NASA/National Geographic/Getty Images
The Hubble Telescope gave us never-before-seen images -- like this picture of radiation from a stellar burst ricocheting off dust particles.

Before ­1990, our view of space came from ground-based light telescopes. The images were interesting, but not very clear, and the optics couldn't see far enough to give us the views astronomers had in mind. Earth's atmosphere, with all its clouds, water and gas vapors, isn't terribly conducive to conducting light, a requirement for capturing clear images.

The solution was clear: Put a telescope on the other side of Earth's atmosphere, where the light would travel to distant objects and bounce back unhindered. Named after astronomer Edwin Hubble, the telescope offered the first clear views of the universe beyond our galaxy. Hubble developed a theory based on the changing nature of stars light years away. The Hubble Space Telescope would let astronomers prove his theory that the universe is expanding.

 

The work began in 1975. It took 15 years to launch Hubble. Scientists spent eight years assembling and testing the telescope's 400,000 parts and 26,000 miles (41,843 km) of wiring. It would have been in orbit in the late '80s, but the Challenger disaster in 1986 pushed the launch date back to 1990.

 

The Hubble Space Telescope lets us watch the expansion of the universe in a way never before imagined. Not only does it have 10 times the resolution of a ground-based telescope and 50 times the sensitivity, but another development around the same time made its unprecedented views of the universe more accessible than any previous scientific advance. With the advent of the Internet, people could sit at home and watch the universe unfold in all hi-resolution, full-color glory. Hubble revealed the world, going out billions of light years from Earth, to anyone who cared to see it.

 

Of course, Hubble was only state-of-the-art for a short time. As is typical with scientific innovations, it was outdated in less than a decade. The Chandra telescope uses X-rays instead of visible light to capture the most amazing views of the universe to date.

 

 

NASA/CXC/MIT/F.K.Baganoff/Getty Images
The Chandra X-ray Observatory has created amazing images -- like this one of bright flares visible near the event horizon of a super-massive black hole in the center of the Milky Way.

In 1999, NASA launched the most sensitive X-ray telescope in the world. It can see­ things no one has ever seen before, such as the split second when space particles disappear into a black hole.

X-ray telescopes are different than light telescopes. Instead of relying on visible light to form an image, Chandra X-ray Observatory uses higher-energy particles, namely X-rays, to record images based on energy fluctuations. This allows for far greater sensitivity and clarity than Hubble, with Chandra focusing on the highest-energy portions of the universe. Add to that the fact that Chandra is orbiting the Earth at 200 times the altitude of Hubble and it's 25 times more sensitive than any other X-ray telescope, and we've got ourselves the most amazing astronomical sights we've ever seen [source: Harvard].

Chandra X-ray observatory has so far delivered clear images of supernova remnants, quasars, exploding stars and events like the disappearance of matter into black holes. It has shown us supermassive black holes, nebulae and dark matter. It has recorded light that has been in existence for 10 billion years. With this technological advancement, the possibilities are startling. Chandra will contribute to our understanding of the origins of our universe and of life itself.

 

Speaking of life itself, how about the kind that might exist on other planets? Next on our list of NASA successes is Pioneer 10, the first-ever interplanetary space flight. But that's not all Pioneer 10 accomplished.

John G. Mabanglo/AFP/Getty Images
An artist's rendition of the Pioneer 10 spacecraft as it passes the planet Jupiter.

Before 1972, no man-made objec­t had made it to an outer planet. No one had even tried ­it. Pioneer 10 changed all that with a mission that paved the way for some of the most daring goals of the space program.

Pioneer 10 left Kennedy Space Center in 1972, bound for Jupiter, the farthest planet from Earth. Since there is a known asteroid belt between Earth and Jupiter, astronomers had long believed it to be impassable. This asteroid belt was blocking the path to the universe beyond the outer planets. Pioneer 10 made it through the asteroid belt.

