HEMPT: Breakthrough Electrical Propulsion for a new wave of satellites

The rush is on to launch a new wave of small satellites into low Earth orbit, vastly improving current services and adding a wide variety of new ones for both consumers and organisations of all types.


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Iridium® NEXT, for example, is a constellation of 66 interconnected satellites at a low altitude of 780 kilometers, providing unprecedented global connectivity for communications on the move—people, ships, land vehicles and aircraft. The constellation was built with Thales Alenia Space as prime contractor.

Ambitious constellations of the like aim to close the ‘Global Digital Divide’ so that the 45 per cent of the world’s people without access today to Internet will be able to benefit from that rich resource of knowledge, education and contact---a true key to boosting investment in the developing world.

“Satellites are first launched by a rocket, like Ariane 6, but they will then need to reach their operational orbit, which lies at a higher altitude,” says Julien Degremont, Thales product line manager for space products. For that critical maneuver, electrical propulsion is the key technology needed to carefully place a satellite in orbit. It also makes adjustments when necessary to keep it in perfect position to fulfill its mission.

The demand for such propulsion is booming along with the big growth in the new generation of smaller satellites at lower orbits, with that demand coming not only for telecommunications services. It’s also being generated for earth observation satellites for both civilian (meteorology, oceanography, monitoring climate change, agricultural and urban development, and emergency response) and military purposes, as well as navigation and positioning.

Overall, electrical propulsion offers a huge cost saving over chemical propulsion in terms of mass of the spacecraft and so launch costs.

In particular, Thales’ unique electrical propulsion satellite thruster called HEMPT, the High Efficiency Multistage Plasma Thruster, offers even greater savings; it is designed for cost-effectiveness, flexibility, and reliability.

A HEMPT thruster generates its force by the acceleration of gas ions in an electric field formed as a result of an electrical potential between the anode and the cathode of the neutraliser. The ions are generated in a plasma discharge channel and are confined by a system of periodically arranged permanent magnets. The neutraliser, while generating oppositely-charged ions, protect the satellite from getting electrically charged.

Julien Degremont explains, "The HEMPT is fuel-flexible, which can be a big cost-saver; it can use krypton without any design modifications, which is one tenth the cost of the commonly-used gas, xenon. Loaded with krypton, HEMPT is also one of the most efficient in its class."

He also points out that the HEMPT is also  ahead of others because of its patented system of permanent magnets for plasma confinement.  “We have a patented process of using permanent magnets to control the ions in their acceleration. Through this confinement, there is no discharge channel erosion and the technology provides excellent lifetime, which is a unique,e feature of the HEMPT. Our family of thrusters will capitalise on those advantages, first to provide a relevant solution for constellations, then to board bigger satellites, with a goal of providing long lifetime propulsion for lunar activities and interplanetary travel”.

Julien Degremont credits Thales long experience and expertise  for HEMPT’s technological and performance leadership.

He says, “With HEMPT, 85 per cent of our process and materials are based on the Thales heritage of Traveling Wave Tubes which use electrons to amplify radio frequency signals. That has been used in a variety of deep space missions to assure signals are strong enough to come back to Earth, and Thales has produced thousands of TWTs , each lasting more than 15 years in space.”

In the process of developing such a unique thruster,Thales is contributing to Europe’s program to develop electrical propulsion systems (EPIC, for Electric Propulsion Innovation & Competitiveness) with the HEMPT-NG consortium, helping the company  to develop the next-generation HEMPT thrusters. Julien Degremont concludes, “We’re proud to be part of this European ecosystem to develop electrical propulsion and are looking forward to seeing the HEMPT set off for the first time in a German space agency satellite launch in 2021. Our partners include the DLR, as well as German, French and Italian companies and universities. We are convinced that we can be a critical success factor in its future success”.