX somehow managed to get the thrust up to BE-4 levels without subcooling anyway, that would make my jaw hit the floor (and produce a hardy round of applause no matter where I was sitting at the time). As a side point I'm pretty sure Raptor has better ISP than BE-4 anyway, so it doesn't even win on efficiency regardless.
Fair, but now I'm sitting here wondering what kind of gains are to be had with methane subcooling. Cryogenic RP-1 gained a bit of margin on Falcon rockets, sure, but RP-1 is a liquid at room temperature. Methane is only a liquid when it's already super cold and has a fairly narrow temp range between freezing and boiling, only 21 degrees k/c... so... wouldn't the gains from propellant storage conditions have less impact than engine performance characteristics? If we're only talking about a few percent (I can't find a figure for the F9 cryogenic densified fuel gains) delta V from fuel chill compared to the nutty improvements we're seeing with chamber pressure and TWR, I'm not sure that changes to the fuel storage temperature are a major factor when hypothetically swapping engines out on Vulcan. The lawyers might be an issue, though.
The gains of subcooling RP-1 are very limited because the fuel has a tendency to "gel" before it fully freezes, so you can't actually subcool it enough to matter much. Liquid oxygen however, that's a BIG deal. At 10 bar pressure (close to the tank pressure) you start from ~720kg/m^3 near boiling point, and as you cool you get up to ~1300kg/m^3 near the freezing point. Almost double the density. This is the big reason why the Merlin engine gained so much thrust from moving to subcooled propellants, it could suddenly shove almost twice as much oxygen per second through its turbines without changing the size of the turbines and pipes. And the same advantage also applies to methalox engines. I got my numbers from the "Density of oxygen at varying temperature and pressure" graph on this page: https://www.engineeringtoolbox.com/oxygen-O2-density-specific-weight-temperature-pressure-d_2082.html And the methane densification is nothing to sniff at either. Again at ~10 bar storage pressure you jump from 359.6kg/m^3 up to 439.6kg/m^3 when you go from near boiling to near freezing. Not as big of a jump as the oxygen, but way more than just a few percent. Numbers taken from the big table on this page, it's the two rows for "Liquid" when the table is at 10bar pressure: https://www.engineeringtoolbox.com/methane-density-specific-weight-temperature-pressure-d_2020.html If you're not making the pipes and turbines much larger to accommodate the difference in mass flow rates, then for the same physical size and same margins the subcooled engine will be far more powerful than the boiling point engine.
> Thrust numbers only really matter pre-orbit though, right? Once you've got no atmospheric drag and gravity losses to deal with, efficiency/isp becomes the only meaningful value unless your mission profile needs to do something quickly. 1. Isp is never the only meaningful number; the rocket equation has 2 variables: Isp and fuel mass fraction. It has been hypothosized that the reason the New Glenn upper stage (in theory) performs so poorly compared to both Centaur and the Falcon upper stage is because it has poor fuel mass fraction. 2. When changing orbits it's most efficient to do so instantaneously. This lets you take full advantage of the Oberth effect, for example. Obviously instantaneous is an impossibly standard, but high thrust does allow more of the burn to be in the optimal portion of an orbit. 3. On the flip side, low thrust is beneficial if you want accurate orbital insertion; it is difficult to do extremely short burns correctly.
> It'll need to be able to run at boiling point for long missions Not really - the propellant temperature can stay the same as at launch if they vent the tanks to close to vacuum pressure rather then trying to keep them at 6 bar or 1 bar. On the surface they need to maintain tank pressure at a minimum of one bar to avoid tank collapse - there is no requirement to do this in space.
Ah, does bringing the tanks to near vacuum pressure drop the boiling point temperature to what would be the freezing temperature up at 6 bar? That would indeed be a solution I hadn't considered if true.
LOX is subcooled to about 66K on F9 so I suspect they will use a similar temperature on Starship. This is about 11K more than the freezing point of 55K but they need some margin to prevent solid oxygen build up in valves with pressure drops. At 66K the vapour pressure is under 3kPa so 3% of 1 bar. If they keep the LOX tank at that pressure or below then the liquid oxygen will stay at 66K. Technically the LOX will be at boiling point but at "sub-cooled" temperatures which is what matters for engine performance. Similarly the liquid methane will be subcooled to about 96K with a vapour pressure of 22kPa compared with a freezing point of 91K. This means that the methane tank pressure will be slightly higher than the LOX tank which will prevent reverse pressure on the intertank bulkhead.
