Abort options for Starship and Starship/SuperHeavy

[steveleach]

<snip>

The numbers are kinda all over the place.

It could be that Starship never quite makes the calculated terminal velocity.  There might not be time to do so.

My guess is that 66 m/s is the design target, 90 m/s is the average for SN8 (distance divided by time), and 75-78 m/s is what the (overweight and unoptimised) SN8 got down to before attempting the flip.

It might be higher if there were a crew cabin and people on board.

True, but it might be lower if they decide to put larger flaperons on variants designed to land with people on board.

If the vehicle design aims for 66 m/s then that's what I'd suggest any survival structure design discussions use as well.

[Lee Jay]

<snip>

The numbers are kinda all over the place.

It could be that Starship never quite makes the calculated terminal velocity.  There might not be time to do so.

My guess is that 66 m/s is the design target, 90 m/s is the average for SN8 (distance divided by time), and 75-78 m/s is what the (overweight and unoptimised) SN8 got down to before attempting the flip.

It might be higher if there were a crew cabin and people on board.

True, but it might be lower if they decide to put larger flaperons on variants designed to land with people on board.

If the vehicle design aims for 66 m/s then that's what I'd suggest any survival structure design discussions use as well.

I think anything but a perfect landing should be considered unsurvivable.  The vehicle has lox and methane on board, and there's no way to guarantee it won't ignite.

[steveleach]

<snip>

My guess is that 66 m/s is the design target, 90 m/s is the average for SN8 (distance divided by time), and 75-78 m/s is what the (overweight and unoptimised) SN8 got down to before attempting the flip.

It might be higher if there were a crew cabin and people on board.

True, but it might be lower if they decide to put larger flaperons on variants designed to land with people on board.

If the vehicle design aims for 66 m/s then that's what I'd suggest any survival structure design discussions use as well.

I think anything but a perfect landing should be considered unsurvivable. 

Yep, you've made that very clear over the last twenty pages or so.

The vehicle has lox and methane on board, and there's no way to guarantee it won't ignite.

No-one's looking for guarantees.

Anyway, I've already spent longer than I want to on this multi-page thread derailment.

[meekGee]

To match motorcycles you can have 30 fatalities per 100 million miles travelled. So around 4000 orbits. Or 250 days in orbit continuously.

Or a fatality every 10 days.

That seems achievable.

The per-mile metric is irrelevant, you need to measure per normal use-case.

To make the point, imagine a device that teleports you clear across the galaxy, but kills you 90% of the time.

Per mile, it's probably the safest transport system ever devised, yet I doubt you want to ride in it.

[meekGee]

The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

You forgot "IMO".

No I didn't. I'm sorry, but if you believe that rocket travel/space travel can become as safe or routine as commercial air travel, I don't know what to tell you. It's orders of magnitude more complex and way more things to go wrong with far fewer redundancies.

.. and airplanes are an order of magnitude more complicated than cars.  I thought we covered this already.

[meekGee]

The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

Right.  With hard work and a lot of flights, that might be able to take us from 5 orders or magnitude worse than an airliner down to 4 orders of magnitude worse.  But not 1 or 0.

I think 1-2 is feasible.

To get to the same safety as airliners for long haul flight, Starship needs to get to one in a million survivability.

The global fatal accident rate for airliners is about 1 in 10 million.

...(of course, that means no unsurvivable failures…).

You think it's likely that they could do 10,000 launches and 10,000 EDL's in a row without an unsurvivable failure?  I don't.

There were times when nobody would have believed that air travel can be as safe as it is today.

I get why aspects of rocketry are more complex/dangerous than aviation, but same can be applied to airplanes vs. cars.

In fact if you look at the reasons we still have accidents in modern aviation, you'll see that many of them (pilot error, maintenance errors, bird strikes and volcanic ash) are either impossible or less likely with space flight.

You'd be surprised how safe it can become.

[TheRadicalModerate]

I think anything but a perfect landing should be considered unsurvivable.  The vehicle has lox and methane on board, and there's no way to guarantee it won't ignite.

It's worth investigating whether Starship could be made crashworthy.  But if you're going to do that, you need to assume a lot of worst-case scenarios.  And when you armor/fireproof/crushcore the crew system adequately (and I'm still pretty sure that there's isn't an adequate crush core budget), it's heavy.  That drives up the ballistic coefficient, which in turn drives up the terminal speed.