The probe travelled onboard the Atlas launch vehicle, equipped with more than 400,000 pounds of thrust. When it made it to Jupiter, it delivered the first-ever direct observations of an outer planet. And then it moved on. Pioneer 10 travelled farther in space than any other man-made object when it left our solar system and entered interstellar space in 1983. When it sent its last transmission in 2003, it was 7.6 billion miles (12.2 billion km) from Earth [source: NASA].

 

Another spacecraft, launched two years before Pioneer 10, also achieved the seemingly impossible. This time, it wasn't the successful navigation of an impenetrable asteroid belt; it was the recovery of a crew that by all logical reasoning should have been forever lost in space.

 

 

Chet/Central Press/Getty Images
The Apollo 13 astronauts received a ticker-tape welcome upon their safe return.

Apollo 13 was headed for the moon. On April 11, 1970, the spacecraft lifted off. Fifty-five hours and 55 minutes later, an explosion shut down almost every system necessary to sustain life onboard.

The string of events leading to the explosion began with one of the engines shutting down two minutes early on liftoff. The string of events set off by the explosion set into motion one of the most amazing collaborative rescues in history. So many things went wrong on Apollo 13, it's an engineering miracle that the crew -- astronauts James Lovell, John Swigert and Fred Hayes -- made it home at all, let alone alive and well.

 

Minutes after the crew completed a television broadcast from space, telling America everything was going well, an explosion shook the spacecraft. It was one of the two oxygen tanks, and one disaster led to another. When the first tank blew up, the force caused to second oxygen tank to malfunction. Immediately after, two of the craft's three fuel cells shut down. Apollo 13 was venting oxygen into space, and all of their life support and navigation systems -- oxygen, power, water, heat and light -- were offline.

 

The ingenuity that followed is a testament to the genius of the human mind and spirit. To conserve whatever power, food, water and oxygen was left, the astronauts onboard Apollo 13 survived on almost no food, water and sleep and in temperatures that dropped to near freezing. The crew members lost a combined 31.5 pounds (14.3 kg) in less than six days, due almost entirely to dehydration.

 

Meanwhile, the people on duty at NASA's Mission Control center from April 11 through April 17 found a way to get the men home. They did months of calculation in days. They found a way to get the lunar module to support the crew and get the spacecraft back to Earth, although it was never intended for that purpose. The canisters that removed carbon dioxide from the command module didn't fit the system in the lunar module. So Mission Control found a way for the astronauts to make them fit using tools they had onboard: cardboard, plastic bags and tape.

 

Still, with no controls, no extended life support and no navigation system, the biggest problem of all was how to get the craft into a trajectory for an Earth landing. Apollo 13 had already made the planned adjustments for a moon landing before the initial explosion.

Mission control developed a plan. The onboard navigation was based on finding a key star. That system was out. In three hours, NASA found a way to use the sun instead, a series of calculations that would normally take three months; and they found a way to use the moon's pull to get the craft into the right position, because they had to save all of the power for the trip home.

 

The calculations based on the sun turned out to be accurate to within less than 1 degree. Apollo 13 rounded the moon and descended toward Earth. So much condensation had built up on the walls of the lunar module from the days of cold that when the spacecraft finally powered up -- and heated up -- for the trip home, it rained inside the cabin [source: NASA]. Apollo 13 landed successfully on April 17 in the Pacific Ocean.

While all of the astronauts were fine, the spacecraft, of course, was not. But that was typical for the time. NASA didn't have a working reusable a spacecraft until 1981, when the first space shuttle, named Columbia, made history.

Hank Morgan/Time and Life Pictures/Getty Images
The Space Shuttle Columbia lifted off from Cape Kennedy in 1981.

In 1972, the Apollo program was winding down, and NASA was doing some technological soul-searching. The Apollo rockets were sin­gle-use spacecraft. The cost per mission was astronomical. A reusable spacecraft wouldn't only save money, but it would also be an amazing technological advance.­

After President Nixon announced the plan to build a reusable spacecraft that would run multiple, perhaps indefinite numbers of missions, NASA developed the basic design: two solid rocket boosters attached to an orbiter module and an external fuel tank.

