Abort options for Starship and Starship/SuperHeavy

[sebk]

Nope.

There is such thing as material annealing. The steel the ship is made from was hardened (it's cold rolled -- it's a type of work hardening; 300 series stainless hardens very well and its yield strength gets increased a few times). Stainless starts to slowly lose this strength above 700K and does so practically immediately above 1200K. But it's not melting point. 304 stainless steel melts at 1570K to 1630K. Shuttle tiles were to withstand 1530K. As far as we know Starship tiles are the same.


The vehicle needs its full strength primarily on ascent when its tanks are pressurized to 6bar while it faces ~35kPa max-q loads or 3.5g late booster burn load, all the while filled with 1200t of ascent propellant (so for example its skirt has to handle about 5000t load; 3.5g * ~1400t). But during EDL the vehicle is an order of magnitude lighter, dynamic loads are ~20kPa, tanks don't need high pressurization and likely are pressurized as little as possible because ullage gas has non-trivial mass. Suddenly skin doesn't have to survive stress of a 6bar, when the pressure is 2bar. Your skin structural margin increased from 40% to over 400%. The thing could become 4x weaker and it would still hold.


But after such overheating the vehicle would be a write-off (unless the overheating affected only a small patch, then a repair is an option). 300 series remains annealed after it's annealed, it doesn't heal (it doesn't age harden appreciably). You need to work harden it again (this is one of the reasons SpaceX had some initial trouble with popping tanks: weld's anneal the base material; they implemented a better controlled welding process and they also planish many welds which restores some of the strength, and they use weld doublers where fixing up seams is not feasible).

I don't buy this.

The RCC was for entry temperatures *above* 1530K.  You're equating that with a *melting* temperature in the same range.  These are NOT the same thing.  A material just below its melting point has lost most of its strength and will fail soon, if not immediately.  At 1000C 304 is 8 times weaker (lower yield stress) than at 600C.

We're talking about what to do in an off-nominal entry.  Off-nominal likely means damage (tiles or other) or loss of control.  I suspect in either case the assumption that there's nothing you can do is actually correct.  Damage will likely lead to burn through from loss of strength or full blown melting and that's worse on this vehicle than on Shuttle simply because burn through is on a pressurized tank you have to have to land safely.  Loss of control is probably worse.  So I seriously doubt that the intrinsic design of this vehicle makes it more robust against off-nominal entry conditions, and I certainly don't know of an abort option for that situation.

I'm not talking about RCC. There's no need for RCC on Starship because it doesn't have tight curvatures pointing into incoming air.

I'm talking about silica tiles, the ones which had limit of 1533K and didn't reach that on nominal entry.

Also in the localized HS failure you have the backside of an exposed skin fragment providing cooling, so the expected temperature is about 0.84 of a thermally insulated one. So burn through is less likely than it initially seems.

[TheRadicalModerate]

If solid rockets don't work then there is no pad abort for a Starship loaded up to 1400t with fuel.

You've over-constrained the problem.  You don't need 1400t of prop.  You don't even need cargo.  You need a ~20t crew module and just enough prop to get to LEO and do an EDL abort from orbit.  Once you're in LEO, you transfer to something else (an LSS or a fully-featured crew system suitable for either lunar surface or Mars journeys).  When you come back to LEO, the abort-safe crew version takes you back through EDL.

That said, 5 gee pull-away might not be adequate.  There might not be a viable way to launch a Starship from a mated SuperHeavy.  But even if you can get through these two problems, there are other abort modes that probably need an escape capsule.

your same arguments apply to having a crew dragon in the cargo compartment.

I don't understand what you're saying here.  If the argument is that you don't need robust abort modes for most if not all flight phases, then it's a tautology.  But if it's not then... you do?

Don't get too hung up on the D2.  But you need some kind of escape system if it's important to meet NASA pLOC standards--or responsible corporate standards, for that matter.

So if there is no pad abort, and ascent abort works with current design, and there is no ELD abort, I'm flummoxed as to what abort system there needs to be at all.

Again, you've constructed a tautology on a false premise.  It is of course true that if you need no abort contingencies, then you need no abort mechanism.

I don't see a reality where there isn't a viable pad abort.  All the flight failure trees get convolved with all the Stage 0 failure trees, and then there are any number of exogenous events.

And how did you make the leap to no EDL abort?  There may not be abort options through the entire hypersonic regime, but that's true for all human orbital spacecraft.  And you certainly need to deal with descent, landing, and nav contingencies. 

Landing abort is all that's left.   "can't get to catch tower" means water abort, which works with a robust cargo compartment.

