January 22, 2014

The Mun is a Harsh Mistress Part Three: There and Back Again

Bill Kerman is on the planet Eve, sheltering in the shattered wreckage of his lander, waiting for rescue.

Bill Kerman waiting on Eve

Bob Kerman is on the Mun, sitting in his detached capsule, waiting for rescue.
Bob Kerman waiting on the Mun

Philmon Kerman is on the Mun, sitting in his lander, with empty fuel tanks, waiting for rescue.

Philmon Kerman waiting on the Mun

I am Jebediah Kerman, but today my name is Rescue.
Bob Kerman flew to the Mun on a Kermotaur I test vehicle. His reports and the collected flight data indicate that it's performance was a bit below what we here at the Royal Squirrel Patrol Space Force like, and of course the fact that his capsule decoupled from the lander unexpectedly hardly counts a positive feature. So we scrapped that design.Philmon Kerman flew to the Mun on a Kelphin I vehicle. His launch stage was a good, stable platform, but it came up a little short, and he had to use his transfer stage to get him into orbit, and from there things just got worse, as he was using his return fuel budget to get him into a munar arrival orbit and down onto the surface of the Mun. So we scrapped that design as well.Today I will go into space aboard the Kelphin II vehicle. For this rocket, we've returned to the concept of simplicity, and we've told our engineers to put away their slide rules and return to the successful strategy of "you can never have too much thrust." As with all of our recent designs, we utilize a star pattern of launch stages, then a transfer stage, and finally a lander. Our launch stages on this rocket should get us into space, and if I fly it properly, I should even achieve an orbit on the launch stages, but we don't expect to achieve a perfectly circular 100km orbit from the launcher.The transfer stage takes a page from Bill Kerman's Eve vehicle, with a central tank surrounded by four nuclear rockets, but a bit smaller in this version as we don't need to go nearly as far. The resulting higher thrust to weight ratio should let me use this stage to circularize my orbit if necessary, and still carry me through to a circular orbit above the crater where Bob and Philmon are waiting for me. The lander is designed for simplicity, with nothing that isn't needed to get me down and the Mun near Bob and Philmon, and then get us all back to Kerbin.

Kelphin II Rescue Rocket on the pad

T-00:00:15 The rocket has been eerily quiet to this point, with just a light rustle from the wind on the capsule. But now, massive pumps are stirring into life beneath me, as five giant mainsail and twelve mark-55 radial rockets arouse themselves to readiness. I can identify the distinct sounds, as one mainsail and four radials transmit their vibrations straight up the central tank into the seat beneath me, and the slightly muffled sounds from the others mounted in the outer boosters. The rocket settles down onto the gantry as the mounts flex. I can see the readiness of my rocket in the console lights, hear it in the noises, and feel it in the vibrations. This will be a good launch.

Jebediah and the Kelphin II Rescue Rocket to the rescue

T+00:00:05 Liftoff was the smoothest I've had. This rocket is heavy, heavier than any I've flown, but it's squat, and the power seems ideal for it's mass. My speed is building smoothly. I'm at 90% thrust to keep the engines from overheating, but still I watch the velocity climb, slowly but steadily.

Kelphin II rocketing skyward over the KSC

T+00:00:25 There are good points to a daytime launch, but I love nighttime launches the most. I can see the stars, and features like the Milky Way, a taste of what is to come, but with the sheltering presence of mother Kerbin still around me.

Kelphin II boosting with the Milky Way in the background

T+00:00:36 The first stage boosters are away. The craft slows noticeably with their thrust gone, but I was just about to throttle back anyways as my speed was approaching supersonic. The engineers did an excellent job on the staging system, my cameras show the boosters pulling sharply away from the central craft, they are well clear before they begin to spin and tumble.

Kelphin II first stage ejection

T+00:01:20 The second stage boosters are away as well. Again separation is clean. With only the central engines behind me, the ride is now much calmer. This has been the roughest point of several previous flights, as the power drops and I find myself at the end of a long flexing speak balanced on a thin bit of fire, but this rocket remains stable.

