Launch Escape Systems: 0.23 vs. 0.23.5

[Starstrider42]

Something got my curiosity...

0.23 Escape Rocket

11 parts (Strut + 8 separatrons + Nose cone + Decoupler)

750 kg wet mass

117 kN of thrust (2.4 G with a Mark 1-2 Command Pod)

3.3 s burn time

0.23.5 Escape Rocket

2 parts (Launch Escape System + Decoupler)

1127 kg wet mass

750 kN of thrust (14.4 G with a Mark 1-2 Command Pod)

0.5 s burn time

Given that most launch rockets have a TWR of 2, it seems like the old-school version is a better choice even if you're worried about your main engines not shutting down -- it's lighter, and it doesn't kill your crew.

So when do you want to use the new LES?

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Edited April 14, 2014 by Starstrider42

[Taki117]

generally the new LES also pushes your rocket to the side. yes the same effect can be achieved with the old school LES with tweakables, but the new LES also just looks better and its a small matter to add a decoupler to the bottom of it.

[juanml82]

What's the fun in an abort sequence which is simple and has no chance of failure?

[Starstrider42]

generally the new LES also pushes your rocket to the side. yes the same effect can be achieved with the old school LES with tweakables, but the new LES also just looks better and its a small matter to add a decoupler to the bottom of it.

Aha, I didn't know that. My escape rockets always pulled straight forward; once they ran out of fuel gravity and air resistance took care of getting them out the main rocket's way.

So is it worth paying 400 kg for side thrust... hmm.

What's the fun in an abort sequence which is simple and has no chance of failure?

In context you seem to be saying the old version was simpler...?

Edited April 13, 2014 by Starstrider42

[juanml82]

In context you seem to be saying the old version was simpler...?

Nah, I'm just kidding. I've never used either. All my abort sequences always consisted in preparing the abort action group so decouplers detach, parachutes open, landing legs open and I need to first tilt the surviving upper stage so when the decouplers fire it doesn't get in the way of the incoming mess below.

I even succeed with that with a crazy design that had three separate landers in a triangular pattern. And when the first tries crashed, I've used that to fire away to safety all three landers at once.

[Armchair Rocket Scientist]

Aha, I didn't know that. My escape rockets always pulled straight forward; once they ran out of fuel gravity and air resistance took care of getting them out the main rocket's way.

So is it worth paying 400 kg for side thrust... hmm.

In context you seem to be saying the old version was simpler...?

The reaction wheels on the MK1-2 have more than enough torque to tilt the pod (and change its direction) anyway. If you really need side thrust, an extra sepatron should do the trick, and that's a lot less than 400 kg.

[Jouni]

I think there is a bug in the LES, like someone mistook the dry mass for the amount of fuel. While the LES has a reasonable amount of thrust for its job, it runs out of fuel in half a second. In practice, it can't get the command pod out of harm's way, unless you can shut down the engines first.

[BudgetHedgehog]

I think there is a bug in the LES, like someone mistook the dry mass for the amount of fuel. While the LES has a reasonable amount of thrust for its job, it runs out of fuel in half a second. In practice, it can't get the command pod out of harm's way, unless you can shut down the engines first.

Would you mind showing pictures of this? Because I successfully escaped a launch with a TWR of over 8 with no ill effects - yes, the pod din't exactly go up, but the sideways force was more than enough to get it out of harms way so there was no problems. A launch TWR of 8 is very extreme and a worst case scenario, but it still managed to escape successfully. Not sure why you think there is a bug, is all.

[Jouni]

The amount of fuel in the LES is only about 10% of its total mass, which feels quite ridiculous. Real launch escape systems have fuel for about 5 seconds, not for 0.5 seconds. If we switch the dry mass and the fuel mass of the LES, we get something that performs as it should.

If I try to use the LES during the early part of the ascent, atmospheric drag makes it almost useless. The capsule only makes a small hop, and pretty much any rocket can catch the pod before it can escape.

I can't test it right now, because I have an ion-powered ship trying to reach Moho. It'll take a while to complete the burns.

[MaverickSawyer]

I upgraded the stock LAS tower. Double the fuel, 33% more thrust. It hauls ass now.

[Deathsoul097]

-Snip-

0.23.5 Escape Rocket

2 parts (Launch Escape System + Decoupler)

1127 kg wet mass

750 kN of thrust (14.4 G with a Mark 1-2 Command Pod)

0.5 s burn time

Given that most launch rockets have a TWR of 2, it seems like the old-school version is a better choice even if you're worried about your main engines not shutting down -- it's lighter, and it doesn't kill your crew.

-Snip-

I think that people could survive 14.5 Gs for half a second. I cant remember the exact number, but you can survive over 50Gs if it's instantaneous. If that 15Gs was for an extended duration, then I would agree with you.

[Starstrider42]

I think that people could survive 14.5 Gs for half a second. I cant remember the exact number, but you can survive over 50Gs if it's instantaneous. If that 15Gs was for an extended duration, then I would agree with you.

I meant in the context of the game (I'm pretty sure I read somewhere that real launch escape systems do cause pilots to black out). Though part of it may be that I've been playing Deadly Reentry for so long that I don't remember how stock KSP handles high G-forces...

My original question assumed that most people had already figured the new tech out (I actually haven't had time to try out the new parts myself, since I have a bunch of ongoing missions I want to finish first). Since it seems that there's no consensus on LES and how/whether it works... well, I guess that's my answer. Setting thread to [Answered!]...

[SpacedCowboy]

I'm sorry but, I wouldn't like to use either of them. At least not till there were a couple of radial chutes on the command pod! (Might come in handy)

[Claw]

Perhaps many of you haven't heard of Dr. John Stapp who voluntarily damaged his body a great deal in answering the question "how many g's can a person handle."

Anyway, here's the most relevant quote from the wiki:

By riding the decelerator sled himself, Stapp demonstrated that a human can withstand at least 45 g (440 m/s²) in the forward position, with adequate harness. This is the highest known acceleration voluntarily encountered by a human. Stapp believed that the tolerance of humans to acceleration had not yet been reached in tests, and is much greater than ordinarily thought possible.

Also, turns out people are best left on their backs or chests (transverse Gs). The same level of Gs from head to toe causes all sorts of bad things happen to the parts that connect your organs together...

Like so many other aspects of this game, use it if you like it and ignore it if you don't. I, too, would like to see an escape tower that includes a parachute. Or at least a new in-line parachute that you could place underneath the tower. But I suppose the radials work okay too.

I will also say that I agree, the launch tower seems a bit overly heavy for not including a parachute. Perhaps lightening the tower or putting in a chute would be a good balance.

By the way, you can tweak the thrust limiter on the tower if you think the G load is excessive for your design.

Edited April 14, 2014 by Claw