The Death Dive

[Talavar]

  I recently started playing KSP again. Ive collected lots of data from the Jool system, and Jebedia is ready to come home.. however... i have a problem.. I flew through the system in a way that would cause my orbit to slow around the sun while I was collecting my data (used slings to get from one moon to the next to grab data from high over a few moons) Anyway, my ship comes out the other side of the jool system and is falling to kerbin, just as I had planned... I have 978 DV left in my engine, and I can set my rendezvous with kerbin using only about 210 of it.  My problem is.. Since I'm falling basically straight to kerbin, my relative velocity is roughly 11-12k KPS when I get there.. I have a heat sheild that is 2.5 which is actually a size larger than my return capsule (All my data is collected and stored in the capsule, I knew it was going to be tricky on the return so I took all experiments and ditched the equipment in space) .. Anyway.. Soon as I hit around 67k periapsis on kerbin, my ship blows up immediately.. I was wondering if anyone else had managed to get in this situation, and if they had a good remedy for the entry rather than a rescue mission. Cheers!

[Waterlimon]

Can you do some aerobreaking passes to form a less energetic orbit around kerbin before finally landing?

If even that is too fast (ie cant slow down enough to actually stay in kerbin system after first pass thru atmo), then idk. Maybe pull some crazy maneuvres using the moons?

[Mr. Peabody]

I'm guessing your re-entry was far too steep. In situations like this it is important to aerobrake slowly on a shallow angle. If you had fuel left, you could also have used careful rocket burns to slow down before aerobraking.

[Talavar]

8 minutes ago, Waterlimon said:

Can you do some aerobreaking passes to form a less energetic orbit around kerbin before finally landing?

If even that is too fast (ie cant slow down enough to actually stay in kerbin system after first pass thru atmo), then idk. Maybe pull some crazy maneuvres using the moons?

 I already thought of that one. However, the game is saved after my exit of jool.. All i have to work with are the moons of kerbin, and they are respectively left and right of kerbin at my entry point. and they don't have enough gravity to hold me close to the surface to do a complete 180 whip maneuver to launch me back out.. although that would probably just end up giving me more delta-V to deal with.

3 minutes ago, The Dunatian said:

I'm guessing your re-entry was far too steep. In situations like this it is important to aerobrake slowly on a shallow angle. If you had fuel left, you could also have used careful rocket burns to slow down before aerobraking.

  nah. my periapsis is at 67k. my ship still explodes at that shallow of a dip.. My speed is causing some MAJOR g's and heat as soon as I touch the atmosphere.. lol.. I tried burning all my fuel.. that brings me closer to 11 kps. but it's still exceedingly too fast.

Edited August 9, 2017 by Talavar

[Waterlimon]

3 minutes ago, Talavar said:

 I already thought of that one. However, the game is saved after my exit of jool.. All i have to work with are the moons of kerbin, and they are respectively left and right of kerbin at my entry point. and they don't have enough gravity to hold me close to the surface to do a complete 180 whip maneuver to launch me back out.. although that would probably just end up giving me more delta-V to deal with.

In KSP saves folder, theres 5 (by default) autosave backups. That might be far enough to take you back to an earlier point. I dont know how to actually access them since theres no ingame way to load autosave backups (I assume you just replace some main save file or move the backup to the regular saves folder - but dont do anything without looking up exactly how, and even then backup the folder before trying anything)

Edited August 9, 2017 by Waterlimon

[Talavar]

 

1 minute ago, Waterlimon said:

In KSP saves folder, theres 5 (by default) autosave backups. That might be far enough to take you back to an earlier point. I dont know how to actually access them since theres no ingame way to load autosave backups (I assume you just replace some file or move it to the regular saves folder - but dont do anything without looking up exactly how, and even then backup the folder before trying anything)

 Hmm.. I don't want to go too far backwards.. that will take the fun out of having to deal with the outcome.   .. I can always do a rescue if I must.. I was just seeing if anyone had any suggestions.

[Mr. Peabody]

Just now, Talavar said:

Hmm.. I don't want to go too far backwards.. that will take the fun out of having to deal with the outcome.   .. I can always do a rescue if I must.. I was just seeing if anyone had any suggestions.

Something tells me docking with a craft orbiting that fast is going to be interesting. You may need quite a large rocket to dock and then slow down for re-entry.

[Waterlimon]

The only remaining option is to use kerbin to alter your trajectory (without landing), bounce around the system a little more, and hope the second intercept is both possible and slow enough.

