To Duna or Bust

[zeppelinmage]

I decided, while I wait for transfer windows to open up, that I'd attempt something more ambitious. I decided to try for a manned "There and Back Again" Duna mission. It took a couple days messing around in the VAB, but I finally got a lander I was happy with. Unsurprisingly, it was startlingly similar to my Munar/Minmusar lander. Then I needed the Orbital Transfer section (read: large gas tank). I had "back of napkin" calculated (read: pulled from the wiki) my needed Delta-V for the various burns:

Launch to LKO: 4500 m/s

LKO to Duna: 1100 m/s

Possible Ike encounter?: 300 m/s

Duna landing: 1000 m/s

Launch to LDO: 2000 m/s

Duna to Kerbin: 700 m/s

Final recovery burn: 500 m/s

Total Delta-V for entire trip: 10100 m/s

During construction, I gave myself plenty of buffer - a few hundred m/s in most cases.

My first thought was to launch the whole ship in one go. ...yeah, that didn't work. I'd need to put 100t into LKO; something I'm not skilled enough for. (Plus, I don't have those cool orange tanks yet.) So, I decided to launch it in two pieces and assemble it in orbit. Slightly saner option, despite my lack of docking experience.

The lander was pretty easy. It was only 24t, so a standard setup worked a treat. Got it into a fairly circular orbit ~79km.

Note the orbital stage still attached. I wasn't sure yet if I'd need that extra ~200 m/s delta-V in the tank, so I let it be for now.

Then it was time to build the pusher module that would get the unit to Duna, and loiter in Dunar orbit for the lander to re-dock and return to Kerbin.

Well, to get the target Delta-V to push 24t to Duna, the gas tanks ended up at 46t. Nearly twice the weight of the lander itself! So, my previous lifter wouldn't do the job. I rebuilt the lifter a dozen times before trying an option I hadn't tried yet - Asparagus.

After much experimentation (just about 6 hours of playing last night), I finally got one that worked. An asparagus-staged main lifter. Two rings of six double-stacked X200 tanks, with 4x LV-T45s under each.

I ended up getting it into a nice circular orbit 2km below my lander, with a whole ~150 m/s left in the main tank. Pretty good, if you ask me. I jettisonned the remainder (deleting the orbital debris so it didn't cause... problems), and jumped over to the Lander. I realized I didn't need that extra gas (plus, it was in the way of my docking port), so I jettisoned it. I had added a probe body to it specifically to burn for re-entry, so there was no need to delete the debris. Then it was time to do the time warp again while the transfer module caught up to the lander.

50 orbits later...

Finally, we're close. I decided to begin my approach ~7 km, to give plenty of time before the units passed each other. Approach, slow, approach, slow, approach, slow... (Thank you, Scott Manley.) Got the units close enough to turn on RCS, and began the final docking sequence. They were still 45+m apart, but some good RCS and patience closed that gap. Before long, I had them lined up and began approaching at ~0.3 m/s.

Closer, closer... Uh oh, alignment is off... Fire rotational RCS to try and line up better, slow to ~0.1 m/s and the magnets begin pulling it together. Both units rocked back and forth a few times, until finally... Lock!

I was extremely relieved. This was my second docking procedure on orbit. (Third, if you count a "basket capture" of a command module.) Now, my Duna Explorer sits in a nice 79km orbit, awaiting a launch window to the red planet.

Next installment: To Duna!

[Scotius]

Very nice setup for early tech. It's rare to see a Poodle as a transfer stage main engine - i can't wait to see how it will work for you. Another thing: have you tried your lander on Kerbin's surface, to see how much it weight will compress landing legs? Four small legs for a heavy lander? I would be worried...

[zeppelinmage]

I have, briefly. But not on this exact lander. My Munar/Minmusar lander was extremely similar; the only things it lacked were the reaction wheels and RCS.

...oh, and a bit more fuel, too.

[zeppelinmage]

An update, since my window finally opened up. (Yes, more than a month later. lol.)

