Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Space Elevators Are Possible

techblog.co

Post reply on HN
Print view View original

61–70 of 82 posts

Re: Space Elevators Are Possible

#61

Post by kamaal »

jccooper wrote: post #56
kamaal wrote: post #49

At the risk of appearing stupid, I just have few simple questions 1. What exactly holds the counter weight in position? 2. Such a long rope, which the article says is around 62000 miles, won't it function more like rubber band than function like a rope? Due to mere stretching/elastic effect? 3. I'm sure traveling 62000 miles is nothing like fuel efficient especially when you travel in the direction of highest frictio…

1. The counterweight is in geosynchronous orbit. It is "held up" by its absurd speed like any other satellite. 2. One of the reasons you need a very strong material. The tether will be in tension, but probably will have quite a bit of movement to it. The tether dynamics are not a solved problem. 3. Most plans suggest that power will be beamed from the ground to the climber, either as microwaves or visible light. Some…

Yes, sorry the centripetal-centrifugal force balance thing was completely off my mind when I asked that question.

But with all the remaining two points look in the domain of SciFi to me. I'm sure tether dynamics are going to a materials engineering problem like never seen in history of mankind.

Plus the energy problem is still by and large a very problem. Sending electricity down the tether looks very inefficient give the article says it will 62K miles long.

In short we are still may be what, say 50 years away from this?

Re: Space Elevators Are Possible

#62

Post by jccooper »

phest wrote: post #42
avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

In theory, could elevators replace satellites? If so perhaps an initial batch of elevators could also be used to clean up the space junk (including the now obsolete satellites).

The counterweight platforms would be a great place for services now performed by geosync satellites. Probably you would also have major GEO platforms in areas not (yet) served by a tether. Take a tug there from the nearest tether. Would really cut down on discrete sats.

Services that need to be done away from the equator (monitoring of the surface, communications at high latitudes) would still need orbits like todays LEO sats. The same model of discrete satellites may prevail, but you might also see larger platforms housing multiple services.

We might see a tether vastly increase the amount of orbital activity, but decrease the number of discrete objects.

Re: Space Elevators Are Possible

#63

Post by Sharlin »

jccooper wrote: post #56
kamaal wrote: post #49

At the risk of appearing stupid, I just have few simple questions 1. What exactly holds the counter weight in position? 2. Such a long rope, which the article says is around 62000 miles, won't it function more like rubber band than function like a rope? Due to mere stretching/elastic effect? 3. I'm sure traveling 62000 miles is nothing like fuel efficient especially when you travel in the direction of highest frictio…

1. The counterweight is in geosynchronous orbit. It is "held up" by its absurd speed like any other satellite. 2. One of the reasons you need a very strong material. The tether will be in tension, but probably will have quite a bit of movement to it. The tether dynamics are not a solved problem. 3. Most plans suggest that power will be beamed from the ground to the climber, either as microwaves or visible light. Some…

The center of gravity of the whole system must be in the geosynchronous orbit (36000 km up) so that the thing stays up. This means that half its weight (not mass!) must be above 36000 km; in the modern proposals there's no separate counterweight, but the ribbon itself extends to ~100000 km up. In practice, the CoG must be a bit above 36000 km so that payloads going up don't pull the ribbon down.

Re: Space Elevators Are Possible

#64

Post by Sharlin »

kamaal wrote: post #61
jccooper wrote: post #56

Earlier quoted context omitted.

1. The counterweight is in geosynchronous orbit. It is "held up" by its absurd speed like any other satellite. 2. One of the reasons you need a very strong material. The tether will be in tension, but probably will have quite a bit of movement to it. The tether dynamics are not a solved problem. 3. Most plans suggest that power will be beamed from the ground to the climber, either as microwaves or visible light. Some…

Yes, sorry the centripetal-centrifugal force balance thing was completely off my mind when I asked that question. But with all the remaining two points look in the domain of SciFi to me. I'm sure tether dynamics are going to a materials engineering problem like never seen in history of mankind. Plus the energy problem is still by and large a very problem. Sending electricity down the tether looks very inefficient giv…

Solar power satellites would most likely beam the power to Earth using microwaves.

Re: Space Elevators Are Possible

#65

Post by Crito »

jccooper wrote: post #52
S4M wrote: post #41

Earlier quoted context omitted.

How about making the elevator start in the North pole (or South pole) and go vertically from there. That way, we can be sure that it will never meet the trajectory of a satellite? Of course, it would prove harder to build it in those cold regions.

Impossible. It must be on the equator. Attaching a line from the ground to a large object in geosynchronous orbit is the essential plan, and GEO only happens above the equator.

You could attach the tether at a higher or lower latitude, but standing on the ground next to it, it would appear to rise into the sky at a rather alarming angle (more or less parallel with the equatorial plane). More of the cable would be going through the atmosphere. Centrifugal force would hold it taunt and a great deal of tension at the base would be required to keep the entire system in that configuration. At no point along the cable would the cable be following a valid orbit (the center of mass of the cable would not be in geosynchronous orbit). You would need a much stronger cable, and the result would be far less useful.

Edit: http://gassend.net/publications/NonEquatorialUniformStressSp...

Re: Space Elevators Are Possible

#66

Post by jccooper »

kamaal wrote: post #61
jccooper wrote: post #56

Earlier quoted context omitted.

1. The counterweight is in geosynchronous orbit. It is "held up" by its absurd speed like any other satellite. 2. One of the reasons you need a very strong material. The tether will be in tension, but probably will have quite a bit of movement to it. The tether dynamics are not a solved problem. 3. Most plans suggest that power will be beamed from the ground to the climber, either as microwaves or visible light. Some…

Yes, sorry the centripetal-centrifugal force balance thing was completely off my mind when I asked that question. But with all the remaining two points look in the domain of SciFi to me. I'm sure tether dynamics are going to a materials engineering problem like never seen in history of mankind. Plus the energy problem is still by and large a very problem. Sending electricity down the tether looks very inefficient giv…

Quite possibly. I'm not concerned with power transmission so much; that's just engineering, and the tiny Centennial Challenge teams were doing well enough over a few years that it seems quite soluble. We will probably have UAVs flying on beamed power regularly within a few years.

The tether materials are obviously the long pile in this tent. We have theoretical materials that will work, which is great, but we really need practical materials. The day you can go buy nano tube thread you can formulate an actual timeline for a space elevator. Until then, its only a dream.

Re: Space Elevators Are Possible

#67

Post by flurdy »

InclinedPlane wrote: post #44
avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

It's not as big a problem as it seems. Space is big, even tethers are small, the amount of time between a collision occurring would normally be quite long. Satellites can have their orbits adjusted just enough every once in a while to avoid the tether. The value of the tether would be so high that it would be worth the cost of keeping every satellite diverted around it.

That would assume you could adjust all the satellites' orbits. Whilst some satellites have proper propulsion, I think many just have minor systems to only adjust their rotation, and a lot have none. And don't forget all the dead ones that are orbiting space junk.

Re: Space Elevators Are Possible

#70

Post by Schwolop »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

Couldn't the tether just have a friendly robot in charge of what I'll politely refer to as "catch and release"?
Post reply on HN