[Talavar]

Just now, The Dunatian said:

Something tells me docking with a craft orbiting that fast is going to be interesting. You may need quite a large rocket to dock and then slow down for re-entry.

 yeah, if i let it slide past kerbin and orbit the sun.. it takes roughly 7500-8000 DV just to launch and dock with it and that is at it's apoapsis near jools orbit.. Atleast that's the calculation that I keep ending up with. Then I'll need a few thousand to get it into a more circular orbit that matches up with kerbin.. lol

1 minute ago, Waterlimon said:

The only remaining option is to use kerbin to alter your trajectory (without landing), bounce around the system a little more, and hope the second intercept is both possible and slow enough.

 Already looking at my options with this one. I may be waiting for Jool to return... lol

[MythicalHeFF]

I had an experience like this a long time ago. Unfortunately, at over around 8-9 km/s, your heat shield will always overheat and you will die no matter what your periapsis is. So yeah, you'll have to send a rescue mission, unless you want to cheat and turn off reentry heat. My rescue vessel needed 14 or so km/s of dV to intercept the shipwreck and slow down before reentry. I'd recommend using asparagus staging on your nuclear stage (only 1 engine). It's very slow, but it will save you.

Good luck 

[ZooNamedGames]

If you always end up early/late with the moon's ahead/behind you, try burning radial/anti-radial early in your burn and try to delay your arrival to the Kerbin system. Make take up to 20, 30 tries but eventually just play around with the amount of fuel used to get an encounter with the mun/minmus, hopefully a free return trajectory.

[Talavar]

Here's a shot of my situation.. lol..

7 minutes ago, Jack Joseph Kerman said:

I had an experience like this a long time ago. Unfortunately, at over around 8-9 km/s, your heat shield will always overheat and you will die no matter what your periapsis is. So yeah, you'll have to send a rescue mission, unless you want to cheat and turn off reentry heat. My rescue vessel needed 14 or so km/s of dV to intercept the shipwreck and slow down before reentry. I'd recommend using asparagus staging on your nuclear stage (only 1 engine). It's very slow, but it will save you.

Good luck 

 Don't have the nuclear engine yet.. lol.. I was planning on unlocking it after returning from this mission.

 

5 minutes ago, ZooNamedGames said:

If you always end up early/late with the moon's ahead/behind you, try burning radial/anti-radial early in your burn and try to delay your arrival to the Kerbin system. Make take up to 20, 30 tries but eventually just play around with the amount of fuel used to get an encounter with the mun/minmus, hopefully a free return trajectory.

Too late on my save for this one. I could try something after orbiting the sun once though.

[regex]

25 minutes ago, Talavar said:

Here's a shot of my situation.. lol..

Welp.

I mean, seriously, your only option is to do it incrementally, and it's going to take forever, if you can do it at all. Maybe try setting up a slingshot for a braking pass or raising your periapsis away from the sun.

[Talavar]

Anyone know what the absolute lowest possible peri is around the sun? I'm trying something.. lol
 I was just saying that regex.. lol

Edited August 9, 2017 by Talavar

[adsii1970]

Just now, Talavar said:

Anyone know what the absolute lowest possible peri is around the sun? I'm trying something.. lol

Hmmm, cooking Kermen, are we?

[Talavar]

4 minutes ago, adsii1970 said:

Hmmm, cooking Kermen, are we?

Edited August 9, 2017 by Talavar

[Cpt Kerbalkrunch]

@Talavar, you need to use Eve, Kerbin, or Jool for a gravity assist. Any one of them can dramatically alter your orbit. I have survived an 8km/s reentry, but any more than that results in almost immediate death; no matter how shallow your angle. Check the Retro Solar Rescue on the Challenges subforum (on my phone, so not sure how to link it). You'll see some pretty amazing gravity-assist wizardry on there. Good luck.

 

[Talavar]

2 minutes ago, Cpt Kerbalkrunch said:

@Talavar, you need to use Eve, Kerbin, or Jool for a gravity assist. Any one of them can dramatically alter your orbit. I have survived an 8km/s reentry, but any more than that results in almost immediate death; no matter how shallow your angle. Check the Retro Solar Rescue on the Challenges subforum (on my phone, so not sure how to link it). You'll see some pretty amazing gravity-assist wizardry on there. Good luck.

 

 I've gotten pretty good with GA's, My problem on this one was that I didn't anticipate the speed at which I'd be entering Kerbin. lol

 I decided to go with a typical rescue.. I circularized the orbit as much as I possibly could and Im planning a rendezvous as we speak.

[MythicalHeFF]

33 minutes ago, Talavar said:

 I've gotten pretty good with GA's, My problem on this one was that I didn't anticipate the speed at which I'd be entering Kerbin. lol

 I decided to go with a typical rescue.. I circularized the orbit as much as I possibly could and Im planning a rendezvous as we speak.

