An economically sustainable mean of space transport

The future of space travel is not rockets, essentially large fuel tanks capable of carrying only a tiny amount of payload. Getting things into space with rockets is inefficient and too expensive.

Space elevators could be used to go into space with less fuel and more load, but at the moment they are only science fiction.

A simpler alternative that we can really build is the Skyhook or Space Hook.

It is simply a huge rope, hundreds or thousands of kilometers long, connected and held in place by a counterweight, both placed in space.

The long cable can be used by spacecraft as a ladder to reach greater heights and speeds.

And it works even better if it rotates. The end of the rotating cable slows down when it is closer to the ground, in order to lock the aircraft, and then accelerates when it reaches the top. Basically it works like a catapult.

In this way it is possible to transfer energy from the rope to the spaceship, and provide it with a considerable thrust when released, equivalent to twice the rotation speed of the cable.

Special fibers already exist that can withstand the stresses a Skyhook would be subjected to. And to protect the cable from cuts and collisions with debris and meteorites, we can insert a network of redundant fibers.

The orbiting space hook would pass over the same spot on earth several times during the day, allowing small reusable shuttles to intercept it.

At its lowest point, the end of the cable whizzes through the atmosphere at around 12,000 km/h. To avoid overheating the Skyhook, due to air friction, it should immerse itself in the atmosphere down to a height of 80–150 kilometers, and no lower.

Reaching a cable that whizzes at Mach 12, 100 km above the ground, is no easy feat.

We need specialized aircraft capable of catching the extremity, and to do so they have a time window of no more than 60–90 seconds.

The task could be facilitated if the end of the cable were connected to a 1 km long rope and to a navigation drone that helps the spacecraft connect.

Another challenge is to keep the hook in orbit: as the spacecraft connect and are released, they take advantage of the momentum that the space hook possesses. If we do nothing the hook slows down and crashes into the atmosphere.

To overcome this, it is possible to balance the load entering and exiting, treating the hook as an orbital energy battery.

Ships routed to Earth add energy to the cable, which can be passed on to other departing ships. In this way the structure does not lose energy, and the more we use it, the cheaper it becomes.

In case we still lose energy at each launch, we could recover it with small electric or chemical motors that would constantly correct the position of the Skyhook.

A system of hooks around Earth and one around Mars would make travel between planets fast, simple, and low-cost compared to rockets.

Earth’s hook would be stationed in low orbit to grab people and loads and launch them towards Mars. The Mars hook retrieves them and slows them down for landing on the surface.

On Mars, the hook could pick up a moving vehicle in the thin atmosphere at just 1000 km/h (not much faster than airplanes on earth) and send it back to Earth, where it can be intercepted and brought to the surface.

The hooks could shorten travels between the two planets from 9 months to just 3, and reduce the size required by rockets by 84–96%.

And even better, people would have the opportunity to travel with more luxury, because we could afford to invest in comforts.

These structures around Earth and Mars could provide such a fast and efficient system that would make space travel very affordable.

From Mars, a hook could launch ships towards the asteroid belt.

The first vehicle sent to an asteroid would need thrusters to slow down on arrival.

Later arrivals may instead find a hook waiting for them, to pick them up and send them back for free.

Reaching asteroids economically is a crucial factor in accessing the resources of the solar system. Precious metals and minerals could be brought to Mars just a few weeks after they are mined.

The moons of Mars are also very well-situated, the only ones in the solar system to orbit so close to their planet.

Fobos is so heavy that we don’t even have to worry about slowing it down, which makes it the perfect mooring spot for massive 6000 km long hooks.

The lower end would fly just above the surface of Mars and would be very easy to reach.

The upper end could catapult ships to Jupiter and Saturn.

This same super-hook would also bring the inner solar system closer. Venus and Mercury would be just a launch away. And unlike Mars, they boil with solar energy and are rich in minerals and metals.

In the long term, nothing prevents humanity from building a zero-fuel transportation network between terrestrial planets, centered on Martian moons.