Going Up: Could Partial Space Elevators Take Us Into Space?

A trip to the moon on gossamer strings? A "partial" space elevator that could carry satellites to geosynchronous orbit might be just the ticket. (See also: "Escaping Earth: Could a Space Elevator Work?")

A space elevator untethered to Earth, with both of its ends hanging in space, might cut the costs of space travel to high orbit by 40 percent, researchers report in a new Acta Astronautica study.

Inspired by science fiction maven Arthur C. Clarke's 1979 novel, The Fountains of Paradise, scientists have long studied the concept of a full space elevator, which would stretch from an equatorial spot on Earth's surface into space about a quarter of the distance to the moon. A partial space elevator would be less than half as long and wouldn't need to be anchored to Earth.

"I think in parallel to full space elevators, partial space elevators are definitely worth exploring more," says space engineer Stephen Cohen, a physics professor at Vanier College in Montreal, Canada, and author of The Engineer's Pulse blog, who wasn't involved in the new study.

Underlying the idea of a space elevator is the high cost of space rockets. It now costs about $25,00 per kilogram (2.2 pounds) to put something into geosynchronous orbit, where communications and television satellites reside.

Today's materials aren't strong enough to support a huge, full space elevator to those heights, the McGill University study argues. Instead, a much smaller elevator looks less far-fetched.

"We could view it as the first building blocks of a [full] space elevator," says study co-author Pamela Woo of McGill University in Montreal, Canada. "We might start off with the partial elevator and then maybe extend it to Earth."

Saving Energy

The base would sit somewhere in low Earth orbit, which extends from roughly 99 miles (160 kilometers) to 1,243 miles (2,000 kilometers) above the planet's surface.

If built, a partial space elevator would have four parts: a base, a counterweight, a tether, and a climber.

The actual elevator, or “climber,”

would ascend the tether from the base to deliver its cargo to geosynchronous orbit.

A strong, ribbon-like cable called a tether would connect the base to a much higher counterweight above geosynchro-
nous orbit.

The goal of the elevator would be to carry satellites from this base to geosynchronous orbit, some 26,200 miles (42,164 kilometers) above Earth.

Counterweight

60,000 miles

from Earth

Base

Climber

Tether

Earth

Rocket vs. Elevator

In the study, Woo and her McGill co-author Arun Misra calculated the energy requirements for sending a spacecraft from low Earth orbit to geosynchronous orbit along two different paths: In the first, a rocket carries the spacecraft straight to geosynchronous orbit; in the second, a rocket carries the spacecraft to a partial space elevator's base, where a climber then transports it to geosynchronous orbit.

For most scenarios, the partial space elevator was far more efficient than the traditional, rocket-powered transportation. "In general, using longer tethers resulted in more energy savings," Woo explains.

The costs of low-Earth orbit launch are lower than those of geosynchronous launches, at around $5,000 to $10,000 per kilogram (2.2 pounds), accounting for some of the savings.

If the elevator is solar powered, it may be even more energy efficient, Cohen suggests. Still, a full elevator would be better, as it does away with rockets altogether, he says.

Peter Swan, president of the International Space Elevator Consortium, agrees: "If we keep working with rockets, we are destined to live in a shake, rattle, and roll world of high costs to orbit."