Abort options for Starship and Starship/SuperHeavy

[Robotbeat]

Powered parachutes are non-trivial, huge fan (dangerous blades) and motor on your back. Paraglider makes more sense.

As I recall, the world's largest parafoil supported the 25,000 pound x-38.  Quite a way to go to something this size

Oh, I thought the person was suggesting this for ejecting crew, not the whole vehicle.

[Barley]

Parachutes can land on runways.  They can land on the small cross on the 35-yard line.  Not sure why you need much cross range from a SS returning to Boca Chica or Kennedy but the record flight for a powered parachute is over 1000 km.

I would want to know what weather conditions SS would be flying in before I committed to parachuting. Of course than I would have to commit myself to learn how to parachute which I don't see as a plus, but I have never shied away from flying in small aircraft.

Edit: I think the big hesitation here is thinking aircraft deploying aircraft is pure science fiction when in fact it was done by the US Navy in the 1930's. Not only were aircraft deployed, but they were also recovered.

A parachute is an aircraft.  An aircraft that folds up nicely, is very light because it is an inflatable aircraft (much of its structure is air), and can very easily be deployed from another aircraft.  You can add a small cabin, use a paraglider designed for maneuverability and add an engine for cross range and it's still far lighter than anything else that can do the job, which is to start at say 10km altitude and land safely.  Why do you think anything more is needed?  What does it need to do that that requires metal wings or a jet engine?  Why on or above Earth is recovering it in the air useful?

[steveleach]

²Two very difficult things:
1) The separation plane has to work through the ventral TPS tiles.
2) The separation plane has to bear all canard loads during reentry, but still be able to jettison.

Could you get it to fit with a chomper design, such that the separation happens entirely within the leeward side of the Starship hull?

The chomper also lets you release the D2 as part of normal operations for crew EDL, to support crewed missions while the data on Starship EDL reliability is being gathered.

[Robotbeat]

I just wanna say that one of the ways to GUARANTEE Starship never gets close to even General Aviation true demonstrated safety levels is to include so much extra complexity, mass, and cost in the name of “safety” that the per-person price of flying on it means Starship only flies a handful of times per year like Starliner or Orion.

Any abort options need to keep that in mind, just like safety measures for airliners do (which are compact and lightweight, like deployable inflatable rafts, engine-out capability, etc).

[Negan]

Powered parachutes are non-trivial, huge fan (dangerous blades) and motor on your back. Paraglider makes more sense.

As I recall, the world's largest parafoil supported the 25,000 pound x-38.  Quite a way to go to something this size

Oh, I thought the person was suggesting this for ejecting crew, not the whole vehicle.

You're correct. Basically, using it as a safety measure to prevent any loss of crew if the final part of the landing phase goes wrong.

[Negan]

Parachutes can land on runways.  They can land on the small cross on the 35-yard line.  Not sure why you need much cross range from a SS returning to Boca Chica or Kennedy but the record flight for a powered parachute is over 1000 km.

I would want to know what weather conditions SS would be flying in before I committed to parachuting. Of course than I would have to commit myself to learn how to parachute which I don't see as a plus, but I have never shied away from flying in small aircraft.

Edit: I think the big hesitation here is thinking aircraft deploying aircraft is pure science fiction when in fact it was done by the US Navy in the 1930's. Not only were aircraft deployed, but they were also recovered.

A parachute is an aircraft.  An aircraft that folds up nicely, is very light because it is an inflatable aircraft (much of its structure is air), and can very easily be deployed from another aircraft.  You can add a small cabin, use a paraglider designed for maneuverability and add an engine for cross range and it's still far lighter than anything else that can do the job, which is to start at say 10km altitude and land safely.  Why do you think anything more is needed?  What does it need to do that that requires metal wings or a jet engine?  Why on or above Earth is recovering it in the air useful?

If what you suggest above already exists or can be developed and certified quickly and cheaply I see no issues with it. Otherwise, there's a plethora of already developed and certified aircraft to choose from.

