Author Topic: Should the BFR have a launch escape system?  (Read 16176 times)

Offline matthewkantar

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Re: Should the ITS have a launch escape system?
« Reply #20 on: 09/21/2017 03:02 AM »
Maybe SpaceX could give the passengers a choice, letting those individuals pick from a menu. Earth surface to Mars on a single vehicle with no LES would cost $500,000. If you want go up on a falcon and transfer to ITS, the additional cost might be $3,000,000, or one seventh of a twenty or so million dollar F-9 launch.

I know what I would choose.

Matthew

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Re: Should the ITS have a launch escape system?
« Reply #21 on: 09/21/2017 03:31 AM »
If the big(gest) ITS could eventually show a loss-of-mission safety ratio about one-third that of a busy, commercial airliner - that would be more than good enough for me. But we would be waiting some years for that to happen...
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Offline GORDAP

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Re: Should the ITS have a launch escape system?
« Reply #22 on: 09/21/2017 12:04 PM »
I've always wondered just what is wrong with the BFS being its own LES. 

I know that it doesn't have high T/W ratio, and that the turbopumps take a few seconds to spin up, but it's not like you're going to outrun a true detonation event in the booster anyway, no matter how quickly a human 'pod' can skedaddle out of there.  It seems that it should only be required to outrun a conflagration of the booster, right?

Can anyone point to a realistic booster failure scenario in which a traditional LES would save the passengers, but in which the planned BFS LES would not?

Offline envy887

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Re: Should the ITS have a launch escape system?
« Reply #23 on: 09/21/2017 01:51 PM »
I've always wondered just what is wrong with the BFS being its own LES. 

I know that it doesn't have high T/W ratio, and that the turbopumps take a few seconds to spin up, but it's not like you're going to outrun a true detonation event in the booster anyway, no matter how quickly a human 'pod' can skedaddle out of there.  It seems that it should only be required to outrun a conflagration of the booster, right?

Can anyone point to a realistic booster failure scenario in which a traditional LES would save the passengers, but in which the planned BFS LES would not?

Any launch where the vehicle fails to control its angle of attack in the atmosphere (like Ariane 501 or the Challenger breakup) would be much easier to survive in a capsule than an integrated stage/capsule. I'm not sure the ship will be designed to survive a high AoA at max-Q pressures, and a clean separation is also very tricky.

Also any failures that happen on or near the launch pad, like AMOS-6 or the Proton nosedive in 2013, would not leave the ship with enough altitude and velocity to get away with it's low TWR at sea level. Not an issue with a capsule.

Offline GORDAP

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Re: Should the ITS have a launch escape system?
« Reply #24 on: 09/21/2017 03:16 PM »
I've always wondered just what is wrong with the BFS being its own LES. 

I know that it doesn't have high T/W ratio, and that the turbopumps take a few seconds to spin up, but it's not like you're going to outrun a true detonation event in the booster anyway, no matter how quickly a human 'pod' can skedaddle out of there.  It seems that it should only be required to outrun a conflagration of the booster, right?

Can anyone point to a realistic booster failure scenario in which a traditional LES would save the passengers, but in which the planned BFS LES would not?

Any launch where the vehicle fails to control its angle of attack in the atmosphere (like Ariane 501 or the Challenger breakup) would be much easier to survive in a capsule than an integrated stage/capsule. I'm not sure the ship will be designed to survive a high AoA at max-Q pressures, and a clean separation is also very tricky.

Also any failures that happen on or near the launch pad, like AMOS-6 or the Proton nosedive in 2013, would not leave the ship with enough altitude and velocity to get away with it's low TWR at sea level. Not an issue with a capsule.

Hmm, are you saying the BFS would have a TWR less than 1 at sea level?  I think that's hard to imagine with all 9 engines screaming at full thrust (yes, I realize that 6 of these would be overexpanded at sea level, but it seems this would be acceptable for a small amount of time during a dire emergency).

It appears you are saying that a capsule with appropriate LES had a much better chance of survival than a vehicle that depends upon aerodynamics during this critical phase, right? (correct me if I'm wrong.)  But I'm not suggesting that the BFR fly like an airplane during an abort, I'm suggesting that if flies, then lands as a rocket ship in the same mode as its final decent on Mars and Earth.  Sure, it will have to hover for a good while to burn off fuel, but that shouldn't be an issue. 

I'm still not seeing why a capsule with LES would be inherently safer than a BFS, unless one can make a credible argument that getting away from a disintegrating booster underneath you - in a great hurry - is critical.

