Resistojet configurations


Below an overview is given of the configuration of some resistojets, including:

  • Aerojet MR-501B
  • HiPEHT
  • J3 3 kW resistojet
  • UoS Mark III resistojet
  • NASA multipropellant resistojet
  • MBB multipropellant resistojet
  • Russian EHT-15 resistojet
  • EDB Fakel resistojet

Power Augmented Catalytic Thruster (PACT) [ERNO]

PACT was developed at then MBB-ERNO (currently part of EADS) for ESA. It essentially is a conventional catalytic hydrazine thruster. However, it is different in that it uses an electrically conducting Tungsten - 26 Rhenium heater exchanger capable of directly heating the hydrazine decomposition products up from the decomposition temperature to more than 2000K. Depending on the degree of ammonia dissociation, the temperature of the hydrazine decomposition products is in the range 866K if the ammonia is fully decomposed and higher if not. Without augmented heating PACT allows for a specific impulse of up to about 235s. With augmented heating a 35% increase in specific impulse up to about 300s can be achieved. The next few figures give an overview of the PACT thruster. Technical data are summarised in the table below the figures.



Figure: PACT resistojet 

 Figure: PACT schematic


Figure: Rhenium heater element of PACT


Table: PACT resistojet characteristics

Technical data



Thrust range



Operational pressure range



Specific impulse


3000 (mission average)

Minimum impulse bit



Proof pressure



Burst pressure






Valve power



Bed heater power



Heater element power



Aerojet MR-501B resistojet [Sutton]

The Aerojet developed MR-501B thruster is shown below. It uses hydrazine propellant at a flow rate of 0.045-0.1225 g/s. It consists of two main assemblies: 1) a small catalyst bed with its electro-magnetically operated propellant valve and with heaters to prevent freezing of the propellant, and 2) an electrical resistance spiral-shaped heater surrounded by thin radiation shields made from tungsten and high-temperature electric insulators for supporting the power leads. Power input level may be up to 500 W @ 25 V. thruster mass is 0.9 kg.

Figure: MR-501B resistojet (courtesy Aerojet)

HiPEHT resistojet [Fortescue]

The HiPEHT is an electrothermal hydrazine thruster (EHT) where the hydrazine decomposition products are heated to an even higher temperature using a seperate heater element, see figure below.


Figure: Schematic of HIPEHT resistojet

J3 3 kW resistojet [Donovan]

In the 1970's the rocket propulsion establishment (RPE), Westcott, England did do some substantial development work on a 3 kW resistojet using hydrogen as the propellant resulting in the J3 resisotjet. It consists of a concentric tube heat exchanger and and a conical nozzle, both made out of Rhenium.

Figure: Schematic of J3 thruster


A composite view of the components is shown below. The nozzle is shown in the lower right corner of the picture. It connects to the heater tube just in front (to the left) of it. Typical performances are a thrust of 0.652N, an exhaust velocity of 8.09km/s, and a total power input of 3.3kW. It has a maximum structural temperature of 2530 K and a hydrogen stagnation temperature of 2480K and a stagnation pressure of about 3 bar.


Figure: Components overview of J3 thruster

University of Surrey Mark-III Resistojet [Gibbon]

The next figure illustrates the inside of the university of Surrey Mark-III resistojet, which utilises a packed bed of SiC particles in the form of pellets for the heat exchanger. It uses water as the propellant.


Figure: Schematic of Surrey MarkIII resistojet

The water enters an annular gap between heater and casing through a sintered distribution ring, which keeps the heat transfer material from interacting with the injector and also provides a pressure drop to decouple the inlet pressure from the chamber pressure (otherwise flow oscillations can regulate the inlet flow). The water then flows across the bed, is heated, and passes out through the Power leads Heater thermocouple Cartridge heater heater Sintered stainless water distribution ring Sintered filter (ss) nozzle as super-heated steam. A sintered disk (only used for very small powders) at the aft end ensures to contain the heat transfer material.

NASA multi-propellant resistojet [Morren]

A schematic of a NASA developed laboratory model multi-propellant resistojet is shown below. It consists of a radiation heating element located in an evacuated cavity within an annular heat exchanger body. The heat exchanger consists of two concentric tubes sealed together to permit contained gas flow within the annular region between them. A spiral channel near the rear (inlet end) of the heat exchanger directs the flow circumferentially to reduce heat loss from the rear of the thruster. The flow is then directed axially by 16 small channels in the forward (hottest) section of the heat exchanger after which the gases are expanded in the nozzle. The heating element is made from a coiled tube comprised of 22 turns over a length of 5.8 cm The platinum thruster components are joined by electron beam (EB) welds. To minimise radiative heat losses from the outer surface of the heat exchanger, the thruster is wrapped with radiation shielding consisting of two layers of 0.03 mm platinum foil followed by 13 layers of 0.13 mm stainless steel foil. The layers of the shielding are separated by small-diameter wires. Basic dimensions of the laboratory model resistojet are summarised in the table below the figure.

