Satellites: First they helped international investigators calculate the missing Malaysia flight's last known position. Now, another one has picked up what may be debris from the vanished aircraft. But the underlying technology that made it possible? It's very different. Here's everything you wanted to know about spy satellites.

How good are these things, really?

If you've used Google Earth, you know that free satellite imagery is already pretty good. Google's systems are capable of incredible resolution — down to less than a meter. Some onlookers report that the real figure is actually about half a meter, and is limited only by government restrictions that prevent the image quality from getting too good.

That's consistent with what Mark Lowenthal, a former intelligence official, thinks, too.  According to Lowenthal, president of the Arlington-based Intelligence and Security Academy, commercial satellite imagery can make out objects that are as small as 20 inches across. But Lowenthal notes that according to various press reports military satellites are about twice again as good, capable of resolution down to 10 inches. The Federation of American Scientists has a great side-by-side comparison of the same image sampled at various resolutions.

What did the satellites pick up off the coast of Australia?

As you can see in the images above, gathered March 16, investigators have identified an "object" about 79-feet across. Another is slightly smaller, about 16-feet across. It might be part of the missing plane. Given how big the object is, it seems the high-resolution capabilities were mostly overkill this time. According to the Sydney Morning Herald, the images were provided by U.S. intelligence sources, suggesting a government satellite may have been involved.

If it was that easy, why didn't we see this stuff sooner?

Hang on. Just because the objects — if that's what they really are — were pretty big, the ocean they were floating in was much, much bigger. This is where imagery analysis comes into play. In industry lingo, it's called geospatial intelligence, or GEOINT.

"Over time, [analysts] learn to look for patterns," said Lowenthal in an interview. "They look for patterns and anomalies. They're looking at a dark background and for objects that don't belong there."

If that sounds easy, it's not. It calls for special training — sometimes in cartography, meteorology, even tectonics. You can actually get a degree in GEOINT from places like Penn State.

How far has satellite imaging come? I can't imagine we're still doing it like we did in the Cold War.

Well, the basic idea has mostly remained unchanged — you take pictures of the ground and you have really smart people comb through them for interesting things. But yes, technology has dramatically improved how we gather, retrieve and interpret GEOINT.

In the early days, we used to send planes with cameras to do aerial reconnaissance. That became really common during World War II. Eventually, we graduated to high-altitude spy planes like the U-2 and SR-71. But sending planes over enemy territory eventually became way too dangerous, so in 1960, the United States launched a program known as Corona. The satellites under that program were code-named Key Hole. It looked like a long, thin cigar and carried film in a huge titanium canister — according to Lowenthal, it was about the size of a large medicine ball.

Right. They didn't have digital cameras back then. So how'd they get the pictures back?

It took a long time to run through a whole roll of film. When it was through, says Lowenthal, Corona "would literally burp out the canister" and it would fall back to earth. After deploying a couple of parachutes, the canister would be moving slowly enough that a plane could intercept it and snag it out of the air. Yes, really.

Sometimes the canister would get lost and fall into the ocean. But most of the time, the crazy plan worked. They'd recover the ball, develop the film and send it on to analysts armed with magnifying glasses.

Now, everything's been digitized. Photos come back almost instantly. Satellites can shoot with infrared and other cameras that operate in other parts of the light spectrum. High-tech software lets analysts zoom in, enhance the quality and make other adjustments after the fact.

And this technology is getting better all the time?

You bet. In the early years of the technology, our best resolution was measured in yards, says Lowenthal. We've come a long way since then. For context — here's the first image ever to come back via a U.S. spy satellite.