Space Elevators: The Future Of Space Travel?

Imagine an elevator going into space; press a button and, soon enough, "hello, space!"

It is not as far-fetched as it sounds. There could be a space elevator — that is, an elevator into space — in the not-so-distant future. It is the future of space missions.

The idea, first introduced by Russian scientist Konstantin Tsiolkovsky in 1905, can change the path of space exploration. Large vehicles would no longer be needed to escape the gravitational well of the Earth.

"Gravitational well" is essentially gravity acting like a rubber band pulling on a mass.

The original concept of the space elevator was to build a tower structure from the Earth until the geostationary orbit and the weight supported from below. That is, the elevator would be geosynchronous. It would move with the Earth.

Theoretically the cable would be 144,000 kilometres (km) long. For perspective, at that length it would wrap around the Earth nearly four times!

A more feasible concept is to build a structure supported by tension instead. The basic structure is a cable tethered to the Earth and the other end in orbit above Earth, kept taut by the Earth’s gravitational well, that is, the tether would be suspended from above instead of building it from the ground up.

The gravitational field is the sum of the centrifugal force and the force of gravity on the cable. If the centre of mass is above the geostationary orbit, the net force will be upward and the cable will be held up by tension.

The structure would provide the same stability as with the earlier model, but through easier construction.

The objects required can be transported by tether climbers, which would be powered by solar panels, nuclear power, laser, or various fuels making the operation potentially environment friendly and low-cost. These objects can be released and kept in the geostationary orbit.

The current cost of transporting materials to space is Rs 1,525,300 per kilogram (kg); with space elevators, once built, the cost can be as low as Rs 38,132.50 per kg. That is 40 times less!

Space elevators would be helpful in reducing space debris, making space travel routine, and potentially opening doors to interplanetary travel and, eventually, settlement. Space elevators will be eco-friendlier than rockets and cheaper in the long run.

Parts Of The Space Elevator

A space elevator has four basic elements.

1. The base station and anchor

It is required astrodynamically that the base of the space elevator must be anchored at the equator so that the cable can be stationary with respect to the Earth’s surface. But this anchor cannot be stationary. It needs to be able to have a small range of motion to avoid orbital collisions, lightning, and so on. The advantages of a movable ocean-based anchor over a land-based anchor include:

● Excellent mobility for avoiding low-Earth-orbit objects and storms

● Can be located in the equator with an area with mild weather

● Located in international waters

● Mobile sea platforms are already tested technology

● In the event of cable breakage, 1,000-2,000 km of cable would fall in the ocean (the rest would burn up on reentry), which would be devastating if it fell on land instead

● No high-altitude operational challenges or limited usable land areas

The technical selection considerations to choose an anchor location include the distribution of lightning activity, cyclonic activity, and storms, requirements with respect to locating a power beaming station nearby, available space to allow mobility, ease of construction, access, and operations.

These requirements are fulfilled by the concept of a floating base station, that is, a base station in the sea. This has the additional benefit of allowing nations other than those along the equator to construct space elevators and advance space travel.

2. The counterweight

The counterweight is an important component to ensure that the space elevator is held up by tension. A simple explanation would be to consider it as the ball in the ball-and-string concept where if you tie a ball to a thread and rotate it over your head, the string is kept taut by the centrifugal force exerted and, hence, tension produced in the string. Similarly, the counterweight keeps the elevator cable from collapsing and holds it up through tension between the Earth and the counterweight.

The counterweight keeps the centre of mass well above the geostationary level, which produces enough centrifugal force to counter the gravitational force due to Earth. Proposed materials for the counterweight include asteroids already in orbit, old space debris that can be collected, and, if needed, the initial climbers used to thicken and form the cable that are no longer usable.

This would not require the manufacture of new materials and help reduce space debris.

3. The tether (the cable that connects the surface to space)

The cable would be tapered such that it would be the thickest at the point of highest tension (geosynchronous orbit) and thinnest at the point of lowest tension (the ends at each side). The material of the cable needs to be strong enough to support the entire structure, withstand high tension, and have a minimum weight of its own.

Carbon nanotubes, discovered in 1991, have the promise of being the strongest material yet. Then tensile strength is theorised to be 130 gigapascals (GPa), as compared to steel, at less than 5 GPa, and Kevlar at 3.6 GPa. The density of carbon nanotubes is 1,300 kg per metre cubed, which is lower than that of steel (7,900 kg per metre cubed) and Kevlar (1,440 kg per metre cubed).

Carbon nanotubes are essentially “rolled up” sheets of graphene (carbon atoms held together by double bonds in a trigonal-planar [sp 2] formation), extending their remarkable chemical, tensile, and conductive properties while being useful for engineering purposes.

The technology is maturing, but currently graphene can be made in small amounts in labs. It is 200 times stronger than steel.

A taper is required to provide support strength. The taper ratio refers to the ratio of cross-sectional area at the geosynchronous to the cross-sectional area at Earth. These properties (mass and density, hence the strength-to-weight ratio) play an important role in the taper ratio.

At breaking point, the taper ratio for steel is approximately of the order of 10 raised to 33rd power, for Kevlar it is approximately of the order of 10 raised to 8th power, and for carbon nanotubes it is 1.5. Therefore, carbon nanotubes are much more feasible.

Considering meteoric impacts, the design of the cable should optimally be a ribbon-type composite design made of epoxy and carbon nanotubes. “Ribbon type” here refers to a cable that is much smaller in one cross-section dimension than the other. Although carbon nanotubes seem like an excellent choice for tether, there is no current technology to get the quantity and quality required.

The total length of the cable would be about 96,000 km.

