On Sept. 23, a spacecraft will launch with a clear mission — to keep a constant watch on the sun to help protect Earth from space weather. The satellite, Space Weather Follow-On L1 (SWFO-L1), is launching just in time, as scientists warn our aging fleet of solar sentinels is reaching the end of its life.
“It’s extremely urgent. These satellites, ACE, SOHO, DSCOVR, are all working beyond their design life,” Richard Ullman, deputy director, NOAA Office of Space Weather Observations, said during a media press briefing on Aug. 21. “The need is urgent, and we must replace this capability now.”
For decades, Earth has relied on a handful of satellites parked a million miles away, including NASA’s Advanced Composition Explorer (ACE), launched in 1997, and NOAA’s Deep Space Climate Observatory (DSCOVR), launched in 2015, to provide the first warning when potentially disruptive space weather is headed our way. But many of those spacecraft are operating well past their prime.
Why watching the sun matters
Solar storms do more than spark stunning auroras. When the sun launches eruptions of charged particles, they race across space and slam into Earth’s magnetic field. These events, known as coronal mass ejections (CMEs), can disturb GPS signals, threaten astronauts, damage satellites and in extreme cases, even knock out power grids on the ground.
The only reason operators have time to prepare is thanks to spacecraft stationed at a sweet spot called Lagrange Point 1, or L1. From that lookout point, about 1 million miles (1.6 million kilometers) between Earth and the sun, satellites get a front-row seat to the complex space weather environment, including the solar wind. By measuring the solar wind speed, density and magnetic orientation, these satellites can give Earth anywhere from 15 minutes to an hour of warning before the storm arrives.
“These warnings are the first line of defense against the potentially devastating effects of space weather,” Irene Parker, performing the duties of the assistant administrator, NOAA Satellites, said during the media briefing.
A fleet in crisis
Until now, the job of keeping a watchful eye on the sun has mostly fallen to a handful of older missions. NASA’s ACE spacecraft has been working for nearly three decades, far beyond its intended five-year lifespan. The joint NASA-NOAA DSCOVR mission, launched in 2015 and intended to take over from ACE, has struggled with reliability. As of July 2025, it is offline following a software anomaly. There is currently “no timeline for restoration of data flow,” NOAA told Space.com in an email. For now, NOAA’s Space Weather Prediction Center (SWPC) is again relying on NASA’s ACE spacecraft as its primary source of solar wind data, alongside imagery from ESA/NASA’s Solar and Heliospheric Observatory (SOHO) and NOAA’s GOES-19 satellite, which carries the agency’s first operational compact coronagraph, according to NOAA.
“DSCOVR’s been, sadly, a bit of a disappointment,” Space weather physicist Tamitha Skov told Space.com in an interview. “We were supposed to be able to retire ACE.”
Even SOHO, launched in 1995 as a research mission, is still providing useful solar imagery and data long after its intended retirement in 1998.
The current reliance on a nearly 30-year-old spacecraft highlights just how fragile our space weather monitoring network has become. If any of these missions were to fail without replacement, the consequences could be severe.
“We’re hanging on by a thread, literally, both funding-wise and getting new observations out there,” Skov told Space.com. “We are all used to single-point failures. And so does it frustrate or scare us? Not anymore, it just is the state of things.”
Enter SWFO-L1
NOAA’s new mission is designed to shore up this fragile system, ensuring that if ACE finally fails or DSCOVR cannot be recovered, real-time solar wind monitoring will continue uninterrupted. Once it arrives at L1, SWFO-L1 will measure the solar wind, magnetic fields, and high-energy particles streaming from the sun. These measurements will flow in real time to NOAA’s Space Weather Prediction Center in Boulder, Colorado, where forecasters issue alerts and warnings to everyone from airlines to power grid operators.
“It can’t stop an incoming threat, but it can give us time to prepare,” Parker said. “SWFO-L1 will give our forecasters at NOAA Space Weather Prediction Center the advanced tools they need to protect our country’s critical systems.”
What makes SWFO-L1 different is its focus. While spacecraft like NASA’s Parker Solar Probe or ESA’s Solar Orbiter are revolutionizing our understanding of solar physics, SWFO is dedicated to operations. It is not about scientific discovery as much as it is about reliability: making sure there is always an eye on the sun, feeding data into space weather models.
“We at the Space Weather Prediction Center are extremely eager for SWFO-L1 spacecraft to not only launch but get in position and start receiving solar wind observations into our operations,” said Shawn Dahl, forecaster, Space Weather Prediction Center, NOAA’s National Weather Service. “This is a giant leap forward to our forecast of decision support services that we provide right here at the Space Weather Prediction Center.”
For the scientists who have been pushing for new investments in space weather monitoring, Sept. 23 marks the start of a new chapter.
“This launch is not just about a new satellite, it’s about building a more resilient future, ensuring that technologies we depend on are protected from the sun’s most extreme events,” Parker said.
And for the rest of us, whether we rely on GPS navigation, satellites for communication, or just want to enjoy the auroras, it means the sun will stay firmly in sight.
