The U.S. Missile Defense Agency has said the follow-on program to its missile tracking Space Tracking and Surveillance System (above) is likely to be one part for a multi-mission Defense Department satellite. Credit: MDA.

WASHINGTON — The U.S. Missile Defense Agency and the Pentagon are studying the organization’s long-term need for sensors that detect ballistic missiles, a move that could help determine the size of the agency’s missile-tracking satellite constellation in the 2020s.

The study, known as an analysis of alternatives, would compare alternate sensor architectures and help inform the agency’s future budget requests, Richard Lehner, an MDA spokesman, said. The analysis would include land, sea, airborne and space-based sensors, but ultimately could provide a framework for how many missile-tracking satellites the agency needs.

Already, the MDA is flying two demonstration satellites as part of its Space Tracking and Surveillance System (STSS). Those satellites, built by Northrop Grumman, launched in 2009 into what the MDA describes as a tandem low Earth orbit.

By virtue of their ability to hand off data to one another, the satellites have demonstrated the ability to track target missiles from launch until atmospheric re-entry. Northrop Grumman officials said the satellites have taken part in about a dozen intercept tests and 150 other tests with the agency since their launch.

But for years, industry and government officials have wondered what comes next.

The agency has long hoped to develop a constellation of low Earth orbiting satellites as a cueing tool for its ground-based radars and targeting systems. MDA officials have said repeatedly in recent months they want to make greater use of space.

STSS satellite prepared for delivery. Credit: MDA

“The wealth of data and lessons learned from the STSS satellites efforts continue to provide insights as MDA pursues longer term space sensor needs,” the agency said in its budget request for 2016. “The on-orbit sensors collect invaluable background, scene and target signatures to support” the MDA.

In February, Navy Vice Adm. James Syring, the head of the MDA, said there is still a need for satellites capable of tracking missiles in midflight. But the future for the STSS satellites has been murky at best.

Syring told reporters then that the MDA is “working through concepts on what might be possible” for a follow-on program to STSS, but added that there is no current plan for such a system.

MDA requested $30 million for the STSS program this year and another $94 million through 2020, according to budget documents.

For any future system,  MDA officials have said they would likely work with the Air Force or another Defense Department agency. The STSS demonstration satellites also support the Air Force’s space situational awareness mission, which has taken on increased importance in the last year following a Defense Department review of the military’s space assets and emerging threats from China and Russia.

Northrop Grumman’s own projections show the MDA could provide global protection with 10 satellites, but that the agency could take advantage of more localized protection with fewer satellites, said Randy Weidenheimer, the company’s director of advanced missile defense and warning programs. The analysis is considering both regional and homeland defense mission.

The demonstration satellites had a design life of four years, but Northrop Grumman officials now say they expect the satellites to last as many as six more years, through 2021. In addition, the satellites are now providing data for about 50 minutes of each 100-minute orbit. That figure has been as high as 75 minutes, Weidenheimer said, and is a significant improvement from the 10 minutes per orbit figure the mission originally required.

The analysis of alternatives the MDA and the Pentagon are conducting also would consider the agency’s use of hosted payloads, government and industry officials said. The MDA requested funds this year for the Spacebased Kill Assessment program in which space-based sensors would verify whether incoming missiles have been destroyed by defensive interceptors and thus no longer pose a threat. The program, first disclosed in the MDA’s 2016 budget request, appears to represent the agency’s first known foray into commercially hosted payloads, whereby organizations fly dedicated instruments aboard commercial satellites.

Weidenheimer said the company is doubtful the STSS mission would be a good fit as a hosted payload because of the size of the sensor.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.