WASHINGTON — Boeing unveiled its team March 28 in the competition to build upper stages for NASA’s planned Ares 1 crew launcher, a program that represents the company’s last chance for the next several years to win a major hardware-building role in the emerging U.S. human space exploration program.

Bids are due April 13 for the estimated $900 million contract, scheduled for award late this summer, to produce the hardware based on NASA specifications. The competition pits Boeing’s team, which includes Northrop Grumman, against one led by Alliant Techsystems.

“We are the low-risk offer as everyone on this team has the experience in the jobs we’re going to do on Ares 1, so we’re keeping the risk to NASA low and we think we have a very competitive offer,” Jim Chilton, vice president of Boeing Exploration Launch Systems, Huntsville, Ala., said. “Our team was built around NASA’s requirements.”

Boeing built NASA’s fleet of space shuttles and is prime contractor on the international space station. But the company has yet to land a big piece of Project Constellation, which encompasses the hardware NASA will use to ferry astronauts and associated cargo to low Earth orbit starting in 2015, and to the Moon by 2020.

In August, a Boeing-Northrop Grumman team lost out to Lockheed Martin Space Systems of Denver in the competition for Project Constellation’s biggest plum so far, the $4 billion Orion Crew Exploration Vehicle contract. Orion capsules will be launched by the Ares 1 expendable rocket, whose main stage is being developed by Alliant Techsystems Launch Systems Group based on the space shuttle solid-rocket motors that the company builds.

Boeing and Northrop Grumman billed themselves as a team of equals in the Orion competition. For the Ares 1 upper-stage work, Boeing is clearly the team leader, with Los Angeles-based Northrop Grumman identified as a supplier responsible for producing the composite interstage hardware.

The other members of Boeing’s team are: Hamilton Sundstrand, Windsor Locks, Conn. ; Moog, East Aurora, N.Y.; Orion Propulsion Inc., Madison, Ala. ; SUMMA Technology Inc., Huntsville; Chickasaw Nation Industries, Ada, Okla.; United Launch Alliance, Denver; and United Space Alliance, Houston. United Launch Alliance and United Space Alliance are Boeing-Lockheed Martin joint ventures that operate expendable rockets and the space shuttle, respectively. In its press release, Boeing described Chickasaw Nation Industries as “a tribally-owned small business” that specializes in logistics support and inventory control.

Alliant Techsystems’ competing team, unveiled in September, includes Lockheed Martin and Pratt & Whitney Rocketdyne of Canoga Park, Calif., which is under contract to produce the Ares 1’s upper-stage engine, the J2-X.

NASA expects to award the upper-stage production contract in August. The rocket’s avionics system is being acquired separately, with a request for bids due out this spring, to be followed by a contract award late this year.

Chilton told reporters during a March 28 conference call that the company decided to hold off finalizing its team membership until after NASA had released the final solicitation for the upper-stage work, which occurred Feb. 23.

In contrast to the Orion program , NASA is not asking industry to propose designs for the upper stage. Instead, the agency is seeking only plans for how the bidders would manufacture the NASA-designed hardware reliably and affordably.

“This is not NASA buying a designer. NASA is actually the designer,” Chilton said. “We chose to wait to make sure we built our team around NASA’s requirements.”

Among those requirements is concentrating the engineering work force in Huntsville to work alongside NASA’s civil servant-led design team at Marshall Space Flight Center, and using the Michoud Assembly Facility outside New Orleans for final assembly of the flight hardware.

Another requirement handed down by NASA is that the winning contractor share nearly a fifth of the work with businesses classified as small or disadvantaged.

“This work statement is a natural for small business,” Chilton told reporters.

The Alliant TechSystems team also includes small businesses, including some of the same ones on Boeing’s roster, said Ron Dittemore, president of Alliant’s Launch Systems Group of Promontory, Utah.

“Many of those that you heard today in [Boeing’s] announcement are merchant suppliers that will provide their services and products to both teams just as a matter of course, whether they are small disadvantaged businesses or whether they are somebody like Hamilton Sundstrand or Moog who are known in the industry for their products and will be suppliers to both teams,” Dittemore said in a March 28 interview.

The Ares 1 upper-stage production contract is the biggest award remaining under Project Constellation for the next few years. NASA does not anticipate awarding contracts for Ares 5, the heavy-lift vehicle that will needed to loft cargo in support of astronaut lunar landings, until sometime after 2010.

NASA intends to order two upper stages per year during the early years of the Ares program, and has asked the contractor teams to show how they would ramp up to support a production rate of six per year .

Chilton said the contract could be worth as much as $900 million initially, and potentially much more over the long run. “This could be in production for a long time,” he said. “This is how the United States is going to put people into space.”