When I first heard about the propose MUSES-C mission (the original name of what is now known as Hayabusa), I thought it was an impossible dream. Sample return is hard - it has only been done robotically once (by the Soviet Union) from a planetary surface. It requires many major individual mission accomplishments: rendezvous with a celestial body, operations and science investigations around that body, landing, sampling, capture of the sample, return targeting and flight to Earth, and finally, entry and landing on Earth.

Each of these steps was unprecedented for the Japanese space agency (their only planetary mission to date has been the unsuccessful Nozomi, which flew to Mars but failed its attempt to go into orbit). Furthermore, they were doing it with a new spaceflight propulsion technology: solar electric engines powering low thrust engines that are supposed to work continuously in space.

That all this is hard is borne out by the adventures of Hayabusa, but what I (and many other observers) hadn't realized was just how clever the mission engineers were in programming resiliency and robustness into its spacecraft. They didn't build a spacecraft that did everything right - they built one that could handle a lot of wrongs.

These engineers deserve our great admiration and plaudits for their accomplishment no matter what is inside that sample container (which they will open in few days).

An adoring Japanese public has given them great credit, making Hayabusa (which means Falcon in Japanese) a popular "character" in newspapers, magazines, television, and movies. (Unlike the U.S.'s tradition for personifying spacecraft, Hayabusa is a "he.") The story of the spacecraft is also the subject of a computer-graphic movie, now showing in a planetarium, and, I hope, soon to be released on DVD.

Thousands of well-wishes from the public have been sent to the Japanese Aerospace Exploration Agency (JAXA) website, and hundreds of thousands of names from around the world collected by JAXA and The Planetary Society were sent on the spacecraft.

Hayabusa was launched on the now out-of-date Mu-V rocket in May 2003. He was supposed to launch a few years earlier, but that launch was delayed due to launch vehicle problems.

The solar-electric engines worked well and guided the spacecraft to a rendezvous with the asteroid Itokawa in September 2005. (Their original target was an asteroid named "Nereus", affectionately known as Near-Us.) Itokawa is a called a near-Earth asteroid because its orbit is relatively near the orbit of Earth - in fact it crosses the orbit of Earth. But the asteroid itself was nearly 300 million kilometers from Earth when the spacecraft arrived. At that distance, the round-trip communication time is about a 0.5 hour.

The arrival was terrific, and the first close-up pictures showed the now famous potato-looking object with some very high-resolution photos. The JAXA team from its Japan Space Exploration Center (JSpEC) first deployed a mini-robot to work on the surface - but it missed the asteroid. Their first attempt to land Hayabusa itself on the satellite came close but it too did not succeed. But then, the second attempt did succeed, and he rested on the asteroid for perhaps 30 minutes - but did it capture a sample?

Apparently the sampling device, which was to fire a pellet into the surface, didn't completely work, but there is still hope that some pebbles, or at least dust, were collected. Before descending to the asteroid's surface, Hayabusa deployed the metal capsule with all of our collected names, which now has a permanent home on Itokawa.

That was late in 2005. The return to Earth was to begin shortly after, but first the spacecraft reaction wheels failed and then a propellant leak in the attitude control system occurred. The return trip to Earth appeared doomed, until the JSpEC mission team came up with a clever idea: wait.

Instead of beginning the return to Earth in early 2006 as originally planned, they reprogrammed their spacecraft to wait until April 2007, the next favorable alignment with Earth. By 2007, only two of the original four solar-electric engines were working. Would this now old (beyond its original lifetime) crippled spacecraft make it back?

The engines did work, at least for awhile - long enough to do the job of setting the course for Earth. In late 2009, one of the engines failed and again all seemed doomed. But our clever friends at JSpEC reprogrammed again, taking two crippled engines and combining them to make one good one. The ups and downs of our perception of Hayabusa are graphically chronicled by Emily Lakdawalla on our blog.

Now, Mr. Hayabusa has returned to Earth. In contrast to all of his other adventures on the way to, at, and from Itokawa, his entry and landing on Earth were near-perfect, and the sample capsule has been recovered.

The capsule will now be brought back to where the adventure began - the Sagamihara campus of JAXA (near Tokyo) where JSpEC has its home. There it will be opened, undoubtedly with a huge crowd - both physical and virtual - present to witness discovering what, if anything, is inside.

I hope Shakespeare is wrong: "My falcon now is sharp and passing empty."

If something is the capsule, it will be the first asteroid sample ever brought to Earth. If not, there will still be the great mission accomplishments to celebrate and a lot of experience gained to help us plan for future sample return missions - including from the all-important Mars.