by Satellites in low Earth orbit (LEO) can venture hundreds of miles off their intended trajectory when severe space weather hits. The problem affects the International Space Station, China’s Tiangong space station and many Earth-observing satellites that need a close-up view of our planet.
Experts say this positional uncertainty increases the risk of dangerous orbital collisions, which could worsen space debris problem and making the space around the Earth unsafe.
“500 kilometers high [310 miles]we can stand our satellites with an accuracy of 2 centimeters [0.8 inches]” Alex Saltman, CEO of the California-based satellite company GeoOptics, which makes meteorological measurements of the Earth’s upper atmosphere, told Space.com. “But at lower altitudes, it becomes a big problem.”
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The lower the orbit, the greater the inaccuracy. That’s because space weather affects the density of Earth’s upper atmosphere. As atmospheric density naturally decreases with height, the variations due to space weather are closer to World. The higher the density, the more it drags satellites, slowing them down and causing them to fall towards Earth. At the lowest altitudes, satellites can be hundreds of miles off their predicted paths when too many solar wind blows from the sun, David Vallado, senior research astrodynamycist at the Commercial Space Operations Center (COMSPOC), told Space.com.
Altitudes around 250 miles (400 km) and lower are the worst. It is precisely in these orbital regions that some of the most valuable spacecraft fly. The IS International Space Station circles 250 miles above the Earth, and Tiangong live only a little higher, at 260 miles (425 km). Researchers are looking more and more at these very low Earth orbits because they provide a detailed view of Earth, and plans are underway for new missions to operate in this space.
“The lower you go into the atmosphere, the better you can make certain types of measurements,” Saltman said. “For example, radar measurements get much, much better the lower you can get.”
When satellites run out of the fuel that helps them maintain their altitude, they begin to spiral down. On their way, they pass through this region of heightened uncertainty, threatening operational spacecraft. The trajectories of satellites and pieces of space debris are determined many days in advance, using measurements by ground-based radars and optical sensors. But a strong burst of solar wind from the sun can completely throw off these predictions. This creates challenges for spacecraft operators as they struggle to determine how close their spacecraft might come to other objects.
“It’s a final thing to answer, because the operator has to decide if they’re going to do a collision avoidance maneuver,” Dan Oltrogge, chief scientist at COMSPOC told Space.com. “If they decide to maneuver and space weather changes, which change the drag profiles and where and how close things come together. It can negate the maneuver and actually increase the risk.”
Satellite operators plan maneuvers to avoid collisions several days and many orbits beforehand. But space weather forecasters have a very limited understanding of what it is the sun the next will do. Coronary mass ejections (CME) – a huge burst of superheated plasma from the sun’s upper atmosphere – bursts from sunspots without warning and takes two to three days to reach Earth. In addition, scientists can generally measure the strength of a CME only about 30 minutes before it hits the planet, when it passes the Solar and Heliospheric Observatory (SOHO), a spacecraft operated by the European Space Agency and NASA around 900,000 miles (1.5 million kilometers) together. from the Earth.
“If you have a warning that’s out an hour in advance, that’s probably not enough to get the command and control to plan the maneuver,” Vallado said.
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And it’s not just the sun’s day-to-day behavior that is poorly understood, Vallado added. Number of sunspots, solar flares and CMEs originating from the star vary on longer time scales following a cycle of about 11 years that changes from minimum to next minimum. The problem is that each solar cycle has a different strength, so spacecraft operators can’t plan ahead, because they can’t predict how bad the space weather will be during their next mission. A more active cycle means spacecraft will experience more drag, resulting in them running out of fuel faster and disintegrating sooner. The differences could be significant.
“In general, we plan a five-year life cycle for the satellites,” said Saltman. “But it changes. It’s unlikely to be less than three years, but with the variations [in solar activity] it could be up to 10 or 12 years.”
Saltman added that GeoOptics has lost one operational satellite due to space weather. Drag wasn’t the culprit in that case; increased radiation levels from the solar wind damaged the satellite’s electronics.
“It’s hard to know if the sunspot cycle was responsible, but we haven’t seen any problems like this before,” Saltman said.
Scientists hope that the present solar cycle, the 25th year since records began, will reach its maximum at the end of this year. Since the last maximum in 2014, the number of satellites in orbit has increased sevenfold. Space around Earth is busier than ever, and the dozens of new space companies that have joined the fray since the last time space weather was really vicious are going to have to learn to live with it. Space weather scientists and experts in satellite trajectory prediction are working hard to help. But things may get a little difficult in the next few years.
