President Barack Obama today said without hesitation that the missile that shot down Malaysia Airlines Flight 17 was launched from within territory controlled by pro-Russian separatists in Eastern Ukraine. While he didn’t go into the sources the US used to pinpoint the launch, early reports say that US intelligence had identified the infrared signature of a missile launch just before contact with the airliner was lost.

That information likely came from one of a network of satellites operated by the Air Force and the National Reconnaissance Office (NRO), the US intelligence community’s spy satellite operations agency. Using highly sensitive infrared sensors and other electronic intelligence gathering sensors, these satellites can detect a variety of ground-based missile systems, as well as some aircraft, by their infrared signature. They also carry sensitive electronic intelligence sensors that can detect radar signals associated with anti-aircraft missile systems like the Buk launcher that has been widely pointed to as the culprit in the MH17 downing.

The latest of these satellite systems is the Space Based Infrared System (SBIRS), the successor to the long-running and euphemistically named “Defense Support Program” (DSP) satellite system. The DSP started in the late 1960s and continued in various forms through the last decade. A portion of the DSP constellation of satellites continues to function today and has been considered for use in tracking forest fires and potentially forecasting impending volcanic eruptions.

The unblinking eyes in the sky

DSP satellites were built with Cold War specifications to detect Soviet and Chinese ballistic missile launches. They needed to be able to detect even the relatively low infrared signature of submarine-launched missiles. Because their sensors were so sensitive, they frequently picked up forest fires and refinery fires from space. In December of 1975, a message was sent from the Ford administration’s Deputy National Security Advisor William Hyland to Hal Sonnenfeld, Secretary of State Henry Kissenger’s adviser, about a potential Soviet attempt to blind a DSP satellite with a strong infrared signal. It turned out to be a pipeline fire.

During the Iran-Iraq War of the late 1980s and the Persian Gulf War in 1991, DSP satellites detected the launch of Iraqi “Scud” missiles and even surface-to-air missile batteries. And a capability called “Slow Walker” developed in the 1980s allowed satellites to track aircraft afterburner exhaust, a capability pushed by the US Navy to help it defend against potential attack by Soviet Tu-22 “Backfire” bombers.

In 1995, as the Cold War came to an end and the demands on satellite infrared systems increased, the Air Force launched the SBIRS program. Built under the direction of the US Air Force’s Space and Missile Systems Center’s Infrared Space Systems Directorate, SBIRS was designed for four mission areas:

Strategic ballistic missile launch warning for the president and the Defense Department leadership

Theater and strategic missile defense information, to provide early targeting data to systems such as the Aegis Ballistic Missile Defense system aboard US Navy cruisers

Collecting technical intelligence on potential adversary’s missile systems

“Battlespace awareness”—real-time information provided to military commanders about infrared “events” that could affect forces in the field and provide data for strike planning against launch systems.

The Air Force’s SBIRS program was intended to have two components: “SBIRS High,” the geosynchronous portion of the surveillance network, and “SBIRS Low,” a low-orbit system that could track ballistic missiles from launch through mid-course of their flight.

Plan B

But the SBIRS High program ran into repeated trouble. To verify the functionality of SBIRS Low, two NRO signals intelligence satellites launched into highly elliptical orbits in 2006 and 2008. However, a geosynchronous NRO satellite launched in 2007 failed after only 7 seconds in orbit, resulting in further delays.

The Air Force SBIRS Low program had similar problems. It was cancelled and resurrected as the Space Tracking and Surveillance System (SSTS) and handed over to the Missile Defense Agency (MDA) as the Bush administration pushed ahead with ballistic missile defense research. Two SSTS satellites were put in orbit in September of 2009. But the MDA decided not to take SSTS any further. A month after the SSTS launches, the MDA kicked off the Precision Tracking Space System program—a program that was killed in 2013.

All the while, existing infrared satellites were expiring, and the Air Force started to explore alternatives to SBIRS. The service continued to launch DSP satellites until 2007, at which point its leadership started looking for a SBIRS alternative. That plan B, the Alternate Infrared Surveillance System (AIRSS) was later renamed the Third Generation Infrared Surveillance (3GIRS) program and was led by Raytheon and defense contractor SAIC. It quickly picked up steam as a lower-cost alternative—it used a “full earth staring sensor” that could watch an entire hemisphere of the planet for infrared plumes. But despite being on track and on budget, 3GIRS was cancelled in 2011 as the first SBIRS geosynchronous satellite was successfully put into orbit.

So far, the DOD has spent $2.35 billion on the SBIRS High satellite program, and it has two satellites in orbit. The SSTS satellites and NRO satellites have exceeded their expected lives but still remain in orbit—as do some later DSP satellites. And they have all been pressed into service for monitoring emerging potential threats, such as the flashpoints on Ukraine’s eastern border.

It's for that reason that NRO and Air Force satellite assets were most likely watching the area near Donetsk, Ukraine, yesterday as an anti-aircraft battery launched a single missile at the Malaysian Airlines Boeing 777, bearing witness to a tragedy that no missile defense system was ever intended to thwart.