[♪ 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.

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