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Geek Trivia: Too cool for fuel

What two common chemicals are the primary fuel sources for SpaceShipOne?

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Yuri Gagarin… Neil Armstrong… Mike Melvill?

One of these three is not like the others, but it isn't because Melvill isn't a bona fide figure from space history. On the morning of June 21, 2004, Melvill assumed his place in history among the pantheon of spaceflight legends by becoming the first pilot of a privately funded passenger spacecraft, Scaled Composites' SpaceShipOne.

Just as Gagarin was the first human to orbit the earth, and Neil Armstrong was the first human to set foot on the moon, Melvill is the first human to reach space without the financial and technical backing of an international superpower. As such, Melville received the first pair of commercial astronaut's wings from the U.S. Federal Aviation Administration shortly after guiding SpaceShipOne back to its launch strip in the Mojave Desert.

Yet, despite Melvill's rightfully earned place in history—let alone the fact that he made this historic flight at the tender age of 63—it is SpaceShipOne that has garnered most of the headlines, and perhaps rightly so. Developed over the last nine years for the bargain basement price of a little more than $20 million, SpaceShipOne is currently a leading contender for the Ansari X Prize, a privately funded $10 million reward for the development of a nongovernmental, nonmilitary, reusable spacecraft.

Under the terms of the X Prize, a reusable craft must ferry a three-person crew to a 62.5-mile altitude and return safely—then repeat that same feat within two weeks. In contrast, NASA's space shuttles cost in the neighborhood of an estimated $6 billion to construct (not counting development contracts) and roughly $500 million to launch—and it takes months to recondition these hardy spacecraft for relaunch.

One of the key technical and financial cost drivers of the space shuttle is its fuel sources, which includes highly volatile, highly pressurized, and highly freakin' cold liquid oxygen and liquid hydrogen. To meet the extremely high bar set by the X Prize, SpaceShipOne hopes to do better than the shuttle in terms of a fuel source.

Scaled Composites founder Burt Rutan believes his company has met that challenge by using two surprisingly simple, common, and comparatively safe chemicals as the basis of SpaceShipOne's fuel supply.


What two common chemicals serve as the basis for SpaceShipOne's fuel source, a key technical innovation that, in some respects, has made this privately funded spacecraft safer and more advanced than NASA's space shuttles?

The chemicals are hydroxy-terminated polybutadiene (HTPB) and nitrous oxide (N2O), better known as rubber and laughing gas.

Virtually all rocket motors require two fuel components, a base fuel and an oxidizer. The space shuttle uses liquid hydrogen as the base fuel and liquid oxygen as the oxidizer, but both components are individually explosive, require high pressure storage to remain in liquid form, and are lethally cold when under such pressure.

Some other liquid fuel rockets use kerosene instead of liquid hydrogen, which is just as explosive but easier to store. All liquid fuel rockets mix the fuel sources in flight, and they can shut off the mix reaction to end the fuel burn if necessary, but this requires extremely complicated engine designs.

Solid fuel rockets premix the two fuel components, which is far simpler in terms of rocket design and therefore cost, but it presents the safety problem of an unstoppable fuel burn. Once you ignite a solid rocket motor, it won't stop firing until all of the fuel is exhausted. Moreover, solid rocket motors often use toxic fuel mixtures, as is the case with the shuttle booster mix of ammonium perchlorate and aluminum.

SpaceShipOne's engines are hybrid rocket motors; they combine elements of both solid and liquid fuel engines. The crew preloads solid wedges of HTPB into the engine reaction chamber, and a nozzle sprays these elements with the N2O oxidizer during flight, creating a controllable reaction.

The pilot can halt the reaction, like a liquid fuel rocket, but without all the difficult pressure mechanics of the shuttle engine design. Moreover, N2O is self-pressurizing at room temperature, simplifying things even further. Best of all, the hybrid engine's chemical byproducts are water vapor, carbon dioxide, carbon monoxide, and nitrogen, which are less toxic than the shuttle boosters' byproducts.

Of course, it's not quite that simple. Researchers have studied the N2O and HTPB fuel pairing in the past, and they found that motors employing this combination burned too slowly for use in rockets. Somehow, Scaled Composites has found a way around this problem, probably with some secret ingredient for the fuel mixture. Whatever the solution, that trade secret could mean the difference between the dream of commercial space flight and the reality.

The Quibble of the Week

If you uncover a questionable fact or debatable aspect of this week's Geek Trivia, just post it in the discussion area of the article. Every week, yours truly will choose the best post from the assembled masses and discuss it in the next edition of Geek Trivia.

This week, we're going to reach all the way back to the April 20 edition of Geek Trivia, "Personal success," to highlight a particularly troubling mistake on my part. In this issue, I let a poor choice of words imply that Bill Gates and Paul Allen authored the BASIC programming language that accompanied the legendary Altair 8800 personal computer.

TechRepublic member Jkwiat rightfully pointed out my gross error:

"If a language can be said to belong to anybody, it belongs to the people who developed it. The Altair may have run a licensed version of Bill Gates' and Paul Allen's BASIC interpreter, but the language it interpreted was developed by Dr. John Kemeny and Dr. Thomas Kurtz in 1964 at DartmouthCollege."

For the uninitiated, Kemeny was one of Einstein's personal assistant mathematicians and later president of Dartmouth. Kurtz was one of the pioneering forces of the computer science program at Dartmouth. Both are worthy of geek reverence, and I offer great thanks to Jkwiat for reminding us of these giants.

The Trivia Geek, also known as Jay Garmon, is a former advertising copywriter and Web developer who's duped TechRepublic into underwriting his affinity for movies, sci-fi, comic books, technology, and all things geekish or subcultural.

About Jay Garmon

Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can a...

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