SpaceX SN9 Explodes on Landing • Hacker News Board

Re: SpaceX SN9 Explodes on Landing

#221

Post by gridspy » Wed, Feb 03, 2021, 6:45 AM UTC

onethought wrote: post #205

gridspy wrote: post #110

Earlier quoted context omitted.

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.

Is that right... at orbital velocity I think Mars entry is a problem. Are they planning on landing starships on earth? with Orbital refuelling couldn't they just land it like a Falcon 9 (I mean I guess that'd be super inefficient)

Yes, they plan to land "tanker" starships directly back on earth after they have transferred their fuel to another vessel.

They plan to land passenger ballistic re-entry starships which fly without a booster directly to another city on earth in They plan to land orbital starships, which is like landing the dragon capsule. These are going far faster than the falcon booster ever goes. The second stage (on top of the falcon) never lands, it's disposed of every mission. The StarShip (top half) is essentially a reusable second stage.

The Starship mars or moon editions will remain in orbit and never land on Earth again after initial launch. These do not need hardware for an Earth descent and will rely on refuelling. The Moon edition will have no heat-shield tiles (no need for atmospheric entry) and special thrusters half-way up.

You are correct that interplanetry velocities are very high, so yes... a Mars entry at Earth-Mars transfer velocities is likely to be quite ... exciting. I can't remember how exciting though.

Re: SpaceX SN9 Explodes on Landing

#222

Post by GizmoSwan » Wed, Feb 03, 2021, 6:53 AM UTC

avmich wrote: post #210

GizmoSwan wrote: post #185

Earlier quoted context omitted.

747 can not flip like that; it would stall and crash. The narrow bodied 737s crashed for less. Their fancy flight computer miscalculated because of center of gravity miscalculations. They crashed after 100s of flights. I like your optimism. Good luck. I mean it. I would not fly in that thing even if they paid me a million. Sorry for my lack of faith.

Big airliners do parabolic arcs - "vomit comet", so it's not a huge problem. 737 MAX crashed for different reasons. E.g. Soyuz capsule returns safely despite different loads and different distributions of mass - control systems, even relatively modest ones, can compensate. It's failures which provide most useful information about shortcomings of the system at some point, so they are welcome during testing - if you th…

737-max crashed because they never went through full blown simulation and acceptance procedures for it. They just made the body longer and compensated for differentials in flight control software parameters but they had a blind spot in their assumptions. Those aircrafts have decades of air flight simulation behind them and yet ....

Shuttle is a much finer craft but these guys may have different objectives and that is their prerogative. The fact that there are errors in there that can lead to explosion is troubling to me.

The claim that the explosions will lead towards a better design is an assumption.

Re: SpaceX SN9 Explodes on Landing

#223

Post by avmich » Wed, Feb 03, 2021, 7:12 AM UTC

HarryHirsch wrote: post #216

avmich wrote: post #201

Earlier quoted context omitted.

Briz and Fregat start much smaller - 20 kN - engines with no time constraints, while Starship re-lights 2200 kN engine and rocket immediately does rotation by 90+ degrees, and time is of essence.

Where do thrust and chamber pressure even come into the equation? It's not that the engine exploded, the thing failed to ignite.

> Where do thrust and chamber pressure even come into the equation?

Thrust given to show difference in engine scale. Pressure isn't shown - what do you mean? :)

The point is that re-light of Briz and Fregat is very different and so hard to compare.

Re: SpaceX SN9 Explodes on Landing

#224

Post by gridspy » Wed, Feb 03, 2021, 7:49 AM UTC

GizmoSwan wrote: post #222

avmich wrote: post #210

Earlier quoted context omitted.

Big airliners do parabolic arcs - "vomit comet", so it's not a huge problem. 737 MAX crashed for different reasons. E.g. Soyuz capsule returns safely despite different loads and different distributions of mass - control systems, even relatively modest ones, can compensate. It's failures which provide most useful information about shortcomings of the system at some point, so they are welcome during testing - if you th…

737-max crashed because they never went through full blown simulation and acceptance procedures for it. They just made the body longer and compensated for differentials in flight control software parameters but they had a blind spot in their assumptions. Those aircrafts have decades of air flight simulation behind them and yet .... Shuttle is a much finer craft but these guys may have different objectives and that is…

737-Max crashed because of the "lets analyse this rather than test it" thinking that you described earlier. That and an overly cosy relationship with the FCC and a culture of silencing cautious engineering voices.