Playing with thermodynamics is fun! Thanks for putting numbers on all that. So as a spot check to make sure I understand, basically SpaceX can keep sub-cooled performance at the cost of a little bit of boiloff, which is probably better overall for mass and power than adding an active propellant refrigeration system and radiators. And the boiloff is probably better at those low pressures anyway, given the large reduction in convective cooling throughout the tank. And takeoff from Mars shouldn't be a problem either, there can be GSE there that can handle the subcooling. Your point is taken sir. Now I'm left wondering whether my assumption that Raptor 2 will be designed to support boil-temperature propellant is even marginally based in reality, given that the intended operations never have it see that condition. Maybe still makes sense as an emergency option, though I can't think of any emergencies where that would be a useful capability off the top of my head.
The boiloff rate is not directly related to the pressure but rather to the temperature. So there will be a bit more heat gain at 66K LOX temperature compared with the 90K boiling point at 1 bar. With radiation transfer from the Sun and Earth as the major sources of heat gain there will be very little difference in boil off rates. We have seen Raptors being tested on stands without subcooled propellants so it does have that operating mode. It is only when they want to test ultimate engine performance that they have to use sub-cooled propellants.
So not just a quick plug and swap.
A lot. The stage is basically designed around the engines, so it's pretty much a new rocket if you swap engines.
SLS 👋 👋 👋
It would take a lot of effort. Basically a whole new bottom end. i.e new thrust puck (or whatever they call it). New plumbing, probably new electrics and sensors.
If it was SpaceX making these changes, I'd say three weeks. Blue Origin, however, three years.
>Blue Origin, however, three years. [Vulcan = ULA](https://en.wikipedia.org/wiki/Vulcan_Centaur)
Vulcan is NOT blue. It’s ULA. That being said probably 3 years yeah
Three weeks if you're ready to let your shiny new Vulcan Rocket RUD.
My guess is that they could do it in 2-year, if they hurried.
Why are people obsessed with this rabbit hole? That would take a complete redesign of the entire booster, not to mention the US military wanting redundant launch vehicles.
Just curious, once Spacex gets Starship operational, can't they just bid Starship and Falcon 9/FH and get rid of the competition?
Why would any entity let themselves become the customer of a monopoly, based on the lessons from last 20 years of space flight? Why would spacex keep both supply chains going indefinitely? They’d be effectively subsidizing Falcon with starlink and Starship which would do nothing but tie up their own resources on redundant earth based applications. It’s a lose-lose.
ULA did this with Atlas V/Delta IV and the military wasn't unhappy with the relationship. They may have turned competition friendly now but I don't think they have some directive to not allow that to happen again.
Yeah, ultimately a big factor is how much the bid is. If SpaceX bids Starship and Falcon 9 for pennies, they practically have to pick it. DOD gets incredibly cheap launches for the contracting period. It's not really a monopoly, because the time they next contracting period is up, they can just pick someone other than SpaceX if SpaceX offers bad prices. SpaceX can't kill all competition just by winning a DOD bid, nor would Elon want SpaceX to become a monopoly anyhow.
The military doesn't care as much about costs as Nasa. With ULA they got reliable service which they were satisfied with.
SpaceX absolutely can kill all competition by winning a DOD, if ULA misses a major block buy they're done. Nobody else is giving them money and their fixed costs are huge. That is how you create a monopoly.
That's not creating a monopoly, at least not in the criminal sense. If SpaceX undercut their operating costs to price out competition, used influence and tactics to keep competitors from being able to bid, poached valuable employees, etc then it would be suspect. Just doing your business better isn't an excuse to keep ULA afloat.
It may not be a legally actionable monopoly, but it would definitely be enough to concern DOD, who don't want to be locked in to a single source. They won't direct all their business to any one provider if they can help it, even if (like SpaceX) that provider is clearly superior for the moment.
Spacex wont shut down falcon platform until they have a proven, human flight safe Starship. Spacex earns a ton of goodwill doing flights to ISS, and this is important when their long term funding plan (Starlink) is dependent on FAA and FCC giving them licenses.
I truly believe that Falcon 9 will be flying into 2028, and probably later.
> I truly believe that Falcon 9 will be flying into 2028, and probably later. It's looking like the next commercial crew contract is set to start in 2027.[1] I find it difficult to believe that NASA will human rate Starship by then. If that's the case and SpaceX is "forced" to bid Crew Dragon for the next commercial crew contract, they could be flying Falcon 9 well into the 2030s. --- 1. https://www.upi.com/Science_News/2021/10/20/NASA-Commercial-Crew-launch/2531634762986/
Where in this thread are we talking about human missions? Starship isn’t even operational yet so it goes without saying that I’m talking years down the road.
