When it was originally launched in 1995, the joint NASA and ESA Solar and Heliospheric Observatory was supposed to have an operating phase of two years, but the system is still going strong 25 years later. The intent of the platform was to provide detailed insight into the energy and material flows from the Sun toward Earth. Though initially intended as a tool to better understand the physics of how a star worked, it has evolved into a vital tool providing real-time data on the sun’s activity, helping to inform space weather forecasts.
“At the time SOHO was designed, very few people talked or thought about space weather,” noted SOHO project scientist Bernhard Fleck at ESA. “But now, I look at SOHO observations like weather radar. Now it is as normal as opening your weather app and checking when the rain is coming.”
SOHO’s abilities are enabled by its coronagraphs, specialized telescopes that block the bright face of the sun to allow for better visibility of the faint light extending from the star. A Large Angle and Spectrometric Coronagraph, known as LASCO, provides a 360°-view of the atmosphere around the sun. This device has been used to image coronal mass ejections (CMEs), giving researchers previously unobtainable levels of detail, and thus allowing assessment of their likely impact on orbiting spacecraft and, in extreme circumstances, ground-based power systems.
“Having a coronagraph observing all around the sun helped us to see CMEs coming toward us,” said Terry Kucera, astrophysicist in NASA’s Goddard Space Flight Center’s Solar Physics Laboratory in Greenbelt, Maryland. “That’s been really critical in understanding space weather and allowing scientists to study how CMEs affect us here on Earth.”
Though SOHO’s technology is now old – its imaging camera is a mere one-megapixel, cutting-edge in 1995 – this does not affect the quality of the data it generates. Over the years, the craft has experienced some near-loss events, including the failure of its gyro-stabilization system in 1998, but even this was overcome by some innovative thinking from the project’s software engineers, who developed a system to keep SOHO stabilized without gyros.
The platform is still going strong to this day. “One thing about SOHO that should be emphasized: it is extremely ambitious,” said US project scientist Jack Ireland at NASA’s Goddard Space Flight in Greenbelt, Maryland. “You have 12 instruments on a platform which is a million miles away – 25 years should just be the start. From a scientific point of view, we need to keep going, we can’t take our eyes off the sun.”