Talk:Lunar space elevator
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[edit] Pearson's design
- "Jerome Pearson has proposed a design using M5 fibre {typo?} that would weigh only 6,800 kilograms and be capable of lifting 200 kilograms at the Lunar surface; such an elevator could be sent to the Moon with just one launch of the largest existing launchers."
As I read this, 6,800 kg is the mass of the cable only; the total mass of the elevator would be much greater. The article doesn't seem to say how long a cable Pearson envisions, so it's hard to say what the other components of the system--especially the counterweight--would mass.
—wwoods 05:47, 21 Nov 2004 (UTC)
- The only reference I had was [1], which didn't specify. But it does sound like it's talking about the bare minimum cable, whereas an elevator would have at least a few extra bits added. (The fibre/fiber thing is just one of the usual British/American spelling differences, not a typo. Since I'm a Canadian I randomly oscillate between the two. :) Bryan 06:25, 21 Nov 2004 (UTC)
I wrote the article... yeah, I'm Canadian, so it's "fibre" here. The 6,800 mass is just the cable, but you could add a climber for a few hundred kg more. So, still within the capablities of current launchers. Pearson figures you could continue to strengthen the cable from material gathered on the Moon. - Fraser Cain, Publisher, Universe Today
- Thanks, I've updated the article to make that clear. Bryan 00:47, 17 Dec 2004 (UTC)
- Trouble is (unless I grossly miscalculated) the mass of the counterweight has to be orders of magnitude greater than the mass of the cable. Any old mass will do, including the rockets used to carry the elevator components, but still... An "extremely minimalist" system, for highish values of minimalist, eh?
- —wwoods 03:03, 17 Dec 2004 (UTC)
--195.178.232.139 12:44, 21 August 2006 (UTC)There sems to have bean some misunderstanding, i wrote thew folowing question to Jerome Pearson:
> Hi I am a PhD student at Lund University (Sweden) in electrical
> engineering; this has nothing to do with my research.
> When I read the articles
>
> http://en.wikipedia.org/wiki/Lunar_space_elevator
> http://www.universetoday.com/am/publish/lunar_space_elevator.html
>
> and then your report to NASA at
>
> http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf
>
> I fond some numbers in the articles above that seems to be
> misunderstandings and want
> to sort this out so I can correct the wikipedia article.
>
> The articles say that you proposed a cable with a mass of 6800 kg
> capable of
> lifting 200 kg at the lunar surface. And that this could be launched in
> a single shot with a conventional rocket.
>
> As I read the report you proposed a cable with a mass of 6100 ton
>(6 100 000 kg)
> with a strength (with safety factors) of 2000 N with cross section of
> 0.69 mm^2 at the lunar surface per ribbon and in total tree ribbons.
>
> In both cases the used fibre is M5.
>
> I think the numbers in the articles sounds unrealistic as the mean
> cross section of the ribbon could not be more than 0.025 mm^2. 200 kg
> sounds as someone has "converted" 2000 N to 200 kg using the untrue
> assumption g appreciative = 10.
>
> Have you proposed booth designs or are the articles wrong?
>
> Regards
> Lars Lindgren
I got this answer:
>Dear Mr. Lindgren:
>
>Thank you for your inquiry. I produced the numbers in the report to NIAC,
>but not the numbers in the Wikipedia article. No one consulted with me on
>the Wikipedia article, and I have no idea who wrote it. (This is
>surprising, since I invented the lunar space elevator.) I stand behind my
>NIAC report numbers.
>
>You might also want to consult the discussion and papers referenced on the
>Space Elevator page of the STAR, Inc. website, at www.star-tech-inc.com.
>
>Jerome Pearson, President
>Star Technology and Research, Inc.
>
Based on this i will change the numbers and remove the proposal with a single launch.
[edit] Fibre Material
There may be cost advantages in building the lunar space elevator from fibreglass rather than M5. Fibreglass is made from silicon which is the second most common element in Lunar soil. M5 is made from carbon which is very rare on the Moon and has to be brought from the Earth. The skeleton of the cable can still be made from M5.
Andrew Swallow 05:49, 11 September 2007 (UTC)
[edit] Height of L1 and L2
The height of L1 and L2 given in this article and Pearson's report are different. The ones in the report also have an error band. The correct values need determining. Andrew Swallow 19:24, 15 April 2007 (UTC)
Mystery solved. The report used figures from the centre of the moon rather than its surface.
Near side L1 = 58,021 +/- 3183 km from the centre of the moon Far side L2 = 64,517 +/- 3539 km from the centre of the moon
[edit] "Center of gravity" vs "center of mass"
"A lunar space elevator ... is similar in concept to the better known Earth space elevator idea (a cable suspended above Earth, with its center of gravity in geostationary orbit)." -- "Center of mass" would be better in in this context than "center of gravity", yes? (center of gravity also redirects to center of mass) -- 201.51.239.119 17:59, 9 June 2007 (UTC)
- No, I don't think so. The center of gravity would be at geostationary orbit, but the center of mass would be much further out, close to the counterweight. But I welcome a third opinion. 81.235.136.245 00:25, 2 September 2007 (UTC)
-
- Center of gravity is a term used implying gravitional force acting on an object is equivalent to the total force acting through the center of mass. In this case the lunar elevator is stabilized by a counterweight such that the design tension load is kept on the cable/tether stucture attached to the lunar surface. The center of mass created by the counterweight and tether together would be only slightly above the lunar surface synchronous orbit. Otherwise the tension in the tether/structure would be too great. So there are three forces acting on the structure: gravity through the center of mass of the system, centrifugal force out from unbalanced mass above the synchronous orbit, tension in the tether/structure to the surface. Lazyquasar 02:56, 25 September 2007 (UTC)
-
-
- Careful here, gravity doesn't act at the centre of mass in any significantly non linear gravity field.WolfKeeper 03:30, 25 September 2007 (UTC)
-
