Military Embedded Systems

Airborne and satellite sensor systems


October 22, 2015

Ray Alderman

VITA Standards Organization

EVOLUTION OF WARFARE Blog: Those nations that are best prepared often succeed the most at winning conflicts or avoiding them in the first place. This thought is expressed even better in Latin: "Si vis pacem, para bellum." Translated as "you want peace, prepare for war," and originally stated by Publius Flavius Vegetius Renatus in De Re Militari around the 4th or 5th century BC.

A key part of such preparation are aerial reconnaissance missions, which started in earnest in World War I (WWI), with biplane pilots flying over enemy territory and drawing maps of their troop and artillery positions. Upon landing, those maps were given to U.S. ground commanders, to use in deploying defenses and planning offensive missions.

Aerial intelligence platforms

Airplanes changed everything about reconnaissance, from PHOTINT (PHOTographic INTelligence) and IMINT (IMaging INTelligence) to COMINT*, ELINT*, and TELINT*. There are basically two levels of aerial RECON: tactical and strategic. Tactical missions direction find the transmitters of enemy forces on the local battlefield and direct artillery fire or bombing missions on those positions. Strategic missions direction find and locate enemy air defense systems (SAMs, anti-aircraft artillery, etc) for destruction by bomber aircraft or cruise missiles in a time of war.

Aerial intelligence platforms range from single-engine QU-22 planes with a pilot and an intercept operator, to RC-135 platforms (converted KC-135 tankers) with a full crew of linguists, intercept operators, and ELINT specialists.In between, Aerial RECON missions used converted B-47 bombers, C-123, and C-130 converted cargo planes, U-2’s and SR-71’s, early unmanned drones, and a host of other platforms too numerous to list here. For a complete recap of all these planes and missions, read Col. Bill Grimes book, “The History of Big Safari." The Big Safari program was responsible for building these specialized platforms, and they consistently did it in a matter of months and under budget.

To read more Evolution of Warfare Blogs by Alderman, click here.

As you can imagine, the first aviation platforms for intelligence were equipped with cameras and film. Some of these cameras were the size of a car, which is why they used converted cargo planes for their missions. The early PHOTINT systems used film that was 18 inches by 36 inches, to get the needed resolution. Once the pictures were taken, the planes flew back to base, handed over the film canisters, and prepared for their next mission. Meanwhile, the film would be flown by other planes half way around the world, to the National Security Agency (NSA) in Maryland for processing and analysis. Eventually, those RECON planes housed radio receivers, intercept operators, and linguists to record all manner of electronic signals.

One particular mission stands out, to give you an idea of what the Air Force was doing during the Cold War. In the 1980’s, the U.S. Air Force was running COMBAT SENT operations in the Black Sea, to collect ELINT (Electronic Intelligence) information on Russia's new SA-5 and SA-10 surface-to-air missile radar (by collecting waveforms, frequencies, protocols, etc) during their military exercises. Maj. John “Box” Elder was flying his RC-135U, a four-engine jet-powered KC-135 tanker plane converted for intelligence missions, with a crew of analysts, Russian linguists, and intercept operators. He spotted a Kiev-class Russian carrier and swung into position so the Russians would track him with their air defense radar and he could intercept and record their signals.

The Russians knew he was an ELINT plane, so the carrier turned-off their SAM radar to thwart his mission. Elder then turned his aircraft into a rear approach to the carrier, began to reduce his altitude and speed on the proper slope, turned on his landing lights, lowered his landing gear, lowered his flaps, and maintained a perfect glide-slope as if he was preparing to land on the carrier deck. The Russians were waving him off with signal paddles and on their radios in English, but, Elder stayed on slope in a perfect landing pattern. So, the Russians turned-on their SA-5 and SA-10 SAM radar systems, to lock-on Elder’s plane to shoot it down before it could crash-land on the flight deck. Elder’s crew then recorded all the radar signals they came for and flew away.

