Author Topic: IAC 2017-BFR v0.2 How to have an Escape System for BFS  (Read 6937 times)

Offline RocketmanUS

From  IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech) thread
Is anyone else spooked by all this talk of "no need for an escape system, we'll be safe like an airline?" The parallels with the shuttle program seem almost too obvious.

If an escape system were to be added to the 2017 version of BFS how might it be?

Needs to work for lift off and landing for Earth, Lunar , and Mars.

Could be for smaller crew size less than the 100 expected crew size as crew size for many years will most likely be much small to a colony is built.

So what kind off ideas might work for an escape system for BFS.

Edit:
Thread for design of an escape system.  Not a debate thread to have one or not, there has been plenty of discussion on that part already.
« Last Edit: 10/06/2017 07:57 PM by RocketmanUS »
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Offline RonM

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #1 on: 10/06/2017 08:12 PM »
Early crewed flights won't have 100 people. They'll have much smaller crews for either Luna on Mars exploration and base construction. No need for an escape system because crews can be transferred in LEO via a Dragon or two and there's nowhere to go if there's a problem on Luna or Mars.

Quote
"You knew the job was dangerous when you took it, Fred!" - Super Chicken, 1967

By the time we get to colonization flights, the system will have a long flight history. Especially the booster, so there will be good reliability data. Design changes can be made if needed.

If the decision is made to add an escape option, the crew compartment can be its own stage with abort motors. It would reduce cargo capacity, but could be used for launch on any planet. By then there will be the possibility of rescue from a lunar or Mars base.

Offline rakaydos

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #2 on: 10/06/2017 08:49 PM »
Early crewed flights won't have 100 people. They'll have much smaller crews for either Luna on Mars exploration and base construction. No need for an escape system because crews can be transferred in LEO via a Dragon or two and there's nowhere to go if there's a problem on Luna or Mars.
What if the BFR booster explodes on the pad or shortly after liftoff? I am afraid it will be LOC without a LAS so a LAS is a must if SpX are even contemplating putting crew on this thing.
In another thread, someone suggested an "emergency abort" mode for the BFS if there is a problem with the BFR.

Basically, it's dangerous to run the vac engines in atmosphere... but less dangerous than being next to an exploding booster. Burn vac engines at 120% (potentially damaging the engines, but bringing the pressure closer to the expansion ratio) to burn off fuel as quickly as possible, to try and get the ship's TWR above 1 for landing.

Offline DJPledger

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #3 on: 10/06/2017 08:51 PM »
Early crewed flights won't have 100 people. They'll have much smaller crews for either Luna on Mars exploration and base construction. No need for an escape system because crews can be transferred in LEO via a Dragon or two and there's nowhere to go if there's a problem on Luna or Mars.
What if the BFR booster explodes on the pad or shortly after liftoff? I am afraid it will be LOC without a LAS so a LAS is a must if SpX are even contemplating putting crew on this thing.

I see you missed the part about using Dragon to transfer crew in LEO. In this small crew scenario, the BFR launches from Earth without the crew.
EM said in Adelaide that SpX will phase out all their existing and upcoming systems in favour of BFR so crew will have to go up on it if there is nothing else to launch them. This is why it needs a LAS.

A LAS for BFR ship could consist of the ship's Raptors which could have an emergency thrust of around 2x normal rating for a few seconds to give sufficient thrust to clear the failing booster. The Raptor vacs could detach their nozzle extensions on launch escape command so they can operate in atm. Need to be able to spool up Raptors' TP's fast enough to give required thrust ASAP.

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #4 on: 10/06/2017 09:33 PM »
This thread was for discussing the DESIGN of a LAS, not whether or not it is needed. Read the first post please! Especially everyone who posted below the first post. I should have hit the 'report to mod' button on every single one of them. Even before RocketmanUS emphasised it on his edit. Writing a post is easier in this case.

I am very much interested in a design. It might turn out there is none that would work. I would very much like to know if that is true or not.
« Last Edit: 10/06/2017 09:34 PM by Semmel »

Online RotoSequence

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #5 on: 10/06/2017 10:07 PM »
If a launch escape system is going to compromise the pressure vessels of the ship, how much of the pressure vessel compromising can be done with shaped charges against an otherwise unmodified carbon fiber structure?