Offline RonM

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Re: Should the ITS have a launch escape system?
« Reply #25 on: 09/21/2017 04:14 PM »
I'm still not seeing why a capsule with LES would be inherently safer than a BFS, unless one can make a credible argument that getting away from a disintegrating booster underneath you - in a great hurry - is critical.

Look at Apollo, Orion, Soyuz, Shenzhou, Starliner, and Dragon. Somebody thinks it's critical.

Offline GORDAP

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Re: Should the ITS have a launch escape system?
« Reply #26 on: 09/21/2017 05:01 PM »
I'm still not seeing why a capsule with LES would be inherently safer than a BFS, unless one can make a credible argument that getting away from a disintegrating booster underneath you - in a great hurry - is critical.

Look at Apollo, Orion, Soyuz, Shenzhou, Starliner, and Dragon. Somebody thinks it's critical.

Ron, I fully understand that getting away is critical.  I underlined the 'great hurry' part to distinguish the argument that a few seconds delay and/or slower acceleration is somehow an important differentiator.  I'm asking for someone to explain how/why this would make the difference between success and loss of life.

Offline RonM

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Re: Should the ITS have a launch escape system?
« Reply #27 on: 09/21/2017 05:27 PM »
I'm still not seeing why a capsule with LES would be inherently safer than a BFS, unless one can make a credible argument that getting away from a disintegrating booster underneath you - in a great hurry - is critical.

Look at Apollo, Orion, Soyuz, Shenzhou, Starliner, and Dragon. Somebody thinks it's critical.

Ron, I fully understand that getting away is critical.  I underlined the 'great hurry' part to distinguish the argument that a few seconds delay and/or slower acceleration is somehow an important differentiator.  I'm asking for someone to explain how/why this would make the difference between success and loss of life.

Look at some old rocket explosion videos. It should become obvious. An emergency on the pad or early in flight require a high gee acceleration to escape. Later in the flight, more gentle aborts will work. That's why Apollo, Orion, Soyuz, and Shenzhou jettison their LAS before reaching orbit; it's no longer needed.

Even high gee LAS won't save the crew all of the time. If there's no indication of a problem before a massive explosion, no LAS is going to do the job.

There will always be a chance the crew will be killed. That's ok for daring astronauts on exploration missions, but what about 100 passengers wanting a new start at a Mars colony? If there isn't a LAS on ITS spacecraft, then the booster better be as reliable as a modern aircraft. Either that or the passengers need to be well informed about the danger.

Offline AncientU

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Re: Should the ITS have a launch escape system?
« Reply #28 on: 09/21/2017 05:37 PM »
I'm still not seeing why a capsule with LES would be inherently safer than a BFS, unless one can make a credible argument that getting away from a disintegrating booster underneath you - in a great hurry - is critical.

Look at Apollo, Orion, Soyuz, Shenzhou, Starliner, and Dragon. Somebody thinks it's critical.

Ron, I fully understand that getting away is critical.  I underlined the 'great hurry' part to distinguish the argument that a few seconds delay and/or slower acceleration is somehow an important differentiator.  I'm asking for someone to explain how/why this would make the difference between success and loss of life.

Look at some old rocket explosion videos. It should become obvious. An emergency on the pad or early in flight require a high gee acceleration to escape. Later in the flight, more gentle aborts will work. That's why Apollo, Orion, Soyuz, and Shenzhou jettison their LAS before reaching orbit; it's no longer needed.

Even high gee LAS won't save the crew all of the time. If there's no indication of a problem before a massive explosion, no LAS is going to do the job.

There will always be a chance the crew will be killed. That's ok for daring astronauts on exploration missions, but what about 100 passengers wanting a new start at a Mars colony? If there isn't a LAS on ITS spacecraft, then the booster better be as reliable as a modern aircraft. Either that or the passengers need to be well informed about the danger.

People by the millions flew on commercial aircraft 30-40 years ago when they were a fraction as safe as 'modern aircraft.'  People by the millions (billions) do all sorts of crazy things today that aren't as safe as 'modern aircraft,' like driving to work, or skiing, or jumping out of airplanes that aren't on fire...

Inform passengers of the risk, have them sign on the dotted line, and get on with it. 

Don't go if your standard is as safe as 'modern aircraft'... won't happen.


« Last Edit: 09/21/2017 05:38 PM by AncientU »
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Offline envy887

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Re: Should the ITS have a launch escape system?
« Reply #29 on: 09/21/2017 06:23 PM »
Look at some old rocket explosion videos. It should become obvious. An emergency on the pad or early in flight require a high gee acceleration to escape. Later in the flight, more gentle aborts will work. That's why Apollo, Orion, Soyuz, and Shenzhou jettison their LAS before reaching orbit; it's no longer needed.

