Air Launch Orbital Shuttle

Concept space plane. Mk1

The issue I was having with space planes was the ideal shape for ascent being very different to the ideal shape for re-entry which again is very different to the ideal shape for subsonic gliding and landing. This shuttle attempts to accommodate all of these different requirements by being able to change shape whilst in flight.

The twin boom fuselages can be spread or contracted and the wings can be folded up or down, dramatically changing the flight characteristics.

I’m considering this a vanilla build although I’ve made some limited use of the tinker panel. Where there are tanks that intersect other tanks for aesthetic reasons, I’ve estimated the intersecting volume and reduced mass accordingly. The fuel levels also reflects these proportions. There are elements in the cargo bay which again are aesthetic and can be considered lightweight casings, I’ve also reduced the mass of these parts. The inboard wings have collision detection switched off. The safe procedure for closing the booms being first fold inboard wings then contract booms, to open booms it’s vice versa. I found this a bit of a chore and easy to forget so for convenience the inboard wings are very forgiving.

I’ve included a 10,000 Kg payload as proof this craft can do some useful work. The extra weight up front also serves as ballast to keep the shuttle more stable during separation and ascent.

Activation groups

1. MS. Lnd Gear/Beacon (Mothership Landing Gear and beacons, includes beacons on the shuttle)
2. Aft Elevators (switch these off when inboard wings are folded)
3. Fold Inboard Wings
4. Spread Booms
5. Fold Outboard Wings (don’t do this with the external tanks still on!)
6. Cargo Bay (Bay doors/lights/extend docking port)
7. Landing Gear
8. Main Engines
9. RCS Aux (a smaller subset of RCS nozzles for delicate translations)
10. RCS

Slider 1 operates elevation flaps.
Slider 2 controls all other moving parts subject to activation.

FLIGHT NOTES

Auto pilot doesn’t work well with this (any ideas?) so I fly manually.

Preflight
Slider 2 to 100% draws the twin booms together. The idea is to reduce drag during ascent.

Stage 1
Take off and climb slowly. Lateral velocity is quickly gained at lower altitude so build speed before ascending to between 15 - 20km.

Use slider 1 rather than pitch to keep vertical velocity down. As you gain altitude lift will decrease, ease slider 1 back to zero. For the rest of the ascent use pitch control.

Stage 2
As the air thins the jets produce less thrust and performance drops. Stage 2 fires up the two Mage engines onboard the shuttle. Tanks in the side fuselages of the mothership supply the fuel. Select one of these (painted blue) to keep an eye on how much fuel is left. During this stage the centre of thrust is well above the centre of lift so it’s necessary to apply more elevator, gradually increase to -100%. I generally avoid slider 1 in addition to pitch control as it’s best to keep the climb gentle, the aim is to build surface speed.
Once surface velocity is above 1000m/s and altitude around 30Km, rocket fuel aboard the mothership is running low. It’s time to break loose.

Stage 3
With pitch at -100%, if not already, hit stage 3. As soon as the shuttle begins to lift away from the mothership ZERO PITCH. Stabilising the shuttle’s trajectory is now the priority. At all costs avoid the shuttle pitching up too far, the drag will make recovery very difficult and if it flips backwards give up and head for home. Increase angle of attack and climb steeply once the shuttle is safely on its way.
Successful separation from the mothership can be a challenge, it’s a good idea to quick save shortly before and do this in slow motion the first few times.

Stage 4
Reaching Space. Once the trauma of separation has been overcome there should be enough fuel in the external tanks for most of the climb to about 60Km depending on payload. Select one of the lower external tanks to keep an eye on fuel levels. Ease off the throttle once the apoapsis is clear of the atmosphere. Jettisoning the external tanks generally goes without problems.

Orbital insertion
As with the rest of the flight I do this manually, using the navsphere for guidance only. Begin to align prograde and start the injection burn once the apoapsis draws near. Back off the throttle if the apoapsis slips too far ahead. I find it best to keep the apoapsis just a few seconds ahead once lined up.

Reentry
In the case of Droo it’s possible to use a feathered reentry strategy. The Booms are spread for stability and to quote Wikipedia on the subject, “The wings are rotated upward into the feather configuration that provides a shuttlecock effect”. Think flying squirrel. From a low orbit I generally retro burn to set the periapsis quite high in the atmosphere (above 45Km). Keep a careful eye on vertical velocity and use pitch control (aft elevators ON) to surf along in the upper atmospheric to lose orbital velocity. There’s only been a few accidents on reentry in test flights so it’s generally quite safe but be patient, there’s no heat shielding...

Approaching Subsonic flight
Rotate the wings back to horizontal (or slightly angled if preferred) once a safe speed has been reached, otherwise relax and have fun, it doesn’t glide too badly.