Since President Ronald Reagan's time, U.S. Missile Defense experts have pursued the notion of “birth-to-death” tracking of ballistic missiles to improve the chances of an intercept. Though the billions of dollars spent on a new missile warning system have begun to bear fruit, the Pentagon is still struggling with workable blueprint to provide solid coverage, particularly in the infrared spectrum, during the crucial midcourse of a missile's flight—when it is most likely to be intercepted.

Advances with two Space Tracking and Surveillance System (STSS) demonstration satellites have proved that midcourse, space-based infrared tracking can alert Navy ships to launch interceptors accurately before their radars can see the incoming missiles. A test in February was an eye-opener for the Navy, which now hopes that improved sensors outside of the ship's radar—combined with responsive communications links—can reduce the number of Aegis assets needed to patrol for the anti-ballistic missile mission.

But, only months after the seminal test, the Pentagon announced in its fiscal 2014 budget request it was terminating the Precision Tracking Space System (PTSS), a follow-on to STSS. Through PTSS, the U.S. Missile Defense Agency was pursuing a more simple satellite under the leadership of the Johns Hopkins University Applied Physics Laboratory (APL).

The termination comes as the U.S. intelligence community has all eyes watching for a mobile missile launch from North Korea, which has vowed to attack American cities and interests abroad. Though the Pentagon is building more interceptors as a response to Pyongyang's aggression, a hole in the U.S. missile defense tracking net remains. And, missiles from North Korea, China and possibly Iran are becoming more sophisticated, potentially able to deploy more complex countermeasures that could fool radars.

The termination was partly a result of harsh fiscal cutbacks at the Defense Department. But, some in industry wonder whether the steps taken by then-MDA Director Army Lt. Gen. (ret.) Patrick O'Reilly in developing the program doomed it. He assigned the laboratory to lead the design and build of the first two PTSS demonstrator satellites, an unconventional approach possibly crafted to reduce industry's influence over the design. MDA officials, at the time, were concerned with poor quality control in industry and a perception of high fees charged for services. O'Reilly's strategy never won full support from industry and its powerful lobbies in Congress.

So, Pentagon officials are once again studying options. Some question whether the Pentagon is merely “studying the question to death” in order to avoid proposing a new, high-cost satellite program to Congress.

By launching on remote—as was done in February—operators have more time to engage a target because the satellites are able from the vantage of space to see the ballistic missile before it can be detected by the Aegis ship's SPY-1 radar. “Launch-on-remote” depends on disparate systems to work in concert as one weapon using communications infrastructures.

This is key for an overarching missile defense, which by nature requires global engagements that far exceed the abilities of any one set of sensors or interceptors.

STSS demonstrated the “art of the possible” of tracking ballistic missile targets from space, Air Force Space Command chief Gen. William Shelton told Aviation Week this month. “If you have got the capability to provide [infrared] tracking from space, you can do really cold-body tracking [and] you can rely less on ground-based radars” for midcourse discrimination.

STSS was designed with both acquisition and tracking sensors—separate systems optimized to acquire the target as it is boosting and track it against the cold backdrop of space in its midcourse of flight. In an effort to reduce the price of the program, officials at the APL suggested a design that allows for Space-Based Infrared System (Sbirs) High satellites to manage the target acquisition role, leaving only the infrared bands on a PTSS sensor required for cold-body tracking in the midcourse of flight. And, PTSS was to prioritize a larger telescope than STSS and rely on subtle movements in space for tracking, not a sophisticated, gimbaled design.

MDA had planned to launch two PTSS demonstration satellites in 2017, which is now off the table. They were to be a follow-on demonstration to Northrop Grumman's STSS spacecraft that placed two satellites in orbit in 2009.

The PTSS termination raises a question of whether the Pentagon is risking a midcourse tracking gap. The STSS satellites were designed for a two-year in-orbit life, which has already been exceeded. And the spacecraft, which carry gimbaled infrared sensors, still have redundant systems. “If you don't get a failure early on in [a satellite's] life, it could go on for a long time,” says one industry official. Northrop is working to extend their service lives. “Current trends suggest that these satellites should be available for several more years,” says Bob Bishop, a company spokesman. However, program officials have not said just how long the satellites could last in orbit. Furthermore, STSS was intended to be a demonstration and, in its inclined position in low Earth orbit, provide only limited coverage with two satellites operating in tandem.