Sorry about the dearth of pictures. I completely forgot about this thread until just now. >_>

The burn to Duna was fairly standard, got a good intercept right from Kerbin. It was a few million km too high, so I had a couple correctoin burns. One halfway there, and another just inside Duna SOI. Between the two, I think I burned somewhere near 200-300 m/s of delta-V. Luckily, I have plenty.

Got an aerocapture at 12km ASL altitude, and simply circularized at 53km on the other side. Another few hundred m/s. My orbit isn't perfect; 70 degree inclination. I'll have to drop inclination when I leave for Kerbin again.

Anyway, once I got in orbit, I separated my landing module from the unmanned CM. A quick burn to drop periapsis below the surface, I waited for entry. I calculated a "suicide burn" to get a good idea of when I need to start bleeding off speed, even though I have 'chutes. I wanted to make sure I got a good landing.

Landing ended up partially powered as I burned about 800 m/s or so to drop orbital speed before popping my drogue and main chutes. Getting close to landing I was still above 10 m/s, so I burned a little more to drop landing speed to around 5.

Success! Jeb is my first Kerbal to stand on a body outside Kerbin SOI.

Later, I'll lift off, re-dock with the CM, and head back home.

Edited February 2, 2014 by zeppelinmage

[zeppelinmage]

Update!

After the successful landing on Duna, and SCIENCE performed, Jeb re-boarded the lander to return home. I was debating on leaving him on the surface until a Kerbin window opened up, but since the CM was on a polar orbit, that could have been... problematic. Instead, I lifted off pretty much immediately.

During descent, EVA and ascent, the CM had completed exactly one orbit of Duna, so lining up the rendezvous was quite routine.

While docking, I began to reconsider the wisdom of using the CM as a return stage back to Kerbin. Both the CM and lander were, effectively, half empty. Why lug around that extra CM weight when I can transfer all that fuel to the lander and use that as my return stage by itself. So, once docked, I transferred the fuel, jettisoned the CM, then gave it a lithobraking trajectory.

After that, I had 3000 m/s of Delta-V in my lander. With so much left, I decided to give Ike a visit.

Unfortunately, I had to burn ~1100 m/s just to fix my inclination. By the time I got to LIO, I had 1500 in the tank. Just shy of being able to land, take off, and return home. Ah well, would have liked to plant a flag. Next time, Ike.

So, instead, I left the lander in LIO while I awaited a window to Kerbin. While I was up there I took the time to EVA Jeb and repack the 'chutes for Kerbin landing.

The return burn was pretty straight-forward, had a couple mid-course corrections to give an aerobrake trajectory. Locked in at 32km. Took two orbits to burn off enough speed to land.

When I started to descend for landing, I noticed a worrying sight... Those mountains look rather close, don't they?

To make sure I didn't lithobrake unintentionally, I burned a little retrograde to ensure my landing was in one of the valleys. It was a bit hairy coming in. Then my parachutes didn't deploy when I staged them. (Next time I'll make an action group.) But with some deft fingers and strategic use of land render lag, I got all four opened with about 80m left (The drogue was more cooperative, since I manually deployed that one earlier.)

And we landed! Hooray! Jeb is happy to be home after a two-year mission. And, of course, he is raring to go on the next rocket.

I collected 800 science. I could have gotten more if I hit more biomes, but I've already maxed out the tree, so it wasn't a priority.

Lessons learned:

* Add about 1000 m/s more Delta-V to visit Ike. My calculations above only included an encounter. Though I might have been able to land if I was a little more burn-conservative.

* Action group for parachutes! Especially if one is planning to re-pack to use later.

* The Poodle worked well enough for this mission. But next time I will probably stick with just 909s. I didn't see much appreciable difference in burn times between the two... and Poodles are heavy.

* Plan to jettison more weight to save fuel. If I had planned on it, I could have collected the science from my instruments and jettisoned them, saving quite a bit of weight. Plus, if I had a small tank and 909 under the capsule I could have got rid of those other 4 tanks. Redesign for next time.

Edited February 3, 2014 by zeppelinmage