There were considerable hurdles facing the project. Since the equipment that protected previous spacecraft from Earth's searing atmosphere essentially disintegrated during re-entry, NASA needed an entirely new heat-shield concept. It came up with a method of coating the craft with ceramic tiles that would absorb the heat without degrading. The other major redesign had to do with the landing itself. T­he old spacecraft basically plummeted through the atmosphere and splashed down in the ocean. It's tough to reuse equipment after a water landing. The new spacecraft would land more like a glider, on an actual landing strip.

It took nine years from the start of the project to the first flight. In 1981, the Space Shuttle Columbia lifted off, and it was a successful mission. NASA had succeeded in creating a reusable spacecraft, and the fruits of its labor are still in use today.

 

­Many of the shuttle's missions include a stay at the International Space Station (ISS), an amazing creation that at last marked a significant collaboration between the United States and Russia to advance space exploration. The ISS has surpassed all expectations and is now a true space destination, massive in size and technological capabilities. And it's not just for astronauts anymore

 

NASA/Newsmakers/Getty Images
The Expedition One crew hosts a group of visitors in the International Space Station.

Missi­ons to space lasting several weeks can­ a­chieve some amazing results. We can reach the moon, service satellites and telescopes and test all sorts of equipment. But here's the thing: Exploring other planets, or what's beyond our solar system, is going to require serious time -- months, even years. The human body isn't designed to live in space. So getting us to the point of exploring farther than ever before requires long-term tests on the effects of space life on the human body. That's where a permanent space station comes in.

 

The International Space Station isn't the first space station, but it's by far the most impressive. Russia launched Salyut 1 in 1971, which orbited Earth for less than a year due to a series of equipment failures. The United States sent up Skylab in 1973, which failed as well, lasting less than two years. Russia launched its second station in 1986. That was Mir, and it was in operation until 2001, when it was purposefully decommissioned. Mir measured 107 feet (33 meters) long and 90 feet (27 meters) wide and weighed more than 100 tons, and it hosted astronauts almost continuously throughout its time in space [source: NASA]. But it was nowhere near the ISS in accommodations. The ISS is an orbiting, top-of-the-line laboratory. When it's done in 2010, the ISS will measure 356 feet (108.5 meters) long and 238.8 feet (72.8 meters) wide and weigh 450 tons [source: JAXA].

It's a feat of engineering unmatched by any other permanent home in space. The first two modules of the station arrived in orbit in 1998, where they were attached to form the initial structure. In 2000, the first crew arrived to stay awhile. Since then, the U.S., Russia and 13 other countries have sent additional modules, equipment and crews to the ISS, and it's now manned continuously. Several astronauts have spent hundreds of days onboard.

­During the last eight years, occupants of the station have studied human bone loss during extended time in microgravity, radiation levels in space and how to protect against them, different techniques for doing in-space soldering to repair equipment, and countless other experiments, repairs, space walks and robotics innovations. They've also studied the effects of space on several "space tourists" who pay tens of millions of dollars to experience life in orbit.

 

Everything we're learning is getting us closer to a manned mission to Mars. Without the ISS, we'd be stuck close to home, unsure whether astronauts could survive a trip to the outer limits, let alone function well enough after months in space to perform tests within the harsh environment of Mars. And speaking of Mars...

 

 

Space Frontiers/Hulton Archive/Getty Images
The Sojourner Rover, a component of the Mars Pathfinder exploratory mission, analyzes the Yogi Rock on the red planet's surface.

The Mars Pathfinder mission was supposed to prove the viability of unmanned exploration of the red planet. Comprised of a lander module and a rover module, the objective was to make it through Mars' atmosphere, land safely on the surface, a­nd set free a robot to roam the planet. All this would be accomplished in an efficient and cost-effective way. The rest -- and there was quite a bit more -- was gravy.

