When the image of Houston was collected, Landsat 7 was working as advertised, but it has been limping along since its Scan Line Corrector failed on May 31, 2003. The device, which is not backed up by an on-board spare, compensates for the forward movement of the spacecraft in orbit so its adjacent surface scenes line up properly. Since the failure, the satellite data leave about 22% of the ground below its track blank. Until a year ago, Landsat 5 was helping fill in the dataset, but it finally stopped working after 27 years.

The Landsat system is operated by the U.S. Geological Survey (USGS), with NASA in charge of developing and launching the spacecraft. That is what the space agency does best, but the split in responsibility has made it difficult to keep the funding stream flowing against competing priorities.

Now that the two branches of government are getting serious about deficit reduction, that situation is likely to worsen. The budget belt-tightening comes at a time when long-range data are growing in importance as scientists and their political bosses try to gauge just how much of climate change is the result of man-made inputs that can be changed, measurements Irons says Landsat can help make.