Zubrin and McKay plans for terraforming Mars with giant orbital mirrors cited by Elon Musk

The McKay-Zubrin plan for terraforming Mars in 50 years was cited by Elon Musk.

Orbital mirrors with 100 km radius are required to vaporize the CO2 in the south polar cap. If manufactured of solar sail like material, such mirrors would have a mass on the order of 200,000 tonnes. If manufactured in space out of asteroidal or Martian moon material, about 120 MWe-years of energy would be needed to produce the required aluminum.

The use of orbiting mirrors is another way for hydrosphere activation. For example, if the 125 km radius reflector discussed earlier for use in vaporizing the pole were to concentrate its power on a smaller region, 27 TW would be available to melt lakes or volatilize nitrate beds. This is triple the power available from the impact of a 10 billion tonne asteroid per year, and in all probability would be far more controllable. A single such mirror could drive vast amounts of water out of the permafrost and into the nascent Martian ecosystem very quickly. Thus while the engineering of such mirrors may be somewhat grandiose, the benefits to terraforming of being able to wield tens of TW of power in a controllable way can hardly be overstated.

Energy for making the aluminum can use near-term multimegawatt nuclear power units, such as the 5 MWe
modules now under consideration for NEP spacecraft.

Los Alamos and NASA are researching a 35-ton two-megawatt Megapower reactor.

Four large nuclear thermal rockets to move four big asterods

Orbital transfer of very massive bodies from the outer solar system can be accomplished using nuclear thermal rocket engines using the asteroid’s volatile material as propellant. Using major planets for gravity assists, the rocket DV required to move an outer solar system asteroid onto a collision trajectory with Mars can be as little as 300 m/s. If the asteroid is made of NH3, specific impulses of about 400 seconds can be attained, and as little as 10% of the asteroid will be required for propellant. Four 5000 MWt NTR engines would require a 10 year burn time to push a 10 billion tonne asteroid through a DV of 300 m/s. About 4 such objects would be sufficient to greenhouse Mars.

An asteroid made of frozen ammonia with a mass of 10 billion tonnes orbiting the sun at a distance of 12 AU. Such an object, if spherical, would have a diameter of about 2.6 km, and changing its orbit to intersect Saturn’s.

Alternative – bacteria to make Ammonia and methane

A possible improvement to the ammonia asteroidal impact method would use bacteria which can metabolize nitrogen and water to produce ammonia. If an initial greenhouse condition were to be created by ammonia object importation, it may be possible that a bacterial ecology could be set up on the planet’s surface that would recycle the nitrogen resulting from ammonia photolysis back into the atmosphere as ammonia, thereby maintaining the system without the need for further impacts. Similar schemes might also be feasible for cycling methane, another short-lived natural greenhouse gas which might be imported to the planet.

Alternative- One gigawatt reactor to make halocarbon – CF4 to trigger warming effect

Greenhousing Mars via the manufacture of halocarbon gases on the planet’s surface may well be the most practical option. Total surface power requirements to drive planetary warming using this method are calculated and found to be on the order of 1000 MWe, and the required times scale for climate and atmosphere modification is on the order of 50 years.

The amount of a greenhouse gas needed to heat a planet is roughly proportional to the square of the temperature change required, driving Mars into a runaway greenhouse with an artificial 4 K temperature rise only requires about 1/200th the engineering effort that would be needed if the entire 55 K rise had to be engineered by brute force.

The dynamics of the regolith gas-release process are only approximately understood, and the total available reserves of CO2 won’t be known until human explorers journey to Mars to make a detailed assessment.