Yeah, a ridiculously low periapsis around Kerbol results in some pretty stupid re-entry speeds. The fastest I ever did was 9.5 km/s, and my periapsis was only just below Moho's! 

 Good job circularizing

Disappointed that we aren't cooking Kerbals anymore though.. 

 

[Talavar]

1 minute ago, Jack Joseph Kerman said:

Yeah, a ridiculously low periapsis around Kerbol results in some pretty stupid re-entry speeds. The fastest I ever did was 9.5 km/s, and my periapsis was only just below Moho's! 

 Good job circularizing

Disappointed that we aren't cooking Kerbals anymore though.. 

 

 lol.. they are still cooking. I only slightly circularized. Kerbol Per is 1.5 mill. My apo is still halfway between Duna and Jool. Meat is STILL on the menu! .. It's a good thing I had that oblator shield. Otherwise there would have been nobody left on the ship to actually eat the meat.. lol.. Still gets pretty hot in there when near Kerbol!

[Cpt Kerbalkrunch]

1 hour ago, Talavar said:

 I've gotten pretty good with GA's, My problem on this one was that I didn't anticipate the speed at which I'd be entering Kerbin. lol

 I decided to go with a typical rescue.. I circularized the orbit as much as I possibly could and Im planning a rendezvous as we speak.

Good deal. Rescues are always fun. Especially when I cut it too close and need a rescue for the rescue. 

[Human Person]

Forget about reentry. Get to 8 km/s and it becomes possible. I'd. Try to do a gravity assist instead and come down on another pass.

[Talavar]

On 8/9/2017 at 4:00 PM, Physics Student said:

Forget about reentry. Get to 8 km/s and it becomes possible. I'd. Try to do a gravity assist instead and come down on another pass.

I managed to attach to it and slow it down to about 8300. It took a few reloads on the re-entry, but I got it after about 4 tries. Jebediah lives on! .. Thanks for all your feedback everyone.

[purpleivan]

On 09/08/2017 at 7:43 PM, The Dunatian said:

Something tells me docking with a craft orbiting that fast is going to be interesting. You may need quite a large rocket to dock and then slow down for re-entry.

I've done something similar, although at not as high a velocity, with a vehicle returning from Jool. In it's case I just didn't have sufficient fuel on the vehicle to get it closer than a few thousand km away from Kerbin as a return orbit, leaving it zooming past at about 4.5km/s.

The fix I chose was to launch a fuel transfer vehicle I had at my Minmus fuel mining base towards the incoming vehicle, dock with it and transfer what fuel was left on the rescue vehicle and then adjust my Jool vehicle's incoming trajectory.

So a similar problem, just not as extreme as the OP, although my rescue vehicle wasn't designed for the purpose and could have been a much more efficient deliverer of fuel.

[Snark]

17 hours ago, Talavar said:

I managed to attach to it and slow it down to about 8300. It took a few reloads on the re-entry, but I got it after about 4 tries. Jebediah lives on! .. Thanks for all your feedback everyone.

Woot!  Glad it worked out for you. 

If you'd been looking to get the most bang for your buck out of your 978 m/s of dV, and if you were patient (i.e. willing to wait a few kerbal years to get home), I might have suggested this:

• Burn most of your dV out at Jool's orbit, solar-prograde, so as to lift your solar Pe as much as you can.
  • Ideally you'd lift it right up to Kerbin's orbit, so that it's tangent to it.
  • You probably can't-- a little poking at the vis-viva equation tells me that to have a Pe down at Kerbin's orbit, you'd need to have a solar orbital velocity of about 2400 m/s out at Jool's distance from the sun, and with your Pe so low right now, I'm guessing your solar orbital velocity upon ejection from Jool is a whole lot less than 1000.  So you probably don't have enough dV to manage a Kerbin-tangent orbit.
  • However, you can probably lift it a lot of the way (especially if you can manage to do much of your burn down close to Jool, to maximize Oberth effect).  This will greatly reduce your Kerbin-relative speed upon reentry.
• This will get you a good geometry for intercept... except likely Kerbin will be in the wrong place when your orbit crosses Kerbin's.   And at this point you will have only a tiny sliver of dV remaining.  So what you do is to prepare a burn at solar Pe, and use the multiple-orbits-ahead planning trick with maneuver nodes so that you can do a tiny burn on your initial periapsis so that you can get a Kerbin intercept several orbits after that.  Plan enough orbits ahead, and you can probably get an intercept with only a very small investment of dV.

Just my two cents, for future reference.