Offline cppetrie

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #6 on: 10/06/2017 10:25 PM »
An airliner is safe not because it doesn't fail, but because it has such a wide variety of intact abort modes.  Not having an abort system on a crewed vessel is a show-stopper.
It has redundancy and large safety margins but not an escape system. There’s no parachutes onboard for all passengers. Any passengers actually.

I didn't say anything about an escape system.
Thread title says escape system. If we’re simply talking about a means of landing the BFS safely should the booster suffer multiple engine failures on launch that would prevent reaching orbit, then the system is already capable of that. You simply separate the BFS just like a staging event and go land the ship as if it were re-entry. If an engine on landing goes out you use the other one. It has two for that reason. A RUD on launch is the equivalent of a wing full of fuel on the plane blowing up. The plane isn’t surviving that failure mode.

Offline KelvinZero

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #7 on: 10/06/2017 11:11 PM »
Thread for design of an escape system.  Not a debate thread to have one or not, there has been plenty of discussion on that part already.

Bolding mine :-)

Ideas:
* Some extra safety can be built into the launch tower. The AMOS-6 incident suggests that a robust launch tower could survive even a quite large unscheduled disassembly of the vehicle, and perhaps crew in such an event could have survived so long as the launch tower kept a hold on it.

* Perhaps we could design some extremely rapid way of dumping propellant, to give the US the thrust to weight ratio to pull away quickly. I guess it is more effective to dump all the oxygen first since it has the most weight and density. Also dumping one component without the other is probably safer. You keep the landing tanks intact of course.

* Then we get into full on escape system. Lots of people are saying we won't need it. I don't think it is as simple as saying the 747 does not have a LAS, because there are many options to survive in a 747. I think it is perfectly valid to pose the question: What if the BFR is now a standard tool of safe, with good safety for space, but has still not proven itself safe enough for whatever standards of airplane flight are accepted by then? They may be stricter than even today. At that point isn't it quite reasonable that an entirely new massive engineering project could be engaged in to extend the BFS to be able to grab the airline market? In other words just go with it.

Offline Aussie_Space_Nut

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #8 on: 10/07/2017 12:20 AM »
I agree with earlier posts that SpaceX are in the process of creating a Spaceship system with airliner reliability.

Given that autonomy is now so well done, do we even need humans on board during the developement cycle?

So in other words, prove out the "airliner reliability" without humans on board. Once proven then add humans. No escape system required.

That said if for some reason you want to have an escape system during the developement cycle I imagine something like an F111 cockpit ejection system where the whole cockpit seperated from the aircraft. Obviously we are not talking about a system for 100 people.

If you want to go for the full passenger escape system then you need to build the system in 3 parts.
1) BFR 1st stage.
2a) BFS Lower Rocket & Cargo section.
2b) BFS Upper Hab section.
I'm not talking about a true 3rd stage here but a BFS that in an emergency can separate into the 2 halves. You would have to design it such that it would be stable to "fly" using its existing heatshield. Superdracos to land anywhere. But if you did all of this it would weigh quite a lot.

Offline Nathan2go

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #9 on: 10/07/2017 12:33 AM »
I think there might be an escape system of sort already in BFS:

Unlike a normal upper stage, there are propellant fill/drain lines at the back of the Ship; Musk said they were the same lines normally used to fill the tanks and stated they would be used for on-orbit refilling.

I imagine there still must be a side-mounted umbilical connection for use on Mars.  So I wonder if there isn't another reason for the connection location?

I've thought it would be cool to launch with the ship only 15% filled, and transfer the rest of the propellant from the first stage during the flight.  That way, the ship has enough thrust (2+ gees) to escape from a failed booster on launch.  The vacuum engines might need to have jettisonable bell extensions though for sea level operation.

If propellant is transferred in flight, it would probably be pumped, since the pressure would get high pretty quickly (the hydro-static pressure increases as the depletion increases the head, and the acceleration rises).

Of course this does not work on Mars (unless a small booster is added), but the BFR has 5x more engines than the ship, so presumably the risk of serious failure is greater.

[this is duplicated from another thread http://forum.nasaspaceflight.com/index.php?topic=43851.msg1730875#msg1730875]
« Last Edit: 10/07/2017 12:35 AM by Nathan2go »

Offline Rocket Science

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #10 on: 10/07/2017 12:45 AM »
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Offline RocketmanUS

When the BFS does launch with crew I expect it would be with a crew size no more than 12 people. The rest of the payload mass would be cargo. It would be years before the crew size would need to be larger.