[Lee Jay]

Powered parachutes are non-trivial, huge fan (dangerous blades) and motor on your back. Paraglider makes more sense.

As I recall, the world's largest parafoil supported the 25,000 pound x-38.  Quite a way to go to something this size

Oh, I thought the person was suggesting this for ejecting crew, not the whole vehicle.

You're correct. Basically, using it as a safety measure to prevent any loss of crew if the final part of the landing phase goes wrong.

My mistake.  I thought it was for the whole vehicle.

[DanClemmensen]

Back to emergency water landing:
Earlier we were discussing the prpblem of "toppling" the Starshipafter and emergency vertical "landing" on the sea surface, and how to keep Starship from breaking up after toppling. Question: can toppling be slowed down by using a big reaction wheel? How much angular momentum would you need to store in the wheel? Precession has always been a black art for me.

[Robotbeat]

Yes, but it’d be insanely heavy. Think to what a commercial airliner might do, and probably something like deployable airbags of some sort could stabilize a starship as it transitions to horizontal.

[DanClemmensen]

Yes, but it’d be insanely heavy. Think to what a commercial airliner might do, and probably something like deployable airbags of some sort could stabilize a starship as it transitions to horizontal.

Most of the abort hardware we are discussing is heavy. The question is how heavy (and how much volume, of course).  I asked about angular momentum instead of mass because the same mass provides more angular momentum if you can spin it faster, limited by the radial tension the wheel material can support. Also, it's a curve. Presumably, the bigger the wheel the more it helps, but we don't need to reduce the topple rate to zero, we only need to reduce it to a survivable rate. Presumably, the existence of this ridiculously oversized reaction wheel will also reduce the  need for RCS propellant in normal operation and might reduce the mass of the RCS.

[Robotbeat]

It Works In Kerbal Space Program.

[DanClemmensen]

Yes, but it’d be insanely heavy. Think to what a commercial airliner might do, and probably something like deployable airbags of some sort could stabilize a starship as it transitions to horizontal.

Most of the abort hardware we are discussing is heavy. The question is how heavy (and how much volume, of course).  I asked about angular momentum instead of mass because the same mass provides more angular momentum if you can spin it faster, limited by the radial tension the wheel material can support. Also, it's a curve. Presumably, the bigger the wheel the more it helps, but we don't need to reduce the topple rate to zero, we only need to reduce it to a survivable rate. Presumably, the existence of this ridiculously oversized reaction wheel will also reduce the  need for RCS propellant in normal operation and might reduce the mass of the RCS.

OK, let's increase the insanity. Use the reaction wheel and RCS to keep Starship balanced on its tail as long as possible. This should take less energy than a controlled topple. Open valves in the LOX tank to let gas out at the top and water in at the bottom to slowly sink the ship into the water. Vent the methane tank down to about 2 atm to reduce the CoM. When it gets low enough, shut the OX and float like a spar buoy, nice and stable.

[Barley]

Back to emergency water landing:
Earlier we were discussing the prpblem of "toppling" the Starshipafter and emergency vertical "landing" on the sea surface, and how to keep Starship from breaking up after toppling. Question: can toppling be slowed down by using a big reaction wheel? How much angular momentum would you need to store in the wheel? Precession has always been a black art for me.

There is a short story where a spacecraft with an enormous gyroscope lands.  The pilot debarks to plant his flag, glances back at the ship and realizes with horror that one of the landing legs has failed to deploy and the gyroscope is about to reach it's limit.

[TheRadicalModerate]

Back to emergency water landing:
Earlier we were discussing the prpblem of "toppling" the Starshipafter and emergency vertical "landing" on the sea surface, and how to keep Starship from breaking up after toppling. Question: can toppling be slowed down by using a big reaction wheel? How much angular momentum would you need to store in the wheel? Precession has always been a black art for me.

There is a short story where a spacecraft with an enormous gyroscope lands.  The pilot debarks to plant his flag, glances back at the ship and realizes with horror that one of the landing legs has failed to deploy and the gyroscope is about to reach it's limit.

