Abort options for Starship and Starship/SuperHeavy

[sebk]

And "reasonably flat land" isn't as common as you think.

and runways are all over the place.

Reasonably flat land is at least as common as runways

Runways are reasonably flat, if you can land a spaceplane you can land vertically. 

That assumes you can steer to reasonably flat land.  SS has very little cross range.  A space plane can steer to a runway because it has enormous cross range - in the 1000km range.

SS has about half of cross range of Shuttle, i.e. right with the other space planes (Shuttle had an extreme cross range even for a spaceplane because AOA for polar orbits requirement; its cross range was about 2500km).

I've no idea where did't you come with the notion that SS entry is ballistic (or anywhere close to that).

Elon said so, and published a video demonstrating that.  It comes in with an AOA of about 90 degrees, which means no lift.

Source? All the published videos as well as slides with descent profiles say otherwise.

You almost certainly got it wrong, unless 60 = 90.

90°AoA is only on the terminal subsonic descent.

[sebk]

Survivable re-entry emergencies would be stuff like when one of the fins seized and controls are now very limited and surviving hypersonic portion takes priority and let's worry about landing spot once the vehicle is transsonic.

And at this point you have no idea what the cross range capacity is and very little time to find out.  There will not be a lot of choices, the automation needs to pick one of the less awful ones PDQ.

Yes, you have about 20km diameter circle to chose landing spot from. Not great, not hopeless.

[Robotbeat]

SpaceX WILL have variants of Starship that land (after reentry) on legs. Point to point cargo for the military, Mars Starship. Lunar HLS, though it won’t have heatshield tiles, it will definitely have legs.

SpaceX has, of course, tested various Starship prototypes with legs on multiple occasions successfully.

“SpaceX may sometimes try to catch Starship with the catching arms” is not the same thing as “it’s not feasible for SpaceX’s Starship to use legs if required for some reason.” And I’m not sure why people have difficulty with this logic.

The legs they've tested have basically all failed, and they've made a big deal about getting rid of them for the chopsticks.

I haven't seen any drawings or sketches of legs that are wider than the base of the vehicle, which isn't wide enough to land on anything but pretty flat ground.  I'm not sure legs like on F9 are viable on a vehicle this size.

They didn’t all totally fail or the landings wouldn’t have worked. (Also, early test failures don’t mean the concept isn’t sound, see F9’s own history.)

Starship HLS (although without tiles) is one that most definitely WILL use legs, and renders of it exist. Not much of USAF’s point to point has been made public, but they would necessarily require landing, not just catching. (And the stand-in renders show legs.)

[sebk]

SpaceX WILL have variants of Starship that land (after reentry) on legs. Point to point cargo for the military, Mars Starship. Lunar HLS, though it won’t have heatshield tiles, it will definitely have legs.

SpaceX has, of course, tested various Starship prototypes with legs on multiple occasions successfully.

“SpaceX may sometimes try to catch Starship with the catching arms” is not the same thing as “it’s not feasible for SpaceX’s Starship to use legs if required for some reason.” And I’m not sure why people have difficulty with this logic.

The legs they've tested have basically all failed, and they've made a big deal about getting rid of them for the chopsticks.

Nope. Sn-15 landed OK. Legs worked.

I haven't seen any drawings or sketches of legs that are wider than the base of the vehicle, which isn't wide enough to land on anything but pretty flat ground.  I'm not sure legs like on F9 are viable on a vehicle this size.

You'd need to support this assertion with numbers. Especially when I saw estimates here in NFS saying otherwise.

[chopsticks]

Elon said so, and published a video demonstrating that.  It comes in with an AOA of about 90 degrees, which means no lift.

Wrong.

https://forum.nasaspaceflight.com/index.php?topic=50748.msg2310002#msg2310002

The legs they've tested have basically all failed

The legs on SN5, SN6, and SN15 did not fail. They were very rudimentary crush core legs that did their job.

[chopsticks]

What I would like to know is how a SS with legs (Earth) would be safed. With SN15 they just opened the valves and vented the prop to the atmosphere. This took hours. Also venting methane a lot like this probably won't be considered acceptable if this is regular operations. It's not exactly environmentally friendly.

