COLORADO SPRINGS, Colo. — The U.S. Missile Defense Agency (MDA) will not include a target-acquisition sensor in its forthcoming missile-tracking satellites, as part of an effort to streamline the system and control costs.

The agency’s new design for its next space-based missile-tracking system will be simpler than the two Northrop Grumman Space Tracking and Surveillance System (STSS) satellites now conducting a demonstration in space, according to MDA and industry officials.

The decision was made following a recommendation from the Johns Hopkins University Applied Physics Laboratory (APL), which has a lead role in studying design options for the forthcoming Precision Tracking Space System (PTSS).

Two Northrop Grumman satellites, which were born out of the former Space-Based Infrared System Low program, are now in orbit. They contain both target acquisition and tracking sensors. Together, the sensors have proven the ability to conduct “birth-to-death” sensing of ballistic missile launches. While the acquisition sensor is designed for detecting a hot missile plume, the tracking sensor is optimized for tracking a cold warhead during its difficult-to-detect midcourse of flight.

For PTSS, however, MDA is opting to forgo the target-acquisition sensor and design a satellite only with tracking capability, according to defense officials. This approach is taken mainly to simplify the satellite design and with an eye toward lowering risk and cost in making the satellites.

Although the STSS approach relied on a self-cueing capability with the onboard target acquisition sensor, PTSS will drive MDA toward improved sensor command-and-control and networking capabilities. A PTSS satellite would have to rely on offboard cues — likely from missile-warning satellites in geosynchronous orbit — to begin searching for a target prior to tracking. STSS, and the future PTSS satellites are designed for operations in low Earth orbit.

This design choice comes as a surprise to some industry officials who expected the Pentagon to buy clones of the STSS spacecraft in an effort to reduce risk by producing an existing design.

This decision clearly derails Northrop Grumman’s attempts to sell copies of STSS. However, the company is still pursuing the business, along with several other contractors.

APL is conducting a study to sort out a final design. In March, MDA conducted a system requirements review with APL for PTSS.

APL has issued six subcontracts to companies that can provide input for the final design, but an acquisition and manufacturing plan is not yet firm. Those six companies are Lockheed Martin, Boeing, Northrop Grumman, Raytheon, Ball Aerospace and Orbital Sciences Corp.

Ultimately, MDA hopes to award a contract for 9-12 satellites in fiscal 2014. The agency has requested about $1.2 billion over five years in the fiscal 2012 budget for PTSS.