Space Elevators

[Gallowglacht]

I kinda like the idea of Aubine having a space elevator or two. But its a tech level 12 world and I cant help thinking that grav technology makes them obsolete.

Anybody know of a good reason for a standard world to have a space elevator in the Traveller universe?

 

[Plankowner]

It was built at a lower TL and still exists, just upgraded through the years.

There is no reason that the Beanstalk can't be gravitic as well. A stable platform with essentially free power might still be economical even at higher TLs. I can see the cars all being gravitic but also taking advantage of the gravitational potential difference as a supplimental power source.

Everything that makes a Space Elevator economical is still valid with gravitics. The profit margins might just be a bit lower.

Go for it.

 

[kafka47]

Grav technology should help you visualize even larger space elevators. They would be viewed as the poor man's lift into orbit where they may go for business or pleasure when the commercial grav vehicles will do so at a cost but really rake it in when it comes to accomodations. Much as the whole resort industry does today. However, if you catch a series of local flight to almost any Third World country, find a local hotel that might not have as many perks that the 5 star resort does...but, you might have a richer and more meaningful vacation. So, it is with Space Elevators, on a world with only orbital transfer points, Space Elevators become ways to hop onto tramp traders, take a spaceship to a Starport located on another world cheaply by hitching a ride. A technological level is not neccessarily reflective also of the aviability of a particular mode of transport. Maybe, grav vehicles are restricted for some reason just as SUVs have been banned in some parts of Europe...maybe gravitons have associated health risks...

 

[Gallowglacht]

Or how about to pick up slingshot minerals from the asteroid belt, picked up by tugs and lowered by the beanstalk rather than mass-drive bombarding your own planet?
Orriflamme built fusion drive not irradiating your atmosphere and system ships without expensive contra-grav.

Thanks guys, was looking forward to describing them to the players. Both the working ones on Aubine and the collapsed beanstalk caused devistation of the one destroyed on Orriflamme.

If anyone else can think of good reasons for one, please feel free to add them...

 

[fredofmars]

<snip>Both the working ones on Aubine and the collapsed beanstalk caused devistation of the one destroyed on Orriflamme.</snip>

If the beanstalk is built on the current concept of a high strength cable to orbit that has a capsule climbing the cable, then breaking the cable is not going to do much devastation. Most of the heavy part would be at the high end as counterweight, so that part would just leave orbit (it might hit something else in orbit on the way out, but that wouldn't have a direct effect on the planet). The rest is just cable coming down, probably over a length of several miles. If the cable is carbon nano-tube based as the current concepts go, then it's pretty light stuff - more like a string of tissue paper that spreads itself over many miles of length.

The beanstalk in David Brin's novel Sundiver is described more like a hollow tower. Destroying something like that would cause much more damage in the immediate area than the simple cable version. On the other hand, the heaviest part would still take off out of orbit and miss the planet entirely.

 

[veltyen]

The rest is just cable coming down, probably over a length of several miles. If the cable is carbon nano-tube based as the current concepts go, then it's pretty light stuff - more like a string of tissue paper that spreads itself over many miles of length.

The problem is that that many miles of length happens to be around the planet.

Geosynchronous orbit for Earth is about 40,000 km, which happens to be approximately the circumference of the earth. An elevator (without huge continuous energy input) needs its centre of mass at approximately this point.

Assuming a complete failure of the elevator then half the mass of the elevator comes down, and half stays in orbit or leaves. Even silly string gets heavy with 40,000 kilometres of the stuff. While carbon nanotubes may be "light" that is more a density thing then an absolute mass thing, the likely mass would still be kilograms per metre.

Assuming a non-complete failure (say the station/counterweight falls off the end but the beanstalk stays in one piece) then you have the worse problem of dragging down the entire beanstalk from the bottom. The last couple of segments have been accelerated at near surface gravity all the way from orbit - they are going to hit like Thor

At 10+ km/s even tissue paper hurts.

Rough back of the envelope calculations would place the final pieces of the whip hitting at 30 km/s 45 minutes after the failure.

A kilogram at that speed is a LOT of energy (about 10^9 joules) in the same order of magnitude as a MOAB

 

[Gallowglacht]

I was going with the cable idea and think along the same lines of veltyen. Thousands of miles of mass falling very quickly.

