Saving a Kerbal on a ballistic trajectory

[lajoswinkler]

Tombles Kerman is on a ballistic trajectory with apoapsis of 1000 km. He's ascending at the moment, after his rocket launched his capsule straight up.

Deadly Reentry is installed. Heatshield is present and can survive the ablation, but the peak decelleration is around 25 G. The capsule barely survives it after Tombles gets killed.

I've tried lowering the apoapsis to 540 km. It does not work, the forces are still too high. Burning sideways at apoapsis, doesn't work. Raising apoapsis and then burning sideways also doesn't work. There isn't much dV left.

I've also tried launching an automated rescue capsule, but I can't rendezvous with Tombles. What can I do to save him?

[Kerba Fett]

You could revert the flight. That would save him.

Why would you even keep the engine running after your AP was above a couple of hundred km? Is it just a test of rescue systems?

Aside from reverting you could also bail out of the capsule and see if all the fuel in your EVA pack would be enough to get your PE out of the atmosphere. He'd still be stranded, but that's easier to fix than dead.

[Blackstar]

Abandon ship and and try to circularize on EVA? I don't remember how much deltaV an EVA pack has, but with an apoapsis of 1000km, you might just have enough. If you can get him into a stable orbit, then you can take as much time as you need to get a rescue ship to rendezvous.

[Brapness]

Get out and push? That's the only idea I've got

[SkyRender]

If you can, raise your periapsis to 25KM by firing horizontally at apoapsis. That might be a lot to ask, of course, since you apparently went straight up, but it's worth a shot. Either way, your best bet is to gain horizontal velocity while at apoapsis.

[ScallopPotato]

Uninstall deadly reentry for his descent? And then bounce?

[lajoswinkler]

I can't revert the flight anymore, that's why I need to save him.

I was testing reentry protocols with straight up launches, trying to find a sweet spot where deadly decellerations begin, but I've accidentally pressed F5 and now I can't revert the flight anymore.

I think EVA pack has 500-550 m/s. That might work, thanks. I totally forgot about that. I'll reach apoapsis, fire engines horizontally and then get out and fire the jetpack.

If someone knows a procedure how to rendezvous, I'll be happy to test it. From his initial position, it's 16 minutes till AP and a bit more from AP to reentry.

If I uninstall reentry, heatshields are gone, and I think the whole craft with the Kerbal inside will be wiped from existence.

Edited February 22, 2014 by lajoswinkler

[Taki117]

If you can, raise your periapsis to 25KM by firing horizontally at apoapsis. That might be a lot to ask, of course, since you apparently went straight up, but it's worth a shot. Either way, your best bet is to gain horizontal velocity while at apoapsis.

I agree with this, Depending on how long you have you can start burning almost dead horizontal to get your Periapsis as high as possible (Alternitively you can set a maneuver doe at APoapsis and pull prograde to achieve the same effect) Once your rocket is out of dV you can then get out and push to continue to raise your periapsis if it's not at the desired point.

One question though did you perform a

Because having an Apoapsis of 1Mm without a stable orbit is a tad ridiculous, even if you are going interplanetary.

The EVA Pack has 600m/s dV for a kerbal, less if you are pushing. However, once you burn your engines I HIGHLY suggest jettisoning everything you don't need, leaving only the capsule so that you aren't pushing a whole lot of mass. As far as rendezvousing with him, not a chance. You would have to catch up, match velocity, get close, it's not going to happen, you'd need almost twice the dV of the original rocket.

Edited February 22, 2014 by Taki117
More Info Recieved

[Claw]

I can't revert the flight anymore, that's why I need to save him.

I was testing reentry protocols with straight up launches, trying to find a sweet spot where deadly decellerations begin, but I've accidentally pressed F5 and now I can't revert the flight anymore.

I think EVA pack has 500-550 m/s. That might work, thanks. I totally forgot about that. I'll reach apoapsis, fire engines horizontally and then get out and fire the jetpack.

If someone knows a procedure how to rendezvous, I'll be happy to test it. From his initial position, it's 16 minutes till AP and a bit more from AP to reentry.

If I uninstall reentry, heatshields are gone, and I think the whole craft with the Kerbal inside will be wiped from existence.

You should be able to revert the flight still as long as you didn't switch to another craft or press F9 and load the quicksave.

