Although 60% of Earth’s nearly 6,000 satellites are non-operational and needlessly occupying the planet's orbit, attempts to remove this "space junk" are sparse. But a Russian physicist has been fine-tuning a method to eliminate defunct satellites — using space-borne lasers to melt them into plasma — to ensure it won't inadvertently create even more debris.
Egor Loktionov is the laboratory head of Bauman Moscow State Technical University and lead author of a new study about this work that is forthcoming in the April issue of Acta Astronautica. He explained to The Academic Times that his team members have been testing a variety of spacecraft materials that they believe could become satellite laser targets to see how the materials react when exposed to laser pulse emissions, also called irradiation. They found that solar cells could pose a hazard, but propose that using lasers in space rather than on land could address this potential concern.
Loktionov has thoroughly researched the use of laser pulses to melt space junk, also called space debris, into plasma. The researcher believes this technique, referred to as laser ablation, is the ideal way to reduce the number of useless objects in our orbit, such as defunct satellites.
“Many ways to capture debris have been suggested to date, few are tested and none really practiced,” Loktionov said. “Laser space debris removal, to my mind, should provide a cheaper, more reliable and flexible way to do the job.”
Laser ablation isn't a new concept; it's often used to address medical concerns such as small tumor removal. In research published in 2019, Loktionov took this concept a step further by proposing its use on a grander scale, as a cost-effective and environmentally friendly remedy to the issue of space debris, because the lasers are reusable.
In 2020 alone, Elon Musk’s SpaceX deployed more than 800 satellites to support his broadband internet system endeavor, Starlink. As technology progresses, so will the need for satellites. And as satellites are released, Loktionov warns that space debris removal will become a necessity rather than an option.
Loktionov's stance on targeted laser ablation for the destruction of defunct satellites has been widely researched. For instance, Chinese physicists created numerical simulations in 2018 to study the effectiveness of a space-based laser. The idea is also entertained by some space organizations, including Russian agency Roscosmos, as a practical mechanism to solve the ongoing issue of space debris accumulation.
Even though Loktionov's team plans to test additional materials, as the first to gauge the impact of irradiation on solar cells, the researchers found that their results required immediate publication — especially for space agencies that may be inclined to move forward with the proposed mechanism.
“If solar array grinding is not considered, one big detectable and manageable piece can be turned into a cloud of small pieces almost impossible to clean out,” Loktionov stressed.
Solar cells are present on satellites as their characteristic solar arrays, and the paper heavily emphasizes that these arrays should be avoided when positioning lasers. However, the authors maintain that as long as pulses are emitted away from the panels, laser ablation remains tenable as a method of obliterating defunct satellites.
Loktionov recommends that agencies use a space-borne laser to ensure that solar arrays are not hit by pulses. Such a laser would increase point accuracy by circumventing atmospheric interference that would otherwise distort the laser beams and therefore lower pulse precision, he says.
“Ground-based [lasers] might appear easier, but those cannot provide a small spot due to distance and passing through the atmosphere. This means solar arrays would almost inevitably be irradiated," Loktionov said. “We suggest considering more precise impact with space-borne lasers or our recycling concept."
That concept calls back to Loktionov's 2019 research, in which he argued that space debris, melted into plasma, could potentially be recycled as fuel for spacecraft powered by laser thrusters. That's because the thrusters would be able to accept a variety of fuels, including the plasma byproduct of laser ablation, providing a cost-effective way to rewrite the problem of space debris as a useful tool.
This technology could also reduce risks to humans and obstacles to other important spacecraft, Loktionov pointed out.
Releasing a single satellite into space requires millions of dollars purely for the send-off, and depending on the weight of the vehicle, costs can reach an astounding $400 million. But despite the generous sum dedicated to the beginning of a satellite’s tenure, space agencies place little emphasis on managing the end, when the spacecraft become dysfunctional and are deemed space junk. Often, the craft are left in orbit until they explode, which creates other pieces of debris that can threaten orbiting spacecraft that are still in use.
If taken care of, the debris is either moved to an empty orbit called a graveyard orbit or burnt upon re-entry into the atmosphere. The latter can endanger humans if shards of the burnt spacecraft fall to Earth.
The paper, “Unintended consequences with laser nudging or re-entry of satellites,” will be published in the April 2021 issue of Acta Astronautica. It was authored by Egor Loktionov and Elizaveta Sharaborova, Bauman Moscow State Technical University; and Claude Phipps, Photonic Associates LLC. The lead author was Egor Loktionov.