While carbon nannotubes are theoretically strong enough & light enough we can so far only make very short ones and cannot bind them into cables with anything like the strength/weight properties required. There is some very promising work from CRIRO and Uni of Texas twisting them into ‘yarn’ and a company has been able to launch and attract investment on the basis of the Space Elevator but there is also some work which suggests we can never make cables with the strength required! Not out of carbon nannotubes anyway and nothing else comes close.

I think we all fervently hope the materials problems can be overcome as it would deliver the cheap access to space that we need to make space exploration/exploitation truly economically viable.

I would have thought the man rating existing boosters would be far easier. Gemini and Mercury all used modified ICBMs. The only purpose designed manned rocket was Apollo and the Saturn V. The Soyuz launches both manned and unmanned payloads and was developed from an ICBM.

There is just something about the ’stick’ design of the Crew Launch Vehicle that does not look right. The EELV launchers were considered however I think political reasons to reuse as much of the shuttle hardware as possible took over.

http://www.geocities.com/i_s_s_alpha/launch_vehicles.htm

Admittedly, ISS assembly isn’t necessarily the smartest or easiest, either. But we are learning by experience. I think there’s something to be said for launching larger packages on larger launchers with less assembly. Shuttle isn’t necessarily the best plan, either. I’m not committed either way. There are trade offs that have to be made to come up with a plan.

>Also what happens if the HLLV fails at launch – then your whole mission is destroyed. At least with module assembly the whole mission is not in one flight.

True, but depending upon orbital periods, resource constraints (such as cryo fuel), and other factors, there may be time constraints for on-orbit that do not go well with a critical element in the middle of the assembly sequence disappearing. It isn’t economical or practical to built two of everything on the off chance there’s an explosion, so the recovery plan in that case would need to be developed carefully. All of which just means we need a good, thorough plan before we begin work.

>The shuttle is the first manned spacecraft to use solid rockets and that was against the objections of some experienced hands.

Let me be clear, I’m not advocating solid boosters. I agree with your objections. My objection was to crew-rating the existing rocket designs after the fact. It may be doable, but is it really cheaper than designing from scratch a unique launcher for this application?

>To man rate a Delta 4 or Atlas 5 the destruct charge has to be removed and a few dummy flights made. However there is nothing in their design that is different from the Atlas rocket that launched all the Gemini missions.

I’m not so certain of this, though I don’t really know the details. There are certain reliability levels that we would want for a crew-rated vehicle that are not necessarily required for a non-crewed launcher.

The shuttle is the first manned spacecraft to use solid rockets and that was against the objections of some experienced hands. It came down to nothing else would get the thing off the ground and it was to expensive to develop liquid boosters.

The main problem with solid rockets is that once you light the blue touch powder they are off and unstoppable. Liquid fuel boosters can always be shut off in an emergency. If there is a problem with the solid booster at launch the CEV has to somehow seperate from a unstoppable rocket at hypersonic speeds and dynamic pressures. The Saturn V of Apollo had no solids neither does the Soyuz launcher.

To man rate a Delta 4 or Atlas 5 the destruct charge has to be removed and a few dummy flights made. However there is nothing in their design that is different from the Atlas rocket that launched all the Gemini missions.

What I found impressive was that the carbon nano-tube fabrication and strength issues are largely already being addressed in industry for other purposes, which means the space elevator tether would be more of an adaptation of commercially available materials than an original, stand-alone need. That means the manufacturing costs and availability are more reliable and cheaper than they would be otherwise. The bulk of the problems left to be resolved are purely engineering work, and not basic science or new technology drivers. That greatly supports the overall feasibility of the concept.

I’m heartened by the recent space elevator challenges that have been initiated to work on designs for climbing tethers powered by light. That is an element of the outlined plan that needs more attention.

The Space Elevator concept is a launch and return method that pushes the envelope while opening up space to greater exploration and commercial access. It truly is a new approach, as opposed to the current Moon/Mars plan.