Even high gee LAS won't save the crew all of the time. If there's no indication of a problem before a massive explosion, no LAS is going to do the job.

The high acceleration is mainly to get away from any debris thrown during a booster breakup that might damage the capsule, as well as the potential overpressure wave and thermal damage. Not every booster failure results in debris, pressure, or thermals that threaten the crew vehicle, and there are situations where the low thrust and delayed start of the upper stage Raptors would be sufficient to save the crew.

Hmm, are you saying the BFS would have a TWR less than 1 at sea level?  I think that's hard to imagine with all 9 engines screaming at full thrust (yes, I realize that 6 of these would be overexpanded at sea level, but it seems this would be acceptable for a small amount of time during a dire emergency).

It appears you are saying that a capsule with appropriate LES had a much better chance of survival than a vehicle that depends upon aerodynamics during this critical phase, right? (correct me if I'm wrong.)  But I'm not suggesting that the BFR fly like an airplane during an abort, I'm suggesting that if flies, then lands as a rocket ship in the same mode as its final decent on Mars and Earth.  Sure, it will have to hover for a good while to burn off fuel, but that shouldn't be an issue.

The ITS ship as presented at IAC 2016 would definitely have a TWR very near 1, because the overexpanded vacuum nozzles reduce the available thrust from those engines. That design might change to something more useful for a pad abort.

The biggest issue with using the Raptors for abort is the potential loss of control during the delay for startup, especially near Max-Q. That stage is going to have a much tougher time flying sideways at Mach 1 than a capsule would. Perhaps the RCS system and/or body flaps could be used for control while the Raptors spin up.

Offline spacenut

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Re: Should the ITS have a launch escape system?
« Reply #30 on: 09/21/2017 06:25 PM »
The 9m ITS will probably send 5-10 unmanned cargo ships to Mars first with equipment, habitats, solar panels, etc.  One ship will make fuel for return.  These will probably be sent in one synod.  Then the next synod, humans will go.  To begin with I say a small crew, no more than say 30 on the smaller ITS.  So ITS while refueling can easily have 2-3 Dragons or other spacecraft dock and transfer their people.  One Dragon (6), one CTS-100 (4), Soyuz (3), the Chinese craft (3), That is 16, maybe others on their spacecrafts.  So I don't see ITS having a LES, probably ever.  Docking for fueling will probably be done from the sides.  Docking for visiting spacecraft transfering people can be done from the nose while it is refueling for a trip to Mars.  These early ships will be a mix of crew and cargo.  Maybe even husband-wife astronauts or specialists in botony, or mining, or chemistry. 

Offline GORDAP

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Re: Should the ITS have a launch escape system?
« Reply #31 on: 09/21/2017 09:17 PM »
Look at some old rocket explosion videos. It should become obvious. An emergency on the pad or early in flight require a high gee acceleration to escape. Later in the flight, more gentle aborts will work. That's why Apollo, Orion, Soyuz, and Shenzhou jettison their LAS before reaching orbit; it's no longer needed.

Even high gee LAS won't save the crew all of the time. If there's no indication of a problem before a massive explosion, no LAS is going to do the job.

The high acceleration is mainly to get away from any debris thrown during a booster breakup that might damage the capsule, as well as the potential overpressure wave and thermal damage. Not every booster failure results in debris, pressure, or thermals that threaten the crew vehicle, and there are situations where the low thrust and delayed start of the upper stage Raptors would be sufficient to save the crew.

Hmm, are you saying the BFS would have a TWR less than 1 at sea level?  I think that's hard to imagine with all 9 engines screaming at full thrust (yes, I realize that 6 of these would be overexpanded at sea level, but it seems this would be acceptable for a small amount of time during a dire emergency).

It appears you are saying that a capsule with appropriate LES had a much better chance of survival than a vehicle that depends upon aerodynamics during this critical phase, right? (correct me if I'm wrong.)  But I'm not suggesting that the BFR fly like an airplane during an abort, I'm suggesting that if flies, then lands as a rocket ship in the same mode as its final decent on Mars and Earth.  Sure, it will have to hover for a good while to burn off fuel, but that shouldn't be an issue.

The ITS ship as presented at IAC 2016 would definitely have a TWR very near 1, because the overexpanded vacuum nozzles reduce the available thrust from those engines. That design might change to something more useful for a pad abort.