First, I don't think it necessarily works with a robust nose.  It'll work if the entire ship is robust enough, but prop tanks tend to blow up if they rupture.

Second, what about "got to catch tower but catch failed"?

Failure to ignite or correctly use engines due to the remaining single points of failure (which is tank pressurization and gimbaling) happens at such a low altitude abort would be difficult.   Blasting a crew dragon horizontally won't be useful, and neither will solid rockets in the base.

Are you talking about ascent or descent here?  On descent, if you start the rotation high enough, there's absolutely nothing wrong with a horizontal D2 abort; it'll steer into the proper orientation for parachute opening.  And if the rotation is complete, then it's aborting vertically.

On the pad, failure to ignite isn't the problem.  A failure anywhere in the final launch sequence is a problem.

And a crew dragon wouldn't blast horizontally for any pad or ascent abort; it would go up vertically (or axially, after pitchover), after popping the fairing open.

I suspect gimbaling can be made redundant barring frozen parts¹, so really we are just left with inadequate pressure in the header tanks as the remaining single point of failure.

If I ran a crew safety group, I'd have a jar where anybody who said the words, "Really we are just left with..." had to put $20.

Slosh causing gas ingestion into the turbines?
Eloneron failure during rotation?
Post-ignition engine explosion?
Nav/guidance failures?
Unexpected, large, cross-wind gusts?
Chopstick malfunctions?  Plain ol' catch failures?
Leg failures for uncaught landings?  Rough surface landings?
Foreign object damage on landing?

That's an off-the-top-of-my-head list.  I'm sure it can be made longer.

[sebk]

We're talking about what to do in an off-nominal entry.  Off-nominal likely means damage (tiles or other) or loss of control.  I suspect in either case the assumption that there's nothing you can do is actually correct.

I still think that the fact that Starship can hold some non-trivial amount of propellant and has working engines during hypersonic flight means that there might be a portion of that regime where an abort back to orbit might be viable.  This is really the first spacecraft with main propulsion capability during reentry.

Off-hand, I'd think that the proper trajectory was pretty much at whatever the steepest viable angle of attack was.  Then, once clear of the atmosphere, you'd burn tangential at apogee until you'd raised your perigee to the necessary altitude.

I doubt this works below a certain speed/altitude, but it would likely work deep enough into reentry that you'd get diagnostics of something going wrong.  But there's a mass penalty, because you need to hang on to more prop than you need to land.

I doubt it'd buy you much.

Starship descent profile has a switch-over from max heating to max g-load (i.e the point of the worst stress) at about Mach 15. You're about 3km/s below orbit then. That's way away.

Even with Shuttle descent profile you'd have that point aroud Mach 20. Still about 1.5km/s away from orbit. Columbia got down to that point despite an actual hole in its skin.

What you could do is to have a lot of sensors and if there's abnormal heating somewhere during the first ~300m/s slowdown, you boost back to orbit. But this doesn't solve mechanical failures of fins, heatshield failures later in the EDL, etc. It's usefulness is very narrow.

[InterestedEngineer]

Slosh causing gas ingestion into the turbines?
Eloneron failure during rotation?
Post-ignition engine explosion?
Nav/guidance failures?
Unexpected, large, cross-wind gusts?
Chopstick malfunctions?  Plain ol' catch failures?
Leg failures for uncaught landings?  Rough surface landings?
Foreign object damage on landing?

1. Slosh can be solved by design
2. Airlines can suffer wing and control surface failures as well.   See jackscrew:  https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261
3. Jet engines can explode.  They have protective shell around them to prevent further damage.  Just like SpaceX is working on.  These can be tested and are.
4. Nav/Guidance - triple redundant systems, bog standard stuff unless you are a cheapskate like Boeing and try to maintain trim from one sensor.
5.  Cross-wind-gusts - Airplanes have same problem
6.  Catch failures.   Yep, a problem.   Practice makes perfect.  Took a while to get carrier landings to be reliable too.
7.  Leg failures - landing gear fails all the time too.  Wait, I thought we were catching?
8.  FOD.   While catching?  In any case SpaceX has already been testing that for over two years with their suborbital stands.  The worst that happened was "we have to replace a Raptor".


Airplanes are remarkably fragile.   They are made better by constant feedback and iteration.  The same can and will be done for rockets.

[TheRadicalModerate]

Slosh causing gas ingestion into the turbines?
Eloneron failure during rotation?
Post-ignition engine explosion?
Nav/guidance failures?
Unexpected, large, cross-wind gusts?
Chopstick malfunctions?  Plain ol' catch failures?
Leg failures for uncaught landings?  Rough surface landings?
Foreign object damage on landing?