If chopstick landings become routine and acceptable for crewed flights, all is well I guess, since they will presumably reconnect the QD plate and drain the residual prop*. However, if there is some problem and the vehicle has to divert to a landing pad, then what? Some sort of a robot with a QD and LOX and methane tanks drives up that drains the prop so the crew can get out safely? Inflatable slide to slide down and run away as fast as possible? This poses other concerns since astronauts are helped out of their seats after being in space. They don't even exit the capsule themselves.

In an extreme event such as SN10, I can see that being a serious enough emergency requiring a slide and hoping that the crew inside are mobile and capable enough to get away before it goes boom. What other choice do you have here? But what if there's just a bad sensor on the stix or something relatively minor where the SS decides it needs to land on its "backup legs" or even the skirt. Nothing catastrophic has happened, no fires, gentle touchdown. Now what? We just wait for hours until the prop has boiled off? This is a dangerous situation since there are explosive gasses about and no way to abort (if there's no abort system). And the crew is stuck inside.

And if all crewed landings end up landing on legs you still have to solve the same problem, even assuming a nominal touchdown.

A few scenarios:

1. Just wait until prop has boiled off. Problem: This takes a long time, and is risky since the crew are stuck inside until everything has boiled off. There's a chance of an explosion at any point while methane is being vented. Pad abort capability would be nice here.

2. GSE robot approaches, connects the QD and drains the prop. Let's say this takes 30 minutes or so. Once the vehicle is declared safe, the crew egresses normally. Pad abort capability would still be nice here until it's declared safe.

3. Crew unbuckles and egresses while the vehicle is venting methane and oxygen. This is nuts.

4.

*I might add that even a crewed chopsticks landing might need a pad abort capability. You want to be able to get away until the vehicle is drained of propellant.

[Lee Jay]

Elon said so, and published a video demonstrating that.  It comes in with an AOA of about 90 degrees, which means no lift.

Wrong.

https://forum.nasaspaceflight.com/index.php?topic=50748.msg2310002#msg2310002

Fine - 70 degrees (the video shows 90).  But a cylinder at 70 degrees, even with fins, isn't going to have much lift.  The fins are in deep, deep stall.

[eriblo]

Elon said so, and published a video demonstrating that.  It comes in with an AOA of about 90 degrees, which means no lift.

Wrong.

https://forum.nasaspaceflight.com/index.php?topic=50748.msg2310002#msg2310002

Fine - 70 degrees (the video shows 90).  But a cylinder at 70 degrees, even with fins, isn't going to have much lift.  The fins are in deep, deep stall.

You have the numbers in the thread linked in the first post. Starship can be expected to have a hypersonic L/D of 0.5 - 0.6.

[Robotbeat]

Elon said so, and published a video demonstrating that.  It comes in with an AOA of about 90 degrees, which means no lift.

Wrong.

https://forum.nasaspaceflight.com/index.php?topic=50748.msg2310002#msg2310002

Fine - 70 degrees (the video shows 90).  But a cylinder at 70 degrees, even with fins, isn't going to have much lift.  The fins are in deep, deep stall.

Bet it’ll have at least as much lift as a typical capsule.

[InterestedEngineer]

What I would like to know is how a SS with legs (Earth) would be safed. With SN15 they just opened the valves and vented the prop to the atmosphere. This took hours. Also venting methane a lot like this probably won't be considered acceptable if this is regular operations. It's not exactly environmentally friendly.

If chopstick landings become routine and acceptable for crewed flights, all is well I guess, since they will presumably reconnect the QD plate and drain the residual prop*. However, if there is some problem and the vehicle has to divert to a landing pad, then what? Some sort of a robot with a QD and LOX and methane tanks drives up that drains the prop so the crew can get out safely? Inflatable slide to slide down and run away as fast as possible? This poses other concerns since astronauts are helped out of their seats after being in space. They don't even exit the capsule themselves.

In an extreme event such as SN10, I can see that being a serious enough emergency requiring a slide and hoping that the crew inside are mobile and capable enough to get away before it goes boom. What other choice do you have here? But what if there's just a bad sensor on the stix or something relatively minor where the SS decides it needs to land on its "backup legs" or even the skirt. Nothing catastrophic has happened, no fires, gentle touchdown. Now what? We just wait for hours until the prop has boiled off? This is a dangerous situation since there are explosive gasses about and no way to abort (if there's no abort system). And the crew is stuck inside.

