Los Alamos boffins whip up a speedometer for satellites Scientists at America's Los Alamos National Laboratory (LANL) in New Mexico say they have developed a Spacecraft Speedometer that satellites can use in orbit to ideally avoid orbital collisions. Working with the US Air Force Academy, the LANL boffins say they have come up with a novel device capable of determining the velocity …
GPS on board is common now, before that is was usually ground-based ranging via the TT&C transponder to get precise orbital information, or for debris and dead (or non-cooperative) satellite using radar in LEO, or even sets of angles from optical records:
https://bollerandchivens.com/?p=561
Also worth noting is this new offering measures the speed against the plasma, not in any inertial frame, so it is more analogous to an aircraft's air speed indicator which is not telling you quite what you are doing agains the ground. Which matters if you want to avoid mountains, etc....
I guess maybe this gizmo might tell the satellite how much drag it is experiencing since the satellite presumably knows its orbital parameters and what it's drag free velocity would be. But I'm having a bit of difficulty seeing how that helps avoid collisions unless the satellite somehow knows the ephemeris (a table of calculated positions overtime) of the objects it is trying to avoid. And if it knows their ephemerides, how come it doesn't know its own?
Interesting technology. And probably its good for something. But I'm not sure what.
...this new offering measures the speed against the plasma...
I'm not sure if that's a problem. If the craft was going in a straight line then yes but they are in orbit so the angle of incidence to the plasma stream is constantly and predictably changing so it should be easy (after an orbit or two) to allow for that and calculate an accurate speed.
I think you're right that calculating speed would be easy. Except that the density of the plasma is constantly changing. Some of the changes are (e.g. those due to time of day) are predictable. At least in concept. Some (.e.g. those due to variations in the "solar wind") aren't.
You're not entirely wrong,but it's a bit more complex than that. See https://en.wikipedia.org/wiki/Ellipse and https://en.wikipedia.org/wiki/Elliptic_orbit for way more information than you really wanted to know about the properties of an ellipse and of elliptical orbits.
The handful of systems I'm familiar with used Cartesian coordinates based on the Earth's Center, the plane of the Ecliptic, and something called the First Point of Aires (basically a line from the center of the Earth to the center of the Sun at the instant when the Sun appears to cross the Earth's equatorial plane in the Spring). But you can use any coordinate system you please although the math is likely to be messy if you were to choose, for example, an egocentric system based on the location of your stomach and a vector to the nearest pub.
"We'll assume the eggheads have been able to determine the speed component of a satellite's velocity vector using this gadget.
Many many decades ago when I was receiving my schooling speed |v| = √(v.v) or √(vx2+vy2+vz2) in Cartesian coordinates.
And we're not talking rocket scientists ... actually we are, I suppose.
The idea seems like a Pitot gauge but with bodgy mass specs.
I think a description of these laminated plasma spectrometers can be read in An Ultra-Low Resource Ion Mass Spectrometer for CubeSat Platforms.
I suppose these spectrometers are really measuring the speed or velocity of the ions in the surrounding plasma relative to the satellite or more specifically the kinetic energy (the deviation caused by the device's magnet field allows the determination of the ion's mass which with the kinetic energy the speed.)
A fair bit of computation might be required to pull the speed from the measurement of a sample ion energies and masses to take into account the energy distribution (Boltzmann?) of the plasma's ion and other effects.
"This latest device can deliver critical velocity data for operations when ground station tracking fails, such as during severe space weather events"
Erm, tell us, how often does this velocity data change, during space weather events? And, by what magnitude?
Also, during a particularly bad space weather event, how does the velocity data get transferred, from the onboard sensor, to the ground station?
Finally, it would seem that, during bad space weather events, the "actual" ratio of "ram" to "wake" events might deviate from "expected", given ionic "cross-winds" ? Maybe that's not the best time to rely on the speedometer?
Seems like this is a solution looking for a problem.
* simple version: objects at rest stay at rest, objects in motion stay in motion. In other words, Inertia is a thing, and is related to F=ma
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