Eve and the Seven Kerbals

[Jouni]

When 0.23.5 came with better engines and stronger joints, I realized that it would be possible to build an Eve lander around the Mk1-2 Command Pod with a reasonable effort. By the end of April, I had landed on all planets, so it was the time to start thinking about a bigger Eve landing. This thread is the story of that mission.

1. Planning

My original idea was to build a simple lander without fuel lines. Quick sketching with a spreadsheet revealed that a simple four-stage lander would have 11300 m/s of delta-v, which would be almost enough for a sea-level landing. When I started building the lander in VAB, its general shape turned out to be very unwieldy, so I had to start over from scratch.

I went for the standard Eve lander design: a core with 2-3 vertical stages and 9 pairs of asparagus boosters. By then, my standard command pod was no longer just the Mk1-2, but a Mk1-2 with a hitchhiker. I decided to check whether the lander could carry 2.5 tonnes of additional payload, and the numbers worked out. I ended up with a design with almost 7 tonnes of payload, a Skipper in the upper stage, an KS-25x4 in the lower stage, and 18 LFBs in the boosters.

With asparagus staging, I had 12300 m/s at my disposal, which was more than enough. Switching to three layers of onion staging reduced it to 11800 m/s, which was still acceptable. I chose onion staging for its simplicity.

Because the lander weighted almost 1600 tonnes, I decided to forgo landing struts, and land directly on the LFBs. This had the drawback that the crew could not walk below the engines, so I had to build more complicated ladder arrangements.

To reduce the part count, I went for a minimal set of parachutes (18 drogues and 36 radials), which put the landing speed to 15-20 m/s. I had to do a powered landing, but the margins seemed high enough for it.

During the flight tests, two problems emerged. The ship started to rotate during the ascent, forcing me to add more struts. This made the ship rigid enough to stop rotating, but the frame rate decreased noticeably. The separation of the first booster set tended to result in explosions, because the decouplers actually pushed the boosters away, which is almost never the desired behavior. After experimenting with different sepratron arrangements, I found one that was acceptable. The boosters would still collide with the rest of the ship, resulting in violent shaking, but the ship survived.

Finally I added some RCS thrusters for rotating the lander in orbit, and decided that it was ready for action.

[Jouni]

2. Preparations

I didn't want to build a lifter for the lander, because the part count was already over 300. The lander had to reach Eve under its own power, possibly with the help of a set of boosters. Quick calculations revealed that it was borderline possible to reach Eve orbit from Kerbin without refueling, assuming that the TWR didn't fall too soon. Choosing onion staging over asparagus staging helped with that, and the lander became my first single-stage-to-Eve.

Now I had to refuel the ship at Eve orbit. Because I needed almost 40 orange tanks of fuel, I either had to send a fleet of fuel tankers, or do several kethane mining trips to Gilly. I chose the latter approach, which turned out to be quite time-consuming. Launching the fuel tankers would probably have been faster.

Therefore the plan was to match the orbital inclination of Gilly in a highly eccentric orbit, with apoapsis beyond Gilly's orbit, and wait for the kethane miner to complete five refueling trips.

The margins were quite low for a sea level landing, so I needed a separate deorbiting stage. I had an old fuel tanker orbiting Kerbin, and it seemed good enough for the purpose.

The only problem was that the lander didn't have room for a big docking port, so I had to use a small docking port to connect with the deorbiting stage. Therefore I had to do some tests to determine how hard the deorbiter could push without causing any problems.

The answer turned out to be 400-500 kN.

At some point, I realized that I had room for seven kerbals, but the lander only had a crew of three. That seemed unsatisfactory, so I launched a crew shuttle to rendezvous with an interplanetary ship orbiting Kerbin, refueled the ship, and launched to Eve at the best speed, ignoring all launch windows.

Piloting the normal-sized ship next to the big lander was fun. I started to think that maybe KSP should have extendable docking tubes similar to airport gates.

Finally, after weeks of real time, everything was ready for the landing.

[Jouni]

3. Landing

The lander had its apoapsis at over 20000 km, so deorbiting didn't require too much fuel. As a drawback, the area I could land at was pretty bad: a lot of seas, mountains, and hills.

The first attempt ended in a sea, but I learned that the joints were strong enough to withstand deploying parachutes.

Over the course of several landing attempts, I found a ~100 m vertical window that resulted in a landing at a reasonably level plateau at around 2100 m. It was higher than I wanted, but it had to do.

I learned more during the next landing attempts. For example, LFBs are quite bad engines for atmospheric powered landings.

Because of low visibility, I ended up using around 30 tonnes of fuel for the landing. The landing speed had to be below 5 m/s, because the ground wasn't perfectly level, and the joints between LFBs and orange tanks could not withstand the impact otherwise.

Walking seven kerbals down from 30 m took surprisingly long.

After a successful landing, the kerbals were so excited that they could not stand still.

[Cashen]

This is impressive. I'll be watching to see your progress. Eve landing and return is something I have in mind way down the road for my own mission logs thread, but I've not wanted to tackle it quite yet due to the complexity.

[Jouni]

4. Ascent

Now it was time for the ultimate test. I had seven kerbals on Eve, trusting that my calculations were correct enough to get them back to orbit.

A proper Eve takeoff begins with the lander shedding off useless stuff.

The fireworks were nice.

The explosions never seemed to finish.

After takeoff, the first booster set burned out very soon. Fortunately they fell off in a controlled manner, despite the problems during the flight tests.

The second set also burned out quickly, and even the third set didn't last for too long. Then it was only the core left. TWR went down with the last set of boosters, and the ship slowed down considerably.

Still, the rocket had its nose pointing to 30 degrees when the time came to drop the lower stage.

A big cartridge for a small bullet.

I didn't care too much about terminal velocity during the ascent, because the landing site was relatively high. That wasn't a problem, because the upper stage reached a 130 km orbit with over 1000 m/s of delta-v remaining.

I still have four ships orbiting Eve, so I'll have to clean up some day.

[Technical Ben]

Wow. Great one. You succeeded where many fail.

[-RanZ-]

7 kerbals from Eve... very nice. I would say you have won KSP

[astroadrian99]

Whats the part count?

[Jouni]

The part count is 351. You can reduce it to 291 by not detaching parachutes and RCS fuel tanks before liftoff. If you can figure out a way to detach the first set of boosters without decouplers pushing them away, you can get it down to 267 by removing a few sepratrons.