1. Slosh can be solved by design

Not necessarily in a rotating tank with uncertain levels at any given point in the landing profile.

2. Airlines can suffer wing and control surface failures as well.   See jackscrew:  https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261

Failures are incredibly rare, and are based on hydraulic technology with 80 years of flight heritage.  And aircraft aren't covered in TPS tiles.

(BTW, the Alaska jackscrew crash was the result of nearly criminal maintenance decisions.  However I'm assuming that SpaceX ops crew won't start getting lackadaisical for at least another ten years.)

3. Jet engines can explode.  They have protective shell around them to prevent further damage.  Just like SpaceX is working on.  These can be tested and are.

Jet engines aren't started up less than 20 seconds before landing, nor do they ramp from 0-300bar chamber pressure in a couple  hundred milliseconds.  And the distances between Raptors is considerably less than the best-case distance between aircraft engines.

And exactly how long did it take until practice made perfect enough to enable passenger traffic--with no regulatory oversight?

4. Nav/Guidance - triple redundant systems, bog standard stuff unless you are a cheapskate like Boeing and try to maintain trim from one sensor.

Fair--once all the different ground clutter and de-jamming procedures are worked out in detail.

5.  Cross-wind-gusts - Airplanes have same problem

Airplanes can go around or even divert to another airport.  Starship might be able to pop up a time or to for a missed approach, but then you're adding prop that eats into your acceleration margin (more prop=lower escape acceleration) on launch.

6.  Catch failures.   Yep, a problem.   Practice makes perfect.  Took a while to get carrier landings to be reliable too.

I assert that NASA would never crew-certify a spacecraft that had as dangerous a return architecture as a carrier landing.  It's a civilian program, and the public expectations are different from a military program.

7.  Leg failures - landing gear fails all the time too.  Wait, I thought we were catching?

You have to catch sometimes, and you have land elsewhere occasionally.  If you want to argue that pOffNominalTarget * pLegCollapse is small enough to be negligible, that's a legitimate argument. 

Aircraft landing gear failures are indeed a finite probability.  But they're non-fatal events more often than not.  If a Starship falls over on landing, it'll explode.  My guess is that the difference in lethality is pretty marked.

8.  FOD.   While catching?  In any case SpaceX has already been testing that for over two years with their suborbital stands.  The worst that happened was "we have to replace a Raptor".

Mostly during a rough-surface landing.  And that's a very different environment than the one under a test stand.

Airplanes are remarkably fragile.   They are made better by constant feedback and iteration.  The same can and will be done for rockets.

You're talking about a timeframe that I would classify as science fiction.  I'm talking about 8-10 years from now.  I don't dispute that tail-down reusable spacecraft will become incredibly reliable over time.  But aircraft analogy telescopes 120 years of experience into about one tenth that time.  That's wishful thinking.

[TheRadicalModerate]

I doubt it'd buy you much.

Starship descent profile has a switch-over from max heating to max g-load (i.e the point of the worst stress) at about Mach 15. You're about 3km/s below orbit then. That's way away.

Even with Shuttle descent profile you'd have that point aroud Mach 20. Still about 1.5km/s away from orbit. Columbia got down to that point despite an actual hole in its skin.

What you could do is to have a lot of sensors and if there's abnormal heating somewhere during the first ~300m/s slowdown, you boost back to orbit. But this doesn't solve mechanical failures of fins, heatshield failures later in the EDL, etc. It's usefulness is very narrow.

Good analysis.  What I was mostly thinking about was early anomaly detection.  Thousands of m/s of delta-v probably isn't in the cards, but 500 probably is.

[InterestedEngineer]

5.  Cross-wind-gusts - Airplanes have same problem

Airplanes can go around or even divert to another airport.  Starship might be able to pop up a time or to for a missed approach, but then you're adding prop that eats into your acceleration margin (more prop=lower escape acceleration) on launch.

Airplanes fly at 500mph and take hours to get to airports where the weather can change.   Weather changes faster than they can fly, and they run out of fuel eventually.

Starship can orbit until the weather clears, and land within an hour of de-orbiting.   Furthermore regional weather effects aren't a problem if you have some landing areas 1000km apart.

Spacecraft in general have far less risk from weather than airplanes.

All the risks noted are airplane level risks, which are rounding error for rockets.  Not worth worrying about.

My guess is the new landing technique is the biggest risk.  Do the flip over water, and abort-to-water alleviates a large chunk of that risk.    Which is exactly the F9 experience, that's where the video came from.

