Satellites aren't built to last forever, so it's not a big surprise that the third and last laser on NASA's Ice, Cloud and Land Elevation Satellite (ICESat) quit working on October 11, outlasting its designed mission length by three and a half years. Since its launch in 2003 ICESat has been a critical instrument for continuously monitoring how much ice sheets in Antarctica and Greenland are contributing to the rise of the world's oceans and how much the swath of sea ice in the Arctic Ocean is thinning—both of which are occurring faster than projected.
The loss of ICESat, however, is a signal of what the future holds for NASA's ailing Earth Observing System (EOS), which is dying just as it is most needed to inform decisions and policy on climate change.
Today, 14 of the 15 satellites currently making climatic observations on Earth are far beyond their designed life-expectancies, with the exception being the Ocean Surface Topography Mission (OSTM):
- Landsat 7
- Tropical Rainfall Measuring Mission (TRMM)
- Quik Scatterometer (QuikSCAT)
- Active Cavity Radiometer Irradiance Monitor Satellite (ACRIMSAT)
- Earth Observing 1
- Jason 1
- Ice, Cloud and land Elevation Satellite (ICESat)
- Gravity Recovery and Climate Experiment (GRACE)
- Solar Radiation and Climate Experiment (SORCE)
- Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)
- Ocean Surface Topography Mission (OSTM)
Several of these are expected to "go dark" in the next two years, robbing scientists of critical data needed for monitoring climate change and verifying international agreements, just as a critical mass of global players is agreeing that such agreements are essential to the future health of the world's people and economies.
For more than a decade these Earth-observing satellites have provided some of the first environmental measurements on a global scale, including large-scale changes in the mass of polar ice. Scientists have learned how fast oceans are rising and why. They've also found out how hurricanes develop, strengthen and weaken.
Planned replacements for Earth-observing satellites are inadequate, too. The various airplanes that carry the instruments for ICE Bridge, a stopgap measure until ICESat's successor is launched five years from now, have limited coverage. So, consecutive measurements for tracking global ice patterns will not resume until 2015, after ICESat 2 enters orbit.
"If we don't have continuous measurements, we basically close our eyes for awhile," says senior scientist Thorsten Markus, head of the Cyropheric Sciences Branch at the NASA Goddard Space Flight Center. "It is critical that we continue those time-series observations. For climate change, the satellite provides the only means to truly monitor the Earth on a global basis. There is simply no other way."
Satellite imagery is used for all sorts of climate study, from identifying conditions that allow infectious diseases like West Nile virus and cholera to emerge, to creating models for predicting hurricanes, to distinguishing natural resources such as wind, water and sunlight.
"We are impaired in our ability to understand what is happening and how the Earth works," explains Waleed Abdalati, a former NASA scientist and director of the Earth Science and Observation Center at the University of Colorado at Boulder's Cooperative Institute for Research in Environmental Sciences. "In the last five years the ice has been changing in ways no one predicted. When you combine continuous measurement, you get the complete story. With a piecemeal approach, such as the one we have now, you get far less."
In addition to ICESat's breakdown and the failed launch of the Orbiting Carbon Observatory in February 2009, other vital EOS satellites are in trouble. An antenna on QuikScat stopped working in November. Landsat 7 has a problem with its Scan Line Corrector, causing gaps in data.
"As soon as Landsat 7 fails completely, we will not have Landsat observations until 2013 when LandSat's successor is scheduled for launch," says senior scientist Compton Tucker of NASA's Hydrospheric and Biospheric Sciences Lab at Goddard. Tucker uses remote sensing to study vegetation and land use. "If you want to understand emissions, you need to understand land use and land cover change, especially when you have forests cut down and replaced by herbaceous vegetation."
NASA is developing or studying just seven Earth-observing scientific satellites for launch in the next seven years:
- NPOESS Preparatory Project (NPP)
- Soil Moisture Active-Passive (SMAP)
- LandSat Data Continuity Mission (LDCM)
- Global Precipitation Measurement (GPM)
- Ice, Cloud and land Elevation Satellite (ICESat 2)