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danielravennest t1_iwbr3xx wrote

Reply to comment by stewartm0205 in Researchers Make Rocket Fuel Using Actual Regolith From the Moon by The_Weekend_Baker

For the Moon, the arm is about 6-8 times the payload mass. A complete system with drive motor and solar array is heavier. The figure of merit for these systems is the "Mass return ratio". That's how many tons of material delivered over their operating life, divided by tons of mining equipment, including catapults.

For a full discussion, see the Lunar Catapults section of my Space Systems Engineering book.

To verify authorship, click the View History tab on any page of the book and see the edits have the same user name as I have here.

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stewartm0205 t1_iwinued wrote

Total mass over lifetime. I would have liked to have seen a similar calculation for the linear system.

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danielravennest t1_iwlb1a7 wrote

The original space colony work by Gerard O'Neill and others assumed a "Mass Driver" (coilgun) which launched 4 kg lumps of lunar soil at 4 times a second, which amounts to 500,000 tons per year.

The gun would be 300 meters long and each payload takes 1/3 of a second to get up to speed. That means slightly more than one payload is in the gun at a time, and a near steady-state power supply.

Assuming perfect efficiency of the gun, it then requires 32 MW of constant electric power. With more realistic efficiency and running other stuff for mining or packaging the payloads, you are looking at 40 MW of power.

For comparison, this is in the range of a naval nuclear reactor, except you don't have the ocean to dump waste heat to. Current NASA work is towards 10-30 kW electric reactors for the Lunar suface. So factor of 1000 too small.

But such an electric catapult still needs 24 MW of peak power for launching single payloads at a lower rate. That's because all the acceleration happens over 1/3 of a second. So you need some kind of storage if your power source is smaller, and then release it in a burst.

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stewartm0205 t1_iwnntqj wrote

Solar panels and super capacitors should be enough.

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