TWO tiny satellites are on their way to the International Space Station. What makes them different is that they will be tied together by a 10 metre long steel cable. And it’s the first step towards what could eventually become a colossal space elevator.

Researchers from Japan’s Shizuoka University will later this month attempt to test how the concept works in orbit.

According to a report in Japan’s Mainichi news service, two small 10cm square satellites will be released from the International Space Station after being delivered on September 11.

Once in free orbit, the satellites will uncoil a 10m length of cable. A small motorised container will then slide between the two ends.

Cameras attached to each satellite will record its movements.

Researchers will be looking for any unanticipated oscillations or changes in orientation as the weight of the moving container shifts.

If successful, it could become the first step towards proving the concept of a cargo-carrying space elevator.

“In theory, a space elevator is highly plausible. Space travel may become something popular in the future,” research team leader Yoji Ishikawa said.

The idea sounds immensely attractive.

Instead of using heavy, volatile, fuel-hungry rockets to launch people and cargo to the ISS, electric elevator capsules could climb an ultra-strong cable between the ground and orbit. This could offer low-cost and safe gateway to space.

Japanese firm Obayashi Corp, which is participating in the study, wants to plant a space station some 36,000km in orbit, with a long line tethered to a platform in the Pacific Ocean, by 2050.

It has plans to build six elevators, each measuring 18m in length by 7.2m in diameter. It says they will have the capacity to hold 30 people, and move at 200km an hour. It would take one more than a week to travel between the ground and the orbital outpost.

Obayashi Corp ambitiously places the cost of the project at about 10 trillion yen ($A125 billion). But several key technical hurdles remain.

Not least among them is finding and manufacturing a super-strong, yet ultralight weight material to act as the tether.