In any case, based on your description I would agree with others that firing the engines and jumping ship to EVA is your best bet. Rendezvous in this position is a bit tough since you're probably not going to have the time to match downward velocities for the intercept. But after you jump ship and get on orbit, you should be able to get a rescue craft up there.

Just remember to save some EVA propellant if you can to make the pickup easier. Even if he dips a bit into the atmosphere, leaving your kerbal "on-rails" (i.e. not your game focus) will allow him to stay in orbit without aerobraking. You'll be able to join on him and rescue while outside of the atmosphere.

[SkyRender]

Rendezvous with that Kerbal should actually be pretty easy as long as you don't mind it taking a few orbits for the rescue craft. First get your Kerbal's periapsis up just above the atmosphere. Just launch something up that has enough fuel to get into stable orbit around the Mun (ie. around 1100m/s dV to spare after circularizing), put it in a 70KM orbit, and then target the incoming Kerbal and wait. Once he's getting close, do an adjustment so you have an encounter along the next pass (only fire prograde to do this or you'll re-enter the atmosphere!), and perform a standard intercept procedure of firing to match orbits in Target mode once the craft and Kerbal are close. Then you just need to adjust your orbit as you see fit (I'd suggest dropping periapsis at apoapsis as that's the least expensive solution dV-wise) and you're golden.

[Streetwind]

First get your Kerbal's periapsis up just above the atmosphere..

Which is exactly the thing he cannot do, as he stated multiple times...

[Rodyle]

I can't revert the flight anymore, that's why I need to save him.

I was testing reentry protocols with straight up launches, trying to find a sweet spot where deadly decellerations begin, but I've accidentally pressed F5 and now I can't revert the flight anymore.

I think EVA pack has 500-550 m/s. That might work, thanks. I totally forgot about that. I'll reach apoapsis, fire engines horizontally and then get out and fire the jetpack.

If someone knows a procedure how to rendezvous, I'll be happy to test it. From his initial position, it's 16 minutes till AP and a bit more from AP to reentry.

If I uninstall reentry, heatshields are gone, and I think the whole craft with the Kerbal inside will be wiped from existence.

Does the rocket have parachutes and stuff? If so, you wouldn't need for the periapis to completely leave the atmosphere, since you could spread out the deceleration over a longer time frame.

[lajoswinkler]

Does the rocket have parachutes and stuff? If so, you wouldn't need for the periapis to completely leave the atmosphere, since you could spread out the deceleration over a longer time frame.

Yes, it can land safely. There isn't enough dV to push PE outside Kerbin's crust. The only chance I've got is to fire the engines at AP and then use the jetpack. Unfortunately I can't test it because I'm away from my computer.

I was hoping for some advice on rendezvous by another vehicle but I understand it is very hard.

[Rakaydos]

On your way up, have you tried burning 45 degrees downward and laterally?

The idea being to both lower your absolute velocity, and give yourself slightly more atmosphere to slow down in.

[Kryxal]

There's always the "get out and push" method on the way up ... see how well it works before you get up there. Does that really not use monoprop?

[Claw]

Yes, it can land safely. There isn't enough dV to push PE outside Kerbin's crust. The only chance I've got is to fire the engines at AP and then use the jetpack. Unfortunately I can't test it because I'm away from my computer.

I was hoping for some advice on rendezvous by another vehicle but I understand it is very hard.

If he is coming straight back down, a vertical rendezvous would be very difficult because you don't have offset orbits to sit through while things align themselves. If he's only going up to 1M, then there might not even be enough time to launch a rocket to rejoin with him.

I've never tried, but my guess is you'll need a rocket with descent dV because not only will you have to really move your orbit around to catch him, but you'll also have to have enough dV to get into a reasonable orbit after that so you don't burn up the rescue ship.

What I can guess at is to launch the rescue ship. You'll have to wait till you're on the opposite side of the planet from your Kerbal and move your AP up high enough to catch up with him, although you'll have to aim below him to ensure your ship is below him when it arrives at his ballistic trajectory. As it approaches his descent path, fire retrograde to stop your orbital velocity so that your rescue ship is dropping straight down on the same descent path as the kerbal.