So an escape system that can handle 12 people and not use up to much of the payload mass.

If a launch escape system is going to compromise the pressure vessels of the ship, how much of the pressure vessel compromising can be done with shaped charges against an otherwise unmodified carbon fiber structure?
Excellent point. So that could take out the idea of the top nose section being used as an escape capsule. However what about the top section were the big windows are shown? It is already cut out for windows. So if part of that area was used and could separate from the rest of the ship. Dragon 2 has how much mass in propellant? That carries 7 crew and this idea carries 12, so that might almost double the needed  escape propellant mass. BFS would still have the same outer mold line.

Parachutes would not work on the moon, so no need for then. The escape system would be all propulsive.

For Mars or Lunar I assume there would have already been pressurized rovers and habs preplaced on the surface. So if an escape system had to be used on Mars or Lunar then a rover could pick the crew up. I expect the escape system to have life support for a minimum of 24 hours for crew rescue. I also from the t/Space Lunar concept that there would be two BFS flying together for added safety.
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Offline Robotbeat

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #12 on: 10/07/2017 01:06 AM »
Once you get to a certain reliability level, adding a LAS actually makes you significantly less safe. (And an LAS only adds about a factor of 10 improvement for expendable rockets to begin with...)

For instance, the LAS on Orion would kill the astronauts if it fails to jettison.

So if you're going to bother with a LAS, you had better make it safe to begin with. Or just make sure the rocket has flown a few hundred times...
« Last Edit: 10/07/2017 01:11 AM by Robotbeat »
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Offline Lar

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #13 on: 10/07/2017 01:07 AM »
All posts[1] that were just debating whether an escape system is needed or not were removed. if the post has something about escape systems but also debate, I left it.. .please edit the debate out.

These posts are now merged into the existing "should?" thread,

https://forum.nasaspaceflight.com/index.php?topic=43438

1 - including some of mine...
« Last Edit: 10/07/2017 03:09 AM by Lar »
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Offline KelvinZero

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #14 on: 10/07/2017 01:27 AM »
Expanding on earlier: Maybe you could solve this with an additional LAS rocket engine design, where the goal is pretty much to create the shittiest rocket ever. It's whole goal is to gush out fuel at an absurd rate.

Probably somewhere between a real rocket and this: https://en.wikipedia.org/wiki/Water_rocket

Although this gives you a ridiculously bad ISP, it could give you a very high thrust for a short period out of a lightweight engine with no bell that is little more than a big valve, so it solves three problems in one:

* Immediate thrust capable of lifting the upper stage.
* Reducing mass quickly so that your real rockets can pull you away, and fight gravity, and land you.
* Getting all that fuel away from the passengers.

Additionally, it would be useful if these LAS rockets dumped oxygen first and methane second: faster reduction in weight, less explosive mix.

Delivering all this fuel to these LAS rockets might possibly make the BFS plumbing more similar to the booster plumbing, which can feed 30-ish engines.

We don't need to worry about this right now though. There will probably be more than one iterations of the BFS between the first cargo BFS and any point to point passenger version.
« Last Edit: 10/07/2017 04:29 AM by KelvinZero »

Offline rakaydos

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #15 on: 10/07/2017 04:01 AM »
* Perhaps we could design some extremely rapid way of dumping propellant, to give the US the thrust to weight ratio to pull away quickly. I guess it is more effective to dump all the oxygen first since it has the most weight and density. Also dumping one component without the other is probably safer. You keep the landing tanks intact of course.
An interesting thought- Aborting with the fuel transfer valves open, so you're dumping fuel and oxidiser on the fireball as you're trying to flee from it, to make the spaceship light enough to maybe land safely. Combined with burning the vacraptors at 140% to get the vac bells to be not-as-badly overexpanded (and dump even more fuel- it's a thousand ton tank, it takes a LOT of work to drain quickly) you might be able to get a safe abort speed.

