WASHINGTON โ€” NASA could be forced to delay two approved, top-tier Earth science missions by up to one year due to congressional inaction on the presidentโ€™s 2011 spending request, which has U.S. federal agencies operating at their 2010 spending levels, according to sources and documents.

NASA had hoped to spend about $5 billion on Earth- and space-science missions in 2011, but the funding available under the current stopgap spending measure, or continuing resolution, falls $450 million short of that total, the documents show. U.S. President Barack Obama requested $19 billion for NASA in 2011, but the agency currently is constrained to spending rates commensurate with the $18.72 billion appropriated for 2010.

According to a March 9 laundry list detailing potential program impacts to NASAโ€™s Science Mission Directorate (SMD), the shortfall could delay the Ice, Cloud and Land Elevation Satellite 2 (ICESat-2) and Soil Moisture Active and Passive (SMAP) missions while increasing their cost. A copy of the list was obtained by Space News.

Although NASA requested $75 million and $132 million this year for ICESat-2 and SMAP, respectively, SMD could be forced to reduce planned spending on ICESat-2 by $22 million in order to stay within the $1.4 billion spending ceiling Congress appropriated for Earth science initiatives last year. SMAP funding would have to be reduced by $30 million, according to the document.

Both missions topped the National Research Councilโ€™s list of large-scale climate-monitoring priorities in its 2007 Earth science decadal survey. ICESat-2, led by NASAโ€™s Goddard Space Flight Center in Greenbelt, Md., is a follow-on mission to the ICESat spacecraft currently in orbit. It is designed to continue measurements of changes in polar ice-sheet mass to anticipate changes to global sea levels.

Although NASA does not expect to nail down a cost estimate for ICESat-2 until it undergoes a key design review in November, budget documents show the agency projects spending $500 million-$600 million between 2008 and 2016. NASA is budgeting roughly $100 million for ICESat-2โ€™s launch but has yet to settle on a rocket to send it into a 450 kilometer polar orbit in January 2016. The one-year launch delay could eliminate a potential dual-launch opportunity, adding to the overall cost of the mission, according to the document.

SMAP, designed to improve weather forecasts and flood and drought predictions, is expected to cost between $780 million and $900 million. Led by the Jet Propulsion Laboratory in Pasadena, Calif., it is slated for launch in November 2014.

Budget woes have already forced NASA to shelve a pair of big-ticket environmental monitoring missions โ€” the Climate Absolute Radiance and Refractivity Observatory and the Deformation, Ecosystem Structure and Dynamics of Ice satellite โ€” that just last year were planned for launch 2017. The presidentโ€™s latest budget request includes future-year funding projections that are considerably lower than those released last year.

Another mission likely to be affected by the continuing resolution is the Global Precipitation Measurement satellite, a rain- and snow-monitoring mission NASA is developing with the Japanese Aerospace Exploration Agency. The missionโ€™s planned July 2013 launch could be delayed if NASA is forced to trim its budget by $15 million, the March 9 document shows.

NASA has already scaled back the precipitation measuring mission by abandoning plans to fly a carbon copy of its microwave-imaging instrument aboard a spacecraft operating in a low-inclination orbit to focus on the Earthโ€™s equatorial regions.

Meanwhile, House and Senate lawmakers are continuing to negotiate a continuing resolution that would fund the federal government for the remainder of the current fiscal year. The current stopgap funding measure expires March 18.

The House in February passed a measure that provides just $18.1 billion for NASA. Companion legislation introduced by the Senateโ€™s Democratic majority would have provided $18.5 billion for NASA, but that measure was defeated in a floor vote.

The House bill, which likewise failed to pass the Senate during a March 9 floor vote, would leave NASAโ€™s Science Mission Directorate funded at the $4.4 billion Congress appropriated last year. The Senate bill would have increased that by roughly $350 million.

Although lawmakers are unlikely to reach agreement before the current continuing resolution expires, congressional aides said they expect House and Senate leaders to approve yet another short-term continuing resolution that will keep the government running for an additional three weeks.