Ceres/Mars as manufacturing outposts (analytic exercise)

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  • #26
jkn
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Marcus,

Of course shorter pylon (more like a cable) is easier to build. It
needs to be build from local materials anyway. So why not continue
until you have tip speed for Hohmann orbit to Earth? Ion engine is
too slow for transporting anything alive. We cannot completely stop
cosmic radiation, so we need to minimize travel time. 10 m of water
would give same protection as our atmosphere, but it would not stop
all. I don't know how much would be needed. Also every traveler
would like to use faster transport.

R^3 = GM*(9 hours/2π)^2

Test it with Earth:

G=6.67384e-11 N m^2 / kg^2
M = 5.9742412e+24 kg
R = (6.67384e-11*5.9742412e+24*(86164 / 3.1415927/2)^2)^(1/3) =
42168048 m

Which is correct, according to my memory. Of course cable must be
longer than that. How much longer depends on mass of the counterweight.

mfb,

Acceleration with strength of cable material determine how much it
needs to be tapered. Even with Hohmann speed, Ceres space elevator
needs 1/10 of material strength or 1/10 of tapering compared to Earth
space elevator. Earth space elevator is theoretically possible.



Drilling to center of Ceres would be difficult. Again most of
equipment needs to be made of local materials. Under very high
pressure solids are not so solid anymore. Borehole will close
itself. In ice this happens easier than in solid rock. Of course low
temperature will reduce problem. Drilling equipment needs to moved
down to drilled shaft. Otherwise changing drill bits would take too
long. More like mining operation than simple drilling.

Reason to do it? To find out what is there of course. Even Kola
drilling produced surprising data. Ceres might be largest body we
could drill/mine down to center. Dark mater interacts with normal
mater only by gravitation. Do planets have dark mater in their cores?
Something else unknown? I guess in Ceres light elements are on the
top and heavier are close to center. If we need heavier elements we
have to dig deep.

To center of Ceres idea come to my mind, when I tried to find reasons
to go to Ceres. Smaller asteroids or martian moons are easier targets.
 
  • #27
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Acceleration with strength of cable material determine how much it
needs to be tapered. Even with Hohmann speed, Ceres space elevator
needs 1/10 of material strength or 1/10 of tapering compared to Earth
space elevator. Earth space elevator is theoretically possible.
It is not acceleration alone. Length is also relevant. As acceleration is dependent on distance, you have to take the integral of acceleration over the length. This is difference in potential (in rotating coordinate systems), which translates to tip speed, neglecting the gravity of Ceres.
For earth it roughly translates to escape velocity.
 
  • #28
marcus
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Hi RKN, thanks for your response.

You may not have considered my assumptions A and B, or thought they were reasonable. Perhaps you have different but unstated assumptions! You talk about human-grade shielding and say ion propulsion is too slow.
This is not relevant to a robotic chemical industry shipping primarily to other locations besides Earth.

You talk about wanting Hohmann transfer velocity to get to Earth, your idea of a space elevator should provide this. This is not relevant. The ships would not be going to Earth. They would be taking chemical/materials to other (unspecified) customer locations where there was a need.

Thanks for checking the formula for geostationary orbit radius. It does indeed give about 42,000 km for Earth which is right! For Ceres the altitude is about 700 km, but then one needs to extend past that and put a counterweight to keep the structure in tension. How much farther than 700 km, would be desirable I do not know. Can you help with a guess?



 
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  • #29
jkn
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Marcus,

I hope that we don't develop complex manufacturing system capable to
operate without human presence. So there must be manned space station
and fastest practical travel to and from. Note that a long space
elevator would be useful for traveling to anywhere in outer solar
system. Delivery from Ceres with long space elevator would be a year(?)
faster than by using ion engines.


Minimum length of space elevator depends on mass of counter weight.
Total mass is smallest if counter weight is replaced by longer cable.
My guess is total 1400 km. Both 700 km halfs balance each other. This
is not correct, but I don't want to search my old calculation now or
recalculate it. Perhaps a small counter weight is needed at 1400 km.



mfb,

Solution shows that cable diameter grows exponentially. For this
discussion acceleration is close enough approximation for me. 'Ceres -
Hohmann to Earth' space elevator would be about 10 * easier than
'Earth - GEO' elevator.



In my list of space tech development first step is cheaper access to
LEO. Spacex is doing best work for that now. Asteroid base is in
5.th place.
 
  • #30
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@marcus: an earth orbit is certainly an interesting target for all sorts of materials. If you find some cheaper way than rocket launches from Earth, it is interesting.
 
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  • #31
marcus
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@marcus: an earth orbit is certainly an interesting target for all sorts of materials. If you find some cheaper way than rocket launches from Earth, it is interesting.
WOW! Thanks for pointing that out!
I was thinking, oh well, the earth has plenty of resources. Ceres would never be selling chemical/material products to Earth.
But maybe that's short-sighted. Maybe Earth orbit would be a possible customer for a Ceres chemical industry.

I don't feel able to evaluate that possibility and do the numbers based on realistic assumptions, so I can't pursue it. Just have to keep the possibility in mind, avoid dismissing it.

At the moment some questions in my mind are:
Does Ceres have nitrogen---N-containing minerals, ammonium compounds?
Does it have a range of metals, in surface rubble, or accessible in other places?
Presumably it does have water, and some compounds of carbon---that seems fair to assume.

Where might there eventually be a market for Ceres water? It is probably some of the cheapest water in the inner solar system. Johnny Morales made this point in post #2 of this thread. But what sort of customers might there be? And where might they be located?
 
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  • #32
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Not sure if it was already mentioned, but Ceres does have the added benefit of having launch window periods at a little more than a year over Mars' 26 months. Launches can be done at nearly twice the frequency for Ceres, even if it is double the distance of Mars. No matter what, any current mission will have to deal with leaving Earth to get to its destination, or vice versa. This huge difference in launch windows may play a big role in maintaining any sort of mining/manufacturing base on Ceres versus immediately colonizing Mars.
 
  • #33
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Where is the point in having more frequent launch windows if the trip between Ceres and Earth takes as long as the time between Mars launch windows (26 months)?
Only in rare occasions (Mars launch window closed recently, Ceres launch window coming soon) Ceres would be "faster" to reach.
 

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