What if we built a space elevator?

Today, people go to space on huge rockets.

What if you could ride an elevator to space instead? Up, up, up!

Every trip to space today rides on a rocket, which burns enormous amounts of fuel to climb away from Earth. Engineers have long wondered about another way: a cable reaching from the ground into space, with machines that climb it like an elevator.

So here is a thought experiment: what if we built a space elevator? How long would the cable be, what could it be made of, and what would the ride be like? You can explore all three, and find out which parts have actually been tested.

Launch to orbit is dominated by rocket propulsion, which must carry its own propellant. A space elevator would replace the rocket with a fixed structure: a tether reaching from the equator up through geostationary orbit, orbiting in step with Earth's rotation, climbed by vehicles powered from outside.

This thought experiment examines the concept's geometry, its materials problem and the climbers. It distinguishes established physics and actual small-scale tests from proposals and projections, which are numerous and optimistic.

Rockets are very powerful. They burn lots of fuel to get to space.

No one has built a space elevator yet. It is still an idea.

Today, satellites, cargo and astronauts reach orbit on rockets. A space elevator has never been built. But it's not just science fiction: NASA held a workshop on space elevators in 1999, and its engineers wrote that the idea had moved from science fiction toward the realm of possibility, perhaps late in this century.

NASA's 2016 Spinoff report notes that the idea has been proposed since at least the late 1890s, and the writer Arthur C. Clarke made it famous in a 1979 novel.

No space elevator exists. NASA's Marshall Space Flight Center held a space elevator workshop in 1999; the resulting paper (Smitherman and Howell, 2000) concluded the concept may well be possible in the latter part of the 21st century if planning and technology development resolved key issues.

NASA's Spinoff (2016) traces the idea to at least the late 1890s and notes Arthur C. Clarke's 1979 novel The Fountains of Paradise popularized it. A 2004 to 2005 cooperative study between NASA Marshall and the Institute for Scientific Research examined the critical technologies required.

Let's pretend we build a giant cable from the ground up into space.

Robot climbers ride up the cable carrying cargo. No rocket needed!

Imagine a cable rising from a base on the equator, up and up for 35,786 kilometers to a special orbit where a satellite goes around once a day and seems to hang still above the same spot. Robot climbers would carry cargo up the cable.

NASA engineers wrote that moving things up and down an elevator takes so little energy that it might lower the cost of reaching orbit to less than $10 per kilogram. That's a big promise, but it depends on solving very hard problems first. Those benefits are ideas, not results.

The tether's center of mass would sit at geostationary altitude, 35,786 km, so the structure completes one orbit every 24 hours and stays above the same equatorial point (NASA). Climbers would ascend under external power.

Because lifting payload along a fixed structure needs little energy compared with rocket propulsion, the 1999 workshop paper argued an elevator is one of only a few concepts with the potential to lower cost to orbit below $10 per kilogram. That figure is a projection contingent on materials, construction and operations no one has yet demonstrated.

The cable would be very, very long. It must hold up its own weight.

No one can make a cable that strong and that long yet.

A cable 35,786 kilometers long would have to hold up its own enormous weight, plus the climbers, without snapping. Ordinary steel cable couldn't do it.

NASA engineers say carbon nanotubes, tiny tubes of carbon discovered in the early 1990s, were the first hint that a strong enough material might be possible. But a 2005 NASA study said the most critical technology still to be developed is a super-strong carbon nanotube composite, far stronger than any material made in long lengths today.

A tether tens of thousands of kilometers long must support its own weight and climbers under tension, so the material's strength relative to its density is decisive. Smitherman (NASA, 2005) wrote that the discovery of carbon nanotubes in the early 1990s was the first indication such a material might exist.

The same report concluded that the most critical technology for Earth-based elevators is ultra-high-strength carbon nanotube reinforced composite ribbon in the 100 GPa range. Its development remains the central unsolved problem; other concerns include construction in orbit and powering climbers over such distances.

Scientists have tested tiny pieces of the idea.

A robot climbed a cable hanging from a helicopter. A tiny climber was sent into space to try moving along a cable!

Small parts of the idea have been tested. In 2009, in a NASA-funded challenge, a team called LaserMotive powered a robot climber with a laser beam aimed from the ground. It climbed a cable hanging from a helicopter a full kilometer, four times, at up to 3.97 meters per second, and won $900,000.

In 2018, Japan launched STARS-Me, built at Shizuoka University: two tiny satellites joined by a 10-meter cable, with a small robot car designed to move along the cable in space.

NASA's Centennial Challenges ran a Power Beaming Challenge (2005 to 2009) because climbers could not use wires and batteries lacked adequate power. In 2009 entrants had to climb 1 km of helicopter-suspended cable at no less than 2 m/s; LaserMotive's laser-powered climber did so four times, topping out at 3.97 m/s, and won $900,000 (NASA Spinoff).

STARS-Me, launched September 22, 2018, comprised two 10 cm satellites linked by a 10 m tether and a 3 cm by 6 cm climber, designed as the first test of movement along a tether in space (Science News). Science News reported in 2018 that Obayashi Corporation hoped to build an elevator by 2050, while saying current technology was not yet sufficient.