DART

Tomorrow NASA is to launch a DART at an asteroid. The plan is to test how to redirect a nearby space rock using inelastic collisions from Newton.

When I saw this in the news I vaguely remembered that project... being canceled. Sure enough: the Asteroid Redirect Mission, which was supposed to happen next month, is dead. But instead we're getting another mission that does the same thing under a different name, launching a week earlier. Um.

Seems like bureaucratic shuffling to me. But hey.

I expect this collision will end up knocking rubble about. Possible it doesn't move the main body out by much, diffusing much momentum to kicking pebbles off the other side. Still, knowing that is good too.

Besides the benefit to planetary defence, someday we might want to move a rock (or part of it) not just away but closer. Say we had a monster like Eros in TLL4, or SVL4.

LAUNCHED 11/24: Falcon 9 does the job. We've long been at the point that's not even newsworthy.

Dustposting, V

Not much worth our time this day (apart from, you know, getting paid) so: I'll dump Dust on y'all.

"Hey It's Me" was interesting. "Nine Minutes" was good.

"The Lonely Orbit" was neither. "Life Support" (I'd actually seen this over a week ago) was not good.

"The Atlas of False Desires" was not... even a movie. It was Karenware. "Horses on Mars" was also not a movie but had the benefit of not being preachy, just boring.

Segue to "Tales from the Multiverse", Rick and Morty tier, not as funny or insightful as it pretends to be. "Untitled Earth Sim 64" stands in for an Animatrix short that thankfully never made it. "Rocket Roaches" meh; doing for Georges Méliès what "The Beacon" was doing for Ridley Scott. Might have been interesting if it had come out before Scorsese's Hugo a DECADE ago.

University of Austin

It's a scam.

As we could guess from its origins, with Bari Weiss and her homosexual lover she calls "wife". Far be it from me, Gay/Straight Alliance alum, to complain about one's preferences; but more than that, I am an academic, and I shall never accept Weiss' redefinition of terms. If a soi-disant university tolerates a redefinition of terms then I class it alongside Trump University.

Something else Vox was right about.

The Byzantine system refutes itself

Per Justinian's Flea, Kyle Harper was the last straw for some; I had a comment on Mordechai's rebuttal myself (going against Razib Khan no less). Now, it's being argued more-forcefully that, ouais; Yersinia est une peste. Elle toujours erait.

PierrePeter Sarris has the full argument, thankfully not paywalled.

Even in 2019 when I was taking Mordechai seriously I had to say his economic argument was an own-goal for him. Sarris brings Justinian's response: the chastening which has been sent by God’s goodness [should have made workers] better people [but instead] they have turned to avarice. The working class wish to live like the bourgeoisie. No, says the Emperor!

We must agree that Justinian's early-540s measures (including ecclestiastical) kept the rattletrap going for another few more generations. But they didn't make 'em love 'im, that's fer sartan shure.

Balancing Deimos

Deimos is the kind of place we talk "semimajor" rather than, like dangerous Phobos, "altitude". Once it gets mamerostationary down to 20428 km semimajor, it needs to stay there.

Also, there's much room to boost this moon's mass. If we're also parking Libration satellites in the vicinity: I reckoned last year up to 2.56 × 10²² kg; so, Tritonlike. Deimos is nowhere near this; even Phobos (seven times heavier) isn't near this. The following applies whether that mass at 20428 km is still mostly Deimian or has been overtaken by Phobos material, however that has been done.

As Deimos pulls more mass from below, even if just from Phobos which is as noted starts over seven times Deimos' mass, eventually it will fall below the ideal (stationary) orbit. Conservation of momentum suggests to take on additional momentum from outside Mars' 1.52 AU.

Deimos (and Mars generally) is sited well to take on material from the asteroids. Some of these rocks are considered "Near Earth"; those as don't cross Earth's orbit are "Amors". Eros at 1.4579 AU is the ultra Amor. So we're looking beyond 1.52 AU.

Beyond Mars, the Belt happens to have subsections, delimited by Kirkwood back in the mid 1800s. Among those gaps are 5:1 and 4:1 resonance with Jupiter. That's 1.78 and 2.065 AU from the Sun. Mars has ensured the rocks here don't cross that orbit so - low eccentricity. The asteroids 1.78 - 2.065 AU are the Hungaria group; they trend 16-34° inclination.

Deimos should call dibs on the Hungariae.

Ganymed-no-E is a problem. 2.66 AU but perihelion 1.24 AU. It might actually strike this system one day. The Beltalowda need to fix this.

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.

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.