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SpaceX SN9 Explodes on Landing

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Re: SpaceX SN9 Explodes on Landing

#101

Post by avmich »

GizmoSwan wrote: post #91
reasonabl_human wrote: post #81

Earlier quoted context omitted.

I loved the explosion. These guys get stuff done. Move fast and break things

It should not have been an experiment leading to explosion at this stage. You are not seriously willing to justify the explosion, are you? I hope that you are being sarcastic. The experimental flying of rockets of this size are the 1960s thing. They should have acquired proper specs by now.

You can choose to develop rockets - especially of such size - this way instead of putting (much) more efforts in calculating how it would behave and prepare for all cases.

Re: SpaceX SN9 Explodes on Landing

#102

Post by GizmoSwan »

ctdonath wrote: post #97
GizmoSwan wrote: post #91

Earlier quoted context omitted.

It should not have been an experiment leading to explosion at this stage. You are not seriously willing to justify the explosion, are you? I hope that you are being sarcastic. The experimental flying of rockets of this size are the 1960s thing. They should have acquired proper specs by now.

SpaceX Starship is way outside established industry specifications.

How so?

Re: SpaceX SN9 Explodes on Landing

#103

Post by avmich »

valuearb wrote: post #35
NikolaeVarius wrote: post #27

Earlier quoted context omitted.

> As of 2020, there have been 15 astronaut and 4 cosmonaut fatalities during spaceflight. Astronauts have also died while training for space missions, such as the Apollo 1 launch pad fire which killed an entire crew of three The numbers don't really seem to support your assertion that NASA is generally much safer than Soviet/Russia

At least 126 technicians and cosmonauts were killed by accidents during the Soviet space program. It’s rumored that additional cosmonauts died on missions that the Soviets covered up.

That's likely to include the Nedelin catastrophe ( https://en.wikipedia.org/wiki/Nedelin_catastrophe ) -

"The most recent estimated death toll, released by Roscosmos on the 50th anniversary of the accident and originating with agency engineer Boris Chertok, was that 126 people had died, but the agency qualified the number by saying that the actual number could be anywhere from 60 to 150 dead."

Re: SpaceX SN9 Explodes on Landing

#104

Post by gridspy »

jzer0cool wrote: post #93

(1) I think that is a "hard" landing ;) I say it it the mark. (2) The Question: I ain't no rocket scientist, but even if the engine failure had turned on, did the engines all just turn on quite late? Just trying here some crazy college physics so not sure if this checks out but, here goes. Again, just for fun. If it takes X: (summation of thrust) to fly that high over x seconds, then it would take the X + some at the…

Nice analysis. I can answer your question by illuminating two major points you missed.

1. The StarShip reaches a terminal velocity (in "the bellyflop") of about 200 km/h downwards and remains at that velocity until the "flip maneuver" at the end.

That's essentially a free force vector upwards due to drag which is free thrust on descent.

2. The weight of fuel reduces drastically on ascent which is why less engines are required as the StarShip soars higher into the air (they shut down when one reaches the 40% min thrust)

You'll see during the hover at the top that StarShip balanced on one engine for some time without moving. So that is the thrust required for station keeping. What we saw here was a combination of reaching a target location and burning excess fuel.

---

So, landing burn is (supposed to be) done with two fully throttled raptors, which is essentially 4x the hover thrust. Here with SN9 you see what happens when only one of those raptors is actually working.

Here is an Excellent SN8 (not SN9) video with carefully reconstructed telemetry (based on pixel counting video references) and you can see the velocities on descent. Rewind the video for full detail:

https://youtu.be/XJZ7VWzqtJM?t=867 [How to simulate a Starship launch!]

Re: SpaceX SN9 Explodes on Landing

#105

Post by GizmoSwan »

avmich wrote: post #101
GizmoSwan wrote: post #91

Earlier quoted context omitted.

It should not have been an experiment leading to explosion at this stage. You are not seriously willing to justify the explosion, are you? I hope that you are being sarcastic. The experimental flying of rockets of this size are the 1960s thing. They should have acquired proper specs by now.

You can choose to develop rockets - especially of such size - this way instead of putting (much) more efforts in calculating how it would behave and prepare for all cases.

