WASHINGTON — NASA is pressing on with its instrument contribution to a joint 2016 Mars mission with Europe, despite the fact that the White House has yet to commit to the Mars sample return campaign of which that mission is a part.

“At this time, we’ve provided no direction other than ‘proceed as originally planned’ to all the members of the 2016 team,” Jim Green, director of NASA’s Planetary Science division, said on a Dec. 21 conference call with members of the NASA Advisory Council’s planetary science subcommittee.

NASA in 2009 said it wanted to work with the European Space Agency (ESA) on a multi-mission campaign to Mars that would eventually return samples of the martian surface to Earth.

The original plan was for NASA to provide an Atlas 5 rocket in 2016 to launch a telecommunications and science orbiter that also contained an ESA-developed entry, descent and landing technology demonstration. Last year, NASA said it could not afford to provide the launcher, or to provide what was supposed to be one of two Mars rovers for the second mission in the ExoMars campaign, which was to launch in 2018.

The White House has since withheld approval to proceed with NASA’s revised contribution to the 2018 mission — an entry, descent and landing system for a joint NASA/ESA rover, according to planetary science advocates who met with White House budget officials last fall. The administration of U.S. President Barack Obama views a multiyear commitment to Mars sample return as unaffordable, these people said. Notable among the planetary science advocates who publicly described such meetings is Steven Squyres, the Cornell University professor  appointed chairman of the NASA Advisory Council in November.

Notwithstanding the 2018 Mars mission’s cloudy outlook, NASA is continuing work on the four science instruments it is contributing to the ESA-led Trace Gas Orbiter mission launching in 2016.

To make up for the loss of the NASA-provided launch, ESA has invited Russia to join the Mars sample return campaign as a full partner — on the condition that it provide a Proton rocket for the 2016 mission’s launch. After a Dec. 7 meeting between NASA, ESA and Russian space officials, a task group was formed to evaluate Proton’s suitability for the mission.

NASA will not make any commitment one way or another to the 2018 mission until at least February, when Obama releases his 2013 budget request for NASA.

“Any NASA decision on this matter, in terms of whether NASA’s participation is going to continue, will be based on the outcome of the technical discussions and following the release of the president’s 2013 budget, which will be in February 2012,” Green said on the Dec. 21 call.

The Mars sample return campaign was the top-priority flagship mission in the last planetary decadal survey, which was released by the National Research Council in March and established the planetary science community’s pecking order for missions from 2013 through 2022.

The second-highest flagship priority was a mission to Jupiter’s icy moon Europa.

NASA had envisioned a flagship excursion to Europa led by a craft called the Jupiter Europa Orbiter. Hopes that that mission would fly this decade were dashed when the White House unveiled a five-year plan  last winter to trim the planetary science budget to $1.26 billion by 2016, or about 15 percent below current levels. That effectively ruled out the $4.7 billion Jupiter Europa Orbiter.

Curt Niebur, a program scientist at NASA headquarters here, said Dec. 21 that the agency is now working on a descoped Europa flagship that would, excluding the price of launch, cost NASA about $1.5 billion. The mission’s launch date, duration and precise science objectives are still being evaluated, Niebur said. A report outlining those details is expected to be presented to Congress in May or June, Niebur said.

Europa mission concepts NASA is now considering, Green told Space News Jan. 6, include multiple Europa flybys and radar scanning, the tactic used by NASA’s Cassini orbiter, which is now orbiting Saturn’s moon Titan.

The question NASA would have to address if it chooses the Cassini method, Green said, is “how many flybys of Europa would it take to do the Europa science that is delineated in the decadal and previous reports?”

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.