4. The climber (the elevator carriage)

Climbers are elevator vehicles that would carry payloads up the cable. To avoid moving cables (as in normal elevators) to reduce the length of the cable needed, climbers need to be used. Instead of two moving cables, there will be one fixed cable and climbers will supply the power needed to go up and down. The energy needed by the climber can be calculated by using the potential energy formula:

E = mgh

The climber needs to have an expandable design to allow the addition of motors, increasing the strength of the structures, accommodating larger cable spools, the addition of photovoltaic panels, and so on.

The primary job of the first 207 (approximately) climbers will be to deploy cables as they climb and attach it to the main cable piece by piece. The tensions on the cable need to be monitored carefully to ensure no breakage or damage and proper attachment of the cable segments.

First, these cable segments should widen the main cable up to roughly 30 centimetres (cm) wide to reduce the possibility of catastrophic meteor damage. Then, after that, thicken the cable further.

The second aspect is the epoxy and application. The adhesion of the epoxy should be controlled such that the deployed cable segment remains in contact with the existing cable and should harden properly in the harsh environment of space (solar radiations, temperature fluctuations, flares).

The structure of the climber will be designed for gradually varying load in the vertical direction, with primary structural loads between the cable and locomotion system. The design should consider thermal aspects as well.

The climber would be used for repairs of the cable, strengthening weak sections of the cable via epoxifying and reapplying protective coating against atomic oxygen erosion and further damages.

There will be a specific climber designed only for rescue missions, called a rescue climber.

How will we send it to space?

A good plan would be to deploy parts to low-Earth orbit by spacecraft. Astronauts will assemble the pieces in low-Earth orbit and the entire structure will be sent to geosynchronous orbit. This would be simpler and less risky than trying to build the entire elevator in space. There are still a lot of factors to consider. It is a challenge, but it is not impossible.

Scope And Applications Of Space Elevators

The space elevator will be able to:

● Place heavy and fragile payloads in any Earth orbit (with a circularising rocket) or send them to other planets

● Deliver payloads with minimal vibration

● Bring heavy and fragile payloads down from space

● Deliver payloads to space at a small fraction of current costs

● Send a payload into space or receive a payload from space every few days

● Be used to quickly produce additional cables or increase its own capacity

With these abilities, we can expect the following developments rapidly after the creation of a space elevator:

Cheap delivery of satellites into space with over 50 per cent reduction in delivery costs, depending upon the orbit and the satellite. This enables easier and cheaper access to space.

Repairing malfunctioning spacecraft instead of entirely replacing them. This would reduce waste and save valuable time and resources, especially for telecommunication companies.

Large-scale manufacturing in microgravity. Space has little to no gravity, hence materials can be manufactured at a higher quality. This includes computer chips and medical equipment. In short, high purity and perfect metal structures.

Inexpensive global satellite systems. Television and telephone systems would become much easier and less expensive to set up.

Large orbiting solar power collectors. If large solar panels are set up, power can be harnessed and supplied to people all over the world, including rural areas, at a low cost.

Multiple large and inexpensive spacecraft for solar system exploration. Sending spacecraft into space, even for small observational missions, at the moment is very expensive. Instead, we could have less-expensive, larger spacecraft doing long-term planetary studies with more valuable scientific instruments on board to fully understand our solar system.

Larger orbiting observatories and interferometers. Observatories and interferometers would be many times the size and power of Hubble or any Earth-based radio telescope. These could search, locate, and image cosmological bodies better than ever before.

An inhabited space station at geosynchronous equatorial orbit (GEO) for research, satellite repair, commercial manufacturing operations, and preparation facility for deep space and solar system exploration. This would be a giant step in humanity’s occupation of space and it would come soon after the construction of the first elevator. Space exploration would become a booming industry and provide many jobs as well. A large station could be placed in orbit and occupied by a permanent crew (not only professional astronauts) for valuable research.

Mars exploration and settlement. Large-scale research can be conducted by sending several exploratory vehicles to study the planet Mars better and for potential large-scale habitation with an affordable budget.

Removal of human-made space debris in Earth orbit. Space debris can be damaging to satellites and potentially fatal to astronauts in the International Space Station or any space mission. The current efforts to clean up space debris would be greatly aided, and become much easier, with the construction of a space elevator.

Future mining of asteroids for rare metals. Asteroids contain rare metals, but are extremely costly to mine, making the net profit negligible. This would become considerably cheaper and easier.

Easier access to space for the general population. This won’t happen soon after space elevator operations begin, but with the reduction of cost for a trip to space, even the general population can afford the journey.

Formation of a galactic harbour in the future would be closer than ever before with a space elevator, but this will take some time. There will need to be a systematic allotment of space elevators to carry out missions and transport. There will be massive business development in the GEO region, such as spacecraft assembly, refuelling operational satellites, solar power collection, and trips to interplanetary destinations.

Lunar space elevator. The easier step would be to build a lunar space elevator first. The low gravity on the Moon would significantly reduce the costs and enable humans to use resources available on the Moon. A lunar space elevator using existing high-strength composites with a lifting capacity of 2,000 N at the base equipped with solar-powered capsules moving at 100 kph could lift 584,000 kg/year of lunar material into high Earth orbit. Since launch costs may be about $1,000 per kg then, this material would be worth more than half a billion dollars per year, resulting in greatly reduced costs and opening a new chapter in space development.

In combination with a space elevator on Earth, it would be the highway between the Moon and Earth orbit and to carry supplies from Earth orbit to a lunar base. This will make the spacecraft leaving Earth lighter.

This article has been published as part of Swasti 22, the Swarajya Science and Technology Initiative 2022. Read other Swasti 22 submissions.

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