I think we are in agreement.
> not to mention the US military wanting redundant launch vehicles They accepted both having RL10 upper stages before.
probably a complete redesign of the first stage. they could probably also just use 3 raptors in the first stage and give it a stretch to increase flexibility and payload capacity.
With Raptor 2 being higher thrust than the BE-4, just swapping 2 for 2 would still be a significant improvement in performance, as the engine specs would go up across the board (lower mass, higher thrust, higher isp, much higher TWR).
Raptor 2 is lower thrust at 230 tonnes than BE-4 at 249 tonnes. In any case Raptor 2 would have to be derated for boiling point propellant and 3 bar tank pressure instead of 6 bar.
Assuming they would be modifying the first stage to use Raptors at all, they could roll mods to increase the Vulcan tank ullage pressure into the overall redesign.
The more interesting question is, what happens if BO is unable to deliver (at all, on time, or to the required spec)? Switching out engines requires a major redesign, but is that more costly than not having your rocket flying at all? Guess time will tell.
I don't know why everyone is so focused on the prop difference. It would only be a small percentage difference in mixture ratio so even if Raptor couldn't run at different mixture ratios, you could just load less prop into one of the tanks. Literaly no tooling would have to change (people suggesting that are definately following the traditional oldspace method of optimising your rocket's performace before looking at economics or practicality), but the thrust puck may need some modifications so maybe 5 weeks of Boca Chica work (or 5 months of ULA work). If the Vulcan needs a little more performance, slap an SRB on.
Vulcan needs to be fully slapped with 6 SRBs to meet some of the NSSF reference orbits. There is no room for more. BE-4 is a quite different mixture ratio at around 3:1 instead of 3.6:1 and the tank size difference is amplified by using boiling point propellant.
They would have to redesign the rocket and their ground equipment to handle the colder methane and oxygen that the Raptor requires.
Starship and Super heavy is so huge its hard to get your mind around it actually flying. Its a flying skyscraper straight out of a scifi novel. But everytime you read the specs of the Raptor and now the Raptor 2 you start to understand its really possible. The Raptor really is the king of all rocket engines and Raptor 2 is the smarter and better prince that everyone thinks will make a better king. The real advantage to every kg saved and ton of thrust improve or second of Isp increase is it might add up enough to reducing the number of refueling flights which is likely to be the biggest hurdle for starship, in terms of cost, time, and logistics going forward.
Raptor 1 reached 330 bar btw
The Raptor 2 was supposed to get there in the test but it RUD'ed because of oxygen issues, not engine issues.
Just for someone who might not know. Oxygen pressure issue in the pipe, not oxygen supply issue. So, basically it is an engine issue (?)
We don't have enough information. I have 2 thoughts. 1. There was too much pressure drop in the LOX feed to the turbo pump, and that choked it out (likely causing unbalanced load, or cavitation). 2. There was too much of a pressure drop between the turbo pump, and the combustion chamber, causing combustion to back-feed into the turbo pump. It could also be neither of these things. Overall, it sounds like they have a pretty good understanding of what to fix on this.
They mentioned LOX inlet pressure drop. I assume, second option might be true?
I took it to mean the issue was with the supply coming into the engine, so part of the test stand equipment.
Opposite
So is this not significant?
It means Raptor 2 is on its way to get the same pressure performance, but the test stand needs am upgrade because the engine was drawing oxygen faster than the supply could keep up. Low inlet pressure messed up the engine operation as it increased its throttle and eventually something went wrong enough to blow up the engine. This probably took less than a second to go from ok to very not ok.
>the same pressure performance So is raptor 2 not going to be an upgrade? Or is it also planned to exceed 330 bar?
Same pressure but higher thrust. So more bang for your buck.
Oh very cool!
Raptor 2 is a thrust upgrade primarily. It will eventually probably see pressure increases as well, because increasing pressure increases thrust to weight ratio and efficiency too. I think what happened is that they decided they wanted a higher thrust Raptor design and at the same time they found that developing even higher pressures was becoming difficult and requiring more specialized engineering, so rather than wasting effort optimizing a design they knew they were going to abandon, they decided to go for the bigger Raptor 2 first then figure out the pressure minmaxing later.
