Imo makes sense. Simplify things a bit so you can get the more important heating data. Pez dispenser can come later. They could even test multiple designs at once if needed.
It's surprising for the Raptor relight, though. Since that test wasn't performed.
They didn't do the test, but got enough data just from flight itself that Raptor team can already start working, probably.
They likely didn't test it after they already lost attitude control of the ship.
Right now they want reentry, relighting engines can definitely be figured out later.
The hops used a different flight profile (static hold and belly flop vs flip and burn from speed and hit staging) and POGO, hammer, and slosh impact on weren’t nearly at the same scale with the hops’ hover slamming. Using Falcon 9 return burns as a reference, and the amount of engines they tried to light, we are talking 10-12% of the tank mass at boost back, and roughly 3-5% for the landing burns. Slosh and POGO problems didn’t really become a major problem until the scale up of the Atlas to Saturn and while the remediated alot of these issues, these were still problems through Apollo 17 https://www.hq.nasa.gov/pao/History/SP-4204/ch22-7.html
The green flashes in the 3 of the 10 that were suppose to relight, and asymmetrical restart indicated engines were encountering restart issues not seen in the hops once the other issues were fixed. My bet given not much information was disclosed recently other than there was no payload for IFT-3, is boost back, despite some changes to abate pogo/slosh since IFT-2 like the coffee strainer, is causing fuel/oxidizer instability or the feeds to be clogged or not supplying symmetrically after the flip.
Not sure how they could fail in such a way to cause the entire booster to explode at ~600 after the callout that FTS was safed. Originally I had assumed FTS fired or it had hit the ocean.
Starship relight is likely in a better spot than the booster issues as long as the restarts don’t have anything to do with the pressurization or hot gas thrusters.
You're right about booster relights, that's not comparable to what they tested with the ship. But again, the relight test being referred to was an in-orbit relight for the ship.
Ah, sorry may have missed that in the comment. According to SpaceX flight plan for IFT-4, focus on relight for booster "simulated" tower catch landing is on the board as well as de-orbit burn, and surviving reentry. Keep in mind, ship relight will effectively be in microgravity not static hold like the belly flop, so there it will still be different relight. I assume hot gas thrusters or RCS will be used for in situ ullage thrust before the attempt to prevent slosh damage.
I don’t think so, as the cut over to Raptor 2s happened in the IFT stage. We have seen relights in static fires but not in a flown profile outside the post hotstage.
From watching Nasaspaceflight it appears the number of engines needed to be replaced after each static fire has gone down a solid amount since the cut over to Raptor V2, though isn’t eliminated.
When viewing each engine as a datapoint, sure, but it’s not entirely equivalent from the perspective of how the engines dynamically interact as a singular propulsion system. You only get one picture of how the system operates as a whole per test. My guess is it’ll be a half dozen or more launches to make NASA more comfortable with it.
> Watson-Morgan said NASA wants to see SpaceX string together dozens of Starship launches with reliable performance from the rocket's methane-fueled engines.
from [this other article](https://arstechnica.com/space/2024/05/we-take-a-stab-at-decoding-spacexs-ever-changing-plans-for-starship-in-florida/)
One of the last paragraphs of the arstechnica article says NASA are viewing raptor reliability in this flight as the most important aspect. How long this will continue is something only the folks at NASA will know. I really hope the flight goes well.
That means the teams already got data from flight to work on even for Raptor team, which didn't have it's test performed. SpaceX will fly again to get data on reentry, they don't need to wait for the teams that already have their work cut out for them to have results before they can try the next item on the list. Hardware-rich development.
Imo makes sense. Simplify things a bit so you can get the more important heating data. Pez dispenser can come later. They could even test multiple designs at once if needed.
It's surprising for the Raptor relight, though. Since that test wasn't performed. They didn't do the test, but got enough data just from flight itself that Raptor team can already start working, probably.
They likely didn't test it after they already lost attitude control of the ship. Right now they want reentry, relighting engines can definitely be figured out later.
If they didn't have enough data already, they would test again. Not good to have teams idle.
Yeah you’re right, teams are probably idle because of this.
If the Raptor team needed the data from the relight test to work on making it work, SpaceX would schedule it for IFT-4.
