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Rescue from a very high *retrograde* Sun orbit.


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This game is going to kill me. I took the contract, I built a rescue craft of good 10,000m/s, then I began hunting for encounter and I hovered over the descending node. -177 degrees.

screenshot38.png

The girl and her craft need to be rescued from an orbit beyond Jool, that goes in the opposite direction as all the planets.

Can I do it on 10k dV? In reasonable time?

Currently I have two ideas. First, raise my Sun apoapsis a lot, until my orbital speed there becomes manageable, and then just turn around. The other involves Eve flyby, with Oberth maneuver bringing me into a reasonably low retrograde Sun orbit, Then a burn around the Sun to reach the hulk, connected with plane alignment, and finally a burn at the encounter - or somewhere beyond, a bielliptic transfer.

Well, that's not all. I still need to turn the hulk around and bring it back to Kerbin. I'm pondering a Jool assist and again a turn around the Sun - even if I bring her into *any* solar prograde orbit, that will be manageable through a second craft.

Any good suggestions? Comments?

Edited by Sharpy
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Well, the higher up you go, the slower your orbital speed is, I would suggest you get your apoapsis quite high then burn full retrograde until you get into the orbit you want. To get back you might need to send a second rescue mission like you said, however i think it would be easier for you to rendezvous with the first craft if you can first get it in an orbit around any other planet. That way you can get an incounter with the planet and perform the standard redezvous from there. Good luck, Also how much are they paying you?

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Wow that's a tough one! Some of the "Rescue from around the Sun" missions are brutal. As far as options it's going to depend. Is the 10 km/s of dV you mention at Kerbin surface or in LKO? (if it's not a LKO number I don't think even rendezvous will be possible) The biggest problem here by far is getting turned around retrograde, this will be easier at higher altitudes the Eve assist idea probably won't work, basically gravity assists can't typically turn you around though they can make the turn less expensive (oberth) but in that case I recommend doing it at Jool due to Jool's orbit speed around Sun being slower. From there as worir 4 mentions you can probably drop the craft into a Jool capture and make the return to Kerbin much easier.

Although as I say this I am remembering that I have not done aerobraking at Jool since re-entry heat was a thing, that could make the whole plan moot. In that case you will almost certainly need more dV. I'm not sure of the orbital speed of the craft you are rendezvousing with but basically if you go up to a very high altitude and then turn around you usually end up spending between 2 and 1 km/s depending on your patience. I would then guess that the rendezvous will cost about 1.6 km/s dV. (based on estimating that craft's orbital velocity as 3.8 km/s) Going home to kerbin should then be around another 2 km/s though that will bring you in backward and very fast so again reentry could be serious problem.

Those are my thoughts. I may try a bit of a simulation run in a sandbox edition and see what I find. All-in-all it seems like a really interesting challenge.

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No need for anything fancy. A 2200-2300 m/s burn from LKO will raise your solar apoapsis to the right altitude. Time your departure right, and you'll rendezvous with the target ship at the apoapsis. Matching speeds / circularizing to a retrograde orbit should take something like 5200-5300 m/s.

On the way back, it only takes around 200 m/s to get an encounter with Jool, where you can use gravity assists to head back to Kerbin. You could also uses Jool/Tylo/Laythe gravity assists to reach the retrograde orbit, but then it's harder to get a rendezvous in a reasonable time.

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Well, the higher up you go, the slower your orbital speed is,[...] Good luck, Also how much are they paying you?

and the longer the mission takes...

Meager 363,000 out of which 250,000 went for the vehicle already. But it's a living kerbal!

Is the 10 km/s of dV you mention at Kerbin surface or in LKO?

LKO.

1023 left from the launch stage (Mainsail+Orange Tank)

4688 in the first transfer stage (medium MK3 LF + 4 nukes)

5082 in the second transfer stage (small LF fuselages, 1 nuke)

1300 in the rescue unit (LF+Ox, Vernors only.)

