Author Topic: IAC 2017-BFR v0.2 How to have an Escape System for BFS  (Read 4306 times)

Offline speedevil

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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?

Offline speedevil

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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

Offline 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.

Online envy887

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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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Offline Semmel

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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 »

Offline Semmel

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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