In late 2021, operators of the European Space Agency’s (ESA) Swarm constellation noticed something troubling: satellites, which measure the magnetic field around Earth, began to sink into the atmosphere at an unusually fast rate — ten times faster than before. The change coincided with the start of the new solar cycle, and experts believe it could be the start of some tough years for spacecraft orbiting our planet.
“In the past five or six years, satellites have sunk two and a half kilometers [1.5 miles] “Every year,” Anya Ström, ESA’s Swarm mission manager, told Space.com. But since December of last year, they’ve been virtually diving. The average drowning between December and April was 20 km [12 miles] every year.”
Satellites orbit near a land You always face the withdrawal of the remainder ambiance, which will gradually slow the spacecraft and eventually make it back to the planet. (Normally it does not survive this so-called return and burns up in the atmosphere.) This atmospheric drag forces the International Space StationControl devices for normal performance “Replay” maneuvers To maintain the station’s orbit 250 miles (400 km) above Earth.
This cloud also helps clean the near-Earth environment of space junk. Scientists know that the intensity of these clouds depends on solar activity – the amount of solar wind throw it the sunwhich varies depending on the file 11 year solar cycle. The last cycle, which officially ended in December 2019, was somewhat dormant, with fewer than average per month. sunspots And long duration at least hardly any activity. But since last fall, star It was waking up, spewing more and more solar winds and generating sunspots, solar flares And the Coronal mass ejection at an increasing rate. The effects were felt by Earth’s upper atmosphere.
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“There’s a lot of complex physics that we still don’t fully understand happening in the upper layers of the atmosphere where they interact with the solar wind,” Strom said. “We know that this interaction causes an uplift in the atmosphere. This means that the denser air travels upwards to higher altitudes.”
Dense air means higher clouds for satellites. Although this density is still incredibly low at 250 miles above Earth, the resulting increase in the water level in the atmosphere is enough to send some low-orbiting satellites down.
“It’s like running with the wind against you,” Strom said. “It’s harder, it’s drag — so it slows down the satellites, and when they slow down, they sink.”
hit by a solar storm
The Swarm constellation, launched in 2013, consists of three satellites, two of which orbit Earth at an altitude of 270 miles (430 km), about 20 miles (30 km) above the International Space Station. The third Swarm satellite orbits the planet somewhat higher – about 320 miles (515 km) above Earth. Strom said the two spacecraft, which were in low orbit, were hit more by the sun’s influence than the higher satellite.
The situation with the bottom two became so precarious that by May, operators had to start raising the altitude of the satellites using onboard thrust to save them.
The European Space Agency’s Swarm satellites aren’t the only spacecraft struggling with deteriorating space weather. in february, SpaceX has lost 40 new Starlink satellites that was injured by a solar storm Immediately after launch.
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In such storms, satellites suddenly descend to lower altitudes. The lower the orbit of the satellites when a solar storm hits, the greater the risk that the spacecraft will not be able to recover, leaving operators helplessly watching as the craft descends into the atmosphere.
star link The satellites have operational orbits of 340 miles (550 km), which is higher than the most vulnerable area. However, after launch, Falcon 9 The rockets deposit satellite thrusts very low, only about 217 miles (350 km) above Earth. SpaceX then raises the satellites’ orbits using onboard thrusters. The company says that this approach has advantages, as any satellite that encounters technical problems after launch will quickly return to Earth and not turn into annoying space debris. However, the increased and unpredictable behavior of the Sun makes those satellites vulnerable to accidents.
New space and unexpected sun
All spacecraft orbiting around 250 miles in altitude will certainly have problems, Strom said. This includes the International Space Station, which will have to perform more frequent re-enhancement maneuvers to stay afloat, but also hundreds of cubes and small satellites that have inhabited low Earth orbit in the past decade. These satellites – the product of a new space movement led by private entrepreneurs for simple and cheap technologies – are particularly at risk.
“Many of these [new satellites] They don’t have payment systems, Strom said. They have no ways to advance. This basically means that they will have a shorter lifespan in orbit. They will re-enter sooner than if they were during the solar minimum.”
By chance (or beginner’s luck), the beginning of the new space revolution came during that quiet solar cycle. These new operators are now facing the solar limit. But not only this. The sun’s activity last year turned out to be much more intense than solar weather forecasters had predicted, with more sunspots, more coronal mass ejections and more solar winds hitting our planet.
“Solar activity is much higher than official expectations,” Hugh Lewis, a professor of engineering and physical sciences at the University of Southampton in the United Kingdom who studies the behavior of satellites in low Earth orbit, told Space.com. “In fact, the current activity is already very close to the peak level that was projected for this solar cycle, and we are still two to three years away from the solar maximum.”
Ström confirmed those observations. “Solar cycle 25 that we’re entering now is increasing very sharply,” she said. “We don’t know if that means it’s going to be a very difficult solar cycle. It could slow down, and it could become a very weak solar cycle. But it’s increasing rapidly at the moment.”
While the harsh solar activity is bad news for satellite operators, who will see the life of their missions shortened (even onboard thruster satellites will run out of fuel faster due to the need for frequent altitude boosts), the situation will be a welcome bit of filtering effects on space. around the earth.
In addition to being populated by hundreds of new satellites over the past decade, this region of space is riddled with chaos. An alarming amount of space debris (Old satellites, spent rocket stages and collision fragments). Researchers such as Lewis have long warned that the ubiquitous garbage rushing around the planet threatens the safety of satellite services, forcing operators to perform frequent avoidance maneuvers. Furthermore, debris may lead to an out-of-control condition known as Kessler syndromea series of unstoppable collisions as depicted in the 2013 Academy Award winning movie “Gravity.”
“Overall, the increase in solar activity – and its effect on the upper atmosphere – is good news from a space debris perspective, because it reduces the orbital life of debris and provides a ‘helpful clean-up service,'” Lewis said.
According to Jonathan McDowell, a space debris expert at the Harvard-Smithsonian Center for Astrophysics, the positive effect can already be observed, as the fragments produced by November 2021 Test of a Russian anti-satellite missile It is now dropping much faster than before.
However, there is a downside to this cleansing process.
“It can be seen to increase the rate of decomposition of debris bodies almost like rain,” Lewis said. “When solar activity is high, the rate of ‘rain’ is higher, and missions at lower altitudes are likely to see larger debris flows.”
A larger flow of debris means more frequent maneuvers are needed to avoid burning fuel and temporarily increase the risk of collisions, which can generate more dangerous shrapnel.
Strom and her colleagues are currently raising the orbits of two low-orbit Swarm satellites by 28 miles (45 km). She added that the satellites may require further modifications later this year. The goal is to help the mission, which is currently in its ninth year and beyond its originally planned lifespan, to traverse the solar cycle. The team’s success largely depends on the behavior of the Sun.
“We still have the fuel to hope to get through another solar cycle,” Strom said. “If I slept like now, I’d run out of fuel before the solar cycle ends. If I slowed down a bit, I might save it through the solar cycle.”
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