Kerbal Space Program Grand Tour

Posted on Wed 05 July 2023 in games

I wanted a challenge, so I decided to try a "Grand Tour" of the Kerbolar system in Kerbal Space Program. A "Grand Tour" is a single mission where you visit all bodies in the Kerbolar system. The definition of "visit" varies from fly-by to manned landing, depending on how challenging you want things to be.

I decided to try the "manned landing"-variant in a fully reusable craft, except for Eve (and Jool and Kerbol, since you can't land there).

Going around the entire Kerbol system requires about 20km/s of ∆v. That's a lot. So I decided to equip my ship with an ISRU and mine extra fuel along the way.

Eve – Moho

The Eve–Moho hop is the most challenging hop ∆v-wise. A fairly good transfer window still requires 3480m/s from Low Eve Orbit to Low Moho Orbit, plus an additional ~1000m/s for landing. By departing from Gilly and diving into Eve's gravity well to maximize the Oberth effect, I was able to reduce this to around 2600m/s, depending on the chosen transfer window.

This particular transfer requires a low-TWR burn from Gilly to dive into Eve of about 530m/s. At Eve periapsis, we need to do an escape burn of 930m/s, at reasonably high TWR, since we lose Oberth effect fast when this burn takes too long. The capture burn is 870m/s, also at high TWR. Finally we need to circularize the orbit around Moho with an additional 320m/s, but that can be low-TWR and split between orbits. Landing can start out at low TWR, but should end up well above 2.7m/s² (Moho's surface gravity).


Landing on Tylo is hard, with a beefy 2300m/s of speed to bleed off and no atmosphere to help with the breaking. Tylo also has a surface gravity of 7.85m/s², so to do some actual breaking, we're looking at at least 10m/s² (TWR=1.3) of thrust, but preferably 16m/s² (TWR=2) or more.

Getting to Tylo is easiest from Pol, where it's easy to refuel. The trip needs approximately 1000m/s of ∆v: The Pol escape burn of 215m/s can be done at low TWR, since the low gravity of Pol doesn't yield much Oberth-effect gains. Arriving at Tylo, we only need about 42m/s at a periapsis of 20kmAGL to remain in orbit around Tylo. Circularizing needs another 800m/s, but we can split that out over multiple orbits.

The ship

With the above constraints in mind, I set out to design a spaceship. I started with a spaceplane design, but couldn't get enough ∆v packed into it. I guess the "dead mass" of the gears, wings and control surfaces adds up. In addition, I needed an extra set of downward pointing engines for landing on bodies without atmosphere, adding to the dead mass. So I ended up with this Single Stage To Orbit (SSTO) rocket:

My Single Stage To Orbit Rocket

The rocket consists of a Mk1-3 Command Pod, topped with a Shielded Docking Port. Underneath is the Convert-O-Tron and a 2.5m to Mk3 Adapter. On the adapter are 4 Airbrakes to assist in orienting the rocket engines-first during atmospheric re-entry, as well as 4 Vernor RCS engines to keep the rocket upright at touchdown. The 8 parachutes are attached here as well. Next up is the short Mk3 cargo bay with an ore tank, the Narrow-band Scanner to pinpoint landing locations, as well as a comm dish to be able to access KerbNet. I also packed a bit of extra torque to manoeuvre this thing a bit better. Next are fuel tanks: A Mk3 Rocket Fuel, a Mk3 Liquid Fuel and 4 Jumbo-64 tanks. The central column has the NERV engine, the 4 side tanks are fitted with a Vector engine. At the bottom I added a Drill-O-Matic Junior on a piston to be able to reach the ground. Power is generated by a PB-NUK for normal operations, 4 Gigantors and a Fuel Cell Array during mining. Cooling is provided by 4 small Thermal Control Systems.

It has enough fuel to do the Eve–Moho leg described above, with 1000m/s to spare. The Pol–Tylo leg also has enough fuel, and leaves us with 3700m/s for the 2300m/s landing. When using all engines, we can start our landing burn at 18.7m/s² (TWR=2.4), increasing to 70m/s² (TWR=8.9) when empty. When fully re-fueled, we still get 16.4m/s² (TWR=2.1) for takeoff.

The Trip

My trip around the solar system obviously started at the KSC on Kerbin. From there I went to:

Minmus Minmus

Mun Mun

Back to Minmus to refuel for the trip to Gilly Gilly

Moho Moho

Gilly again Gilly

Ike Ike

Duna Duna

Ike again Ike

Dres Dres

Pol Pol

Tylo Tylo

Bop Bop

Val Vall

Laythe Laythe

Back to Pol for a refuel and a really long wait for a transfer window to Eeloo Eeloo

Then straight to Minmus, which was on the edge of the ∆v capabilities of the ship. Minmus

And finally back home on Kerbin, after about 45 years of travel. Kerbin