The energy costs for launching via a gun launch or a rocket won't be much different to a space elevator given the parasitic weight of the climber's laser receivers, motors, radiators, wheels etc plus <25% efficient electricity transmission to the elevator so need on the order of 100kWh per kg payload (cost ~$10/kg). Rockets like Falcon Heavy currently also have fuel costs of about $10 per kg of payload launched, though that is dropped to $5/kg if using methane as a fuel, while skylon is more like $30-40/kg due to expensive hydrogen and atmospheric drag losses. But realistically energy is a very small part of total costs.
By the numbers you quote (500x35000kg) = 17 million kg per year for $1 billion in operations/maintenance and optimistically $2 billion in capital costs on a $17 billion investment would mean $150-200 per kg lifted. Skylon for comparison is also projected to get as low as $1-200 per kg once high launch volumes are achieved, using known materials and technology. High rate gun/ram accelerator launch systems are likely to be even cheaper with much lower capital costs. The key point with the low orbit elevator strung between a high and a low station is that it can be done with available materials like UHMWPE, PBO or Carbon Fiber for the cable rather than unobtainium. And by the simple expedient of reducing the delta-V requirement for a launch by 1-2km/s it can double or triple a rocket's payload to reduce costs by 50-70%. Combined with Skylon this could drop launch costs to $50-100 per kg, low enough to enable 100's of millions of people to be able to afford the trip. There are obviously a lot of huge problems both technical and economic to be overcome before a practical space elevator can be realised. While it is worth doing some low level research, we should be concentrating on developing cheaper options using available technology. On 11 April 2012 23:43, Jed Rothwell <[email protected]> wrote: > Robert Lynn <[email protected]> wrote: > >> A space-elevator must climb about 40000km, even at 200km/hr that will >> take more than a week . . . > > > For freight, this is a non-issue. It takes a week or more to ship goods from > China to the U.S. but that does not bother anyone. > > Note that after a few days of travel, the force of gravity is greatly > reduced and the climber puts little strain on the ribbon. Therefore, on a > 200 ton capacity ribbon, 35-ton payload climbers can be dispatched every 7.5 > hours. You can have 24 at a time on the ribbon. (E&W, p. 168) > > >> and requires a huge amount of power to be >> supplied to the climber. > > > This can be done with ground based lasers and a photo array. It is not a > huge amount of power. > >> >> That makes it a very slow and expensive >> method . . . > > > The energy cost is small. With cold fusion it would be nonexistent. E&W note > that small fusion reactors would be ideal. They were not aware of cold > fusion. > >> >> for getting mass into space with huge maintenance and capital >> costs dominating any potential savings from energy efficiency. > > > The maintenance and capital costs would be 2 to 5 orders of magnitude > cheaper than any other method, once the thing is scaled up and many tracks > are installed. The initial costs are high. Roughly $8.3 billion for the > first 2 ribbons, of 13 ton capacity. > > An ideal practical system would have 2 large ribbons (200-ton) and one or > two small ones (13-ton). The 13-ton would be the pilot ribbon. The big ones > are the up-track and the small one is the down-track, for empty crawlers or > 2-passenger crawlers. That's roughly $17 billion. That would allow 500 trips > per year with 35 tons each, and a daily cost of maintenance and ops. of > around $2 or 3 million. > > >> >> Additionally the materials issues are likely beyond our abilities to >> solve, we have had nanotubes for 20 years, yet our inability to find a >> suitable matrix to join them means that we can still not even equal >> the strength of carbon fibre composites. > > > How much money has been invested in this research? That may be like saying > that little progress has been made in cold fusion. It seems likely the > problem can be fixed. We just need someone like Rossi to come along. Only, > let us hope he or she is a more reasonable human being. > > >> >> The near earth space environment is really nasty, with atomic oxygen >> that will eat away the carbon, micrometeoroids that will very >> frequently impact and damage the cable (even <1mm can be catastrophic >> at >1km/s, . . . > > > Not according to E&W. That isn't to say they are right, but they have > studied these issues longer and more carefully than you have, so you should > read their book before commenting. (The book is "The Space Elevator") > > >> and we can't track stuff that small). > > > We can if the sensors are in crawlers on a spare track, in space, set there > to intercept the junk. > > >> >> Space junk is a huge >> issue, that is only getting worse and is expected to get into >> catastrophic run-away territory in the next few decades as satellites >> start to collide with each other and create ever increasing clouds of >> shrapnel. > > > A specially constructed climber on a 13-ton track could be the ideal way to > fix this problem, by eliminating the junk completely. It would not have use > the track full-time. It could be lowered for periodic down-traffic of empty > crawlers that pile up at the terminal. > > Another method is to launch LEO rockets from a specially designed 200-ton > heavy-duty crawler that goes only 100 to 200 km up before launching, then > comes back to earth, clearing the ribbon for regular traffic. This can be > done in a few hours. It would be far cheaper than present-day methods. > > E&W describe this in some detail. The problem has to be fixed in any case. > We might as well use the cheapest and best method. > > >> >> But there is probably a better option: >> >> A partial elevator that bridges a few hundred to a few thousand km >> between a higher space station and a very low space station that skims >> along at 120-150km altitude. > > > That is an interesting idea. But if you have the carbon material that can do > this, it can probably be used for a full elevator, so why not build the > whole thing? > > - Jed >
