Over at The Space Elevator Reference, Dr. Bradley Edwards gives us his thoughts on designing the optimal climber. This is a fine, detailed analysis with lots of practical information.
The Space Elevator Blog
For scalable, inexpensive access to space…
It seems I can’t comment on the referenced post so I’ll comment here, if you don’t mind Ted.
Not that I’ve anything of genuine value to contribute, just a minor point. Keeping in mind that I’m but a humble IT guy and not an engineer …
To reduce the mass of the systems, advanced materials (composites) are needed in all structural components.
Edwards mentions mass several times. While mass is a certainly important I wonder if it is that critical. It certainly is important in most aerospace applications – ounces matter when you have to haul your fuel along with you.
But it miight not be such a pressing concern in a lifter. We’re dealing – after all – with a vehicle that leaves it’s motor and fuel on the earth. It could be that we can build major components out of fairly standard material and save on construction and design costs.
We have decades of experience building with aluminum. Not so many with advanced (composite) material.
Another poin to keep in mind the lifter need only last for one trip, and not a kilometer longer.
I am reminded that when Victor Belenko flew his Mig-25 to Japan the intel and aerospace guys were surprised to see rivets in areas that a Western aircraft would not have had them. They key was cost – it was cheaper to use rivets – and that the rivets were not exposed to areas with great amounts of stress. Lower cost, greater reliability.
The motor IS on the lifter, and it’s going to have to carry itself, plus the payload.
The major advantage of the SE will be how cheaply it can carry something out of earth’s gravity well. Every ounce that can be removed from the lifter structure means more ounces that it can carry.
And you can comment here anytime 🙂
Every ounce that can be removed from the lifter structure means more ounces that it can carry.
True and I expanded on that on my own blog. But there is a trade-off between using advanced (expensive) composites and ‘good enough’ (cheap) materials.
With (say) an airplane it makes sense to make those tradeoffs. You’ll want that machine to have a long service life and to run as cheaply as possible.
With a SE lifter … not so much perhaps. The plan isn’t to reuse them but to send them up and park them at the bitter end.
I should have that ‘good enough’ as applied to the ‘getting to orbit’ problem is covered very well in John London’s ‘LEO on the Cheap’.
Google the book title for a PDF download. Excellent – and lengthy read on how to get to space cheaply. While the concepts and ideas London lays out don’t apply directly to space elevators (he’s talking about rockets to LEO obviously) the basic principles should apply.
One of those is ‘good enough’ and cheap beats ‘best of breed’ and expensive.
Another take-away is that a common bus would reduce price across the industry. As of a few years ago nearly every bus was custom designed for the payload, which increases the cost. How this might apply to space elevators is that the SE operator publishes a standard for the lifter bus, then makes the customer design their cargo for that.
The cargo climbers may be one way but the capsules from the manned ones will be returning to Earth. The capsule could return by parachute or climb down a ribbon. Once back on Earth it may be reused.
I’m not intimately familiar with the science of this concept, but I am fascinated by the idea. Why does the elevator need to carry its own power source? Why not run electrical power through the tether? We power trains with a ‘3rd’ rail and no power source on board the vehicle. I think a back-up power source on board is a good idea if the main tether power source fails. Are there challenges with running power through the tether itself?
Hi, Rick.
Why does the elevator need to carry its own power source?
Because 100,000 km is along way to run a 3rd rail.
Also note that it’s envisioned that the motor is aboard the lifter but the power source is to be a laser on the ground.