All Aboard the Uber to Mars
A realistic approach to artificial gravity in space.

The universe holds great potential for exploration, yet humanity needs a totally different breed of spacecraft before it can enter the multi-planetary era. Self-sustaining cosmic habitats will pave the way to space colonies, but they have to be developed first.
Jeff Bezos’ Blue Origin and Musk’s SpaceX are competing head-to-head to deliver cargo to space at prices lower than ever. It’s no secret that Elon Musk wants to colonize Mars to make humans a multi-planetary species. The solar system’s second-smallest planet is mineral resource-rich, has a similar day to Earth’s, has an atmosphere that protects from cosmic radiation, and is only 35,800,000 miles away (on a good day). Next July, Mars will be closer to Earth than it has been in over fourteen years.
If you’re an adult reading this in 2017, the overwhelming likelihood is that Musk’s 80,000-person colony will become a reality long after you are gone, but is that a reason for us to give up on the goal? Absolutely not. The intermediate steps that need to be taken prior to colonizing another planet are interesting and worthwhile in and of themselves. As new technologies are developed for space exploration, some will have applications right here on Earth as well.
Matt Damon and author Andy Weir showed us in the Martian that growing plants and providing food for ourselves on Mars isn’t outside the realm of reason. Interstellar showed us that space pioneers will face colossal challenges as they attempt to explore and settle on other planets. Star Wars showed us that having a lightspeed hyperdrive is helpful, and it’s handy to have a wookiee in your flight crew.
Science fiction is considered fiction for a reason, but it offers glimpses into specific elements of a future reality that can inspire us to move the needle forward. Earth has an incredibly unique ability to sustain life, but the search for another planet like ours continues in hopes that humans can eventually inhabit it.
While many space researchers are documenting their findings about distant exoplanets, others have focused on terraforming methods that could make planets like Mars more like home. One NASA-funded project involves an attempt to grow photosynthetic algae and cyanobacteria in Martian soil to generate oxygen for Mars’ atmosphere prior to human settlement.
Astronomers have found that a select group of the most suitable exoplanets still have exceptionally harsh or exotic environments, making Mars look like a five-star resort by comparison. With an average surface temperature of 446 °F, the ‘steamy waterworld’ GJ 1214b contains large amounts of water such that its atmosphere is mostly composed of steam. Studies of 55 Cancri e have suggested that the planet could be covered with supercritical fluids and diamonds. Yet another, TrES-2b, is covered with a coal-black gas that reflects less light than the blackest acrylic paint.
Despite its similar gravity, our neighboring planet Venus has shown little capacity to support life. One of its days lasts 243 Earth-days, longer than it takes the planet to orbit the sun. Its atmospheric pressure is 92 times stronger than Earth’s, and it is surrounded by a thick layer of clouds that rain sulfuric acid down on the planet. Hurricane-force winds sweep through the upper clouds. With a particularly severe form of the greenhouse effect, the surface temperature of 870 °F is hot enough to melt lead. If that doesn’t kill a traveler, cell damage caused by cosmic radiation penetrating the toxic fog would eventually kill a person. The longest any unmanned spacecraft has lasted on Venus is 110 minutes.
By comparison, Mars is quite close and habitable, yet it has a long, long way to go before having an environment anything like Earth’s. None of the ecological mineral cycles (i.e. sulfur, nitrogen, and phosphorus cycles) are available to support plant growth, so any sort of station that would be placed on Mars would initially need to sustain itself with only sunlight and its cargo. Since we need a self-sustaining habitat anyway, would it be worth building that habitat closer to Earth where we can test its effectiveness in space before sending it millions of miles away? The risk for catastrophic failure is mitigated when NASA can bring the crew home in a matter of days rather than months or years.
Next-Level Space Stations and Spaceships
NASA is addressing the need for a self-sustaining space habitat with several projects, particularly the well-known International Space Station. One of the key challenges they’ve found during the missions to the ISS is that weightlessness, although enticing at first, is damaging to human health over long periods of time. Bone and muscle mass are lost, and other effects are still being evaluated. Astronaut Scott Kelly suffered serious health issues following his one-year stay in the ISS, including swollen legs, vision problems, sensitive skin, and flu-like symptoms.
