Wednesday, 15 April 2020

Elevator to the Moon, it's possible!






Space elevator  to reach the moon is no longer a distant dream,; it is now a possibility. And the elevator between Earth and moon is more than a possibility. It can be a reality soon. It will be the longest elevator ever built. It will help to transport men and material to the moon and in turn transport rare minerals mined from the moon....

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It’s an incredible idea to install an elevator to Moon. It might sound crazy or weird. Actually it’s possible. It’s easier and less expensive than you think. In 1910 scientist Fredrich Zander described an elevator to the moon in his notes. And in 2019 Cambridge University student Zephyr Penoyre and Columbia University student, Sandford proposed Spaceline, a lunar space elevator to carry humans and cargo to and  from the Moon.

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.



Sending rockets to the moon is too expensive, and if we have to settle there, hundreds of trips might be needed every year. A permanent space elevator might work out cheaper to transport men and material. A lunar elevator could significantly reduce the costs and improve reliability of soft-landing equipment on the lunar surface. For example, it would permit the use of mass-efficient, low thrust drives such as ion drives which otherwise cannot land on the Moon. Since the docking port would be connected to the cable in a microgravity environment, these and other drives can reach the cable from low Earth orbit (LEO) with minimal launched fuel from Earth. With conventional rockets, the fuel needed to reach the lunar surface from LEO is many times the landed mass, thus the elevator can reduce launch costs for payloads bound for the lunar surface by a similar factor.

 Since it was first dreamed up by the Russian rocket scientist, Konstantin Tsiolkovsky, supposedly inspired by looking at the Eiffel Tower, and later refined by another Soviet engineer in 1959, many people have pointed to a space elevator as the solution. The latest proposal—that building a space elevator from the moon to Earth orbit is theoretically feasible.

A lunar space elevator or lunar spacelift is a proposed transportation system for moving a mechanical climbing vehicle up and down a ribbon-shaped tethered cable that is set between the surface of the Moon "at the bottom" and a docking port suspended tens of thousands of kilometers above in space at the top.

Spaceline – 321,869 km-long cable fixed on moon surface, thin as pencil lead and made from Kevlar might cost around $ 1 billion. The cable from the moon will end thousands of kilometers above earth. Rockets will to carry you to the end of the rope. Solar powered robotic capsules glide to and from the Moon. About 53 trips needed to recover cost of Spaceline. It will cart rare metals like neodymium and gadolinium, which are used in electronics, from Moon mines to Earth orbit.

The basic idea behind a space elevator is to do away with the requirement of carrying all that fuel with you while going up, by building a giant cable and climbing up it. This isn’t as ludicrous as it sounds. Imagine such a cable, extending into space with an orbiting counterweight, which could be an asteroid or a space station, on the end of it. Just like in a game of tetherball, the centrifugal force from that orbiting counterweight as it rotates around the Earth pulls the rope taut. If the cable is long enough, that centrifugal force can be enough to support the weight of the cable, suspending it: a vast elevator to the sky. 
Once you have this elevator to space, robotic ‘climbers’ on the outside crawl up the rope. You can send payloads into low Earth orbit, geostationary orbit, or further out into space—all just by choosing how far to climb. If the tower is tall enough, simply letting go at the top flings you into deep space, escaping Earth’s orbit entirely.

Regardless of the design, the economics of the space elevator always look glorious: sending mass into low Earth orbit could be reduced from $10,000 per pound to $400 per pound. Some estimate that an elevator could be constructed for as little as $6 billion. Compare this to the space shuttle program, which cost a total of $209 billion by one estimate.

It sounds wonderful. But, of course, all the creative designs so far have been torpedoed by one flaw: What do you make the cable from? The cable has to support a tremendous amount of tension without snapping. Since part of that tension is supporting the cable’s own weight, the less dense the material, the less force it will feel. So you need a material that’s lightweight and can be pulled without breaking. Steel, titanium, and almost everything else you can think of would simply snap under the forces involved.



For a while, it was thought that maybe carbon nanotubes might provide the solution—they’re the first material designed that might get up to the strength required. But issues abound here, too. Manufacturing them at sufficient purity is extremely difficult. A single defect can ruin the strength of the material. Then there’s the fact that the cable might be vulnerable to lightning strikes and, if you’re not sold yet, the fact that the longest ever carbon nanotube cable manufactured was around half a meter, falling an agonizing 35,768 kilometers short of the length required.

The new design, which the authors dub the Spaceline, circumvents some of these nasty requirements by proposing that the cable should be built on the moon and dangle down to Earth orbit. This immediately does away with the counterweight. The Earth’s gravity pulling down on the cable is sufficient to hold it taut.

The major advantage is that the cable does not need to be nearly as strong, as it need not support large amounts of cable mass in Earth’s strong gravitational field, but instead in the weaker lunar field. This means that you could actually make such a cable with materials that exist: the authors note that Kevlar, the same material used in bulletproof vests, could be up to the challenge.

The major disadvantage is that the cable can only extend slightly closer than geostationary orbit, which is still a long distance from Earth’s surface. So you’ll have to make that first stage of the journey and grab the rope by yourself. But for the cool price of a billion dollars, this lunar space elevator could enable regular travel to the moon’s surface with only a third of the fuel.

While this doesn’t solve the problem of escaping Earth’s gravitational field—you’ll still need rockets and the miserable physics of space launch to reach the Spaceline in the first place—the authors envisage some potential advantages, alongside saving fuel costs once you reach the line. For example, the cable would run through the Lagrange point between the Earth and the Moon—in other words, where the Earth’s gravitational pull cancels out the Moon’s gravitational pull. This is one of the regions in space where you can actually dream of stably constructing a floating base. And the Spaceline could transport materials from the moon to Earth orbit for, well, for whatever it is we want to build there—satellites, spacecraft, space stations, you name it.

The idea of using the Lagrange points as stepping stones—beyond our only current space outpost, the ISS—is an exciting one that offers many benefits. Not least, it gives humanity a workable project to focus on whereby we can develop all of the ancillary technologies that are going to be necessary to achieve anything practical in space. If we are ever to leave the cradle of our civilization, we’ll need all the ingenious ideas we can get.

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.








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