For Jeff Privette, a scientist at the National Oceanic and Atmospheric Administration's National Climatic Data Center, 2011 was not a great year.
Privette keeps track of climate sensors on satellites as part of his job, and one of the climate sensor programs he follows was having issues.
This sensor, currently mounted on a satellite mission known as SORCE, tracks how much energy from the sun hits the top of Earth's atmosphere, a measure known as total solar irradiance. Climate scientists need to monitor total solar irradiance because changes in that energy quantity could affect the Earth's climate.
"The sun is a major energy input to the Earth system," Privette said. "If we don't measure the sun ... there is no chance of understanding climate change and variability."
SORCE launched in 2003, and it's now on its last legs. Even in 2011, scientists like Privette were eager for its replacement to get up and running.
But in spring 2011, the launch of a satellite called Glory, which carried the newest version of the solar irradiance sensor, failed, and Glory plummeted into the Pacific Ocean, carrying the sensor with it.
That wasn't Privette's only problem. After Glory, the next satellite scheduled to carry a total solar irradiance sensor had been part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS), the over-budget, never-completed satellite effort that was canceled in 2010.
And the program put in place to replace NPOESS, known as the Joint Polar Satellite System (JPSS), was years away from launching a solar irradiance sensor.
"Because the JPSS is delayed, our ability to get a [total solar irradiance] instrument up and flying to overlap SORCE became a huge concern," Privette said. "We didn't know what to do."
If SORCE stopped working before another, similar instrument got up and going, scientists would have a big problem.
To ensure it is working correctly, a new instrument's measurements have to be compared with the existing ones, while both are in orbit. Especially because changes in solar irradiance are very small, this is the best way for scientists to be sure they are getting accurate data. They can tweak the new instrument, if necessary.
Without instrument overlap, there is no good way to test the new sensors. In 2011, it looked to Privette, and others in the field, like 35 years of continuous data might come to an end as SORCE slowly decayed, alone in space.
In early 2012, though, Privette's luck changed. It turned out the Air Force had some extra room on a satellite it was planning to launch in fall 2013. Now NOAA just needed a spare sensor.
That's where Greg Kopp came in. Kopp's a senior research scientist at the University of Colorado's Laboratory for Atmospheric and Space Physics. His lab had made the sensor on SORCE and had another sensor it thought could fit on the Air Force satellite.
"So they did a very quick engineering study, and by late spring of last year they realized, on paper, this looks like it could work," Privette said.
By the standards of satellite instrument procurement and launch, this was a lightning-fast transition. Privette called it "phenomenal."
This sensor, once it is launched, should provide a bridge between the SORCE sensor and its planned follow-up on the polar satellites, slated to launch in 2017. Yet while Privette and others worried about the solar sensors are understandably relieved, in many ways, the high-drama saga is more a cautionary tale than a celebratory one.
Risky business gets more so
Big satellite programs, at least in recent history, have suffered from long delays and budget overruns. These problems threaten the continuity of not just solar climate data records, but many other satellite-based monitoring systems that play a key role in human understanding of how the Earth and its weather and climate work.