Offline HMXHMX

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #16 on: 10/07/2017 05:32 AM »
* Perhaps we could design some extremely rapid way of dumping propellant, to give the US the thrust to weight ratio to pull away quickly. I guess it is more effective to dump all the oxygen first since it has the most weight and density. Also dumping one component without the other is probably safer. You keep the landing tanks intact of course.
An interesting thought- Aborting with the fuel transfer valves open, so you're dumping fuel and oxidiser on the fireball as you're trying to flee from it, to make the spaceship light enough to maybe land safely. Combined with burning the vacraptors at 140% to get the vac bells to be not-as-badly overexpanded (and dump even more fuel- it's a thousand ton tank, it takes a LOT of work to drain quickly) you might be able to get a safe abort speed.

The fastest way to dump propellant is though a functioning rocket engine – safer, too.  ;)

Offline KelvinZero

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #17 on: 10/07/2017 07:08 AM »
The fastest way to dump propellant is though a functioning rocket engine – safer, too.  ;)
This seems to me to be one really basic not too controversial thing you can do for a later passenger version. Use some of your 150 ton payload on a few more sea-level raptors so that at least your upper stage can pull away from your booster, even on the launch pad.

Also now you have plenty of options for landing rockets, even if the center cluster is taken out, so long as two symmetrically placed rockets still function. also now you have a good suborbital rocket that might be able to make useful hops.

I don't know if there is any use to adding my "shittiest rocket" idea to this. You might be able to get higher thrust for lower weight at the expense of truely awful ISP. It would come down to numbers and maybe there is not enough point in the end.

(edit) Thinking about it some more, once you have added enough thrust to get away from danger, the need to dump fuel goes away. I think the case for a peculiar engine variant possibly with peculiar plumbing becomes much more dubious. Just add some additional sea level engines.

Question:
About how much is a sea level raptor meant to mass? and how much when you count the mass of additional plumbing?
« Last Edit: 10/07/2017 10:40 AM by KelvinZero »

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #18 on: 10/07/2017 11:30 AM »
There are several problems with more raptor engines or any abort using the main propulsion system.

* they need to spin up which takes several seconds. In an abort, the BFR propulsion is shut down if it still exists and then BFS gets away against the airstream. This takes a long time no matter how many raptors are firing. I can't think of any scenarios where the BFS propulsion makes a reasonable difference in case of a BFE RUD except for the most gentle one. In which case additional raptors are not needed. The software should just be capable of landing at any time of the earth ascend path, no matter how much fuel is in the main tanks.
* any abort strategy involving the main propulsion of BFS would be useless on the moon or Mars since that's what you are trying to get away from. For Mars and moon ascend, the software should just be capable to abort to surface assuming raptor vac engine out but no major problem.

I think if you want a meaningful LAS from an energetic event, it must be something else.

Offline KelvinZero

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #19 on: 10/07/2017 12:09 PM »
Ok, good point, I have not thought about how fast a conventional sea level raptor can start. I don't know how long that takes.

That could become a reason to require a different type of engine.

As I understand it there is a reason to need additional thrust. I think the upper stage does not have the thrust to lift it's own weight when it's tanks are full. This is absolutely fatal if the accident happens before or seconds after lift-off.

After those first few seconds, the extra thrust may or may not make the difference.
« Last Edit: 10/07/2017 12:35 PM by KelvinZero »

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #20 on: 10/07/2017 12:38 PM »
The fastest way to dump propellant is though a functioning rocket engine – safer, too.  ;)
BFS has ~1000 tons of propellant it can burn in ~5 minutes, or around 3 tons a second.

Four 25cm dump valves will dump the same amount.
(50PSIg tank, liquid oxygen density).

If the ready tanks in the BFS are in fact all you need for landing, and it is a bad enough day, and the internal pressurisation is enough to cope, dumping all of the oxygen makes you 860 tons lighter.

This is enough - with a light cargo - to be within the specs for SL raptors alone to land.
(clearly, dumping all of the oxygen through dump valves is problematic, the tank bottom is after all curved).

If you can rapidly dump methane, then rapidly dump oxygen, you can in principle get the craft light enough to land in ~30s, which would reduce the 'black zone' quite a lot.

The dump valves needed in both tanks are large, of the order of sixteen 50cm, sized to dump the tank in ten seconds.

(10s dump most oxidiser, close valves, 10s, dump most methane, close valves).

Dumping ~70 tons a second is going to cause control issues, that may be too great for the SL raptors to cope with - I haven't worked it out.

The size and number of the valves, together with their obviously critical status means that if you can possibly just run the engines, that's clearly the better way.