[sebk]

Few random notes:

Airplane engines have only partial shielding. If the fan loses some blades the shield will work. If turbine disc fails it will fragment and penetrate whatever happens on its way. Sometimes things come out lucky like in that Qantas A380 which lost 2 hydraulic systems and outboard engine control (inboard engine was the one which exploded) but landed fine without casualties. Sometimes things come out worse like that Southwest passenger who died when a turbine disc in the 737 they were flying failed, and turbine disc fragments penetrated the cabin.

There were airplane designs with engines extremely close to one another: Concorde, VC-10, IL-62, Tu-144, and many military planes. And there were (and are) multiple designs with engines very close to vital systems: practically all T-tails planes are like that.


The primary problem with loss of control during reentry is not a burn through or a thermal failure. It's actually the structural failure due to a structural overload. The problem is that atmospheric density grows exponentially with reducing altitude. If a reentering vehicle loses control it tends to switch to a ballistic path and it enters denser layers early and structural load goes easily into 6~10g territory. Heatshield (including silica tiles) would tend to ablate before failing so it would hold for quite a bit, but the structure may not be able to keep up.

The holy grail would be a shape which is passively stable in hypersonic regime while it keeps producing lift. There are some indications/allegations that Starship with its fins in V config could be such a shape.

[Lee Jay]

5.  Cross-wind-gusts - Airplanes have same problem

Airplanes can go around or even divert to another airport.  Starship might be able to pop up a time or to for a missed approach, but then you're adding prop that eats into your acceleration margin (more prop=lower escape acceleration) on launch.

Airplanes fly at 500mph and take hours to get to airports where the weather can change.   Weather changes faster than they can fly, and they run out of fuel eventually.

How often do planes run out of fuel trying to get to an airport where the weather allows a landing?

Essentially never.

[DanClemmensen]

5.  Cross-wind-gusts - Airplanes have same problem

Airplanes can go around or even divert to another airport.  Starship might be able to pop up a time or to for a missed approach, but then you're adding prop that eats into your acceleration margin (more prop=lower escape acceleration) on launch.

Airplanes fly at 500mph and take hours to get to airports where the weather can change.   Weather changes faster than they can fly, and they run out of fuel eventually.

How often do planes run out of fuel trying to get to an airport where the weather allows a landing?

Essentially never.

See:
   https://en.wikipedia.org/wiki/Gimli_Glider
For more examples see:
   https://en.wikipedia.org/wiki/Category:Airliner_accidents_and_incidents_caused_by_fuel_exhaustion

[edzieba]

5.  Cross-wind-gusts - Airplanes have same problem

Airplanes can go around or even divert to another airport.  Starship might be able to pop up a time or to for a missed approach, but then you're adding prop that eats into your acceleration margin (more prop=lower escape acceleration) on launch.

Airplanes fly at 500mph and take hours to get to airports where the weather can change.   Weather changes faster than they can fly, and they run out of fuel eventually.

How often do planes run out of fuel trying to get to an airport where the weather allows a landing?

Essentially never.

ALM Flight 980, UA 173, Air Canada 143 (the 'Gimli Glider'), Avianca 052, etc.

[Cherokee43v6]

5.  Cross-wind-gusts - Airplanes have same problem

Airplanes can go around or even divert to another airport.  Starship might be able to pop up a time or to for a missed approach, but then you're adding prop that eats into your acceleration margin (more prop=lower escape acceleration) on launch.

Airplanes fly at 500mph and take hours to get to airports where the weather can change.   Weather changes faster than they can fly, and they run out of fuel eventually.

How often do planes run out of fuel trying to get to an airport where the weather allows a landing?

Essentially never.

ALM Flight 980, UA 173, Air Canada 143 (the 'Gimli Glider'), Avianca 052, etc.

A LOT more often than you would believe.  Check out the 'Mentour Pilot' channel on youtube for a sampling.

[Barley]

My guess is the new landing technique is the biggest risk.  Do the flip over water, and abort-to-water alleviates a large chunk of that risk.    Which is exactly the F9 experience, that's where the video came from.

Abort-to-water landing reduces the risk to people on the ground, not to the rocket or the crew.

This abort thread is full of examples of alternate landing modes that are claimed to reduce risk but are only to be used for emergencies.

If water landing* is in fact safer it should be feasible to plan to use it and treat SS as expendable for the first dozen or more crewed landings.

* Or anything else, for example if a large flat landing area would reduce risk landing at Edwards AFB and abandoning the airframe should not be off the table

[Robotbeat]

…
My guess is the new landing technique is the biggest risk.  Do the flip over water, and abort-to-water alleviates a large chunk of that risk.    Which is exactly the F9 experience, that's where the video came from.