It's seemed cheaper to tack larger engines and new software onto the old air-frame than to redesign the aircraft to be mechanically stable and update the cockpit.

Not surprising that the same company (Boeing) that campaigned for analysis over testing in spaceship design (they claimed SpaceX couldn't do commercial crew) also failed to design a working and stable aircraft.

I'd argue that the bureaucracy involved in "signing off" an new aircraft design contributed to these problems. Designing a aircraft or spacecraft from first principles and then refining through testing does have its advantages.

My point about aircraft was that the lift vector is perpendicular to the wings, even if the aircraft flips (rolls) upside-down there is still a force that pushes you toward the deck if you are inside the plane. In the StarShip there is a similar upwards force from the engines (when lit) towards the nose regardless of which direction the ship is oriented with respect to the Earth.

The reason why flying a plane in clouds is so dangerous is that your sense of up and down in a plane is invalid. You'll always think the deck is down without the aid of either a view of the horizon or the correct use of functioning instrumentation.

Re: SpaceX SN9 Explodes on Landing

#225

Post by iruoy » Wed, Feb 03, 2021, 8:10 AM UTC

WalterBright wrote: post #202

consumer451 wrote: post #176

Here is my favorite footage so far, by Cosmic Perspective: https://www.youtube.com/watch?v=Ep8XJanoFgw This is 4k slow motion and it is gorgeous. The giant sheets of stainless steel floating down at the end are noteworthy, among other details. Michael Bay has nothing on Cosmic Perspective + SpaceX.

The sheets of stainless steel appear to have separated at the joints. This says the sheets are stronger than the joints, meaning they're overweight :-)

They're experimenting with 3mm steel instead of 4mm steel. A test tank they've built already passed an initial pressure test on 26 Jan.

One Starship requires 15 rings, a nosecone, a bottom and tanks. If they would all move from 4mm to 3mm then that would save a lot of weight. About 7-10 tonnes according to [1].

[1]: https://forum.nasaspaceflight.com/index.php?topic=52701.160

Re: SpaceX SN9 Explodes on Landing

#226

Post by GizmoSwan » Wed, Feb 03, 2021, 8:26 AM UTC

gridspy wrote: post #224

GizmoSwan wrote: post #222

Earlier quoted context omitted.

737-max crashed because they never went through full blown simulation and acceptance procedures for it. They just made the body longer and compensated for differentials in flight control software parameters but they had a blind spot in their assumptions. Those aircrafts have decades of air flight simulation behind them and yet .... Shuttle is a much finer craft but these guys may have different objectives and that is…

737-Max crashed because of the "lets analyse this rather than test it" thinking that you described earlier. That and an overly cosy relationship with the FCC and a culture of silencing cautious engineering voices. It's seemed cheaper to tack larger engines and new software onto the old air-frame than to redesign the aircraft to be mechanically stable and update the cockpit. Not surprising that the same company (Boein…

Nope. A purposely designed aircraft is simulated is not one that is elongated with flight control data being patched.

Example of how it works: https://www.darcorp.com/advanced-aircraft-analysis-software/

The bureaucracy had nothing to do with it. They did not want to spend the money to create a new craft. The long bodies aircraft was not airworthy physically speaking and so the software was designed to limit its pitch to prevent it from stalling.

All aircrafts can stall and some angle of attack but a long+narrow aircraft is way more sensitive.

Design of an aircraft from scratch would have flagged it as poor design right away.

Re: SpaceX SN9 Explodes on Landing

#227

Post by paul_f » Wed, Feb 03, 2021, 9:18 AM UTC

JumpCrisscross wrote: post #84

omgwtfbyobbq wrote: post #71

Can they relight sooner to improve their odds of landing successfully, or is the window for when they can relight relatively small? Or does it not matter because a few more seconds won't increase the chances they'll be able to relight?

