Low Earth orbit is reaching capacity as tech companies such as SpaceX, OneWeb and Amazon race to industrialize space with satellites, and in response, physicists are attempting to lay out safe and affordable options for expanding the market into medium Earth orbit, a much riskier arena.
While recognizing that tapping into medium Earth orbit is ultimately safer than continuing to pack its lower counterpart with even more spacecraft, the authors of a new study say the new endeavor will be associated with its own expenses and potential dangers. The analysis, published May 3 in Acta Astronautica, proposes a twofold solution: a lower-cost launch plan involving a stop in low Earth orbit, and added protections to prolong the life of spacecraft.
Medium Earth orbit is largely unused because of the Van Allen radiation belts. These belts entrap harmful energetic particles flung from the sun, endangering spacecraft in the vicinity. The clustered particles are what cause the northern lights.
"We can't just send satellites there," study author Thorben Löffler, a Ph.D. candidate at the Institute of Space Systems at the University of Stuttgart, told The Academic Times. "This will be a long journey."
There are around 3,000 functional satellites operating in orbit, he says. Nine in 10 are either in low Earth orbit, below 2,000 kilometers (1,243 miles) from Earth, or very high geostationary orbit, above 35,000 kilometers (21,748 miles) from Earth. Only about one in 10 resides between the two, in an area called medium Earth orbit.
Even that 10% of spacecraft are in specific regions that scientists have deemed safe, called slots. This includes navigation satellites from companies such as BeiDou in China and Russia's Global Navigation Satellite System, or GLONASS. When SpaceX, OneWeb and Amazon, for instance, send satellites to space, they typically target low Earth orbit because it is known to be safe from the radiation belts.
"The first step when we look at human spaceflight is to develop technology which can protect us in the space environment and which is also protecting itself," Löffler said. "You don't want your onboard computer to degrade in the space environment."
In lieu of a direct flight, the team's primary suggestion is to first send spacecraft into low Earth orbit, then use a built-in propulsion system, or thruster, to push it up to medium Earth orbit. To build such a mechanism, the researchers say normal materials from well-established electronic manufacturers can be used, rather than expensive space-grade types.
"Currently, flying to low Earth orbit is much cheaper than flying to medium Earth orbit — it's a cost factor of at least five times," Löffler said. "It depends on where you get the thruster and what kind of thruster it is … but it will be still cheaper."
That high cost mainly stems from demand. Because there is no competition for a method of launching directly into medium Earth orbit, demand for getting there is high but supply of means for doing so is low. The authors' proposal would be similar to taking a flight from the United States to India, for example, but with a layover as opposed to a more pricey one-way trip.
As low Earth orbit is readily accessed and has lots of supply, it's cheaper. For instance, Elon Musk is already authorized to send 12,000 satellites into orbit for his upcoming broadband internet, Starlink, and has requested permission for another 30,000. Amazon has received approval to send 3,236 satellites into the low orbit.
Lowering travel costs would help with the researchers' second suggestion: Companies should place as many bulk safety materials as possible on each spacecraft, forming a sort of fail-safe system. This is necessary, Löffler says, because prior to launching satellites, companies tend to send demonstration prototypes that are almost certain to break — their carcasses eventually polluting space. That may be avoided by adding many levels of protection on the spacecraft, such as an extra shield on the outside, to reduce the chances that it quickly malfunctions.
"The strategy is to use a vast variety of different techniques to lower your risk of losing your satellite," he said. "It's risk management."
Risk management is vital because a sizable part of the interest in medium Earth orbit stems from space junk — essentially trash orbiting the Earth — taking over low Earth orbit. According to the European Space Agency, there are about 28,160 pieces of regularly tracked debris in orbit.
"We wanted to develop a method for how you can put satellites there without the risk of them ending up as space debris," Löffler said, "You make a strategic mission design that no matter what goes wrong in your technology demonstration … you don't fill up the environment with trash."
If a company decides, for instance, to launch 100 demonstration satellites into medium Earth orbit and the technology fails, 100 satellites will have become trash, perpetuating the issue that spurred the need to expand Earth's orbital real estate in the first place.
"It's not like you're on Earth; that you can test it in a laboratory and if something goes wrong, it's not so bad," Löffler said. "You have this responsibility — for all the other researchers who also want to put their work into space — that you don't leave anything behind."
Space debris can include items such as shards of glass from broken rockets, complete satellites that don't work anymore and pieces of metal from equipment launched into orbit.
"The biggest risk are non-operational satellites just floating around," Löffler said. "They are just, like, bullets in space."
The high-profile debacle surrounding a piece of China's largest rocket falling uncontrolled from the sky is a testament to the problem of space junk. This debris landed May 8, just west of the Maldives, after most of it burned up while reentering the atmosphere — a great relief to experts who had been speculating about how much harm it might cause on Earth.
So, Löffler says, it is crucial to ensure that companies looking to the sky do not add to the chaos of space debris. The team has employed its own initiative that plans to send a satellite, referred to as ROMEO, into space, and use data from the space-borne system to study how the proposed strategies will play out. The launch is scheduled for 2024.
The study, "Orbit-raising strategies for cost-efficient access to lower Medium Earth Orbit without risking space debris," published May 3 in Acta Astronautica, was authored by Thorben Löffler, Jonas Burgdorf and Sabine Klinkner, University of Stuttgart.
Correction: A previous version of this story misstated the proximity of the upper boundary of low Earth orbit. The error has been corrected.