* Posts by Brian Dunbar

3 posts • joined 5 Jun 2007

Space elevator business plan crashes to Earth

Brian Dunbar

Deployment in a nutshell

"How do you manage to float several tons of material into orbit in the first place?"

Very carefully.

The plan is to loft the seed ribbon in several flights by rocket to LEO. Mate the components together. The now complete deployment vehicle reels the earth end down and in while the vehicle deploys up and out.

Eventually you end up with a 100,000 km ribbon, with the deployment vehicle at the bitter end, forming part of the counterweight. The lifters that are used to add on to the ribbon are parked nose-tail at the bitter end, forming the rest of the counterweight.

Readers of el Reg - who are a perceptive bunch - will note this plan is fraught with difficulty and issues. How many flights and how much cable makes up the seed ribbon? We don't know - it depends on the composition of the ribbon and how strong it is. On orbit assembly is problematic in that the only example of that to-date has been ISS. We only get one shot at deploying the ribbon. And so on.

In our defense; We have put some thought into this - more than my poor summary at least. The plan takes advantage of current state of the art and does not require really large rockets to deploy - which don't exist and might never exist. It's flexible in that we know things are going to change and we'll adapt to take advantage as we need.

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Brian Dunbar

"It's only a model"

John,

KSR's "Mars Trilogy" was only a book.

He built his space elevator so it would have a catastrophic effect when the bad guys (or good guys - it has been a few years since I've read it) brought it down a the end of the first book.

Mr. Robinson was kind enough to write an essay in our book (hey - go buy a copy while you can at our website) expressing this sentiment. He said a great deal better than I did of course.

Back here in the real world several things prevent a catastrophic 'Red Mars' scenario.

* We can't make a material strong enough to survive the heat of re-entry, and maintain it's integrity, and smash into the ground, then wrap itself around the planet. No one can.

* If anyone proposes to build a structure that can visit that much destruction, you'd be right to oppose them and tell them they can't build it.

What we think - and this is only one area that needs more study - will happen if the ribbon is severed is this; the bit below the break comes down. The bit above goes up and out. Stress from the break may sheer the ribbon material apart. Re-entry shock for any parts of the ribbon above the atmosphere will burn the ribbon up. Any intact sections are paper light per kilometer and should not cause damage.

Note the liberal use of modifiers; "should" "we think" etc. We simply don't know what will happen - anyone who says they know for sure is not being honest. Before this system can deploy a great deal of study is needed so we know what will happen when things break.

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Brian Dunbar

Well THIS is exciting

How nifty. A project I'm involved with has hit The Register. One could have wished for better circumstances. My mind's ear can hear this article in a snark Beeb accent ..

"Anyone outside of government grants who invests in this idea at this early of a stage is nuts."

"Nobody's betting very much of the farm on these guys producing some sort of licensable technology that might develop from the quest for a beanstalk, which is fair enough."

It is, possibly, worth noting that none of our investors have complained. Which, if they are nuts, is reasonable. I take the more charitable approach and remember that

* We were never blatant about our investment - and all mention of investing was removed from our website over two years ago.

* We turned down large sums (by our standards) of money from people whom we felt could not afford to invest it.

* Our investment doc was structured so that (it felt) half of it was filled with warnings and wave-offs and long lists of reasons why investing with us was a terribly bad idea.

* We had a fixed amount that could be invested.

"A more realistic plan would be incremental build-up: First build a minimal system that can only carry a few kilograms. Then use that to ferry masses up to build a larger satellite and at the same time make the cable thicker. Eventually, you can build a system that can take serious workloads. But even a minimal system is going to be expensive, so I'm not holding my breath."

That is actually the approach we're going with. A seed ribbon that will sustain itself and a few climbers. Deployment climbers ascend and layer on more CNT composite as they ascend.

Take terms like 'expensive' with a grain of salt. Our last roadmap (summer of 2006) calculated an optimistic completion date of 2031 and a total (2006 dollars) of between 25-30 billion.

This might be wildly optimistic - but it's hard to see where else money could be spent, given our assumptions.

I will allow our assumptions could be faulty: no one is perfect.

Please note that some of the people (not LiftPort) working on this idea think that we're being very pessimistic with cost and time estimates. We look like dour Lutherans by comparison with some published estimates.

"...who would have told them that you need an impossibly strong material to make the cable out of. "

Well .. we did put a lot of language in our investment docs to that effect.

"Materials with the tensile strength needed for the tether, if these can ever be developed, will be deployed in much longer suspension bridges than are currently possible first, so don't hold your breath."

We never claimed we'd be the first user - it would be foolish to think that using a new material in such a critical application is a good idea; clearly it's not

Brian Dunbar

LiftPort

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