Rescue from a solar retrograde orbit?

[uncle_jew]

Hello,

I have a contract to rescue a kerbonaut from an elliptical Kerbol orbit (periapsis near the Kerbin oribit, apoapsis behind the Dres orbit). Only after accepting it, did I learn that the he was in a [B]retrograde[/B] orbit around Kerbol.

Are there any "smart" options to rescue him without needing crazy amounts of delta-v? Rescuing him near the periapsis would need 14-16km/s of delta-v just to reverse the orbit direction, pick him up and reverse the orbit direction again. I understand I can pull this off by strapping an external command seat to an ion drive, but are there any tricks with orbital mechanics that would let me accomplish the mission with chemical rockets?

I hate the ion drive, because it is so slow, even with the 4x physics warp I would have to wait for almost an hour to get the desired delta v.

[Temstar]

Multistage deep space nuclear rocket and/or [url=https://en.wikipedia.org/wiki/Bi-elliptic_transfer]bi-elliptic transfer[/url] might get you the necessary delta-v. It will take one extremely unwieldy spacecraft and extremely long time to complete the maneuver though. Once you match orbit with his spacecraft you can probably work out an encounter with Kerbin directly without reversing orbital direction again, bring many many layers of heat shield because you will be coming in hot.

It's probably better to write him off and just eat the rep damage.

I like to know how he got into that orbit in the first place. Basically whatever put him there in retrograde kerbolar orbit, that's what you need to recreate to get him back. Edited November 18, 2015 by Temstar

[kerbiloid]

1. Persistent Thrust mod allows to use ions when time warp is on.
[url]http://forum.kerbalspaceprogram.com/threads/133735-WIP-1-0-5-PersistentThrust-v1-0-4-alpha[/url]
Of course, the flight lasts for years.

2. You can launch a ship onto an orbit around Sun with very large apoapsis. Near its apoapsis you can easily turn the velocity direction for 180 degrees, this will cost just hundreds of m/s for you.
It would require less energy than a direct flight from Kerbin with but also requires some years of time and still much energy or an Oberth maneuver near a massive planet.

3. You can correct your retrograde orbit to pass close a massive planet to be thrown away from Sun. Being enough far from Sun you would change your orbit direction - as in p.2.

4. You can use KSPInterstellar Extended mod or USI Nuclear Rockets mod to create a nuclear tug with high delta-V.

5. You can send a light solar sail (SolarSailNavigator mod [url]http://forum.kerbalspaceprogram.com/threads/119579-WIP-1-0-5-SolarSailNavigator-v1-0-6-alpha[/url] , or still KSPInterstellar-Ext) with a relatively small rocket, attach it to your ship and return, using PersistentThrust named above. Also you can attach this part to any ship as a rescue measure.

[eddiew]

You can use HyperEdit to make him orbit prograde ¬_¬

Dirty, but tbh when the game throws contracts at you that are highly impractical, it doesn't seem totally cheaty...

[Seajay]

[quote name='Temstar']Once you match orbit with his spacecraft you can probably work out an encounter with Kerbin directly without reversing orbital direction again, bring many many layers of heat shield because you will be coming in hot.[/QUOTE]

Have you ever tried this (I haven't)? I think you would be coming in at ~21k m/s (Kerbin orbital speed of ~9k + escape velocity ~3k + your orbital speed ~9k(depending on the orbit you're rescuing from)). No way are you going to aerocapture at that speed and for the sort of engines you would need for a deep space mission like this you aren't going to be able to complete your capture burn in less than a couple of hours which means no significant benefit to doing it near a planet. That means coming back the same way you went out (probably a gravity assist from Jool to give you a highly elliptical, easy reversed orbit).

Out of curiosity, does the game know that this is hard and offer a correspondingly high reward or is it a similar contract value to any other Kerbol rescue? Edited November 18, 2015 by Seajay

[cantab]

You may be able to snag a Jool gravity assist to help a lot, or even multiple assists to get the desired result. Time could be an issue though, check the contract doesn't expire too soon.

Otherwise, yeah, ions. Make sure it doesn't jitter too much in Hold X mode on the SAS, then watch a film or something while your burns run.

[Oafman]

That contract is ridiculous. I'm in the hyperedit camp

[BenCushwa]

The killer for this probably isn't the deltaV you'd need, it's likely the time limit on the contract. It's relatively easy to get into a retrograde orbit without gobs of deltaV, but it can take quite a long time to do.

One could say an astronomically long time. Ba dum bum....

(Sorry, I couldn't resist.)

Unless the contract has an obscenely long duration you're likely stuck with the high deltaV or HyperEdit options. A Jool gravity assist may help, but getting the [I]right[/I] assist would be tricky.

[Racescort666]

I have a similar contract and I was wondering what people would suggest for it. I have been considering hyperedit for a while and this thread confirms it. The challenge of doing seems like fun except I have a bunch of other stuff to do in career mode.

[diggzakk]

[quote name='kerbiloid']1. Persistent Thrust mod allows to use ions when time warp is on.
[URL]http://forum.kerbalspaceprogram.com/threads/133735-WIP-1-0-5-PersistentThrust-v1-0-4-alpha[/URL]
Of course, the flight lasts for years.

2. You can launch a ship onto an orbit around Sun with very large apoapsis. Near its apoapsis you can easily turn the velocity direction for 180 degrees, this will cost just hundreds of m/s for you.
It would require less energy than a direct flight from Kerbin with but also requires some years of time and still much energy or an Oberth maneuver near a massive planet.

3. You can correct your retrograde orbit to pass close a massive planet to be thrown away from Sun. Being enough far from Sun you would change your orbit direction - as in p.2.

4. You can use KSPInterstellar Extended mod or USI Nuclear Rockets mod to create a nuclear tug with high delta-V.

5. You can send a light solar sail (SolarSailNavigator mod [URL]http://forum.kerbalspaceprogram.com/threads/119579-WIP-1-0-5-SolarSailNavigator-v1-0-6-alpha[/URL] , or still KSPInterstellar-Ext) with a relatively small rocket, attach it to your ship and return, using PersistentThrust named above. Also you can attach this part to any ship as a rescue measure.[/QUOTE]

should it be enough to start the rocket in the other direction than normal to have the retrograde orbit initially? just thinking, dont know if this would be helpful Edited November 19, 2015 by diggzakk

[MaxL_1023]

The best way I can think of to get to a retrograde orbit is to encounter jool in such a way as to pass just in front of it, getting a reverse gravity assist. Make a burn at Jool Perapsis (you will be travelling due retrograde relative to the sun) and you should be able to match the solar perapsis you need. Then, match orbits at your Kerbol PE. 3 Burns (Jool Transfer from Kerbin, Jool PE and then your orbit matching burn).

Time might be an issue here however.

When in doubt, strap a seat and a couple gigantors to a xenon tank and ion engine, then fly by Eve to save delta-V and kill some of your horizontal velocity. Eve can probably come close to throwing you retrograde on its own if you skim the atmosphere.

[Kryxal]

I'd say, take a nuke craft with drop tanks, and an ion upper stage. If you worry about debris, drop the drop tanks into Jool and save enough fuel in the nuke section to run into something.

[FancyMouse]

[URL="http://forum.kerbalspaceprogram.com/threads/128510-Rescue-from-a-very-high-*retrograde*-Sun-orbit"]Previous discussion[/URL]

[Kerbart]

Yeah, I was offered an orbit like that. The 179° inclination made me think... "I'm declining it!"

The would-be hit on my rep [I]then[/I] made me think "I'll let it expire!"