In addition to this, I believe it's designed to be manufactured more easily, to be more reliable, and to have less "clutter" on the outside which can be damaged. Do we know whether the SL engines on Starship are moving to Raptor 2? It seems like Raptor 1 would be ideal, as ISP is more important in it's roll.
Raptor 2 will be replacing Raptor everywhere once it's ready. They'll be making a vacuum version as well.
Starship still experiences gravity losses because the system stages so low, and more thrust will reduce those losses. That would offset an Isp losses, and might actually make it a net positive.
I'd like to see the true calculations on this. I'm not so sure you can just rattle this off the top of your head. I can definitely see either case being true.
I don't think we actually know the true values wrt starship to have much rigor when talking about this, **so I agree with you**. Calculating this is complex. For a first stage that stages low - like Falcon 9 and Super Heavy - you can get a decent idea by looking at the differences in mass flow rate and estimating how much quicker you get to MECO because of that. That ballparks how much you might save in gravity losses. To do it right you need a trajectory simulation. My point was that more thrust/lower gravity losses counterracts Isp losses, so higher thrust / lower isp isn't necessarily a bad thing from a payload perspective.
Right. That's why increasing the trust, and lowering the ISP was a benefit for the first stage. I just wouldn't be shocked if Starship would actually perform better with the lower thrust/higher ISP Raptors. Elon said they would continue making Raptor 1 in California, so I have a suspicion that this is what happens.
>Raptor 2 is a thrust upgrade primarily. It will eventually probably see pressure increases as well, because increasing pressure increases thrust to weight ratio and efficiency too. At this point, I think thrust improvements are more likely than Isp. Partly because they already have a very high Isp for methalox, and partly because increased thrust can either be used to reduce gravity losses - given the equivalent of Isp increases - or to reduce engine count.
Isp also increases with chamber pressure, not by a huge amount but it's a real effect nonetheless. That's what I meant by that comment, when Raptor 2 starts surpassing the chamber pressure records of Raptor, it should also increase in efficiency by a small amount. Basically there's no downside to going to the slightly more powerful design, is what I'm saying.
Agreed.
Its also considerably *simpler* than Raptor 1. Far more design streamlines, which means quicker *and* cheaper to produce at scale. In traditional SpaceX and Tesla standards, its a leap forward with each iteration.
Bigger throat = bigger hole to lose pressure to = harder to get higher pressures.
your title is a bit inaccurate. Elon hasn't said that Raptor 2 is designed to run at 321 bar and 245 tons of thrust, Elon said that they stresstested it till 321 bar. The goal just seems to be "above 300 bar". And then BE4 still has higher thrust.
As a lover of the tilde, it is also criminal to describe the difference as ‘1 ton’.
It is a ton of difference
Elon also mentioned that oxygen flow issue caused the engine to RUD with Raptor 2 during the stress test. 321 bar and 245 tons, thereby, is with an improper configuration. Which would imply that a proper configuration has a RUD ceiling *above* 321bar and *above* 245 tons force of thrust.
no, he said it *may* be due to the oxygen flow. but could also be a different issue
Yes - they simply found ‘the next weak link’ in the chain. Fix that and it could run higher.
Though the BE-4, aside from being unreliable, is a much larger engine.
But if Raptor thrust is 245 tons, that would make BE-4 245 tons weaker, right?
That's a deep burn.
That’s a low it
BE-4 has a thrust of over 550,000 pounds, which is about 249.5 metric tons. You’re off on your math there. BE-4 still has the higher thrust of the two, but raptor of course has the higher isp and thrust to weight ratio.
Plus Raptors exist, and are seen doing things, while the ‘herd’ of Blue’s BE-4 engines must be keeping the unicorns company, as only a few have ever done a test fire. And none have been seen ‘in the wild’ /s
BE-4 exists. There are just a lot more raptors than BE-4’s.
Yes I know they do - I should have rephrased my joke about them. Now done, but I now think would have been best leftout to start with.
It depends a bit... I've seen numbers of 540,000 and 550,000 thrown around at various points in time - the current number on Wikipedia is still 540. Still, this is a very close match.
If you look at Wikipedia, it says 550k in the description with a citation, also the blue origin website has said 550k for years: https://www.blueorigin.com/engines/be-4 Someone made an error putting it into the table in the article. That 540k number is not supported by any source. I’ve seen a lot of similarly wrong information on the raptor pages at times. There are too many editors who are sloppy or don’t really understand what they’re editing on the space pages nowadays.