For many years, these aerial intelligence platforms violated Russian airspace, to test Russia’s air defenses. In September of 1958, Russian MIGs shot-down Sun Valley 1, a C-130 SIGINT platform, killing all 17 intelligence people onboard near Sasnashen, Armenia. In December 1965, Pee Wee III, an RB-57 ELINT plane was shot down by Russian MIGs over the Black Sea, killing the pilot and the mission operator. From 1950 to 1969, 16 U.S. planes were shot-down by the Soviet Union. And that does not include the U.S. intelligence planes shot-down by the North Koreans and Chinese in the history of the aerial reconnaissance. In April 1969, the North Koreans shot-down a Navy EC-121 SIGINT* plane off their coast.

The history of IMINT and SIGINT reconnaissance is wide and deep, too much to recount here. Again, read "The History of Big Safari” by Col. Bill Grimes, and then read “By Any Means Necessary: America’s Secret Air War In The Cold war” by William E. Burrows for more entertaining detail. For the Vietnam era, read “Unlikely Warriors” by Lonnie M. Long and Gary B. Blackburn. This book covers the missions of my old military intelligence alma mater, the Army Security Agency.

After Francis Gary Powers' U-2 was shot down over Russia in May 1960, and Rudolf Anderson’s U-2 was shot-down over Cuba in October of 1962, it was time to find a better way to collect intelligence from the air.


First, let’s get some satellite classifications out of the way. There are four basic mission categories for intelligence satellites: (1) early warning (missile launch detection), (2) nuclear explosion detection, (3) photo/image surveillance (two types: close look and area scanning), and (4) electronic surveillance (capturing signals).

Another way to classify satellites is by their size. Presently, we have platforms in orbit ranging from the size of a school bus to a soccer ball. Newer satellites (both planned and in orbit) come in four different sizes: Micro (10-100Kg), Nano (1-10Kg), Pico (0.1-1Kg) and Femto (<100 grams).

If you doubt these small satellites, look at the Army’s SMDC-One: 100mm x100mm x 300mm (a CubeSat) weighing 4.5Kg (9.9 lbs). Seven have been built. Four have been launched since 2010. If you want more information, look at the technical specifications NASA says it costs about $10,000 per pound to put an object into orbit, so we have to make them smaller and lighter.

Starting in 1959, the U.S. launched 144 Corona satellites into space to photograph Russia and China. They were designated KH-x satellite systems with progressively upgraded IMINT packages. KH was the acronym for “Keyhole”, the mission codeword. The KH-4A and 4B satellites carried the first ELINT packages and were in use through the 1970’s. KH-9 Hexagon was referred to as “Big Bird”, with an advanced camera that had a resolution of 3 to 4 feet.

Strange as this may sound, these PHOTINT satellites would drop “film buckets” (reentry capsules) from space into the atmosphere, where they would eventually shed their heat shields, deploy a parachute, and be caught by the Fulton Recovery System on a C-130 aircraft flying in the reentry area. It was a big net attached to the plane. You have to see it in old photos to believe it. The film buckets, once caught, would be winched aboard the aircraft and carried back to base, transferred to another long-range plane, and flown to a top secret location in Maryland for film processing and distribution to intelligence analysts. This was the first space-based sensor network ever deployed, crude as it was. The Russians followed suit by launching over 500 of their own Zenit PHOTINT/IMINT (and then ELINT) satellites from 1961 to 1994.

In the early 1960s through the 1970s, 12 Vela satellites were launched by the U.S. (designated Vela 5A, 5B, 6A, 6B types). The mission was MASINT: to detect nuclear explosions from weapons testing by Russia, China, and other nations. The signature double-flash of the explosion, the associated gamma ray burst, and the electroMagnetic pulse, or EMP, are all indicators of a nuclear explosion. Vela always knew where it happened and who did it. That’s why North Korea tests their nuclear weapons underground.