One thing you can do for almost all abort scenarios is ensure that the amount of methalox is just adequate for worst-case landing.  That's not a trivial amount, but it's an amount that wouldn't make a primary fire burn for hours or even minutes.  Of course, there are scenarios where the crash occurs in the tank farm.  That would be bad.

I'm still firmly on Team Escape, though.

[Lee Jay]

One thing you can do for almost all abort scenarios is ensure that the amount of methalox is just adequate for worst-case landing. 

That makes it worse for some situations, however, such as the wind gust thing.  If you can hover for a while, the wind gust type of failure can be dramatically mitigated.  But that means many tons of extra fuel, reduced payload and way more fuel to burn if you crash.

[Lee Jay]

In fact if you look at the reasons we still have accidents in modern aviation, you'll see that many of them (pilot error, maintenance errors, bird strikes and volcanic ash) are either impossible or less likely with space flight.

We've already had a bird strike on a rocket (didn't cause a crash, but there are two or more a day on airliners that don't cause crashes either), and you don't think maintenance error and pilot error can happen on a rocket?  Even if the controls are automated, think about how many times Tesla Autopilot has made an error and caused an accident.  It may be reduced for cars compared to people (I kind of doubt it if you exclude intoxicated/high people) but I'd be surprised if it's reduced for rockets yet, and it's for sure not reduced to zero.

[meekGee]

In fact if you look at the reasons we still have accidents in modern aviation, you'll see that many of them (pilot error, maintenance errors, bird strikes and volcanic ash) are either impossible or less likely with space flight.

We've already had a bird strike on a rocket (didn't cause a crash, but there are two or more a day on airliners that don't cause crashes either), and you don't think maintenance error and pilot error can happen on a rocket?  Even if the controls are automated, think about how many times Tesla Autopilot has made an error and caused an accident.  It may be reduced for cars compared to people (I kind of doubt it if you exclude intoxicated/high people) but I'd be surprised if it's reduced for rockets yet, and it's for sure not reduced to zero.

Cars and airplanes operate in an unstructured environment, hence the need (and problems associated with) human pilots. Rockets can be entirely automated.

Not having giant air breathing engines goes a long way toward minimizing the risks posed by birds and volcanic ash.

Maintenance wise, rockets to airplanes is like airplanes to cars. Also performance monitoring.

So yes, the consequences of a malfunction in a rocket are much more dire then they are in a plane, but the same can be said for planes vs. cars.

Airplanes make up for their (car-) relative fragility by improved procedures and control, and rockets will do the same relative to airplanes.

Note that we accept the higher risk of road travel (and general aviation) and so rockets don't have to match the safety record of aviation, they just need to be closer to the standards of mainstream transport systems.

[TheRadicalModerate]

One thing you can do for almost all abort scenarios is ensure that the amount of methalox is just adequate for worst-case landing. 

That makes it worse for some situations, however, such as the wind gust thing.  If you can hover for a while, the wind gust type of failure can be dramatically mitigated.  But that means many tons of extra fuel, reduced payload and way more fuel to burn if you crash.

I'm thinking more of a launch abort (assuming that hot-staging will work, which it probably won't).  You can burn off all of the prop needed to get to orbit via an out-and-back RTLS maneuver.  But yeah, you have 250m/s-ish of delta-v on board for landing.  For a 95t payload (what I arm-waved up-thread for armoring and crash mitigation), that's like 17t of methalox, with the mains drained down to the sumps and the working prop in a combination of the headers and the downcomers.  Note that the downcomers have to go right past the crew module, which ain't great.  No matter what, it's a pretty good barbecue, but something vaguely in the realm of survivable with enough armoring.  Again, I'm just playing Devil's Advocate.

[TheRadicalModerate]

Orion is 6.4g, D2 is 5G, and Starliner is 6G, so i just stuck with 6G.

Orion and Starliner sit on top of hydrolox stages.  Starship sits on top of methalox, but it's a lot of methalox.  6G sounds plausible, but it's impossible to tell without blast modeling.

6G requires 20 SDs, which is getting up there, but still viable from an engine vs. real estate perspective.  (60% of the skirt would be nozzles.)