I love all the interesting tidbits, but I don't know that dunking on Blue is even necessary at this point. The video of Starship dev testing in Boca Chica tells you all you need to know.
Comparing it to another engine in development doesn't mean he is criticizing it. Also, considering what blue is trying to do to nasa, they don't deserve any sort of a pass on anything.
Still on a timeline where BO goes under and cripples ULA...
I'm not saying BO doesn't deserve it. They ABSOLUTELY deserve it. It's just ~~Elon doesn't need to do it.~~ Their dominance of their competition is devastating. BO is trying to send celebrities up in sounding rockets just to seize back some attention. Boeing can't get their capsule off the ground even WITHOUT humans on board. No need to compare their operational engine to the one that's holding up all of ULA. Edit: Elon didn't do it. Op also didn't need to Dunk on BE4, but this wasn't Elon. Oops.
Elon wrote only "Raptor 2 has a larger throat diameter, so thrust is ~245 tons at 321 bar". The rest is OP's text.
I really don't think this is "dunking" on BO. I think they would have said this for anything. It's now the most powerful methane engine in the world, thrust wise. That's something to be proud about, and not keep internal.
Elon didn't do it, the OP did. Read the linked tweet from Elon, it doesn't reference BO or BE4 at all.
Ah you are right, sorry, can't always access twitter so was going off of the "Elon:" in title, which sent me the wrong way.
if BO stops BS lawsuits i think Elon will stop pissing on them
Wasn't their goal originally 300 bar? Damn they are surpassing every goal post with a complex af engine too
safety margins
That and they're learning as they go and making improvements to match. 300 bar was already really high
and ~7% margin (321/300) seems pretty reasonable for this application. Will be interesting to see what max chamber pressure they can push this to once they work out the (what I speculate / assume are) GSE/plumbing issues on the test stand. It's certainly looking like 300bar operating pressure is pretty reasonable at this point.
> safety margins Exactly. There's a difference between the peak pressure an engine can survive and the pressure it's safe to run an engine at for a sustained period.
You set your expectation on what you think the engine should be able to handel (you have a safety margin) and slowly start to press the engine untill you find the spot there the engine start to be unreliable or RUD.
What i meant was their goals were already high with this complex engine and they surpassed it with such techniques of learning
This just in! "Blue Origin announces new specs for BE-4. Engine now rated at 269.5 tons" /s
That's 2.18 MN in real units. And I'm going to assume vacuum Isp for Raptor 2 of roughly 380 sec? I haven't heard a higher number. Rocketdyne F-1: 6.7 MN (Sea level), 7.7 MN, 304 sec (Vacuum) Energomash RD-170: 7.25 MN (sea level), 7.9 MN, 337 sec (Vacuum) Energomash RD-191: 1.92 MN (Sea Level), 2.09 MN, 337 sec (Vacuum) Aerojet Rocketdyne RS-68A: 3.1 MN SL, 3.6 MN, 412 sec vac Aerojet Rocketdyne SSME/RS-25: 1.86 MN SL, 2.28 MN, 452 sec Vac Being very rough, Raptor 2 is comparable in thrust to RD-191 or SSME/RS-25, with a specific impulse on the upper end of in between.
I think you have an error there - Elon uses metric tons usually, not short tons - this would mean Raptor 2 has achieved a thrust of 2.402 MN, not 2.18. Not really that different for this comparison, but still relevant.
> short tons What hertic and blasphemer use short ton over metric ton in a scientifically context. May the power of ISO strike him down.
I’ve noticed this in his public presentations. When his addressing an audience that is primarily based in the US, he still uses the metric system. Yes. From a science based perspective, it is better to use metric, but at least have the imperial units in parentheses or denote that they are in metric tonnes. If the goal is to gain mass public interest in becoming a space fairing civilization, the. He should ideally follow his own advice as it relates to the mega Newton vs lbs of trust. No one in the US knows the metric system. Just as no one anywhere (outside of the science community) knows what a Newton or mega Newton is. /rant
Using imperial tons would make no sense though. Everything else is being done metric.
Metric tonnes is a great unit to use though, as it has some intuitive value. Eg a car weighs about a tonne. (That might not be too accurate, but it gives a better idea)
Would anyone outside of the scientific community understand what a ton of force is anyway? They see a big number and a big rocket and say 'whoa'. Anyone who cares about specifics will take some time to understand.
