Reaching for the Stars…Literally
The best way to get into orbit might just be taking its cue from the Jack and the Beanstalk fable: Space elevators!
Our future in space depends upon many factors: our continued ability to pay for research, development, and missions; discovering new and innovative ways to reach orbit that are more efficient; and ensuring educational opportunities in STEM subjects to foster the upcoming generations of space and rocket scientists to name just a few.
Being able to take mass from the surface of Earth, out of our gravity well and into zero-G orbit has always been one of the most expensive pieces of the puzzle. It takes enormous sums of energy, and therefore fuel and money, to get even a few pounds of something into space. What we’ve been doing so far is firing large rockets, already heavily-laden with tons of fuel, up through the atmosphere, each one carrying a payload that is tiny in comparison to the mass of the fuel and rocket. It’s been inefficient, to say the least.
One of the ways that many engineers believe is a viable alternative is for us to build space elevators. These aren’t elevators in the conventional sense of course. While SEs will indeed move objects up and down, it is more useful to think of them as railroads.
An SE would be a gigantic tether cable that reaches from the ground to a point at least 22,000 miles above Earth (with some plans stretching as far out as 62,000 miles) to a space station that acts as a counterweight in geostationary orbit. The power of the Earth’s spin will be what keeps the SE straight, pointing out at the stars, via centrifugal force. Elevator “cars”, what we’ll call climbers, would move up and down the tether via electrical power to carry cargo and people to and from orbit.
The advantages to using SEs as opposed to traditional rocketry would be many. SEs could reduce the cost of sending mass into space from roughly $10,000 per pound to only $100 per pound. SEs, once proven, would likely be much safer than rocket travel for humans: The journey skyward would be slower, but there wouldn’t be high-G forces to wreak havoc on organic or inorganic cargo. And cargo capacity would be far greater than any rocket could ever manage.
The origins of the SE idea might be traced back to Soviet Russian rocket scientist Konstantin Tsiolkovsky, who first wrote about the concept as early as 1895. Alongside Goddard and Oberth, Tsiolkovsky is one of the godfathers of rocket science. Tsiolkovsky’s proposal was basically a tower built so high it reached outer space. Our modern idea of a space elevator really comes from Yuri Artsutanov, another Russian scientist, who in 1959 conceived of a “tensile structure” that would be held in place via centrifugal force.
Aside from the sheer cost of building an SE structure in its totality, the primary hurdle is for our modern R&D to settle on the strongest and lightest material possible with which to construct the tether. Carbon nanotubes are commonly viewed as a best option, but there are other possibilities: silicon carbide, silicon nitride, and silica nanowires.
Space elevators will be comprised of 6 major sections: the ground station, the tether, the counterweight, the space station, climbers, and climber power sources. The counterweight must be positioned at the furthest end of the tether, while the station itself would be located at a point where there is an equal amount of mass above it as below. The power sources driving the climbers on their high altitude treks will likely be a combination of lasers and solar cells. It is also probable that by the time the carbon nanotube construction technology becomes feasible we would also be able to use fusion reactors to power SEs.
Multiple trips up and down an SE can be made in a single day. In addition, an SE would require far fewer personnel overall to staff on a regular basis than a rocket launch base.
One journey by a climber can also result in multiple opportunities for various parties, since the climbers will take cargo and people to four major points of egress. As a climber rises through the upper atmosphere and past low Earth orbit, objects such as weather stations and satellites can be jettisoned at points where they can enter stable orbits. These objects might not have enough velocity to maintain an orbit, however, and would therefore need some added acceleration capability, such as a small liquid-fuel cryogenic rocket engine. At the space station, more cargo and personnel can exit and utilize shuttle transport to other space stations. In addition, the tether can continue well beyond the space station and toward the counterweight, accelerating objects to greater speeds and then sending them on to much farther destinations such as the Moon, Mars, asteroid belt, and beyond.
Even though SEs will give us a way to get into orbit without using rockets on a regular basis, we will need traditional transport to actually construct one. The first step in the process will be to build what could be referred to as a “seed ribbon” made of tether material in orbit. This will be lofted into space via rocket and deployed via a small space station that would serve as a base of construction and ultimately become the counterweight. Eventually the seed ribbon will reach the ground station on Earth. After that, more material can be added to the tether and climbers can begin moving workers and 3D printers up and down the new space elevator.
With carbon nanotubes as its foundation, an SE tether only 7 cm thick would be capable of moving 1000 tons of cargo every single day — equivalent to the entire ISS which took over a decade to fully agglomerate in orbit. According to Ben Shelef’s analysis in his paper for The Spaceward Foundation found here, the specific strength (a measure of stress/density known asPascals) required for a tether would be between 30–40milliYuris, or 30–40 million Pascals: roughly 75 times the specific strength of steel wire.
While companies like SpaceX are focusing on improving the efficiency of our existing rocket technology, and rightfully so, the real future of Earth-to-orbit transport probably lies with the adoption of space elevators. They will ultimately:
- Give governments and corporations a faster and cheaper means to get material and people into space and do work there.
- Make the construction of space stations and colonies on the Moon and Mars much more feasible and doable over shorter timelines.
- Provide a safer and more reliable route to a viable space tourism industry.
- Help get us to a point where more clean power can be used on Earth by allowing for the easier construction and launch of many thousands of solar mirrors.
- Reduce the need for extensive training of space-based workers. The highly capable and specialized astronauts of today will still be needed, and in greater numbers, but with the use of SEs a more robust and diverse workforce of thousands will be able to reach space via an easier path.
Space elevators are the next big “leap” we need. Let’s do what we can to support the funding and research to make them a reality.
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