The U.S. government faces billion-dollar class investments if it opts to restore the high-priority environmental measurements that were dropped last year from a new generation of civil-military weather satellites, according to a NASA official.

For example, just one dedicated mission to fly climate-change monitoring instruments lost in the restructuring of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) likely would cost more than $1 billion, according to Bryant Cramer, NASA’s

deputy director of Earth science.

Long-term restoration of ocean-surface topography measurements that also have been eliminated from the NPOESS platforms could cost another $2 billion, according to charts from a briefing given by Cramer at a recent meeting on the topic in Washington.

The charts provide an update of an ongoing study by NASA and the U.S. National Oceanic and Atmospheric Administration (NOAA) on options for ensuring Earth-science data continuity in the wake of the NPOESS restructuring. Preliminary results of the White House-mandated study are expected in mid July.

Many of the measurements in question are carried out today by a variety of satellites comprising NASA’s Earth Observing System. The government decided several years ago that instead of building replacements for these spacecraft, it would rely more on the NPOESS weather satellites to host the sensors. That plan unraveled last year when massive cost growth forced a restructuring of NPOESS.

Among the options being looked at in the study are restoring some of the canceled instruments to the NPOESS satellites. In fact,

the Senate Appropriations Committee

on June 28 proposed giving NOAA $30 million next year to do just that.

But Cramer, in an interview June 22, said this option is unattractive because of concerns that it would disrupt NPOESS, a joint effort of the U.S. Air Force and NOAA that already is well behind its original schedule.

Indeed, Air Force Brig. Gen. Susan Mashiko, the NPOESS program executive officer

, told Congress June 7 that the design of the first NPOESS satellite, now scheduled to launch around 2013, has

been effectively frozen to avoid risk. Similarly, Air Force and NOAA officials are wary of complicating work on subsequent NPOESS platforms, Cramer said.

Cramer emphasized that no decisions have been made regarding the restoration of the Earth-science and climate-change measurements. Currently there is no money in the U.S. federal budget for such missions.

According to the briefing charts, a dedicated climate-change research satellite would host

three of the

instruments no longer manifested on

NPOESS: The Total Solar Irradiance Sensor, which helps scientists differentiate between natural and human-induced causes of global warming; the Earth Radiation Budget Sensor, which monitors subtle long-term shifts in climate patterns; and the Ozone Mapping and Profiler Suite-Limb Subsystem, which measures the vertical distribution of radiation-absorbing ozone.

Cramer said the government would need commit to the first of these satellites by mid-2009 to avoid a break in the data record.

According to the briefing charts, a single satellite carrying this instrument payload would cost between $700 million and $1.1 billion, not including $300 million to $400 million in science-support costs. For long-term data continuity, Cramer said, two satellites would be needed, one launching in 2014 and the other in 2020. He added that the second satellite likely would be less expensive than the first, and that

the cost estimates depicted in the charts are preliminary.

The government might be able to keep the costs at the lower end of the range by procuring what the charts characterized as a “research” satellite with a five-year design life and limited system redundancy that would launch on a “non-standard” rocket and leverage existing ground infrastructure. The more expensive alternative would feature an “operational” satellite with a seven-year lifetime, launched atop a “standard” rocket and requiring some additional investment in ground infrastructure, the briefing charts show.

The government also is studying the possibility of adding a Total Solar Irradiance Sensor to NASA’s Landsat Data Continuity Mission spacecraft, scheduled to launch in 2011, and pursuing a flight of opportunity for the sensor in 2017, Cramer said. These would be in addition to the solar irradiance sensors on the dedicated climate-research satellites.

Also lost in the NPOESS reshuffle were instruments designed to collect sea-surface altimetry data. These measurements currently are taken by the U.S.-French Jason 1 satellite, with a follow on Jason 2 satellite scheduled to launch next year.

Cramer said the orbits of the NPOESS satellites are not ideal for the collection of ocean altimetry data.

Among the options being considered is a U.S.-European Jason 3 satellite that would launch

in 2013, to be followed by more advanced satellites in 2017 and 2020. The estimated cost of these missions runs between $1.5 billion and $2.1 billion, not including $200 million in support costs, the charts show.