How to add escape tower for emergencies?

[SneakyBastd]

I would like to add a small tower with rockets to the top of my capsule, Apollo style, so that it can fire and send my capsule free if (when) the lower stages go *boom*.

But I don't know how to trigger it. The emergency could happen at any time, so I need some way to trigger that stage at ANY point during the launch. I will also want to have it as part of my normal stage sequence I guess, so that I can discard it when no longer needed.

Is this possible? Do I need a mod? Sorry if it's a stupid question, I'm new to this game!

Thanks for your help.

[RoboRay]

You can construct escape towers out of stock parts, but they greatly add to your part-count (decreasing performance) and frankly don't work very well (limited acceleration, when fired).

NovaPunch has a couple of very effective mod Launch Escape System towers, and there is also one in the Stock Parts Expansion Pack, both available on the Spaceport. The KSPX pack tower doesn't include the decoupler function found in the NovaPunch version, but it looks nicer. If you're comfortable editing the part.cfg file with a text editor, you can add the decoupler capability to the one in KSPX, or just stick it on a decoupler as intended.

You want to set up the Abort Action Group to fire the LES motors and decouple the command pod from the rest of the vehicle, and shut down all the other motors on the vehicle. Set the LES tower up in your normal staging to decouple itself from the command pod and fire the LES motor.

[Rhomphaia]

Action groups. You can set them up in VAB just to the left of the name, there is even a special one for abort which would be activated in flight by hitting backspace. the others are 0-9 keys.

[SneakyBastd]

Thankyou! That was exactly the info I needed.

[Sovek]

There is a nice one in the KSPX mod.

[capi3101]

You probably could do something with a stack decoupler and some Sepratrons. Probably would want to set that up with an action group, like folks are suggesting; that way you can activate it whenever you need to.

[lobsterbark]

The problem with ksp is that rocket engines have a really low twr, compared to real-life rockets. Stock escape towers never have the twr to escape a launch. Even using two of the demo srbs isn't enough. So you have to use a mod.

[MBobrik]

What about simply adding a lot of separatrons ? AFAIK they have the best T/W ratio in the entire game. 3 sec running time should be enough to distance the pod from the wreckage and land on parachutes. Never tried it actually, gonna to try it myself.

[ThatBum]

How's about this:

It's still pretty weak. KSPX's escape tower's TWR is 14.27 with this setup, and even that's not powerful enough sometimes.

Edited April 29, 2013 by ThatBum

[CalculusWarrior]

Only 10? I put two rows of 8 Sepatrons on mine--that gives it more than enough acceleration to boost the capsule to safety! I put the parachutes on a seperate action group so that I can deploy them manually; if they fire at the same time as the LES, I find they decrease its effectiveness...

BTW, what mod are you using that allows you to add more than 8x symmetry, ThatBum?

[Temstar]

Set your abort group to also shut down all liquid fuelled engines, deploy any parachutes and fire all retrograde engines when you abort. Do not separate any SRB powered stages! This will cause the rest of the rocket to instantly lose thrust if it's running on all LFE or at least cause a large loss of TWR as the dead weight of engines and fuel drag down any thrust that burning SRBs are putting out. Also if you have a service module with a surface TWR better than 1 then instead of just decoupling the command pod and LES tower you can instead decouple the entire spacecraft with the SM and use combined LES tower motor + SM engine thrust to ensure clean separation from the booster. In fact if your spacecraft is powerful enough you can get away with using no LES at all and just rely on your SM engine to escape from the booster.

[ThatBum]

DEADB33F'S Editor Tools, same guy who made Subassembly Loader. Be sure to read the readme.

With 16 sepratrons, the TWR is 4.95. I suppose that's sufficient for most rockets, as they're supposed to have a TWR around 2, but if the rocket under you is potentially exploding, you'd want to get the Hell out of dodge faster than that.

Edited April 29, 2013 by ThatBum

[magnemoe]

The problem with ksp is that rocket engines have a really low twr, compared to real-life rockets. Stock escape towers never have the twr to escape a launch. Even using two of the demo srbs isn't enough. So you have to use a mod.

However exploding rockets in KSP don't have an blast radius, 4-6 seperatrons give you an good enough twr to get away.

In the abort sequense, you disable all engines, seperate pod from upper stage and fire the seperatrons. you need one other key to separate the tower from pod, let this fire the seperatrons to and you can use it to get rid of tower during some part of the gravity turn.

And yes one key to open the parachute.

One escape sequence I often use without tower is just kill engines, separate pod and open parachute. Its not as safe but work well if rocket is tumbling.