NB:  I don't really see a problem with using solids if it comes to that, but I'd think that if SpaceX were going to implement escape, they'd like to do it with as many off-the-shelf parts as they could.

I'm curious what you are going to do if hypergolics start leaking.  With D2 it's always in the open air so leaks can be mostly waited out.  (see the videos of how careful they are after splashdown).

But with your poposal you've got ~10-15t of hypergolics sitting in an enclosed space.   Yikes.

No.  With 350m/s of delta-v, it's 3.5t of prop.  ~25t wet mass.  But it really doesn't matter how much prop there is beyond a few tens of kg.  It's not an armored system, and any explosion is likely to be a bad day.  But that's true of Dragon as well.

Fair point on leaks from the escape system into the fairing.  But they have these newfangled things called vents.  And it's not like MMH/NTO inside a fairing is new tech.

Now, if you proposed that the entire 9m  x 15m diameter cargo+nosecone be one huge escape capsule you could just have a scaled up Dragon and other than the horrifying idea of 10-15t of hypergolics underneath you only have left to figure out how to have a parachute deceleration 50-70t of humans+stuff to < 10m/sec for a splashdown.

The whole nose is massive overkill.  Remember that you don't have to cause the entire crew system to escape.  This is just for launch and landing.  The crew would presumably move into a bigger on-orbit module after launch.  That offloads a lot of the consumables, ECLSS, and creature comforts outside of the escape system.  You still need enough stuff to keep the crew alive for 30-60 minutes post-launch, and for several hours bobbing around in the middle of the ocean, but neither of those is particularly difficult.

That said, I'd be very happy if you could replace the nose and part of the ogive with a blow-off system.  Three problems, two big and one small:

1) The header tanks are a serious problem, given that they need to be far forward for stability reasons.

2) The canards can't be attached to the escape system without a way of blowing them off.  I think that's worse than popping a fairing with the canards off, but I admit that both are non-trivial.  If the canards and headers could be moved back behind an escape nose, that would approach the no-brainer level in favor of escape.  But I don't think that's possible.

3) If the escape system is on the outside, it needs TPS for nominal EDL.  That's not the end of the world, but it makes it heavier.

I go back and forth on parachutes vs. propulsive landing.  My guess is that 350m/s is a bit light for both escape and landing. 450m/s would work fine, though.

I'm up to 25t with my arm-wave.  That's within the envelope of things that can land with a parachute, but low altitude escapes complicate matters.

Remember that the reason that SpaceX abandoned D2 propulsive landings was because NASA got squirrelly with the landing feet deploying through the heat shield.  But there's no heat shield necessary here.

[Twark_Main]

6G requires 20 SDs, which is getting up there, but still viable from an engine vs. real estate perspective.  (60% of the skirt would be nozzles.)

I've always assumed any whole-Starship LAS would be mounted on the interstage, offloading the mass penalty onto Stage 1 and benefiting from a 5:1 mass-to-orbit penalty instead of 1:1.

[TheRadicalModerate]

6G requires 20 SDs, which is getting up there, but still viable from an engine vs. real estate perspective.  (60% of the skirt would be nozzles.)

I've always assumed any whole-Starship LAS would be mounted on the interstage, offloading the mass penalty onto Stage 1 and benefiting from a 5:1 mass-to-orbit penalty instead of 1:1.

Problems:

1) You need at least 300m/s of escape delta-v (about what D2 has, per the FAA abort test environmental assessment from way back when).  When I fiddled with this using an SRB with the same Isp and ε as an SLS SRB, it needed to have a step mass of 63.7t.
 
2) You have to carry the whole Starship away, fully fueled, at T/W = ~5-7.  Even if the crew module is only 20t and the Starship is under-filled to the absolute minimum to make LEO, you're looking at 120t + 15t + 300t = 435t.  To get T/W = 5 on escape, that's 21.3MN of thrust.  Note that, if you're trying to avoid even worse hot-staging problems than using the Raptors, there will also be cosine losses that'll crank up both the prop mass and thrust even more.

3) This doesn't help you abort a bad landing.  It's only a replacement for hot-staging.  That's... nice, given that you've improved your time to separation and you can set the thrust to be sorta-kinda arbitrarily high, but it's not a full system.

4) With the canards on the front of the nose, the whole thing is unstable.