Pathfinder left Earth in December 1996, traveled the 309 million miles to Mars, and landed in July 1997 [source: Space Today]. No previous spacecraft had landed on a planet without first orbiting it. The landing gear consisted of a parachute and a series of airbags; the module landed on a bed of rocks unharmed, and the rover took off. The mission was a success. Not only did Mars Pathfinder return a total of 2.3 billion bits of data back to NASA (more than 17,000 photos among that mass of information), but it outlived its projected life [source: NASA]. The lander was supposed to remain in working order, recording data and images, for about three months; it kept sending information for a year. The rover had a projected lifespan of several days. It ended up roaming Mars for a month [sources: Space Today, NASA].

 

Among other things, the Mars Pathfinder taught us that Mars was probably once warm, wet, and far more friendly, in human-survival terms, than it is now.

 

Mars Pathfinder taught us that Mars exploration is possible. Someday, NASA may even get a human there. But without the next achievement on our list, astronauts wouldn't be going anywhere at all.

 

Time Life Pictures/NASA/Time Life Pictures/Getty Images
Astronaut Alan B. Shepard aboard the Mercury 3 space capsule on the Freedom 7 mission.

The first American astronaut to orbit the Earth was named Alan Shepard, and he left Earth on May 5, 1961. He wasn't the first human in s­pace -- a Soviet astronaut named Yuri Gagarin has that distinction. But Shepard was NASA's entry into the annals of human space flight.

It was a nervous day for NASA. The countdown, divided for the first time into two parts so Shepard didn't have to spend an entire day on the launch pad, took more than 24 hours. NASA halted it several times for minor equipment checks, and finally it was T-15 minutes to liftoff. Shepard was onboard, the pilots of the launch vehicle were ready, and all systems were go. Then the clouds moved in.

The weather wasn't a problem for the launch. But it was a problem for the photographer covering the biggest NASA event to date. So NASA postponed the launch until the clouds cleared. During that hold, one of the orbiter's power inverters showed signs of trouble, and engineers fixed the problem in 86 minutes. At T-15, NASA decided to double-check a piece of navigation equipment.

The rest of the countdown went uninterrupted, and the launch, at 9:34 AM, about 25 hours after the start of the countdown, went off without a hitch. Shepard reached Earth orbit at an altitude of 116.5 miles (187.5 km). He spent 15 minutes and 28 seconds up there, travelling 303 miles around the Earth at 5,134 miles per hour (8,262 kph) [source: NASA]. When he splashed down in the Atlantic Ocean, he had completed a perfect mission and led the way for every NASA manned mission to come.

The manned mission that put NASA in the record books came eight years later. It was so monumental that conspiracy theorists question its validity to this day

 

Time Life Pictures/NASA/Time Life Pictures/Getty Images
Astronaut Edwin E. Aldrin, lunar module pilot, walks near the module during Apollo 11's extravehicular activity.

Just 20 days after Alan Shepard orbited the Earth, Pres­ident Kennedy announced the mission that would be NASA's greatest achievement: America was going to the moon. NASA immediately initiated the Apollo program.

It took eight years from that announcement to get there. Apollo 1 in 1967 was a disaster -- all three astronauts onboard died in a fire on the launch pad. Over the next two years, NASA ran nine more missions, testing various aspects of the operation. The work moved quickly: When equipment delays came up, NASA just switched to other equipment.

But Apollo 11 was the first mission to actually land men on the moon. When astronaut Neil Armstrong set foot on its surface on July 20, 1969, and spoke the words "One small step for man, one giant leap for mankind," the entire world was watching. The landing was such a big event, there are those who believe it couldn't have happened -- that the whole thing was staged.

Granted, it was an event of Hollywood proportions -- it was both scripted and choreographed. But that's because the lunar landing was NASA's moment in the spotlight, a first for the record books and an almost inconceivable achievement in the space age.

There were five more Apollo missions to the moon. The moon landing was such an important accomplishment, President George W. Bush announced in 2004 that America would set about going back, 35 years after the initial landing.

For more information on NASA, space and related topics, explore the links on the next page.