Trouble with Minmus-centric satellite contract

[The Science Bucket]

I'm still learning the finer points of orbital maneuvers and I accepted a satellite contract out at Minmus that required the vehicle be in line-of-site with a ground station on the moon. I got out there, got inclination, AP and PE correct and I'm just out of line-of-sight range of the dish on the ground. I know Minmus spins pretty rapidly, should I just fast forward a few orbits until that base comes in sight and wait my ten seconds? Or should I mess with my AP or PE to speed up or slow down the orbit?

I'm perfectly circular now, dead on the contractual orbit so I don't really want to deviate from that. Any maneuvers I make cause my orbit to become out of round. Then I waste gas trying to make a bunch of tiny 1 second burns. Can I point directly at (or away from) the pink target marker and retain my circular orbit by thrusting straight out or in from Minmus... sort of like during a rendezvous? I've only got about 25-30% fuel in the tanks and don't want to waste it by taking 3 steps forward and 2 steps back. I'd like to nail this as it's a $240K payoff.

Thoughts? Thanks!

Edited June 16, 2015 by The Science Bucket

[Prepper-Jack]

Minmus, as you say, spins fast. Usually this can be resolved by a quick time acceleration, though if your circular orbit is near-synchronous it can take a while. Synchronous orbit for Minmus is 357.94 km. How long it takes you to get in sight of your target depends on how far you are from that spot. If you're very close to that specific orbit, you'll want to burn either prograde or retrograde (depending upon where the ground spot is), then loop back around and fix the orbit. At Minmus, this shouldn't take more than 100 dV.

[The Science Bucket]

Cool thank you. I'll keep trying.

[Snark]

What's the text of your contract? Is it "Put a satellite in a synchronous orbit of Minmus"?

Reason I ask: In my experience, the only times a satellite contract ever gives me a condition of "must have LOS to a particular location on the ground" is when it's a synchronous orbit. This means that if you have successfully gotten to the orbit, you're rotating in lockstep with Minmus, and waiting a few orbits won't really help you.

If that's the case, however, it's pretty easy to fix (especially at Minmus, where the orbital velocities are really low and it takes vey little dV to make an adjustment). The following advice assumes that you are indeed on a synchronous orbit, that you have already successfully matched the orbit, and that the only problem is that you don't quite have LOS to the target point on the ground. If that's the case, you need to do one of two things, depending on which direction you're too far from the LOS point.

If you're too far east from the LOS point:

1. You're too far ahead of the LOS point. You need to fix this by slowing down a little to let the surface catch up to you

2. To do this, make a small prograde burn. Anywhere on the orbit will do. Doesn't have to be big, say; something that will raise your orbit (on the opposite side from where you make your burn) by 10-20% or so.

3. Wait an orbit (or two, or three; whatever it takes). With each orbit, Minmus will rotate a bit faster than you, and the LOS point on the ground will catch up to you.

4. After you have completed enough orbits to get LOS, set a maneuver node at the same place where you originally did your prograde burn. This time you burn retrograde, by the exact same amount that you originally burned prograde. This restores your orbit to what it originally was (i.e. the correct orbit specified by the contract).

5. Profit!

If you're too far west from the LOS point:

You have the same problem, but in the opposite direction. Do exactly the above, but in reverse. In step 2, you burn retrograde instead of prograde, to lower your orbit and make you go faster, so that you'll catch up to the LOS point. In step 4, you then burn prograde to restore your orbit.

[DeMatt]

I'm still learning the finer points of orbital maneuvers and I accepted a satellite contract out at Minmus that required the vehicle be in line-of-site with a ground station on the moon. I got out there, got inclination, AP and PE correct and I'm just out of line-of-sight range of the dish on the ground. I know Minmus spins pretty rapidly, should I just fast forward a few orbits until that base comes in sight and wait my ten seconds? Or should I mess with my AP or PE to speed up or slow down the orbit?

I'm perfectly circular now, dead on the contractual orbit so I don't really want to deviate from that. Any maneuvers I make cause my orbit to become out of round. Then I waste gas trying to make a bunch of tiny 1 second burns. Can I point directly at (or away from) the pink target marker and retain my circular orbit by thrusting straight out or in from Minmus... sort of like during a rendezvous? I've only got about 25-30% fuel in the tanks and don't want to waste it by taking 3 steps forward and 2 steps back. I'd like to nail this as it's a $240K payoff.

You're going to have to deviate from the contract orbit. See, the contracts that call for line-of-sight with a ground station ALSO ask for a synchronous orbit. So despite Minmus spinning fast, your satellite (if it is in the contract orbit) is orbiting at the exact same rate, and will never arrive in line-of-sight.

If you're behind the ground station, do a small retrograde burn at the designated apoapsis; this will shorten your orbit and let you "catch up" to it. If you're ahead, do a prograde burn at periapsis. In both cases, you're trying to only adjust your orbit by a minimal amount - 1 or 2 metres per second. It may take several orbits to achieve line-of-sight (watch the contracts tab for the tick mark), after which you do the reverse burn to put you back on the contract orbit. Larger burns will obviously make the process faster, but cost more fuel at both ends.

Also, if you're having trouble with your engine being too powerful for these fine maneuvers, you can right-click on it and adjust the "Throttle Limiter" down. Combined with the standard throttle, you can fine-tune your engine thrust down to less than 1% of its rated maximum.

[The Science Bucket]

Yeah it's a synchronous contract and right now I've been holding at the required orbit. Wasn't sure if prograde or retro would be the correct answer or just try to wait it out. Thanks for the detailed answers. That really helps my understanding of what movements affect my placement in orbit. Engine is a LV-909 so it's been pretty easy to make fine adjustments.

[The Science Bucket]

I got it!

Was going to leave it alone for a few days but last night I did a few tourist contracts and then checked in on my lonely Minmus machine. All the needs were checked off except for the orbital circumference. A few tiny, tiny burns here and there and everything clicked. YES! Spent that money on a new R&D facility.