Funny, I just re-read that about a week ago:  It's Grendel, by Larry Niven.  And the pilot is actually the villain, monologuing before killing the hero, when the hero asks him what's holding his ship up.  Even in the 26th century, monologuing is still a terrible idea.

[InterestedEngineer]

Yes, but it’d be insanely heavy. Think to what a commercial airliner might do, and probably something like deployable airbags of some sort could stabilize a starship as it transitions to horizontal.

Most of the abort hardware we are discussing is heavy. The question is how heavy (and how much volume, of course).  I asked about angular momentum instead of mass because the same mass provides more angular momentum if you can spin it faster, limited by the radial tension the wheel material can support. Also, it's a curve. Presumably, the bigger the wheel the more it helps, but we don't need to reduce the topple rate to zero, we only need to reduce it to a survivable rate. Presumably, the existence of this ridiculously oversized reaction wheel will also reduce the  need for RCS propellant in normal operation and might reduce the mass of the RCS.

OK, let's increase the insanity. Use the reaction wheel and RCS to keep Starship balanced on its tail as long as possible. This should take less energy than a controlled topple. Open valves in the LOX tank to let gas out at the top and water in at the bottom to slowly sink the ship into the water. Vent the methane tank down to about 2 atm to reduce the CoM. When it gets low enough, shut the OX and float like a spar buoy, nice and stable.

In a previous post I calculated the moment of inertia for a Starship at 100e6 kg-m²(1/3mL^2) based on a simple stick model.

The angular momentum for a rotating body is:

L = Iw

w = 0.75 radians/sec for a Starship just about to hit the water when falling over using the "simple stick" model.  That gives an angular momentum of 75e6 kg⋅m²⋅s^-1

A disc has a moment of inertia as I = 0.5mr².   This has to be at the bottom of the Starship, so I have no idea where we'd put it.  Suppose we give it a radius of 2m and a mass of 10t, that gives I = 0.5*10e3*2² = 20e3 kg-m²

Solving L=Iw for w, we get w=L/I =75e6 / 20e3 = 3,750 radians per second = 35,000 rpm.

I don't think that's gonna work.


https://forum.nasaspaceflight.com/index.php?topic=56632.msg2434461#msg2434461

https://en.wikipedia.org/wiki/Angular_momentum

[spacenut]

Point to point is not going to happen anytime soon.  So, that is why I think ejection seats for crew would be the lowest mass solution.  It might not be safe during the entire launch, but it might be safe for a bad landing situation.  I think landings are going to be harder for Starship. 

Now, when they test landed one time, it toppled over after touchdown.  It finally landed.  However, the landing legs they used to me were problematic.  Better landing legs and they might have landed more than once in testing.  Of course, that too adds mass.  They have got to land on Mars, so better legs seems to be a necessity. 

[TheRadicalModerate]

OK, let's increase the insanity. Use the reaction wheel and RCS to keep Starship balanced on its tail as long as possible. This should take less energy than a controlled topple. Open valves in the LOX tank to let gas out at the top and water in at the bottom to slowly sink the ship into the water. Vent the methane tank down to about 2 atm to reduce the CoM. When it gets low enough, shut the OX and float like a spar buoy, nice and stable.

Think about what happens when you let seawater @ 290K into a tank filled with LOX @ 90K.  If you're flooding to keep from toppling, you have to do it at a tonne or two per second.  I don't know if a big block of ice freezes off your inlets or if there's vaporization overpressure that does you in, but there are some problems.

And remember that you've got at least three contingencies for EDL abort:

1) Nav failure over water (vertical floating might work).
2) Nav failure over land (might be avoidable as long as you don't allow interplanetary direct EDL).
3) Suicide burn abort (no solution other than an escape system).

[InterestedEngineer]

Yes, but it’d be insanely heavy. Think to what a commercial airliner might do, and probably something like deployable airbags of some sort could stabilize a starship as it transitions to horizontal.

