Colonization of asteroids

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Advantages of asteroids:

  • Easy diggability (piles of loose regolith & gravel)
  • Perfect shielding against space radiation even with just a few meters of rock (in contrast to O'Neill cylinders)
  • Large open volumes with low risk of rupture even in the case of larger meteorite impacts (in contrast to O'Neill cylinders)
  • Eventual minability all the way down to the the (weightless) core – at least for the smaller asteroids

Disadvantages and challenges of asteroids:

  • Big communication lags due to speed of light => Big data-caches replicating Earth's internet
  • Risk of "gravel gas" Kessler syndrome? Strategies against this issue?

Reasons for presence of larger human crowds

  • space sports
  • space tourism
  • mining? perhaps unlikely given advancing automation by then likely needing minimal to no human presence
  • having been born there
  • ...

A nice place for humans

Environment optimized for human well being / human psychology – the "zero gravity cavern park":

  • what would be the optimal cavern size?
    – probably pretty darn big to give an open air feeling
    – but probably not as big as O'Neill cylinders making crossing the cavern with an microgravity locomotion suit unpleasantly slow and possibly even dangerous
  • shape of the cavern – not too simple not too complex e.g. big bean shaped main body with some places tapering down into somewhat branching tunnels
  • putting plants on the walls of the cavern
  • putting ladders on the walls of the cavern
  • lighting choices in the caverns – at times full brightness artificial sunlight
  • emulated weather? – wind?, rain???
  • "open air" restaurants as half open slowly rotating relatively small centrifuges in the walls of the much bigger cavern
  • "open air" playgrounds, sports-grounds, art & educational galleries, ...
  • entry points to the passenger transportation system
  • maybe some areas of the cavern transparently sealed showing the actual asteroid underground environment
  • Living quarters "underground" – also in small centrifuges big enough to not cause nausea
  • centrifuge ponds??
  • how would pets get around???

(wiki-TODO: this needs an atmospheric illustration)

Transport and Locomotion

  • Effects of slow rotation of the asteroid on human locomotion in big voids
  • Effects of minute gravity on human locomotion in big voids

Resources

  • Widely varying in the main asteroid belt – located at a good distance from the sun
  • Silicate rich, carbon rich, metals rich, and even some water ice
  • Resources not in the form of more easily processable gasses or liquids available
    – well Ceres might have some liquid brine water underground

The oddities of free-space-crossing big open very slightly rotating mesogravity caverns

Note: The usually very low asteroid gravity (well except on the very largest ones like e.g.: Ceres, Vesta, Psyche, ...)
is always bigger than the centrifugal forces. Otherwise the asteroids would not have been stable in the first place.
The two can come surprisingly close though (there are asteroids with oblate shape from fast spinning).
Assuming a small asteroid: If the main cavity is a big part of the size of the whole asteroid gravity becomes highly nonlinear (but also very weak).

Note: In all the following assumed is repulsion from the walls and than purely inertial drift.

  • Assumed is no employment of acceleration capabilities of a microgravity locomotion suit
  • Effects of air resistance are in first approximation ignored. This might be significant for big caverns though.

Assumptions on the cavern: If the cavern ...

  • is not at the center of the asteroid and
  • is reasonably round

then it has eight special cavern wall areas.
It might be useful to conspicuously mark them to make the weak forces over long ranges
when crossing the cavern more comprehensible and more predictable.

The six special cavern wall areas falling in three groups:

  • centrifugal bottom (aka radial top, asteroid outside)
  • centrigugal top (aka radial bottom, asteroid inside)
  • prograde direction (towards the in rotation most leading parts of the cavern)
  • retrogate direction (towards the most most lagging point of the cavern)
  • rotational north direction
  • rotational south direction

Prograde to retrograde cavern crossing (The easiest to understand crossing):
Standing truly still (that is standing still in the non-rotating frame of reference) one moves:

  • from the prograde cavern walls
  • to the retrograde cavern walls

with the northern and southern cavern walls moving in circular arcs.
In the rotating frame of reference the centrifugal force balances out pretty much exactly with the coriolis force.
The absolute speed in the rotating frame of reference stays constant.
Only it's direction changes such that the motion follows a circular arc.
That is: Watching the walls from within the north and south cavern walls moves in circular arcs - (slowly).

Well, the asteroids gravity will add a bit of a parabolic rise (given centrifugal down is gravitative up) to that.
Falling and crashing into the "centrifugal ceiling" can get unpleasant to dangerous for very big asteroids and/or very big caverns.
(TODO: as a fun exercise: plot the danger-limits in the asteroid mass vs cavern radius chart)

Crossing prorgade walls to retrograde walls slower than the speed that fully compensates the asteroids rotation velocity (ignoring gravity for now)
in the limit just leaves mostly centrifugal force. The falling speed that amasses from that centrifugal force then in turn
accelerates you circumferentailly towards the retrograde cavern walls.

(wiki-TODO: check typical rotation speeds of asteroids of different size classes – to which size is reaching the full rotation compensation speed realistic)

Going prograde to retrograde gives you a boost, that is it gets you farther.

  • at some first critical speed (in this direction!) the trajectories curvature flips from curving "downwards" to curving upwards
  • at some second critical speed (in this direction!) the trajectory will turn into a circular "upwards" arc around the asteroids center of mass – without considering gravity this second critical speed (rotating frame) would be minus the rotation speed of the asteroid at that radius (static frame) – with gravity considered though this second critical speed gets reduced and the circular trajectory essentially is a segment of circular orbit around the asteroids center of mass.

Retrograde to prograde cavern crossing:
Moving the other direction things get a bit less trivial.
Let's assume we try to naively trace back the way we came from by only
reflecting the speed (full rotation compensation speed) on arrival at the retrograde wall and doeing nothing else. Initially we still have:

  • still zero radial speed and
  • but now we have double the circumferential speed that the asteroid rotates at our current radial distance from the center of mass.

Initially the coriolis force is coaxial to the the centrifugal force and doubles it which introduces and raises a radial "falling" speed component
then, with increasing radial "falling" speed, the coriolis force picks up a component that reduces the circumferential speed component.
Slowing down motion in the direction you want to go.
The overall effect is that while crossing the cavern retrograde walls to prograde walls
you'll "fall" and drift from the targeted "prograde cavern walls" more or less towards the "centrifugal bottom" cavern walls.

Top to bottom cavern crossing:
The same as for retrograde to prograde applies but here you already start out with zero circumferential speed.
So effectively you drift from the targeted bottom cavern walls towards the retrograde cavern walls.

Bottom to top cavern crossing:
The coriolis force makes you speed up in the cirumferential direction.
So effectively you drift from the targeted top cavern walls towards the prograde cavern walls

North to south (and vice versa) cavern crossing: Since the intended main motion is coaxial to the rotation axis an increase in starting speed does not amplify the drift There is though the baseline drift from initially radially and circumferentially rotating exactly matched up with the rotating frame of reference.
This gives a drift towards a a direction between the retrograde cavern walls and the centrifugal-bottom cavern walls.

  • (wiki-TODO: this needs some example trajectories)
  • (wiki-TODO: this needs some sketches)
  • (wiki-TODO: above text needs review)
  • (wiki-TODO: analyze the effects of air resistance – at which cavern sizes an asteroid masses do the effects become significant – say 25% more drift or so)

Related

External links

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