The effects of low gravity have also been investigated in plants, which have trouble growing in a low-gravity environment. Careful steps must be taken to get the plants to survive, flower, and produce seeds. Life support systems aboard the spacecraft must also be specifically designed to operate in a zero-gravity environment.
Sci-fi writers and NASA engineers have long known about centripetal force as a solution to weightlessness in space. Artificial gravity is depicted in countless space movies from Passengers to 2001: A Space Odyssey. In essence, simulated gravity requires a very large ship that pulls humans and objects against the outer surface simply by rotating. If the rotational diameter is too small, your head will experience less gravity than your feet, leading to roller-coaster-style dizziness and serious health issues in the long term.
According to John Page, an aerospace design lecturer, the diameter needs to be larger than a football field to achieve 100% gravity that doesn’t cause dizziness. So how do you build a ship that large without spending billions of taxpayer dollars? So far, most of the concepts have only been widely displayed in video games, movies, and drawings. The Nautilus-X was a spacecraft concept developed by NASA engineers to combat the issue of low gravity on the ISS by attaching an on-board human centrifuge, but astronauts clearly couldn’t spend their whole day in this section, and small-diameter rotation would have continued to cause problems.
The solution lies in a unique concept known as tethered rotation, or tethered artificial gravity. Like the Hyperloop, it probably won’t catch on until we give it a fun name. Why don’t we call it Terograv (tethered rotational gravity)? That sounds a lot like “terragrav,” which translates to “Earth’s gravity.”
With this approach, a tether holds two modules together or holds a module to a large weight. One or both ends are propelled by small thrusters until the whole spacecraft rotates at a constant velocity that mimics Earth’s gravity. For a video demo, click the link beneath the photo below. It isn’t frequently considered because it hasn’t appeared in any blockbuster sci-fi movies yet and doesn’t look visually elegant, but the advantage is clear: astronauts would feel gravity in space with minimal costs.

Relatively minor adjustments would need to be made to existing spacecraft (such as the ISS) to begin testing a tethered rotation system for months at a time. A long tether cable would need to be attached to the space station along with a heavy weight at the other end of the cable. Since it’s not cheap to lift heavy cargo into space, entrepreneur Joe Carroll has suggested that the counterweight could be a spent rocket booster. Both the counterweight and the ISS station would need to have thrusters attached to start and stop rotation without impacting the craft’s trajectory.
As people move around the space station, their shifting weight can create small deviations to the system’s center of gravity, and the counterweight needs to be able to correct for that. An automated control system would need to be in place to move the counterweight toward and away from the rotational center in order to counterbalance small fluctuations in the habitat module.
In 1966, NASA attempted a tethered rotation experiment with Gemini XI. The lack of gravity itself initially made it difficult for the astronauts to follow the steps needed to complete the experiment, so they had to make a few attempts. Despite several technical issues, the astronauts Pete Conrad and Dick Gordon ultimately succeeded in creating what was likely the first Terograv in space. In a historic moment, they dropped a camera which was pulled to the floor by a tiny amount of artificial gravity.
In its efforts to effectively send travelers through space, NASA needs a self-sustaining mobile space hub with Earth-like gravity that can serve as a “gas station” along the interplanetary highway. Mars is extremely far away in terms of today’s space-tech, and very few humans have spent extended periods in space. Without Terograv on NASA’s habitable spacecraft, minor surprises could lead to catastrophic mission failure as agencies attempt to send humans to Mars. It’s worth having space stations and spaceships in which astronauts and their food-bearing plants can not only survive, but also thrive.
Once NASA successfully tests the tethered rotation technology on a larger scale near Earth, it can apply it to spacecraft that are expected to transport people on long journeys throughout the cosmos. The lesser-known aerospace design could make a reality out of Elon Musk’s and other space enthusiasts’ dreams.
