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This topic is offered as a follow up to a discussion between Void and Calliban...
The first post will be a quote of Calliban's post in one of Void's topics.
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Quoted from a topic of Void's
Orbital energy is in many ways more promissing on Mars than on Earth. A Martian space elevator can be made from conventional carbon fibre ropes. This means that a Martian SPS can transmit power to the surface using HV DC cables. No need for microwaves. Cables would have to be angled such that they miss the orbit of Phobos.
Ultimately, a heavily developed Mars could construct a complete orbital ring structure at geostationary point, some 17,038km above the equatorial surface. Solar powerplants could be tethered to the ring, allowing them to generate power 90% of the time and send that power to Mars surface by cable. Human habitats could also be tethered to the ring. Eventually, Mars orbital space would become one of the best locations in the solar system.
The circumference of aerostationary orbit is 128,350km. The mass of Phobos is 1.07E16kg. If Phobos is fully deconstructed, it will provide some 83 million tonnes of construction material per kilometre of ring circumference. That is more than enough to build an extensive ring structure all around Mars, with enough SPS infrastructure to power the planet many times over. I think the population of Mars could ultimately greatly exceed that of Earth. Many of those people would no doubt live in orbit. But getting between the ring and the surface of Mars would be much easier than attempting the same thing on Earth.
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On the topic of Phobos, the wiki article on the moon notes that it appears to be covered with thick layers of fine regolith. This may have near term application as propellant for the large ship that Robert is developing.
I have already written about using fibre lasers to vapourise this material and accelerating the resultant plasma using an arc jet. There are three problems with this idea: (1) Even fibre lasers are relatively inefficient and power hungry; (2) If the propellant does not vaporise uniformly, the reaction chamber and laser optics could end up being peppered with molten rock particles; (3) Oxygen ions in the plasma, would attack the arcjet cathode, limiting its life.
An alternative would be a modified VASIMR engine.
https://en.m.wikipedia.org/wiki/Variabl … sma_Rocket
We inject pellets consisting of 10% water ice and 90% micron sized regolith fines. Radio frequency generators would heat the water to millions of Kelvin, forming a plasma of hydrogen and oxygen ions. The micron sized dust particles would be vaporised by molecular collision and radiated heat. The resulting mixed plasma is contained away from the engine walls by a strong solenoid static magnetic field. This functions as an expansive engine nozzle at the rear of the engine.
With an exhaust velocity of 50km/s, a large ship should be able to fly from low Mars orbit to LEO and back on a single propellant load. This would allow Phobos regolith to become the source of some 90% of propellant reaction mass. The other 10% can be recycled black water from the ship. This is convenient, because Phobos L1 point is only about 1km above Stickney crater. The large ship could dock there on its return flight to Earth. It should therefore be simple to refill the ship with propellant dust from a small facility on Phobos.
Last edited by Calliban (2024-01-09 08:14:12)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #3
Your post about using fine regolith as propellant seems (to me at least) to have near-universal application throughout the Solar system.
Please consider adding it to Interplanetary Transportation as a topic on it's own.
Void's idea, which this topic was created to develop, appears to be about taking advantage of the geosynchronous orbit around Mars, to make a permanent structure of some kind. I'd like to see that idea fleshed out beyond hand waving.
We do a lot of hand waving in this forum. Hand waving is a necessary precursor to useful ideas.
Your propulsion suggestion appears to have a chance of development and application in the Real Universe, but it does need some work.
For example, the concept of using a fixed magnetic field to contain hot plasma particles on their way to the exit from a propulsion device could use some development.
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