Some mechanism, either explicit, or implicit (the nozzles have a tear line) for running the vac raptors at sea level seems vastly preferable.

BFS of course, even at maximum emergency thrust, neglecting other issues, does not have any significant thrust left over to escape a fireball.

Offline rakaydos

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #21 on: 10/07/2017 02:49 PM »
I wonder if the booster could be designed to assist? Isolated RCS tanks that could push the rapidly fireballing booster away from the spinning-up Ship?

Offline Zed_Noir

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #22 on: 10/07/2017 09:50 PM »
....
....
BFS of course, even at maximum emergency thrust, neglecting other issues, does not have any significant thrust left over to escape a fireball.

The BFS might not be able to outrun a fireball. But if separate from the booster and all engines firing at the max. Could the BFS ride out the shock wave with the retro burn shielding the BFS?

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #23 on: 10/08/2017 11:58 AM »
....
....
BFS of course, even at maximum emergency thrust, neglecting other issues, does not have any significant thrust left over to escape a fireball.

The BFS might not be able to outrun a fireball. But if separate from the booster and all engines firing at the max. Could the BFS ride out the shock wave with the retro burn shielding the BFS?

Sure.
Not being able to outrun a fireball doesn't mean your vehicle is dead.

You'd need careful calculation to work out the risks of various sorts of damage and consequences.

Thermal damage - does the fireball directly or indirectly (radiant heat) overheat and damage anything.
Propellant damage - does fuel, oxidiser, or a combination of the two, splashed or gaseous on your craft do bad things, from prompt explosions to fire later.
Fragmentation - what's directly damaged by fragments.
Control - do you have enough control authority to remain pointed in a safe direction.
Landing - are your sensors and available landing pads in good shape to get safely down.
Amongst others.

Offline octavo

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #24 on: 10/08/2017 02:01 PM »
....
....
BFS of course, even at maximum emergency thrust, neglecting other issues, does not have any significant thrust left over to escape a fireball.

The BFS might not be able to outrun a fireball. But if separate from the booster and all engines firing at the max. Could the BFS ride out the shock wave with the retro burn shielding the BFS?

Sure.
Not being able to outrun a fireball doesn't mean your vehicle is dead.

You'd need careful calculation to work out the risks of various sorts of damage and consequences.

Thermal damage - does the fireball directly or indirectly (radiant heat) overheat and damage anything.
Propellant damage - does fuel, oxidiser, or a combination of the two, splashed or gaseous on your craft do bad things, from prompt explosions to fire later.
Fragmentation - what's directly damaged by fragments.
Control - do you have enough control authority to remain pointed in a safe direction.
Landing - are your sensors and available landing pads in good shape to get safely down.
Amongst others.

Thinking back to footage of Amos-6, helium COPV's look like likely fragmentation damage candidates. I believe the BFB will not use these?
« Last Edit: 10/08/2017 02:01 PM by octavo »

Offline Zed_Noir

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #25 on: 10/09/2017 04:40 AM »
....
....
BFS of course, even at maximum emergency thrust, neglecting other issues, does not have any significant thrust left over to escape a fireball.

The BFS might not be able to outrun a fireball. But if separate from the booster and all engines firing at the max. Could the BFS ride out the shock wave with the retro burn shielding the BFS?

Sure.
Not being able to outrun a fireball doesn't mean your vehicle is dead.

You'd need careful calculation to work out the risks of various sorts of damage and consequences.

Thermal damage - does the fireball directly or indirectly (radiant heat) overheat and damage anything.
Propellant damage - does fuel, oxidiser, or a combination of the two, splashed or gaseous on your craft do bad things, from prompt explosions to fire later.
Fragmentation - what's directly damaged by fragments.
Control - do you have enough control authority to remain pointed in a safe direction.
Landing - are your sensors and available landing pads in good shape to get safely down.
Amongst others.

Much better than zero chance.

But that brings up the OT issue of the chances that a damaged BFS's crew be able to survive a hover slam crash. Someone else can continued this OT issue on another thread.  :-X

Online TomH

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #26 on: 10/09/2017 04:45 AM »
helium COPV's...I believe the BFB will not use these?

Correct.

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #27 on: 10/09/2017 04:46 PM »
helium COPV's...I believe the BFB will not use these?

Correct.

