WASHINGTON — A bipartisan group of 32 House lawmakers is asking U.S. President Barack Obama to spell out long-term plans for crewed deep-space missions using the Space Launch System (SLS) and Orion crew capsule NASA is spending about $3 billion a year to build.

“Congress has done its part in helping to codify a future deep space exploration architecture in the NASA Authorization Act of 2010 (PL 111-267), and has followed with a robust funding commitment, as most recently expressed in the Consolidated Appropriations Act of 2014,” the lawmakers wrote in a March 21 letter to Obama. “We are concerned, however, about the impact of shifting priorities for NASA and the resulting mixed signals this sends relative to the United States’ dedication and commitment to its leadership role in human deep spaceflight exploration.”

The lawmakers cited “the expansion of human spaceflight programs in countries such as China and Russia over the past decade” in urging the White House to make space exploration a top priority.

An electronic copy of the letter — signed by 15 Republicans and 17 Democrats — was sent to media March 24 from the office of Rep. Steven Palazzo (R-Miss), chairman of the House Science space subcommittee that produces policy-setting NASA authorization bills.

“The next few years provide a crucial window in which we must redouble our efforts to once more launch American astronauts on American rockets from American soil,” Palazzo said in a statement accompanying the letter’s release.

Palazzo and the subcommittee’s ranking Democrat, Rep. Donna Edwards of Maryland, were the first two signatures on the letter, which was also signed by Rep. Lamar Smith (R-Texas), chairman of the full Science Committee.

“Funding for NASA’s exploration programs is an investment, not an expenditure, and history has proven that the economic returns from these investments are significant,” Edwards said in a statement accompanying the letter’s release.

Rep. Eddie Bernice Johnson of Texas, the ranking Democrat on the full committee, did not sign the letter, which was delivered just days before lawmakers were scheduled to hear explanations of the White House’s 2015 federal budget request from Obama’s top science advisor, John Holdren, and NASA Administrator Charles Bolden. Holdren will testify in a House Science Committee hearing March 26; Bolden will appear in a space subcommittee hearing scheduled for March 27.

Congress directed NASA to build SLS and Orion, which were not part of the Obama administration’s original plans for NASA.

NASA has so far identified the funding required for two SLS-Orion missions: an uncrewed test flight in 2017, and a crewed mission in 2021. The vehicles also are integral to NASA’s plan to send astronauts to a small asteroid that the agency hopes to divert to lunar space.

In a March 18 letter to Smith and Rep. Frank Wolf (R-Va.), NASA’s chief appropriator in the House, Bolden defended these plans as both affordable and “consistent with the NASA Authorization Act of 2010.” NASA spokesman Allard Beutel provided a copy of Bolden’s letter March 24 in response to a SpaceNews inquiry about the letter spearheaded by Palazzo and Edwards.

Though apparently united on SLS and Orion, Palazzo and Edwards remain divided over the so-called Asteroid Redirect Mission. Palazzo, who favors returning astronauts to the lunar surface, has characterized the asteroid mission as “a complex and costly distraction.” A previously skeptical Edwards recently threw her support behind the mission, however.

The House Science Committee passed NASA authorization legislation last year barring the agency from spending funds on the Asteroid Redirect Mission, but the bill never made it to the House floor for a vote. House aides working on similar legislation this year say the new version also might include language that would ban NASA from unilaterally canceling either SLS, Orion or the James Webb Space Telescope.

Most of the lawmakers who signed the March 21 letter, including Edwards, Palazzo, and Smith, have a NASA field center in their home states. SLS propulsion systems are tested at NASA’s Stennis Space Center in Palazzo’s Mississippi district, for example, while Orion is managed by the Johnson Space Center in Houston.