An image provided by NASA-TV shows the Cygnus spacecraft nearing the International Space Station on Sunday as both passed over the Atlantic Ocean. AP2013

On Tuesday, NASA celebrates its 55th anniversary. But instead of cake, balloons and streamers, the agency is giving 97 percent of its employees the day off – and they'll be out of work for as long as it takes the government shutdown to end.

“NASA loves countdowns,” spokesman Allard Beutel told America Tonight hours before the shutdown, “but this is definitely not a good countdown.”

Early Tuesday, the impasse between Democrats and Republican members of Congress on the budget for the president’s health care law has given way to the 18th federal government shutdown since 1976. Even before Tuesday, departments and agencies braced themselves for high furlough rates. With the shutdown now in full swing, six federal departments and agencies are projected to have furlough rates of 80 percent or higher, and The New York Times reports as many as 800,000 government employees being furloughed.

But while some departments and agencies face more total employees being furloughed from the shutdown, none of them have a furlough rate as high as NASA. The Office of Management and Budget estimates NASA’s furlough rate for the shutdown at 97 percent, temporarily eliminating 17,701 of its 18,250 civil servants. Just 549 civil servants have been cleared to work during the course of the shutdown.

"NASA will shut down almost entirely, but Mission Control will remain open to support the astronauts serving on the space station," Obama said in a statement Monday, referring to Karen Nyberg and Mike Hopkins, the two astronauts living aboard the International Space Station.

The plan, which was drawn up shortly before the government narrowly avoided being shut down almost two years ago, makes only employees who are “vital to the protection of people and property” as essential, non-furloughed employees. Beutel said that another 1,562 NASA employees are considered “on-call,” meaning they would be called in during an emergency situation that requires them to protect people or property.

Though it’s uncertain how severe the consequences will be from a government shutdown, it could potentially cost NASA hundreds of millions of dollars in the long term on one of its prized projects. The Mars Atmosphere and Volatile EvolutioN, known as MAVEN, will send a space probe to orbit and study the atmosphere of Mars, in hope of discovering what caused Mars’ atmosphere to be inhospitable for life. But the government shutdown potentially compromises the window that NASA has for launching the mission on Nov. 18, Beutel said. Before a government shutdown was avoided in the spring of 2011, a similar situation arose when the funding and preparation for space shuttle Endeavour was on the brink of being halted.

“Once we’re out of that window, the next opportunity to launch isn’t until 2016, which will potentially cost hundreds of millions of dollars in the long term,” Beutel said. “I don’t want to oversell that, but the fact is that’s what could potentially happen, depending on how long the shutdown lasts. It won’t allow us to do the scientific research we’re supposed to be doing.”

Depending on the length of the shutdown, history shows that NASA could be in for some trouble. In November 1995, the government shut down for a total of three weeks, which unfolded in the middle of space shuttle Atlantis' STS-74 mission to Russia's Mir space station. Seven percent of NASA employees reported to work, according to The Associated Press.

"All nonessential personnel were furloughed, which basically meant that from a mission perspective, everyone who was needed to fly the mission was considered necessary, but anyone who was not associated with actually operating the mission and flying it out successfully had to go home,” Robert Pearlman, editor of collectSPACE.com, told Space.com in March 2011.

The 97-percent furlough rate during the shutdown is the latest blow to NASA. In June, the House Appropriations Committee approved a bill giving NASA a $16.6 billion budget in fiscal 2014, cutting its spending by more than $1 billion. In July, the House Committee on Science, Space and Technology voted to bar NASA from pursuing an asteroid, considered to be the main piece of the Obama Administration’s focus on space exploration, according to The New York Times. Critics such as Rep. Steven Palazzo (R-Miss.) described the asteroid plan for NASA as “a costly and complex distraction.”

Late-night hosts such as Stephen Colbert light-heartedly needled NASA’s fate during the shutdown, using a clip from the upcoming movie “Gravity” as NASA’s “last scene.”

But the situation remains tenuous for NASA employees – one that doesn’t have an end in sight.

“It’s not a good situation for anyone,” Beutel said. “Not only do we love to do our jobs, but everyone is affected by this. It’s truly not business as usual.”