Off Topic > General Discussion
Starship!
bknight:
--- Quote from: molesworth on July 30, 2022, 12:32:25 PM ---Arise, necro-thread!!
Looks like things are moving again in Starship-land, with news that they're planning for an orbital test launch in August. There are a lot of rumours about it, but I can't find anything official from SpaceX - which means it may not be true. Still, it looks like the orbital test flight might not be too far away now.
https://www.spacelaunchschedule.com/launch/starship-orbital-flight-test/
https://www.space.com/spacex-starship-rollout-launch-pad-photos
--- End quote ---
They have always played it close to the vest, only giving last minute details about tests. On the other hand Musk it seems publishes ambitious time goals, very few of which is met. But at least it keeps the troops moving ahead.
Peter B:
So, it launched, and then did some spectacular gymnastics I don't remember seeing many rockets perform previously. Does that suggest that, structurally, it's much tougher than most other rockets?
I also noticed that quite a few engine bells were unlit during flight. Can we assume there were engine problems from the start (and thus problems started internally), or that perhaps the base of the rocket was struck by debris thrown up by ignition (and thus problems started externally)?
Any other thoughts?
smartcooky:
--- Quote from: Peter B on April 21, 2023, 01:56:03 AM ---So, it launched, and then did some spectacular gymnastics I don't remember seeing many rockets perform previously. Does that suggest that, structurally, it's much tougher than most other rockets?
I also noticed that quite a few engine bells were unlit during flight. Can we assume there were engine problems from the start (and thus problems started internally), or that perhaps the base of the rocket was struck by debris thrown up by ignition (and thus problems started externally)?
Any other thoughts?
--- End quote ---
My Thoughts: (and I would defer to Jay's experience on these)
1. A few of the Raptor engines failed just after liftoff, and a couple more failed near a minute into the flight. IMO, this could likely be the result of the shock-waves generated by having 33 very powerful rocket engines all running at full noise on the pad, probably because there was no water deluge system to attenuate them. I understand that the intention is to build a water deluge system, but for this test they made the decision to go ahead without it.
2. What I found astonishing was the structural integrity. This thing bloody well cartwheeled (at least four times as far as I could see) and did not disintegrate or even come apart at the inter-stage. I guess that could be a result of skinning it with stainless instead of aluminum - AIUI the stressed skin is a big part of a rocket body's structural robustness.
SpaceX will have the pad repaired pretty smartly, and they already have the next Super Heavy Booster and Starship almost ready to stack for launch within a couple of months.
JayUtah:
--- Quote from: smartcooky on April 21, 2023, 05:12:11 AM ---A few of the Raptor engines failed just after liftoff, and a couple more failed near a minute into the flight. IMO, this could likely be the result of the shock-waves...
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Yes, that's still the best hypothesis. Lots of acoustic loading; no attenuation. I can see the rationale in not waiting for the water deluge system. If you estimate a certain acceptable fallout from reflected shock, and the goal is simply to collect flight test data, then having the data earlier outweighs the marginal improvement in reliability that the deluge system would have provided without measurably improving the quality of the flight data. I was surprised at how long they ran the engines in hold-down. That likely increased the shock damage. I'm interested in seeing what spikes or surges may have happened in the propellant feed system. This always happens at startup, but having so many engines pulling fuel leads to what I would suspect is a fun fluid flow problem.
This is actually a big improvement over the N-1 design, which similarly used a large array of small motors. The Raptor appears to be remarkably fail safe. The usual problem is that rocket engines frequently fail in a mechanical catastrophe, which damages surrounding equipment and can lead to a cascade failure. An overall vehicle design in which each individual motor can contain the effects of its own failure unlocks a lot of possibilities.
--- Quote ---What I found astonishing was the structural integrity. This thing bloody well cartwheeled (at least four times as far as I could see) and did not disintegrate or even come apart at the inter-stage.
--- End quote ---
Indeed, I too expected a structural breakup far sooner than the range-safety abort. That's a very large airframe.
--- Quote ---I guess that could be a result of skinning it with stainless instead of aluminum - AIUI the stressed skin is a big part of a rocket body's structural robustness.
--- End quote ---
Undoubtedly, but the interstage connections are the typical weak point. I want to look more carefully at the last few seconds of flight. It may have been largely in free-body motion in a practical vacuum, which would lessen the stress. Most of the breakups we encounter are in powered flight in an atmosphere.
molesworth:
Scott Manley has quite a good video analysis of both the engine issues and the structural strength of the vehicle. There was a lot of debris flying around which likely caused some engine failures, and possibly other problems.
Musk has said they'll be ready to go again in 1 - 2 months, but I've also seen a report that internally SpaceX reckons about 6 months will be needed to repair the "Stage 0" damage and install some sort of flame diverter.
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