WASHINGTON — The U.S. Senate’s proposed defense spending bill for 2013 includes $50 million to study alternative approaches to space-based secure communications and missile warning, including the use of payloads hosted by satellites with other primary missions.

The proposed Department of Defense Appropriations Bill, 2013, approved Aug. 2 by the Senate Appropriations Committee, includes $20 million in Space Modernization Initiative (SMI) funding for the Space Based Infrared System missile warning system. The added funds would be used to examine ways to provide persistent overhead infrared surveillance, including hosted payloads, the committee said in a report accompanying its proposed legislation.

The Air Force is seeking $14 million next year for work to a follow-on to the Commercially Hosted Infrared Payload, which saw an experimental missile warning sensor launched last year aboard a commercial telecommunications satellite. The House version of the defense spending bill recommended denying that request.

Air Force budgets for major space mission areas including missile warning and communications typically include seed money for next-generation technologies and architectures in addition to funds for the primary development or operational programs. But SMI funds tend to be vulnerable when budgets get tight, as they are today.

A case in point is the Air Force’s Advanced Extremely High Frequency (AEHF) communications satellite system, used to provide secure, jam-proof links to strategic and tactical forces under all conceivable conditions. The AEHF program’s SMI funding falls under a budget subdivision called Evolved AEHF Milsatcom. The Air Force is requesting $53.6 million for Evolved AEHF Milsatcom next year, which is $180 million less than the service previously anticipated it would need.

“While the fiscal constraints that led to reductions in SMI are well understood, the Committee believes that limiting investment in this area increases the risk that the government will be locked into old technologies, suppliers, and concepts,” the Senate report said. Accordingly, the lawmakers recommended increases in SMI funding for the Space Based Infrared and AEHF programs.

The $30 million boost for the AEHF SMI account would be used for “radiation hardened manufacturing, hosted payloads, ‘design for affordability,’ and related efforts,” the report said.

The legislation follows an Air Force report delivered to Capitol Hill this past spring that outlines a number of potential SMI investments in secure satellite communications, including flying a tactical EHF demonstration payload aboard a dedicated small-satellite platform or as a hosted payload. The “Military Satellite Communications Space Modernization Investment Plan,” ordered up by Congress and dated April 2012, said the demonstration mission, if approved, would be completed by 2021.

The demonstration would cost $99.9 million between fiscal year 2013 and 2017 but the full projected cost is not included in the report. The Air Force is still working to determine the full projected cost of the demonstration, according to Christina Greer, a spokeswoman for the Air Force Space and Missile Systems Center in Los Angeles.

The schedule for the demonstration has not been determined because of funding uncertainties, Greer said via email Aug. 3. “If funded, the scope of the demonstration would encompass projected tactical waveforms and a suite of terminals conducting an end-to-end demonstration of protected tactical communication capabilities,” Greer said.

The Air Force report referenced a document approved in September 2010 by the Pentagon’s Joint Requirements Oversight Council that identified a number of gaps in the U.S. military satellite communications capabilities. The council, which helps set Pentagon spending priorities, is made up of the vice chiefs of staff of the U.S. military services.

According to the “Joint Space Communications Layer Initial Capabilities Document,” there will be shortfalls between 2018 and 2025 in both protected-tactical and wideband satellite capacity. Demand for protected tactical satellite communications capacity will grow by 50 percent over that time period, the document says.

The four-satellite AEHF system will be able to meet the Pentagon’s requirement for command and control of nuclear forces, the document says. However, only 25 percent of tactical-user demand will be met by the system, the document said.