Pushing the boundaries of sub-kilowatt electric propulsion technology for space mission concepts

NASA has developed an advanced propulsion technology to facilitate future planetary exploration missions using small spacecraft. Not only will this technology enable new types of planetary science missions, one of NASA’s commercial partners is already preparing to use it for another purpose: to extend the life of spacecraft already in orbit.

Identifying the opportunity for industry to use this new technology not only furthers NASA’s goal of commercializing the technology, it could also potentially create a path for NASA to acquire this important technology from industry for use in future planetary missions .

The new technology

Planetary science missions using small spacecraft will be required to perform challenging propulsion maneuvers – such as achieving planetary escape velocities, capturing orbits and more – requiring a velocity change (delta-v) capability that well exceeds typical commercial needs and the exceeds the current state of affairs. -of-art. Therefore, the key technology for these small spacecraft missions is an electric propulsion system that can perform these high-delta-v maneuvers.

The propulsion system must operate at low power (sub-kilowatt) and have high propellant throughput (i.e. the ability to use a high total mass of propellant over its life) to enable the impulse required to perform these maneuvers .

After many years of research and development, researchers at NASA Glenn Research Center (GRC) have developed an electric propulsion system for small spacecraft to meet these needs: the NASA-H71M sub-kilowatt Hall-effect thruster. Furthermore, the successful commercialization of this new thruster will soon provide at least one such solution to enable the next generation of scientific missions with small spacecraft requiring an astonishing delta-v speed of 8 km/s.

This technical achievement was achieved through the miniaturization of many advanced, high-performance solar-electric propulsion technologies developed over the past decade for applications such as the Power and Propulsion Element of Gateway, humanity’s first space station around the moon.

Benefits of this technology for planetary exploration

Small spacecraft using NASA’s H71M electric propulsion technology will be able to maneuver independently from low Earth orbit (LEO) to the moon or even from geosynchronous transfer orbit (GTO) to Mars.

This capability is especially notable because commercial launch capabilities for LEO and GTO have become routine, and excess launch capacity from such missions is often sold at low cost to deploy secondary spacecraft. The ability to conduct missions originating from these near-Earth orbits could significantly increase the cadence and reduce the cost of science missions to the Moon and Mars.

This propulsion capability will also extend the range of secondary spacecraft, which have historically been limited to science targets aligned with the primary mission’s launch trajectory. This new technology will allow secondary missions to deviate substantially from the trajectory of the primary mission, facilitating the exploration of a broader range of science targets.

Furthermore, these secondary spacecraft science missions would typically have only a short period to collect data during a quick flyby of a distant body. This increased propulsion power will enable deceleration and orbital insertion at asteroids for long-term scientific research.

Furthermore, small spacecraft equipped with such significant propulsion power will be better equipped to manage changes in the final phase of the primary mission’s launch trajectory. Such changes often pose a major risk to science missions of small spacecraft with limited onboard propulsion power, which rely on the initial launch trajectory to achieve their science goal.

Commercial applications

The megaconstellations of small spacecraft now forming in low Earth orbits have made low-power Hall effect thrusters the most common electric propulsion system used in space today. These systems use propellant very efficiently, allowing for entry into orbit, deorbit and many years of collision avoidance and rephasing.

However, the cost-conscious design of these commercial electric propulsion systems has inevitably limited their service life to typically less than a few thousand hours of operation, and these systems can only handle about 10% or less of a small spacecraft’s initial mass of propellant.

In contrast, planetary science missions that take advantage of NASA’s H71M electric propulsion system technology could last 15,000 hours and handle more than 30% of the small spacecraft’s initial mass in propellant.

This breakthrough capability goes far beyond the needs of most commercial LEO missions and comes at a higher cost that makes commercialization of such applications unlikely. Therefore, NASA sought and continues to seek partnerships with companies developing innovative commercial mission concepts for small spacecraft with unusually large propellant throughput requirements.

One partner that will soon use NASA’s licensed electric propulsion technology in a commercial small spacecraft application is SpaceLogistics, a wholly owned subsidiary of Northrop Grumman. The Mission Extension Pod (MEP) satellite maintenance vehicle is equipped with a pair of Northrop Grumman NGHT-1X Hall-effect thrusters, the design of which is based on the NASA-H71M.

The small spacecraft’s high propulsion power will allow it to reach geosynchronous Earth orbit (GEO), where it will be mounted on a much larger satellite. Once installed, the MEP will serve as a ‘propulsion jetpack’ to extend the life of the host spacecraft by at least six years.

Northrop Grumman is currently conducting a long-term wear test (LDWT) of the NGHT-1X at GRC’s Vacuum Facility 11 to demonstrate its operational capability over its full service life. The LDWT is funded by Northrop Grumman through a fully reimbursable Space Act Agreement. The first MEP spacecraft is expected to launch in 2025, where they will extend the life of three GEO communications satellites.

Working with U.S. industry to find small spacecraft applications with propulsion requirements comparable to future NASA planetary science missions not only supports U.S. industry to remain a global leader in commercial space systems, but also creates new commercial opportunities for NASA to acquire these important technologies when planetary missions require them.

NASA continues to develop the H71M electric propulsion technologies to expand the range of data and documentation available to U.S. industry with the goal of developing similarly advanced and highly capable low-power electric propulsion devices.