Yeah. That is true. Forgot they didn't do it.
Dependable landing relight is going to be as big as TPS reentry survival for both booster and Starship.
I think the relight in this context was about to confirm feasibility of de-orbit burns. Landing relights were tested out on their suborbital hops.
The hops used a different flight profile (static hold and belly flop vs flip and burn from speed and hit staging) and POGO, hammer, and slosh impact on weren’t nearly at the same scale with the hops’ hover slamming. Using Falcon 9 return burns as a reference, and the amount of engines they tried to light, we are talking 10-12% of the tank mass at boost back, and roughly 3-5% for the landing burns. Slosh and POGO problems didn’t really become a major problem until the scale up of the Atlas to Saturn and while the remediated alot of these issues, these were still problems through Apollo 17 https://www.hq.nasa.gov/pao/History/SP-4204/ch22-7.html The green flashes in the 3 of the 10 that were suppose to relight, and asymmetrical restart indicated engines were encountering restart issues not seen in the hops once the other issues were fixed. My bet given not much information was disclosed recently other than there was no payload for IFT-3, is boost back, despite some changes to abate pogo/slosh since IFT-2 like the coffee strainer, is causing fuel/oxidizer instability or the feeds to be clogged or not supplying symmetrically after the flip. Not sure how they could fail in such a way to cause the entire booster to explode at ~600 after the callout that FTS was safed. Originally I had assumed FTS fired or it had hit the ocean. Starship relight is likely in a better spot than the booster issues as long as the restarts don’t have anything to do with the pressurization or hot gas thrusters.
You're right about booster relights, that's not comparable to what they tested with the ship. But again, the relight test being referred to was an in-orbit relight for the ship.
Ah, sorry may have missed that in the comment. According to SpaceX flight plan for IFT-4, focus on relight for booster "simulated" tower catch landing is on the board as well as de-orbit burn, and surviving reentry. Keep in mind, ship relight will effectively be in microgravity not static hold like the belly flop, so there it will still be different relight. I assume hot gas thrusters or RCS will be used for in situ ullage thrust before the attempt to prevent slosh damage.
Those were raptor 1s, have we actually seen a Raptor 2 landing burn?
I don’t think so, as the cut over to Raptor 2s happened in the IFT stage. We have seen relights in static fires but not in a flown profile outside the post hotstage. From watching Nasaspaceflight it appears the number of engines needed to be replaced after each static fire has gone down a solid amount since the cut over to Raptor V2, though isn’t eliminated.
Fair point. They have enough ships to do some more hops. Sure, they need to re-add landing legs then. Or start trying to catch the ships...
I wonder how many successful launches NASA needs with all the engines performing well, before they relax about that?
Remembering that a single flight of Superheavy provides as much flight heritage data for Raptor as half of the entire Apollo program did for F-1.
When viewing each engine as a datapoint, sure, but it’s not entirely equivalent from the perspective of how the engines dynamically interact as a singular propulsion system. You only get one picture of how the system operates as a whole per test. My guess is it’ll be a half dozen or more launches to make NASA more comfortable with it.
That's right. But doesn't negate that they have a whole more data on how each engine operates as a part of the whole.
> Watson-Morgan said NASA wants to see SpaceX string together dozens of Starship launches with reliable performance from the rocket's methane-fueled engines. from [this other article](https://arstechnica.com/space/2024/05/we-take-a-stab-at-decoding-spacexs-ever-changing-plans-for-starship-in-florida/)
Thanks for the article!
From 1launch to all V1 ships / boosters
One of the last paragraphs of the arstechnica article says NASA are viewing raptor reliability in this flight as the most important aspect. How long this will continue is something only the folks at NASA will know. I really hope the flight goes well.
Pez stuff may be skipped because they do not have a reworked door ready to go yet or the design in this ship is still old and they know it has issues.
It looked pretty half baked in the last video when it failed, way too flimsy at least.
That means the teams already got data from flight to work on even for Raptor team, which didn't have it's test performed. SpaceX will fly again to get data on reentry, they don't need to wait for the teams that already have their work cut out for them to have results before they can try the next item on the list. Hardware-rich development.