My Jool 5 Challenge Report

Meithan · November 9, 2014

Well, I finally finished the mission report for my Jool 5 Challenge attempt. I took a lot of screenshots (many more than I show here), so I'll use imgur albums to keep it tidy. I also split the report in multiple posts.

Meithan's Jool 5 Mission

Table of Contents

Objective

To land a kerbal on all five moons of Jool in a single mission.

Mission Overview

Single kerbal lands on all moons
Modular lander design using the same command capsule
Three-stage Tylo lander
Two-stage Laythe lander (parachute descent)
Reusable single-stage mini lander for Vall, Bop and Pol
Large propulsion module for Kerbin <-> Jool transfer
Propulsion module stays in 50,000 km Jool orbit
Orbital transfer ship takes landers to/from the moons

Delta-v Breakdown

I've collected a detailed list of actual delta-v expenditures incurred during the mission, in case it's useful to anyone.

Mods used

Here's the list of mods I used for this mission:

MechJeb 2 (only info screens, no autopilots)
Kerbal Alarm Clock
Environmental Visual Enhancements + Astronomer's Pack
Docking Port Alignment Indicator
HotRockets!
Toolbar
Texture Replacer + Rareden's Real 8k Skybox (at end of mission only)

Publicity shot:

Edited July 31, 2016 by Meithan

Meithan · November 9, 2014

1. Mission Design

Inspired by successful mission reports posted on these forums, my design was a one-kerbal (Jeb, of course) mission using three separate landers and a two-part mothership, comprising a propulsion module for the voyage to and from Jool, and a a smaller detachable module for transfers between the moons of the Joolian system. The whole ship was christened the Prometheus:

More details are given in the following image gallery of the mission hardware:

Note: if the album doesn't display properly here, you can view it directly on imgur.

This mission requires a lot of planning because of the large delta-v expenditures and the fact that each leg depends on the successful completion of the previous ones with a limited margin of error -- which means that fuel has to be very carefully rationed. I decided I needed proper planning for this one, so I wrote a small Python program to pre-compute a flight plan for the entire mission, including all orbit changes and landings (using some conservative delta-v values to have some room for error):

The resulting flight plan was dumped into a spreadsheet, which I used to closely keep track of my fuel consumption along the way. I also uploaded the full version of the spreadsheet as it was at the end of the mission (in Google Drive converted form; the original ODS file is also available).

Finally, here are the full specs of the various ships, in case anyone's interested:

Edited July 31, 2016 by Meithan

Meithan · November 9, 2014

2. Launch and Transfer

The first part to be launched to orbit was the Lower Section, comprising the Propulsion Module as well as the Laythe and Mini landers. The launch vehicle took the payload all the way into a 120 km orbit, so that the Prometheus used none of its fuel, and then deorbited itself.

Note: you can also view the album directly on imgur.

Next, the Upper Section was launched. The small upper stage of the launch vehicle completed the orbital insertion and performed rendezvous with the first half of the ship already in orbit.

Note: you can also view the album directly on imgur.

I chose the Jool launch window occuring on Year 15 day 292, computed using alexmoon's fantastic Launch Window Planner:

After checking all systems, the Prometheus departed on its way to Jool. More than two years later, it used Jool's atmosphere for aerocapture and circularized into a parking orbit between Tylo and Vall. Check the following album for the details.

Note: you can also view the album directly on imgur.

Meithan · November 9, 2014

3. Tylo

Because the Prometheus remained in its parking orbit and only the Orbital Module and a lander transferred to the moons, there was really no forced order in which to do the landings. Still, I decided I'd do the hardest one first: Tylo.

The Tylo Lander undocked from the Prometheus and was transferred to Tylo using the Orbital Module. Then, descent. With a gravity comparable to Kerbin's and no atmosphere, my estimates indicated I'd need at least 5000 m/s to land and return back to orbit. The Tylo lander has 6231 m/s, which gives me a large room for error. It was still a tough landing, requiring experience and good thrust management.

Note: you can also view the album directly on imgur.

It was now time to get back to orbit and rendezvous with the Orbital Module in its 30 km orbit. With no atmosphere, the strategy is pointing towards the horizon almost immediately after takeoff. Unfortunately I had some high mountains to the East and had to be careful to gain enough altitude to clear them.

However, for some reason, during the second stage separation event the discarded fuel tanks exploded, possibly colliding with the central tank. While the ship survived, it imparted a serious kick that destabilized it. By the time I managed to recover a correct attitude I had been thrusting away from the intended direction for too long, and couldn't clear the mountains.

On my second try I shut down the third stage engine just before second stage separation, but the problem occurred again exactly as before. This was weird, since I tried stage separation without problems on my multiple Kerbin tests before the mission. So I decided I'd have to live with it. On my third try I took off on a slightly more vertical trajectory and shut down the engine before staging. This gave me more time to recover orientation after the mishap. It worked.

After rendezvous with the Orbital Module, I used the small RCS tug to deorbit the spent lander stage; no point in ferrying it back to the Prometheus. Finally, I rendezvous'd with the Prometheus in Jool orbit. However, I spent more fuel than planned on the return trip. By this point I was getting really worried.

Pictures below.

Note: you can also view the album directly on imgur.

Meithan · November 9, 2014

4. Laythe

Keeping up with the "most challenging first" strategy, my next target was Laythe. While the atmosphere makes landing almost free, it also conspires with the relatively high gravity to make takeoff quite expensive: about 3300 m/s is required to reach orbit from sea level. I went for a simple two-stage lander design, considerably lighter than the one used for Tylo.

