Satellites in low Earth orbit (LEO) can drift hundreds of kilometers out of their expected orbits when hit by bad space weather. The problem affects the International Space Station, China’s Tiangong space station, and many Earth observation satellites that require close monitoring of our planet.
This positioning uncertainty increases the risk of dangerous orbital collisions, which threatens to make the situation worse, experts say. space debris problem and we make the space around the Earth unsafe.
“At an altitude of 500 kilometers [310 miles]We can determine our location. satellites with an accuracy of 2 centimeters [0.8 inches]”But at lower altitudes, this becomes a big problem,” Alex Saltman, CEO of GeoOptics, a California-based satellite company that makes meteorological measurements of the Earth’s upper atmosphere, told Space.com.
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The lower the orbit, the greater the inaccuracy. This is because space weather affects the density of Earth’s upper atmosphere. Since atmospheric density naturally decreases with altitude, the changes caused by space weather are greater. Soil. The higher the density, the more friction the satellites face, slowing them down and causing them to sink towards Earth. At the lowest altitudes, satellites can be hundreds of miles off their predicted paths when they move too much. solar wind David Vallado, senior research astrodynamicist at the Commercial Space Operations Center (COMSPOC), told Space.com that there are pulses from the sun.
Altitudes around 250 miles (400 km) and lower are hardest hit. Some of the most valuable spacecraft fly in these very orbital regions. international space station It circles 250 miles above the Earth and Tiangong It lies only slightly higher at 260 miles (425 km). Researchers are increasingly studying these very low Earth orbits because they provide a detailed view of the Earth, and plans are being made for new missions in this area.
“The further you get below the atmosphere, the better you can get at certain types of measurements,” Saltman said. “For example, the lower the radar readings, the better.”
When satellites run out of fuel that helps them maintain altitude, they begin to spiral downward. On their way, they pass through this region of higher uncertainty and pose a threat to operational spacecraft. The orbits of satellites and pieces of space debris are determined days in advance using measurements made by ground-based radars and optical sensors. However, a strong burst of solar wind from the sun could completely disprove these predictions. This creates challenges for spacecraft operators, who have difficulty determining how close spacecraft can get to other objects.
“This is the most important thing to answer, because the operator has to decide whether to perform an anti-collision maneuver or not,” Dan Oltrogge, COMSPOC’s chief scientist, told Space.com. “If they decide to maneuver and space weather Changes that change drag profiles and where and how close objects move. “It can invalidate the maneuver and actually increase the risk.”
Satellite operators’ plan collision avoidance maneuvers several days and many orbits in advance. But space weather forecasters have a very limited understanding of what happens. Sun We will do it later. Coronal mass removals (CME) sunspots, large explosions of superheated plasma from the Sun’s upper atmosphere, explode without warning and take two or three days to reach Earth. What’s more, scientists typically detect the strength of a CME about 30 minutes before it hits the planet, when it passes the Solar and Heliospheric Observatory (SOHO), a spacecraft jointly operated by the European Space Agency and NASA, at a distance of about 900,000 miles (1.5 million kilometers). Then they can measure it. from the world.
“If you get a warning an hour in advance, that’s probably not enough to provide the command and control to plan the maneuver,” Vallado said.
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Vallado added that it’s not just the sun’s daily behavior that’s not well understood. The number of sunspots, sunlight and star-derived CMEs vary on longer time scales, following a roughly 11-year cycle that oscillates from minimum to maximum to the next minimum. The problem is that each solar cycle has a different strength, and so spacecraft operators cannot plan ahead because they cannot predict how bad the space weather will be during their next mission. A more active cycle means the spacecraft will face more drag and, as a result, will run out of fuel faster and exit orbit sooner. The differences can be significant.
“In general, we plan to have a five-year lifespan for the satellites,” Saltman said. “But it varies. It’s unlikely to be less than three years, but with changes [in solar activity] “It could be up to 10 or 12 years.”
Saltman added that GeoOptics lost an operational satellite due to space weather. In this case, Drag was not the culprit; Increased radiation levels caused by the solar wind damaged the satellite’s electronics.
“It’s hard to know if the sunspot cycle is responsible, but we haven’t seen a problem like this before,” Saltman said.
Scientists expect the current situation to continue solar cycleIt will reach its maximum at the end of this year, the 25th since records began. The number of satellites in orbit has increased sevenfold since the last maximum in 2014. Space around Earth is now denser than ever before, and the dozens of new space companies that have joined the fray since the last time space weather was truly bad will have to learn to live with it. Space weather scientists and experts in satellite orbit forecasting are working hard to help. But things may get a little complicated in the next few years.