Aldrin’s castle

Travelling to Mars could be dangerous and uncomfortable, but Apollo 11 astronaut Buzz Aldrin has a plan to do it in style

Travelling to Mars can be dangerous and uncomfortable, but Apollo 11 astronaut Buzz Aldrin has a plan to do it in style

When Apollo 11 landed on the Moon in 1969, many at NASA felt there was a good chance they’d be landing astronauts on Mars by 1984. But government priorities changed, and the only part of NASA’s grand exploration plan to come to fruition was the Space Shuttle, which taxied astronauts to the International Space Station and no further. Both George H. W. Bush and George W. Bush tried to recapture the spirit, pitching missions to the Red Planet that would have arrived in 2018, but these never became a reality.

All of these plans and expectations floundered as budgets were cut, and the long build-up for a Mars mission struggled to maintain government support. Now at last the fourth rock from the

Sun feels within reach, with NASA working hard on a return to the Moon and a Mars landing in the 2030s with the help of European Space Agency (ESA) participation. And with SpaceX’s extraordinary progress on its Starship craft that’s looking likely to beat NASA, humankind could arrive on Martian soil during the 2020s.

Both NASA and SpaceX’s plans are based on a conventional mission where an exploration spacecraft is put into Earth orbit and serviced in some way – whether assembly or refuelling. From here it boosts off on a minimum-energy trajectory called a Hohmann transfer, an elliptical orbit that boosts out from that of Earth’s orbit, coasting outwards until it just touches Mars’ orbit on the opposite side of the Sun from where it left our planet. When reaching Mars’ orbit, the spacecraft will make a manoeuvre to swing around the Red Planet before either detaching a lander or landing itself. Hohmann transfers use the least energy, so can get as much as possible to Mars for the least money and propellant, but take around six months to get there.

If we’re depending upon boosting our entire spacecraft on this trajectory, everything must be reduced to the minimum – even with SpaceX’s ambitious plans with Starship – leading to small living spaces, spending months relatively unprotected from the interplanetary radiation environment and no gravity. However, astronaut Buzz Aldrin has been advocating for another route to Mars since the 1980s, and the progress by NASA and SpaceX could enable his plan to provide more comfortable Martian travel.

Aldrin has proposed a cycler spacecraft – nicknamed castles in his studies – where a travelling space habitat is placed into a reoccurring orbit between Earth and Mars. Aldrin’s castles offer several advantages: once placed into the cycling orbit they won’t need more fuel beyond what’s needed to power small thrusters for course correction. As they can be used for multiple trips over many years, it becomes cost effective to build a much larger structure. Akin to hopping on an ocean liner rather than a jet aircraft, the castles could also have greater space, better radiation shielding and the possibility of spininduced gravity. These liners would actually get you to

Mars faster; the cycler orbit can be configured in such a way that a trip that would otherwise take roughly nine months would be shortened to a little over four. But there is a trade-off: while there is a faster outbound trip to Mars, it takes longer to return to Earth. However, it is possible to install a second cycler, which could be placed in a mirror orbit with a quick return to Earth and a longer outbound trip to the Red Planet. Travellers can spend less time in transit while better protected against radiation and microgravity, with cargo taking the spare space on the more lengthy journeys.

The concept does have other challenges, though. One is that the castles never enter orbit around Earth or Mars. Crew would take taxi craft to meet with the castle as it swings by at speeds of 24,000 or 35,000 kilometres (14,900 or 21,750 miles) per hour at Earth and Mars respectively. While the first missions are likely to be selfcontained, as the human presence on Mars becomes established and NASA and SpaceX’s capabilities develop, Aldrin’s castles may well become a bridge to Mars – and one that’s possibly comprised of SpaceX Starships.

“Astronaut

Buzz Aldrin has been advocating for another route to Mars since the 1980s”

1 Deep-space habitat In this concept, the living accommodation is a large, inflatable module like those developed by Bigelow Aerospace. 2 Crew Transfer Vehicles These craft would meet the cycler in Earth orbit and dock on for the ride to Mars before separating to decelerate into Martian orbit. 3 Structural node The cyclers would be built on nodes that joined modules together. This version wouldn’t have spin gravity, but future craft might. 4 Solar power Inner Solar System missions can exploit plentiful solar power and avoid the challenges of nuclear power. 5 Solar electric propulsion Variations in planetary orbits mean the cyclers will need some propulsion for course corrections. 6 Earth orbit Taxi spacecraft would rendezvous with the cycler as it swung past at 24,000 kilometres (14,900 miles) per hour. 7 To Mars The cycler coasts back out into interplanetary space, taking four to five months to reach Mars. 8 Outbound cycler orbit After the fast transit to Mars, the outbound cycler swings out past Mars, taking a long loop back to Earth. 9 Return orbit Rather than having to make a long trip back, a second cycler could be placed in a matching orbit with a quick return path.