Peter Debenham

Peter Debenham

Getting people or satellites into orbit around the Earth is both expensive, an estimate of at least £30,000/kg to Geostationary orbit or £2500/kg to Low Earth Orbit, and dangerous.  You strap yourself on top of a tank of high explosive fuels, light the metaphoric blue-touch paper and are thrown into space amongst high g force acceleration and shakings.  That assumes you even make it into orbit; even “safe” launchers such as the “Delta 2” or the “Soyuz-FG” only have a “orbital success” rate (2015) of 98% - another way of saying that there is around a 1 in 50 chance of your expensive satellite, or even worse your expensively trained personnel experiencing “Rapid unscheduled disassembly” (to take the phrase SpaceX used following the failure upon landing one of its test flights) of the rocket beneath it.

Assuming you are in orbit and want to get back down things do not improve much.  At present the only option is to heat into the atmosphere and use friction between your vehicle and the air to convert the immense kinetic-energy and potential energy of an orbiting space-ship into heat.  For the 100,000kg American Space Shuttle going from a 300km orbit at 7700m/s to stationary at the ground meant losing around 3.2*10^12 Joules – no wonder that some Shuttle surfaces got above 1400 degrees Centigrade.

Despite such costs, complexities, and risk of getting to and from Space even today there are around 2600 operational satellites orbiting the Earth (and around 3500 defunct ones).  Satellite based communications alone have an estimated value of around £130bn per-annum, satellite-based navigation has equipment revenues of nearly $100bn per-annum but has an even larger value to the world economy mediated by the efficiency gains and cost reductions it enables.  A 2017 London Economics report estimated that GNSS was worth £6.6bn per-annum to the UK alone.  Attempts to estimate the wider socio-economic value of Earth Observation satellites, including meteorological measurements, have generally failed to come up with a number other than, “huge.”

Now imagine that instead of costs of £30,000/kg to GEO it was £10.  Instead of violent high-g shaking and a 2% chance of “rapid unscheduled disassembly” it was smooth and as safe as modern day air travel.  That dramatic change would come about if we used a space-elevator rather than rockets.   Sitting on top of a controlled explosion would be replaced with a smooth capsule ride.  The idea of a space elevator is quite old - it can be traced to an essay written in Russian, Grezy O Zemle I Nebe; Na Veste (Dreams of the Earth and the Sky; On the West Side), in 1895 by K. E. Tsiolkovsky (the same Tsiolkovsky who created the Ideal Rocket Equation in 1897) and has been a staple of science fiction writing in books such as Arthur C. Clarke’s Fountains of Paradise (1979).

A Space Elevator is conceived as a ground terminal on the Earth’s surface at the Equator tied to a space station by an enormously long cable on which climbing vehicles could deliver cargo or people to space.  The space station would be in geostationary orbit (approximately 36,000km altitude).  The cable itself would extend maybe twice as far again beyond the space station with a counterweight on the far end keeping the entire system in tension.  Most vehicles would head for geostationary orbit height, but some might climb to the counterweight as a gateway for lunar or deep space activities.  Unlike a rocket needing to carry its entire fuel the climber would be powered by electricity generated either on the ground or the space station reducing the energy cost of achieving orbit even further.

Equally important as getting into space the elevator would give a safe route back down to the Earth’s surface.  Generally controlled re-entry is so difficult it is rarely done other than when returning astronauts back home.  Most end-of-life satellites are left in graveyard orbits or are instructed to re-enter the Earth’s atmosphere such that they burn up.

The feasibility of building a space elevator is under intense discussion with various consortia trying to solve the immense engineering problems.  Even if all the other problems could be solved, of which the truly astronomical building cost is not the biggest, no materials are currently known which are strong enough for the cable even in theory (though we have some which are almost good enough for a similar elevator on the Moon).  But assume a space elevator was built, what would this mean?

For low-Earth orbit, of the type used by the International Space Station, not much would change.  The fuel cost of “kicking” off from the stationary cable is of similar magnitude to that of starting from the ground (at 100km height, gravitational potential energy = 10^6J/kg whilst the kinetic energy of the orbit is around 30 x 10^6J/kg).  Even with a space-elevator low-Earth orbit could remain in the realm of rockets as today.

The gain is geostationary orbit or above.  Here you arrive with the correct velocity so only manoeuvring fuel is required to work in this orbit.  This would allow substantial space-structures to be constructed without the cost, or danger, of rockets.  Rather than the 100m long, 420,000kg International Space Station occupied by less than 10 people we can envisage the possibility of metric mega-ton structures with thousands of inhabitants.  Vast solar collectors would be possible solving Earth’s energy needs in a zero-carbon fashion even if we never get nuclear fusion working.   Building in space would still be difficult and no doubt dangerous but we would no longer be constrained by the cost and danger of actually getting there and back!

We already know of some materials which would be best manufactured in a zero-gravity environment and some experiments again requiring low or zero gravity.  Mass manufacture of such materials would be possible and no doubt some of these exotic materials would change our lives dramatically.  Maybe without gravity getting in the way of crystal formation we could find a way of building room temperature superconductors or even materials strong enough to build a space elevator (a little chicken and egg that one).  It is even conceivable that some of our dirty industry could be moved “off planet” to avoid polluting where we live.  Don’t forget it would also be much easier to build a subsequent elevator once the first is working!

I think this is still ignores some even more important changes a space elevator would allow.  We already have had a couple of companies formed with the idea of obtaining from asteroids mineral and metal resources which are in short supply on Earth.  Even if the problem of capturing a suitable asteroid is solved how do you get things back to the planet’s surface?  Its not just the problem of building re-entry systems but that no-one would feel comfortable with many tons of material, which will not burn up, regularly being “dropped” from above our heads.  With the space elevator such minerals, maybe refined in space, would be safely brought from high orbit smoothly and slowly.

Asteroid mining hints at the other big change a space elevator would allow.  It would give us much easier access to space away from the Earth, the Moon or Mars especially when combined with in-orbit heavy industry.  Currently if we want to send a rocket between Earth and the Moon the rocket and the fuel to go from the Earth’s surface to the Moon (including fuel required to lift the fuel required later in the flight) must be loaded into a single system launched from the Earth.  Starting from the end anchor of the cable, not only are the most dangerous and stressful phases of flight eliminated (take off and re-entry) so too is much of the fuel cost of the journey.  In the final analysis the impact of a space elevator will not be what it allows us to do on Earth but what it allows us to do across the Solar System.