Kelphin II second stage ejection

T+00:01:45 Now I'm in the coast stage. Again this rocket surprises me, I have no difficulty bringing the nose down. It's not a quick process, but it's very stable, the craft doesn't want to pogo on me.

Kelphin II upper stage coasting after the initial boost phase

T+00:06:07 As expected, the launch stage just barely got me into orbit. My periapsis is just barely above the atmosphere. The apoapsis has been pushed up above 90km, but I'm not going to orbit that long, the mun is just below the horizon as I stage, so I'm going for the direct transfer.

Kelphin II Munar transfer boost

T+06:42:21 The nuclear rockets may be weak, and they may scare the populace, but I love the miserly things. They got me from Kerbin to the Mun, put me into a circular orbit inclined to pass over the east nearside crater, and now I'm using the last fuel in the transfer stage to bring myself to a complete halt 35 kilometers above Bob's lander.

Kelphin II decelerating over the rescue site

T+06:43:39 This is where both Bob and Philmon had their biggest problem: aiming for a specific crater, then manuevering to make sure they land on a relatively flat spot. I've chosen not to try and curve my orbit down and choose my spot as I decelerate, and instead I've just come to a complete stop as near to directly above Bob's lander as I can manage. Now I slowly fall straight down, watching the crater expand beneath me, riding the throttles to keep my descent speed reasonable.

Kelphin II descending toward the Mun

T+06:46:42 I've slipped myself sideways a couple of times on the way down to find a good flat space, but it's been a smooth descent. The surface below me is smooth and seems flat, I have virtually no horizontal ground speed, and I'm descending at a steady 25 meters per second. The descent has been so clean in fact that my tension is now rising, a good landing is no longer acceptable, now I'm striving for perfect.

Kelphin II descending toward the Mun

T+06:47:09 The Kelphin has landed. The landing site wasn't as flat as I was hoping, but the lander handled the slope nicely. I'm very glad I had no horizontal velocity though, it could have been ugly. I can't see either Bob or Philmon's landers from here, but the instruments say that I've landed less than a kilometer from Bob's lander, and Philmon's is only a few kilometers farther.

Kelphin II safely landed on the Mun

T+07:08:11 I can see Bob headed my way. He's riding his rocket pack, and moving pretty darn fast. It looks like fun, but I sure hope he's figured out how to slow down and land cleanly.

Bob Kerman flying over the Mun towards the Kelphin II

T+07:32:37 Bob, Philmon and I are gathered outside the Kelphin II capsule for a publicity photo before we leave. Bob left a nice trench in the munar soil when he landed, but aside from being covered in dust he's fine. Philmon managed to bounce off the ground and fly into one of the solar arrays on the lander, but fortunately we have three more, so it shouldn't be a problem. His suit sealed up around the gash the array put in his arm nicely, too. Chicks dig scars, I hear.

Jebediah, Bob, and Philmon Kerman gather in front of the Kelphin II

T+08:02:03 And we're on our way home. We took the time to inspect the lander to make sure it didn't suffer any extra damage from Philmon's little bounce, and we also checked his arm. I think we cleaned all the munar dust out of the gash, hopefully he won't turn into some kind of mutated alien monster before we get home.

Kelphin II departing the Mun

T+14:15:33 I love it when the engineers ignore their slide rules and give me more fuel than I need to get home. We had plenty of fuel to take the fastest transfer orbit home, and we've still got enough to bring our approach speed down, the engineers assure me this capsule can handle a 3,500 meter per second re-entry, but I'd rather not test it. We'll use the last of the fuel to slow that down, then drop the return stage just before aero-braking begins.

Kelphin II decelerating above Kerbin

T+14:18:24 We're under canopy over the great southern desert. Bob and Philmon are understandably happy to be anywhere on Kerbin, but I had enough of deserts while I was on Duna. I should have taken the time to pick a nice tropical island to land on. Maybe next time.

Kelphin II descending towards the deserts of Kerbin

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