The furthering of humankind's expansion into space and establishing of firm footholds on other worlds could depend on a continuously moving, cycling spaceship network. These rapid-transit cycling spaceships would employ the principles of gravity assist , which entails taking a slingshot approach to running people and cargo from one locale to another. The motions of the planets and gravity would be used as a natural fuel.
It may be possible to establish a "recyclable space program"—a vision that is a far cry from the early days of space exploration. As an example, the Apollo Moon landing effort of the 1960s and 1970s involved tossaway technology. All of the stages of the giant Saturn V booster—except for the return capsule that brought the astronauts back to Earth—were thrown away. Even today, the idea of a fully or partially disposable space program is being perpetuated.
Opening up the space frontier, however, requires transcending reusability and recycling barriers to shape a space agenda for the twenty-first century. Putting into place a fully cycling strategy for travel in the inner solar system travel is likely to happen in phases. The first human missions to Mars will install the early segments of the network.
A champion of the cycling spaceship idea is the Apollo 11 astronaut Buzz Aldrin. Aldrin's vision is to have large cycling spaceships swinging permanently between the orbits of Earth and Mars. A cycling spacecraft in an elliptical orbit would transit from Earth to Mars and back again, permanently cycling between the orbits of the two planets. This approach could be used to put in place an interplanetary passenger transport system.
In an Earth-Mars scenario, transfer vehicles ferry passengers from Spaceport Earth to a cycler. At the other end of a Mars cycling trajectory is Spaceport Mars. Cyclers take advantage of the way the Earth, traveling faster on an inside orbit around the Sun, catches up to Mars about every two Earth years. Like a ship using the trade winds, a cycling spacecraft will not follow a linear route to Mars. When the planets are aligned, it will accelerate away from Earth and loop outward, swinging close to Mars five months later.
But instead of stopping, the cycler releases smaller ships that ferry people and supplies to the surface. The cycler acquires some of the planet's momentum using gravity assist and glides on, curving away and eventually back to Earth. It returns home twenty-one months after departure, but it does not stop at that point: With another boost from Earth's gravity it sails onward, and back to Mars. The vehicle becomes a permanent, human-made companion of Earth and Mars, using the free and inexhaustible fuel supply of gravity to maintain its orbit.
The cycler system would eliminate the need to accelerate and decelerate and would also discard the necessity of large and costly spacecraft hardware. Like an ocean liner on a regular route, a cycler would zip perpetually along a predictable orbit. Twin cyclers, one always en route to Mars and the other always in transit back to Earth, would greatly reduce the cost of exploring and, eventually settling, the fourth planet from the Sun: Mars. The pursuit of an economical philosophy may lead to sustainable and recyclable space transportation. Doing so would set in motion expressway traffic carrying humanity into the next great age of exploration, expansion, settlement, and multi-planetary commerce.
see also Accessing Space (volume 1); Aldrin, Buzz (volume 1); Launch Vehicles, Expendable (volume 1); Orbits (volume 2); Vehicles (volume 4).
Aldrin, Buzz, and Malcolm McConnell. Men from Earth. New York: Bantam Books,1991.