When I was asked to write an opinion piece on whether the space shuttle program was worth the cost, I immediately agreed because I have a significant bias toward justifying the program that has dominated my career at NASA. However, because I am very interested in accurately describing the legacy of the shuttle program, I have attempted to make an objective evaluation.

Over 30 years, the shuttle cost $3-5 billion per year for production and operations, plus the loss of two orbiters and flight crews and the potential opportunity cost of focusing NASA's best engineers and technicians on this program.

Out of the yearly budget of $3-5 billion, the shuttle program spent roughly $400 million per flight. The rest was required for the fixed costs of a human spaceflight program, including the specialized labs, test facilities, control centers, integration cells and the expert personnel to staff them. In fact, the program paid for over 90% of the costs of running facilities such as the Kennedy Space Center, the propulsion test stands at the Stennis Space Center in Mississippi and the Mission Control Center in Houston. As the Augustine panel stated, “The shuttle program today carries much of the costs of facilities and infrastructure associated with the human spaceflight program as a whole.”

Because some subset of these fixed costs will be part of any human spaceflight activity, the shuttle should be judged on what was delivered for $400 million per flight. The U.S. gained the most capable, sophisticated spacecraft ever flown, with a safety record better than any other existing launch vehicle.

Critics have postulated that the money spent on the shuttle program could have been used for other research, alternative launch vehicles or unmanned activities with different capabilities or goals. This assertion is speculative, because there is certainly no guarantee that money saved from the shuttle program would have been made available for other space-related activities.

What is not speculation are the tangible accomplishments in the program's 30 years—135 flights, 852 astronauts flown to orbit, 3.5 million lb. of cargo mass delivered and 179 payloads deployed.

The shuttle launched the Galileo spacecraft to Jupiter, the Magellan spacecraft to Venus and the Ulysses spacecraft to study the Sun.

It deployed three of the “Great Observatories”—the Hubble Space Telescope, the Compton Gamma Ray Observatory and the Chandra X-Ray Observatory.

The shuttle has been instrumental in Earth sciences and environmental monitoring, from deployed spacecraft such as the Upper Atmospheric Research Satellite to mapping the Earth's surface with synthetic aperture radar.

U.S. Defense Department missions by the shuttle improved national security; Hubble repair missions allowed scientists to upgrade instruments; and Spacelab and Spacehab missions developed experiment protocols used on the International Space Station (ISS) today. And to finish up the last half of the program, the shuttle visited and resupplied Russia's Mir space station nine times and supported construction of the U.S., Canadian, Japanese and European portions of the ISS during 37 flights, becoming an instrument of partnership with other space-faring nations.

Clearly the shuttle has been an incredible platform for a diverse set of iconic missions. But another legacy—and potentially the most valuable contribution from this launch system—is its value as a learning tool. The shuttle has quite simply enabled the U.S. to understand how to live and operate in low Earth orbit.

The program is much more diverse than most people can imagine. There are expert teams in thousands of fields—logistics, production, integration, packaging of materials, chemical testing, spacesuit design, avionics, materials science and countless other areas that have developed the expertise over 30 years of operations to be able to accomplish a wide variety of activities in low Earth orbit. In fact, the very last shuttle mission, STS-135, was the first that did not require some type of new cargo hardware in the payload bay. The missions that were flown by the shuttle were always changing, and because of those changes the teams were always learning. What was perceived by some as an opportunity cost actually turned out to be one of the best features of the program—take your best engineers and technicians and expose them to a safety culture that demands perfection and requires tangible products on a given schedule.

Even the accidents were learning tools. These were the worst professional experiences imaginable. The teams learned and relearned the importance of attention to the smallest details, the importance of understanding completely how the vehicle is performing in flight and the critical importance of the balance between two words: “Fly Safely.” The accidents also taught us resilience and developed a determination to do better, as well as courage to carry on with the important goals of U.S. space policy even though there can be ultimate consequences.

As the shuttle program shuts down, this combined set of knowledge will be dispersed to various areas. Some will be seeded to the newly forming commercial activities. Most of the combined knowledge base will be used to make the next U.S. human space program successful.

Critics of the shuttle sometimes point back to hyperbole from 40 years ago. There were promises of cheap, routine access to space. However, these promises were made by a NASA that had a total of 25 human orbital spaceflights (four Mercury, 10 Gemini, 11 Apollo). It could be argued that NASA did not have the experience to make those promises at that time. The shuttle, as designed, would never approach those goals, but as the sole American human spaceflight vehicle, it served as a tremendous learning tool. Where we are today in our understanding of how to live, work and operate in the space environment is far beyond where we were after Apollo and Skylab.

Whether you agree with the shuttle approach or not, the result of using this incredible learning tool has been a collection of knowledge about how to live and work in space. This knowledge is ours now, and it is a tremendous asset moving forward. When asked whether the shuttle program was worth the cost, I ask, “How do you place a dollar figure on something that is priceless?”