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LES has to be able to pull away from a LV at max q. I’m pretty sure killing a few hundred km/hr is not a problem.

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39 minutes ago, tater said:

LES systems can deal with pad failures, so they can deal with landing failures.

They need a bit extra, given that they have to cancel their downward velocity AND boost clear of the ensuing fireball.

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A landing failure has a few moments where it is critical, but they still have altitude (they'd land with a chute, presumably).

While supersonic, coming down, if the landing burn fails to start, it aborts. There is no explosion, except when the craft hits the ground. The chute down. In the moments before landing, if there is an engine failure, the vehicle is not moving very fast, as the engines have already fired, so it's moving the wrong way, but very slowly. As you get closer to the ground, it's moving closer to zero velocity. An engine failure an instant before touchdown is effectively a pad failure abort, while supersonic it's likely high enough to pop a chute, anyway, it just needs to kill some velocity to let the booster speed away at terminal velocity into the dirt.

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9 minutes ago, tater said:

...while supersonic it's likely high enough to pop a chute, anyway, it just needs to kill some velocity to let the booster speed away at terminal velocity into the dirt.

And also reduce stress on the chute's lines, so as not to tear them from their mounts.

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22 minutes ago, grungar3x7 said:

And also reduce stress on the chute's lines, so as not to tear them from their mounts.

Yeah, it still has rockets, so it need not stop, just rapidly slow to the point the drogues can pop.

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Rumor has Hispasat moved to Wednesday evening, no confirmations yet.

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Did this thread just finally create justification for real-life escape pods?

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On 23/02/2018 at 4:22 PM, tater said:

 

Wait what? I thought they were letting them sink... Wow, so they did not catch them, but did recover? Cool.

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14 hours ago, tater said:

A landing failure has a few moments where it is critical, but they still have altitude (they'd land with a chute, presumably).

While supersonic, coming down, if the landing burn fails to start, it aborts. There is no explosion, except when the craft hits the ground. The chute down. In the moments before landing, if there is an engine failure, the vehicle is not moving very fast, as the engines have already fired, so it's moving the wrong way, but very slowly. As you get closer to the ground, it's moving closer to zero velocity. An engine failure an instant before touchdown is effectively a pad failure abort, while supersonic it's likely high enough to pop a chute, anyway, it just needs to kill some velocity to let the booster speed away at terminal velocity into the dirt.

The main concern I have here is clearance. As with a pad abort, your escape motor needs to be able to push the vehicle clear of the ensuing fireball. We've all seen the landing failures of Falcon 9 first stages; the BFS would be bigger, and autogenously pressurized, so you're talking about what would essentially be a giant fuel-air bomb.

Successfully pulling away from the doomed ship doesn't do you much good if you chute down into a firestorm.

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25 minutes ago, sevenperforce said:

Successfully pulling away from the doomed ship doesn't do you much good if you chute down into a firestorm

Which is why LAS systems also fly sideways, to get away from that. Also, a BFS should be nearly empty while landing (liftoff is another story) so the fireball won't be that big, and won't leave a firestorm behind as there won't be that much fuel to burn.

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8 minutes ago, StrandedonEarth said:

Which is why LAS systems also fly sideways, to get away from that. Also, a BFS should be nearly empty while landing (liftoff is another story) so the fireball won't be that big, and won't leave a firestorm behind as there won't be that much fuel to burn.

The BFS will have autogenous pressurization, which will tend to make the fireball a good bit bigger. In any case, it's not something I'd like to chute down into.

The point is that the launch escape system will need to be able to not only arrest downward momentum at the BFS's terminal velocity, but reverse it; otherwise it won't be able to get any sideways motion.

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17 minutes ago, sevenperforce said:

The BFS will have autogenous pressurization, which will tend to make the fireball a good bit bigger. In any case, it's not something I'd like to chute down into.

The point is that the launch escape system will need to be able to not only arrest downward momentum at the BFS's terminal velocity, but reverse it; otherwise it won't be able to get any sideways motion.

I think we are taking the idea of a launch escape system way too far. Space is risky.

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12 minutes ago, PB666 said:

I think we are taking the idea of a launch escape system way too far. Space is risky.

Space is hard. Landing on Earth is easy. We've been surviving falls with parachutes for centuries.

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Braking and sideways are not mutually exclusive.