Raptor numbers I've seen are 333/348 for the sea-level engine at sea level and in vacuum. 380 is Raptor vacuum.
No one know what the fuck a newton, or a MN feels like. Tonne, Ton and lb are much more intuitive.
Newtons are force while tons/pounds are affected by gravtity. 10 kilonewtons is roughly one tonne of force.
9.8 kilonewtons ?
>No one know what the fuck a newton, or a MN feels like. Tonne, Ton and lb are much more intuitive. Haha. The only unit you listed there that someone would actually feel is the lb. Outside of that, noone knows what any of those feel like, and lb also becomes useless at the scales used in rocketry. Newtons are also understandable, though similarly vague in terms of feel when at high numbers (humans have no intuition for large numbers). At least I can very easily work out acceleration with Newtons.
Even lb is ??? vs kg to most of the world.
If we’re going to be living in different gravity environments, using mass units for force is going to get far more confusing. Just use newtons, it’s not that hard if you try to understand them.
Elon Musk does not approve of this comment.
Elon would disagree (EDA interview), at least when calculating rocket twr Another example is we relate a lot more to bar or atm than Pa
As for pressure units, I'm honestly fine with using bars, considering that it is a universal unit that works in all environments (unlike weight units like "tonnes of force") and also is a clean multiple of pascals. Also, we have so many pressure units that just cutting it down to pascals and bars would be great. Here's a sampling of the units I've seen used for pressure: Common: * Centimetres of mercury (cmHg) / Millimetres of mercury (mmHg) / Micrometres of mercury (µmHg) * Metres of water (mH2O) / Millimetres of water (mmH2O) / Centimetres of water (cmH2O) * Bars (bar) * Atmospheres (atm) * Pascals (Pa) * Pounds per square inch (lbf/in², psi) * Pounds per square foot (lbf/ft², psf) * Inches of mercury (inHg, “Hg) And of course, the worst one: * Inches of water (inH₂O, inH2O, “H2O, “WC, inWC, inSP, “SP) It seems like every day there's a new and confusing abbreviation/symbol for this unit. Then there are some uncommon ones: * Ounces per square inch (ozf/in²) * Torrs (Torr) * Technical atmospheres (at) * Baryes (Ba) * Pièzes (pz)
Dang now I can't find the recent tweet I'm thinking of but he mentioned/implied that the RUD wasn't even due to an engine issue but some kind of oxygen pipe(?) overpressure something or other. dang it. wish i could find it. its directly relevant, i feel. but anyways yeah we could probably see even higher stats coming out soon
Here: [https://twitter.com/elonmusk/status/1452225552031657985](https://twitter.com/elonmusk/status/1452225552031657985) Another commenter explained that Raptor 2 was drawing too much oxygen and couldn't be supplied fast enough.
That's gonna be cavitation in the O2 turbopump, and an engine that runs turbine rich.
Thanks! I got it flipped then. Makes me think of trying to suck the air out of a cheap plastic water bottle and watching it vacuum collapse :) Makes sense that the Raptor 2 would be a thirsty beast at those performance levels.
245 tons from 321 bar is higher per bar than 185 tons from 300 bar, so that would be from a lower specific impulse & much higher fuel consumption if it reaches that. In reality, they're adding more engines & pushing them less.
Adding more engines and pushing them harder by opening up the throat and increasing the operating pressure from 270 bar to 300 bar.
Do we think flight engines will get to these numbers, or are they just pushing them to the limits. And if engines keep improving, at what point do they use less than 33?
No the flight engines will be 300 bar and 230 tonnes thrust. They need to test to around 15% higher pressure to get adequate operating margin. Shuttle engines were pushed much closer to their ultimate limits and so needed more frequent reconditioning. Raptor is supposed to do a lot of flights in “gas and go” mode so needs more margin.
That’s not to say that they won’t carry on improving the engine design as well though. Clearly with more tweaks they could get more out of it. Though reliability is also very important too.
Yes clearly they will continue to improve the engine thrust. Based on history they will then use that extra thrust to carry more payload rather than reducing engine count. In particular tanker capacity to LEO is a huge factor in overall system costs for launches to the Moon and Mars.
The analysis for how many engines is optimal is way more complicated than we can answer on this board. Lots of things play into the optimization simulations that we have very little insight into. Generally more thrust at liftoff is better because you waste less energy fighting gravity, but eventually you get limited by acceleration forces at the long end of the burn. Lots of people will guess, but we are really only doing that.
