Paul Penzo's intermediate Martian moon(s)

One Paul A. Penzo came here to Boulder in 1984 to discuss "Tethers for Mars Space Operations", specifically a tether anchored above MΦL2. The thesis knocked around for awhile (pdf pp. 69f); until in 2016 Hop David brought it back to attention. That anchor is another satellite, running in a semimajor between those of Phobos and Deimos.

Orbiting at 6155 km above Phobos this could fling masses a tonne at a time toward Earth/Luna; at 7980 km, it can hit Ceres Station. Hop was unsold on any of that unless said exported tonne be of purest osmium or something equally expensive. And a thousand kilometers here and a thousand there, you're talking real money.

And that counterweight doesn't yet exist, obviously. Luckily the core of it is simple dead weight. The material can just be trash silicates fused into a big glassy mass. Add Kevlar or "Zylon" or some other tensile-tolerant cable. Lots and lots and lots of that.

The real prize is Deimos. The counterweight can dangle its rope from a "mere" 940 km over Phobos (~10300 km semimajor). It would fire up cargo to hit Deimos' own tether 2942 km belowdeck: one tonne of Zylon [for] 9 tonnes of payload. With an eight-hour journey in microgravity.

For those new here, they're asking - why does Mars need yet another satellite? Why not get to a low orbit and use Phobos as the one-and-only anchor, whose tether hits Deimos. Because Phobos is too much mass too low to the ground, is this blog's answer. The aim is to plunder Phobos, shifting all its weight for more-useful (but lighter!) satellites mostly lower in orbit, and for Deimos. This counterweight, anticipated temporary, aids the latter.

As we wait between these tether-whips, now they've got a "counterweight" that is shadowing Phobos' orbit rather closer than 940 km. I doubt Mars wants any of this falling into Phobos from above. Can't just nuke the thing and start over.

Hop suggested they winch back the Kevlar and punch the counterweight back up. This can be done in its own good time. I assume Deimos cannot dangle an even longer tether down to 10300 km semimajor to yank it.

Given that, the restoration of the counterweight can be an efficient high-I_sp process: ion-drive, maybe Ebrahimi-Alfvén. Thus: the Momentum Bank. The counterweight (there can be more than one) must actually have such a drive, and propellant, and robots.

How to get it up there in the first place: the options are to drop it from Deimos, which pushes it further out and lowers its mass; to push it from Phobos, which does lower its mass but also drags it down; or to bring it from outside the Martian system entirely, hopefully stealing some momentum from Deimos and/or kicking Phobos itself up a bit, although this process is complex and will certainly strew Mars' Hill Sphere with flying bullets.

Overall I'm thinking: go to Phobos, find a solid boulder of mass maybe 100 kilotonnes, attach a honkin' Orion to that, and knock it up to MΦL2 - at once. This does withdraw from the Trésorerie de Phobos, but we're hoping to reduce the total pain at the end as the moon sends more kilotonnes up there with less blowback.