Nasa did the calculation with with ancient computers and these guys are speculating and not using proper technology to achieve success. It makes no sense in 2021.

They should not be experimenting. Their simulations should be been solid before this stage.

It is good way to burn cash.

Re: SpaceX SN9 Explodes on Landing

#106

Post by hansthehorse »

kens wrote: post #63
valuearb wrote: post #35

Earlier quoted context omitted.

At least 126 technicians and cosmonauts were killed by accidents during the Soviet space program. It’s rumored that additional cosmonauts died on missions that the Soviets covered up.

As far as technicians, I've always felt sad for the two Space Shuttle technicians who died in 1981 after entering a nitrogen-filled engine compartment (John Bjornstad and Forrest Cole).

It's very sad but it's not a bad way to go. I was a nuclear plant supervisor for about 20 years. One day the temp started to increase in the control room. The 3 AC units were behind the control room so I headed there to check on things. Another guy said he'd go with me. These things are as big as locomotives. Well while we were in the room a refrigerant relief valve lifted with a huge roar. Turns out, amazingly, the relief was designed to vent into the room. We made it to the card reader to get back into the control room but my card kept being rejected. I felt myself sliding down the wall and next I knew I was sitting in a chair in the control room feeling better and better. If my buddy hadn't decided to come with me I would have died in that room.

There was no panicky brain screaming "we need air" or any feeling of being O2 short. It was just normal breathing. If you're going to end it all that's the way to do it.

I wrote an incident report with the obvious suggestion to vent the reliefs outside. It was modified the next outage.

Re: SpaceX SN9 Explodes on Landing

#107

Post by kevin_thibedeau »

walrus01 wrote: post #40
d_silin wrote: post #2

Illustration how "move fast and break things" in aerospace domain works.

They landed a lot of falcon 9 first stages without legs on the water, vertically, to test the control system. And a number of attempted barge landings with legs failed, before the first successful landing. Now it's almost a routine thing.

That's probably what FAA was peeved about SN8. They might have been expecting a water landing and didn't like that an unproven rocket was sent back to dry land.

Re: SpaceX SN9 Explodes on Landing

#108

Post by avmich »

Someone wrote: post #64
fpgaminer wrote: post #37

Earlier quoted context omitted.

But the U.S. has sent 3x as many citizens into space: https://en.wikipedia.org/wiki/List_of_space_travelers_by_nat... So combining with your statistic the U.S. has a fatality rate of 4.4% versus Russia's 3.3%. Given the low N it's probably within margin of error.

I don’t think it makes an enormous difference, but not all of those US citizens flew in US rockets (nor did all Russian ones) Also, quite a few of those did multiple flights. Looking at that list, I think that moves the needle in favor of US rocket safety.

Soviet spaceflights were quite long compared to American - Salyut-6 and Salyut-7 both had more expeditions than Skylab, and that's before Mir, while Shuttles were limited to about a month in space per flight. Of course launch and landing are more dangerous phases of flight - Apollo-13 notwithstanding - so it makes harder to pinpoint an objective measure for safety.

Re: SpaceX SN9 Explodes on Landing

#109

Post by avmich »

Layke1123 wrote: post #82
Layke1123 wrote: post #41

Earlier quoted context omitted.

Challenger? What's your point? That Russia didn't beat the US into space? I thought the west at least accepted that fact. Or do you just have to believe the US is ALWAYS "superior"?

Downvoting again? Rather than articulate a response?

I was confused by "Russia didn't beat US into space" - you probably meant "to the Moon" (manned flights), while USSR had quite a few space firsts.

Re: SpaceX SN9 Explodes on Landing

#110

Post by gridspy »

BurningFrog wrote: post #87

I'm very impressed by how it's coasting on the fins down the atmosphere. I had never even heard that idea discussed before I saw SN8 do it. Of course, they'll have to land some other way on Mars or the Moon.

Fortunately the force of gravity is much lower on both these bodies so I imagine the belly flop becomes less important.

On earth it's also about spreading the heat of reentry over a larger area. Fortunately on Mars (I believe that) the heat of reentry is even less of an issue than here on Earth.

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