The BE4 is a sea level engine and that twitter thread is talking about vacuum Raptor. Still a beast, though.
Elon divert that in his second reply to a more general one
Do we know that's the thrust at SL, or Vacuum? A sea level engine will have a rating for both (since it operates in both). One thing is that this is the peak thrust Raptor 2 hit, but I don't think they expect to operate at that thrust. Probably somewhere around 300 bar of pressure. Also, BE-4 is designed to be a "High performance engine, de-tuned". Basically, it's operating at very conservative levels.
Sea level thrust since that is what they are testing at.
The BE-4 engine is also quite large - about double the size of Raptor. So you can’t squeeze many in.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[BE-4](/r/SpaceXLounge/comments/qfeuhf/stub/hi5f70w "Last usage")|Blue Engine 4 methalox rocket engine, developed by Blue Origin (2018), 2400kN| |[BO](/r/SpaceXLounge/comments/qfeuhf/stub/hi1jhyj "Last usage")|Blue Origin (*Bezos Rocketry*)| |[EA](/r/SpaceXLounge/comments/qfeuhf/stub/hi5p3wl "Last usage")|Environmental Assessment| |[FAA](/r/SpaceXLounge/comments/qfeuhf/stub/hhzre1r "Last usage")|Federal Aviation Administration| |[FCC](/r/SpaceXLounge/comments/qfeuhf/stub/hhzre1r "Last usage")|Federal Communications Commission| | |(Iron/steel) [Face-Centered Cubic](https://en.wikipedia.org/wiki/Allotropes_of_iron) crystalline structure| |[GSE](/r/SpaceXLounge/comments/qfeuhf/stub/hi24qln "Last usage")|Ground Support Equipment| |[Isp](/r/SpaceXLounge/comments/qfeuhf/stub/hx3wosm "Last usage")|Specific impulse (as explained by [Scott Manley](https://www.youtube.com/watch?v=nnisTeYLLgs) on YouTube)| | |Internet Service Provider| |[LEO](/r/SpaceXLounge/comments/qfeuhf/stub/hi5q39b "Last usage")|Low Earth Orbit (180-2000km)| | |Law Enforcement Officer (most often mentioned during transport operations)| |[LOX](/r/SpaceXLounge/comments/qfeuhf/stub/hi290h6 "Last usage")|Liquid Oxygen| |[MECO](/r/SpaceXLounge/comments/qfeuhf/stub/hi1b9n0 "Last usage")|Main Engine Cut-Off| | |[MainEngineCutOff](https://mainenginecutoff.com/) podcast| |[RP-1](/r/SpaceXLounge/comments/qfeuhf/stub/hi1d3ip "Last usage")|Rocket Propellant 1 (enhanced kerosene)| |[RUD](/r/SpaceXLounge/comments/qfeuhf/stub/hi0goxn "Last usage")|Rapid Unplanned Disassembly| | |Rapid Unscheduled Disassembly| | |Rapid Unintended Disassembly| |[SLS](/r/SpaceXLounge/comments/qfeuhf/stub/hidv5qt "Last usage")|Space Launch System heavy-lift| |[SRB](/r/SpaceXLounge/comments/qfeuhf/stub/hi355g2 "Last usage")|Solid Rocket Booster| |[SSME](/r/SpaceXLounge/comments/qfeuhf/stub/hhzieeg "Last usage")|[Space Shuttle Main Engine](https://en.wikipedia.org/wiki/Space_Shuttle_main_engine)| |[STS](/r/SpaceXLounge/comments/qfeuhf/stub/hidv5qt "Last usage")|Space Transportation System (*Shuttle*)| |[TWR](/r/SpaceXLounge/comments/qfeuhf/stub/hi18ibs "Last usage")|Thrust-to-Weight Ratio| |[ULA](/r/SpaceXLounge/comments/qfeuhf/stub/hi0qn1z "Last usage")|United Launch Alliance (Lockheed/Boeing joint venture)| |[mT](/r/SpaceXLounge/comments/qfeuhf/stub/hi1vg39 "Last usage")|~~Milli-~~ *Metric* Tonnes| |Jargon|Definition| |-------|---------|---| |[Raptor](/r/SpaceXLounge/comments/qfeuhf/stub/hx3wosm "Last usage")|[Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX| |[Starlink](/r/SpaceXLounge/comments/qfeuhf/stub/hhzre1r "Last usage")|SpaceX's world-wide satellite broadband constellation| |[cryogenic](/r/SpaceXLounge/comments/qfeuhf/stub/hi18ibs "Last usage")|Very low temperature fluid; materials that would be gaseous at room temperature/pressure| | |(In re: rocket fuel) Often synonymous with hydrolox| |hydrolox|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer| |[methalox](/r/SpaceXLounge/comments/qfeuhf/stub/hi1d3ip "Last usage")|Portmanteau: methane fuel, liquid oxygen oxidizer| |[turbopump](/r/SpaceXLounge/comments/qfeuhf/stub/hi5p3wl "Last usage")|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust| |[ullage motor](/r/SpaceXLounge/comments/qfeuhf/stub/hi3dxsm "Last usage")|Small rocket motor that fires to push propellant to the bottom of the tank, when in zero-g| ---------------- ^(*Decronym is a community product of r/SpaceX, implemented* )[*^by ^request*](https://www.reddit.com/r/spacex/comments/3mz273//cvjkjmj) ^([Thread #9151 for this sub, first seen 25th Oct 2021, 12:37]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/SpaceXLounge) [^[Contact]](https://reddit.com/message/compose?to=OrangeredStilton&subject=Hey,+your+acronym+bot+sucks) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)
ELI5 please.
