Grusha (The Pear)

Designed to put the nuclear thermal RD-0410 rocket engine to use, the Grusha (pear in Russian) spacecraft can carry three people to the Moon and return them back to low Earth orbit solely using its propulsion without any aerobrake. It is within the launch capacity of the Proton rocket, though it requires a special fairing due to its large diameter. It can also launch on a Saturn IB or equivalent rocket.

While incredibly efficient thanks to the nuclear engine paired with hydrogen as the propellant, the Grusha does use hypergolic propellants for RCS, and this system is quite limited in its capacity. So, the Grusha is not used for anything except crew transfers to lunar orbit. A variant without the crew compartment and instead more RCS capacity has been contemplated.

Length: 13.6 meters
Diameter: 6.6 meters

Mass
Fueled: 16.905 tons
Dry: 7.267 tons

Engine:
1 x RD-0410
35.5 kN thrust (vac.)
910 s ISP vac.

Main engine propellant:
131752 liters liquid hydrogen
RCS propellant:
134.4 liters UDMH
135.6 liters NTO
RCS: 220N thrusters at 312 s ISP
Total delta-v: 7170 m/s
Burn time: 39 min 20 sec