Of course the numbers will drop a bit once I dock to the target vehicle. Maybe more than a bit if it's, say, an MK3 cockpit...

I'm not sure of the orbital speed of the craft you are rendezvousing with but basically if you go up to a very high altitude and then turn around you usually end up spending between 2 and 1 km/s depending on your patience. I would then guess that the rendezvous will cost about 1.6 km/s dV. (based on estimating that craft's orbital velocity as 3.8 km/s) Going home to kerbin should then be around another 2 km/s though that will bring you in backward and very fast so again reentry could be serious problem.

2090 to achieve the same altitude. 1847 to stop dead (dead drop into the Sun) 3597 to circularize into the same orbit (and that would be the orbital speed of the target). 141 to match orbital plane.

7700 to rdzv. And then return. That's the straightforward approach... and that's 5 years until encounter at best. I began planning a higher apoapsis, but when I saw "20 years" I gave up on that idea.

I couldn't simulate my Eve flyby, too far, nodes too twitchy. Same for Jool..

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But it's a living kerbal!

I treat the contract expire date being when the kerbal loses all its life support, and I feel good.

Maybe more than a bit if it's, say, an MK3 cockpit...

I thought in Astronaut Complex those kerbals will be listed as "Assigned", and you'll know which unit it is staying in? It will be the game part name, not the friendly name shown in VAB, though, but should be guessable.

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On the way back, it only takes around 200 m/s to get an encounter with Jool, where you can use gravity assists to head back to Kerbin. You could also uses Jool/Tylo/Laythe gravity assists to reach the retrograde orbit, but then it's harder to get a rendezvous in a reasonable time.

The cheapest easy return trip I found was a ~2500 m/s retrograde/radial burn during a very low flyby at Jool. By fine-tuning the maneuver node, it was possible to get a direct Kerbin encounter at the next periapsis, which occurred around 18 years after the maneuver. A bit cheaper maneuver would have led to an Eve encounter, which can be used as a gravity assist to get rid of excess orbital speed.

Edit: On the other side of Jool (approaching the moons head-on), the maneuver only took ~2300 m/s, and the ship descended towards Kerbin immediately after departing from Jool.

Edited by Jouni
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I thought in Astronaut Complex those kerbals will be listed as "Assigned", and you'll know which unit it is staying in? It will be the game part name, not the friendly name shown in VAB, though, but should be guessable.

dammit.

screenshot39.jpg

Deadline is 16 years 388 days.

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Maybe a Jool gravity assist? Jool's gravity is so good that you can escape in a retrograde orbit just from one assist.

Could you please help me doing that ?

No matter how I touch the directions on my maneuvre node I can't put the periapsis at the right position for a gravity slow-down. I know I'm supposed to get it "in front" of Jool (where it's heading relatively to the Sun) but I can't make it. I always end up having it perpendiculary to the velocity vector of Jool, which send me very far in the solar system and still in a prograde orbit.

1436797789-2015-07-13-00003.jpg

1436797791-2015-07-13-00004.jpg

1436797790-2015-07-13-00005.jpg

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Could you please help me doing that ?

No matter how I touch the directions on my maneuvre node I can't put the periapsis at the right position for a gravity slow-down. I know I'm supposed to get it "in front" of Jool (where it's heading relatively to the Sun) but I can't make it. I always end up having it perpendiculary to the velocity vector of Jool, which send me very far in the solar system and still in a prograde orbit.

http://image.noelshack.com/fichiers/2015/29/1436797789-2015-07-13-00003.jpg

http://image.noelshack.com/fichiers/2015/29/1436797791-2015-07-13-00004.jpg

http://image.noelshack.com/fichiers/2015/29/1436797790-2015-07-13-00005.jpg

You have to have your periapse close to Jool, and it has to be on the day side of Jool, as it slows you down. Keep your inclination low enough where encountering it is possible again.
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Thanks for your response. I'm as close as the atmoshpere let me be and I'm keeping my inclination as equatorial as I can.

