Space shuttle: What have we learned?

Kennedy Space Center, Florida (CNN) -- When the space shuttle Endeavour blasts off, it will mark the orbiter's last voyage and the second-to-last mission in the 30-year-long space shuttle program.

NASA announced that Friday's scheduled liftoff had been delayed by at least 72 hours due to concerns with the shuttle's heating system.

President Barack Obama, the first family and another high-profile guest -- Rep. Gabrielle Giffords, recovering after being critically wounded in January -- had been among the notables expected to attend Friday's launch at Kennedy Space Center. Giffords' husband, Cmdr. Mark Kelly, is leader of the mission to the international space station.

Final launch for space shuttle Endeavour

After Endeavour is set to return to Earth in mid-May, there will be one last opportunity to watch a space shuttle lift off. The shuttle Atlantis is scheduled to launch at the end of June. It will mark the end of NASA's space shuttle program after three decades.

As shuttle program ends, astronauts want to keep flying

The program conducted a tremendous amount of scientific research and delivered numerous satellites into orbit, but in some ways fell short of its original purpose.

"The shuttle has been disappointing in terms of its delivery of payloads into space," said George Musser, space and physics editor at the magazine Scientific American. "The idea was to bring down the cost of launching a kilogram into orbit to something like $100 per kilogram. In fact, it's probably about a hundred times that ... so it has been very disappointing in that regard."

Musser was a high school freshman when the first shuttle mission took place in 1981. He said it fueled his interest in science and astronomy. "The shuttle was the most complicated machine ever built by human beings. It's an incredible machine," Musser said.

Over the years, he watched shuttle launch after shuttle launch take place while many Americans lost interest. To many, a launch turned into something routine and mundane despite two disastrous accidents that took the lives of 14 astronauts.

Today, it's a challenge to name technological advances seen in everyday life that were a direct result of the work done on the space shuttle program.

"NASA, of course, will tell you that there have been all of these technological spinoffs. We got memory foam, all those kinds of material innovations that come from the space shuttle," Musser said. "But I personally think that the benefits of the space shuttle can't be reduced to those practical spinoffs."

Musser said he believes the advances in astrophysics and planetary science far outweigh the technological advances that came as a result of the program. He cited the Magellan mission to Venus, the Hubble Space Telescope and the Galileo probe to the Jupiter system as examples of space programs in which the space shuttle played a central role.

"These are just incredible instruments that have transformed astronomers' and society's view of the universe," Musser said.

He points to the shuttle-delivered Hubble Space Telescope's discovery that the universe is expanding at an accelerating pace.

First commander reflects on Endeavour's final mission

While the space shuttle program is coming to an end, the science that it made possible will continue to result in new discoveries well into the future. When Endeavour lifts off Friday, it will deliver the Alpha Magnetic Spectrometer to the international space station.

Valued at more than $2 billion, the seven-ton machine will examine cosmic rays coming from exploding stars and black holes.

It could lead to discoveries that explain how the universe is put together. It may even enable researchers to identify the elusive dark matter -- the invisible stuff in space that scientists suspect makes up the majority of the universe.

Most importantly, it may bring us one step closer to answering the age-old question: Why are we here?