In 1970, Marshall Kaplan, then an aerospace engineering professor at Penn State, had a peculiar dream — he wanted to retrieve Sputnik, the world's first orbiting satellite, from space.

Sputnik had been launched by the Russians in 1957, and by 1970 it was no longer operational. Kaplan wanted to go get it.

NASA had never considered space retrieval before, but it thought it was a good idea. Kaplan got the job, but it didn't work out — because the time frame was too short. Sputnik, nearing the end of its life cycle, was already about to deorbit — the technical term for what happens when an object circling the Earth gets close enough to be caught in gravity and burned to cinders in the atmosphere.

But that didn't mean Kaplan needed a new line of work.

In fact, his work was just beginning.

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For the next 40 years, Kaplan, now a senior researcher in the space department at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., has been figuring out how to bring down objects from space.

That makes him one of a few dozen scientists feverishly trying to prevent what he calls a "coming catastrophic disaster" — a collision between a manned spacecraft and orbital debris, or space junk, thousands of pieces of which are zooming at thousands of miles per hour 300 to 800 miles above the Earth, ready to take out anything in their paths.

Space junk is anything that's lost or discarded in orbit — everything from the spare glove astronaut Ed White lost on the first American spacewalk in 1965, to the garbage bags jettisoned by cosmonauts stationed on the Mir space station in the '80s and '90s, to the dangerous remnants of a old weather satellite blasted into smithereens by a Chinese missile in 2007.

The probability of a disastrous orbital collision has been on front pages lately. On Feb. 12, a Russian-made satellite smashed into a commercial U.S. telecommunications satellite, creating the second worst mess (after the deliberate Chinese incident) ever in space.

Fortunately, the telecom satellite was quickly replaced, and the Russian "bird" had long been out of commission.

But a month later, on March 13, the two astronauts and one cosmonaut aboard the International Space Station had to scramble into an escape capsule after they got less than 20 minutes' warning that a piece of speeding junk was heading straight for them.

There wasn't time to reposition the ISS, which could have suffered a fatal loss of pressure had the five-inch piece of an old rocket punctured the walls of a living area. Fortunately, the debris missed.

"This is just a taste of what's to come. Experts are saying we could expect a crash every couple of years, but this is an educated guess," says Michael Krepon, co-founder of The Henry L. Stimson Center, a Washington-based think tank that focuses on security concerns.

"We really don't know the scale of the problem — we just know that we've already done serious damage to a zone of space that's essential to our security."

Our fast-paced, hyperlinked world could not exist without orbital relays; everything from phone calls to GPS devices to banking transfers needs satellites to work.

Even more damaging to satellites, and the enormous potential of the commercial development of space overall, could be a ground-based threat — crippling lawsuits over orbital-debris collisions.

"Liability claims killed the private aviation industry," says Peter Diamandis, founder and chairman of the X Prize Foundation, which sponsors contests and awards for private space ventures and innovation. "In space, we're going to be dealing with 'Your satellite killed my satellite' claims. It's going to be a mess."

No ... it's a mess already.

"We're currently tracking 18,000 objects floating through space," says Kaplan. "But that's only objects larger than 4 inches. At 10,000 mph, even a nut or a bolt could do serious damage."

In the microscopic range, there are literally billions of micro-particles around — too small to puncture a spacecraft's exterior, but enough to have already pitted windows on a space shuttle and destroyed a lens on an orbiting telescope.

It's Kaplan's job to figure out how to get all of this down, and it's a big job.

"This clean-up will cost tens of billions of dollars," he says. "It's going to require a whole new space program to pull off. But we don't have a choice. This is just a cost-benefit analysis. If we don't clean this mess up in the next 20 years, we're going to lose our access to space."

Nations are beginning to act. On Feb. 13, the United Nations endorsed seven "Space Debris Guidelines to Curtail Space Debris in the Future."

The guidelines include adding more shielding to spacecraft and giving satellites extra fuel so they can either deorbit themselves quickly (it normally takes decades) or put themselves into higher, less crowded orbits at the ends of their life cycles.

The Colorado-based Secure World Foundation, a space think tank, is calling for a Civil Space Situational Awareness System — essentially a global air-traffic controller that would track everything in orbit so collisions could be avoided.

That sounds like a no-brainer, but it's something of a problem for the Air Force, to use only one example of a governmental authority that naturally has serious concerns about telling anyone where its surveillance satellites are at any given time.

A Stanford study released in late March suggests that future space junk can be minimized by simply forcing nations to "take out their own garbage" by deorbiting anything after it's done its job.

Most experts feel the U.N. recommendations will be ratified by international treaty, or a similar mechanism for good-conduct rules will be enacted soon.

But while all of these ideas are good planning, they don't get rid of the junk that's already up there.

That's what Kaplan spends most of his time working on.

Recently, he conducted a global survey of orbital waste-management ideas. He got over 100 — some pipe dreams, some crack-pipe dreams, but 30 or 40 of them with merit.

One concept that's gotten attention is the "space broom," a ground-based laser that will use quick pulses to singe orbital debris, changing each piece's trajectory so that it deorbits faster. The idea has considerable merit, and considerable problems — how to hit each piece, for one.

"We don't really know where this junk is with any real sense of accuracy," says Kaplan. "We can get within a few meters, perhaps, but that's not enough for a laser."

You could get a lot closer by putting the lasers on a spacescraft, but that would be a space-based weapon, and those are banned by several international treaties.

"Collection by collision" is another possibility Kaplan is earnestly examining.

The idea is simple — coat a spaceship in something sticky and put it into orbit. Think of it as a giant lint roller — debris will naturally collide with the craft, but instead of bouncing off or tearing through it, the junk will simply adhere. The added mass will lower the ship until it deorbits on its own.

And then there are a bevy of independent thinkers eager to jump into the mix.

Retired aerospace engineer Jim Hollopeter was profiled in a recent Wall Street Journal article, which reported that he wants to load aging rockets with water and bring down debris with what would essentially be the world's largest fire hose.

Meanwhile, the folks at Tether Unlimited, a Washington-based aerospace company funded by the Air Force, have created the "terminator tape," basically a pizza-sized box that can be clamped on to to a defunct satellite.

Once attached, the box opens, several hundred meters of electro-dynamic wire unspool and atmospheric drag does the rest to bring the bird down.

There are also nets, and magnets, and a science-fiction treasure trove of tantalization. The bad news is that none of them, even something as low-tech as the terminator tether, comes cheap.

The good news is that many could be "bootstrap"-financing technologies. There's a fortune to be made in space-mining operations, for example in harvesting nickel from the moon.

Diamandis himself believes this future industry will produce the world's first trillionaire, and if the fortunes of the 19th-century "robber barons" are anything to go by, he may not be wrong.

The point is that cleaning debris out of space means learning how to tow objects around space — a fundamental component of any mining operation.

"You don't even have to go that far out," says Diamandis. "Whatever 'waste management' organization gets the contract for space is looking at heaps of valuable material already floating around above us. You have to remember — one man's waste is another's treasure."