Spaceflight Insider

NASA microthrusters succesfully used on ESA’s LISA Pathfinder


Artist’s concept of the European Space Agency’s LISA Pathfinder spacecraft. Image Credit: ESA / JPL / NASA

Q: What’s harder than moving a spacecraft around in space? A: Holding it perfectly still. NASA’s Jet Propulsion Laboratory, Pasadena, California, has been testing the ST7-DRS (Space Technology 7 Disturbance Reduction System) on board the European Space Agency’s LISA Pathfinder spacecraft.

The collection of thrusters, advanced avionics, and software have been undergoing a long-term study. Since being launched from Kourou, French Guiana, on Dec. 3, 2015, 04:04 GMT (8:04 p.m. PST on Dec.2), ST7-DRS has logged roughly 1,400 hours of in-flight operations and met 100 percent of its mission goals.

A grouping of four colloid thrusters, part of the Disturbance Reduction System developed by NASA is being used to, keep LISA Pathfinder stabilized during its mission. Photo Credit: NASA / JPL

A grouping of four colloid thrusters, part of the Disturbance Reduction System developed by NASA is being used to, keep LISA Pathfinder stabilized during its mission. Photo Credit: NASA / JPL

The system is capable of holding the LISA Pathfinder so still that subtle vibrations in Pathfinder’s position – referred to as “position noise” – are kept to the width of a DNA helix (about 2 nanometers). ST7-DRS has its work cut out as the system needs to overcome external forces including the Sun, which applies 25 micronewtons of force to the spacecraft.

“Here’s another way of thinking about it: when the thrusters fire at full throttle, they produce a maximum force of 30 micronewtons – equivalent to the weight of a mosquito landing on the spacecraft,” said John Ziemer of JPL, ST7-DRS systems lead. “To maintain our precise position, the thrusters can be controlled in 0.1 micronewton increments, equivalent to the weight of that mosquito’s antenna.”

Constructed by Airbus Defence and Space, Ltd., United Kingdom, with Airbus Defence and Space, GmbH, Germany, as the payload architect, the LISA Pathfinder’s ST7-DRS uses eight micro-thrusters positioned on either side of the spacecraft.

The thrusters emit microscopic liquid droplets called a colloid electrospray, which are created and charged through an electric field. These ionized droplets are accelerated by a second electric field with an opposite charge, which pushes them out of the thruster.

The electrospray microthrusters were developed by Busek Co., Inc., Natick, Massachusetts, with technical support from JPL.

“The success of the ST7-DRS mission emphasizes the enormous benefit of one of NASA/JPL’s key charters: to mature high-risk technology that can benefit future space exploration,” said JPL’s Phil Barela, project manager for ST7-DRS. “The collaborative relationship between NASA/JPL, ESA, Busek and Goddard Space Flight Center has been the key enabler for this project’s success.”

Large space observatories and spacecraft carrying out formation-flying missions could both benefit from this technology, Barela noted.

“This achievement represents the last hurdle for this microthruster technology development, which the project has been chartered to perform,” Barela said. “Our successful development and demonstration of this electrospray technology will pave the way for future gravitational wave missions, or other missions requiring precise control of spacecraft position and pointing.”

Caltech located in Pasadena, California, manages JPL for NASA.

Formerly called the Small Missions for Advanced Research in Technology-2 (SMART-2), LISA Pathfinder was launched on Dec. 3, 2015, atop an Arianespace Vega rocket from Kourou, French Guiana’s ELV launch site. The scientific phase of the spacecraft’s mission began in March of this year (2016) and was set to conclude in September.

Just one month after taking to the skies above the jungles of Kourou, ESA announced that LISA Pathfinder had completed one of its objectives – it had paved the way for ESA’s Evolved Laser Interferometer Space Antenna (eLISA). According to a report appearing on Space News, the estimated cost of LISA Pathfinder was some €400 million ($425 million).



Joe Latrell is a life-long avid space enthusiast having created his own rocket company in Roswell, NM in addition to other consumer space endeavors. He continues to design, build and launch his own rockets and has a passion to see the next generation excited about the opportunities of space exploration. Joe lends his experiences from the corporate and small business arenas to organizations such as Teachers In Space, Inc. He is also actively engaged in his church investing his many skills to assist this and other non-profit endeavors.

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