What is a Space Pier?

The Space Pier is a novel space launch concept, conceived by the nanotechnologist and computer scientist Dr. Josh Hall. Dr. Hall presents the Space Pier concept occasionally at conferences, frequently in conjunction with molecular manufacturing, which would likely be necessary to make the concept cost-effective and realistic to implement.

A Space Pier is a structure 100 km (62 miles) tall and 300 km (186 miles) long. A payload goes up one of the 100 km towers in an elevator, then is launched along a horizontal track for 300 km using an electromagnetic mass driver. At only 10 Gs for 80 seconds, which is a tolerable level for humans with padded seats, a projectile can be ejected clear out of the atmosphere. Three humdred kilometers is enough track to take a projectile from zero to around 8.2 km/s (5.1 miles/s) using contemporary electromagnetics technology. If sensitive cargo is not a consideration, even higher accelerations can be used, of magnitude required to reach escape velocity (11.2 km/s or 7.0 miles/s).

The Space Pier is a compromise that was dreamed up in an effort to circumvent several problems of other common post-rocket space tech proposals - a space elevator/orbital skyhook, and an earth-based mass driver, also known as an electromagnetic accelerator or rail gun. The other two proposals get more attention and press, but a Space Pier would be less expensive and more effective than both. On his webpage introducing the idea, Dr. Hall makes the observation that the density of air at 100 km altitude is a mere millionth the density at sea level, making it significantly easier to accelerate a payload to high velocity. A space elevator would get in the way of satellites, which would inevitably collide with it unless taking a geosynchronous orbit. It would also need to be much taller than 100 km, more on the order of 10,000 km or more.

Because it is 100 km tall rather than 10,000 km, a Space Pier could be made from a material than can in theory be mass-produced - diamond. This is in contrast to a space elevator, which would need to be built from atomically precise buckytubes, or carbon nanotubes, in order to support its own weight. Diamonds can already be synthesized in relatively large quantities for moderate cost, but to create the quantities necessary to build a Space Pier megastructure, entirely new manufacturing processes would be required. Unsurprisingly, Dr. Hall proposes molecular manufacturing. The 100 km structure height would also put the Space Pier out of the range of most space junk, which is quickly drawn into a freefall at that altitude.

According to Dr. Hall's calculations, lifting a 10-tonne payload up a 100 km elevator and then accelerating it to 8.2 km/s would only consume about 5,000 US dollars (USD) worth of electricity, working out to about half a dollar per kilogram. This is significantly better than the current launch cost of 10,000 USD per kilogram. The projectile would not have enough velocity to escape the earth at this level of acceleration, but would circle all the way around the planet and stabilize at an altitude of approximately 340 km (211 m). The payload would need to make some slight maneuvers on its own in order to make sure its orbit becomes a regular circle. To escape the earth and reach interplanetary orbits, mass drivers could be put in space as waypoints, or conventional rockets could be used to take the payload out of the earth's gravity well.

One hundred kilometers sounds like an extremely tall height for a series of towers, but note that towers approaching one kilometer (0.62 m) in height are already under construction, and the materials we use for skyscrapers are relatively conventional. Progress in the 21st century will allow us to manufacture in bulk things that were previously expensive, including diamond. The Space Pier is an example of a visionary future application of this technology.