You could put a solid escape stage between the nose and the Starship propulsion module.  Then you only have problems #3 and #4.

[TheRadicalModerate]

2) The canards can't be attached to the escape system without a way of blowing them off.  I think that's worse than popping a fairing with the canards off, but I admit that both are non-trivial.  If the canards and headers could be moved back behind an escape nose, that would approach the no-brainer level in favor of escape.  But I don't think that's possible.

I wonder if you can move the canards back if you ballast the ogive just behind a blow-off escape module, then move the headers... somewhere else.  They can't go behind the blow-off, because that's how the crew would access the non-escape portions of the crew module, but they could go back to the intertank, where the LCH4 header used to be.

This is horribly mass-inefficient, but if all you're doing is ferrying a crew of 10-20 to LEO, it's probably not so mass-inefficient that it doesn't close.

This is a big mod.  But it might be more feasible than a jack-in-the-box escape from a (very quickly) jettisoned fairing.

[Lee Jay]

Think about what "no black zones on ascent" would mean for a rocket design.  How would you implement that?  I can't think of a way that doesn't involve passive use of stored energy to affect a safe landing.  "Passive" doesn't mean no flight controls, it means no propulsion.  The bonus is, it makes landing intrinsically safe since it also doesn't require propulsion, fuel, fuel presuruzation and so on.

The catch, and I believe the reason this vehicle is designed without it, is it won't work without an atmosphere.  This is why an Earth point-to-point ship and a human launcher to to space has to be a fundamentally different vehicle than an interplanetary lander.

[Twark_Main]

6G requires 20 SDs, which is getting up there, but still viable from an engine vs. real estate perspective.  (60% of the skirt would be nozzles.)

I've always assumed any whole-Starship LAS would be mounted on the interstage, offloading the mass penalty onto Stage 1 and benefiting from a 5:1 mass-to-orbit penalty instead of 1:1.

Problems:

1) You need at least 300m/s of escape delta-v (about what D2 has, per the FAA abort test environmental assessment from way back when).  When I fiddled with this using an SRB with the same Isp and ε as an SLS SRB, it needed to have a step mass of 63.7t.

Who said SRB?

I just said attach it to the S1 interstage, not the S2 skirt.
 

2) You have to carry the whole Starship away, fully fueled, at T/W = ~5-7.  Even if the crew module is only 20t and the Starship is under-filled to the absolute minimum to make LEO, you're looking at 120t + 15t + 300t = 435t.  To get T/W = 5 on escape, that's 21.3MN of thrust.  Note that, if you're trying to avoid even worse hot-staging problems than using the Raptors, there will also be cosine losses that'll crank up both the prop mass and thrust even more.

I don't see how attaching to the skirt vs. interstage affects the cosine losses.

3) This doesn't help you abort a bad landing.

No, you're right. Putting a bomb on the bottom of your Starship (solid or liquid) does not help in a bad landing. 

  It's only a replacement for hot-staging.  That's... nice, given that you've improved your time to separation and you can set the thrust to be sorta-kinda arbitrarily high, but it's not a full system.

As I said, "LAS" (Launch Abort System). If you want a system that combines the LAS with other types of abort systems, you might take a different path. Or you might not.

I noticed you're (sneakily) attempting to shape the debate by defining some new terms. In your mind, what is the definition of a "full system" here? 

4) With the canards on the front of the nose, the whole thing is unstable.

This same problem applies to your SuperDracos (mounted to the "skirt"), of course. Mind the plank in thine own eye. 

[TheRadicalModerate]

Think about what "no black zones on ascent" would mean for a rocket design.  How would you implement that?  I can't think of a way that doesn't involve passive use of stored energy to affect a safe landing.  "Passive" doesn't mean no flight controls, it means no propulsion.  The bonus is, it makes landing intrinsically safe since it also doesn't require propulsion, fuel, fuel presuruzation and so on.

The catch, and I believe the reason this vehicle is designed without it, is it won't work without an atmosphere.  This is why an Earth point-to-point ship and a human launcher to to space has to be a fundamentally different vehicle than an interplanetary lander.

