Kerbooster Medium Fly-Back Booster

[Torquemadus]

After making extensive use of my Kerbooster Light to launch a sizeable satellite constellation to Kerbin's moons, I was able to raise enough funds to buy the Tier 3 Launch Pad. This allows me to use the next largest size of launch vehicle from my Kerbooster family. I've built and flown larger versions, but I need to upgrade the R&D building to unlock the parts they use. The Kerbooster Medium is simply an up-scaled version of the Kerbooster Light. It can throw modest sized crewed spacecraft, as well as interplanetary probes.

For my first test flight of 0.90, I'm going to use the Kerbooster to deploy my Kestrel lander. The Kestrel was born out of my earliest experiments with "stack shuttle" configurations. The idea was to make a vehicle that worked more like the original Space Shuttle concept, incorporating a re-useable booster and re-useable orbiter. I was also influenced by Buzz Aldrin's Starbooster concept, which he used in his novel Encounter With Tiber.

The Kerbooster uses an all-solid first stage. It's not recoverable, but it's cheap. I looked at the value of the solids when empty of fuel and discovered that they are worth so little when empty, that their recovery value is dwarfed by the cost of the parachutes needed to land them safely. This is before the performance penalties of carrying the extra weight and drag of the parachutes are accounted for. The parachutes themselves would be recovered downrange at a percentage of their original value, all to recover a bunch of "trash bins empty of boom".

The solids are thrust limited to 70%, which ensures that they burn long enough to lift the stack clear of the dense portion of the atmosphere. The solids are giving their best thrust to weight ratio when the stack is at a high enough altitude not to be hindered by terminal velocity.

After first stage separation, the stack already has an apoapsis above 70km, so the fly-back stage is used to finish the job of accelerating to orbital velocity and circularising. The payload is deployed into an eccentric orbit, minimising the amount of fuel that must be expended by the payload spacecraft to reach it's destination.

In this case, I'm throwing the Kestrel to the Mun, so I use the Kerbooster to perform the departure burn, taking care to leave the Kerbooster on a trajectory that returns it to Kerbin. I don't usually deplete the Kerbooster's fuel tanks this much, but I'm performing a test flight, so I want to see how far I can push the design. The Kestrel is delivered to the Mun with a near full fuel load. The Kerbooster has an adequate, although marginal, reserve of fuel for orbit change manoeuvres for the return trip.

I perform an aerobraking pass, noting that I should actually have performed a course correction burn when I left the Mun, my orbit is slightly inclined, instead of equatorial as I intended.

With marginal fuel remaining, I bring the Kerbooster in for re-entry. Through sheer trial and error, I've figured out how to perform reasonably accurate re-entries, which place me within gliding distance of the KSC. I'm conscious as I do this that the new aerodynamic and re-entry heating in 1.0 are going to have a big effect on my designs. Whether my shuttles are still flyable in 1.0 remains to be seen. Worst case, I'll come up with a new design.

My approach brings me down from space within reasonable distance of the KSC. My re-entry turns out to be pretty accurate.

I still need to turn around and line up with the runway.

[Tank Buddy]

Pretty interesting design. I never thought of making a booster that flies back...