Author Topic: IAC 2017-BFR v0.2 How to have an Escape System for BFS  (Read 4319 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.

Offline Semmel

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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 »

Offline 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?

Online 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.

Online 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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Online 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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Online 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.  ;)

Online 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 »

Offline Semmel

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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.

Online 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 »

Tags: BFR BFS escape system