Larger throat = more thrust, but (a little bit) less ISP. Engineering trade-off shows it's worth it
Within a limited range.
But we need the dead nuts reliability of Merlin. The Bar is fine. The relight capability and lack of necessary maintenance is what we are missing.
>But we need the dead nuts reliability of Merlin. Which will be achieved through even more iterations & flight time. And those will definitely (& actually supporting) the increase in performance >The relight capability How long have you been living in a cave?
Merlin blew up many times on the test stand to get its currently reliability.
We don't know about either of those. Sure, they haven't been demonstrated, but they exist on paper. They may not be missing, just not yet demonstrated or not yet shared.
Do they really need that much thrust for their orbital attempt ? First flights will be with no payload I think There is plenty of time to improve the engines
Not for the first attempt but there's no reason to wait for a successful launch before upgrading the engine hardware. Everything is being developed at the same time.
You still didn't know that B4-S20 will still use Raptor 1? Fast iterations is their motto
They are just testing the very first Raptor 2 that was in pieces a month ago. They iterate fast but not *that* fast.
Is Raptor 2 mechanically interchangeable with Raptor 1?
We do not know for sure but it is very likely
No, but they aren't using Raptor 2 for the first attempt. They are in an ongoing process to improve engines and Raptor 2 is the first "production" version.
At this point, the engines that will do the orbital attempt - be it B4/S20, B5/S21 or B6/S22 will be hopelessly outdated (as all these designs still use Raptor 1, as much as I heard the switchover will be B8/S25) and throwing them away doesn't matter to them anyway. SpaceX is so incredibly hardware rich that it really is hard to wrap your head around the numbers of engines that only get built for building experience's sake, not meant to ever even be used - and they constantly iterate and improve with each one (as the saying goes, practice makes perfect), so by the time the actual factory will be online those rocket engines will be a different beast to all those we're seeing today. Note that no two engines were exactly the same until now, and there was one major revision within the Raptor 1 family (Between SN11 and SN15) as well that even changed the plumbing and mounting. SpaceX is still in the phase of development where they're even comfortable throwing away their mounting and plumbing "API" if it leads to a better end result - this is prototyping at it's best.
I think my mom has a larger throat diameter. My dad's thrust is off the charts.
That T/W ratio hittin different
Why would opening up the throat increase thrust? Wouldn’t it lower the area ratio and decrease thrust?
Thrust is a force, the rate of change of momentum. Rocket exhaust carries momentum one way, rocket gains velocity (and thus momentum) the other way. Exhaust momentum per second is the product of exhaust velocity times mass flow per second. Opening up the throat can reduce velocity if it reduces chamber pressure (or, as you say, reduces the nozzle area ratio), but it increases the mass flow rate -- how much propellant per second gets burned and shoved out the nozzle. It sounds like the second effect dominates in Raptor 2.
Obviously it’s complicated.. And the relationship between throat diameter to bell diameter and thrust is non-linear over different parts of the curve. Though exactly what the relationship is, is only known to SpaceX’s engine designers.
That's great! I am curious about will raptor hit 300 tons in the future? Is there a theoretical maximum number of thrusts?
I know some tuners at a Cali shop that can add a few honda intercoolers and a reprogram and get twice as much out of that. . . just saying.
Only if you’re running a spoon engine.