NEW PAPYRUS: July 2014

Tethered beneath a hydrogen inflated ballute, a crewed Ares 2 (Ares ETLV-2) reusable landing shuttle slowly descends towards the martian surface.

by Marcel Williams

Launching human crews from the surface of the Earth to low Earth orbit (LEO) requires a delta-v of more than 9.3 kilometers per second (km/s). But on the Moon and Mars, the delta-v requirements are significantly lower. Launching humans from the surface of the Moon to lunar orbit can require as little delta-v as 1.87 km/s. And launching human crews from the surface of Mars to low Mars orbit requires a delta-v of only 4.4 km/s.

Landing humans on the surface of the Earth and on the Moon is relatively easy. Only minuscule amounts of delta-v are required to for crews to leave Earth orbit and glide or parachute through the Earth's thick atmosphere to the terrestrial surface. The delta-v required to land a crew on the surface of the Moon from lunar orbit is equivalent to the delta-v required to leave the lunar surface to low lunar orbit.

Unfortunately, landing crews and large payloads on the surface of Mars is much more problematical. The largest spacecraft that NASA has managed to safely deploy to the Martian surface are all below 600 kilograms in mass. The weight of a lunar derived crewed vehicle to the Martian surface is likely to weigh as much as 10 tonnes, not including the substantial amounts of fuel needed to return to orbit around the Red Planet. And NASA eventually wants the ability to deploy as much as 100 tonnes of payload onto the martian surface by a single spacecraft.

Notional ballutes designed to aerobrake into a planetary orbit or to land on the surface of Mars (Credit: NASA)

The problem with landing large masses on the surface of Mars is that even though the martian atmosphere is approximately 1% as dense as the Earth's atmosphere, it's still thick enough to produce substantial amounts of frictional heating as a vehicle plunges at hypersonic speeds through its atmosphere but still not enough friction to sufficiently lower the terminal velocity as it approaches the planet's surface. Small vehicles (less than 600 kg) attempting to land on Mars have, therefore, been designed to have a high drag coefficients. Designing a spacecraft with a high drag coefficient for vehicles weighing several tonnes or more, however, is much more difficult.

This has pushed NASA towards the idea of utilizing large inflatable ballutes to assist heavy payloads and spacecraft entering the martian atmosphere. The large drag coefficient of a toroidal ballute could allow a spacecraft to decelerate at very low densities high in the martian atmosphere with relatively low rates of frictional heating. The low frictional heat experienced by the ballute could allow for light-weight construction techniques that could enhance the ability to deploy more mass to the martian surface. Ballutes inflated with gases that are lighter than the carbon dioxide could also increases static lift. Recent studies suggest that a toroidal ballute with a tube radius of 80 meters could be used to deliver masses the martian surface of approximately 100 tonnes.

Top: ETLV-2 vehicle designed for landing on the surfaces of the Moon and the moons of Mars; Bottom: An ETLV-2 derived Ares 2 vehicle designed to dock with a disposable heat shield and compacted ballute in order to land on the surface of Mars.

Placed on the surface of Mars, a single staged reusable vehicle with an inert weight of approximately 10 tonnes (including payload and crew) designed to travel to and from the lunar surface would require at least 18 tonnes of fuel to transport a crew from the martian surface to low Mars orbit; 22 tonnes of fuel would be required to reach the surface of Phobos and 24 tonnes of fuel would be needed to reach the surface of Deimos from the martian surface. So with a delta-v requirement of less than 5.3 km/s, a fueled single staged crew vehicle weighing nearly 40 tonnes placed on the surface of Mars should be capable of traveling all the way from the martian surface to the surface of Deimos or to high Mars orbit.

Left: Ares 2 docked with a compacted (pre-deployed) ballute, configured to inject the spacecraft towards an aerobraking encounter with the martian atmosphere. Right: After the rocket burn towards Mars, the Ares 2 would reconfigure itself in order to protect the spacecraft and to inflate the ballute in order to aerobrake and to descend through the martian atmosphere.

A liquid hydrogen and oxygen producing water and fuel depot derived from a reusable orbital transfer vehicle. The Ares 2 landing vehicle would fuel up up at the orbital depot before docking with the compacted ballute/heat shield unit. Water would be transferred to the fuel depot from water factories on the martian moons, Deimos and Phobos.

Water factory would utilize mobile microwave water bugs to extract water from the regolith of the martian moons, Deimos and Phobos; WFD-LV would convert water into fuel to launch water to fuel manufacturing depot in high Mars orbit.

A ballute capable of deploying nearly 40 tonnes to the martian surface could also easily deploy habitats and cargo larger than those contemplated for the Altair vehicle to the lunar surface. Cargo missions to the martian surface could utilize ballutes to deploy mobile robots for excavating and sintering the surface of Mars to create landing and launch pads for crewed shuttle vehicles and for regolith shielded outpost similar to those that could be utilized on the lunar surface.

Hydrogen inflated ballute would enable the crewed Ares 2 vehicle to aerobrake and land on the martian surface.

Small nuclear reactors would also need to be deployed to power the martian outpost at night or during periods when sandstorms block out significant amounts of sunlight. Methanol/oxygen fuel cell electric power plants could also be deployed as back up power, utilizing methanol produced from the pyrolysis of human biowaste and oxygen extracted from atmospheric carbon dioxide or from the electrolysis of water.

Water factories than mine water from the martian regolith would also need to be deployed. Mobile microwave robots could be used to melt the ice contained in the martian regolith. Water, of course, is essential for drinking, washing, and growing food but is also essential for the production of oxygen for air. Hydrogen and oxygen can also be used to produce hydrogen and oxygen to fuel the reusable shuttle craft.

Ares 2 hovers near the sintered landing area of a martian outpost.

Under the scenario presented here, fuel depots and rotational human outpost would already be placed in high Mars orbit a few years before the first crewed missions to the martian surface along with water and fuel producing facilities on the surface of the martian moons, Deimos and Phobos. Human interplanetary missions to Mars orbit would utilize an orbital transfer vehicle operating between the Earth-Moon Lagrange points and high Mars orbit.

Rotating regolith shielded (enriched with iron ore) SLS fuel tank derived artificial gravity habitat in high Mars orbit capable of housing as many as 16 astronauts.

Such an interplanetary orbital transfer vehicle would utilize fuel manufactured from water exported from the lunar poles when going to high Mars orbit and fuel manufactured from water from the martian moons when returning to cis-lunar space. Such crewed missions would already transport reusable Ares ETLV-2 vehicles to Mars orbit for docking with orbiting space habitats or transferring crews to the surface of the moons of Mars. A single SLS launch could deploy one or two compacted ballutes plus heat shields to high Mars orbit for one or two human missions to the martian surface.

Three solar powered regolith shielded habitat modules joined together by two inflated corridors. Additional power for the outpost would be provided by a couple of small nuclear reactors buried beneath the regolith, a few hundred meters away.

The Ares ETLV-2 (Ares 2) would fuel up in high Mars orbit at a OTV derived fuel depot before docking with a ballute/heat shield unit. The Ares ETLV- 2 would thin boost the Mars landing vehicle towards Mars. During the short journey from high Mars orbit towards Mars, the Ares 2 would reconfigure itself while also deploying the ballute. The ballute would allow the Ares 2 to aerobrake into orbit around Mars and then descend into the martian atmosphere. The final vertical descent to the martian surface would first drop off the protective heat shield, allowing Ares 2 rockets to slow down the final descent to the sintered surface of a martian outpost.