The biggest issue with using the Raptors for abort is the potential loss of control during the delay for startup, especially near Max-Q. That stage is going to have a much tougher time flying sideways at Mach 1 than a capsule would. Perhaps the RCS system and/or body flaps could be used for control while the Raptors spin up.

I've seen clips of many rockets failing during ascent, and they seem to fall into 3 general categories:  A) Violent explosions (rare), B) Gradual (relatively speaking) disintegration, and C) Quickly moving 'conflagrations' (i.e. Shuttle).

There seems to be agreement that no LES designs will survive type A, with high speed debris and the over pressure wave.  I think both BFS and a capsule would survive type B.  That leaves type C - a rapidly expanding conflagration.  Because of its orientation, the shuttle was instantly in the middle of the fireball, plus sandwiched between the two solids (not a good place to be).   Is there a good reason to believe that a BFS would not survive a 'typical' conflagration type event of the booster (other than the momentary aerodynamic issue raised above)?

I just suspect that when someone runs the actual numbers for failure scenarios, they'd find something like, yeah, a capsule plus traditional LES survives 80% of the failures, and the BFS will only survive 75%.  If this is the case, the "You can't launch 100 civilians without traditional LES" argument is revealed to be too simplistic. 

Offline whitelancer64

Re: Should the ITS have a launch escape system?
« Reply #32 on: 09/21/2017 09:40 PM »
I've seen clips of many rockets failing during ascent, and they seem to fall into 3 general categories:  A) Violent explosions (rare), B) Gradual (relatively speaking) disintegration, and C) Quickly moving 'conflagrations' (i.e. Shuttle).

There seems to be agreement that no LES designs will survive type A, with high speed debris and the over pressure wave.  I think both BFS and a capsule would survive type B.  That leaves type C - a rapidly expanding conflagration.  Because of its orientation, the shuttle was instantly in the middle of the fireball, plus sandwiched between the two solids (not a good place to be).   Is there a good reason to believe that a BFS would not survive a 'typical' conflagration type event of the booster (other than the momentary aerodynamic issue raised above)?

I just suspect that when someone runs the actual numbers for failure scenarios, they'd find something like, yeah, a capsule plus traditional LES survives 80% of the failures, and the BFS will only survive 75%.  If this is the case, the "You can't launch 100 civilians without traditional LES" argument is revealed to be too simplistic.

LES systems are designed for your category A. LES systems can react faster than the blink of an eye. A crewed Dragon v2 on top of Amos-6 would have gotten clear of the explosion easily, for example.
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Offline Norm38

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Re: Should the ITS have a launch escape system?
« Reply #33 on: 09/22/2017 05:43 PM »
LES systems are designed for your category A. LES systems can react faster than the blink of an eye. A crewed Dragon v2 on top of Amos-6 would have gotten clear of the explosion easily, for example.

I have a question about that, regarding the g-forces on the human body. At launch the astronauts are strapped in, facing forward, braced and ready for the acceleration.
Now I supposed that the astronauts will have to be already strapped in before fueling starts, but they won't be braced for an unexpected high g abort.  So they've got their arms about, their head up, looking around, then are suddenly slammed back at several g.  What happens?

Offline cppetrie

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Re: Should the ITS have a launch escape system?
« Reply #34 on: 09/22/2017 08:30 PM »
LES systems are designed for your category A. LES systems can react faster than the blink of an eye. A crewed Dragon v2 on top of Amos-6 would have gotten clear of the explosion easily, for example.

I have a question about that, regarding the g-forces on the human body. At launch the astronauts are strapped in, facing forward, braced and ready for the acceleration.
Now I supposed that the astronauts will have to be already strapped in before fueling starts, but they won't be braced for an unexpected high g abort.  So they've got their arms about, their head up, looking around, then are suddenly slammed back at several g.  What happens?
For Dragon 2, at least, fueling will take approximately 75 minutes. During that time the passengers would be strapped in tightly with little room to move. They won’t be able to move their heads much and there would be little reason to be reaching about in the capsule as everything is automated or controlled from the ground. At most they might be reading something off a display and relating it to ground but even that is probably unnecessary. They will mostly just be confirming they are go for launch when the time comes. The same will be true during ascent. A sudden high-G maneuver could result in injury if they were moving around or not secured properly, but neither should be the case.

Offline eriblo

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Re: Should the ITS have a launch escape system?
« Reply #35 on: 09/22/2017 08:42 PM »
LES systems are designed for your category A. LES systems can react faster than the blink of an eye. A crewed Dragon v2 on top of Amos-6 would have gotten clear of the explosion easily, for example.