[RoboRay]

What about simply adding a lot of separatrons ? AFAIK they have the best T/W ratio in the entire game. 3 sec running time should be enough to distance the pod from the wreckage and land on parachutes. Never tried it actually, gonna to try it myself.

If you double the part count of your launch vehicle adding separatrons, your "escape" tower's TWR is still going to be too low to get out of the way of the still-burning boosters from your disintegrating launch vehicle. It doesn't do you much good to include "shutdown launch-vehicle engine" commands in your Abort group, because those engines are generally no longer even under your control if you need to abort. And if SRBs are tearing loose from the LV... well, good luck with your separatron system. You need a mod part for a functional escape tower; stock ones are just cosmetic.

Edited April 29, 2013 by RoboRay

[MBobrik]

your "escape" tower's TWR is still going to be too low to get out of the way of the still-burning boosters from your disintegrating launch vehicle

.

There is no way to escape a near-empty SRB that went crazy. T/W = 51. good luck escaping from that with anything bigger than a separatron-wrapped bare probe core. A real-life escape tower would not make it either - the best system had T/W 17, while for example a near-empty Ariane 44P booster has T/W nearly 23 and AtlasV SRB over 32.

Edited April 29, 2013 by MBobrik

[CalculusWarrior]

DEADB33F'S Editor Tools, same guy who made Subassembly Loader. Be sure to read the readme.

With 16 sepratrons, the TWR is 4.95. I suppose that's sufficient for most rockets, as they're supposed to have a TWR around 2, but if the rocket under you is potentially exploding, you'd want to get the Hell out of dodge faster than that.

I originally just had 8, and found that out the hard way However, my rocket has a very low TWR (like 1.4) during the beginning stages of the flight where the possibility for failure is greatest, so it works fine. I don't use it much anymore now that I've worked out all the bugs in the design though, and it no longer implodes under the stresses of launch. I guess a LES is only useful if the chance of exploding is fairly high, I only included mine to stick with real-life accuracy (I built the Orion spacecraft and the SLS).

Thanks for the mod, this has just unlocked new possibilities in my rocket designs!

[RoboRay]

.

There is no way to escape a near-empty SRB that went crazy. T/W = 51. good luck escaping from that with anything bigger than a separatron-wrapped bare probe core. A real-life escape tower would not make it either - the best system had T/W 17, while for example a near-empty Ariane 44P booster has T/W nearly 23 and AtlasV SRB over 32.

Outrun, no. Get out of the way, maybe.

And, in any case, the primary design factor in an LES system (ranked just narrowly behind "reliability") is simply raw TWR. Accept nothing less than the maximum feasible for a safety system.

Edited April 29, 2013 by RoboRay

[MBobrik]

Outrun, no. Get out of the way, maybe.

If it it were heading your way, you won't have the time to dodge it. And because you can't know beforehand where a ripped off booster will be heading, it is just a matter of pure luck whether it hits you or not.

[RoboRay]

Then there's no reason for an LES to even exist. Why bother at all, if it can't save you?

Anyway, merely delaying a part of your vehicle still under thrust from overtaking you increases the probability that it will deviate from its default heading... directly at you. Every bit of speed away from the rapid unplanned disassembly is of value.

[MBobrik]

Then there's no reason for an LES to even exist. Why bother at all, if it can't save you?

They can and would save you because they and the super-high T/W ratio boosters aren't used together on the same craft.

[MBobrik]

And, I just tried it in KSP by myself ( my first post with images, let's see how it works out ):

48 Separatrons, 3 655 Kg extra mass, initial T/W ratio 11, and successfully outrunning near empty SRBs (the large ones).

...

Just before disintegration:

...

barely outrunning the speeding SRBs:

...

and still having enough velocity to get 10 Km higher

[iamaphazael]

There is also an escape tower in my set of Apollo parts (http://kerbalspaceprogram.com/apollo-lmcsm-replica/). See the included craft for an example of how to set up the action groups for both an abort sequence as well as a jettison command

[RoboRay]

They can and would save you because they and the super-high T/W ratio boosters aren't used together on the same craft.

Good plan. Install the LES only when you probably don't need it anyway.

[MBobrik]

There is also an escape tower in my set of Apollo parts

Thrust ? Full/empty mass ? Burn time ?

[MBobrik]

Good plan. Install the LES only when you probably don't need it anyway.

I don't think that ripped off near-empty high-T/W SRBs are the major failure mode of manned spacecraft. And even in KSP where it is much more common, I've just demonstrated that it is possible to outrun the big SRB with stock parts only. So just avoid the small RT-10 ( who uses them on rockets big enough to carry the 3 seat pod anyway? ) and your kerbals will be safe.