Shipping sand from Mars to Earth is a relatively simple concept and I will use a new currency called Mars Dollars for Mars only resources and Earth US dollars for Earth based assets.
In 2100 several industries are advanced enough on Mars that they can function independently from Earth.
- Mars has a way to manufacture their own solar or solar thermal power without consuming any Earth resources, using Earth manpower, using Earth computers or machines etc.
- Mars has its own Mass Driver like a coil-gun or railgun that can launch mass from Mars surface to outer space to orbit around the sun. This will not be orbit around Mars but will escape Mars gravity well. Mass Driver construction and repair will be using Mars resources only. The first iteration is likely to be a Coilgun because 1 cm of track can be used to reach 5000 m/s as proven by the Russians in 1970s.
- Mars will be able to provide their own food, and life support without parts made on Earth or any other resources from Earth. This one line doesn’t need to be strictly true just 99.99% true. The time humans spend doing the management of the Mars surface to Earth surface can’t cost Earth resources by virtue of needing food, medicine or other life support form Earth.
- Mars will be able to manufacture or repair Solar Sail space craft. Ideally transferred momentum spacecraft as well but solar sail is sufficient for this plan to work. This spacecraft must be launchable from the mass driver to sun orbit. This includes, solar or thermionic power, star tracker, radio, computer, solar sail actuators etc.
- Mars must be able to manufacture Aero-braking housing to safely get past Earth’s upper atmosphere without burning up.
- Mars must be able to manufacture parachutes so that the cargo can be delivered all the way to Earth surface without damage.
So to proceed:
- Launch solar sails spacecraft
- Launch cargo
- Solar sail space craft captures the free floating cargo
- Solar sail navigates to Earth using Mars version of Deep Space Network comprised of hundreds of small cubist sized spacecraft that were build on Mars with small radio antennas.
- At Earth the solar sails fire the cargo at Earth and then navigate away from Earth so they are not damaged. Then it returns to Mars to pick up the next cargo.
- Cargo is covered in Aero-Brake material and does not burn up during descent
- Cargo fires parachute once it is slowed enough for parachute. Parachute may need some form of navigation to the correct location.
- Surface to Surface with Zero Earth resources consumed. The technology using Mars solar power, mars metals, mars semiconductors or vacuum tubes and other materials are valued in Mars dollars. Once the cargo is on Earth there is a trade of the Mars dollars worth of stuff for some amount of Earth dollars worth of stuff. The transfer rate between Earth dollars and Mars dollars is calculated based on the Earth sale price of the goods vs the Mars sale price of the goods and transit equipment needed to create and ship the cargo.
Now its important to recognize that to be capable of shipping sand profitably doesn’t mean that the total average cost in Earth dollars is cheaper than the sand. Rather it means that the derivative cost is cheaper than the sand. More valuable cargo can be traded to pay off the Earth cost of buying the initial parts used by a colony to build the mass driver and other high tech parts needed. So long as the wear and tear on the Mars infrastructure can be repaired on Mars using Mars resources then the cost is in Mars dollars only and does not cost any Earth dollars. This means that in terms of trade with Earth it will be worthwhile to send extra missions full of sand because the derivative profit is greater than zero.
2100 is 84 years away. 84 years ago it was 1932. Airplanes were less than 30 years from the wright brothers and propeller airplanes were state of the art. Computers didn’t exist. Semi-conductors didn’t exist in mass. Vacuum tubes and radar were just being invented. Manufacturing was very crude compared to today and prices for custom manufacture was expensive. There was no space industry. 2100 will be a much larger amount of change from us than we are from 1932 because our growth is exponential. The tools to have cheap transit to mars will exist as will 3d printing of many forms of technology allowing high tech tools to be printed on Mars to build other high tech tools.