NASA may have to make some tough choices if it wants to continue its space exploration missions, with two particularly efforts -- the Spitzer Space Telescope and part of the NEOWISE mission -- possibly on the chopping block.

Looking at the findings presented after a review by an independent panel, NASA may be forced to shut down one space telescope -- the Spitzer -- to save others, including the Hubble and the Kepler exoplanet-hunter.

Spitzer could be shut down for a lack of funds, while a proposal called MaxWISE meant to re-purpose the NEOWISE -- the Near-Earth Object Wide-field Infrared Survey Explorer --  data for astrophysical studies is also unlikely given the expense.

NASA is facing a Congress that has been zealously tightening the space agency's budget.

Although NASA has cut funding for the 11-year Spitzer program after fiscal 2014, it hasn't completely closed the door and ways to keep the space telescope conducting at least some scientific work.

"The Spitzer project is invited to respond with a request for a budget augmentation to conduct continued operations with reduced operations costs," the agency said in a statement responding to the independent review.

Officials with the Spitzer project were quick to seize on that.

"To be clear: Spitzer has not been canceled. Funding not yet identified, but NASA has asked us for a revised budget," they posted on the projects' Twitter account.

The costs incurred by the Spitzer telescope were of concern to the review panel given its reduced observational capabilities since 2009, when the coolant necessary for the best functioning of its infrared instruments ran out.

The panel did acknowledge that Spitzer has provided a considerable amount of what it called "unexpected science" since then, including studies of exoplanets, brown dwarfs and distant galaxies.

Not everyone on the independent review panel was happy about its recommendations' effect on NASA programs.

"To me it's really sad that this country can't find just a few million bucks more to throw into this to keep these things active and running as they should be," panel chair Ben R. Oppenheimer, an astronomer at the American Museum of Natural History in New York City, told Scientific American.

Spitzer, along with the Hubble telescope and the Chandra X-Ray Observatory, made up what NASA has termed its "Great Observatories."

In the review, funding extensions for both the Hubble and the Chandra instruments were approved.