WASHINGTON — A bipartisan group of more than 60 members of the U.S. House of Representatives wrote to President Barack Obama Tuesday urging that he direct NASA to immediately begin development of a heavy-lift launch vehicle capable of sending NASA's Orion Crew Exploration Vehicle on deep space missions.

In a June 22 letter to the president signed by 62 House lawmakers, including 25 Democrats and 16 members of the powerful House Appropriations Committee, the members say it is in the nation's best interest to leverage the $10 billion NASA has already invested in Constellation, a 5-year-old effort to replace the retiring space shuttle with Orion and the Ares family of rockets. Obama marked the program for cancellation in his 2011 spending proposal delivered to lawmakers in February.

"We support the immediate development and production of a heavy-lift launch vehicle that, in conjunction with the Orion Crew Exploration Vehicle, may be used for either lunar or deep-space exploration to an asteroid and beyond, as you said in Florida," the lawmakers say in the letter. During an April 15 speech at NASA's Kennedy Space Center, Fla., Obama said NASA would continue development of Constellation's Orion crew capsule for use as a lifeboat aboard the international space station and would spend up to five years studying heavy-lift propulsion technologies before initiating development of a heavy-lift launch vehicle no later than 2015.

The lawmakers assert that a "heavy-lift exploration system could be operational within six years and achieved within NASA's Exploration topline budget."

NASA's Exploration Systems Mission Directorate stands to receive a total of $23.6 billion between 2011 and 2015 under White House budget projections released in February. That figure includes $3.1 billion for heavy-lift and in-space propulsion research, $6 billion to foster development of commercial crew systems and $12 billion for various advanced technology research and demonstration projects.

"With no significant breakthroughs on the horizon in regard to heavy-lift propulsion needs, we see no reason to prolong a decision that will result in the loss of a highly-experienced and motivated workforce," the lawmakers state in the letter, which was spearheaded by Rep. Gene Green (D-Texas) and three members of the House Appropriations commerce, justice, science subcommittee that oversees NASA spending, including the ranking minority member Frank Wolf (R-Va.) and Reps. C.A. "Dutch" Ruppersberger (D-Md.) and John Culberson (R-Texas).

While the lawmakers say a robust U.S. deep-space exploration program would ensure that NASA astronauts explore beyond low-Earth orbit to the moon, Mars or "any number of exciting destinations," they remained silent on the president's plans to privatize operations in low-Earth orbit, an omission that did not go unnoticed by at least one company seeking to develop a crew transportation system for missions to the space station.

"It looks like Congress is on the right track, encouraging the Administration to move forward as quickly as possible with heavy-lift," said Lawrence Williams, vice president of strategic relations at Space Exploration Technologies (SpaceX) Corp. "Since President Bush unveiled his Vision for Space Exploration in 2004, the plan has been that NASA would focus its development efforts on moving beyond [low Earth orbit] and use commercially-developed rockets to service the [international space station]."

Hawthorne, Calif.-based SpaceX has spent roughly $350 million in NASA funds since 2006 to develop the Falcon 9 rocket and Dragon capsule with astronaut transport in mind.

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