From 1968 to 1977, the U.S. launched seven Canyon satellites (designated OPS-xxxx) that were specifically built for SIGINT missions. In the 1980s and 1990s, the Canyon systems were replaced by six Vortex satellites (previously named Chalet) with advanced SIGINT packages. The first four carried OPS-xxxx designations, and the last two were USA-xx designated.

Also in the 1970s, the U.S. launched four Rhyolite satellites into space for specific SIGINT missions (designated OPS-xxxx). The Russian military believed that their terrestrial line-of-sight microwave communications links were secure from snooping. U.S. intelligence people found that the microwave signals actually spill-over the receiving dish and go out into space. If the U.S. could position a satellite at the proper tangent to the curvature of the earth, in line with the Russian microwave transmitting dish, they could pick up those signals. That's exactly what Rhyolite did, among other things.

The Rhyolite program was compromised in 1975 when Christopher Boyce (a TRW employee) and his boyhood friend Andrew Daulton Lee (a drug dealer), sold classified information on Rhyolite to the Russians. They were both arrested, tried, and convicted of their crimes. Their story is well told in the book and movie “The Falcon and the Snowman." In 1977, the Rhyolite name was changed to Aquacade.

Next generation satellites were code named “Argus” and “Pyramider," but the Pyramider project was dropped. Argos was said to be doing a lot of physics and atmospheric studies. It weighed 5,491 pounds when launched, and that’s a lot of weight for a flying science lab. Then came Vortex (Mercury) for microwave intercept, and Magnum (Orion) for multifrequency intercept. They keep changing the names of the programs, so it’s hard to create a clear intelligence satellite chronology here in this limited space.

As you can see, we have been conceiving, designing, and implementing very sophisticated sensor networks and “electronic fences” for nearly 70 years. Satellite stuff is very classified material, so one can only imagine what advanced systems we have operating up there now, especially in FISINT*, TELINT*, and MASINT*. For more information about the history of our intelligence satellites, read “Body of Secrets” and “The Puzzle Palace”, both by James Bamford. And, you can look at the list of US satellites in orbit now at

Just remember that all those original 144 Carona satellites -- the ones that spit-out the film canisters -- had a useful life of only 50 to 150 days, before they were out of film. Many are still up there, along with a number of now-inoperative early SIGINT satellites. In the past decade, we have sent-up new satellites that track the 500,000 pieces of space junk, to keep our present operational satellites from being hit by debris traveling at 17,000 mph. And, we have satellites that spy on our enemy’s satellites: they intercept the signals coming to them from earth, and going back down to earth. And we have some up there named "MIRACL." They have onboard lasers to dazzle, blind, and destroy our enemy's intelligence and communications satellites in time of war: they are anti-satellite satellites.

Also, remember that in January 2007, the Chinese shot-down one of their aging weather satellites with a missile launched from a mobile trailer, to prove they could do it. In February 2008, the U.S. shot down a malfunctioning intelligence satellite with a missile fired from the deck of the guide missile cruiser USS Lake Erie, to prove that we could do it. Both events contributed to the the space junk in orbit. But it also proved that China and the U.S. can destroy each other’s satellites in a war. We haven’t seen evidence that the Russians can do it yet.

Today, we have Global Hawk, Predator, Reaper, and Sentinel unmanned aircraft platforms gathering tactical intelligence. We still have a number of the RC-135 aircraft flying intelligence missions. One was involved in a near-miss confrontation with a Chinese fighter plane recently. Latest information available suggests that the U.S. has 549 operational satellites in orbit today (commercial and military), so that suggests at least 100-200 doing intelligence work. But that probably doesn’t include the super-secret stuff up there. As you can see, NSA and the military intelligence groups act like a giant vacuum cleaner, sucking-up every electronic signal emitted by our enemies.

So, how do we process all that data? That is the topic of the next installment.

*Definitions of xxxINT acronyms from the previous installment in this series at


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