New Mars Forums

Martian gravity is the only really difficult thing to simulate though.  The ISS doesn't have that ability does it?

• Do you think we can get a lunar elevator added to this mission?

Here is a suggestion from Landis ...

Although the surface of Venus is an extremely hostile environment, at about 50 kilometers above the surface the atmosphere of Venus is the most earthlike environment (other than Earth itself) in the solar system. It is proposed here that in the near term, human exploration of Venus could take place from aerostat vehicles in the atmosphere, and that in the long term, permanent settlements could be made in the form of cities designed to float at about fifty kilometer altitude in the atmosphere of Venus.

http://powerweb.grc.nasa.gov/pvsee/publ … TAIF03.pdf

No terraforming required.

Site comparing laser and microwave launch ...

http://www.islandone.org/LEOBiblio/SPBI115.HTM

In brief: Lasers have ye olde cloud problem.  Microwaves don't, but the transmission array must be large (>1 km).  Hydrogen propellant may eat the ozone layer.

The rest of the site looks like a good resource as well ...

http://www.islandone.org/LEOBiblio/

http://www.islandone.org/Propulsion/

I finally looked it up.  You use Realtime Kinematic (RTK) Differential GPS (DGPS).  Within 2 seconds from cold start you have 20cm 3D accuracy, if you have 2 minutes you can get that down to 2cm 3D accuracy.  You can be moving at up to 9 km/sec.  Once you have a lock you get a 100 ms refresh.  You need access to the military frequencies for these figures.  Being outside the atmosphere helps enormously.  Ionspheric distortion is actually the biggest source of error for ground-based units.

I may not be understanding, but I think you're suggesting adding weight (extra ribbon layers) without strength (some left unjoined)?  And I keep imagining that there is going to be some poor engineer at the bottom of the cable holding their breath every time a new join is retensioned.  Even if you get full strength 99% of the time, after 50 joins you've got a 40% cumulative chance of breakage.  I wonder how many 9s you'll be able to add for the procedure?

A customized Volkswagen SUV entered by Stanford University became the first autonomous vehicle to cross the finish line of a $2 million Pentagon-sponsored race across the rugged Mojave Desert on Saturday without help from a human driver or remote control.

http://www.mercurynews.com/mld/mercuryn … 854045.htm

You can check out the realtime status board at http://www.grandchallenge.org/

Make sure you check out the other videos on this page ...

http://www.tethers.com/OrbitToOrbit.htm

That page also has papers that answer your questions.  Briefly: between 2-3 km/s, 10 tons for a 2 ton payload, once a month.  It takes a month to reboost because it uses the Earth's magnetic field to generate thrust so that it can be propellantless once deployed.

Certainly the space elevator won’t be built by the private sector, but I agree that if it can be built, then the government should build the first one.  However, the cost of a MXER tether system could very soon fall under a billion – especially with all the tether research and the coming glut of cheap launch vehicles.  And while a 50% - 80% price reduction is “marginal” in space elevator land, I think there are going to be plenty of customers interested in 2 for 1 and 5 for 1 deals.  Murdoch might bankroll it just to get a lock on GEO.

Actually, the Panama Canal analogy is an excellent one – no new tech, just making the trip cheaper.  The space elevator is more like the invention of jet engines.

There is advocacy in those papers, but it doesn’t come anywhere near the rapturous certainty coming from converts to the Church of The Elevator.  You should hear some of those guys!  Every problem, no matter how glaring is dismissed with “easily solved you just use <technology that by itself requires a solid decade of development>.”  Cost estimates vanish in classic I-wish-it-were-true fashion: $40 billion, $10 billion, $1 billion, woosh.  100% utilization is assumed.  The cable is built and repaired as it is being used.  It is immune to the atmosphere and has fleets of tiny robots that pull it to one side so that LEO satellites can pass by safely.  Although the cable is a composite, they are positively offended when it is mentioned that no composite has ever achieved the percentage of theoretical performance they require.  Papers casting doubt on even the theoretical maximum performance are ignored as a matter of course.  They give every sign of being just as successful as the fusion guys – always 25 years away from deployment.

How will the joins not become weak points, or else be too massive?  I haven’t seen any proposals for joins.  It does seem necessary though.  Would it be some sort of splice or a distinct coupling mechanism?