Most of the abort hardware we are discussing is heavy. The question is how heavy (and how much volume, of course).  I asked about angular momentum instead of mass because the same mass provides more angular momentum if you can spin it faster, limited by the radial tension the wheel material can support. Also, it's a curve. Presumably, the bigger the wheel the more it helps, but we don't need to reduce the topple rate to zero, we only need to reduce it to a survivable rate. Presumably, the existence of this ridiculously oversized reaction wheel will also reduce the  need for RCS propellant in normal operation and might reduce the mass of the RCS.

OK, let's increase the insanity. Use the reaction wheel and RCS to keep Starship balanced on its tail as long as possible. This should take less energy than a controlled topple. Open valves in the LOX tank to let gas out at the top and water in at the bottom to slowly sink the ship into the water. Vent the methane tank down to about 2 atm to reduce the CoM. When it gets low enough, shut the OX and float like a spar buoy, nice and stable.

In a previous post I calculated the moment of inertia for a Starship at 100e6 kg-m²(1/3mL^2) based on a simple stick model.

The angular momentum for a rotating body is:

L = Iw

w = 0.75 radians/sec for a Starship just about to hit the water when falling over using the "simple stick" model.  That gives an angular momentum of 75e6 kg⋅m²⋅s^-1

A disc has a moment of inertia as I = 0.5mr².   This has to be at the bottom of the Starship, so I have no idea where we'd put it.  Suppose we give it a radius of 2m and a mass of 10t, that gives I = 0.5*10e3*2² = 20e3 kg-m²

Solving L=Iw for w, we get w=L/I =75e6 / 20e3 = 3,750 radians per second = 35,000 rpm.

I don't think that's gonna work.


https://forum.nasaspaceflight.com/index.php?topic=56632.msg2434461#msg2434461

https://en.wikipedia.org/wiki/Angular_momentum

While I'm in moment of Inertia land, I can calculate what moment of inertia the part under water imparts.

Moments of inertia are piecewise additive:  https://engineeringstatics.org/Chapter_10-moment-of-inertia-of-composite-shapes.html


There's an 18m span of the Starship about 2m under water (base plus elonerons).   rotating the Starship lifts a 1/4 circle of water of 2m radius up, which is a volume of 3.14 * 2² / 4 * 18 = 57m³ of water.

That's 57t of water with a distance of 2m from rotation.   The moment of inertia for that counters the moment of inertia of the Starship itself (75e6), and that counter-inertia is 0.5 * 56e3 * 2² = 112e3.

112e3 is rounding error on 75e6.  So the bottom being 2m in he water is only going to reduce the final rotational velocity a tiny bit.   The 48m that I did as 50m in the original calculation is a bigger error.

I calculated in a thread above that the force of falling over isn't really that bad.  The pressure on the hull is only about 3 bar, and the hull is pressurized to 6 bar and the payload section can be designed to absorb that kind of impact, just like on a car. 

I don't think extra measures need to be taken.

[sevenperforce]

LES means explosives / hypergolics close to the crew.

LES--as well as every RCS system on every single human-rated spacecraft--has meant hypergolics close to the crew for decades and has only caused one accident (Apollo/Soyuz) that I know of.  As for pyrotechnics, they're a pain, but they're also an avoidable pain (cf. D2).

While I generally agree with your points in here, I will note that this isn't quite telling the whole story. Many crew capsules have historically used monopropellant only for the actual re-entry module, keeping the hypergolic bipropellants in a separate service module separated from the crew. I believe that the only crew vehicles to ever contain bipropellants inside the OML of the re-entry vehicle were Gemini, Apollo CM, Shuttle, and Crew Dragon. In contrast, Orion and Starliner and Mercury, plus all of the Soyuz and Soyuz-derived capsules, use or used only monoprop in the actual crew vehicle, keeping bipropellant RCS in the service module. I'm not sure what was/is planned for Dream Chaser and Orel.

Well for one thing you probably don't require the trunk on D2 do you?

Yes, you do.  It's not aerodynamically stable during escape without it.

I've given a lot of thought to this kind of design and I think it's promising. And I agree, you do need to ensure passive aerodynamic stability during escape, AND have a secondary separation plane to remove the fins so that you will flip over and come down with the proper attitude.

