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ESN-106 ALLIGATOR II

ESN-106 ALLIGATOR II (European Spacecraft, Nuclear powered, model 106, Atmosphere/Low-/Lunar-orbit/Interplanetary General-purpose Atomic-powered Transport & Orbital Recovery, generation II) is a highly versatile long range SSTO spaceplane. It’s designed to be a routine transit vessel between KSC and large gateway stations around Duna/Eve/Mun/Minmus, ferrying crew, supply, science data and ore. It’s also suitable for orbital rescue, spacecraft service and recovery missions thanks to its moderate cargo volume.

ESA is evaluating its potential for a long stay in the Jool system, especially around Laythe.
There are also proposals about converting it into a self-sufficient VTOL interplanetary exploration vessel (so-called SSTA) making use of its cargo bays.

Flight Instructions see bottom.

Pure stock, no mods, no DLCs. 159 parts, root part is the Mk1-3 command pod inside the nose cone.

- Custom Mk3 cockpit with 4 seats and docking port, 16 additional seats for passengers.
- 2800-4500m/s dV @ 85x85km LKO depending on payload configuration, see the table above.
- Delivers payload up to 15t to Duna/Eve/Mun/Minmus orbit without refueling. In case of maximum payload: with appropriate aerocapture procedure at Duna/Eve and Kerbin, it can also return home without refueling, but some refueling at the gateway station makes the mission more forgiving.
- Balanced and almost constant CoM regardless of fuel consumption, decent maneuverability and stability during the entire mission. No need to transfer fuel.
- Transfer burn to Duna takes 9min (~1100m/s dV) with a TWR of 0.18-0.20.
- Atmosphere-skipping and good gliding capability.
- Custom 2.5m shock cone intake.

AG1= toggle RAPIER mode
AG2= NERVs on/off
AG3= toggle cargo bay doors
AG4= toggle solar panels (leave them EXTENDED in atmosphere to indicate possible aero glitch, see discussion section)
AG5
AG6
AG7
AG8= store all data (data container beneath the service assembly in aft cargo bay)
AG9= toggle emergency fuel cells (the two small golden fuel tanks are locked for this purpose)
AG0= all engines on/off
Abort (backspace)= ditch drop tanks (separate both docking ports)

- The Mk1 cockpit is angled 5 degrees downwards, do not control from here. Set control from the silver ball on the tail cone if necessary.
- Its overall design is inspired by SR-71 Blackbird and Skylon spaceplane, with various design elements taken from my previous SSTOs.
- Why is the cargo bay divided into two parts which is inconvenient? Because the main wing structure and fuel CoM balancing issue makes this the most satisfying solution I can find for this design.
- Keep an eye on CoM when placing payload in the two sections, don't let it move too much away (more than the diameter of the CoM ball). This would rarely happen anyway.
- The shaping of this craft relies on rational part clipping. Some fuel tanks are left empty to keep its fuel capacity reasonable. The "cockpit" Mk3-2.5m adapter holds strictly 450 units of LF, other fuel tanks are either disabled or full.
- The custom shock cone intakes has no actual functionality, air comes from 6x precoolers and 2x small shock cone intakes.

Ascend: Like usual, 0-5-10 degrees to space!
- MechJeb mod highly recommended, but not absolutely necessary.
- Close cargo bays but leave solar panels extended as glitch indicator.
- Engage SAS, take off, rotate at 120m/s (empty cargo bays) or use whole runway (with payload).
- Keep level flight, accelerate to 400m/s under 400m. Should be flying past the island at this moment.
- Stay away from pitch control, let it slowly pitch up to 5 degrees while accelerating, keep this pitch until 10km.
- At 10km, stay away from pitch control, let it slowly pitch up to 10 degrees, keep this pitch.
- Once speed hardly increases (1450-1500m/s @ 22km), Press AG1 to switch RAPIER mode and AG2 to fire NERVs. Keep aiming for 10 degrees pitch.
- When LOX burns out, lock prograde, finish acsend with NERVs.
- Push AP to desired value, cut off engines. 85km AP should be 5-6min away. Coast and circularize.
- Open cargo bays (AG3), retract solar panels (AG4), ditch drop tanks (Abort), move spaceplane away using RCS (I), extend solar panels again (AG4). It's better to do this before circularization for a bit more dV saving and reducing space debris, but it's OK to do it in peace after achieving orbit.

Descend
- MouseAimFlight mod highly recommended for final landing, but not absolute necessary.
- Burn PE to 40km above target zone.
- Lock radial out (90 degrees AoA) in upper atmosphere to aerobrake.
- Once estimated impact point reaches target zone, reduce AoA to 10-45 degrees. 20 degrees is good for most situations.
- Fire RAPIER engines in air breathing mode if necessary.
- Do big-S turns to bleed off airspeed near landing zone, but avoid high-g maneuvers which could tear it apart. Use airbrakes (Brake action group) with caution.
- Landing speed is around 120m/s, keep a low vertical speed. Deploying drogue chutes is optional.

Wish you enjoy and happy landing!