CAPE CANAVERAL, Fla. — In the '70s, NASA touted the space shuttle as reliable, economical and safe as flying an airplane. It didn't quite work out that way.

During their 25 years of flight, the shuttles were often over budget and risky — as the Challenger and Columbia accidents demonstrated. And instead of the 30 to 60 flights a year, the most flights NASA got was nine in 1985.

This month, NASA marks the silver anniversary of the first shuttle flight, which had astronauts John Young and Bob Crippen at the helm.

The shuttle was a successor to the 1960s Apollo program that sent man to the moon. In a space race with the Soviet Union at the height of the Cold War, Congress and the Kennedy and Johnson administrations generously funded those successful efforts. That support declined in the late 1960s and early 1970s as other national priorities such as the Vietnam War took center stage.

The shuttle that emerged was quite different from NASA's original concept, a result of development and design compromises meant to keep costs low and meet the needs of the Air Force and private companies that wanted to use the shuttles for deploying satellites. One compromise was that the new vehicle didn't have a way for astronauts to escape during launch — the Challenger accident changed that.

NASA promised the program would be self-sufficient and would pay for itself with more than 30 flights a year. But the Challenger disaster in 1986 grounded the shuttles for 2 1/2 years. The death of seven astronauts, including teacher Christa McAuliffe, ended the myth that space flight by shuttle could become as routine as flying an airplane.

Tragedy struck again in 2003 with Columbia's disintegration over Texas, killing another seven astronauts.

Recently, NASA chief Michael Griffin said that NASA's decision to retreat to low-Earth orbit after going to the moon is now "universally regarded as having been a mistake. The race to the moon in the 1960s did more harm to the American space program in the long run than it did good because the buildup was not sustainable, and it was followed by the inevitable build-down, and we've been paying for it for 35 years."

In 2004, President Bush announced the shuttles would be retired in 2010 with the completion of the international space station and replaced by another vehicle that could return humans to the moon and eventually on to Mars.

Despite the broken promises of the shuttle, many NASA officials and shuttle workers say they're going to miss the spacecraft after spending almost three decades working on it.

"It's going to be a bittersweet day when we retire the space shuttle, because the space shuttle really has been my entire career," said Wayne Hale, shuttle program manager. "I understand its shortcomings. But I'm going to be sorry to see it go into the Smithsonian."