One issue with this, though, is that it may not suffice for a flip-and-burn failure, which arguably is the highest-risk regime. If Starship is plummeting belly-first and fails to flip, then activating the abort will send the crew capsule straight forward relative to the horizon. Potential problem there.

Being able to blow the entire pressurized fairing is...well, yikes. Definitely a huge engineering challenge. It might almost be better to have the crew Starship use a different OML where the LES module is attached so as to be entirely clear of the fairing.

[TheRadicalModerate]

LES means explosives / hypergolics close to the crew.

LES--as well as every RCS system on every single human-rated spacecraft--has meant hypergolics close to the crew for decades and has only caused one accident (Apollo/Soyuz) that I know of.  As for pyrotechnics, they're a pain, but they're also an avoidable pain (cf. D2).

While I generally agree with your points in here, I will note that this isn't quite telling the whole story. Many crew capsules have historically used monopropellant only for the actual re-entry module, keeping the hypergolic bipropellants in a separate service module separated from the crew. I believe that the only crew vehicles to ever contain bipropellants inside the OML of the re-entry vehicle were Gemini, Apollo CM, Shuttle, and Crew Dragon. In contrast, Orion and Starliner and Mercury, plus all of the Soyuz and Soyuz-derived capsules, use or used only monoprop in the actual crew vehicle, keeping bipropellant RCS in the service module. I'm not sure what was/is planned for Dream Chaser and Orel.

Fair point, but it begs a question:  Is the big risk a hypergolic explosion, or a leak that poisons the crew?

ISTM the biggest deal is a poisonous leak, and monoprop doesn't help you very much with that.  A hypergolic explosion, even in a separate service module, probably isn't a survivable event.

I can think of a couple good reasons unrelated to an explosion risk why monoprop might be a good choice in a reentry vehicle:

1) It's one less valve to fail at a point in the mission where there's no time to debug it, and the failure jeopardizes reentry.

2) Reentry vehicles are small, and small monoprop thrusters can fit into squirrelly places a bit easier.

One issue with this, though, is that it may not suffice for a flip-and-burn failure, which arguably is the highest-risk regime. If Starship is plummeting belly-first and fails to flip, then activating the abort will send the crew capsule straight forward relative to the horizon. Potential problem there.

I'm pretty sure that there are specs somewhere on what kind of deployment angle CCP spacecraft aborts need to be able to recover from.  It might not be 90º, but I'd kind guess that 45º would be good enough--especially if you're using a pure powered descent instead of 'chutes.

Being able to blow the entire pressurized fairing is...well, yikes. Definitely a huge engineering challenge. It might almost be better to have the crew Starship use a different OML where the LES module is attached so as to be entirely clear of the fairing.

Yeah, this is definitely the green weanie in the pack.  Just to clarify:  The internal fairing is probably neutral static pressure.  But you have to be able to blow it clear at max-q.

You can't have the LES module clear of the fairing because of the canards.  The canards have to be well forward, and there's no way you get a stable separation with those puppies in place.

I've thought about what would happen if you had a design where you could blow the canards off before initiating the separation, but there's still a problem:  for nominal EDL, you need either the header tanks or equivalent ballast in the nose, and that ballast would be:

1) Heavy, and carried along as part of the abort separation, increasing both thrust and prop requirements.

2) Not conducive to flipping nose-up for landing.

I guess you could separate the ballast from the stack before the abort separation, but you're talking about a lot of events needed for an abort that have to go just-so.  Whether that's a bigger "yikes" than blowing the fairing off (with the ballast!) into a max-q slipstream, possibly with thousands of tonnes of methalox downstream, I don't know.

It's all a hideous kludge.  And a fully agree with everybody that the better solution, if time and the design permit, is to increase the empirical reliability to the point where everybody's comfy with no escape system.  I just don't believe that time and the design will permit, at least not before when it becomes really awkward for SpaceX not to have a crewed Starship launch/EDL capability.