Two years removed from the Columbia disaster, the June 2005 issue of Popular Mechanics investigated a growing sentiment that the space shuttle needed to be retired. Safety and staggering operating costs had caused many to question its usefulness in the future of human spaceflight. Here both sides argue the pros and cons of NASA's chariot to the stars. While the Space Shuttle would eventually fly its last flight on July 8, 2011, its contribution to human spaceflight remains immeasurable. Retire It Now The shuttle has cost more than its worth from the very beginning. None of the things that it can theoretically be used for\u2014as a mobile laboratory for pharmaceuticals, for instance, or as an experimental site for manufacturing\u2014has economic viability. One of the great tragedies of the Columbia disaster was that it had no mission. NASA just flew it for the sake of flying it. The agency thinks that it has to be constantly operating the shuttle and doing cool stuff or public and congressional support will wither. But the risk the shuttle poses to astronauts is simply unacceptable: one death for every eight flights. An initial selling point was that as a reusable spacecraft the shuttle would cost less to launch than expendable ones. This claim has proved untrue. It\u2019s the world\u2019s most sophisticated launch vehicle, but it is ruinously expensive. In 1971, NASA predicted shuttle development costs would be $5.2 billion. The Congressional Budget Office reported that by the time the shuttle was declared operational in 1982, $19.5 billion had been spent\u2014an overrun of 375 percent. NASA also predicted that the shuttle would cost $10.5 million per flight. It admits now to spending almost half a billion dollars per flight. Even allowing for inflation, NASA\u2019s projections were off by an order of magnitude. Despite the expense, the shuttle has always flown with engineering problems. NASA identifies technical problems in advance of every launch. (These observations could be compared to someone\u2019s car engine light coming on, which sometimes means something serious, and other times does not.) The agency also keeps track of components that have the potential for catastrophic failure, and labels these \u201cCriticality 1.\u201d At the time of the Challenger accident, NASA waived more than 800 Criticality 1 risks\u2014including the questionable performance of O-ring seals that led to the shuttle\u2019s explosion. After the investigation, there was a great infusion of funds and the agency improved the safety systems. But by the time Columbia exploded, the number of Criticality 1 waivers had doubled. NASA simply couldn\u2019t afford to fix the problems that, by its own criteria, were potentially disastrous. All of these problems grow worse as the shuttle fleet ages. Expendable launch vehicles keep getting better; engineers learn from each previous version and advance future designs. Because shuttles are enormously complicated and expensive to continually fix, they become less efficient to launch. Even with improvements, such as the changes made to external tanks and to the insulating foam, the spacecraft pose a risk to the lives on board. Instead of addressing hard engineering, safety, and economic realities, NASA has just bulled ahead with the shuttle program. It has a vision, dating back to the Apollo era, of getting to Mars. I think NASA feels that reaching Mars is of such overwhelming historical significance that it must persevere, no matter what the obstacles. We\u2019re now presumably operating under President George W. Bush\u2019s mandate, announced in January 2004, to complete the International Space Station, retire the shuttle in 2010, develop a new launch vehicle, and then fly that to the moon and Mars. Since we would use the moon as a launching platform for the Mars mission, it would appear the only reason we\u2019re flying the shuttle now is to complete the space station. But it is of no use except as a safe haven for the shuttle\u2019s crew. It\u2019s a circular argument. If NASA will not abandon the space station, there is an alternative to manned shuttle flights. A compromise would be to send people up on Russian spacecraft. NASA could engineer an unmanned shuttle to fly cargo to the station, and have the astronauts meet the components there for installation. It would be much cheaper since the shuttle wouldn\u2019t have to be made safe enough for human passengers. Russia has charged two civilians $20 million apiece to go up in its spacecraft\u2014a piddling amount when a manned shuttle launch costs half a billion. In any case, we now have light, reliable, smart, automated machines that can do anything in terms of space exploration that humans can do\u2014only better, cheaper and safer. They can travel farther and stay on site longer. Take our small, inexpensive Mars rovers, for example. The two now on Mars are performing way past their predicted expiration date of April 2004. The Viking spacecraft that went to Mars in the 1970s also lasted much longer than expected, and the two Voyager spacecraft launched in 1977 continue to transmit data after nearly three decades. If we put people on Mars, what could they do there that rovers couldn\u2019t? Nothing. The only things humans can do better than machines is smell and taste, and no astronaut is going to smell and taste the Martian atmosphere and soil. Rovers can touch, see, and hear better than people can. They can move around with television cameras and look at anything, magnify it, pick it up, and retrieve it. Rovers can go anywhere humans direct them to go, and if they fall and damage themselves the worst that has occurred is the loss of a machine. The real reason behind sending astronauts to Mars is that it\u2019s thrilling and exciting. In the 1960s, the concept that humans were needed for this exploration may have been true, but it\u2019s now both unrealistic and impractical. I think NASA is in the grips of an ideological agenda. I am not saying that NASA should abandon manned spaceflight altogether, but what we\u2019ve learned from the shuttle is that we desperately need a new launch vehicle that can do what the shuttle was initially supposed to do\u2014that is, dramatically reduce the expense of getting into space. It costs so much to launch the weight of our existing vehicle that taking humans into space is prohibitive. After the Challenger accident, it became clear that NASA should not make the shuttle the centerpiece of its launch capability. It\u2019s a marvelous vehicle, but it\u2019s too costly, too fragile, and too dangerous to handle that role. Keep It Flying I was one of the astronauts on board the International Space Station (ISS) when the Columbia disaster occurred. We were all shaken up. For one thing, we lost our friends. But we also knew the explosion was going to have a serious impact on our program. When something like that happens with a shuttle, you can\u2019t expect to turnaround and fly again in three months. I\u2019ve wanted to be in space from the time I was listening to the radio and heard about John Glenn circling the Earth. Columbia was the kind of blow that could have made me walk away from it. As astronauts, though, we wouldn\u2019t have been on the space station if we didn\u2019t believe in the program. Even after losing our friends and our ride home, we still believed that exploration was important. Is the space shuttle both risky and costly? You bet. We will never fly without risk, even though NASA spends a lot of money minimizing it. For months before I board a shuttle, I ask myself, \u201cWhy am I really doing this? Is it worth the risk that my children maybe without a dad?