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32 minutes ago, tater said:

Braking and sideways are not mutually exclusive.

Landing LES for a propulsively-landed vehicle is just a bit more complicated than the standard pad abort or Max-Q abort.

Passive aerodynamic stability is a big problem. Abort systems are supposed to be fire-and-forget; you don't want to be depending on gimbal or differential thrust for stability during an abort. If you're dropping through the atmosphere at Mach 1.5, your aerodynamic profile will be exactly opposite of what it would be going at the same speed in the other direction.

Standard LES assumes you are already pointed in the right direction.

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The lander can go sideways, if no engines, it keeps going sideways and the escape system halts.

 

Why do you think they keep "missing" the boats currently? Because they don't aim for them until the final landing burn. Then if there is a failure (prop fuel/RCS) it will crash, but a rather gentle crash.

 

That main take away is, aircraft don't have launch abort systems. They don't have chutes. Small craft can benefit from them, but larger ones it adds complexity, and adds *more* points of failure.

Edited by Technical Ben

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10 minutes ago, sevenperforce said:

Landing LES for a propulsively-landed vehicle is just a bit more complicated than the standard pad abort or Max-Q abort.

Passive aerodynamic stability is a big problem. Abort systems are supposed to be fire-and-forget; you don't want to be depending on gimbal or differential thrust for stability during an abort. If you're dropping through the atmosphere at Mach 1.5, your aerodynamic profile will be exactly opposite of what it would be going at the same speed in the other direction.

Standard LES assumes you are already pointed in the right direction.

True, but presumably the escape crew pod is a capsule, and designed for full reentry (they have mass budget to burn here, it could have abort from orbit capability).

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55 minutes ago, Technical Ben said:

The lander can go sideways, if no engines, it keeps going sideways and the escape system halts.

 

Why do you think they keep "missing" the boats currently? Because they don't aim for them until the final landing burn. Then if there is a failure (prop fuel/RCS) it will crash, but a rather gentle crash.

 

That main take away is, aircraft don't have launch abort systems. They don't have chutes. Small craft can benefit from them, but larger ones it adds complexity, and adds *more* points of failure.

One of the issues of landing on water is one you may not consider. The reason for burning out most or all of the fuel is that kerosene is considered an environmental hazard, and so for craft that do not burn up completely, one does want to limit the amount of kerosene let loose in the saltwater. I think that SpaceX is testing their reentry systems continuously both in fail and normal modes, they are doing this rather intentionally to test the lower bounds of reliable performance so that they are not wasting resources. Again there is no rational for block <5 cores because you want the testing done before deploying block 5 as these will be the bread winners. From a commercial POV you want these to have stellar performance so you can PR the hell out of them.

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1 hour ago, Technical Ben said:

That main take away is, aircraft don't have launch abort systems. They don't have chutes. Small craft can benefit from them, but larger ones it adds complexity, and adds *more* points of failure.

Aircraft have engine failure abort modes on landing. It's called "glide".

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7 minutes ago, sevenperforce said:

Aircraft have engine failure abort modes on landing. It's called "glide".

1389806210000-AP-YE-Plane-Splashdown.jpg

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59 minutes ago, sevenperforce said:

Aircraft have engine failure abort modes on landing. It's called "glide".

Generally something to be avoided, ETOPs is a specification for single engine failure over water, for example a mid pacific glide to water landing is the same as a crash, few survivors expected. The hudson river is a bonafida runway, used to be used in the days of transatlantic flights, the pacific ocean is not.

The difference between space flight and air flight is that the risk is high, but you don't do it very often. For aircraft the risk is low and people travel alot. The risk of spaceflight still exceeds that of flight, but one expects that risk to fall over time as we learn more about how to manage risk. Where have we seen this problem before, with flight. Crashes of Airplanes back in the 70s was much more common today (in the west), but has gone down over time do to increased use of aircraft. But before the 70s . .going back to the 1930s . . .it was pretty dangerous.

 


 

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I honestly think the “killer app” for commercial space is tourism. As has been said, most everything is better done by telepresence than humans (and chraper). 

If safety can get to early airline levels, which is still substantially more dangerous than current travel, then the market could grow if the price was also not impossible. Safer still and it becomes a huge, bottomless market (since there will always be new people wanting to experience it).

I don’t think it’s close, but it’s the only economic driver I see that involves decent numbers of people.

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