After 30 years and 135 missions, it's curtains for NASA's Space Shuttle. The Shuttle Atlantis blasted off on Friday for one last rendezvous with the International Space Station, bringing to an end the current era of impressive -- but pricey and dangerous -- manned spaceflight. But never fear! America's space arsenal might be down four giant Shuttles, but there's still plenty of U.S. government hardware orbiting the Earth, much of it top secret. Counting commercial satellites with government missions, Washington has access to around 400 spacecraft -- four times as many as the number-two space power, Moscow. U.S. spacecraft include communications satellites, orbital cameras and other sensors, craft designed to eavesdrop on radio traffic and at least one secretive, robotic space plane similar to in shape to the retiring Shuttle. Here's a sampling of some of the "blackest" of America's secret space fleet. Space Tracking and Surveillance System Spotting missile launches from space is old hat -- the Air Force's Defense Support Program infrared-sensing satellites have been detecting missiles' heat blooms since the 1960s. But when the Pentagon began seriously trying to shoot down ballistic missiles in the 1990s, it realized it needed faster, more accurate space detection -- and that meant flying lower. Enter the Space Tracking and Surveillance System, built by Northrop Grumman and Raytheon on behalf of the Missile Defense Agency and the Air Force and launched beginning in 2009. STSS orbits just 100 miles high, compared to 22,000 miles for the geosynchronous DSP. Northrop happily discusses the accomplishments of the two newest STSS sats, but there's a third bird whose exact mission was classified. The Missile Defense Agency is now trying to coax STSS into automatically providing targeting data to the Navy missile-killing Aegis warships. Photo: Northrop Grumman

Lacrosse Radar in space. That, in a nutshell, is the function of the Lacrosse family of giant satellites, orbiting 400 miles over Earth since the late 1980s. Along with the equally-huge camera-equipped Keyholes, the Lacrosses provide most of America's day-to-day space-based intel. Keyholes are for good weather. Lacrosses, with the ability to see through clouds, are for overcast days. Working in a team, Keyholes and Lacrosses probably helped the CIA plan the May raid that killed Osama Bin Laden in Pakistan. How many of the billion-dollar Lacrosses are there? Probably three. Every few years the secretive National Reconnaissance updates the design and sends a fresh one into orbit, most recently in September, according to some sources. One recent version spotted by amateur sat-tracker John Locker might even come equipped with a sensor dish for gathering up radio signals, essentially mapping a target's electromagnetic signature while also painting a picture of its physical surroundings. Photo: Wikimedia Commons

Keyhole The fair-weather partner of the Lacrosse, Keyhole is what people are actually visualizing when they think "spy satellite." Keyholes are basically telescopes pointed toward Earth instead space. In fact, it seems that NASA modeled the Hubble Space Telescope on the Keyhole's design. There are probably around five 20-ton, $2-billion Keyholes in 150-mile orbit, the latest placed there in January by a Delta IV Heavy rocket launched from California. (That blast-off was so loud that Air Force officials had to tell local inhabitants it wasn't an earthquake.) Washington loves its Keyholes so much it has been building them nonstop since the mid-1970s, but in coming years these giants could be replaced by smaller, cheaper camera sats that don't fly as high or last as long, but can be replaced more often. Photo: National Reconnaissance Office

Misty It could be a figment of the collective imagination of the world's amateur satellite trackers. It could be hype by an author hoping to sell books. Or it could be the world's most secretive spy satellite, an ostensibly undetectable version of the old-school Keyhole orbital camera. "Misty," as it's known by space enthusiasts, was allegedly an attempt by the CIA's Office of Development and Engineering to develop a spacecraft that couldn't be tracked by Soviet trackers, or attacked by Moscow's anti-satellite weapons. That meant wrapping the potentially school-bus-sized satellite in flexible mirrors to deflect sunlight away from Earth-bound viewers, or encase it in a sort of radiation-absorbing balloon (depicted above) that was registered with the U.S. Patent Office soon after the sat's reported launch aboard the Space Shuttle Atlantis in 1990. Author Jeffrey Richelson claims the CIA even collaborated with NORAD to mask the deployment of Misty's stealth shroud, by setting off a staged explosion that the agency claimed was a normal Keyhole malfunctioning in orbit. Photo: U.S. Patent Office

Naval Ocean Surveillance System It was the early 1960s when the Navy realized it had a problem. In those early years of the Space Race, the Air Force possessed "ferret" signals intelligence satellites that could detect radiation from stationary Soviet air-defense systems and pinpoint their locations. But the same satellites couldn't track moving ships at sea. So a decade later the Navy launched the first in a long series of tightly-grouped satellite constellations that traveled together over the world's oceans, triangulating electronic signals from warships in order to keep tabs on their movements. Today, the so-called Naval Ocean Surveillance System is in its third generation. Each $800-million constellation of two or three satellites is launched by a single rocket into low orbit -- low enough that they're frequently mistaken for alien spaceships by panicked Earthlings (see above). These low-fliers don't last last long: just a few years, meaning the Navy is constantly updating them and boosting more into orbit -- quietly, of course. NOSS is one of the Navy's huge but unheralded advantages over rival navies. It's not for no reason that some of China's first modern military satellites were basically copies of the Navy system. Beijing needed some way to spot American aircraft carriers so it could target them with DF-21 ballistic missiles. The solution: the Yaogan constellation, launched beginning in 2006.

Rapid Pathfinder Program The National Reconnaissance Office oversees most of America's spy satellites. And while the NRO announces orbit-bound rocket launches and even releases photos, it rarely describes exactly what's inside those rockets -- though it does sometimes name them. That was the case with the Rapid Pathfinder Program spacecraft, lobbed into low orbit from California aboard a Minotaur rocket in February. "This particular payload carries some of the work we do in techniques and methods to improve intelligence collection," NRO spokesman Rick Oborn said vaguely. But the Minotaur rocket's modest size is a clue. The 40-ton Minotaur can loft only small, lightweight satellites -- say, a few hundred pounds, versus 15 tons for a Lacrosse radar sat. But that would put Pathfinder right in line with other next-gen spy satellites such as the Air Force's ORS-1. The future of orbital snoops is small, because small satellites are cheaper, can be manufactured faster and replaced more frequently with updated hardware. Pathfinder was possibly a test model for the coming wave of tiny, orbital spies. Photo: Air Force

Mentor Some spy satellites watch with cameras or radars. Others listen. The five Mentor satellites, possibly built by TRW, are what's known as "SIGINT" craft -- that stands for "signals intelligence." The geosynchronous Mentors are the latest in a long line of SIGINT birds dating back to the '80s. Originally built to suck up communications from Soviet missiles tests, today they can eavesdrop on radios, radars and pretty much any device that broadcasts a strong enough signal. The key to this sensitivity is one monster set of ears. The Mentors aren't heavy -- just three tons or so. But their receiver dishes are huge. A modified Mentor launched in November boasts the biggest receptor of them all: roughly the size of the football field, making it "the largest satellite in the world," according to NRO director Bruce Carlson. Photo: Wikimedia Commons