 

[Straybow]

If the density is low enough it is easily slowed in the atmosphere, therefore not much damage.

 

[Fritz_Brown]

And, I would never make the density that low.... :devil:

 

[Daneel Olivaw]

If the beanstalk is built on the current concept of a high strength cable to orbit that has a capsule climbing the cable, then breaking the cable is not going to do much devastation. Most of the heavy part would be at the high end as counterweight, so that part would just leave orbit (it might hit something else in orbit on the way out, but that wouldn't have a direct effect on the planet). The rest is just cable coming down, probably over a length of several miles. If the cable is carbon nano-tube based as the current concepts go, then it's pretty light stuff - more like a string of tissue paper that spreads itself over many miles of length.

Kim Stanley Robinson's excellent novel "Red Mars" has a lot to say on the subject - spoiler ahead:

Spoiler:

When the beanstalk is disconnected from its anchor on Phobos, the beanstalk's crash to the surface is a major disaster, destroying a large swath of territory across 9,000 km of the equator.

 

[far-trader]

Wonderful!

Emperor's stars! Where did you discover that wondrous bit of code!

Spoiler:

This is so eloquent! "sblock" is wonderful. Thanks Daneel Olivaw for digging it up and to whoever had the lightbulb idea for it. We now return you to the real discussion.

 

[Anthony]

Kim Stanley Robinson's excellent novel "Red Mars" has a lot to say on the subject

Sadly, while the book may have a lot to say on the subject, what it says is not correct.

 

[Gallowglacht]

Neither are laser rifles and jump drives.

 

[PFVA63]

I have some doubts

Hi,

Over the years I've been intrigued by stuff like space elevators/beanstalks but I have had some doubts about some of what I have read.

Specifically there is an interesting article on them in Wikipedia, much of which appears to be from the LiftPort Group website (or vice verse). However, in the Wikipedia article there is a formula for calculating required diameter versus altitude which accounts for gravitational and centrifugal forces based on the tensile strength of the material. In addition the author indicates that a steel structure just 1cm wide at its base would be severalhundred kilometers wide at geostationary orbit but that a carbon nanotube design could be just a millimeter wide at its base and presumably much narrower at geostationary orbit, due to its better strength to density ratio.

However, none of this appears to take into account the shear strength, bending strength, or fatigue strength of the materials and structure. The article does note issues like coriolis effects, weather, radiation, micrometeorites, and other factors that can cause fatigue stresses, bending moments, and shear forces in the structure but does not appear to account for how they will effect the minimum diameter of the structure and as such, I am unconvinced of much of the rest of the claims in the article about the ultimate weight of the structure and how it will react if damaged.

Anyway, just some thoughts I wanted to add.

Regards

PF

 

[Gallowglacht]

So how would you run them?

 

[veltyen]

So how would you run them?

In traveller?

A connected set of semi-intelligent connected chain units. Each self powered with a small grav drive. Only going to low orbit with a thrust capable station at the top.

It gets rid of the disaster failure mode. If the chain breaks the rest of the links should be able to sustain in place until another chain link is moved into place (the project would need many spares for this eventuality) or if that isn't possible the station should be able to pull away, taking some of the suspended material with it.

My first thought is that an equivalent cost in grav vehicles would allow access to the station more economically (and much more safely) unless the traffic up and down the beanstalk was quite significant (think high speed trains running up and down the beanstalk constantly.)

 

[BlackBat242]

For agricultural worlds, mining worlds, and manufacturing worlds that export/import a lot of bulk material, that could be exactly the case.

 

[Straybow]

Except high speed trains are slower than lift vehicles, and with cheap fusion power lift vehicles can be as arbitrarily large as a train. Delivery rate is higher with lift vehicles over the same pathway.

Furthermore, an elevator limits the origin and pathway whereas lift vehicles can deliver from anywhere on the surface via any arbitrary pathway. The only concern is traffic management.

Beanstocks only work economically with our "real world" power limitations, and then only by amortizing costs over a very long period.

 

[Gallowglacht]

Meh, in the end I went with them.
Because they are cool.

 

[Pickles]

Which is the best reason there is.