NASAs 0.1 Micronewton Thrusters Looking Good

[Clipperride]

These Microthrusters from NASA take precision position holding to a whole new level.  The increment between levels of thrust is just 0.1 micronewton!  Interesting piece from Phys.org 

PS makes caps lock look a little silly in comparison!

Edited November 18, 2016 by Clipperride
Added PS

[Streetwind]

Ooohh, electrospray thrusters. And with such precision, too. Loving it

[p1t1o]

How does a satellite know its position to a high enough degree of accuracy to warrant the use of sub-micronewton increments?

Seems like the sort of thing you'd need if you were a millimeter out of position? At hundreds of miles high and travelling at thousands of miles per hour, that is some quite extreme precision!

**edit**

Holy Balls! I just took a look at the link and apparently the aim is to keep a satellite still (relative to station) to within 2 nanometers... Unsurprisingly, its related to the gravity wave boys - goddang do they do accuracy!

Mind:Blown.

Edited November 18, 2016 by p1t1o

[Clipperride]

9 hours ago, p1t1o said:

How does a satellite know its position to a high enough degree of accuracy to warrant the use of sub-micronewton increments?

Seems like the sort of thing you'd need if you were a millimeter out of position? At hundreds of miles high and travelling at thousands of miles per hour, that is some quite extreme precision!!

Yep! Mind blowing stuff!  By comparison a millimetre is a huge distance to be out!  It's "only" a technical demonstration, but it looks like they on the right track  

[wumpus]

29 minutes ago, Clipperride said:

Yep! Mind blowing stuff!  By comparison a millimetre is a huge distance to be out!  It's "only" a technical demonstration, but it looks like they on the right track  

I'm pretty sure they are more concerned with pointing at specific angles (for telescopes).  They might find a use for millimeter precision now that they have it, but I'm pretty sure the work was for angles.  How would they measure either their location or the correct position to the millimeter, anyway?

[softweir]

32 minutes ago, wumpus said:

I'm pretty sure they are more concerned with pointing at specific angles (for telescopes).  They might find a use for millimeter precision now that they have it, but I'm pretty sure the work was for angles.  How would they measure either their location or the correct position to the millimeter, anyway?

External forces found in space can be so large compared to gravity waves that variations in them could swamp a gravitational wave experiment. Even the effects of sunlight and solar wind would be large enough to upset the equipment needed to detect g-waves. Using these thrusters (according to the article linked) may be able to overcome these problems.

[Clipperride]

24 minutes ago, wumpus said:

I'm pretty sure they are more concerned with pointing at specific angles (for telescopes).  They might find a use for millimeter precision now that they have it, but I'm pretty sure the work was for angles.  How would they measure either their location or the correct position to the millimeter, anyway?

The actual system holds position (ie station keeping) to an accuracy of just 2 nanometers (which is about the same as the diameter of the helix of DNA, hence my comment about 1mm being huge in comparison). It's to be used in future satellites that will look for gravitational waves.  

The thrusters provide between 0.1 to 30 micronewtons of thrust. According to the article, 30 micronewtons is around the same force as a mosquito landing on you, whilst 0.1 micronewton is equivalent to the weight of a single mosquito antenna.

[YNM]

19 hours ago, wumpus said:

I'm pretty sure they are more concerned with pointing at specific angles (for telescopes).  They might find a use for millimeter precision now that they have it, but I'm pretty sure the work was for angles.  How would they measure either their location or the correct position to the millimeter, anyway?

AFAIK :

Gravity waves are detected by calculating the fine (like, very, super, minuscule-y fine) shift in distance. They can't be pointed - instead, there has to be some other line running at angle to the line which is also measured. The direction can be inferred like converting cartesian coordinates to a polar one. The way to measure these minuscule shift are by looking at phases of reflected light - are they in-phase, or out-of-phase ? The change in phases shows how much have the distance shifted (although, there's no way to measure what modes is happening - say, a change from in-phase to out-phase might be a quarter of three-quarter, but luckily the phase change would come sequentially, and as has been demonstrated, the only thing matters is the frequency, not the amplitude). On terrestrial stations, the emitter, detectors and reflectors are anchored to Earth - meaning that even somebody walking at a nearby town or a leaf falls on the ground above (most of the stations are underground, don't ask why) would result in a reading. That's why we want to do them in deep space.

How do the satellites work then ? They have a free-floating sphere inside, which is the real free-falling object (shielded from light, electromagnetic field etc). The satellite has to keep a certain distance from this sphere, and all the instruments are on the satellite, so this is where the thrusters come to play - they station-keep the satellite wrt the sphere. Nano-scale precision is of course welcome...

Edited November 19, 2016 by YNM

[Hast5250]

Woah this stuff is crazy! but why wouldn't they just tether the satellite to the station?

[78stonewobble]

9 minutes ago, Hast5250 said:

Woah this stuff is crazy! but why wouldn't they just tether the satellite to the station?

The spacestation? I think that would introduce too many errors, from astronauts bumping around, drag (the ISS isn't that high), earth gravity anomalies (?), heat flexing and warping and what not...

[Hast5250]

yeah, I did'not think of that...

[Streetwind]

On 25.11.2016 at 3:09 PM, Hast5250 said:

Woah this stuff is crazy! but why wouldn't they just tether the satellite to the station?

The imperfections of Earth's gravity field alone would jostle the satellite around too much. They intentionally put it at a libration point, where the gravity from the most significant sources cancels itself out.

[YNM]

In fact, the full mission (LISA and not eLISA or LISA Pathfinder) would follow some clever trajectories to keep their distance to each other almost the same...

I'm not sure how they'll cope with precession anyway !