And if all crewed landings end up landing on legs you still have to solve the same problem, even assuming a nominal touchdown.

A few scenarios:

1. Just wait until prop has boiled off. Problem: This takes a long time, and is risky since the crew are stuck inside until everything has boiled off. There's a chance of an explosion at any point while methane is being vented. Pad abort capability would be nice here.

2. GSE robot approaches, connects the QD and drains the prop. Let's say this takes 30 minutes or so. Once the vehicle is declared safe, the crew egresses normally. Pad abort capability would still be nice here until it's declared safe.

3. Crew unbuckles and egresses while the vehicle is venting methane and oxygen. This is nuts.

4.

*I might add that even a crewed chopsticks landing might need a pad abort capability. You want to be able to get away until the vehicle is drained of propellant.

Why do airplanes evacuated after crash landings with a decently large chunk of fuel on board?

[Lee Jay]

What I would like to know is how a SS with legs (Earth) would be safed. With SN15 they just opened the valves and vented the prop to the atmosphere. This took hours. Also venting methane a lot like this probably won't be considered acceptable if this is regular operations. It's not exactly environmentally friendly.

If chopstick landings become routine and acceptable for crewed flights, all is well I guess, since they will presumably reconnect the QD plate and drain the residual prop*. However, if there is some problem and the vehicle has to divert to a landing pad, then what? Some sort of a robot with a QD and LOX and methane tanks drives up that drains the prop so the crew can get out safely? Inflatable slide to slide down and run away as fast as possible? This poses other concerns since astronauts are helped out of their seats after being in space. They don't even exit the capsule themselves.

In an extreme event such as SN10, I can see that being a serious enough emergency requiring a slide and hoping that the crew inside are mobile and capable enough to get away before it goes boom. What other choice do you have here? But what if there's just a bad sensor on the stix or something relatively minor where the SS decides it needs to land on its "backup legs" or even the skirt. Nothing catastrophic has happened, no fires, gentle touchdown. Now what? We just wait for hours until the prop has boiled off? This is a dangerous situation since there are explosive gasses about and no way to abort (if there's no abort system). And the crew is stuck inside.

And if all crewed landings end up landing on legs you still have to solve the same problem, even assuming a nominal touchdown.

A few scenarios:

1. Just wait until prop has boiled off. Problem: This takes a long time, and is risky since the crew are stuck inside until everything has boiled off. There's a chance of an explosion at any point while methane is being vented. Pad abort capability would be nice here.

2. GSE robot approaches, connects the QD and drains the prop. Let's say this takes 30 minutes or so. Once the vehicle is declared safe, the crew egresses normally. Pad abort capability would still be nice here until it's declared safe.

3. Crew unbuckles and egresses while the vehicle is venting methane and oxygen. This is nuts.

4.

*I might add that even a crewed chopsticks landing might need a pad abort capability. You want to be able to get away until the vehicle is drained of propellant.

Why do airplanes evacuated after crash landings with a decently large chunk of fuel on board?

That fuel won't rapidly gassify if it gets out.

Kerosene on the ground is massively safer than a mixture of oxygen and methane in the air.

[chopsticks]

What I would like to know is how a SS with legs (Earth) would be safed. With SN15 they just opened the valves and vented the prop to the atmosphere. This took hours. Also venting methane a lot like this probably won't be considered acceptable if this is regular operations. It's not exactly environmentally friendly.

If chopstick landings become routine and acceptable for crewed flights, all is well I guess, since they will presumably reconnect the QD plate and drain the residual prop*. However, if there is some problem and the vehicle has to divert to a landing pad, then what? Some sort of a robot with a QD and LOX and methane tanks drives up that drains the prop so the crew can get out safely? Inflatable slide to slide down and run away as fast as possible? This poses other concerns since astronauts are helped out of their seats after being in space. They don't even exit the capsule themselves.

