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Interesting ideas. My own thinking on the subject has been somewhat more mundane, but perhaps practical.
1. Construct a mirror making facility on the Moon using aluminum primarily, which would use mass drivers or other means to launch them into Mars orbit.
2. The mirrors would unfurl into large low mass solar sails after launch and use solar radiation pressure for attitude control and station-keeping. The orbit would be polar and the sail/mirrors would manuver to remain in constant sunlight and would orient and shape themselves to reflect the sunlight to the surface of Mars.
3. As the mirrors first accumulate in orbit, they will not reflect sunlight onto Mars so that a comprehensive decade long effort to map and scientifically catalog Mars in its present state can be completed. Some of the mirrors could double as solar power sattellites, sending power via microwaves to the science teams and "wiring" Mars from the start.
4. Depending on the rate of mirror production, after a decade insolation can be reasonably increased by 10 to 50 percent and this figure can continue to grow as needed.
5. Shortly after the mirrors begin to reflect sunlight onto Mars, the planet will experience massive floods, aquire a CO2 and water vapor atmosphere, and have incredible windstorms and rain. With an oxygen supply, a human could walk around once the weather settled down.
6. With such control over insolation, people might be able to not just talk about the weather, but actually do something about it!
7. Plants would slowly complete the job.
Steve Mickler
Although a "sun" is usually the solar intensity at Earth's surface: in this context it would be the solar intensity at the average distance of Earth from the Sun or about 1.3KW/m^2.
The solar cell breakthrough I was referring to was from a NASA website, but unfortunately I misplaced the location info. I'll try to find it again, but as important as the efficiency is the idea of using concentrated sunlight as this can greatly increase the power per unit mass or specific power of a photovoltaic array. In addition, the mirrors required do not need extreme optical accuracy to acheive a few hundred "suns" and therefore can be extremely low mass much like solar sails.
The big drawback of low thrust systems in general is that they cannot take advantage of the benefit of thrusting to Mars while deep in Earth's gravity well and moving fast relative to Earth. A small thrust while going fast is much more advantageous than one farther away since a small addition to a big velocity will result in much more speed. To deal with this, the VASIMIR can operate at a lower exhaust velocity and thereby greatly increase its thrust while escaping Earth or Mars.
Even so the resulting thrust is too small to provide all the necessary velocity for a fast trip in the short time a space vehicle has as it whips around in low orbit since the thrusting necessarily raises the orbit. This can be mitigated somewhat by using a series of perigee thrusts to enter a highly elliptical orbit and increase speed at perigee while lowering the amount of thrust required to escape to Mars. On the last "burn" only a couple thousand mph is needed for a fast trip. For this reason a chemical rocket boost may be just the ticket. A solar thermal rocket would be able to acheive a slowish trip without any chemical help this way and its concentrator could be used for a solar cell array for a VASIMIR to add velocity while trans Mars. The electricity could support surface operations from orbit via microwaves to a surface rectenna. Propellent can be derived by boiling off volatiles of Phobos' regolith in a solar furnace.
The real advantage of solar thermal may lie in its ability to use almost anything as propellent including the several million pounds of aluminum alloy in discarded Comsats in or near Clarke orbit. Telerobotically harvesting and processing this space "junk" could jumpstart a first Mars mission, a
"Junkyard Mars" concept if you will.
Steve Mickler
Although it is true that plasma rockets are highly efficient, untill recently with the development of the VASMIR engine by Chaing-Diaz et al, the thrust levels were too low to reduce the transit time to Mars vs. other propulsion technologies. Now the problem is supplying enough electricity for the high energy exhaust since power demand is at least quadrupled for a doubling of exhaust velocity: KE=1/2mv^2. Care must be taken to avoid increasing the vehicle mass too much with power production equip. as this can negate the advantage gained by the higher exhaust velocity particularly on shorter missions. For this reason, nuclear fission reactors are often seen as essential, but this may no longer be true due to recent breakthroughs in solar cell tech. Solar cells of very high specific power operating at 400 suns and 40% efficiency allow the solar option to compete with or even exceed nuclear. Because the cells use concentrated sunlight they can use lightweight concentrator mirrors which can reasonably supply power out to Jupiter and even beyond at a small fraction of equivalent nuclear power's cost.
Actually, the cheapest alternative and one of the fastest to Mars is Solar Thermal which can use the concentrated sunlight to directly heat a propellent.
I quite agree that shortening trip time is possible and desirable.
Ad Astra
Steve Mickler
Atlanta, Ga.
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