But I don't know what maneuvre I should do in order to come in the day side. No matter how I'm randomly trying pushing the vectors I always end up on the night side. If I only use Radial/Anti-radial I only get this small difference :

1436799294-2015-07-13-00008.jpg

1436799290-2015-07-13-00007.jpg

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Thanks for your response. I'm as close as the atmoshpere let me be and I'm keeping my inclination as equatorial as I can.

But I don't know what maneuvre I should to in order to come in the day side. No matter how I'm randomly trying pushing the vectors I always end up on the night side. If I only use Radial/Anti-radial I only get this small difference :

http://image.noelshack.com/fichiers/2015/29/1436799294-2015-07-13-00008.jpg

http://image.noelshack.com/fichiers/2015/29/1436799290-2015-07-13-00007.jpg

Try Prograde and Retrograde.
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If you're within the SOI of Jool, just set your direction to radial in, and burn THROUGH the flip to radial-out. If you're not there yet, it's usually a matter of using a combination of radial and prograde/retrograde.

I wonder ... for a gravity assist, would you be better off NOT making a perfect Hohmann transfer, so you come in not parallel to the orbit?

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Personally, I'd just eat the cost of a failed mission and move on.

Agreed. Or rescue her and ditch her vessel.

There used to be a time when you could aerobrake from 50km/s to zero without problems... I'm afraid this may be a thing of the past, but as they say, you won't know until you tried. What do you have to lose?

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Jool's gravity is not strong enough to throw you directly to a nice retrograde orbit. You must use multiple gravity assists (e.g. Laythe -> Jool -> Tylo on the same pass) or burn at Jool periapsis.

Consider my example from the return trip. I started from a retrograde orbit above Jool, and did a Hohmann transfer for an encounter with Jool. The relative speed during the SoI transition was around 8.5 km/s. With Jool periapsis at 220 km, the gravity assist could only bend my orbit by around 90 degrees, which wasn't nearly enough. I had to do a 2.3 km/s burn at the periapsis to end up at a nice prograde orbit (comparable to the return from Eeloo).

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I'm at the mid-course correction. But that doesn't change anything. No matter how I try pushing the vectors, at the mid-course correction or in the Jool's SOI, I can't make it. The orbit goes inside Jool then comes out more or less the same it was before.

For the Hohmann transfer I don't really know. I'm always getting confused at what happen when I'm changing of SOI... What do you suggest ? If it's too far from a Hohmann transfer I'm just gonna end up consumming more delta-V...

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I'm at the mid-course correction. But that doesn't change anything. No matter how I try pushing the vectors, at the mid-course correction or in the Jool's SOI, I can't make it. The orbit goes inside Jool then comes out more or less the same it was before.

For the Hohmann transfer I don't really know. I'm always getting confused at what happen when I'm changing of SOI... What do you suggest ? If it's too far from a Hohmann transfer I'm just gonna end up consumming more delta-V...

Try doing it at a different place and see what happens.
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I'm at the mid-course correction. But that doesn't change anything. No matter how I try pushing the vectors, at the mid-course correction or in the Jool's SOI, I can't make it. The orbit goes inside Jool then comes out more or less the same it was before.

You'd have to do some insane wizardry with multiple nodes to do it just by flybys. Gravity assist alone is insufficient. You must perform an Oberth maneuver - a serious, strong burn near Jool periapsis, most likely with a large Anti-radial component, probably a good few thousand m/s. It's costly but it's less costly than doing this in open space - first Jool gravity assist does help (a bit), then the dV spent at periapsis converts to much larger orbit changes than spent "out in the open".

Essentially, perform a burn for encounter - with all the radial and normal components required - but do it at a periapsis (or near) - and it will be far more efficient.

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Hmmm things are getting confused here.

My very first problem is that I do a gravity slingshot instead of a gravity breaking because my approach is incorrect and no matter how I try I can't correct that.

I'm not even on the stage of orbiting retrograde.

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