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A space elevator to the moon could be doable — and surprisingly cheap (engineering)

#1
C C Offline
https://www.nbcnews.com/mach/science/spa...cna1051496

EXCERPT: The idea of space elevators isn’t new [...] But Zephyr Penoyre and Emily Sandford envision a system that would be used not to ferry humans and cargo from Earth’s surface to Earth orbit — the goal of so-called classical space elevator concepts — but to provide transportation to and from the moon. In a study published Aug. 25 on the online research archive arXiv, the students contend that it’s technologically and financially feasible to build such a "lunar space elevator," which was first publicly detailed by Jerome Pearson at a conference in 1977 and by Yuri Arsutanov in a separate paper published in 1979.

“It shocks me how cheap it could be,” says study co-author Penoyre, a graduate student in astronomy at the University of Cambridge [...] Penoyre and Sandford, a graduate student in astronomy at Columbia University and a co-author of the study, call their lunar space elevator concept Spaceline. Its central element is a cable that would be anchored to the moon and span more than 200,000 miles to a point above Earth's surface — perhaps an orbit about 27,000 miles from our planet. (The cable of a lunar space elevator couldn’t be anchored to Earth’s surface because the relative motions of the moon and our planet wouldn't permit it.)

As explained in the paper, the simplest version of the Spaceline cable might be barely thicker than the lead in a pencil and might weigh about 88,000 pounds — within the payload capacity of a next-generation NASA or SpaceX rocket. It could be made from Kevlar or other existing materials rather than the exotic and hard-to-make carbon-based materials that have long been seen as the key to building a classical space elevator. Future space travelers would use a spacecraft to fly from Earth to the end of the dangling cable, which would be held taut by Earth's gravity, and then transfer to solar-powered robotic vehicles that would climb up the cable to the moon. The voyage might take days or weeks. Return trips would simply reverse the process.

Why spend hundreds of millions or even billions of dollars erecting a lunar space elevator instead of relying on proven rocket technology? Penoyre and Sandford say in their paper that the former might ultimately be more economical, especially for bringing raw materials back to Earth from moon-based mines. A paper published by the American Institute of Aeronautics and Astronautics estimated that a lunar space elevator system might pay for itself within 53 trips by transporting lunar materials to a space station between the moon and the Earth. (MORE - details)
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#2
billvon Offline
(Sep 15, 2019 06:53 PM)C C Wrote: “It shocks me how cheap it could be,” says study co-author Penoyre, a graduate student in astronomy at the University of Cambridge [...] Penoyre and Sandford, a graduate student in astronomy at Columbia University and a co-author of the study, call their lunar space elevator concept Spaceline. Its central element is a cable that would be anchored to the moon and span more than 200,000 miles to a point above Earth's surface — perhaps an orbit about 27,000 miles from our planet. (The cable of a lunar space elevator couldn’t be anchored to Earth’s surface because the relative motions of the moon and our planet wouldn't permit it.)
Not sure of what the point of this would be.  27,000 miles means you'd have to get hardware beyond geosync orbit - so harder than the hardest normal launches we do today.
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#3
C C Offline
(Sep 22, 2019 12:09 AM)billvon Wrote:
(Sep 15, 2019 06:53 PM)C C Wrote: “It shocks me how cheap it could be,” says study co-author Penoyre, a graduate student in astronomy at the University of Cambridge [...] Penoyre and Sandford, a graduate student in astronomy at Columbia University and a co-author of the study, call their lunar space elevator concept Spaceline. Its central element is a cable that would be anchored to the moon and span more than 200,000 miles to a point above Earth's surface — perhaps an orbit about 27,000 miles from our planet. (The cable of a lunar space elevator couldn’t be anchored to Earth’s surface because the relative motions of the moon and our planet wouldn't permit it.)
Not sure of what the point of this would be.  27,000 miles means you'd have to get hardware beyond geosync orbit - so harder than the hardest normal launches we do today.


The original paper has an appendix that discusses the classic space elevator going (slightly?) beyond geostationary orbit for safety concerns. "The space elevator extends from a anchor point on Earth’s equator to above geostationary orbit. [...] The maximum tension in the cable occurs at geostationary orbit and beyond this point the tension reduces as we move further from the Earth."

They murkily in the same area imply that the Earth-side end for their lunar spaceline would be located (slightly?) past it, too. So 27,000 mi (43,452 km) above the equator may only be an arbitrary number that the pop-sci report circulating around chose for satisfying being above 22,236 mi (35,786 km).

The authors seem to have safety concerns about stress and tension on the spaceline at certain locations (especially L1 below), and mention "room to wander" among other safeguards. I don't know if that and other untidy factors would likewise contribute or not to the location at 27,000 miles (or whatever number would actually be chosen by the engineers).

The original paper talks of establishing a "base camp" for the spaceline at the Earth-Moon Langrange point 1 (L1). According to it that's on the 202,567 mi (326,000 km) spot along the overall 238,856 mi (384,402 km) distance between the planet and its ancient satellite.

The distance between Earth and Moon, of course, also varies +- 50,200 km (31,200 mi) in the course of the latter's orbit.
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#4
billvon Offline
(Sep 22, 2019 04:18 AM)C C Wrote:
(Sep 22, 2019 12:09 AM)billvon Wrote:
(Sep 15, 2019 06:53 PM)C C Wrote: “It shocks me how cheap it could be,” says study co-author Penoyre, a graduate student in astronomy at the University of Cambridge [...] Penoyre and Sandford, a graduate student in astronomy at Columbia University and a co-author of the study, call their lunar space elevator concept Spaceline. Its central element is a cable that would be anchored to the moon and span more than 200,000 miles to a point above Earth's surface — perhaps an orbit about 27,000 miles from our planet. (The cable of a lunar space elevator couldn’t be anchored to Earth’s surface because the relative motions of the moon and our planet wouldn't permit it.)
Not sure of what the point of this would be.  27,000 miles means you'd have to get hardware beyond geosync orbit - so harder than the hardest normal launches we do today.


The original paper has an appendix that discusses the classic space elevator going (slightly?) beyond geostationary orbit for safety concerns. "The space elevator extends from a anchor point on Earth’s equator to above geostationary orbit. [...] The maximum tension in the cable occurs at geostationary orbit and beyond this point the tension reduces as we move further from the Earth."

They murkily in the same area imply that the Earth-side end for their lunar spaceline would be located (slightly?) past it, too. So 27,000 mi (43,452 km) above the equator may only be an arbitrary number that the pop-sci report circulating around chose for satisfying being above 22,236 mi (35,786 km).

The authors seem to have safety concerns about stress and tension on the spaceline at certain locations (especially L1 below), and mention "room to wander" among other safeguards. I don't know if that and other untidy factors would likewise contribute or not to the location at 27,000 miles (or whatever number would actually be chosen by the engineers).

The original paper talks of establishing a "base camp" for the spaceline at the Earth-Moon Langrange point 1 (L1). According to it that's on the 202,567 mi (326,000 km) spot along the overall 238,856 mi (384,402 km) distance between the planet and its ancient satellite.

The distance between Earth and Moon, of course, also varies +- 50,200 km (31,200 mi) in the course of the latter's orbit.
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