Satellites in low Earth orbit (LEO) can deviate hundreds of kilometers from their expected trajectory when bad space weather hits. The problem affects the International Space Station, China’s Tiangong Space Station and many Earth observation satellites that need to get up close to our planet.
Experts say this positioning uncertainty increases the risk of dangerous runway collisions, which threaten to worsen the situation problem of space debris and make the space around Earth unsafe.
“At an altitude of 500 kilometers [310 miles]we can determine the position of our satellites with an accuracy of 2 centimeters [0.8 inches]Alex Saltman, CEO of California-based satellite company GeoOptics, which makes meteorological measurements of Earth’s upper atmosphere, told Space.com. “But at lower altitudes it becomes a big problem.”
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The lower the trajectory, the greater the inaccuracy. That’s because space weather affects the density of Earth’s upper atmosphere. Because atmospheric density naturally decreases with altitude, the variations caused by space weather are greater closer to Earth Soil. The higher the density, the more resistance satellites face, causing them to slow down and sink to Earth. At the lowest altitude, satellites can deviate hundreds of kilometers from their predicted path if they are too much solar wind sun’s rays, David Vallado, a senior research astrodynamist at the Commercial Space Operations Center (COMSPOC), told Space.com.
Altitudes of about 400 km and lower are most affected. It is precisely in these orbital regions that some of the most valuable spacecraft fly. The International Space Station circles 400 kilometers above the Earth, and Tiangong is only slightly higher, at 260 miles (425 km). Researchers are increasingly monitoring these very low Earth orbits because they provide a detailed view of Earth, and there are plans for new missions into this space.
“The lower you go in the atmosphere, the better you can make certain types of measurements,” says Saltman. “For example, radar measurements get much, much better the lower you can go.”
When satellites run out of fuel to help them maintain their altitude, they begin to enter a downward spiral. Along the way, they pass through this area of greater uncertainty, which poses a threat to operational spacecraft. Trajectories of satellites and pieces of space debris are determined many days in advance using measurements by ground radars and optical sensors. But a strong burst of solar wind from the Sun could completely throw these predictions into disarray. This creates challenges for spacecraft operators, as they struggle to determine how close their spacecraft can get to other objects.
“It’s the ultimate answer, because the operator has to decide whether to perform a collision avoidance maneuver or not,” Dan Oltrogge, chief scientist at COMSPOC, told Space.com. “If they decide to maneuver and space again changes, which change the drag profiles and where and how close things come together. It can nullify the maneuver and even increase the risk.”
Satellite operators plan collision avoidance maneuvers several days and many jobs in advance. But space weather forecasters have a very limited understanding of what the sun will do the following. Coronal mass ejections (CME) – huge bursts of superheated plasma from the Sun’s upper atmosphere – explode from sunspots without warning and take two to three days to reach Earth. Furthermore, scientists generally cannot measure the strength of a CME until about 30 minutes before it hits the planet, when it passes the Solar and Heliospheric Observatory (SOHO), a spacecraft operated jointly by the European Space Agency and NASA, so’ n 1.5 million kilometers away. of earth.
“If you get an hour’s notice, that’s probably not enough to get the command and control to get the maneuver planned,” Vallado said.
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And it’s not just the sun’s daily behavior that is not well understood, Vallado added. The number of sunspots, solar flares and CMEs emanating from the star vary on longer timescales following a roughly eleven-year cycle that oscillates from a minimum through a maximum to the next minimum. The problem is that each solar cycle has a different strength, and therefore spacecraft operators cannot plan ahead because they cannot predict how bad space weather will be during their next mission. A more active cycle means spacecraft face more drag, and as a result, run out of fuel more quickly and de-orbit sooner. The differences can be significant.
“In general, we plan for a five-year lifespan for the satellites,” Saltman said. “But it does vary. It’s unlikely to last less than three years, but with the variations [in solar activity] it could take 10 or 12 years.”
Saltman added that GeoOptics has lost one operational satellite due to space weather. Drag was not the culprit in that case; increased radiation levels caused by the solar wind damaged the satellite’s electronics.
“It’s hard to know if the sunspot cycle was responsible, but we’ve never seen problems like this before,” Saltman said.
Scientists expect that the current solar cycle, the 25th since measurements 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 now busier than ever, and dozens of new space companies that have joined the fray since the last time space weather was truly brutal will have to live with it. Space weather scientists and satellite orbit forecasting experts are working hard to help them. But things could get a little tricky in the coming years.