The first part was transferring to Laythe, with a 60 km orbit as target (just above the atmosphere). My original mission plan was to do a propulsive insertion, but in order to make up for overexpenses during the Tylo leg, I decided to take advantage of the atmosphere and perform an aerocapture. With this I ended up expending 467 m/s instead of the planned 700 m/s.

During planning I pre-selected a landing site using Kerbal Maps. It had to be:

At or very close to the equator
Flat, with slopes not exceeding 10Ã‚Â° in a wide area
Around 1000 m ASL, in order to have a reasonable parachute descent speed while reducing takeoff drag losses

After some scouting using Kerbal Maps, I selected a site on one of the larger islands (blue lines indicate the equator and the 0Ã‚Â° longitude meridian):

In the following slope map I indicated the target landing ellipse.

The transfer and landing are documented in the following album.

Note: you can also view the album directly on imgur.

The ascent back to orbit was relatively easy. The lander still had 3951 m/s left, and about 3300 m/s are required. I started the "gravity turn" around 8 km, and flattened the ascent profile from there. I spent 3368 m/s on the ascent to a 60 km orbit. I'm sure it can be done more efficiently.

After rendezvous with the Orbital Module, and deorbiting the ascent stage using the RCS tug, I waited for the planetary positions to be right and then transferred back to the Prometheus. The transfer was again more expensive than expected: 1064 m/s vs. the planned 700 m/s. By this time my overall delta-v deficit for the mission had risen to 624 m/s.

See the ascent to orbit and rendezvous with the Prometheus in the following album.

Note: you can also view the album directly on imgur.

Meithan · November 9, 2014

5. Vall

Now that the two most challenging landings were successfully completed, I moved to the next one in difficulty order: Vall. This was the first mission for the Mini Lander, a small reusable single-stage lander with 2200 m/s of delta-v. Since Vall requires around 1800 m/s, there wasn't a huge amount to spare, and I had to be careful.

Luckily it all went smooth. I spent 940 m/s for the landing and 878 m/s for the ascent back to a 25 km orbit. While the transfers to and from Vall were about as expensive as planned (about 1000 m/s for the round trip), recovered fuel from the lander reduced our global delta-v deficit to about 200 m/s.

The mission to Vall is documented in the following album.

Note: you can also view the album directly on imgur.

Meithan · November 9, 2014

6. Bop

Since Bop and Pol are in the outer Joolian system I figured I'd be easier (read: cheaper) to visit them both in one trip without returning to the Prometheus. The Orbital Module has a lot of delta-v with its tanks full, more than enough to visit both outer moons and refuel the Mini Lander for two landings.

Bop was the first target. The substantial inclination and eccentricity of its orbit make transfers somewhat more complicated. I performed a two-maneuver transfer, first to boost my apoapsis to cross Bop's orbit, then a second to match planes. In the end, the transfer cost 900 m/s, including insertion to a 25 km orbit.

Descent was uneventful, but landing was complicated by the very uneven terrain. I landed on a 20Ã‚Â° slope and only managed to stay upright thanks to the reaction wheels. Delta-v used for landing: 259 m/s.

Before returning to orbit, Jeb was instructed at the last minute to perform a second landing in an area at high latitudes. The Bop Kethane Explorer probe had picked up an anomalous reading on the surface ...

Find out about Jeb's journey to Bop and what he found there in the following album.

Note: you can also view the album directly on imgur.

Meithan · November 9, 2014

7. Pol

Jeb had one more landing to do: the outermost moon Pol. Instead of returning to the Prometheus, Jeb directly transferred to Pol. This saved both fuel and time, and the Orbital Module had more than enough delta-v to visit both outer moons without refueling. From low Bop orbit, the transfer to Pol cost about 900 m/s, including insertion to low Pol orbit.

The Mini Lander is not so mini at Pol: it has a minimum TWR of 38 at 100% thrust, so I had to use the thrust limiter to reduce the engine power. Landing from an 8 km orbit cost about 220 m/s.

Jeb was getting very tired by this point in the mission, but landing brought an interesting unexpected surprise. Find out more in the following album.

Note: you can also view the album directly on imgur.

Meithan · November 9, 2014

8. Return

Having successfully completed all landings, it was now time to return home. The first step was returning to the Prometheus, which remained in orbit around Jool between Vall and Tylo. The transfer was a bit expensive (about 1000 m/s) and complicated (two course corrections after Pol ejection).

Having docked back for the final time with the Propulsion Module, fuel levels were checked. As it turned out, the Bop-Pol leg used considerably less fuel than initially planned, and the Prometheus now had an excess of 980 m/s. Original mission planning called for the Mini Lander to be jettisoned and left in the Joolian system, but this was no longer necessary.

After a final wait of 260 days, the transfer window back to Kerbin opened and Jeb started the return journey, which would take 2 years and 276 days and cost a total of 1026 m/s up to Kerbin SOI arrival. Quite cheap!

After aerobraking several times, the Prometheus entered its final 1000 km orbit around Kerbin, a "graveyard orbit" shared by other interplanetary vessels. A service shuttle was launched with Bill on board. After rendezvous and docking, Jeb reunited with Bill, the first kerbal he had seen in 6 years. Deorbit and reentry were uneventful and both kerbals landed at KSC. The adventure was over!

Browse the following album to see images of the return trip. Note that I installed a nicer-looking skybox before leaving Jool.

Note: you can also view the album directly on imgur.

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My Jool 5 Challenge Report

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