How Spacecraft Thrusters Work

Not every task requiring spacecraft requires the brute power of a massive rocket motor; some tasks need far more subtle actions like changing satellite positioning or giving another craft a gentle push while docking with it.

These low-force thrusters utilize electricity to ionize gases like xenon and krypton, propelling them at high velocity out of the thruster. Their DutyCycle property controls how much engine is running during maneuvers.

Chemical

Chemical spacecraft thrusters function similarly to gasoline car engines in that they use combustion within rocket engines to produce an exhaust gas that shoots out through its nozzle and exerts equal and opposite reaction pressure that propels forward movement of their spacecraft.

Electric thrusters often rely on xenon gas as an expensive propellant that requires large pressurized tanks, complex networks of pipes and valves, pumps and pumps for transportation around a propulsion system. Researchers are exploring other propellants including common elements like iodine.

An iodine-drive thruster could help keep communications satellites in their designated orbits or propel larger cargo or manned spacecraft throughout our solar system, but would require providing tens of kilowatts continuously – something no battery technology is currently capable of providing. Engineers plan to solve this issue with air-scooping electric propulsion (ASEP) thrusters that use air molecules from Earth as fuel – this way enabling travel to Mars or distant outposts without stopping for fuel refills!

Electrothermal

Kepler and Dawn missions utilized spacecraft thrusters with electric propulsion systems that converted electrical energy to xenon propellant. It was then released into space via electromagnetic propulsion to push the spacecraft in its desired direction. Unlike chemical thrusters which have limited power levels and energy capacities, electrothermal propulsion systems offer better fuel management as they don’t limit themselves with fuel restrictions.

Engineers now have access to COMSOL multiphysics for simulating high-temperature conditions of thrusters and evaluating how the temperature increases over time. By using Joule heating in stationary solutions and an increasing current in time-dependent simulations, engineers can predict when their thruster will reach operational temperature of its material.

NASA researchers at Glenn Research Center have successfully developed electrothermal propulsion systems with miniaturized key technologies such as magnetic field topology and the center-mounted cathode. Together with their high specific impulse, these systems could enable future planetary missions such as Mars or asteroids missions.

Electromagnetic

As in an electric car, a spacecraft draws energy from the sun and turns it into an electrical current to power its thruster, which in turn uses it to push forward in whatever direction necessary.

Electromagnetic propulsion systems consume megawatts of electrical power and offer a broad spectrum of specific impulse values for use in space maneuvering tasks such as orbit raising/transfer, station keeping/interplanetary cruise/fine and agile attitude control/long duration missions (air-drag control) etc. NASA Glenn Research Center is currently developing several magnetoplasmadynamic thruster concepts that meet these diverse mission requirements.

This WONDER examines three pulsed electromagnetic propulsion concepts, which span four orders of magnitude in power processing capability (100 W to >100 kW). Furthermore, these systems eliminate reliance on failure-prone electrical switches and gas puff valves, increasing system reliability while streamlining integration into spacecraft power systems.

NSTAR

The NSTAR thruster (named for its use on NASA spacecraft) is a four-grid ion drive with very high specific impulse. It employs low melting-point metals stored in graded-pore nickel sponge, while wicks of this material transport propellant towards an ionizer made of porous tungsten and heated by two resistive heaters; once ionized, propellant enters an acceleration grid and exits through a discharge chamber.

A positive mesh grid in the discharge chamber and a negative grid at its exhaust end combine to produce a net potential difference, which accelerates ions through the chamber. After exiting through an exhaust port, these ions are propelled towards Asteroid Dawn via three NSTAR engines with 475 kg of xenon fuel.

Ion drives can deliver more delta V per weight than chemical rockets, which typically burn through their fuel quickly. Deep Space 1’s NSTARs were capable of contributing approximately 10 km/s in delta V over their flight duration.