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For the past 30 years, the space shuttle has been the only spaceship Americans have known.

On its 135 missions (the last one is set for July 8), it will have rocketed 355 men and women into Earth's orbit and docked with the International Space Station.

While many space enthusiasts acknowledge that the shuttle program should retire after 30 years of space flight, many are disheartened by the lack of an immediate successor.

"It's sad that NASA isn't doing a replacement," said Mike Wirthlin, an associate professor of electrical and computer engineering at Brigham Young University. "It's not so much the end of the shuttle, but the lack of anything to replace it."

NASA stopped the space-shuttle program and instead chose to extend the life of the International Space Station after Congress' new budget required the decision to be made, said NASA Deputy Administrator Lori Garver during an Internet broadcast June 28 during which she answered questions from Twitter users.

NASA astronauts will continue to travel to the International Space Station, but it will be aboard Russian Soyuz capsules launched from that country.

Alliant Techsystem's Utah-based aerospace systems group, which created the reusable solid rocket boosters used to launch the space shuttle, were contracted to create the Ares rockets that originally were going to replace the shuttle. The federal government scrubbed the program, saying it would cost too much and not meet deadlines for reaching the moon and Mars.

Seth Jarvis, director of the Clark Planetarium in Salt Lake City, said he is "troubled" by the fact that no immediate replacement is available. He's also baffled that the shuttle program was cut due to budgetary constraints.

"In the history of the space shuttle, the total cost for all 135 space launches is the same as the AIG bailout: $160 billion," he said. "NASA is one-half of 1 percent of the federal budget, so you're really not saving much by putting the squeeze on them. We've put footprints on the moon, tire tracks on Mars and sent an armada of spacecraft exploring. The NASA budget is truly trivial."

NASA is planning to let private companies design a low-Earth-orbit vehicle that can serve as a replacement for the shuttle, "so we can focus on the more challenging efforts of the space program," Garver said. That includes sending an unmanned spacecraft to an asteroid, one day returning to the moon and eventually going to Mars.

"NASA is about pushing the envelope, and I don't think there are many of us who don't recognize the pull of the red planet as being a human destination," she said.

NASA designed the Orion capsule to carry crew members as part of the discontinued Constellation program. Engineers plan to use that design to create a Multi-Purpose Crew Vehicle. There are also plans for a heavy-lift vehicle to carry cargo, and ATK may have a role in designing the rockets for that spacecraft. That contract has not officially been awarded, but ATK is already working on a new design for booster rockets under a previous contract. Those rockets will be part of an upcoming ground test in September.

But not having a definite plan in place leaves many feeling at a bit of a loss, including Troy Munro, who is entering the mechanical and aerospace engineering master's program at Utah State University.

"Without having a space shuttle or have something that America can send Americans up in, we don't have anything that can inspire the next generation," Munro said. "I've been watching a lot about the Apollo program, and it was awesome that we could build that and then the space shuttle. But now, we have nothing."

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