DARPA Wants to Put Satellites Where Other Spacecraft Go to Die
- DARPA funding research into ‘very low’ 200km–400km orbits
- Challenges include atmospheric drag, oxygen exposure damage
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The Pentagon’s research and development agency is exploring the upside of satellites at a range most space companies aim to avoid.
Companies can’t launch the same spacecraft in “very low Earth orbit,” or VLEO, that they do in other orbits, leaving a gap in development about 250 kilometers deep. The Defense Advanced Research Projects Agency’s goal is to spur new ideas and technology from the private sector.
DARPA defines very low Earth orbit as anything below 450 kilometers. The lower limit is around 200 kilometers, according to senior analyst Caleb Henry at space analytics firm Quilty Analytics. He added that there is no clear line where exactly it starts.
In documents for an upcoming contract, DARPA says VLEO’s proximity to Earth offers benefits worth exploring, including better imaging performance and more accurate geospatial positioning systems.
If sensors and cameras perform better at altitudes closer in than “low Earth orbit,” DARPA wants spacecraft that can operate there.
A classified event for prospective vendors on the Daedalus program Nov. 7 will likely provide more insight into the agency’s expectations for its three-phase research and development contract.
Daedalus will include multiple awards under accelerated “other transaction” authority and is expected to run for at least 51 months. OTA procurement allows agencies to fund research and development programs and buy certain goods and services more quickly than would otherwise be possible under standard federal acquisition rules.
DARPA declined to comment beyond what was included in the solicitation.
Space is filling up with government and commercial satellites, particularly at low Earth orbit levels. DARPA touts lower risks of radiation damage and collisions with space debris compared to satellites in LEO. But operating in VLEO comes with its own issues, including increased drag and the effects of atmospheric oxygen.
The VLEO radius is also a graveyard of defunct spacecraft sent by satellite operators to burn up during reentry from space. “You’re essentially hanging out in the area where people send their spacecraft to die,” Henry said.
Henry said VLEO is a “self-cleaning orbit” because of its tendency to burn up hardware. That also makes it the “disposal orbit.” Navigating the debris means operators “have to keep an eye out for derelict spacecraft that others have abandoned or are actively in the process of disposing.”
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The Earth’s atmosphere is also a potentially disastrous impediment to satellite velocity. Overcoming aerodynamic drag to keep spacecraft from slowing down and de-orbiting requires a certain amount of propulsion, which means fuel.
“Whatever fuel they need, they’ll need to carry a lot of it,” senior engineer at RAND Bonnie Triezenberg said.
The costs of storing and then constantly burning fuel will only arise, however, if space firms can figure out how to achieve propulsion in such thin atmosphere, Triezenberg said.
Once that bit of “little innovation” to generate the necessary thrust in VLEO occurs, next come the questions about how to run the satellite and the tools it carries at the same time, she said.
Existing satellites aren’t designed to operate their sensors and equipment while thrusters are firing.
Existing satellites and other spacecraft are also built out of materials that can be damaged by highly reactive atmospheric oxygen, requiring prospective VLEO operators to find new materials and methods to protect their systems.
Anything going into VLEO orbit has to be optimized “not only for the extremes of space, but also for the extremes of earth’s upper atmosphere,” Henry said.
Triezenberg laid out the scientific upsides of solving the problems of lower orbit. They include learning more about the nature of propulsion, understanding how to navigate an orbit previously considered unusable, and leveraging that knowledge for future innovation.
On the practical level, the ability to get sharp images from smaller, cheaper cameras than those required for LEO or geostationary orbit could be appealing to government and commercial satellite operators.
VLEO satellites are so close to Earth, however, their operators face the choice between looking at very specific parts of the planet or fielding multiple satellites to cover more areas.
“If you imagine that the satellite is a flashlight and the Earth is a wall, the closer you hold the flashlight to the wall, the less of that surface you’re going to see,” Henry said. “You have the potential to get really high quality images, but you’re also looking through a soda straw.”
It’s unclear if the cost saving on imaging sensors would be greater than the added costs of developing new satellites and operating them in VLEO.
“There’s a reason its a DARPA program. It’s experimental, but it does look to me like something if you could pull it off it might change a lot of things. It’s enough of a change that it will change how people think of space,” Triezenberg said.
In addition to DARPA’s Daedalus program, the agency also has the Ouija program. Ouija announced an award to Spire Global Inc. on Tuesday for a VLEO satellite to carry high-frequency radio wave sensors.
“It stretches the limits of our capabilities and we’re really looking forward to undertaking this in a way that allows us to go piece by piece, phase by phase,” Chuck Cash, Spire’s vice president of federal sales, said in an interview, adding that propulsion at VLEO is one of the obstacles they are studying.
Cash said the space industry has a history of government-funded innovation unlocking new business lines both on the public and commercial side.
Some companies, including Starlink, have plans to operate satellites between 200 and 400 kilometers. If DARPA’s projects are successful, expect to see more companies pursuing the technology.
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