KerbalX

Intended as a follow-on to the 40t payload Roc, Leviathan is a truly massive SSTO, designed to carry the heaviest and bulkiest space station components to a 350km orbit. It shares the same cranked-arrow wingplan, with 16 Rapiers providing most of the thrust and an additional aerospike for an extra boost and improved ISP for orbital maneuvers.

100T payloads fit comfortably inside the 5m x 15m payload bay. The front half of the bay is slightly constrained by the MK2 crew compartment, but a 3.75m payload will still fit without clipping if offset down slightly. 4 massive LFO RCS blocks feed from the ample fuel tanks for docking either with the ventral MK2 block, or an internal docking port attached to the finished interior of the cargo bay. Small runabouts like the KRV can even be carried internally, if desired.

Flightplan with a 80t load:

Ensure that all hatches and drag fins are fully retracted, then fire up the Rapiers. Start rotating at 120m/s, you should get wheels up at the end of the runway. Consider using the aerospike for takeoff with heavier loads. (AG 2 to toggle off and on.)
Once airborne, stay level and accelerate to 450m/s, slowly pitch up to 15 degrees. Level out slightly at 8km, use AG1 to switch Rapier modes when acceleration slows and (re)engage the aerospike. For maximum economy, cut the Rapiers out between 37-40km and use the aerospike alone as a sustainer motor. It’s a long, flat ascent, but typically drama-free.

For reentry from a 350km orbit, set the periapsis around 35km over the KSC, re-enter at a 45 degree AoA. Once below 35km or so, hit AG0 to dump the remaining oxidizer, AG 3 for airbrakes, and AG4 to cut out the wing Rapiers for better control during powered flight.

Pop the dragchutes immediately on touchdown to reduce bounce, the lower airbrakes are disconnected from the wheel brakes to avoid unintentional lithiobraking.

Mod Note: In order to fly this plane effectively, you need to bump up the temp rating of the NFLV 5m nosecone from the standard 1200k (yikes!) to a higher rating. 2000k is a minimum (and matches the rest of the tanks,) 2400K is quite comfortable.
Use the file path KSP/GameData/NearFutureLaunchVehicles/Parts/Fueltank/NFLV-Fueltank-Nosecone-5-1.cfg and scroll down to //Parameters.

Mods

• Making History DLC
• Near Future Launch Vehicles
• Squad (stock)