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ESN-98 ATLAS

ESN-98 ATLAS (European Spacecraft - Nuclear powered - model 98: Automated Transit, Long-range Atomic Spaceplane) is a high-performance 8-seat pilotless SSTO interplanetary shuttle. It's designed for crew rotation missions of Duna/Eve/Mun/Minmus gateway stations and long-duration non-stop space tours.

After new-generation nuclear thermal rocket engines have proven their high reliability and intrinsic safety even under extreme conditions, ESA finally approves their application on spacecrafts that plan to reenter atmosphere. Fully reusable interplanetary vessel for routine flights is no longer a dream.

100% Stock, 85 parts. Root part is an Mk2 crew cabin.

- Orbit Duna/Eve/Mun/Minmus and return without refueling.
- 3700m/s dV @ 85x85km LKO, 5910m/s dV if fully refueled (LF only).
- Balanced and almost constant CoM regardless of fuel consumption, great maneuverability and stability during the entire mission.
- All fuel tanks are clickable from outside (in normal camera view), and are either empty or full, refueling is simplified.
- 0-10 Degrees to Space! (See Flight Instructions at the bottom for details.)
- Transfer burn from LKO to Duna takes 8min (~1100m/s dV) with a TWR of ~0.24.

- This craft combines designs from ES-95 and ES-97, so that it has a draggy airframe but flies well. Doesn't glide very well due to the drag, pity for its smooth appearance.
- The shaping of this craft relies on "rational" part clipping. Some fuel tanks are disabled, because I want to keep its fuel capacity reasonable.
- There is a hidden LF tank behind the nosecone to replace LOX in that adapter.
- There is a RTG between the NERVs that provides sufficient power. You can choose to either remove this or remove the solar panels inside the service bay.
- If you remove the RTG, remember to pay attention to its orientation before entering time-wrap: make sure the solar panels are exposed to the sun. If it enters time-wrap with its belly facing the sun, the battery will soon die and control will be lost for perhaps half a year. Should this sadly happen, you can let a Kerbal go EVA and push the craft into a rotation with the RCS backpack. If there's no one on board...good luck!
- There are 45 units of ore as ballast in the nosecone. I pretend that this is the extra weight of heat-resistant material necessary for multiple aerocaptures.
- As an automated interplanetary vessel, I think it deserves the top-tier HAL 9000 Unit Mk2 drone core instead of the makeshift combination of fly-by-wire nosecone and low-end drone cores.
- Main wings have a small incidence angle, so that drag from the bulky airframe is minimized during ascent.
- Because of the angled vertical stabilizers, its roll is not 100% stable and needs minor manual correction now and then. I think fly-by-wire system should totally be able to deal with this correction, but KSP technology is weird.

Ascent: 0-10deg to Space!
- Highly recommended: install MechJeb device.
- Engage SAS, launch, rotate at 120m/s.
- Keep leveled flight at low altitude until airspeed exceeds 400m/s.
- Stay away from pitch control (W/S), let it slowly pitch up while accelerating.
- Correct roll angle (Q/E) from time to time. Such intervention also helps to reduce ascent rate, which is beneficial.
- When pitch reaches 10deg, keep it there or very slightly under 10deg.
- When speed hardly increases (~1500m/s @ 20km), hit AG1 to switch RAPIERs mode.
- At 25km, hit AG2 to activate NERVs.
- Lock prograde shortly before LOX burnout, finish the ascent with NERV.
- Hit AG1 again or shut down RAPIERs (AG0 then AG2) for a correct dV reading.
- An 85km AP should be 5-6min away from engine cutoff. Coast and circularize.

Aerocapture at Duna
- Aerocapture is an art. I only describe the idea, exact orbit values require many save and loads.
- Best way in theory: after transfer burn at LKO, fine-tune the trajectory and have the spaceplane closely flyby Duna at ~35km.
- I've never succeeded in that way. I do normal capture burn upon arrival at Duna with a very high AP, and burn PE to ~35km. It costs more dV, but is much easier and safer to do. The ATLAS has enough dV anyway.
- Maintain high AoA in atmosphere and monitor AP value.
- Once AP drops near desired value, lock prograde and leave atmosphere, fine-tune orbit and circularize.
- I'm not familiar with Eve, but it should be similar.

Return to Kerbin
- It should be a descent following a similar aerocapture. PE should be ~40km.
- It doesn't glide very well due to how KSP calculates drag. Use RAPIERs in air-breathing mode to assist landing.

Wish you enjoy and happy landing!