Stairway To Heaven

Space may still be the final frontier, but getting there could soon be almost as simple as stepping into the office lift at the start of the day.

The race is on to build the first "space elevator' - long dismissed as science fiction - to carry people and materials into orbit along a cable thousands of miles long.

In a significant step, American aviation regulators have just given permission for the opening trials of a prototype, while a competition to be launched next month follows in the wake of the $10 million (£5.6 million) "X Prize'', which led to the first privately developed craft leaving the Earth's atmosphere, briefly, last year.

Supporters of the elevator concept promise a future in space that is both cheap and accessible, and contrast it to Nasa's announcement last week that it will be relying on 40-year-old technology from the Apollo programme for its $105 billion plan to return to the Moon by 2018. The companies behind the space elevator say they will be able to lift material into orbit for as little as $400 a pound, compared with $20,000 a pound using existing rockets.

That would open up the possibility of tourists visiting a sky hotel in stationary orbit 22,000 miles above the Earth, with a view previously enjoyed only by astronauts.

It would also allow for far cheaper travel to the Moon and other planets within the solar system, since most of the energy required by rockets is used simply to escape Earth's gravity.

Russian scientists first envisaged a fixed link to space, and the idea was popularised by the British sci-fi writer and vision-ary, Arthur C Clarke, in his 1978 novel, The Fountains of Paradise.

The theory behind the space elevator is deceptively simple. With a base station on Earth and an orbiting satellite, solar-powered "climbers'', each carrying up to 20 tons, would crawl up a single cable into space over several days. The cable would be held up by the rotation of a 600-ton satellite counter-weight, much like a heavy object at the end of a spinning rope.

Until recently, the concept seemed doomed by the technology available, not least finding a material strong enough to make such a long cable, able to withstand extreme temperatures.

Scientists now believe that a material known as carbon nanotubes could be bound together to make a ribbon, rather than a cable, three-feet across but just half the width of a pencil.

Nanotubes, which are microscopic cylinders of carbon, are currently being developed by a number of companies, including GE and IBM. In one experiment, a sheet of nanotubes one-thousandth the thickness of a human hair could support 50,000 times its own mass.

"Elevator 2010'', which is to be launched on October 21 in California, will offer an annual first prize of $50,000 for the best design for both a tether - or ribbon - and a lightweight climber. It is being run by the Spaceward Foundation, which promotes space exploration, and has the backing of Nasa, which has given $400,000 in prize money. At least 10 teams will take part in the first contest.

Brad Edwards, a board member of the foundation, says the initial development could be ready "in the next couple of years", with the elevator itself being built in another decade.

"We are talking about getting this up in about 15 years,'' Dr Edwards predicted.

A rival design is being produced in Seattle by the LiftPort Group, which is counting down to a first voyage into space on April 12, 2018. The Federal Aviation Authority last week cleared an experiment by LiftPort that would use a mile-long tether attached to a balloon, something the company calls: "A critical step.''

Fears that an aircraft would crash into the elevator ribbon is just one concern. Space debris and terrorism are others.

Developers propose a floating base station near the equator, more than 400 miles from the nearest flight path.

Should the 800-ton ribbon break, it would either fly into space or fall back to the ground in fragments that would, in theory, hit no harder than a sheet of paper.

Space Elevators: Some Not-So-Talked About Problems that need Solving

Energy released when a fiber snaps.

A carbon nanotube that is stretched to 65 GPa has a very high energy density. I have estimated that if that energy is all converted into heat, the carbon nanotube would heat up on the order of 1000K to 4000K (depending on assumptions on the Young's modulus and the heat capacity of the material).

If a thread of the space elevator ribbon breaks and a significant amount of the energy it contains is released as heat, the resulting temperature rise could be sufficient to damage the adhesives that are supposed to be holding the thread to do load redistribution, and possibly damage the interconnect. The broken thread could also zip past many interconnects before the inertia of the free end of the thread prevents the energy to be released too violently (the heat radiates away very fast). This would leave lots of long threads sticking out of the elevator ribbon, ready to get tangled on advancing climbers. Given current estimates, it would seem that there would be many breaks per square meter of ribbon per year, so there would be a lot of these threads around.

The elastic energy that gets converted into kinetic energy could also have a negative impact on the interconnects, possibly damaging them or allowing the thread to zip through.

Thermal cycling when ribbon twists.

In space, the temperature of the ribbon is governed by radiative heat transport. When the ribbon is facing the sun, it equilibrates to a temperature around 300K. When it is perpendicular to the sun, it equilibrates to a temperature around 100K (I haven't checked these numbers myself, but they are in the right ball park). Because it is so thin, the ribbon's temperature will equilibrate within a few seconds only. Therefore, if the ribbon is twisting around randomly, it will be repeatedly be cycling from hot to cold to hot. This temperature cycling could cause some severe fatigue issues as it is repeated year after year after year. In fact, just the large range of temperatures could be a problem; polymers tend to have mechanical characteristics that vary significantly with temperature. Certainly a challenge for the materials folks. The thermal expansion caused by the temperature change could also induce oscillations in the ribbon, but I think that is a lesser concern.

One broken elevator could kill all deployed elevators.

If a space elevator breaks, a number of very long pieces of ribbon result. Ones attached to the Earth will fall down (pretty harmlessly for the people on the Earth); the others will orbit the Earth going West (unless I am mixed up). These ribbons will probably have a bit of motion out of the equatorial plane (at least tens of km in amplitude), and the total length of broken ribbon is very long, so there is a very good chance that they will strike other elevators that are around (and that are very large targets). The collision itself will usually be at relatively small velocities, so it shouldn't be a problem. On the other hand, after colliding, the ribbons may rub against each other, get caught on each other resulting in ribbon damage, or increase each other's tension. It seems to me that this could severely damage or even break the elevator that is still standing.

Having multiple elevators was supposed to be insurance; it may turn out to be more like putting all your explosives in the same box.

The "space elevator" is an ingenious idea and I hope it becomes feasible someday, but this dig about NASA using 40 year old technology is just plain wrong.

It's that, and idiotic as well. There IS no other technology that will do the job.

Sadly, although the X-Prize successes were entertaining, they really did nothing to advance the state of the art in space access. I know I'm jumping to a slightly different topic, but the same idocy seems to surround that event as well.

Building a two stage vehicle (yes, it was two stages, the first being very slow and powered with turbine engines), which goes up to the edge of space, and then falls back down is of little value.

To compare the relative cost and complexity of the X-Prise vehicle with the original Mercury flights is meaningless. Those first few flights were just baby step tests of a vehicle which was intended to go into orbit, and return.

Had the X-Prise required orbit, then the X-Prise winner would have been very similar to either a Mercury like system, or a Space Shuttle like system.

[Sadly, although the X-Prize successes were entertaining, they really did nothing to advance the state of the art in space access.]

Any progress we make toward getting ourselves and our payloads into space will necessitate us refining and improving current solid rocket and liquid fuel engine technology and also rethinking how we use the technology as wisely as possible within a NASA program.

The space shuttle is an example of a program that can't grow to be much more than what it was decades ago because of it's reliance on 1 vehicle to do everything from lifting cargo to getting people into orbit or repairing satellites.

Building specialized vehicles which are tailored to their specific functions is going to be the way to perform these tasks in the future, but all of these vehicles are going to be powered by modern versions of Robert H. Goddard's technology.

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