Wednesday, April 23, 2014

Kerbals (almost) on Duna

Kerbal Space Prorgam can be breathtakingly beautiful at times.
Pictured: one of my first orbiters.
I finally put in a serious effort in to get to Duna (Mars) in KSP. It was an epic journey that taught me a lot about orbital mechanics.

Some new parts that KSP added finally allowed me to make a decent orbital fuel delivery vehicle (kind of a requirement for inter-planetary missions). No more franken-rocket creations that ultimately fall short or wind up using the fuel they were meant to lift (if they don't blow up before either event). I now had a system that could get full tanks into orbit reliably. I still need to work on my space station's design, but that's another project for another day. Much like NASA, I'm more interested in going to Duna than practical stuff like making it easier to do so with a much more functional space station. Who needs practicality in space anyway?

Fuel in orbit and docked (after bumping the space station because not enough RCS thrusters), check. Inter-planetary ship in orbit (after a dozen redesigns due to thrust to weight issues), check. The lift goes a lot better than I expect, and I still have 80% fuel in the stage I plan to use for the Duna transfer. Refueling almost seems unnecessary, but I top the tanks off anyway. Docking with the station goes quite well. MechJeb completely fails me on plotting a decent Duna encounter, so I do it manually. I find one that gets me to Duna in 144 days and only needs 1,300 meters/second of delta V to put me on the path. I've got nearly 6,000 m/s of delta V in the tanks, so that sounds great. I hand the plot over to MechJeb to execute. The first burn is slightly off course, but that's to be expected. I plot another burn for a day later that corrects the course and sets me on a decent Duna encounter.

Nearly six months go by in Kerbal time. It's a good thing Kerbals don't need oxygen, and they never get bored. About a week out from Duna I start making minor corrections to my course through retro-burns. This does two things... it slows me down and gets my Duna encounter under 5 million meters. Things are looking good. I can see Duna approaching, and my lateral trajectory will bring Duna within 100,000 meters. Then I realize I have a serious problem.

I neglected one important detail... I was figuring for an orbital velocity of around 2,200 m/s, which is normal for Kerbal (Earth). Only this is not Kerbal, this is Duna, with 1/3 of the gravity. That means the orbital velocity is also only about 1/3 of Kerbal's. I'm doing 3,000 m/s, or about three times as fast as I should be going. I look at my delta V and realize I don't have enough fuel in the main stage to shed that much speed. Houston, we have a problem. No worries, I think, I can dip into the lander engine tanks a bit. Delta V gets recalculated... I have enough fuel, barely. I burn the engines, and I get the ship under escape velocity. Now I have another problem.

There's not enough fuel left to make orbit, and I'm on a parabolic trajectory which smacks the ship right into Duna. I burn the last of the fuel in the main stage to shed a bit more speed, and then ditch it. My ridiculously optimistic plan to lift off and return to Kerbal is completely in shambles by this point, but I hope I can at least land the ship. The lander's tanks are sitting at about 15% fuel. I hope it's enough, because that's all I can do at this point. Landing begins... I throttle up and I'm shedding speed, everything's looking okay, but the fuel is rapidly disappearing.

At 3,500 meters above the surface of Duna, the landing engines flame out. The tanks are empty. I fire the RCS thrusters straight down, but I know it's hopeless. I tell the Kermans I'm sorry, and then watch as they crash into the surface at about 500 m/s. There are no survivors.

They will be remembered, those brave, stupid Kermans.

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