ESA's Air Breathing Satellite

A novel concept for satellites has popped up in the news in recent days.

ESA in cooperation with Polish company QuinteScience and Italian space company SITAEL have developed, and vacuum chamber tested, an ion engine that could operate in very low Earth orbit.

Schematic figure of a low Earth orbit ion engine.
(there are no CC or PD images of this engine so I made one myself. Feel free to use it yourself if you think it is accurate enough)

This air breathing ion engine scoops up molecules from the upper atmosphere, compresses and ionizes them and then uses electric fields to accelerate them out the back at extremely high velocity.

The power for the electric fields and acceleration would come from solar panels attached to the outside of the craft. There are no complex moving parts so the engine should in theory be quite robust and long-lived.

This idea, if it works, could be used for satellites that are in very low Earth orbit. The atmosphere, although extremely thin, still generates drag on the craft. Without a constant source of thrust the orbit of non-powered satellites would decay and the satellite would eventually re-enter the atmosphere and burn up.

The uses for such a low orbiting, ion engine powered craft might be for spy activities (I guess) or better yet, to reduce the ping times for internet satellites. This is good news for remote gamers.

The craft being so low in orbit would have to be somewhat stream-lined. The solar panels would have to lie flat against the body of the craft to reduce drag.

Orbit Details

The craft will need to carry batteries large enough to operate the engine through the dark half of the orbit. I will explain why.

The orbital period for a small body in orbit around a large body is (equation image taken from Wikipedia):

where
T is the orbital period,
a is the length of the semi-major axis, in this case just r for radius,
M is the mass of the Earth (5.97237×10²⁴ kg),
m is the mass of the satellite and is so small it can be set to zero.
G is the gravitational constant (6.674×10⁻¹¹ m³⋅kg⁻¹⋅s⁻²) and
π is ~3.1415926535 ...

Let's set the orbit height as 150 km (150,000 m). The radius from the Earth's centre is 6378 km plus 150 km = 6528 km (6,528,000 m).

Plug in all those numbers and I get an orbital period of 5249 seconds (87.5 minutes).

This means that the craft will be in the dark for about 44 minutes on every orbit.

One can't provide thrust just on the day side of the orbit. This will only raise the apogee (position 1 in figure) on the other side of the orbit making that higher and higher with each orbital pass.

In this situation the orbit on the day side (position 2 in figure) will not be raised, in fact due to drag it will decay a few metres on each orbit. Eventually the craft will get too low into the atmosphere and crash.

This means that a hefty battery pack will be needed for 45 minutes per orbit so that the engine can always run and all parts of the orbits can be raised.

Closing Words

All in all, this is a nifty concept, satellites that can breath the atmosphere and use it for thrust.

Hell, if it reduces the ping times in Overwatch for Antarctic researchers then I am all for it.

Post Source

https://www.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster

Thank you for reading my post.

Postscript

Speaking of decaying satellites you may want to check out my post on the Chinese Space Station That May Be Coming To Your Backyard.