When NASA space flight chief Bill Readdy told a Senate subcommittee last year that relying on expendable rockets to assemble and resupply the international space station would take longer and cost more than using the space shuttle, the subcommittee’s chairman said he did not believe NASA had done enough homework to rule out alternative approaches.

Sen. Sam Brownback (R-Kan .), then chairman of the Senate Commerce science, technology and space subcommittee, said during the May 2004 hearing that he especially was not convinced that NASA had conducted a thorough assessment of whether it might be cheaper in the long run for the United States to retire the shuttle immediately and switch to commercial vehicles to supply and finish building the international space station.

Shortly after the hearing, Brownback and his counterpart on the House Science Committee, Rep. Dana Rohrabacher (R-Calif.), asked the U.S. Government Accountability Office (GAO) — the investigative arm of the U.S. Congress — to find out and report back just how much homework NASA had done before Readdy’s testimony to the subcommittee.

The GAO’s report, “More Knowledge Needed to Determine Best Alternatives to Provide Space Station Logistics Support,” was sent to Brownback and Rohrabacher May 18 and publicly released May 31.

The GAO concluded that while NASA was probably right about the difficulty and expense of offloading space station assembly missions this late in the program to launchers other than the shuttle, NASA had reached its conclusions primarily on the basis of an informal assessment by senior managers at the space agency’s headquarters here.

On the issue of space station logistics, however, the GAO took NASA to task for not doing a more thorough job investigating alternatives to the space shuttle for delivering supplies and equipment to the space station, questioning the validity of NASA’s conclusions.

“NASA’s assessment was insufficient to conclude that the shuttle was the best option for logistics support missions prior to the proposed retirement of the space shuttle in 2010,” the GAO report stated . “While we recognize that the extensive experience of its senior managers is an important element in evaluating alternatives, NASA relied primarily on headquarters expertise to conduct the informal assessment. NASA officials did not document the proceedings and decisions reached in its assessment. As a result, the existence of this assessment of alternatives cannot be verified, nor can the conclusions be validated.”

“It’s now clear that NASA had not done its homework on vetting space shuttle alternatives,” Brownback said in a statement issued ahead of the GAO report’s public release. “In particular NASA has not looked at very promising commercial opportunities to resupply the space station.”

Brownback said that NASA finally appears ready to take a serious look at commercial alternatives to the space shuttle, a change he attributed to the leadership of Mike Griffin, the agency’s new administrator.

Griffin was sworn in as NASA administrator April 14, about the time the GAO was wrapping up its nine-month investigation, and has said he plans to buy space station resupply services from commercial launch firms in the years ahead as a way to alleviate the demands on the space shuttle between now and its planned 2010 retirement.

Griffin has made the retirement of the shuttle orbiter fleet a top priority; he has said in congressional testimony and numerous public speeches he intends to pursue that course even if it means flying significantly fewer than the 28 flights Readdy and his team identified last year as essential to finishing the international space station. According to Griffin, only 18 of the planned 28 flights are station assembly flights. The rest are logistics and utilization flights that Griffin said could be either eliminated or possibly performed by vehicles other than shuttle.

NASA is currently evaluating how many shuttle missions it must fly to complete the international space station to the satisfaction of its partners in Europe and Japan, as well as NASA’s own research goals for the program. NASA’s current five-year budget plan, according to U.S. government sources, was built around the assumption that the agency ultimately will conduct fewer than 18 shuttle missions before retiring the orbiter fleet by October 2010, the start of the 2011 budget year.

One of Griffin’s first actions as administrator was to take away the responsibility of finding alternatives to the shuttle for resupplying the station from Associate Administrator Readdy and the Space Operations Mission Directorate and giving it to the Exploration Systems Mission Directorate, headed by retired U.S. Navy Rear Adm. Craig Steidle.

NASA currently is evaluating 26 informal proposals it received late last year from companies interested in delivering cargo to the international space station. NASA plans to release a request for formal proposals before the end of the summer.

In NASA’s response to the GAO, the agency said it agreed with the report’s findings and outlined the steps it was taking to pursue the purchase of space station resupply services from the commercial launch industry. NASA spokeswoman Katherine Trinidad said the agency declined any further comment on the report’s findings.

Comments: bberger@space.com