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.
"You knew the job was dangerous when you took it, Fred!" - Super Chicken, 1967
Quote from: RonM on 10/06/2017 08:12 pmEarly 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.
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 from: DJPledger on 10/06/2017 08:26 pmQuote from: RonM on 10/06/2017 08:12 pmEarly 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.
Quote from: cppetrie on 10/06/2017 07:43 pmQuote from: Lee Jay on 10/06/2017 07:32 pmAn 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.
Quote from: Lee Jay on 10/06/2017 07:32 pmAn 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.
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.
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.
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?
* 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.
Quote from: KelvinZero on 10/06/2017 11:11 pm* 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.
Quote from: HMXHMX on 10/07/2017 05:32 am........BFS of course, even at maximum emergency thrust, neglecting other issues, does not have any significant thrust left over to escape a fireball.
....
Quote from: speedevil on 10/07/2017 12:38 pmQuote from: HMXHMX on 10/07/2017 05:32 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?
Quote from: Zed_Noir on 10/07/2017 09:50 pmQuote from: speedevil on 10/07/2017 12:38 pmQuote from: HMXHMX on 10/07/2017 05:32 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.
helium COPV's...I believe the BFB will not use these?
Quote from: octavo on 10/08/2017 02:01 pmhelium COPV's...I believe the BFB will not use these?Correct.
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?
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?
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.
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?