Figure: Schematic of NASA multi-propellant resistojet


Table: Multi-propellant resistojet design characteristics

Shell/nozzle     Material     Nozzle throat diameter, mm     Nozzle area ratio     Nozzle half angle, deg     Body length, cm     Body diameter, cm

  Grain-stabilized platinum 0.84 82 20 13.0 1.92

Heat exchanger     Material     Number of channels

  Grain-stabilized platinum 16

Heater element     Material     Tubing (OD), mm     Tubing (ID), mm     Coil length, cm     Coil diameter, cm     Maximum operating temperature, deg C     Design life, hr

  Grain-stabilized platinum 2.03 1.52 5.82 0.10 1400 10000

Experiments using seven different gases including hydrogen, helium, methane, nitrogen, air, argon and carbon dioxide indicated thrust levels in the range from 90-420 mN at input power levels ranging from 140 to 240 W. The propellant inlet pressure ranged from 1 bar to 1.7 bar.

MBB-ERNO Multi-Propellant Resistojet [IRS(b)]

A schematic of a multi-propellant resistojet developed by then MBB-ERNO (currently EADS) is shown below. It employs a separate heater element and heat exchanger. The heater and heat exchanger may thus be each made of different materials each favourable to its own design. The heat exchanger is located within the annular heat exchanger. Heat is transferred from the heater element to the exchanger by radiation heat transfer. Heater element and heat exchanger are located in a metal shell that is evacuated to preserve life of heater element and heat exchanger. The heating element is made from a coiled rod comprised of 20 turns. The heat exchanger is made from a coiled tube through which the propellant flows. The inside of the metal shell is covered with radiation shielding to minimise heat loss to the environment.

Figure: Multi-propellant resistojet

Typical propellants considered are hydrogen, helium, methane, nitrogen, air, argon, and carbon dioxide. Typical chamber pressures are in the range 1.3-2.8 bar. Heater power is in the range 140-520 W and heater resistance is in the range 0.47 - 0.94 W. Typical heater currents and voltages are in the range 18-23 A and 10-20 V, respectively. Operational lifetime of the thruster is 10000 hours with a maximum operating temperature of about 1700 K.


Table: Multipropellant resistojet characteristic data

Technical data



Thrust range



Operational pressure range


< 10

Specific impulse


< 138

Operational life



Propellant temperature


293 +/- 5

Heater element power


> 350

Russian EHT-15 resistojet [IRS,a]

The Russian electrothermal hydrazine thruster (EHT-15) thruster developed at NIIEM-ELKOS is shown below.

Figure: EHT-15 resistojet schematic

The hydrazine propellant can be regulated as it flows through the supply line (2) into the jet and from there is conveyed into the outer chamber (6). Next the "cold" propellant flows over an insulating powder layer (5) through the porous heat exchanger element (4) into the inner chamber. The propellant heated in this way is then released in the nozzle (8). During operation the electrical resistors heat up to over 2300 K, the insulators and insulating powder to approximately 2100 K and the heat exchanger element to 1900 K.

Fakel resistojet [IRS, a]

An early resistojet developed by EDB (Engineering Design Bureau) Fakel is shown in the next figure.

Figure: Schematic of early EDB Fakel resistojet

An electrical graphite resistance heater element is mounted in an annular heat exchanger element which contains small channels through which the propellant fluid flows. The heater element is heated ohmically up to 2500K. This heater element than heats up the heat exchanger via radiation heat transfer. The hot heat exchanger than transfers the heat flowing from the heater element to the fluid flowing through the heat exchanger via convection heat transfer. Typical performances using Ammonia as the propellant are a thrust in the range 0.02N - 0.05N, power input in the range 80 - 200 W and an effective exhaust velocity of 2500 m/s.


  1. Donovan J.A., Lord W.T., and Sherwood P.J., Fabrication and preliminary testing of a 3 kW hydrogen resistojet, AIAA 72-449, 1972.
  2. ERNO, "Monopropellant Hydrazine Propulsion Technology - for Satellites, Platforms, Space Station Elements", MBB-ERNO Space Systems Group, Orbital Systems and Launcher Division, Sept. 1988
  3. Fortescue, P., and Stark, J. "Spacecraft Systems Engineering", 2nd ed., John Wiley and Sons Ltd., Chichester, England, 1995.
  4. Gibbon, D., "Resistojet research at the University of Surrey, 2006.
  5. IRS (a), "Triebwerksentwikkling in Russia",, 2005
  6. IRS (b), "Resistojets MPR", RESEARCH/EL_PROP/RES/e_res_mpr.html, 2005
  7. Morren W.E., Whalen M.V., and Sowey J.S., Performance and Endurance Tests of a Laboratory Model Multipropellant Resistojet, J. Propulsion, Vol.6, No.1, 1990.
  8. Sutton, G.P., Rocket Propulsion Elements, 6th ed., John Wiley & Sons, New York, 1992.

Name author: B.T.C. Zandbergen
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