Rescue Before Crashing into Mun?

[sardia]

I have a rescue mission at the bottom left, which has a PE in the mun, which mean it's gonna crash.  I have a nerv vehicle which I originally planned to return to kerbin, but this mission looks awfully hard. Are rescue missions suppose to get this hard?

Edited May 5, 2016 by sardia

[LameLefty]

52 minutes ago, sardia said:

I have a rescue mission at the bottom left, which has a PE in the mun, which mean it's gonna crash.  I have a nerv vehicle which I originally planned to return to kerbin, but this mission looks awfully hard. Are rescue missions suppose to get this hard?

They can be, yes. I've had the same kind of contract pop up in my current save. The trick is to use a very light, very high-thrust, very high-dV rescue vehicle to match trajectories with the target, transfer over the kerbal and then bug out ASAP. That is, after you get the rescue-ee onboard, burn radially to move your Pe to a low but survivable altitude (like say 10km - 15 km at least) to miss the Mün, then decide what you want to do next. Usually it's easy enough to blow past the Mün's SOI back into high Kerbin orbit and then plan your return.

[sardia]

Was the game assuming I was gonna attempt a rescue from my ship from the mun? Or was it assuming I could have rescued it by launching a fast ship from Kerbin? I did manage to rescue him. I did a pretty much direct burned to him, roughly 2000 delta v.

[Pecan]

Just now, LameLefty said:

...The trick is to use a very light, very high-thrust, very high-dV rescue vehicle...

Ay, there's the rub [Hamlet]
Light, high-thrust AND high dV - well It's like the old, "we want it quickly, cheaply and good", you can usually choose any two you like but aren't likely to get all three.
As LameLefty implies though, you can do the rescue in more than one phase - snatch that thing away from the imminent crash (light, high thrust) and then rescue the rescue (high thrust, high dV).

[LameLefty]

14 minutes ago, Pecan said:

Ay, there's the rub [Hamlet]
Light, high-thrust AND high dV - well It's like the old, "we want it quickly, cheaply and good", you can usually choose any two you like but aren't likely to get all three.
As LameLefty implies though, you can do the rescue in more than one phase - snatch that thing away from the imminent crash (light, high thrust) and then rescue the rescue (high thrust, high dV).

Actually, it's not that hard to do: big fuel tanks, big engines, no scientific payload, minimal equipment, minimal heat shield, etc. Launch a single Mk1 capsule with a probe on top and a parachute on top of that; big-engined transfer stage with a matching large fuel tank; and a booster segment with 2-4 strap on side boosters. Mainsail-powered liquid fueled rockets gives you much better ISP than solids and even though nukes give better ISP, their low T/W ratio may be counterproductive for a time-sensitive rescue mission. You ought to be able to get anyway from 6700 - 7500 m/s dV out of a stack like this pretty easily. Burn hard for an intercept, match velocities at the closest approach, then once out of the Mün's SOI, burn at or near Ap to bring your Pe back down to 32km or so for recovery.

But now the rub: depending on the payout on the contract and any strategies you have in place, the cost of the launch vehicle may well be a big chunk of your return.

[Pecan]

Just now, LameLefty said:

...Mk1 capsule with a probe on top and a parachute on top of that; big-engined transfer stage with a matching large fuel tank; and a booster segment with 2-4 strap on side boosters.

:-) I know what you mean, but that hardly describes "light".

[LameLefty]

Just now, Pecan said:

:-) I know what you mean, but that hardly describes "light".

Well, perhaps I should've been more precise: "a very light rescue capsule boosted by a launch system with a very high thrust/weight ratio."

[Venusgate]

I'll just leave this here:

 

[bewing]

Heh. In these sorts of situations, all I aim for is a high-speed flyby of the doomed ship. Take some little (very light) unmanned satellite kind of ship, and burn for a 2.2km close approach.

When the rendezvous happens, EVA the kerbonaut from the doomed ship ASAP, and they can use their own jetpacks to do the first half of their own rescue. Once they are in LMO, they are much easier to collect.

[Quasar]

These days I put a spare seat on every one of my orbital satellites. They weigh barely anything and I just *know* sooner or later it's going to come in handy (or more pessimistically, I'll get a mission like this perfectly lined up with one of my old seat-less satellites).

[Wemb]

8 hours ago, bewing said:

Heh. In these sorts of situations, all I aim for is a high-speed flyby of the doomed ship. Take some little (very light) unmanned satellite kind of ship, and burn for a 2.2km close approach.

When the rendezvous happens, EVA the kerbonaut from the doomed ship ASAP, and they can use their own jetpacks to do the first half of their own rescue. Once they are in LMO, they are much easier to collect.

This - there's nothing stopping you flying two missions - one to stop him crashing and the other to bring him home.  

Wemb

[sardia]

17 hours ago, bewing said:

Heh. In these sorts of situations, all I aim for is a high-speed flyby of the doomed ship. Take some little (very light) unmanned satellite kind of ship, and burn for a 2.2km close approach.

When the rendezvous happens, EVA the kerbonaut from the doomed ship ASAP, and they can use their own jetpacks to do the first half of their own rescue. Once they are in LMO, they are much easier to collect.

That's actually what I did.

I was curious ifa ship from Kerbin could make it to the moon before the rescue pod crashed into they Moon. The window doesn't look bigger than 12 hours. 

[bewing]

You'd need about 30km/s of dv (with high TWR) to get there just before it hits the ground, plus perfect maneuvering. I don't think it's possible.

But (to answer your original question) I do not think that the contract system has the ability to figure out how "hard" a contract is going to be. I really doubt that the intention was to create a suborbital trajectory, when it generated that random orbit.