I have a question about that, regarding the g-forces on the human body. At launch the astronauts are strapped in, facing forward, braced and ready for the acceleration.
Now I supposed that the astronauts will have to be already strapped in before fueling starts, but they won't be braced for an unexpected high g abort.  So they've got their arms about, their head up, looking around, then are suddenly slammed back at several g.  What happens?
For Dragon 2, at least, fueling will take approximately 75 minutes. During that time the passengers would be strapped in tightly with little room to move. They won’t be able to move their heads much and there would be little reason to be reaching about in the capsule as everything is automated or controlled from the ground. At most they might be reading something off a display and relating it to ground but even that is probably unnecessary. They will mostly just be confirming they are go for launch when the time comes. The same will be true during ascent. A sudden high-G maneuver could result in injury if they were moving around or not secured properly, but neither should be the case.
I agree with cppetrie and my basic-physics guess is that worst case scenario is a dislocated/broken arm or two and strained neck muscles. The initial g-force is about 6 g in the best possible direction ("eyeballs in") which is comparable to at most a 8 m/s (29 kph, 18 mph) rear end collision (assuming equal weight cars and 1 m ideal crumple zone). The acceleration will of course continue for much longer but then you have time to tense up and use your muscles.

Offline docmordrid

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Re: Should the ITS have a launch escape system?
« Reply #36 on: 09/22/2017 10:11 PM »
For comparison, the highst G coaster is the 'Tower of Terror' at Gold Reef City, South Africa

6.3G

http://entertainmentdesigner.com/news/top-seven-most-thrilling-roller-coasters-in-the-world/
DM

Offline Norm38

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Re: Should the ITS have a launch escape system?
« Reply #37 on: 09/23/2017 04:05 AM »
Okay, so in the equation of whether I as a paying passenger want an LES or not;
The choice is airline like operations at higher risk, or astronaut level precautions.

One way colonists may tolerate that. But there's some frequency limit to that.

Offline cppetrie

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Re: Should the ITS have a launch escape system?
« Reply #38 on: 09/23/2017 05:09 AM »
LES systems are designed for your category A. LES systems can react faster than the blink of an eye. A crewed Dragon v2 on top of Amos-6 would have gotten clear of the explosion easily, for example.

I have a question about that, regarding the g-forces on the human body. At launch the astronauts are strapped in, facing forward, braced and ready for the acceleration.
Now I supposed that the astronauts will have to be already strapped in before fueling starts, but they won't be braced for an unexpected high g abort.  So they've got their arms about, their head up, looking around, then are suddenly slammed back at several g.  What happens?
For Dragon 2, at least, fueling will take approximately 75 minutes. During that time the passengers would be strapped in tightly with little room to move. They won’t be able to move their heads much and there would be little reason to be reaching about in the capsule as everything is automated or controlled from the ground. At most they might be reading something off a display and relating it to ground but even that is probably unnecessary. They will mostly just be confirming they are go for launch when the time comes. The same will be true during ascent. A sudden high-G maneuver could result in injury if they were moving around or not secured properly, but neither should be the case.
I agree with cppetrie and my basic-physics guess is that worst case scenario is a dislocated/broken arm or two and strained neck muscles. The initial g-force is about 6 g in the best possible direction ("eyeballs in") which is comparable to at most a 8 m/s (29 kph, 18 mph) rear end collision (assuming equal weight cars and 1 m ideal crumple zone). The acceleration will of course continue for much longer but then you have time to tense up and use your muscles.
A traumatic brain injury is possible if it is possible for the passenger to flex forward enough to create sufficient gap that upon activation of the abort system the head was accelerated back towards some sort of headrest. But why would they even permit that level of movement? There is no need for it. The passengers should be restrained almost to the point of being immobile so as to virtually eliminate the possibility of injury from abort system activation. I would think even passengers on ITS would be largely constrained in some sort of restraint system akin to a mix between 5 point racing harness and roller coaster restraints. So long as the ship itself remained intact I would think severe injuries would be very unlikely.

Online octavo

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Re: Should the ITS have a launch escape system?
« Reply #39 on: 09/23/2017 08:02 AM »
For comparison, the highst G coaster is the 'Tower of Terror' at Gold Reef City, South Africa

6.3G

http://entertainmentdesigner.com/news/top-seven-most-thrilling-roller-coasters-in-the-world/
It's a really short duration though. I've ridden it several times in a row on a quiet day - great fun, but, whoosh and it's over.

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