[♪ INTRO] Even when there isn’t a cloud
in the sky, I’ll sometimes check the weather forecast, because I don’t want to get soaked
if I leave home without an umbrella. But when it comes to launching satellites, keeping them safe
from space weather is a bit more complicated. SpaceX engineers learned that the hard way in
2022. They were all prepped to shoot another round of Starlink satellites into orbit. They’d checked
the space weather forecast, and had run their own models and made sure everything would be a-ok. But
out of the 49 satellites that launched, 38 fell out of the sky! That’s a little worse than having
to walk around in wet clothes. And if scientists and engineers hope to avoid a similar incident in
the future, we’re going to have to learn a lot more about how space weather works. In the area
surrounding Earth, space weather is driven mostly by the Sun’s activity, how often and
intensely it’s burping stuff like matter and light into space. And the way that Starlink satellites
operate makes them particularly vulnerable to bad space weather. Like many modern satellites,
the Starlink constellation resides in low Earth orbit. This region ranges from 160 to one or two
thousand kilometers above Earth’s surface, depending on who you ask. SpaceX targets the
lowest part of low Earth orbit, launching each Starlink satellite into an initial orbit of 210
kilometers. They do this so that if a satellite malfunctions, it’ll quickly fall and burn up in
the atmosphere. And preventing ‘dead’ satellites from floating around like zombies is incredibly
important. A broken satellite careening around up there could hit other satellites
or a spacecraft carrying astronauts. Once a Starlink satellite is functioning correctly,
it can use its little booster rockets to push itself into a more permanent orbit at
500 kilometers. But it’s the same phenomenon that helps prevent Starlink zombies that caused those
38 to tumble out of the sky: the drag that comes from flying through the few, but still present,
molecules of Earth’s atmosphere. In fact, the drag was 50% higher than normal, at least compared to
previous launches, and much higher than SpaceX engineers were expecting from the forecast. You
can think of this extra drag like trying to pedal your bicycle into the wind. That extra push in the
opposite direction makes it harder for you to go in the direction you want. So most of the Starlink
satellites weren’t able to boost themselves into their higher, more stable orbit. Instead,
they fell back to Earth and burned up in the atmosphere. A few days later, SpaceX engineers
figured out that the extra drag was caused by a storm in space that they’d underestimated. Before
the Starlink launch, the Sun had ejected a large amount of plasma in an event called a coronal mass
ejection. This plasma traveled through space, and reached Earth on launch day. The plasma’s magnetic
field interacted with the Earth’s magnetic field, and transferred some extra energy to the
atmosphere. This energy inflated the atmosphere, sending more molecules to higher altitudes, making
the air around any given satellite more dense, and more difficult to move through. By the time
engineers figured out how bad the storm’s effects were, it was too late. Most of the satellites were
kaput. So why was the weather forecast, or the models that the Starlink team ran based on that
forecast, so wrong? A group of scientists at the Space Weather Prediction Center monitors
the weather in space, and issues warnings if that weather will impact a launch. They’re based at the
National Oceanic and Atmospheric Administration, or NOAA for short, which is the same group that
gives us Earth-based weather reports. While they knew this space storm was coming, they
didn’t think it would cause damage. In fact, they classified it as ‘minor’. But they didn’t report
any effects the storm would have on atmospheric drag, so the Starlink team had to run the numbers
themselves. And they miscalculated. So that was the drama happening in very low Earth orbit. But
what about everywhere else? Putting satellites at such low altitudes just wasn’t a popular thing to
do until Starlink came along in 2019. Beyond low Earth orbit, the other common spots to
plop a satellite include geosynchronous orbit at 35,000 km, and medium Earth orbit, a zone between
low Earth orbit and geosynchronous orbit. And for satellites up there, it was the minor storm
that NOAA accurately predicted. At these higher altitudes, sudden increases in drag aren’t much
of a threat. There just isn’t a large enough change in the number of air molecules to make
much of a difference. But space weather can still cause two main types of damage up there. First,
it can increase the abundance of high energy electrons. Those electrons can then cause an
electric charge to build up on a satellite’s surface or inside its circuitry. Worst case
scenario, that charge creates an electrical short that damages the circuits or the solar
panels responsible for powering the satellite. And second, a satellite can be struck by a single
charged particle that damages its circuitry. But it isn’t clear how often high altitude satellites
experience space-weather-related damage. It’s not in companies’ best interests to report their
satellites’ failures, and they might not even know if a failure was caused by space weather.
So science doesn’t have much data to go on. But one thing we do know is that all satellite
operators are in for a rocky few years. Right now, we’re in a new-ish solar cycle called Solar Cycle
25. Solar cycles measure the Sun’s activity, which moves from calm to stormy and back again.
A new one starts every eleven years. Solar Cycle 25 started in 2019, and it’s building
toward maximum activity in 2025. It’s already been a more active solar cycle than predicted,
so even more plasma eruptions, like the one that caused the Starlink satellites to fall out of
orbit are probably on the way. It’s important to better understand how space weather impacts
satellites in all orbits. But it’s extra important for satellites in low and very low Earth orbits.
Those satellites can be cheaper to launch and can offer more detailed images and higher connection
speeds. So companies and governments are planning to launch many more low Earth orbit constellations
in the coming years, some with thousands of individual satellites. But things are looking
up. Shortly after the incident, SpaceX modified their launch program. They sent the next batch of
Starlinks to a slightly higher initial altitude of 300 kilometers to give the satellites more time,
and less drag, to boost themselves into their final orbit. And so far, this approach has
worked. Researchers are also working on improving their space weather forecasts. Starlink is sharing
information with NOAA so they have more data to refine their prediction models. And NASA is
planning to launch a constellation of satellites dedicated to studying how different types of space
weather change the environment where low Earth orbit satellites operate. Hopefully, all these
efforts will help everything engineers launch into space get where they’re supposed to go, and stay
where they’re supposed to stay. Because the last thing I want to hear in my weather forecast before
I step out the door is a chance of satellite rain! Thanks for watching this episode of SciShow. And
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[♪ OUTRO]