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World-first firing of air-breathing electric thruster
In a world-first, an ESA-led team has built and fired an electric thruster to ingest scarce air molecules from the top of the atmosphere for propellant, opening the way to satellites flying in very low orbits for years on end.
[...] Replacing onboard propellant with atmospheric molecules would create a new class of satellites able to operate in very low orbits for long periods. Air-breathing electric thrusters could also be used at the outer fringes of atmospheres of other planets, drawing on the carbon dioxide of Mars, for instance.
"This project began with a novel design to scoop up air molecules as propellant from the top of Earth's atmosphere at around 200 km altitude with a typical speed of 7.8 km/s," explains ESA's Louis Walpot.
A complete thruster was developed for testing the concept by Sitael in Italy, which was performed in a vacuum chamber in their test facilities, simulating the environment at 200 km altitude.
(Score: 1) by DECbot on Wednesday March 07 2018, @04:41PM (5 children)
Imagine a car with a snorkel plowing through the bottom of a lake....
cats~$ sudo chown -R us /home/base
(Score: 2) by JoeMerchant on Wednesday March 07 2018, @05:01PM (4 children)
Well, air density at sea level is about 1225g/m3 while on-orbit around 200km up it's about 1/25 billionth as much at ~0.05ug/m3 [dtic.mil]. So, even though you are moving 500x as fast as the speedboat through air, and drag is a function of the square of velocity (does that hold in ultra-low densities?), that's still less than 1/100,000th the air-drag on a speedboat doing 30 knots.
🌻🌻 [google.com]
(Score: 2) by bob_super on Wednesday March 07 2018, @05:30PM (2 children)
The better analogy would be an air-breathing cannonball using a ramjet to expend reach, but without any control surfaces.
> drag is a function of the square of velocity (does that hold in ultra-low densities?)
That is a very good question, and I'm really curious what the answer could be. Obviously, moving the molecules out of the way is the same effect on the surface they bounce on, but the fact that they don't have neighbors preventing them from bouncing off has to account for some reduction. Does a spaceship traveling extremely fast in very-low density atmosphere create a spaceship-shaped tunnel that is temporarily a true void?
(Score: 2) by JoeMerchant on Wednesday March 07 2018, @06:09PM
If you're really curious, that paper I referenced above probably tell you in a roundabout fashion how they calculated drag... Seems like more attention span and time than I possess at the moment, especially compared to how curious I really am.
🌻🌻 [google.com]
(Score: 2) by JoeMerchant on Wednesday March 07 2018, @06:12PM
The thing that a spaceship has that your average pirate-era cannon ball doesn't is gyro control of orientation...
🌻🌻 [google.com]
(Score: 0) by Anonymous Coward on Wednesday March 07 2018, @05:38PM
At ultra-low densities, molecules don't interfere much with each other, so drag is simply determined by kinetic energy. It's that equation K=0.5mvv with vv being v squared.
At high densities, the fluid is viscous. Drag can be much higher.