BFS will still have COPVs, they just will be holding gaseous O2 and CH4 instead of cryohelium. And they won't be in a LOX tank.

Those COPVs will be feeding pressure-fed gaseous methalox RCS thrusters. And they could be one way to implement a LAS: sepearte the crew cabin from the prop tanks and cargo, and use (lots of) those thrusters to rocket away. Then land on chutes.

It would need about 50 ten-tonne-force thusters to mimic Dragon's abort.
« Last Edit: 10/09/2017 04:50 PM by envy887 »

Offline Robotbeat

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #28 on: 10/09/2017 05:09 PM »
Those will only be COPVs in the strict sense. Pressure will be far lower than current tanks and design/structure will be very different.
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Offline RocketmanUS

NSF member Lobo said it would be OK for me to share his escape system concept.

He came up with using Chomper , what Elon called the unpressurized version of BFS at 30:34 on the IAC 2017 presentation from the SpaceX Youtube channel.

Remove the clam shell cargo bay door and install a module, BFS would still have the same OML ( outer mold line ). In an abort situation the lifeboat would fire forward and away from the rest of the ship. This concept uses a modified Chomper to bring crew to LEO.

From Lobo's concept I came up with what I draw in the first attached image. Using the Chomper version of BFS adding two modules, the lower and the upper module. The lower module has life support, storage, crew cabins, cargo egress hatch, crew egress hatch, storm shelter. The upper module is the escape pod. The crew egresses between both through a hatch in the upper section of the lower module and a hatch in the lower section of the upper module. Crew is in the upper module during lift off , landing, and main engine firing for course correction(s) ( as needed ). If an abort is needed the module ejects from the BFS ( Chomper ) to safety. That is it could land on water or land by propulsive means. If an abort is needed in space or an abort to orbit happens then a rescue vehicle is sent. I assume there would be at lest two crew vehicle flying together to Mars or moon for safety reasons ( from the t/Space Lunar concept ).

With this concept the whole module could be lowered to Mars surface for unloading. That is once a crane could be constructed on Mars.

Second attached image shows an escape pod in the upper section of a BFS. But this might require to much of a design change to the pressurized version of BFS.

Edit:
First image showing modules before being installed.
« Last Edit: 10/10/2017 03:43 AM by RocketmanUS »
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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #30 on: 10/10/2017 06:39 AM »
An interesting concept. The first here that would actually get the passengers out of harms way of a fireball. But getting away is the easy part. I am afraid. Does it has a heat shield to abort in high velocity situations on earth assent or is it just good for abort from BFR? Even harder, how does it land on earth, Mars or the moon?

@edit: What is exactly the mission envelope the LAS should work? Only for the BFR phase of the flight on Earth and only for BFS ascent on the Moon and Mars? How about the vertical lending part when under power? What are the expected failure modes this LAS should be able to handle? Engine out or fuel tank rupture? It seems we need to answer this question first before starting on a design. I know its boring, but thats how engineering works (successful engineering I might add). First be absolutely clear what exactly you want before starting to find solutions.

For the record: I expect that a useful LAS is impossible for BFR/BFS that works on Earth, Moon and Mars, but lets at least try to design one since my working hypothesis is impossible to prove. If against all odds we figure out how to do a LAS that works for the three bodies, we need to figure out how much mass it requires and then the question will be: is it worth it for flights to the Moon or Mars? How does it impact the maximal number of passengers?
« Last Edit: 10/10/2017 07:23 AM by Semmel »

Offline Patchouli

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #31 on: 10/10/2017 07:15 AM »
Since it mostly likely would fly with 25 or so people on board during early missions they could use a couple of Dragon capsules as an escape pod similar to how Rockwell proposed using an Apollo capsule as an escape pod on the shuttle.

The real question can a Dragon V2 handle being fired out sideways from the ship's cargo bay?

« Last Edit: 10/10/2017 07:27 AM by Patchouli »

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #32 on: 10/10/2017 07:27 AM »
Yeah, I also thought of Dragon. But only one dragon in the nose with maximum of 10 passengers and larger fuel tanks, so a slightly bigger version. This must have enough fuel to get away in an emergency and must be able to land with the remaining fuel. It must have enough ECLSS and food to wait for help as well.

