Reuniting Deimos

Deimos at 23459 km semimajor is presumed the main waystation for Mars to anywhere. It were even better if 20428 km: that's mamerostationary. Luckily Deimos is small enough that it can lose some altitude just by exporting propellant and pushing back on outgoing craft.

Less-luckily Deimos has a countervail: Phobos, ripping by at semimajor 9378 km, and tidally pushing it further out. (Pace David Dickinson, solid Mars does not have tides: this is Phobos.) Meanwhile as Phobos loses energy to Deimos, Phobos falls further down, below its altitude 5989 km. Phobos is to crash Mars in a few million years which presents a Damoclean headache for the colonies we're hoping to host down there. And Phobos limits the length of a Deimos-anchored space-elevator: 23455.5-9517.58 = 13,937.92 km as a straight up/down line (a little longer of actual fabric given the "elevator" is, thereby, an unanchored rope at the bottom).

So: how about dismantling Phobos. Meanwhile Deimos can hold back on extending THAT long of a tether; we'll get to that, later.

Phobos has a lot of mass; if it were a "Near Earth" it would be in the Ganymed-no-E range. I don't know if the Martians even want the material that is on it, since they have plenty of metallics and supplies on the surface. Carl Sagan thought the Martians would blanket their soil with the moons' dark dust to warm it. But Phobos is already at 9378 km up. Phobos could sell its excess further up.

Phobos' best immediate customer is Deimos, roughly whence both moons came from, over a billion years back [doi 10.1038/s41550-021-01306-2]. Phobos-to-Deimos is delta-V 750 m/s but never mind that; its upward-bound exports should hit the Deimos-dangled tether, periodically closer. Deimos uses solar energy and whatever other power-sources to pull the cargo up, with a winch. Thus, I believe, dropping Deimos further down which is long-term what Mars and Deimos want.

Before you ask: I get pretty gonzo on this blog but I do not envision physically chaining Deimos to Phobos.

It should be clear from the above, Mars deems a tether dangling from Phobos to be an evil. The last things Mars much less its Ring Of Iron want for Phobos are for that moon to gain mass and get pulled even further downward. Also Mars doesn't want Phobos to collapse into an orbiting ring of rubble. But the evil can be mitigated if the mass Phobos gain from below be offset by removal of greater mass upward.