Above & Beyond - Rescuing A Ship Around Minmus

[illectro]

Remember my first Minmus trip, the one I performed first thing after starting 0.15 - it ended up with a successful landing, but my brave kermans ony had enough fuel to get into a low orbit around Minmus.

They were stuck there for days while other missions came and went, but finally a rescue mission was sent, using a bigger rocket and the latest in MechJeb technology to make some of the maneuvers easier.

Unfortunately mechjeb ultimately proved to be more problematic, the atomatic ascent went fine, but after that it was nothing more than dead weight. The Minmus transfer was a failure necessitating a series of mid course burns to bring us to the target.

The orbital insertion was aborted at the last minute as the pilots realised they were going to be orbiting in the opposite direction to the target ship, and in their panic they failed to take advantage of the oberth effect and had to burn more fuel than necessary to perform the turnaround into a new capture orbit.

Capture was performed manually, and the orbits were aligned, then the pilots couldn\'t figure out the mechjeb orbit syncing which was probably going to have problems with the eccentric orbits anyway. So the orbits were manually synced and the second stage was ditched on a minmus colliding trajectory.

Then it was a case of flying slower than the orbit wanted the ship to fly using periodic radial burns to maintain altitude, and finally within 1km the rescue vehicle deployed its capture apparatus and final approach was intended.

When the crew caught a good look at the stranded ship they realised that the stranded pilots hadn\'t jettisoned the final stage and were carrying more mass that was desired, so a quick exchange was needed to trigger the stage separation.

Back in the rescue vehicle, the approach continued and initially was a slight miss, a second attempt was made and all things looked good until Danner Kerman realised he\'d been holding the mission plan upside down, which is very easy in space where concepts like \'up\' and \'down\' are subjective, the approach was coming in the direction needed for a retrograde de-orbit burn rather than the required direct boost burn.

So, everything flipped around and on this third attempt contact was made, the pilots struggled to control the rotation the new capsule induced, becuase it was unable to land perfectly centered. You see the original plan had MechJeb doing a lot of work, and that needed a liquid engine for maneuvering it wasn\'t rated for flying via RCS, so that engine was sitting in the middle of the capture aparatus.

This was known to be a problem prior to launch but after consideration the engineers accepted this despite the drawbacks. In retrospect, mechjeb would be left behind for future rescue flights in this configuration.

So, having achieved contact the pilots checked that the orbital alignment was conducive to a return burn, and after Jeb yelled \'get on with it\' over comms the RCS burn was initiated. The off center mass required a lot of control corrections to control the spin, but thankfully, the crew were able to enable MechJeb to control the spin, although this hardly qualified as a successful use of the system since the induced rotation was entirely due to the design compromises made to fit MechJeb in the first place.

After 1.5 RCS tanks worth of fuel the 2 ships found themselves on a Kerbin return trajectory, and at t+40:09:49:48 the bold pioneers, Bill, Bob and Jeb Kerman returned home after their ordeal

[Zephram Kerman]

Rescue missions are the extreme challenge of KSP. I love reading such logs, because they always include additional problem solving along the way.

Congratulations. Job well done.

[Kreuzung]

until Danner Kerman realised he\'d been holding the mission plan upside down

That\'s creative adn fits the kerbalness thing very well. ;D