Could work if you distribute the transport to Mars differently. Instead of one passenger and ~10 cargo flights, you would have just 10 passenger flights with lots of cargo. Might be less efficient but has the potential to gain a LAS on all parts of the flight envelope except in transit.

Offline KelvinZero

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #33 on: 10/10/2017 08:19 AM »
Since it mostly likely would fly with 25 or so people on board during early missions they could use a couple of Dragon capsules as an escape pod similar to how Rockwell proposed using an Apollo capsule as an escape pod on the shuttle.

The real question can a Dragon V2 handle being fired out sideways from the ship's cargo bay?
I started a thread pretty much on this here: http://forum.nasaspaceflight.com/index.php?topic=43862.0

Originally I was thinking of this as a quick initial Cargo+Dragon crew version. Turns out abort will probably be very very hard, especially if you (of course) want to be able to escape during ascent, descent, and from orbit.

I still like the idea but I think of it not so much as a quickfix, as a difficult but worthwhile problem for another variant.
* Cargo variant
* Crew variant (actually, passengers as cargo)
* A Shuttle on steroids variant. 6-ish crew, some workspace, lots of cargo.

This is a variant for actually doing work in. Also exploration missions where there is not backup and support at the other end, such as an asteroid mission. (Asteroids have the real risk of debris that could damage heatshields as well so there are multiple safety advantages. Additionally the Dragon could be an exploration module)

Offline RocketmanUS

An interesting concept. The first here that would actually get the passengers out of harms way of a fireball. But getting away is the easy part. I am afraid. Does it has a heat shield to abort in high velocity situations on earth assent or is it just good for abort from BFR? Even harder, how does it land on earth, Mars or the moon?

@edit: What is exactly the mission envelope the LAS should work? Only for the BFR phase of the flight on Earth and only for BFS ascent on the Moon and Mars? How about the vertical lending part when under power? What are the expected failure modes this LAS should be able to handle? Engine out or fuel tank rupture? It seems we need to answer this question first before starting on a design. I know its boring, but thats how engineering works (successful engineering I might add). First be absolutely clear what exactly you want before starting to find solutions.

For the record: I expect that a useful LAS is impossible for BFR/BFS that works on Earth, Moon and Mars, but lets at least try to design one since my working hypothesis is impossible to prove. If against all odds we figure out how to do a LAS that works for the three bodies, we need to figure out how much mass it requires and then the question will be: is it worth it for flights to the Moon or Mars? How does it impact the maximal number of passengers?
Abort for launch and land from earth , Mars and moon. Includes once separated from BFR, plus in transit between planets if needed.
Yes would have a heat shield good for one use. All propulsive landing.

I expect the number of passenger for the near future would not exceed 12 people. This abort system would reduce the amount of payload if crew and cargo are sent together. More of an impact for Lunar, but large mass cargo is better sent on a dedicated BFS to Lunar, no escape system for cargo only.
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Offline intrepidpursuit

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #35 on: 10/13/2017 11:14 PM »
I stated in the other thread that the point to point system is in much greater need of a LAS than the space systems, both statistically and perceptively.

Could the BFS just fly with nearly empty tanks so that it has a T/W >1? The booster is huge and people are relatively light. The consensus seems to be that firing the vacuum raptors in the atmosphere could damage them from flow separation but they would still provide thrust. From what I've seen the thrust to weight isn't actually that far off on the ship, so it could still carry landing fuel and some additional delta-v for the main mission even keeping weight down.

Does that seem possible?

Offline Robotbeat

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #36 on: 10/13/2017 11:27 PM »
I don't think so. If it's not as reliable as, say, a private jet which doesn't have a LAS, then it won't be viable from a cost point of view anyway.

And LAS add their own failure modes while also reducing the payload margin that can be used for increasing robustness of the vehicle.
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Offline intrepidpursuit

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #37 on: 10/13/2017 11:32 PM »
I don't think so. If it's not as reliable as, say, a private jet which doesn't have a LAS, then it won't be viable from a cost point of view anyway.

And LAS add their own failure modes while also reducing the payload margin that can be used for increasing robustness of the vehicle.

Are you replying to my post? I'm not suggesting they add a LAS that has it's own failure modes, just that they take precautions to make certain failure modes survivable. The precautions seem to be inherent in the design.

They are already building the vehicle they are building. If it doesn't need a full fuel load to get where it is going then adding more doesn't add any benefit.