Now you'll have to thrust up/down against gravity to adjust your height and speed to meet up with the kerbal. Might be worth switching back and forth between the kerbal (to use EVA fuel) and the ship (to save dV).

After the join up, your rescue ship will have to have enough dV to reenter an orbit that will prevent burnup.

Again, I've never tried that, but it would be my first attempt. I think the time involved is going to be a big problem depending on where your kerbal is in his trajectory at the save point.

Easy as pi.

EDIT: Maybe make a copy of your current quicksave.sfs or persistent.sfs to allow you more quicksaves while trying to get all this aligned.

I just went back and looked, with only 16 minutes you won't have enough time for all that. Unless he happens to be over the launch pad (or very near it) I don't think 16 minutes is enough time to get another rocket up. If he is over the launch pad, then you could try launching another rocket straight up and adjust the AP to meet up with him. You'll still need a lot of dV to flatten out the approach after intercept.

Edited February 23, 2014 by Claw

[thereaverofdarkness]

Your apoapsis is unimportant. You can survive a direct entry from outside of the Kerbol system if your periapsis is high enough. With a good heatshield setup you should be fine with a skimming periapsis, just so you're hitting the atmosphere at a strong angle. But if you have no heatshield and are coming in with an interplanetary or interstellar speed, you'd want to come in really shallow, probably 25km or higher, barely enough to successfully pull your apoapsis inside the Kerbin system. You can actually be on an "escape" trajectory and dip a ways out of the Kerbin SOI and still fall back in. But all my deadly reentry experienced is based on watching Scott Manley do it.

Hope that helps.

[MarvinKitFox]

Tombles Kerman is on a ballistic trajectory with apoapsis of 1000 km. He's ascending at the moment, after his rocket launched his capsule straight up.

Deadly Reentry is installed. Heatshield is present and can survive the ablation, but the peak decelleration is around 25 G. The capsule barely survives it after Tombles gets killed.

I've tried lowering the apoapsis to 540 km. It does not work, the forces are still too high. Burning sideways at apoapsis, doesn't work. Raising apoapsis and then burning sideways also doesn't work. There isn't much dV left.

I've also tried launching an automated rescue capsule, but I can't rendezvous with Tombles. What can I do to save him?

Lets throw this problem to the mathematicians..

Your current Apo is 1000Km, straight vertical launch from KSC.

You state that you have ability to lower this to 540, this you have about 451m/s of juice left. (this is just after you left atmosphere, right?)

Tombles has a backpack of EVA juice.

Trivial Solution 1) Boost upward with your remaining juice.. new apo is 2871km, you have 2 hours to rescue Tombles. If you launch immediate from KSC, your launch angle is off by less than 5 degrees, easily correctible.

Trivial solution 2) Boost upwards with your remaining juice. Get out, and have Jeb boost upwards for about 350M/s (say 4/5 of an EVA tank). This gives you two WEEKS to go fetch him, and he still has juice in his tank to make rendevous-rescue easy.

2b. When at your 65000 km apo, have Tombles burn sideways with remaining fuel. That puts him in a mostly-stable 65000km x 400Km Kerbin orbit.

Non-Trivial solution 3) Boost up with ship. Boost up with Jeb. Aerobrake around EVE. YES, HE has that much d-v available to him!

(I was going to be snarky and say he should land on EVE, a naked Kerbal can do it, if you land him right at water edge, and on his head... Terminal is only about 63m/s, but I remember you have DR installed. Might fry the poor critter)

Edited February 23, 2014 by MarvinKitFox
fixx ed ref to your Kerbal name.

[brooklyn666]

You can just remove the DeadlyReentry.dll, and leave the rest of the folder. That way the heatshield will stay put, but no DR effects will happen. Once he returns safely, you can put the .dll back.

[LordOfTheOrbits]

MarvinKitFox seems to have calculated that you have about 450 m/s of delta-v left. Assuming that you don't have any lateral speed, you would need to use 1110m/s of delta-v to raise your periapsis to 35km. But kerbin is rotating at 174m/s, so assuming that you only burned straight upwards you only need 936m/s. So after you have burned the 450m/s you have still left 486 m/s to go. You have unlimited dV by simply going out and pushing(don't forget to go back into the capsule to refill), so there should be no problem with that. It will still take some time and you will need to refuel multiple times, but it's definitely possible.