With the federal government in partial shutdown, NASA is implementing drastic, across-the-board furloughs that will severely curtail ongoing research and development and shut down the agency's widely visited web site and satellite television channels.

But officials say flight controllers will continue to oversee the operation of the International Space Station, home to two NASA astronauts, an Italian flier and three Russian cosmonauts, and provide uninterrupted support for spacecraft in Earth orbit and across the solar system.

Of NASA's 18,250 civil servants, 16,135 -- nearly 90 percent -- will not be allowed to work during the shutdown. Of the 2,115 who have been deemed exempt, only 549 are considered full or part-time workers, cleared to use agency offices and facilities as required.

Bob Jacobs, a senior public affairs officer at agency headquarters in Washington, said the rest are "on call," ready to respond to an emergency or some other contingency, but not allowed to go to work, even voluntarily, or use NASA email, phones or other services to conduct official business.

According to a NASA "frequently asked questions" document, the shutdown plan recognizes three major areas of exempted work:

• Space launch hardware processing required to prevent "harm to life or property"
  
  
• International Space Station tracking, operation and support "and operating satellites necessary for safety and protection of life and property"
  
  
• "Completion or phase down of research activities in cases where serious damage to property would result from temporary suspension of the activity"

"As far as the International Space Station goes, that operation continues, because we obviously need to protect the lives of the six crew members in orbit and of course, the safety and security of the space station and other hardware," Jacobs said. "So those programs will continue.

"And our existing satellite missions that are in operation -- again, since the overriding issue is to protect those assets -- we will continue to collect the data and maintain them."

The Curiosity Mars rover, the Messenger probe in orbit around Mercury, the Cassini Saturn mission, the Juno orbiter on the way to Jupiter, the New Horizons spacecraft en route to Pluto and dozens of other spacecraft will be monitored and controlled as usual.

How much returning data will reach researchers is unclear. Many university-based scientists receive data from NASA spacecraft autonomously via the internet. Whether those pathways will remain open is not yet known.

The Jet Propulsion Laboratory in Pasadena, Calif., where many interplanetary spacecraft are controlled, is operated by the California Institute of Technology under contract to NASA.

A JPL spokeswoman said Monday a shutdown would not trigger any furloughs there, but without NASA web support, photos and updates would not be widely disseminated.

NASA's multiple websites are among the most widely viewed on the web. During the furlough, however, the web sites effecticely will be shut down. Early Tuesday, the NASA home page redirected viewers to a USA.gov site, which showed a static page saying "due to the lapse in federal government funding, this website is not available. We sincerely regret this inconvenience."

Likewise, the agency's social media presence and its three satellite television channels, carried by many cable companies across the nation, will be shut down for the duration with no live updates on space station operations or any others.

"Due to the lapse in government funding NASA Television will be unavailable to the public, news organizations, satellite service providers and cable television distributers," according to a notice on NASA's public TV channel.

"In addition, the NASA Television feeds from www.nasa.gov also will be unavailable until further notice. We sincerely regret this inconvenience."

NASA faced a similar reduction in force when the government shut down for five days in November 1995 and then again the following month when a record 21-day shutdown was implemented. The former occurred during a shuttle mission to the Russian Mir space station, forcing the agency to operate the flight with a reduced staff.

This time around, the workforce reduction is more severe, but Jacobs said the agency would do everything required to protect valuable resources, even if normal processing is suspended.

"For space launch hardware, again, as necessary to protect the launch vehicles and ensure the public safety, some of that processing will continue," he said.

But work on programs that are not time critical, like NASA's new Space Launch System heavy-lift rocket, the Orion deep space exploration capsule and the James Webb Space Telescope, will grind to a halt, including work on NASA's next Mars probe, known as MAVEN, that is scheduled for launch in November.

Depending on how long the government shutdown remains in effect, "MAVEN could miss its scheduled launch date," Jacobs said. "And if that happens, the next launch opportunity isn't until 2016."

In a Sept. 27 letter to the Office of Management and Budget, NASA's chief financial officer said the agency would "narrowly construe the available exceptions in determining which activities can continue" and exempt "only those employees who contribute directly to those actions."

"All other employees would be furloughed immediately after an orderly shutdown," the letter said. "Employees furloughed would be informed that NASA cannot promise that they will be paid for the period during which they are on furlough. Pay for those days would depend on future appropriations."