\u201d And I say yes. I do so because the process of sending people into flight molds our ability to judge risk. One might liken it to a surgeon with no previous experience operating on a patient: That same surgeon has a better idea how to assess risk after having done multiple surgeries. Well, our engineers and technicians will use the experience they gain now in the next program. When you take time off, it becomes harder and harder to make these tough decisions. You don\u2019t want to just stop cold. One of the risks we weigh is created by a Criticality 1 part. If it fails, you could lose the vehicle. There are a lot of those parts on the shuttle, and we go through a very rigorous process to identify each one. Then we ask, \u201cIs this something we can actually change, or is this something that we have to accept?\u201d We involve as many people as possible in the discussion, and the process is as important as the outcome. A Real Fixer-Upper NASA spent two years overhauling Discovery. High-speed sensors: New sensors at the leading edge of each wing include 22 temperature gauges and 66 accelerometers that pin-point dings. Each takes 20,000 readings per second. Tile overhaul: NASA used to replace about 100 damaged Thermal Protection System tiles after each flight. For Discovery , NASA replaced 1900. Low-tech Rain Gear: Tyvek replaces butcher paper as the material of choice to rainproof the orbiter's forward Reaction Control System when it is on the launchpad. Sleek cockpit: Discovery 's new "glass cockpit" has 11 flat-panel displays instead of 32 gauges, electro-mechanical displays and four cathode-ray-tube displays. Orbiter boom: Along the Payload Bay, engineers installed a 50-ft. Orbiter Boom Sensor System with a camera, laser, and sensor. The shuttle's robotic can wield the device to scan the underside of the orbiter for damage. Live-feed camera: A digital camera in the belly of the orbiter will beam launch imagery to astronauts and then to ground control. Previous cameras used film, which wasn't developed until the shuttle returned to Earth. RCC panels: More than 400 sq. ft. of Reinforced-Carbon-Carbon panels were removed from the shuttle and blasted with ultrasounds, CT scans, and new flash thermography to check for internal flaws. Sealing out the heat: A thermal protection barrier has been added to the carrier that bridge seams along the leading edge of the wings. This will prevent hot plasma from penetrating the wing structure in the event of a breach. The mission of the Discovery crew is worth pursuing: the completion of the space station. There we can learn how to live in space, how to keep equipment working, and how to pro-vide food, air and water to the crews on board. We\u2019re studying how humans change when they go into microgravity as well. One of the experiments I participated in examined the relationship between muscle activity and bone mass loss. If we can understand the mechanism behind losing bone density, it could help us understand diseases like osteoporosis here on Earth. Internationally, the space station is an important tool for diplomacy. Millions of things in the world pull us apart as nations, and having the space station to hold us together is really valuable. Right now, the shuttle is the only vehicle the United States possesses that can rendezvous with the ISS. Other vehicles could launch the cargo, but it would take quite a bit of research to develop the software for docking. And as for flying with Russia on its spacecraft to complete the station, there\u2019s a law that prevents us from spending the amount of money necessary to do so. The Iran Nonproliferation Act of 2000 says we can\u2019t send money to the Russian Aviation and Space Agency unless the Russian government can demonstrate that it is not assisting Iran with the development of nuclear technology. A shuttle flight is risky, but we\u2019ve done more than ever to make it as safe as it can be. On the external tank, we\u2019ve removed the bipod ramp foam that came off during the Columbia flight and replaced it with electric heaters. Foam on other parts of the tank has been stripped off, and new foam has been applied using processes with a higher level of control. There is also an inner tank area that we believe was particularly subject to nitrogen ice formation. Liquid air would pool at the edge and seep underneath the foam, so we now apply sealant in that area. Behind the reinforced carbon-carbon (RCC) heat panels on the wing, we have placed extra heat-shielding material, and material to block hot gas should one of those breach. There also have been modifications to systems that were not implicated in any previous accident, but which we knew had mechanical issues. For example, we\u2019ve adjusted the devices on the rudder speed-brake mechanisms, and the flow liners for the propellant lines. We\u2019re trying to dig deeper to find problems and work harder to communicate, too. That may not sound like much, but it\u2019s difficult. Breakdowns in communication have led to some of the worst accidents in NASA history: the 1967 fire in the command module of Apollo 1, the Challenger explosion in 1986, and the Columbia tragedy in 2003. When we analyzed those situations, it was frustrating to discover how close we were to catching the problems that caused the disasters. NASA needs to figure out how to move information around in our huge program so that we can make ourselves safer. Finally, I\u2019d like to add that manned exploration itself is a noble thing. The astronauts\u2014along with the teams that put the vehicles together, build the flight plans and design the missions\u2014help to build a road out into our solar system. People are going to leave Earth someday with regularity, and we as Americans are taking the baby steps now. Mars seems to be the planet most hospitable to life. We don\u2019t have to be in a big hurry to get there, but we\u2019ll learn a lot in the process. We want to build a better vehicle forgetting our crews into orbit, but launching the shuttle again is worthwhile. It lays the foundation for further exploration. Traveling into the unknown is a deep human desire, and you can\u2019t take humans out of that equation.