U.S. lawmakers ironing out the differences between the House and Senate versions of the Department of Energy’s 2010 spending bill denied President Barack Obama’s request for $30 million to restart domestic production of plutonium-238 (pu-238), a critical material used by NASA in long-lasting nuclear batteries for deep space missions.

The U.S. House of Representatives had approved $10 million in July for a pu-238 production restart — the Senate bill provided no funding — but during a Sept. 30 House and Senate legislative conference on the Energy and Water Development and Related Agencies Appropriations Act of 2010, conferees opted for no funding until the administration puts forward a detailed plan for resuming production.

“The conference agreement provides no funding for the Pu-238 Restart Project,” the conference report language states. “The conferees agree with language proposed by the House regarding a start-up plan which shall include the role and contribution of major users of Pu-238, such as [NASA], and shall be submitted with the fiscal year 2011 budget submission.”

The conference spending bill passed the House Oct. 1 by a vote of 308 to 114. The Senate was poised to vote on the measure the week of Oct. 5. The United States shut down production of the material in the late 1980s, opting to rely instead on Russian stockpiles for the occasional NASA mission that required nuclear fuel. However, Russia’s stockpile has dwindled, leaving NASA in competition for the remaining U.S. supplies with unspecified national security customers.