I love this line, "...is an asteroid-sized moon orbiting a few thousand miles (or kilometers) above the Martian surface..." A few thousand miles...or kilometers, we don't care, pick your favorite.
I don’t know all of the details of this mission, but it seems like they’ve just lowered the lowest point in its orbit - called periapsis - until it sits low enough in the atmosphere to get enough drag that the orbit slowly decays over a decade.
The lowest part of the orbit would only drop a little bit, but the highest part of the orbit woukd reduce more with each orbit. If you do it slowly enough, the orbit would circularise and then it would begin to decay more evenly. As it falls deeper into the atmosphere the orbit would decay faster and faster until it can no longer sustain orbit, and then it falls deeper into the atmosphere and burns up in just a few minutes.
The reason for this I can only guess at - it wouldn’t take a whole lot more fuel to just deorbit all at once. My best guess is that it has something to do with reentering at the lowest possible speed. If you fall from a high orbit and reenter, you have a lot more speed and have to dissipate more energy all at once. It’s possible this increases the risk that the satellite will fail to deobrit, and break up and send pieces off in less predictable orbits. If it breaks up from a low circular orbit, there’s no chance of any parts escaping back into orbit.
The time thing is interesting, but I feel like no one talks much about the appearance of passing objects. That is, I wonder how the image of a passing celestial object might distort due to length contraction and any other effects. I’m still trying to understand that. This article seems pretty digestible, so far.
The first link leads to an older article that does explain it. What they mean is that the planets’ orbits are in resonance, which means that their orbital periods are related by integer ratios. (For example one planet completing exactly three orbits in the time it takes another to complete two)
Okay, that’s really cool and 25 megabits per second is actually very good compared to what they get back from other probes. At speeds like that, they could send back 4k pictures, which would be extremely high resolution for craft like this.
space.com
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