NASA microthrusters achieve success on ESA's LISA pathfinder

NASA microthrusters achieve success on ESA's LISA pathfinder
An artist's concept of the European Space Agency's LISA Pathfinder spacecraft, designed to pave the way for a mission detecting gravitational waves. NASA/JPL developed a thruster system on board. Credit: NASA

A next-generation technology demonstration mission has just passed a big milestone.

The Space Technology 7 Disturbance Reduction System (ST7-DRS) is a system of thrusters, advanced avionics and software managed by NASA's Jet Propulsion Laboratory, Pasadena, California. It has been flying on the European Space Agency's LISA Pathfinder spacecraft, which launched from Kourou, French Guiana on Dec. 3, 2015 GMT (Dec. 2 PST). As of Oct. 17, the system had logged roughly 1,400 hours of in-flight operations and met 100 percent of its mission goals.

Most thrusters are designed to move a spacecraft, but ST7-DRS has a different purpose: to hold Pathfinder as perfectly still as possible. This allows the spacecraft to test technologies used in the detection of gravitational waves, whose effects are so miniscule that it requires extreme steadiness to detect them.

Just how steady is that? Steady enough that "position noise"—subtle vibrations in Pathfinder's position—won't exceed 2 nanometers. That's about the diameter of a DNA helix. This kind of precision is needed to counteract the biggest disturbance to Pathfinder: the pressure from sunlight pushing on the spacecraft (about 25 micronewtons).

"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."

NASA microthrusters achieve success on ESA's LISA pathfinder
This cluster of four colloid thrusters, part of the Disturbance Reduction System developed by NASA/JPL, helps keep the LISA Pathfinder spacecraft extremely stable. Credit: NASA

Balancing all the disturbances on the spacecraft allows Pathfinder's instruments to stay in near-perfect free fall. This lays the groundwork for a future Pathfinder-type mission, which will need this kind of stability to cancel out any force other than the subtle tug of , produced by supermassive objects like black holes.

"This achievement represents the last hurdle for this microthruster technology development, which the project has been chartered to perform," said JPL's Phil Barela, project manager for ST7-DRS. "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."

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

ST7-DRS is a system of eight thrusters positioned on either side of the Pathfinder spacecraft. Each thruster emits 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 force of that reaction provides the "thrust" that steadies the .

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," Barela said. "The collaborative relationship between NASA/JPL, ESA, Busek and Goddard Space Flight Center has been the key enabler for this project's success."


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LISA pathfinder thrusters operated successfully

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Nov 17, 2016
The precision is remarkable. I imagine they fire a lot. I wonder if this would be a nice job for EM thrusters which would never run out of reaction mass and which have miniscule thrust anyway?

If they turn out to be real that is. A paper was recently leaked.
http://www.e-catw...journal/

Nov 17, 2016
could. this level of precision be used to measure dark energy effects?
I mean: Put two pathfinders far away from each other in deep space. Use the thrusters to counteract residual gravity and solar wind, and use laser interferometry to measure any increase of distance over the time, ( it sounds pretty similar to what they do to detect gravitational waves)

Nov 17, 2016
using an emDrive for this purpose looks a bit weird. If it has no fuel you need to use solar panels to give energy to the emDrive, and the emDrive to counteract the solar wind impulse that its own solar panels are producing, plus the extra weight to carry them and the emDrive. Also, putting the emDrive and its magnetron inside Pathfinder does not sound to help to maintain stability precisely

Nov 17, 2016
ok Ill bite
using an emDrive for this purpose looks a bit weird. If it has no fuel you need to use solar panels to give energy to the emDrive
Did you notice the solar on the pathfinder above? And no, you can use radioisotope thermoelectric generators or even reactors for power.
and the emDrive to counteract the solar wind impulse that its own solar panels are producing, plus the extra weight to carry them and the emDrive
Without propellent the EM drives might save weight.
Also, putting the emDrive and its magnetron inside Pathfinder does not sound to help to maintain stability precisely
Im assuming arrays of tiny EM drives like the thrusters in the article. I dont know if theres a size limit or what the range of thrust would be. Neither do you.

Nov 17, 2016
that negates your own proposal to not use fuel. Nuclear requires fuel (radioisotopes) , and RTG weights more than equivalent solar panels. A nuclear emDrive can not be of a "tiny" size due to extra weight. The cost of nuclear is also much more than the other solutions.

Nov 18, 2016
that negates your own proposal to not use fuel. Nuclear requires fuel (radioisotopes) , and RTG weights more than equivalent solar panels
Either way a satellite will have PV or RTG. I would think the extra load for EM microthrusters would be minimal.
A nuclear emDrive can not be of a "tiny" size due to extra weight
That doesnt make any sense. Neither of us knows size or weight constraints. Thats why i said 'I wonder'.

Proponents are saying that EM would increase performance enormously due to the absence of reaction mass. This should be true for microthrusters as well if they're feasible.
The cost of nuclear is also much more than the other solutions
How do you know that? And why do you think cost would be a factor?

Nov 18, 2016
It may be like turning arrays of light bulbs on and off with similar power reqts and response.

Nov 18, 2016
ST7-DRS is a system of eight thrusters positioned on either side of the Pathfinder spacecraft. Each thruster emits 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 force of that reaction provides the "thrust" that steadies the spacecraft

Read more at: http://phys.org/n...html#jCp

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