If the sandwich is glued together, don’t you have to replace the entire sandwich?  How do you incorporate the new layer into the old join?  Don’t you have to rejoin when you add a new layer?  Are there any existing analogs for this?

There goes the payload down to 12000 kg/climber.  May be we should just drop it to 10000 kg/climber to account for the in built cable repair system and spare cable sections?

The tether has forever to resolve its position using GPS and anything else it needs.  The payload vehicle can use the tether’s information until it gets close enough to gather it’s own – if this is even necessary.  It looks like they’ve already looked at all this and the net is sufficient.

Useless for people, but not for robots and supplies.

Yep.  No argument from me on that.  Life extension technologies change everything as well.  For example, they might let me live long enough to see a space elevator built.

Yes but the experience gained with the LEO-GEO tether will make it just another evolutionary step.  Standard research funding.  No Manhattan project required.

Oh, you’re right.  It won’t be Murdoch that funds the tether, it will be Allen, Bezos or Brandon.

It's a plus if you can still get the strength you need.  If the other polymer is just a weak point, then you've got a problem.

I'll give you replacement of kilometer-scale segments in the atmosphere, but higher up you are dreaming.  There is a reason that cable has to be so strong.  It'd be easier to replace the whole cable.  Maybe if there was a continuous unwinding from GEO so that the entire 35000 km is replaced every few years.

Hmmm, I wonder what proportion of the power is required for those first 50 km?  What with it being deep in a gravity well and all.  I'm not sure you'd want to commit to storing that on board your climber. 

I'll collect hyper-accurate positioning info at tether control then use lasers for range finding and communication to and from the payload - a positioning phase lock loop.

How about the net in this May 2005 brochure ...

http://www.nasa.gov/centers/marshall/pd … XER_TS.pdf

This 2003 document also has a picture of a net ...

http://www.tethers.com/papers/MXERJPC2003Paper.pdf

And note that they've broken up their 100 km into more manageable 10 km lengths.  That's the sort of thing you do when you're planning for deployment.

There's a 2004 document I won't link to that's marked ...

Sounds pretty serious to me.  Someone thinks this is worth pursuing.

$30m x 12 x 10 = $3.6b savings over 10 years, and I don't have the billion/year operating costs of the space elevator.  I bet I can extract a good chunk of that.  Even if I'm near break-even on the first tether, I'll be earning a billion a year for each one thereafter.  I'm still calling 1Q2012 for the IPO.

Just like the first major application of computers was to design better computers, the first major application of off-planet industry will be to build better off-planet industry.  You'll be hiring whoever launches the MXER tethers to build Earth's first space elevator.

The above documents talk about 2000 kg, but you know why they're starting small?  Because this is a real project.  They are actually going to have to deliver on their promises.  They don't get to pretend that the problems are already solved.  They actually have to solve them.

Even you are assuming that if we get to $100/lb then demand will outstrip supply.  The costs to reach SO can be very low.  I hope we have to sell orbital timeshares to make it profitable.

I think you've got a few years maximum to make the space elevator such a sure thing that no investor will touch MXERs.  If not, they'll be built by private industry.

Even when it's wet?

Perhaps less sparse in the Ozone layer?

The problem is that all the calculations are assuming that the 100+ GPa micro-property can translate into a macro-property.  But my understanding is that 3-5% of theoretical performance is considered standard in a composite, with 12-14% being the rarified heights.  Here we're asking for somewhere between 50% and 100% of theoretical.  The closer you want to 100%, the closer your macro-cable has to be to pure, unbroken CNTs.  And in fact, there has to be a good reason for anything else because it adds weight without strength.

Isn't NASA's tether competition coming up soon?  It'll be interesting to see how far along we are.

Why water?  If you can create the vacuum in the tube, why not just let air push the payload?  Although if you can create and maintain some sort of vacuum, you might just want to turn it into a giant rail gun for higher throughput 

It's an increase in difficulty, but I don't think so much so that you should just rule it out like that.  It has many of the benefits of a geosynchronous space elevator.

If we really need a larger synchronization window, you could arrange them into a wheel, a helix or even just an unconnected series perhaps with different rotation rates.

Again, there doesn't have to be just one of these things.  They are relatively cheap.   

I can't find any reboost time figures, but I imagine it to be on the order of days or weeks, not months.  Is that really too slow?