Offline KelvinZero

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #38 on: 10/13/2017 11:43 PM »
I stated in the other thread that the point to point system is in much greater need of a LAS than the space systems, both statistically and perceptively.

Could the BFS just fly with nearly empty tanks so that it has a T/W >1? The booster is huge and people are relatively light. The consensus seems to be that firing the vacuum raptors in the atmosphere could damage them from flow separation but they would still provide thrust. From what I've seen the thrust to weight isn't actually that far off on the ship, so it could still carry landing fuel and some additional delta-v for the main mission even keeping weight down.

Does that seem possible?
(layman's speculation)
Hey that is a good point.. I have heard something about the BFS only being able to land 50 tons.. so that means the passenger version could also only take off with 50 tons.. so maybe it does have enough T/W to counter gravity after all? The ship mass+cargo excluding propellant is now about 80+50= 130t instead of 80+150 = 230t, so the propellant mass could go down by a similar fraction.. almost a factor of 2? .. and maybe you won't be lifting even 50t anyway.

Someone said that the raptor engines cannot be started fast enough to be used as an abort though. I thought perhaps you could have a special new engine whose whole point was to just gush out propellant quickly. High thrust but ridiculously bad ISP. Maybe this could get you away from the booster and give the other engines time to start if starting them late still serves any purpose..such as reaching the best landing site. It might be a very light engine because pretty much no bell and I guess no turbines or pre burner or other gadgets. Maybe just a hugely oxygen rich pressure fed engine to pump out as much mass as possible in the shortest possible time?

For a safer passenger version perhaps it would be worth spending a bit more mass creating more separation between the stages. The goal could be that if the lower stage blew apart, sort of gently like the AMOS-6 explosion, then there would still be a good chance that the BFS engines would be untouched.

Offline wmt587kc

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Re: IAC 2017-BFR v0.2 How to have an Escape System for BFS
« Reply #39 on: 10/14/2017 05:21 AM »
In order to successfully accommodate any escape system, the BFS V0.2 must undergo further design evolution.

The current BFS V0.2 design has the payload fully had integrated into the ship mold design whereby each BFS copy variant has a specific designed mission, role and function as a transporter, tanker or dispenser.

I merit advocate that Elon adopt and apply the "open architecture", "plug-n-play", "modular", and "hot swappable" design concepts from the IT Industry to the current BFS design in order to improve its safety, versatility, flexibility, utility and overall loss risk.   And, go to a totally independent modular payload concept that preserves all existing payload options, add others and has other benefits including the addition of an escape system to the manned transporter modules.

With this idea, you could independently separate the BFS hard design payload compartments from the propulsion elements and the rest of the ship at the top of the tankaage.  And, then insert a relatively small conventional type interstage-payload adapter that would be readily adaptable and could accept a wide variety of modular payloads  and payload interfaces including fuel transfers.

The exposed tankage elements could be protected by heat shielding within the interstage area as necessary for the thermal protection and aerodynamics.

So, instead of multiple BFS's each with its own specific design function and role, you would produce standardized BFS's with adaptable mold line modular payload interfaces.

Most payload modules would remain attached to the BFS to fulfill mission profiles.  However, in certain unmanned LEO/GEO pusher plate type delivery configurations the BFS and the Payload Modules could be separated and operated independently.

Such mold line payload modules in accordance with the original objectives would include but not be limited to:
    *  Conical/Ballistic shaped Manned Lunar/Mars Transport Module (with Escape System)
    *  Conical/Ballistic shaped Unmanned Tanker Module
    *  Conical/Ballistic shaped LEO/GEO Satellite Dispenser Module
    *  Flat Pusher Plate Module - For customized or oversized LEO/BEO Payloads
        *  Using conventional payload fairings (Recoverable or Expendable)
        *  Allows For Full Ballistic Mold Line (9 m) or Wide Ballistic Hammerhead (12 m) payload designs

Yes, some additional redesign and development costs which could be offset by additional flexibility and utility as well as increased safety and decreased LOV/LOM/LOC risks.

Additional structural weight could be offset by propulsive and performance gains in the Raptors.

Surely, replacement and stand down costs in hardware and time for the loss of just one specific BFS with or without crew would be enormously impactful to any future timeline or plans.

Would be interested if someone would dig into the feasibility of this concept further. 
 

Tags: BFR BFS escape system