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ESN-99 ALLIGATOR

Introducing the most challenging SSTO to fly in my entire fleet: the ALLIGATOR.

Please leave solar panels in the cargo bays EXTENDED. They serve as a game glitch indicator - they will be safe if everything goes well. If they suddenly break due to aerodynamic forces mid-flight, that means KSP messed up and started to calculate drag of everything inside the closed cargo bay. With this enormous extra drag, the craft could hardly accelerate and reach orbit as intended. This glitch seems to happen randomly, and can only be solved by launching again.

V1.1 Change log:
(Special thanks to @hangdog for suggesting the following changes!)
- Unmanned core in the tail cone now visible from outside, good for manually switching control point after docking
- Action groups overhaul:
AG1=switch RAPIERs mode
AG2=Nerv ON/OFF
AG3=toggle cargo bay doors
AG4=toggle solar panels <NEW!>
AG7=toggle reaction wheels
AG8=toggle capture robot RCS <NEW!>
AG0=all engines ON/OFF

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ESN-99 ALLIGATOR (European Spacecraft - Nuclear powered - model 99, Atmosphere/Low-/Lunar-orbit/Interplanetary General-purpose Atomic-powered Transport & Orbital Recovery) is a highly versatile long-range SSTO spaceplane. It fills the gap between small cargo shuttles and heavylift launch vehicles, suitable for a large variety of medium duty operations, most notably orbital spacecraft service and recovery missions.

100% Stock, 170 parts. Root part is the Mk1-3 command pod in nosecone.

- Custom Mk3 cockpit with 6 seats and docking port.
- 2000m/s dV @ 85x85km LKO with 11t example payload of a capture robot and a LF tank, capable of orbiting Mun/Minmus and return with all the payload and without refueling.
- If enabled, this LF tank provides extra 1100m/s dV, allowing interplanetary operations to Duna or Eve without refueling.
- Balanced and almost constant CoM regardless of fuel consumption, great maneuverability and stability during the entire mission.
- All functional fuel tanks are clickable from outside (in normal camera view) and are either empty or full, refueling is simplified.
- Transfer burn to Mun takes 8min (~860m/s dV) with a TWR of ~0.18, with 11t example payload.
- Atmosphere-skipping and good gliding capability.
- A Munar orbit mission costs <10k credits if nicely recovered.

- This craft is designed for a Munar orbit wreckage recovery contract in my career save, but such a vehicle surely would be much more useful than just that.
- The shaping of this craft relies on "rational" part clipping. Some fuel tanks are left empty to keep its fuel capacity reasonable.
- Inside the "engine nacelles" are 4 sets of empty precooler + Mk1 reaction wheel + Mk1 battery bank. If you are not comfortable with reaction wheels while flying in atmosphere, you can toggle them off via AG7, however in my tests I don't see much difference.
- Fuel in frontal shuttle wings DOES affect CoM a little bit, but it will be burnt at first before the craft achieves any significant airspeed, and long before it has to reenter atmosphere. Good balance will be achieved after these two wings are empty.
- The Mk1 cockpit is slightly angled downwards, do not control form there. Spacebar automatically sets control from a forward-facing drone core between the NERVs, or do it manually.

Ascent: 0-5-10 Degrees to Space!
- Highly recommended: install MechJeb device.
- Leave solar panels extended due to reasons listed above. Close cargo bays while still in SPH.
- Engage SAS, launch, Vr=110m/s, keep level flight at low altitude until airspeed exceeds 400m/s. (Should be flying past the island at this moment.)
- Let go of pitch control, let it slowly pitch up to 5deg while accelerating, then keep it there. This is to avoid a too fast ascent and insufficient acceleration of air-breathing RAPIERs.
- At ~10km, let go of pitch control again and let it pitch up. Finding the most efficient altitude requires experience.
- Once speed hardly increases (~1420m/s @ 20km), hit AG1 to switch RAPIERs mode, aim for 10deg pitch.
- At 25km, hit AG2 to fire NERVs.
- Lock prograde shortly before LOX burnout, finish ascent with NERVs only. Would be a long and flat ascent.
- If you find it necessary, pitch up at upper atmosphere for a quicker atmosphere escape.
- A 85km AP would likely be more than 10min away, and circularization burn takes around 40m/s dV.

Spacecraft Recovery
- If you used up the LF in the orange tank and wish to jettison it, first undock the robot. It will drift forward and soon re-dock to the Mk1 crew cabin. Then undock the fuel tank and use RCS to move away. Finally undock the robot, let it drift backwards and dock back to the docking port - or just leave it there if you are OK with it.
- Rendezvous with target, deploy robot and capture the target from an appropriate angle.
- Have both the robot and ALLIGATOR lock prograde (orbit), move ALLIGATOR towards the robot and dock with it. This is because RCS of robot + target spacecraft is not balanced and won't be precise.
- It's possible to have the robot remain docked with the ALLIGATOR and move the whole thing to capture target spacecraft, but according to my experience, this would be inefficient and frustrating.

Descent
- Burn PE to 40km above target zone (if returning from beyond LKO, pin-point unpowered landing mostly depends on your luck, but you can always use RAPIERs to fly to destination.)
- Lock radial-out to aerobrake, you can retract solar panels due to the glitch mentioned above. It's not too bad if this glitch happens during reentry.
- When estimated impact point draws near landing site, reduce AoA to 10-45deg.
- With a 10deg AoA and an altitude of 20-30km, it can perform atmosphere-skipping and glide from the Great Desert to KSC unpowered.
- Use Brake action group to further slow down when near landing site.
- Keep a low vertical speed before touchdown to avoid bouncing. Deploy drogue chutes, brake for a full stop.


Wish you enjoy and happy landing!