The ultimate goal from more than a decade ago was near-persistent coverage, a concept unlikely to be palatable in today's budget environment, and one that is being reevaluated. Officials are said to be once-again reviewing architecture concepts. Still on the table are hosted payloads, though operators are loath to consign missile-tracking sensors to a backseat when it comes to a primary spacecraft's mission, which is typically the case for a hosted payload. Radar advocates are also pushing for the use of such capabilities as the AN/TPY-2, multiples of which can be “stacked” for improved range. Radars, however, require a protected area from which to operate, which can be tricky when dealing with some host nations.

At issue in these studies is striking a balance between the infrared and radar phenomonologies. “Radar does its job by reflecting off of objects and IR does its job by detecting differences in temperature” between a missile and the cold backdrop of space, the industry source says. “Having two phenomonologies look at something makes it easier to do . . . discrimination” of a warhead and countermeasures.

The STSS satellites were crafted from parts fabricated during the defunct Air Force Sbirs-Low program and later put in storage once that project was terminated. Sbirs Low was intended to be a low-Earth-orbiting complement to the service's Sbirs-High infrared missile-detection satellites. Once resurrected as STSS, the program was transferred to MDA for management, and the Air Force focused on Sbirs High, but dropped the “high” portion of the moniker.

Sbirs has billions of dollars worth of overruns relating to technical problems and years of delay in service. But, after all of this scar tissue, commanders crow about its performance.

Two Sbirs payloads are in highly elliptical orbit (HEO) on classified host satellites, and the second satellite was lofted into geosynchronous (GEO) orbit in March. Though the GEO satellites are not yet certified for missile-warning messages, Air Force officials brag about their capabilities in detecting targets after launch. And, they are capable of capturing “dimmer” targets, Shelton says. These include shorter-range missiles or other “infrared events,” such as rocket flashes. “Has it been more expensive than it should have been? Absolutely. But, we are getting great operational capability from HEO and GEO.”

The second Sbirs satellite achieved “first light,” and officials expect that it will be certified to warn commanders of ballistic missiles by year-end, says Jeff Smith, vice president of the program for prime contractor Lockheed Martin.

First light means the cover for the sensitive infrared payloads—a scanner and a starer—were removed. The system is now being calibrated.

This satellite was launched March 19 on an Atlas V from Cape Canaveral. GEO-1 was launched in May 2011. Its scanner has yet to be certified to deliver Integrated Tactical Warning/Attack Assessment messages, though approval is expected soon. These ITWAA messages are used to tip off U.S. missile defenses on incoming targets. The Air Force has prioritized use of the scanning sensor, leaving the newer staring sensor for certification later. The Sbirs scanner is faster than the Defense Support Program (DSP), which scans its field of view once every 10 sec.

As a replacement for the DSP, Sbirs will be responsible for providing information on targets—such as launch point, vector and impact point. Its data will be fed into the Missile Defense Agency's Command, Control Battle Management and Communications System, which links to sea- and ground-based interceptors in the field.

Because Sbirs GEO-1 was the first of a new breed of spacecraft, ITWAA certification has been a long journey. Officials, citing security concerns, will not provide details on what, specifically, has taken so long to vet. But, Smith says GEO-1's scanner is in what is expected to be the final, 30-day trial period. “It is a rigid structured process, and we are just checking every box.”

GEO-2 is in en route to its operational location. Once in place, the two GEOs in orbit will be able to provide “stereo” coverage from launches from the Middle East to the Pacific region. “That gives you a much more accurate . . . launch point, state vector and impact point” for targets. Shelton refers to an accurate state vector at booster burnout as the “holy grail.”

Two scanning payloads are also continuing operations on separate, classified satellites in highly elliptical orbit.

Meanwhile, Lockheed Martin has begun work on GEO-3, and HEO-3 is slated for delivery within six weeks. The company has submitted a proposal to the Air Force for production of GEO satellites 5 and 6. A contract award is expected by the end of September, when the fiscal year ends.