Keep in mind that every millilitre of fuel burned has to be carried from the start. If you want to start burning a few seconds early on landing by policy, you need to lift that fuel, and the fuel to lift that fuel, from the surface to space and then decelerate all of that. Just for those seconds. If you’re doing this from Mars, you also have to accelerate that mass around the Solar System and out of the Martian gravi…

It's just a question of money. Starship will eventually be re-fueled in earth orbit.

Re: SpaceX SN9 Explodes on Landing

#228

Post by nickik » Wed, Feb 03, 2021, 9:59 AM UTC

GizmoSwan wrote: post #218

nickik wrote: post #178

Earlier quoted context omitted.

You are so confident in your opinion and you are so incredibly wrong. Pretty much every NASA engineer that has worked with SpaceX has been incredibly impressed by their methods. Literally every single one of their competitors, including nation states have started to change their who launch strategy because they saw no other way to compete with Spacex (and they are still failing) all of them have expressed how impress…

I just want to know how you know that "you" are incredibly right in this. You are just speculating like everybody else here. There is no quality or quantitative measurement available here for you to make these absolute statements. The only thing that I can gather from your text is that a lot can go wrong in fact. Having the prototype that is exploding is NOT fine at this stage and that is "my" opinion. Your opinion i…

I know that because that is what Elon Musk and other SpaceX engineers and have said. They have explained this in multiple presentations and interviews over the last 5 years. This is not a mystery. I am not speculating.

There is a whole community that has been following this project since day 1. There are people filming the production site every day. The analyze every part they see and try to figure out what changed. Some people in the community can get questions to Elon Musk and others.

The reason you are getting down-voted is that you seem to have not studied it at all what SpaceX is actually doing, and simply jump into the comments and make strong statements that what SpaceX is doing is wrong.

And your justification for this opinion is totally unconvincing for anybody that has actually studied the problem.

> I don't care who you believe they are beating in the market place and how magnificent you believe this rocket is.

Its really not about believe. Its a simple fact that everybody has acknowledged.

Re: SpaceX SN9 Explodes on Landing

#229

Post by Acinyx » Wed, Feb 03, 2021, 10:09 AM UTC

unanswered wrote: post #215

hyperion2010 wrote: post #186

Earlier quoted context omitted.

"Deal with" == "Not blow up" == "No RUD" in the event of a single engine failure. Manned space flight kind of has this kind of important additional requirement that things like ICBMs don't, which is that they can't just "go up" the have to come back down and not end in a ball of fire.

Unless I am much mistaken what what blew up was a first stage, not a manned stage. I do not believe that SpaceX plans on doing suicide burns to retrieve humans from flight.

What blew up is the second stage, the stage that would contain the astronauts. If this landing profile is also the profile they will use for a manned starship is unknown.

It feels to me like there is no backup plan for engine failures, but they can take so many paths here that I don't think anyone knows except people within SpaceX. Example paths:

* Don't launch it with people until it has landed unmanned so frequently that everyone trusts it. * Land cargo versions like this to get max payload, while manned versions light a lot sooner, with possibly more engines, and sacrifice some fuel for increased reliability. * Catch starship just like the booster in case of failure, with a longer travel to support higher speeds and lower G's. * Add a parachute or increase the flap sizes to lower terminal speed so much that it is survivable to land without engines.

The test articles for the first stage are still being built and are expected to land similar to the falcon 9, which the big difference that Elon is talking about them being catched by a tower instead of landing on their own legs. This seems far enough away though that I would not be surprised if that changes radically.

Re: SpaceX SN9 Explodes on Landing

#230

Post by andygates » Wed, Feb 03, 2021, 10:39 AM UTC

omgwtfbyobbq wrote: post #71

Can they relight sooner to improve their odds of landing successfully, or is the window for when they can relight relatively small? Or does it not matter because a few more seconds won't increase the chances they'll be able to relight?

The landing propellant comes from very small header tanks (to reduce slosh), and those tank sizes constrain how long they can run a landing burn. Future iterations may end up with a bigger header: these are still early prototypes.