Asteroidal RoI

Jensen’s article had “ROI” as quickndirty diameter / deltaV. I detect a tension between this “ROI” and how easily we colonise an asteroid; between sections 2 and 3…

The reason Section 2 RoI for that R part is sheer bulk is that volume is radius-cubed (times-pi/4), not diameter. For that I part - well, Jensen assumes a mining-camp, not a Janhunen shuttle. So where Janhunen can just massdrive stuff off the Moon and not even a lot of mass of stuff, Jensen requires internally generated propulsion: in short, Tsiolkovsky. The reason deltaV swamps its competion is that Tsiolkovsky proved its energy cost exponential. The RoI equation needs to be r³e^-δv. Atira's not looking so good anymore is it?

Looking at the 6-8 realm, this makes 175706 / 1996 FG3 look relatively even better and Bennu (which didn't make the list) that much worse... but. f(R)/f(dV) further disregards mass, therefore density. This affects ease of digging, ease of spinning; and the deltaV is entirely Earthbased, so there’s little on incoming solar energy aka "flux". (Volume, at least, might imply water-supply, a big help to R against I assuming the same flux.) And we got nothing on whether the mass' orbit is useful or if we’d rather dismantle the whole place, to move elsewhere.

If the rubblepile is housing wetwork, such as miners, then Bennu (which radius he marks 263 m mean) marks the minimum space to live in. That mass (as a C type) is 73.3e+9 kg. Jensen’s article proposes Atira as more-massive than Bennu in a convenient orbit averaging between Venus and Earth. This got me researching if Bennulikes exist down there as well. It turns out – they do! As of now Wiki presents to me three rocks 580-590 m diameter. In order of semimajor: Venus, then Atira; then…

• 2023 EL
• (613676) 2006 WE₄
• 2020 HA10

Atira remains queen of these 0.72-0.82 semimajors. Besides the three hot Bennulikes, nothing between Venus/Atira and Cruithne/Earth exceeds half the size of Jensen’s minimum. So let’s look at these particular three which make Jensen’s cut.

For more economical comparison against Atira: for each of the three the delta-V is lower, and the hollowing-out is faster, and the spinning-up is cheaper.

First: being small has its perks, as momentum goes, more so close to the Sun. This can be done quicker for Bennulikes down here; even if Atira runs closer on average, Atira as nine times more massive is nine times slower to shift. If they start small they might not even need propellant.

Less happily I expect all three hot Bennulikes not to protect their volatiles as well as does Atira. These three will be (even) drier. But: protons come from the aforementioned solar-wind. Can their colonists trap the water, hydrazine, methane as they expose oxides, nitrates, carbonates in the rock…? Can the sails, also, be designed to catch protons?

And these three planetoids can work with the Atira-to-Venus project. If someone is hoping to get Atira into a Cruithnelike 1:1 Venus-resonant orbit then, whilst Atira is kicking materiel to Earth, it might as well kick materiel to 2023 EL on up. As noted Atira has gravity so will be getting massdrivers. For Bennulikes honestly a slingshot or a catapult would do for getting ingots off before raising sail.