In an extreme event such as SN10, I can see that being a serious enough emergency requiring a slide and hoping that the crew inside are mobile and capable enough to get away before it goes boom. What other choice do you have here? But what if there's just a bad sensor on the stix or something relatively minor where the SS decides it needs to land on its "backup legs" or even the skirt. Nothing catastrophic has happened, no fires, gentle touchdown. Now what? We just wait for hours until the prop has boiled off? This is a dangerous situation since there are explosive gasses about and no way to abort (if there's no abort system). And the crew is stuck inside.

And if all crewed landings end up landing on legs you still have to solve the same problem, even assuming a nominal touchdown.

A few scenarios:

1. Just wait until prop has boiled off. Problem: This takes a long time, and is risky since the crew are stuck inside until everything has boiled off. There's a chance of an explosion at any point while methane is being vented. Pad abort capability would be nice here.

2. GSE robot approaches, connects the QD and drains the prop. Let's say this takes 30 minutes or so. Once the vehicle is declared safe, the crew egresses normally. Pad abort capability would still be nice here until it's declared safe.

3. Crew unbuckles and egresses while the vehicle is venting methane and oxygen. This is nuts.

4.

*I might add that even a crewed chopsticks landing might need a pad abort capability. You want to be able to get away until the vehicle is drained of propellant.

Why do airplanes evacuated after crash landings with a decently large chunk of fuel on board?

That's totally different. Liquid kerosene is stable at atmospheric pressure and density, cryogenic methane and oxygen are not. The tanks they are in have to be vented to prevent them from exploding, very much not the case with kerosene.

And gaseous methane + oxygen living next door to each other is just way more explody than jet fuel.

[Robotbeat]

There are solutions to this. Trucks that carry LNG or whatever deal with this all the time, and you pass them in your family car.

[chopsticks]

Elon said so, and published a video demonstrating that.  It comes in with an AOA of about 90 degrees, which means no lift.

Wrong.

https://forum.nasaspaceflight.com/index.php?topic=50748.msg2310002#msg2310002

Fine - 70 degrees (the video shows 90).  But a cylinder at 70 degrees, even with fins, isn't going to have much lift.  The fins are in deep, deep stall.

The video is just a fan made video with numerous errors (AoA being one of them). And yes, the fins are in a deep stall as intended. However it still should allow for decent cross range - further down Elon responded "probably" to Scott Manley's question: "With a 70 degree AoA how much cross range does it have? Will it be enough to ensure at least one landing opportunity per day?"

FWIW

[chopsticks]

There are solutions to this. Trucks that carry LNG or whatever deal with this all the time, and you pass them in your family car.

Care to expand a bit? I was under the impression that those tanker trailers had pretty thick walls to withstand a lot of pressure, or is the cryogenic liquid actively cooled?

Edit: I don't know anything about cryogenic tanker trailers but it seems like they are all pretty well insulated and have pretty low boiloff rates. LNG ships are also insulated, and many use the boiloff gas for propulsion or it gets reliquified.

Starship is just a thin metal can where the cryogenics don't want to stay cryogenic very much. Unless SpaceX decides to heavily insulate SS to slow pressure buildup over a long period of time, I'm not sure how these current solutions (cryo tanker for example) apply to SS.

[Robotbeat]

The trucks don’t have super thick walls, there’s plenty of boiloff. Starship will have more but it could use a similar strategy.

[sebk]

Elon said so, and published a video demonstrating that.  It comes in with an AOA of about 90 degrees, which means no lift.

Wrong.

https://forum.nasaspaceflight.com/index.php?topic=50748.msg2310002#msg2310002

Fine - 70 degrees (the video shows 90).  But a cylinder at 70 degrees, even with fins, isn't going to have much lift.  The fins are in deep, deep stall.

You have the numbers in the thread linked in the first post. Starship can be expected to have a hypersonic L/D of 0.5 - 0.6.

Yup. And to put that in perspective, Shuttle had barely more than 1 (something around 1.2:1). And that was enough for ~2500km cross range.

Preconceptions from subsonic operations and aerodynamics in general don't work at all in re-entry conditions.

1. There's essentially no such thing as stall, or rather everything is stalled in hypersonic regime. Hypersonic vehicles fly more like kids kites (extreme AoA, low L:D) than airplanes (small AoA, high L:D) as high L:D is not possible at all.

