Rescue a kerbal stuck in a inclined kerbin orbit on collision course with the moon??

[MissStabby]

Just accepted my second "rescue a kerbal" contract thinking it was just a simple rendevous and transfer mission in LKO.

I was wrong....

Turns out poor Newdard got himself stuck in a noncircular, inclined orbit that will hit the moon in about 3 orbits after i accepted the contract.

The orbit runs from 11.5k km to 8.2k km high

After flying to him with my small mun rocket made for orbiting the mun, aligning orbits sort of and then beginning a chase to catch up to him, i discovered that after a few orbits the guy encounters the moon and, depending on reloading, gets impacted or slung out of kerbins SOI to go hang out with eve...

So now i'd have to figure out a way to basically fly directly towards him, pick him up and leave the orbit.

I cant accept/do any other missions now because if i do the time i have for the moon impact occurring is reduced.

I got patched conics upgraded and the launchpad and VAB are both level 2 with the science tree somewhere halfway the 90science tier, i got the superlong boosters and long 1.25m tanks though, so i got that going for me...

my current craft is barely capable of matching orbits with the stranded pod doing a hoffman transfer.

here is some more information:

Are there any good ways to intercept towards such a non-standard orbit?

Edited May 11, 2015 by MissStabby

[Trenchfoot]

alt f12?

[cybersol]

I'm not clear on you goals. Are you going back to an old save and wanting to construct a new craft that will save him in time?

[bonyetty]

Moar boosters!

Sorry had to be done. What a pickle you are in and my skills arnt up the to the job.

Possibly post the save as a challenge and ask for a video of the resque. I would like to see it done and give it a go myself.

[FancyMouse]

Inclination on Mun orbit is actually easier to deal with. You don't need a lot more extra dV to handle that (less than 50). But do spare yourself a total of about 5.5km/s vac dV to prepare for rescue maneuvers you would need on Mun orbit.

To get inclined Mun orbit, you can use a maneuver-in-the-middle method:

First get LKO. Next, maneuver to Mun's SOI, with Pe close to the desired orbit. Then (crucial part) in the middle of the eclipse, fire normal or anti-normal to change the inclination - this should be really easy; by properly adjusting both the previous intercept maneuver and this middle maneuver, you should be able to get any orbit you want with little extra dV.

And all these are better handled when you focus view on Mun.

There's another trick of doing rescue missions from orbit. Actually you don't need to match the orbit of your ship with the poor man's. I've done many times to rescue LKO poor mans with a ship staying Ap~100km Pe~70km. The point is, as long as you can get close enough (which requires some dV adjustment) to take control, you can just use EVA jetpack to match your ship's orbit instead. Jetpack is much more powerful than it looks:D, and it saves your dV from your mothership a LOT. You can even just put a hitchhiker there and it effectively scans the whole circular orbit in a few periods and it's really effective batch rescuing.

[MissStabby]

@Cybersol, After i discovered the "curveball" i was thrown with this mission i reverted back to VAB to build a stronger rocket, though also i had to do some other non-ksp things

Gonna try the approach tonight.

@FancyMouse, note that the stuck kerbal is not stuck inside the moons SOI, though it will pass through it in a few orbits, i know about the jetpack trick and have used it in the past a lot, though the range you have to get to is relatively veeeery close when dealing with 10k km orbits.

The biggest challenge is the fact that both the orbit is inclined, the inclination point is nowhere near apoapsis/periapsis, the apoapsis and periapsis vary by about 2900 km and if its not done fast enough my kerbal guy gets to hang out with eve.

Also as a bonus, if i "fail" the mission i have to take a huuuuuge rep and money penalty!

Is there any ways to get more precise info on the orbit specs, ill post them so someone can see place a pod the same orbit in their game.

[tomf]

With 3 orbits this ought to be possible if a little complicted to explain. I would -

Build a rocket with 7500m/s ish deltav

Wait until KSC passes directly through the inclined plane of the target orbit

Launch straight into the correct inclination - instead of rolling due east I would roll somewhere north or south in order to match the inclination. I use Kerbal engineer to tell my my inclination relative to target to help with this but you can eyeball it

Circularize the orbit as low as possilbe

Perfect the inclination

At about the same phase angle as you use for the Mun create a maneuvre node burning prograde until it just touches the target orbit

Drag the node around your orbit until you get an encounter. you will need to adjust the amount of prograde as you drag it round to keep you AP exactly touching the target orbit.

Finely adjust to prograde-retrograde, maneuvre time and inclination to get the closest encounter you can

Make the burn

About half way create another maneuvre node and use it to tweak the encounter

When you arrive at your encounter you will hve a high relative velocity - create another node to match the target orbit to work out roughly how long that burn is going to take.

