American Scientist

To the Editors:

"Filling Up with Hydrogen" by David Schneider (Science Observer, September-October) notes that regeneration of the ammonia borane "is critical." But it must be cheap too. Hydrogen-as-hydride in boranes is a large, difficult, and expensive thermodynamic step from the elemental molecule or the hydrogen ion. The post-Sputnik High Energy Fuels (HEF) program, in which I had a part, expended tens of millions of dollars and failed to get boranes production costs below the dollars-per-pound range, far higher than the cents-per-pound requirement for a hydrocarbon replacement fuel.

Richard A. Carpenter
Charlottesville, VA

To the Editors:

I read "Filling Up with Hydrogen" with much interest. The article says that ammonia borane and ammonium borohydride were studied in the 1950s for their possible use in rocket fuel. I would appreciate it if you could tell me why this idea was later abandoned.

Judy Budny
Natick, MA

Dr. Schneider replies:

My article noted that regeneration of ammonia borane "by somehow putting the hydrogen back" was "necessary for this scheme to be economical for anything but niche applications." And it suggested that such regeneration indeed remains a great technical challenge. But Mr. Carpenter is correct that my reporting gave short shrift to the history of attempts to make and use such fuels in the past. According to an article by David Schubert of U.S. Borax, the HEF program, in fact, began in 1956 (a year before the launch of Sputnik) and was the last of three secret military programs in the United States to develop boron-hydride fuels for rockets and jet aircraft. My article noted only that these compounds were investigated in the 1950s for possible use in rocket fuel, so I thank Mr. Carpenter and Ms. Budny for prompting me to look further into this fascinating piece of aerospace history.