Author Topic: Starship!  (Read 65253 times)

Offline jfb

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Re: Starship!
« Reply #225 on: September 27, 2021, 09:02:17 AM »
Center of mass is going to be relatively low, and the legs will almost certainly be self-leveling.  I wouldn’t take any concept renders as gospel at this point - I’m pretty sure the design is still in flux, and will probably be tweaked further after they start flying and attempting to land orbital prototypes. 

Offline Peter B

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Re: Starship!
« Reply #226 on: September 27, 2021, 09:20:22 AM »
Center of mass is going to be relatively low, and the legs will almost certainly be self-leveling.  I wouldn’t take any concept renders as gospel at this point - I’m pretty sure the design is still in flux, and will probably be tweaked further after they start flying and attempting to land orbital prototypes.

How would that work?

Legs touching the ground cant upwards as the spacecraft descends, and only lock when all the legs are touching the ground? Something like that?
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Offline cjameshuff

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Re: Starship!
« Reply #227 on: September 27, 2021, 12:22:52 PM »
Center of mass is going to be relatively low, and the legs will almost certainly be self-leveling.  I wouldn’t take any concept renders as gospel at this point - I’m pretty sure the design is still in flux, and will probably be tweaked further after they start flying and attempting to land orbital prototypes.

How would that work?

Legs touching the ground cant upwards as the spacecraft descends, and only lock when all the legs are touching the ground? Something like that?

There's many ways to implement self-leveling. Even the quick and dirty crumple legs they have on the prototypes can handle some degree of ground variation, and a similar approach was used on the Apollo landers. An active hydraulic or electromechanical system using pressure and attitude sensors might be worth the mass for the moon and Mars versions.

Offline Peter B

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Re: Starship!
« Reply #228 on: September 29, 2021, 11:08:59 PM »
Here's an article from our Australian ABC about Starship:

https://www.abc.net.au/news/2021-09-30/elon-musk-starship-to-get-back-to-the-moon-and-on-to-mars/100498076

Nothing particularly quote-worthy, just a backgrounder on SpaceX's achievements and plans, and a bit about BO's gripes.

The article is related to an episode of the ABC's "Foreign Correspondent" show which should be available on catch-up TV in the next day or so.
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Offline molesworth

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Re: Starship!
« Reply #229 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

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Offline bknight

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Re: Starship!
« Reply #230 on: July 30, 2022, 04:07:14 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

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.
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Offline Peter B

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Re: Starship!
« Reply #231 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?
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Offline smartcooky

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Re: Starship!
« Reply #232 on: April 21, 2023, 05:12:11 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?

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.
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Offline JayUtah

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Re: Starship!
« Reply #233 on: April 21, 2023, 10:46:30 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...

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.

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.

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.
"Facts are stubborn things." --John Adams

Offline molesworth

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Re: Starship!
« Reply #234 on: April 22, 2023, 11:46:45 AM »
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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Offline JayUtah

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Re: Starship!
« Reply #235 on: April 22, 2023, 11:48:45 AM »
Yes, as usual, Scott knocks it out of the park.
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Offline bknight

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Re: Starship!
« Reply #236 on: April 22, 2023, 02:30:57 PM »
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.



There could have been mechanical damage as well during the ignition prior to the vehicle rising far enough that the exhaust didn't affect the ground.  Here is a video taken looking at the launch from the ground.  Lots of debris raing down.


At least Jarrah finally got his crater below a rocket.   ::)
« Last Edit: April 22, 2023, 02:33:10 PM by bknight »
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Offline Bryanpoprobson

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Re: Starship!
« Reply #237 on: April 22, 2023, 06:53:29 PM »
No flame trench, insufficient water suppression, the static test was only done at 50% thrust, no testing at 100%. Elon Musk confirmed that the concrete on the pad didn’t just corrode from the thrust, it was literally blasted to bits. This was probably why a few of the raptors were taken out and some failed later 7/8 in all.
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Offline Peter B

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Re: Starship!
« Reply #238 on: April 22, 2023, 08:26:26 PM »
A couple of questions from the numpty, if I may.

First, I noticed that one of the engines restarted during flight. Seriously? How does that happen? Would they have been going through some re-ignition process or would that have been something the engine managed itself? Or could it have been a dodgy signal from an engine that was fine?

Second, (and apologies that I don't remember the terminology), I understand that rocket first stages generally attempt to follow a pre-determined course, and that upper stages have more freedom to match available resources to achievable orbits? Anyway, given that SpaceX seems to have an attitude that Super Heavy is going to have engines fail (and I noticed Manley pointed out the rocket seemed to have an off-angle thrust at one point) is that necessarily the most efficient way to run things? I suppose what I'm asking is, why the two different approaches to guidance between first stage and upper stages? If Super Heavy is going to lose engines, isn't it more fuel efficient to let the rocket decide its own course based on the available engines?

Thank you!
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Offline cjameshuff

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Re: Starship!
« Reply #239 on: April 23, 2023, 12:13:03 PM »
The restarting engine was probably bad telemetry, or even human error if someone was manually updating that part of the dashboard. The outer ring requires ground infrastructure to spin up turbopumps and deliver gases to the torch igniters.

I'm not sure what you're asking for the second part, the question seems self contradictory. You're simultaneously asking why the booster didn't have the freedom to change the trajectory to account for available engines, and why it did so. This was very much not the planned trajectory, it was much lower altitude and slower, and burned longer trying to correct things, presumably using the propellant normally reserved for boostback and landing.