WASHINGTON — NASA has started turning over piles of documents about its human spaceflight program to a U.S. Senate panel, as demanded by several lawmakers last month in a letter to NASA Administrator Charles Bolden.

A congressional source said June 6 that NASA has delivered some — but not all — of the documents sought by the leaders of the Senate Commerce, Science and Transportation Committee, which authorizes funding for NASA. The agency delivered the documents June 3, which was the deadline set by the committee leaders in their  May 18 letter to Bolden.

NASA spokesman Michael Cabbage did not reply to a request for comment.

Among the documents that NASA turned over last week were: Records of agency discussions about modifying existing contracts to build the new heavy-lift rocket and crew capsule Congress wrote into the latest NASA authorization law; internal briefings NASA conducted about rocket configurations that could fulfill Congress’ mandate for a new heavy launch vehicle; and a copy of a NASA-commissioned Aerospace Corp. study, presented to the agency in April, that concluded crew launches by a U.S.-based commercial provider would cost two to three times more than continuing to buy seats on Russia’s Soyuz vehicle.

The Senate committee leaders wrote to Bolden last month to demand an update on the space agency’s compliance with the NASA Authorization Act of 2010. That legislation, which was signed into law Oct. 11, directed NASA to begin work on a new heavy-lift Space Launch System (SLS) and multipurpose crew vehicle. The law also charged NASA to complete this work by utilizing, whenever possible, space shuttle infrastructure and contracts awarded under the Constellation program.

The crew capsule Congress ordered will be constructed by Denver-based Lockheed Martin Space Systems under the Orion Crew Exploration Vehicle the company was awarded in 2006 under the Constellation program. NASA has not said whether it would be practical to use Constellation contracts to construct the SLS.

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.