The surprising spinoff of Projects Bumblebee and SQUID

Basic research, its proponents argue, is worth funding because of its sometimes surprising and valuable spinoffs. When Glenn Seaborg and his colleagues began making new transuranic elements in the 1940s, they didn’t have in mind the use of one of them, americium, in household smoke detectors. Applied research, even mission-directed research, can have surprising spinoffs, too.

In 1945 John Fenn was invited by James Mullen of Bell Labs join Project Bumblebee, a program to develop ram-jet powered antiaircraft missiles for the US Navy. Up to that point, Fenn, who had earned a PhD at Yale in electrochemistry, had worked for Monsanto in Anniston, Alabama, and for Sharples Chemicals in Wyandotte, Michigan. He had no experience in jet combustion and propulsion.

Then, having acquired at least a reputation for expertise in jets, Fenn was recruited to lead Project SQUID, a program at Princeton University funded by the Office of Naval Research. Like Bumblebee, SQUID was about jet propulsion, but it was more open-ended. Its goal was to elucidate the physics and chemistry of hot gases expelled from nozzles.

If you read the article by Dawn Manley, Andrew McIlroy, and Craig A. Taatjes, “Research needs for future internal combustion engines” (Physics Today, November 2008, page 47 ), you might remember that ignition and combustion are difficult to study in detail. Indeed, it remains impossible to model what goes on inside a car engine on all the relevant scales of length and time.

Tackling a similar modeling challenge but with 1950s tools, Fenn realized that he could make more progress by studying a simpler system: the expansion through a nozzle of jets of cold molecular gas. In 1989, having worked on molecular jets for three decades, Fenn and his colleagues published the unexpected culmination of that realization in Science.

In that paper, Fenn’s team demonstrated a new method for determining the molecular weight of bulky biomolecules. Squirting a solution of molecules through an electrified nozzle forms a spray of ionized droplets. The solvent surrounding each molecule evaporates to leave single molecular ions, whose mass can be measured by a mass spectrometer.

The photo shows Fenn’s first electrospray ionization mass spectrometer, an invention for which he shared the 2002 Nobel Prize in Chemistry.

Another unexpected spinoff from applied research—again with a naval history—arose from a commission that Lord Rayleigh received in 1917 from the British Admiralty. Why, the admiralty wanted to know, were the rapidly spinning propellers of turbine-driven warships deteriorating so rapidly?

Rayleigh identified the cause: cavitation. As a ship’s propeller spins, it subjects the surrounding water to rapid and intense changes in pressure. At low pressure, voids—cavities of vapor—form on the propeller surface. At high pressure, the cavities collapse and in doing so direct a jet of liquid at the surface. The cumulative effect of that bombardment eventually creates pits in the propeller’s steel surface.

The formulas that Rayleigh developed to characterize cavitation apply in a quite different and beneficial context: extracorporeal shock wave lithotripsy , the noninvasive destruction of kidney stones using ultrasound.