April 02, 2014

The Wings of Ikarus

Hello, hello, good afternoon all and welcome back to the Kerbal Space Center for today's briefing.  I am Bob Kerman, and today I'll be presenting the mission review of the Ikarus mission to Moho.  Here on stage with me are Lanlo Kerman and Doodbus Kerman, the other members of the Royal Squirrel Patrol Space Force that accompanied me on this mission.


Ikarus Moho Voyager on the launch pad at KSC

As I hope you're all aware, Moho is the planet in our system closest to Kerbol.  Moho is a cratered, rocky body orbiting about 6 million kilometers from the surface of Kerbol, and it has an orbit inclined about 9 degrees from the equatorial plane.  What with that inclination, how close it is to the sun, and consequently how fast it's moving, reaching Moho is quite the challenge.  To meet that challenge, we have the Ikarus Moho Voyager.

At the top we have a two stage lander with space for three astronauts.  The first stage is used to land on Moho, and the second stage brings the lander back up to orbit where it will rendezvous with the interplanetary mothership.  The interplanetary mothership also comes in two stages, having a central core with four Nerva rockets, and two external tanks with another three Nerva rockets each.  All that fuel and thrust is necessary to get to Moho's orbit and then match velocities.

The launch vehicle is a pretty standard array of large fuel tanks pushed by mighty Mainsail engines, with a set of heavy solid rocket boosters attached to the corner tanks for extra thrust during the launch boost.

Ikarus launching from the KSC

Our launch went beautifully, the Ikarus leapt off the pad eagerly and climbed into the atmosphere, flying straight up on the flight profile.  As expected, we emptied the first two sets of tanks quite rapidly, dropping them right back over the KSC before we even began our gravity turn.

Ikarus starting the gravity turn

The third set of tanks with the attached boosters lasted quite a bit longer, getting us high into the atmosphere.  The last set of launch boosters ran dry a few seconds before we reached our target parking orbit 650 kilometers above Kerbin.

Ikarus staging high over Kerbin

Almost all of our missions to date have chosen parking orbits around 100 kilometers.  For this mission we chose a much higher orbit, as a higher orbit will greatly improve the accuracy of our interplanetary transfer burn, and it also eases the penalty of having to make a long burn at low thrust.

Ikarus burning to depart Kerbin

If we attempted a straight intercept path to Moho, we'd have to conduct a massive burn departing Kerbin, another massive burn later to match inclination with Moho, and finally a third massive burn to match velocities with Moho.  The combined velocity change of these three burns would exceed 12 kilometers per second, and the procurement division, still reeling from the massive expenditures of the Kassie program, refused to give us a rocket that large.  So our flight planners got clever, and came up with a mission profile using a near flyby of Eve to slingshot us toward Moho.  Using the gravity of Eve, combined with a pair of burns in the Eve sphere of influence, we were able to bend our initial trajectory to one much closer to our final Moho approach for much less thrust.

Ikarus approaching Eve for a gravity boost

After we passed Eve, our orbit had been inclined up out of the equatorial plane, and instead of the massively hyberbolic trajectory we had started with, we now had an orbit with a periapsis at Moho orbit and an apoapsis at Eve orbit.  We made one additional burn as we reached the descending node of our trajectory, matching our inclination to that of Moho.  During this burn, we finally drained the drop tanks on the mothership and cast them loose into space.

Ikarus deep space burn at the descending node with Moho

Of course, by launching on a path to fly by Eve, and using Eve to place us onto a slower, more circular intercept of Moho, our mission was made much longer than if we'd been able to fly straight to Moho.  But finally, nearly 200 days after launch, we began our deceleration burn on approach to Moho.

Ikarus decelerating on Moho approach

Our approach to Moho was tense, I must admit I've never been as scared as I was then.  The mission plan was for us to arrive in Moho orbit with the mothership still heavy with fuel, but we hadn't done as well with the Eve flyby as we hoped, and the mothership ran out of fuel before we even reached Moho orbit.  The lander still had plenty of fuel for the landing and ascent, but it seemed quite possible that we'd have to spend a year or more at Moho waiting for a tanker.  

Regardless, Lanlo, Doodbus and I were getting real eager to get out of our capsule and stretch our limbs, so we fired up the lander engines and began our descent to the surface of Moho.

Ikarus braking to descend from Moho orbit

The lander is equipped with a pair of Nerva rockets on the core, and four LV-909 rockets on the outer lander stages.  We decided to leave those outer engines idle in the hope that we could manage a landing on the Nervas alone, thus saving a significant amount of fuel.  Unfortunately since the lander legs were on those outer stages, we couldn't simply detach them to save weight.

Ikarus descending to a Moho landing

The pair of Nerva rockets proved sufficient for the landing, though only barely.  We were forced to burn at nearly full throttle all the way down from 20 kilometers, but as the surface rushed up to us and we were reaching to activate the additional rockets, our descent speed finally came down to something reasonable, and we made a safe, though rough, landing on the surface of Moho.  It didn't take long at all for all three of us to climb outside to stretch our limbs and enjoy being able to see more than a meter in all directions.

Ikarus landed on Moho with Bob, Lanlo and Doodbus Kerman

After getting our fill of the empty space and conducting a variety of experiments, we reluctantly boarded the lander for our ascent back to orbit.

Ikarus departing from Moho

The Ikarus lander carries significant monopropellant stores that were to be used for the planned rendezvous and docking with the mothership at this point.  Lanlo had the clever idea of using the RCS thrusters to boost our orbit, getting us a little closer to home, and more importantly getting rid of the mass of all that fuel.  We used the Nerva's to get us into an inital 20 kilometer orbit above Moho, and then ran the RCS thrusters dry expanding that to a final orbit of 116 kilometers.

We then spent several days, and most of our pencils and napkins, trying to determine if we had enough thrust to make it back to Kerbin, or whether we were better off staying at Moho, or perhaps heading to Eve, there to wait for a fuel tanker.  After doing the math several times each, we determined that we had enough fuel to put us on a direct intercept trajectory with Kerbin.  We'd be entering Kerbin's sphere of influence at a rate above 5 kilometers per second, with almost no fuel for braking or to correct our trajectory, but we decided to put our faith in our piloting skills and go for it.

Ikarus approaching Kerbin

In the event, our departure burn from Moho placed us on a trajectory that would bring us well inside the orbit of the Mun, and a short correction burn aimed us deep into the atmosphere for aerobraking.

Ikarus re-entry

Reports from the ground are that our re-entry was visible in broad daylight from horizon to horizon, and the deceleration was enough to black out all three of us, but the chutes opened automatically as they are supposed to, and we made a safe splashdown only a few dozen kilometers northeast of KSC.

Ikarus splashdown

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