Earlier this month, a U.S. satellite known as F17 - which was primarily used for meteorological measurements - experienced operational failures that compromised the integrity of its data. And while there are similar satellites in orbit that can take over the data collection for now, they're old enough that scientists are unsure how much longer they'll last.
Now, with no government plans to launch a replacement any time soon, scientists who rely on these satellites for valuable climate data are beginning to worry about the future of their research. The problem comes at a vital time, too - one when the Arctic, and other remote regions, are seeing rapid changes and scientists badly need these instruments to track them.
Just last month, the National Snow and Ice Data Center (NSIDC) reported that the maximum extent of Arctic sea ice this past winter - the time of year when the ice reaches its annual peak - was at a record low for the second straight year. The Arctic sea ice record has been one of the most important ways scientists have tracked the progress of climate change over time. But as of April 12, the NSIDC was forced to release a statement explaining that its daily sea ice updates were suspended until further notice due to technical difficulties with F17.
F17 - and its predecessors - have been "one of the primary resources for monitoring sea ice extent and concentration," said Walt Meier, a research scientist and sea ice expert at NASA's Goddard Space Flight Center.
F17 was just one of many satellites launched by the Defense Meteorological Satellite Program (DMSP) over the years. It's one of the country's oldest satellite programs, created in 1962, and has been a source of valuable meteorological data for decades.
In 1987, the program became of particular use to climate scientists when it began launching satellites containing special instruments known as a passive microwave sensors. These instruments are able to detect microwaves emitted by the Earth, which can be used to measure atmospheric properties, such as temperature and humidity, as well as certain features on the earth's surface. One of these sensors is carried on F17.
One of the technology's most important uses is its ability to detect sea ice at the earth's poles without having to rely on visual imagery, Meier said.
"The passive microwave [technology] is particularly good because it's not affected by clouds and you don't need sunlight," he said. As a result, the DMSP satellites are a primary resource for sea ice monitoring. Prior to 1987, the technology was carried on one other research satellite, which was launched in 1978 - so altogether, the program has helped establish a nearly 40-year continuous record on sea ice extent. This is critical research for scientists attempting to monitor the ways climate change is affecting the Earth's poles, which are some of the most delicate and rapidly changing regions on the planet.
But that uninterrupted record could be coming to an end within the next few years. The DMSP satellites currently in orbit are getting to the end of their lifespans - F17 being the most recent evidence of this - and there are no immediate plans to launch any more of them. Without another similarly equipped satellite to take over, scientists like Meier will be forced to switch to new, and potentially lower quality, data sources, interrupting decades-long continuous climate records in the process.
The problem with the satellites is that they don't last forever - they're only designed to have a lifetime of about five years, Meier said. So, since 1987, DMSP has been launching a new satellite every few years. The most recent of these was called F19, launched in 2014.
In general, new satellites have been launched before the old ones have failed, to prevent interruptions in data collection. This means that at the time F19 was launched, there were several operational satellites still in service. This was lucky, because F19 failed unusually quickly - scientists lost communication with the satellite just this past February.
When that happened, the still-operational F17 satellite - which has been in orbit since 2006 - was reassigned as the primary platform for data collection, according to Julienne Stroeve, a senior research scientist with the National Snow and Ice Data Center. But in the past few weeks, adjustments made to the satellite's solar panels have caused technical difficulties that may be beyond repair.
Luckily, there are still a few other DMSP satellites with the appropriate sensing equipment in orbit that scientists can turn to in the meantime - but these are thought to be reaching the end of their lives as well. And, thanks to a lack of funding, the government has no immediate plans to launch another.
The last satellite built for the DMSP program - F20 - was originally intended to be launched within the next few years. But last year, the Air Force's funding request for the program was denied by Congress and the launch plans shelved. Consequently, the already-built satellite has remained on the ground in storage, and Tina Greer, a public affairs officer with the Air Force Space Command's Space and Missile Systems Center, confirmed that there is no DMSP satellite currently on the launch manifest.
Fortunately, the DMSP satellites are not the sole source of sea ice data, Meier said. Other types of instruments can still be used to collect measurements.
But data collected from different types of instruments would be difficult to integrate with the passive microwave record from satellites such as F17. And even if the funding situation changed and new sensors were launched at a later date, any gap in the data collection would effectively end a decades-long record and start a new one.
"You can do a trend up to that point and a trend after that point that you have confidence in, but across that gap you have much lower confidence," Meier said. "So it really would end that high quality, consistent, continuous nearly 40-year record - which would be a shame to lose, and I think would have an impact on certainly the monitoring of the sea ice and potentially on our understanding of the changes in the climate system."
He added that gaps in these types of long-term trends can also throw off climate models that use historical data to make predictions about the future.
It's not just sea ice data that would suffer, either. The DMSP satellites have also been useful for other climate-related data collection, such as the monitoring of precipitation and wind speeds, said Wesley Berg, an atmospheric scientist at Colorado State University, who's also closely involved with NASA's Global Precipitation Measurement Mission.
"Precipitation varies dramatically in space and time, and we need as much high-quality data from sensors as possible," Berg said. "It's kind of a blow to us as well that we're losing these sensors and we don't have follow-on ones."
For these types of measurements, he said that it's also possible to fall back on other types of sensors carried by other satellites - infrared monitoring, for example - but the data wouldn't be of the same quality. "It's going to degrade things," he said.
It's possible that there may be an opportunity to share data with other countries in the future, Meier said. Japan has a satellite in orbit that collects microwave data, although Meier noted that it's a slightly different type of sensor which could cause difficulties integrating its measurements with the data already collected from the DMSP satellites. However, the Japanese satellite was launched in 2012, so it's unclear how much longer it will last.
The European Meteorological Agency has also made plans to launch a series of satellites intended for polar research, but likely not until after 2020. This means there's still a potential for a data gap if the currently operating satellites fail before then.
For now, scientists are hoping that the remaining DMSP satellites will hold out until a solution is reached or another satellite is launched to take over. And while F20 remains grounded for now, Greer said that "there's always a possibility that things might change" - and Meier still holds on to the hope that Congress could reverse its decision about the funding at a later date.
"That would be my hope, given the situation," he said. "I think that we're in a really serious threat of having a gap in the coverage from the passive microwave [data] and a real reduction in climate monitoring capabilities."