Exactly what I was thinking. And I think a Starship could actually land on one of their existing droneships.

[InterestedEngineer]

5.  Cross-wind-gusts - Airplanes have same problem

Airplanes can go around or even divert to another airport.  Starship might be able to pop up a time or to for a missed approach, but then you're adding prop that eats into your acceleration margin (more prop=lower escape acceleration) on launch.

Airplanes fly at 500mph and take hours to get to airports where the weather can change.   Weather changes faster than they can fly, and they run out of fuel eventually.

How often do planes run out of fuel trying to get to an airport where the weather allows a landing?

Essentially never.

Thanks y'all for providing the examples of running out of fuel on airplanes. 

Other as numerous examples are the bad cockpit decisions made because of having to deal with fuel management and weather. Like landing in unsafe weather for worry of fuel, or having no alternative airports because all that are within fuel range have weather problems. What one might call "non-direct consequences of a constraint problem".

One biggest disagreement with a lot of the abort proposals are the non-direct constraints they impose.  The non-direct consequences from whatever scheme was proposed.   There's a lot of linear thinking going on, but it's the multi-variate aspect of the solution that's the mains source of the problems.

Take for example, having hypergolic fuel on a Dragon 2 that is *enclosed*.  A little leak and suddenly there's toxic fuel all over the cargo compartment.   Is the space going to be ventlated?

Have you seen all the rigamarole that they go through to test and avoid toxic levels of hypergolic fuel on the Crew Dragon splashdown?  Now imagine doing that 30 meters in the air.

Spacecraft in general don't have much of a weather constraint problem for landing  because extra orbits are fuel free, and there's an entire circumference of the planet to put landing sites on.

Removing constraints will make the spacecraft safer.   That's the best abort option of all.

[TheRadicalModerate]

I think we've managed to boil this down to the point where the two sides of this argument aren't going to be moved by the others' points any more.  However, I'm willing to bet 1,000,000 Internet Toldja So Points that NASA won't crew-certify Starship for crew launch/EDL any time before 2035 without an escape system.  And I'm willing to bet 250,000 ITSPs that SpaceX won't either.

[InterestedEngineer]

I think we've managed to boil this down to the point where the two sides of this argument aren't going to be moved by the others' points any more.  However, I'm willing to bet 1,000,000 Internet Toldja So Points that NASA won't crew-certify Starship for crew launch/EDL any time before 2035 without an escape system.  And I'm willing to bet 250,000 ITSPs that SpaceX won't either.

I'm not so pessimistic on either front.  You've agreed with a few of my points, and I've agreed with a few of yours.  There was even a hint of you deciding something was a non-requirement, which I promptly upvoted.  i also give you credit for posting a real proposal with a real diagram.

If the flights per year go like this and most of the LOC happen before 2026:

2023:  6
2024:  24
2025:  48
2026:  96
2027:  192

Then crew certification will happen before 2030 (the last two years I left missing are purely bureaucratic latency)

[Lee Jay]

I think we've managed to boil this down to the point where the two sides of this argument aren't going to be moved by the others' points any more.  However, I'm willing to bet 1,000,000 Internet Toldja So Points that NASA won't crew-certify Starship for crew launch/EDL any time before 2035 without an escape system.  And I'm willing to bet 250,000 ITSPs that SpaceX won't either.

I agree with your ideas, though I suspect some sort of pressure will be brought to bear to allow crew on this vehicle at some point.  But it's an inherently bad architecture.  Let this thing launch cargo and launch crew on something with abort systems - like F9 and Dragon.

I know, I know - upper-stage reusability.  Whatever, it's still an inherently unsafe architecture, reusable or not.

[Hog]

I think we've managed to boil this down to the point where the two sides of this argument aren't going to be moved by the others' points any more.  However, I'm willing to bet 1,000,000 Internet Toldja So Points that NASA won't crew-certify Starship for crew launch/EDL any time before 2035 without an escape system.  And I'm willing to bet 250,000 ITSPs that SpaceX won't either.

So a Space X crew rating of SS for Earth-Orbital Velocity-Earth missions is 4 times as likely than the same rating from NASA?
Hmm.


I've always had a mental picture of a Starship stack launching after a TeslaMotorWorks bus dropped off tens of humans for loading onto the "shiny rocket".

[chopsticks]

Let this thing launch cargo and launch crew on something with abort systems - like F9 and Dragon.

But that's what this thread is about though, right? Using an abort system so it would be just as safe as Dragon? If it's got an abort system, it is any more unsafe than the other crewed capsules out there?