I don't think you'd have any black zones as long as you had either a parachuting or propulsive escape system:

1) Pad:  Escape, then land on either parachutes or propulsively.
2) Low launch:  Escape, then land on either parachutes or propulsive, likely in water.
3) Max q:  Escape, then land in the water.
4) Pre- or just post-SH separation.  Starship would be able to do separation and RTLS, then land either nominally, or if things go pear-shaped, via escape.
5) Downrange Starship failure:  perform EDL, then escape and land in water on chutes or propulsively.  (Farther downrange:  land in a field in Ireland after escaping).
6) Abort once-around:  If cross range works, land nominally.  Otherwise, escape at low altitude and land on chutes/propulsively.
7) Abort to orbit:  Await rescue, or perform nominal EDL.
8 ) All landing aborts:  Escape, then land on chutes or propulsvie.

I think that covers it.  Remaining black zones are really just something secondarily bad happening during Starship Entry/Descent.  Those are low-runners, and there's nothing to be done.  Escape is also possible, depending on how hot the escape has to be.

[Twark_Main]

Think about what "no black zones on ascent" would mean for a rocket design.  How would you implement that?  I can't think of a way that doesn't involve passive use of stored energy to affect a safe landing.  "Passive" doesn't mean no flight controls, it means no propulsion.  The bonus is, it makes landing intrinsically safe since it also doesn't require propulsion, fuel, fuel presuruzation and so on.

The catch, and I believe the reason this vehicle is designed without it, is it won't work without an atmosphere.  This is why an Earth point-to-point ship and a human launcher to to space has to be a fundamentally different vehicle than an interplanetary lander.

I don't think you'd have any black zones as long as you had either a parachuting or propulsive escape system:

1) Pad:  Escape, then land on either parachutes or propulsively.
2) Low launch:  Escape, then land on either parachutes or propulsive, likely in water.
3) Max q:  Escape, then land in the water.
4) Pre- or just post-SH separation.  Starship would be able to do separation and RTLS, then land either nominally, or if things go pear-shaped, via escape.
5) Downrange Starship failure:  perform EDL, then escape and land in water on chutes or propulsively.  (Farther downrange:  land in a field in Ireland after escaping).
6) Abort once-around:  If cross range works, land nominally.  Otherwise, escape at low altitude and land on chutes/propulsively.
7) Abort to orbit:  Await rescue, or perform nominal EDL.
8 ) All landing aborts:  Escape, then land on chutes or propulsvie.

I think that covers it.  Remaining black zones are really just something secondarily bad happening during Starship Entry/Descent.  Those are low-runners, and there's nothing to be done.  Escape is also possible, depending on how hot the escape has to be.

Seems this is what you mean by "full system" abort. Thanks.

So basically a capsule, instead of using escape thrusters on the skirt/interstage.

[Lee Jay]

Think about what "no black zones on ascent" would mean for a rocket design.  How would you implement that?  I can't think of a way that doesn't involve passive use of stored energy to affect a safe landing.  "Passive" doesn't mean no flight controls, it means no propulsion.  The bonus is, it makes landing intrinsically safe since it also doesn't require propulsion, fuel, fuel presuruzation and so on.

The catch, and I believe the reason this vehicle is designed without it, is it won't work without an atmosphere.  This is why an Earth point-to-point ship and a human launcher to to space has to be a fundamentally different vehicle than an interplanetary lander.

I don't think you'd have any black zones as long as you had either a parachuting or propulsive escape system:

1) Pad:  Escape, then land on either parachutes or propulsively.
2) Low launch:  Escape, then land on either parachutes or propulsive, likely in water.
3) Max q:  Escape, then land in the water.
4) Pre- or just post-SH separation.  Starship would be able to do separation and RTLS, then land either nominally, or if things go pear-shaped, via escape.
5) Downrange Starship failure:  perform EDL, then escape and land in water on chutes or propulsively.  (Farther downrange:  land in a field in Ireland after escaping).
6) Abort once-around:  If cross range works, land nominally.  Otherwise, escape at low altitude and land on chutes/propulsively.
7) Abort to orbit:  Await rescue, or perform nominal EDL.
8 ) All landing aborts:  Escape, then land on chutes or propulsvie.

I think that covers it.  Remaining black zones are really just something secondarily bad happening during Starship Entry/Descent.  Those are low-runners, and there's nothing to be done.  Escape is also possible, depending on how hot the escape has to be.

Propulsive landing always has black zones.  Think about losing propulsion 20 meters off the ground.