BAK-9900 Seraph
by Brikoleur
uploaded 2019-06-23
(updated 2019-06-25)
stock+DLC lifter
#eve #lifter #recoverable #helicopter


  • Update: A much better orbiter and a variety of QoL improvements.

The BAK-9900 Seraph is not an Eve SSTO.

It is the next best thing: a fully reusable launch system capable of delivering one (1) kerbal to orbit from Eve sea level – if you have the infrastructure and the patience to operate it.

The Seraph’s six pairs of rotary wings are powered by three heavy rotors mounted on freewheels along the spine of the vessel. She uses them to take off – very carefully – then climb to 26 kilometres or so. Climb peaks at around 15 m/s vertical speed between 13 and 15 km or so, and the craft takes about 40 minutes to reach its ceiling.

After it has reached its operating ceiling, it disengages rotors and sets collective to 90 degrees, lights up its Vector, and gets into a parabolic arc that peaks at over 70 km. It launches its orbiter, which flies to orbit.

After the orbiter is safely injected, the lifter falls back to the surface, initially braking with its rotors flat against the air, subsequently by autorotation. It then autorotates to a soft landing.

The orbiter will return to Eve. It is designed to withstand the thermal and physical stresses of re-entry, can glide to its final landing spot, and uses its parachute for the last bit of the way.

The whole mission from surface to orbit and soft landing for the lifter stage will take over an hour real time, as the Seraph is not physics warp friendly, but it is doable and not too difficult.

Then all you need to do is figure out how to refuel the lifter, get the orbiter to it, and re-mount it on its nose.


  • To take off, set SAS to radial out, collective to 4.0 and increase throttle until the craft lifts off, then, keeping an eye on RPM, decrease throttle to prevent them from rising so that the blades don’t buckle.
  • To climb, gradually increase collective to 7.0 while increasing throttle to keep the RPM steady. If the blades buckle (the craft lurches and if you have the aero overlay enabled you will see the vectors jump), decrease throttle until the lurching stops. You can apply full throttle at 7.0 degrees collective around 5 km altitude.
  • Resist fiddling with the collective until your climb drops below 2 m/s (over 25 km altitude). At that point, gradually decrease collective to 5.5 degrees to wring a bit more ceiling out of it.
  • Once your climb has slowed to below 2 m/s or so and there’s nothing you can do with collective to increase it (around 26.5 km), start the acceleration phase: lock blades to 90 degrees, brake on, stage the Vector, and make a gravity turn more or less like you would on Kerbin except a bit steeper. Aim for an Ap ideally above 70 km, but anywhere over 60 km ought to do it.
  • When your Vector runs out of fuel, immediately stage the orbiter and fly to orbit. Climb fairly steeply to get the Ap well out of the atmosphere, once you yourself are out of it (or almost), nose down to lift the Pe out of it as well: this is not the most efficient way to get to orbit but you have the dV and can’t afford to get too fancy, because…
  • …once safely in orbit, switch back to the lifter. Rotate blades to 0 degrees for maximum aerodynamic high-speed braking.
  • Once you’re falling at < 100 m/s, set collective to 4.0 and release the rotor brake. You will start autorotating. Set SAS to radial out, and as soon as your craft has stabilised, switch SAS off and hibernate the probe core to save electricity, allowing the craft to autorotate down. It will descend at about 10 m/s, slightly slower when it gets into the lower atmosphere.
  • Once you’re close to the ground – around 3 km radar altitude – fine-tune your landing spot; try to find a level piece of ground. Adjust your vector like you’re flying a helicopter – lean into the direction you want to go (switch SAS to regular if necessary). Decrease collective to slow down your descent.
  • When you’re about to touch down, decrease collective in steps to 0.2. The craft’s descent will slow to < 2 m/s. Time the final reduction so it’s just before touching down and you will make a very gentle landing indeed.
  • The orbiter is fairly robust and has survived entry to Eve atmosphere on a variety of moderately energetic corridors. Take a slightly tail-first attitude at around 70 degrees angle and hold it through the thermal phase, and she will remain within her thermal limits. One verified corridor is Ap 91 km, Pe 24 km, no fuel load.

1 - toggle fuel cells and rotor engagement
2 - collective 0.2 (touchdown)
3 - collective 4 (take-off, autorotation at around 5 m/s descent)
4 - collective 5.5 (climb below 3 km and above 25 km, autorotation at around 10 m/s descent)
5 - collective 7.0 (climb to 25 km)
6 - collective 90 (ballistic phase)
9 - collective 0 (brake from ballistic phase)
0 - toggle probe hibernation

Throttle - Torque
U/D - Collective

A stock rocket called BAK-9900 Seraph. Built with 74 of the finest parts, its root part is Size1p5.Size2.Adapter.01.

Built in the VAB in KSP version 1.7.2.


  • Type: VAB
  • Class: lifter
  • Part Count: 74
  • Pure Stock
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