|Country of origin||USSR/Russia|
|Propellant||Mode 1: LOX / LH2&RP-1;|
Mode 2: LOX / LH2
|Thrust (vac.)||Mode 1: 900,000 lbf (4 MN)|
Mode 2: 357,000 lbf (1.6 MN)
|Thrust (SL)||Mode 1: 714,000 lbf (3.2 MN)|
|Chamber pressure||Mode 1: 30 MPa (4,400 psi)|
Mode 2: 15 MPa (2,200 psi)
|Isp (vac.)||Mode 1: 415 s (4.07 km/s)|
Mode 2: 460 s (4.5 km/s)
|Isp (SL)||Mode 1: 330 s (3.2 km/s)|
|Diameter||94 in (2,400 mm) (1 nozzle)|
|Dry weight||4,240 lb (1,923 kg)|
The RD-701 (Russian: Раке́тный дви́гатель 701, Rocket Engine 701) is a liquid-fuel rocket engine developed by Energomash, Russia. It was proposed to propel the reusable MAKS space plane before the cancellation of that project. The RD-701 is a tripropellant engine that uses a staged combustion cycle with afterburning of oxidizer-rich hot turbine gas. The RD-701 has two modes. Mode 1 uses three components: LOX as an oxidizer and a fuel mixture of RP-1 / LH2 which is used in the lower atmosphere. Mode 2 also uses LOX, with LH2 as fuel in vacuum where atmospheric influence is negligible.
The use of less dense fuel components at maximum efficiency conditions allows minimizing the volume of fuel tanks and subsequently their mass down to 30%. The RD-701 was developed into the RD-704 with one combustion chamber.
Until 2020, the engine held the record for the highest pressure successfully recorded in a combustion chamber with a pressure of 30 MPa (300 bar; 4,400 psi). This record was later surpassed by the SpaceX Raptor engine with 330 bar in August of 2020.
The 'RD-701' is a two chamber engine. It is able to operate in two modes. In the first, it burns both kerosene and hydrogen, granting it greater thrust and impulse density, allowing for smaller, lighter tanks. In the second, it burns only hydrogen, allowing for greater specific impulse. The RD-701 has two preburners per combustion chamber, both of which run oxygen rich. One is used to pump kerosene and oxygen, the other is used to pump hydrogen and oxygen. 
In mode one, both burn kerosene. Liquid hydrogen is combined with kerosene and oxygen rich preburner exhaust in the combustion chamber. In this mode, it produces 4 MN of thrust, with a vacuum specific impulse of 415s, using 73.7 kg/s of kerosene, 29.5 kg/s of hydrogen, and 388.4 kg/s of oxygen.
In mode two, the preburner used to pump kerosene is shut down, and the other is switched to burning hydrogen. A small amount of kerosene is still used to ensure oxygen is effectively atomised. Gases from the preburner combined with hydrogen in the combustion chamber. In this mode it burns 27.4 kg/s of hydrogen, and 148 kg/s of oxygen. Thrust reduces to 1.6 MN, and specific impulse increases to 460s.