The Eco Pros and Cons of the Space Shuttle Program
Today’s final landing of space shuttle Atlantis marks the end of an era for NASA, closing the careers of countless engineers, specialists, mission control personnel and even astronauts. The shuttle program was ground-breaking, innovative, exciting to witness and resulted in countless advances in technology of all kinds: spaceflight, engineering and telecommunications just for starters.
One questions that gets asked today (that probably didn’t get asked during the early days of the program 30 years ago) is: was the shuttle program green, or at least carbon-neutral? Or was it harmful? Did it produce any advances in environmental science? Was it the sort of program a person who loves the planet could support enthusiastically?
The definitive answer is “Yes.” And “No.”
Clear as mud, huh? Visit the message board underneath any recent news item about a shuttle roll-out, launch or landing, and inevitably you will find comments discussing the shuttle’s impact on the environment – either good or bad – and whether the “bad” was offset by “good” (green) technologies the shuttle program either directly developed or helped put in place.
The most visible element of a shuttle launch is, of course, acres and acres of what looks like smoke billowing from the launch
platform. Most of this, however, is actually water vapor, produced as a byproduct of burning liquid hydrogen and also from the shuttle’s sound suppression water system. Seconds before ignition of the shuttle’s main engines, nearby water tanks flood the launch platform with 300,000 gallons of water to help insulate against the intense sound waves produced by the shuttle’s ignition and to help protect the platform itself (it being a rather pricey item to rebuild after each launch).
That’s not to say there are no nasty emissions produced by a shuttle launch, and it’s hard to argue that any vehicle that produces 37 million horsepower by burning five tons of super-cooled propellant each second, using as much energy as a single American in his or her entire lifetime, can be “green.”
So let’s examine the program in terms of “pros” and “cons,” and get the “bad” over with first.
Hydrazine. The shuttle’s auxiliary power units (APUs) use hydrazine, a highly toxic and dangerously unstable inorganic compound that is a known carcinogen (in addition to causing all sorts of other nasty health problems such as irritation of the nose and throat; itching, burning and swelling of the eyes; and damage to the kidney, liver and blood cells, even at relatively low concentrations). Hydrazine, a commonly used rocket mono-propellant (meaning it can work as a propellant all on its own without the need to react with some other substance, like an oxidizer) is the result of pairing two ammonia molecules together and then removing a hydrogen from each. Hydrazine’s unstable and dangerous nature is precisely what makes it so valuable for spacecrafts: because it needs no other compound to react with to burn, it can be used as a propellant to fire engines in space. It’s tough to ignite things in space, so the fact that hydrazine is so unstable (it can ignite spontaneously when mixed with an oxidizer: no spark necessary) means it’s ideal to help rockets fire and create thrust in the vacuum of space (or near-vacuum of orbit) in order to help the shuttle change position or angles. It’s also an ideal propellant if you want a quick “start and stop” engine burn in space: since it doesn’t actually require a second compound, like an oxidizer, it can fire an engine for a short period of time and then shut off quickly. With fuels like hydrogen that require an oxidizer, an engine generally must burn until it uses up all the fuel and oxidizer. With hydrazine, the burn can be started and stopped at will.
The fact that hydrazine is so ideal for spacecrafts means that it’s hard to replace. But its health risks are well known: it’s water-soluble and can be absorbed through the skin, which is what makes it such a dangerous human health hazard. In fact, the long, drawn-out procedures NASA goes through after a shuttle landing before the astronauts are allowed to disembark are primarily an effort to ensure that no hydrazine lingers around the shuttle or its exhaust ports before personnel are allowed to approach the immediate exterior of the craft. (It’s also why NASA took such pains to make sure that anyone encountering debris from the break-up of shuttle Columbia in 2003 during its re-entry understood not to touch or even approach the bits.)
Hydrochloric acid. Most emissions produced by the shuttle during launch come from the craft’s solid rocket boosters (SRBs) – which produce more than 70 percent of the thrust needed to lift the shuttle into orbit – and the binding and curing agents that are used for the fuels they consume. One of these binding agents is hydrogen chloride which, when mixed with water, becomes hydrochloric acid. The SRB exhaust also contains some other problematic substances: chlorine, a respiratory irritant; carbon dioxide, which is, of course, a greenhouse gas, and nitrogen oxide, another pollutant. Additionally, the primary component of the solid rocket boosters, the oxidizer ammonium perchlorate, is known to cause thyroid problems.
Other damage. Environment groups also point out that the shuttle launches can cause harm in the form of noise pollution and acoustic bursts during launch and re-entry (when a sonic boom occurs when the vehicle hits the atmosphere) that have the potential to harm or disorient nearby wildlife, though there has been no evidence of any major damage to local flora or fauna near launch and landing sites.
Others have expressed concern about the potential for leaks or mishandling of dangerous cleaning solvents, fuels and other toxic compounds used in spacecrafts and rocket propulsion. During the 30-year course of the shuttle program, of course, two shuttles have been lost: the Challenger during launch in 1986 and the Columbia during re-entry in 2003. In both cases, dangerously contaminated debris rained down on earth, requiring extensive clean-up in an effort to protect both life and the environmental health of the disaster sites.
