Another "How to dock"-Question... But not that simple

[Tokay Gris]

YES! I need some tips.

Or the confirmation that what I am trying to do ist nearly impossible.

And the problem is not one of docking (I can do that), but one of rendevous.

And while it is technically a rendevous in orbit, it is a rendevous in a Hohmann-orbit.

I am planning a mission to Jool. After some calculations based on my ship, I found out that getting there is no problem. STAYING there (i.e. getting into orbit) requires some tricks. Either aerobraking, gravitational breaking or both. AND even if this works, the delta-V to get back could be not enough.

So: Is it possible to send a tanker along with the actual vessel, rendevous (and dock) in transit?

I imagine that it would be quite easy, IF I could send them at the same moment. Which I can't.

Hm... maybe I can try to tackle it like there was no gravity. Orbits of that size (i.e. transfer orbits) look pretty straight, if looked at on a closer scale. AND I have quite a long time to get it to work. Haven't checked, but the transfer to Jool should be well over a year.

Any ideas and/or tips on this?

Can't try that right now myself. Thursday at the earliest. Anyone tried that so far?

[Pursuedtank]

It would be very difficult to do that, you would be better off docking while in orbit around Kerbin or Jool.

[Awaras]

Yes, unless you launch the vessels very quickly one after the other on the exact same trajectory (which is very, very difficult), you will probably waste a great deal of fuel getting them to meet up. Just do your rendezvous and refueling once you get to where you are going.

[Tokay Gris]

At Kerbin is no use. The ship is filled up to the brim.

And docking at Jool still leaves the problem of how to get into orbit there. That could be the solution though. But essential to that would be that the aerobraking works as planned.

And I have no idea so far how to actually PLAN that. I can only try... But (except for excessive usage of the quicksave) it has to be on the first try.

Hm... can I somehow really "save" the quicksave? Copy it to some other place? That would include the persistence file as well, I guess. That could be said to be cheating (on myself), but to start from scratch after a failed attempt is not really an option, not with those rare transfer windows.

[MBobrik]

go for aerobraking. saves almost all fuel.then dock on jool orbit

[Tokay Gris]

Yes, that will be the way I do it. Thursday, that is. Those 2600 m/s give me headaches.

[Tokay Gris]

IF I can save 1200 m/s by aerobraking, I am in an orbit around Jool.

IF I can save the whole 2600 m/s, I'd have 1400 m/s left to get back. Of course not enough.

BUT the weight of my vessel will be about half of what it was, since I plan to leave four probes around Jool and it's moons.

That should give me roughly 2800 m/s (if my halfassed maths are even in the ballpark). And THAT should be enough to get back to Kerbin. (calculated to be 965 + 950 for the way back and about 1000 for braking back into orbit (is that number mission on the usual delta-V chart?).

Hm... But the Calculator (http://ksp.olex.biz) gives an ejection burn from Jool with around 2800 m/s. That would mean I am left without any to brake into Kerbin orbit....

[Stochasty]

You don't brake into Kerbin orbit. You just land. Let the air do all the hard work of stopping you.

[Tokay Gris]

Can't.

The vessel is space-only. No landing capacity.

The idea of that vessel was an interplanetary tug. So I build it that way. It did lift once. But will never do so again.

So it seems there is no way around either packing more fuel or sending a tanker to Jool as well. The latter is what I will most likely do.

[MBobrik]

The vessel is space-only. No landing capacity.

.

You've got some landers, right ? there is a chance that your Laythe lander could land on Kerbin as well. So if you just move all your kerbals there, decouple from the rest of the ship, you can proceed with the landing normally.

.

And if not, you can still aerobrake into kerbin orbit with minimum delta-v, dock your landing capsule there and land.

Edited May 20, 2013 by MBobrik

[Tokay Gris]

No landers planned on that mission. Just probes to orbit.

[MBobrik]

then aerobrake at kerbin too. should save you most of the fuel.

[capi3101]

How are you on RCS? You could still aerobrake at any point and use RCS thrust at the apoap to put the periap above the atmosphere. It's what I've got on my interplanetary tug (and like yours, it's not designed to land).

Got a similar problem at this point - sent Jeb to Eve by mistake, standard lander so no landing there, so I shot for Gilly and missed; wasted a hell of a lot of fuel and now a return is looking unlikely, so I thought I'd send a resupply mission to rendezvous. Possible? Yes. Difficult? Better believe it.

[Stochasty]

Can't.

The vessel is space-only. No landing capacity.

Everything is air-droppable at least once.

[HoY]

I built a space only ship the other day... The TWR was abysmal so when it returns from its first jool run and arrives at kerbin I have a new payload for it that docks and de orbits it, includes landing gear and TONNES of chutes. Quantum struts needed of course . I'll post a couple pics tonight if you want some ideas

[Tokay Gris]

RCS.... Weeeell. I do have RCS. And a big tank for it.

BUT! I thought I'd only need it for quick orientation changes. So I only have the small "snap anywhere" (or whatever the name was) on...

[capi3101]

You'd be amazed what you can accomplish with those little RCS blocks. A couple of quick puffs forward or backwards (H-key or N-key) with as few as four RV-105s (the multi-directional Apollo Service Module blocks) can raise or lower an apsis by a kilometer or more, if you apply them at the right time. As for reorienting your craft, try shutting both RCS and SAS off and turning on torque only. You'll need to be patient if your craft has a lot of mass, but it'll save on RCS fuel. Use RCS to re-orient only in an emergency (like if you absolutely have to have to have to have your ship pointing in X direction right that moment or you'll miss a transfer burn, stuff like that).

[PaleoGamer]

Strongly agree with this. I managed to strand myself in this orbit without fuel in my main tank. (Check my resources) I was able to get it back to Kerbin and land within sight of the Space Center using just my RCS thrusters. To be fair, it took like 5 minutes of thrusting at apoapsis but it worked.

[Tokay Gris]

That's the problem: I didn't install RCS-blocks. Just the single ones.

The idea was that I'd only need them for quick orientation changes. Slow ones I do with SAS-torque.

Well, next time, I'll put the thruster blocks on instead.