This ought to get you a close encounter with the target in about a 1/4 of an orbit - plenty of time before the Mun encounter.

[FancyMouse]

ah now I get what you mean - it was an unfortunate orbit to begin with. You would need to reach him within one or two period.

My take for high orbit rescues are, fix inclination in low orbit (including at launch), then go Hoffman, but make Ap slightly inwards, while being slightly behind. Then when reach Ap, circularize, and then do adjustment from there. It took me some trial and error to get it right, but at least it worked for me in terms of precision, and the adjustment shouldn't result in more than half period to reach the rescue point.

Edited May 11, 2015 by FancyMouse

[ElWanderer]

Can you set manoeuvre nodes?

I have a similar rescue on going (it came as a bit of a shock to find a stranded Kerbal so far out), though further out than the Mum's orbit in my case - I don't think I have a collision to worry about. My steps:

Get into LKO.

Target the stranded craft and find which ascending/descending node it'll pass through next.

Set a manoeuvre on your orbit opposite that node and plot a burn out to it. You want the intercept marker to appear bang on the node and for the target craft not to have reached it at that point. If it has gone past, you'll have to aim for the other node.

Right-click the node and advance the burn orbit by orbit until the nearest approach is closest to the intercept. Ideally they'd meet, but this is unlikely.

Play with burn (e.g. add a bit of radial) to change the transit time so that the target craft catches up/is caught by you, until the intercept is within a few km.

Plot a second burn at the intercept point and add a whole bunch of prograde, radial and normal until the orbit you'll go into matches the target pretty closely. I never actually execute this burn as plotted (I do the normal rendezvous of reducing relative velocity whilst pushing the retrograde marker towards the away-from-target marker), but it lets me know what to expect in terms of delta-v and burn time. The good news is that matching inclination out here is much cheaper than doing it in LKO, especially when combining it with the prograde (and radial, as you're unlikely to meet at an apsis) component.

Going from a 100km by 100km orbit to 11.5Mm by 8.2Mm costs 1250m/s, not including any inclination change.

It should then be about 400m/s to drop your periapsis into Kerbin's atmosphere... if low on fuel by then in your case, just reduce the apoapsis to get out of the way of the Mum - you can send up a second rescue craft to meet the first one! But I would have thought that if you can orbit the Mum and return, you'd have enough fuel for this intercept and return, unless you're trying to match inclination in LKO. Your craft (guessing what you have based on the image) has about 3200m/s in the first stages (assuming the liquid engine is off until SRB jettison, which may be a bit hard to manoeuvre) and you have about 2800m/s in the upper stage. If it takes you 4000m/s to get.into orbit, the remaining 2000m/s should be enough.

Doing this without manoeuvre nodes would be a lot trickier. You can burn out to meet at a node visually, but I don't know how you'd calculate when to do the burn so as to intercept the target.

[FancyMouse]

And one more suggestion - replace your pilot pod with a probe. That saves a lot of mass. Ignore this suggestion if you're using RemoteTech.

[MissStabby]

@ Tomf sounds like a solid plan, im definitely going to try that, though is there a way to get a good deltaV estimate without KerbalEngineer?

@Elwandeer yes i have patched conics so i can plan maneuvers, i did a moon trip before i could though, relying on the old pre-maneuver node alpha skills

@ fancymouse It does yes, though it also prevents any SAS from happening so its tedious during launch to get a "perfect" 90 LKO orbit

I could have jeb just leave the rocket as soon as LKO has been achieved though...

Edited May 11, 2015 by MissStabby

[cybersol]

DeltaV is relatively easy, see here:

http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheet

All you need is the full and empty weights for each stage (remove the fuel) and the ISP of the engine (right click menu).

[tomf]

If you have a rocket that can get to the Mun and back then that should be plenty in terms of delta v.

If you can get the octo probe core unlocked that has SAS built in.

[FancyMouse]

@ fancymouse It does yes, though it also prevents any SAS from happening so its tedious during launch to get a "perfect" 90 LKO orbit

I could have jeb just leave the rocket as soon as LKO has been achieved though...

Only the most basic sphere probe doesn't have SAS. All the other one has SAS (including OKTO which you should already have given your R&D tree), it's just its built-in torque that is tiny (usually 0.5 or so), and you'll just need a reaction wheel - a small one gives your the same torque as a pod, while probe+reaction wheel has a much less mass

In fact, IMO probe is really OP - I pretty much use that all the time when I was in stock, and that's one of the reason I switch to RemoteTech to get a realistic nerf for it.