The environmental upsides of the space shuttle program are many, and few environmentally minded individuals appear to believe that the drawbacks of the program outweighed the benefits.
The hydrogen. While the always up-and-coming Earth-based “Hydrogen Economy” has yet to materialize, hydrogen has been used for a variety of critical mission purposes by NASA for decades.
For starters, hydrogen is the most important element (no pun intended) of the shuttle launch process. Inside the space shuttle’s external fuel tank – the big orange thing – are both liquid hydrogen and liquid oxygen. Hydrogen, which is burned by the shuttle at a rate of 45,000 gallons per minute during launch in concert with 17,000 gallons of liquid oxygen to help the hydrogen burn, is the most abundant element on earth and is high in energy yet extremely clean-burning, so it produces no pollution. (The burning of hydrogen produces water so clean that the astronauts can and do actually drink it.)
But hydrogen isn’t used only as a fuel for the shuttle’s launch. Hydrogen fuel cells provide energy on the orbiter for ordinary operations needs like lighting, life support, computers and scientific equipment. While hydrogen fuel cells are still relatively cutting-edge when it comes to green energy for the wider consumer marketplace, NASA has been using them for manned space travel since the 1960s. The space shuttle is not the first NASA craft to have its orbital energy needs met by hydrogen fuel cells: that honor goes to the Gemini program in the 1960s. (NASA briefly considered using nuclear energy for on-board energy needs, but decided it would be too dangerous.)
In reality, once the shuttle reaches orbit after launch, it uses a negligible amount of energy for operations – all of it provided by hydrogen fuel cells – and tiny positional and course corrections in order to dock with the International Space Station (ISS) and to start its insertion into the earth’s atmosphere for the purpose of descent and landing.
Kinetic energy. When the space shuttle begins its descent to earth, all 115 tons of it are traveling at a brisk 18,000 miles per hour. The friction of the shuttle traveling at high speed hitting the earth’s atmosphere converts this kinetic energy into heat: so much heat that the atmosphere the descending shuttle comes into contact with ionizes into plasma (the fourth state of matter after gas, liquid and solid). The good news is that this energy is free, clean and renewable, in the form of kinetic energy. The shuttle uses the friction and the heat it generates for the purpose of slowing down to effect an efficient re-entry, at which time it essentially turns into a no-power glider. The shuttle’s final slow-down is achieved by the means of some pretty old-fashioned and clean technology: a parachute that uses wind drag to slow the shuttle to a full stop.
Certainly, the shuttle program evolved during its lifetime to be more eco-friendly. Earlier shuttle missions used freon-based foam for some insulation needs. Freon, as we all remember from public service announcements in the 1970s and early 1980s, contributes to depletion of the ozone layer. In later missions, starting with a refitting of the shuttle Discovery, however, NASA swapped out the freon foam to more eco-friendly alternatives.
It’s hard to argue that the space shuttle program, despite its vast use of resources both natural and monetary, hasn’t benefited the planet and its native occupants. The program has launched the Hubble Space Telescope that has greatly furthered our understanding of the universe. It has placed countless satellites, both for telecom and weather and space monitoring, into orbit. It was the most important element in the creation of the International Space Station, having carried a majority of its components into orbit, and it has launched a number of interplanetary probes.
It has also resulted in unintentional ecological benefits. A process developed by NASA called Emulsified Zero-Valent Iron (EZVI) technology – used to clean up launch and vehicle assembly sites contaminated by dangerous solvents – is now part of NASA’s technology transfer program, which means it’s being adapted for commercial use in cleaning up groundwater located at dangerous toxic waste sites all over the world, particularly those contaminated by dense nonaqueous phase liquids, or DNAPLs. EZVI will be useful for cleaning up land that has been polluted by a number of dangerously dirty industries, including dye and paint manufacturing, dry-cleaning, chemical manufacturers, metal cleaning and degreasing facilities, pharmaceutical manufacturing, leather tanning and adhesive and aerosol manufacturing plants.
In addition, the shuttle has deposited a number of satellites into orbit whose job it is to study the earth’s climate and help us better understand how the climate may be changing due to both natural processes and human activity.
While space enthusiasts (like yours truly) will miss the still-thrilling launches, landings and mission updates of the space shuttle program, it’s not hard to understand why the program is being retired. It was an incredibly expensive way to launch payload and humans into space, and in the coming years, we can look forward to more advanced, forward-thinking (not to mention more economical) ways to connect the human race to space, via both governmental agencies like NASA, the Russian Federal Space Agency, the European Space Agency and China’s National Space Administration, plus the efforts of innovative private space enterprises such as Elon Musk’s Space-X or Richard Branson’s Virgin Galactic.
In the meantime, we’ll just have to wait for someone to develop the warp drive. Does anyone know if dilithium crystals are clean-burning and renewable?