2. Contrary to subsonic and low supersonic regime, the bottom of the wing is what produces vast majority of the lift (rather than the upper surface at low speeds). The naive "suspended balls being pushed by incoming vehicle" model is much better approximation of hypersonic aerodynamics than various continuous flow models used for subsonic, transsonic and low supersonic flight. After all if the medium's ambient pressure is ~10Pa (~0.0001bar) your max upper surface underpressure is hard limited by that 10Pa. The whole 150t vehicle with 500m^2 surface would generate ... 5kN of lift that way. It's negligible. Hypersonic lift is generated by extreme (20000:1 or so!) compression by the lower surface. You get 0.1 - 0.2 bar here and and usable 0-20kPa "wing" loading.

3. L:D at high hypersonic regime is always extremely poor compared to anything in subsonic regime.

4. This is not much of a problem, though, because velocity and kinetic energy are extreme. Shuttle could glide for 8000km or so(!) despite so awful low L:D. Your initial kinetic energy is about 6x your mass equivalent in TNT.

5. Also, you're still at significant fraction of orbital speed. At Mach 19 you get half of your lift for fee from flying at over 0.7 of orbital velocity as the rest is "used up" as centripetal force. Thus if you were not losing speed at all and flying horizontally the net gravity felt would be 0.5g. You need to slow down to ~Mach 12 to feel 0.75 of the surface gravity.

In effect, as you fly at say Mach 19 at 60° and produce 1.5g load, you are doing about 1.3g of braking and 0.75g of lift. All the while your locally felt "pull of the Earth" is 0.5g. That means you should fly at 50° bank angle to even stay in the atmosphere. This also means you have 0.57g horizontal component in your 0.75g turn at this very moment. You are free to use that for your cross range (if you're flying too much to the side, just periodically flip to the other turn, executing an S maneuver exactly like Shuttle did).

[JCopernicus]

SpaceX WILL have variants of Starship that land (after reentry) on legs. Point to point cargo for the military, Mars Starship. Lunar HLS, though it won’t have heatshield tiles, it will definitely have legs.

SpaceX has, of course, tested various Starship prototypes with legs on multiple occasions successfully.

“SpaceX may sometimes try to catch Starship with the catching arms” is not the same thing as “it’s not feasible for SpaceX’s Starship to use legs if required for some reason.” And I’m not sure why people have difficulty with this logic.

The legs they've tested have basically all failed, and they've made a big deal about getting rid of them for the chopsticks.

I haven't seen any drawings or sketches of legs that are wider than the base of the vehicle, which isn't wide enough to land on anything but pretty flat ground.  I'm not sure legs like on F9 are viable on a vehicle this size.

A mysterious white Starship model seems to show an early version of the Lunar Starship with deployable solar array/radiators. The model is at the recently opened "Inside Tesla" exhibit at Petersen Automotive Museum.

First photo is from https://twitter.com/SawyerMerritt/status/1594207852159172608

2nd photo is from reddit

[Barley]

Survivable re-entry emergencies would be stuff like when one of the fins seized and controls are now very limited and surviving hypersonic portion takes priority and let's worry about landing spot once the vehicle is transsonic.

And at this point you have no idea what the cross range capacity is and very little time to find out.  There will not be a lot of choices, the automation needs to pick one of the less awful ones PDQ.

Yes, you have about 20km diameter circle to chose landing spot from. Not great, not hopeless.

20km seems generous.  Falcon-9 landings go transsonic at about 8 km altitude.  Can it do a 45° glide?  Are the numbers for SS very different?  Also some of your controls have failed, your cross range may be close to zero, or in an unexpected direction.

[spacenut]

When the Starship lands, it will have very little methane or lox left.  Like someone said, maybe a truck load.  A QD could be attached and the liquid methane drained into one or two trucks.  Oxygen could be vented.  Since there would be very little methane left, it shouldn't take long to drain. 

The engines probably would need to be cooled down to avoid an accidental flash point.  30 minutes shouldn't be that long a wait to deboard.  A truck with a lifting enclosed lift platform could allow the crew or passengers to deboard, lower and drive away. 

Abort is another thing.  Maybe the Starship can ignite the engines quick enough to separate from the booster in case it needed to, then fly back to a safe spot to land.