Engineers and managers at NASA are sure to change their new reference vehicle designs for the government’s next heavy-lift and human-spaceflight vehicles, because they’re already saying they don’t have enough money to carry them out. But key senators are insisting that they do.

Congress and President Barack Obama authorized $6.9 billion over the next three years to develop a new heavy-lift space launch system (SLS), and another $3.92 billion for a multipurpose crew vehicle (MPCV). They also set a Dec. 31, 2016, deadline for “operational capability.” NASA says the funding won’t cover it.

“To date, trade studies performed by the agency have yet to identify heavy-lift and capsule architectures that would both meet all SLS requirements and these goals,” states a 22-page “preliminary” report on its plan to develop the vehicles sent to Congress Jan. 10 under the NASA authorization act signed by Obama last year. “For example, a 2016 first flight of the SLS does not appear to be possible within projected FY 2011 and out-year funding levels.”

Nor, NASA concluded, is “a 2016 crewed first flight” feasible with the funding authorized, even though the agency’s engineers at Marshall Space Flight Center and Johnson Space Center used as much heritage hardware from the space shuttle and the follow-on Ares I and Orion efforts as they could.

On Capitol Hill, senators behind the authorization act rejected the conclusion, urging the agency to try again.

“I talked to [Administrator] Charlie Bolden yesterday and told him he has to follow the law, which requires a new rocket by 2016,” says Sen. Bill Nelson (D-Fla.). “And . . . within the budget the law requires.”

Nelson, who flew as a shuttle passenger under Bolden’s command in 1986 and strongly supported him for the top post at NASA, was joined in his view by other members of the Senate Commerce Committee, which oversees the agency.

“NASA must use its decades of space know-how and billions of dollars in previous investments to come up with a concept that works,” the senators say in a joint bipartisan statement. “We believe it can be done affordably and efficiently—and, it must be a priority.”

The “reference vehicle design” for a heavy-lift SLS incorporates five space shuttle main engines (SSMEs); a core stage based on the 27.5-ft.-dia. shuttle external tank; two five-segment versions of the four-segment solid-fuel shuttle booster rockets and an upper stage powered by one or two J-2X engines in development for the Ares I crew launch vehicle.

For the new MPCVs, crews of two to four would ride in the deep-space version of the Orion crew exploration vehicle, adapted to provide backup flight capability to the International Space Station in case commercial crew vehicles being developed separately do not materialize.

NASA officials stress that while the designs meet congressional requirements that the government’s shuttle follow-ons use existing hardware (the 15 existing SSMEs, for example), contracts and workforce as much as possible, the reference vehicles are not necessarily the final choice. Internal NASA teams also are studying a kerosene-fueled alternative to the liquid-hydrogen-fueled SSME, and a modular approach that would array three smaller-diameter stages in parallel—comparable to the Delta IV-Heavy configuration. In addition, 13 companies are conducting six-month studies of technologies that might help NASA refine its heavy lifter.

Cris Guidi, an engineer who focuses on launch vehicles as deputy director of the Constellation Systems Div. at NASA headquarters, says results of the company and internal-NASA studies will drive the final vehicle design, within whatever budget constraint NASA faces this spring as the new Congress tackles its Fiscal 2011 appropriation and the White House issues a Fiscal 2012 budget request.

“Our baseline position right now is the shuttle-derived/Ares-derived vehicle, but depending on how all [these] data integrate and flow out from the analysis, there is that potential we may change our approach,” she says.

NASA plans to update its designs and details for fulfilling them in April. The agency is currently funded under a continuing resolution that expires March 4, which contains money for work on Constellation programs like the J-2X and the five-segment solid-fuel booster originally intended as the first stage for the Ares I. The Senate’s appropriation report for Fiscal 2011 would fund the heavy-lift SLS at $1.9 billion in Fiscal 2011—$300 million more than carried in the authorization act—and cap its development at $11.5 billion through Fiscal 2017.

For the MPCV, the Senate appropriations language could keep Fiscal 2011 funding at about the $1.1-billion level in Fiscal 2011 that is authorized, and cap overall funding for an “Orion crew exploration vehicle” at $5.5 billion through Fiscal 2017. According to the preliminary report, NASA recently estimated it would need $6.6-7.1 billion through 2015 to achieve a first flight in that year, on top of the $4.9 billion already spent.

The reference vehicle design for the MPCV is the Orion vehicle originally intended to carry crews back to the Moon, with the capability to service the space station. It would support a crew of 2-4 for 21.1 days inside 690.6 cu. ft. of pressurized volume, 316 cu. ft. of that habitable. For spacewalks, the crew compartment would have to be depressurized.

The vehicle’s main engine would generate 7,500 lb. thrust, and on a lunar return the capsule could use a skipped-entry capability to traverse as much as 4,800 nm. from its initial atmospheric entry point. Nominal landing would be in the Pacific Ocean off the California coast.

With those capabilities, NASA concludes, the Orion would be able to support crew operations on deep-space missions beyond the Moon to Lagrange points, asteroids and eventually Mars, as required by Congress. But filling in for a commercial crew vehicle to the ISS would be “highly inefficient.”

Nor is the current uncertainty over the agency’s long-term funding conducive to maintaining the reference vehicle designs or meeting the congressional deadline. For both designs, the report stresses that “development . . . will be dependent on sufficiently stable funding over the long term, coupled with a successful effort on the part of NASA and the eventual industry team to reduce costs and to establish stable, tightly managed requirements.”

On Capitol Hill, NASA faces a new Republican-controlled House where a vocal faction is raising the possibility of a return to Fiscal 2008 funding levels, which would make the space agency’s already difficult fiscal position even more fraught. And the administration’s Fiscal 2012 budget request is due out on Feb. 14. Against that background, NASA is telling Congress that Bolden is insisting that exploration systems be “affordable, sustainable and realistic.”

“[He] is very strongly emphasizing that we’re going to develop a credible plan,” Guidi says, noting that the traditional engineering push for more performance may take second place to practicality in the current funding environment.