BOSTON — The prime contract for the U.S. Air Force’s Transformational Satellite (T-Sat) Communications system is still scheduled for award late this year, but the service is now leaning toward inclusion of a legacy payload that will add considerable weight to the initial spacecraft.

According to Air Force and industry officials, the initial T-Sat satellites now are likely to include a radio-frequency payload that will enable them to communicate directly with their predecessors, the Advanced Extremely High Frequency (EHF) satellites. The Air Force has gone back and forth on the Advanced EHF cross-link requirement, dropping it from the program in 2006, only to add it back within the last month.

The final request for proposals for the multibillion-dollar T-Sat initial prime contract, to include the first two of a planned six satellites, is expected in May, according to industry officials. Contract award is still expected before the end of the year, despite the recent Air Force decision to delay the launch of the first T-Sat satellite from late 2014 to early 2016.

The T-Sat satellites will be equipped with laser cross-links and Internet protocol routers to dramatically increase bandwidth and transmission speeds available to U.S. forces — both stationary and mobile — around the globe. It is the follow on to the Advanced EHF satellite system, slated to launch starting next year, which will rely on radio frequency to provide assured communications to both strategic and tactical users.

Boeing Space and Intelligence Systems of Seal Beach, Calif., and Lockheed Martin Space Systems of Sunnyvale, Calif., are leading the industry teams competing for the T-Sat prime contract. Both teams are working on program technologies and designs under risk-reduction contracts worth $500 million apiece.

Air Force Brig. Gen. Ellen Pawlikowski, commander of the military satellite communications wing at Air Force Space and Missile Systems Center in Los Angeles, said the Advanced EHF cross-links were added back to the T-Sat requirements for two main reasons, one related to transmission security and the other to the decision to delay the program. She cautioned that the cross-link decision still must go through certain Pentagon approvals before becoming final.

When the Air Force first pulled the Advanced EHF cross-link payload from the list of T-Sat requirements, the plan was to rely on ground-based links to connect the two systems, which will operate concurrently for a number of years. However, direct satellite-to-satellite cross-links are considered to be more secure, and in fact the Advanced EHF systems and its predecessor, Milstar, rely on them exclusively, Pawlikowski said in a Feb. 22 interview. All three satellite systems carry the U.S. military’s highest-priority traffic, including messages for the command and control of nuclear weapons .

Sources close to the program said using ground-based relays between the T-Sat and Advanced EHF satellites would reduce the transmission speed and capacity of the systems .

The delay of the first T-Sat launch, which will have a ripple effect on the schedule of the subsequent satellites, also was a factor in the Advanced EHF cross-link decision, Pawlikowski said. The Air Force needs to maintain a constellation of four satellites in geostationary orbit to maintain global coverage in protected communications. The Air Force plans to deploy three Advanced EHF satellites, and the last Milstar satellite was launched in April 2003 .

Restoring the radio frequency cross-links is not technically complex or expected to be costly, but it would add significant weight to the T-Sat satellites, Pawlikowski said. She said the Air Force has not determined whether it will launch the initial satellites on medium- or heavy-lift rockets, but added that the weight of the Advanced EHF cross-links would not be a factor in that decision.

The 18-month T-Sat delay was formally disclosed with the unveiling of the Air Force’s budget request in early February. The Air Force is seeking $964 million for the program in 2008, which is about $500 million less than the service had planned on asking for at this time last year. Air Force officials attributed the decision to congressional reductions to past T-Sat budget requests and competing 2008 funding priorities.

Pawlikowski said a top-level review of the Boeing and Lockheed Martin T-Sat designs is still slated for April, in spite of the new schedule. She said, however, that the pace of work on the program will be slowed down in 2008 and 2009.

The stretch-out ultimately will increase the T-Sat program’s cost, according to industry officials. But Pawlikowski said it will have some benefit, such as better synchronization of the satellites with the U.S. Army’s effort to develop T-Sat user terminals.

Pawlikowski, along with officials of Lockheed Martin and Boeing , expressed a high level of confidence with the maturity of the laser and data-processing capabilities that could give T-Sat a 100-fold increase in bandwidth over secure communications satellites that are on-orbit today.

Pawlikowski said her confidence has been bolstered by independent testing on prototype hardware conducted by engineers at the Massachusetts Institute of Technology’s Lincoln Laboratory. Further evidence of progress on the program could come during the System Design Review scheduled for early April, in which Lockheed Martin and Boeing will present the Air Force with their T-Sat designs and plans, she said.

During a press conference Feb. 20 at the Satellite 2007 industry conference in Washington, John Peterson, T-Sat program director at Boeing Space and Intelligence Systems, said the program is hitting all of its milestones en route to a planned contract award by the end of October.

Under the Air Force’s phased, or block development, approach the first two T-Sat satellites will have less throughput capacity than subsequent versions. Peterson said Block 1 will consist of two satellites, with Block 2 composed of four more-capable satellites, including one ground spare. He said the reason for having five T-Sat satellites on orbit — as opposed to the four typically needed for a global geostationary constellation — has to do with the scaled-back capabilities of the Block 1 spacecraft.

In a Feb. 17 interview, Peterson said his confidence in the T-Sat program is based on the Air Force’s rigor in ensuring that the contractors are meeting technical criteria before clearing them to pass programmatic milestones.

Peterson said the Spaceway broadband communications satellite, built by Boeing for Hughes Network Systems of Rockville, Md., incorporates advanced data processing and routing technologies that are similar to what the company plans to use on the T-Sat program. Boeing also built one of the payloads on the Milstar satellite system.

Lockheed Martin is prime contractor on both the Milstar and Advanced EHF programs, with Northrop Grumman Space Technology of Redondo Beach, Calif., as its major subcontractor. The two have a similar arrangement for the T-Sat competition.

Len Kwiatkowski, vice president and general manager of military space programs at Lockheed Martin Space Systems , said the company’s Milstar and Advanced EHF experience will reduce risk associated with its T-Sat proposal.

Warren Ferster contributed to this story from Washington.