The Power of Conversion

by Dale Easley

April 1st, 2003

I was born into the North Carolina Baptist Bible belt, where walking the aisle was a passage of adolescent life. These teenage conversions were expected by our parents and peers, but seem to have limited impact on subsequent hell-raising. However, the artform of ineffective conversions was raised to a higher level in 1999, and some engineers at NASA needed to do some serious soul-searching. Because of a units conversion problem, the $125-million Mars Climate Orbiter (MCO) was lost, probably burning upon entering the Martian atmosphere or hurtling through space in an orbit around the sun.

The MCO was launched in December, 1998, as the first interplanetary weather satellite. During the nine months it flew towards Mars, its trajectory was constantly adjusted by firing small guidance rockets. Unfortunately, the software that calculated the trajectory used English units. NASA requires the use of metric units, but Lockheed Martin, an outside contractor, supplied the numbers from their software without noting that the units were English (e.g., 1 pound force = 4.45 Newtons). NASA engineers assumed they were metric. Assume = ASS(U + ME).

The use of the wrong units caused very little difference in the trajectory for any individual firing of the guidance rockets. However, over the nine months of interplanetary travel, the small errors compounded. The planned elevation above the Martian surface (initial periapsis) at which the MCO was to have fired its main engine and achieved elliptical orbit was to have been 226km. (See figure below.) As we know from the recent Columbia disaster, the descent through the atmosphere leads to rapid heating. The lowest elevation for the initial periapsis estimated to be survivable by the MCO was 80km. Subsequent studies of the MCO's trajectory determined the elevation to have been 57km.

Figure showing planned (estimated) and actual trajectory, from Mars Climate Orbiter Mishap Investigation Board Phase I Report, November 10, 1999. The report on the investigation of the crash is at http://www.space.com/media/mco_report.pdf

Americans have become accustomed to multiple units of measure. We buy a two-liter Coke but a gallon of gas, run a 10km race but drive 3000 miles between oil changes, and take a 100mg aspirin tablet but weigh 20 pounds more than is healthy. Every industrialized country in the world except the U.S. uses the metric system. We started moving that way in with the Metric Conversion Act of 1975, and a U.S. Metric Board was established to smooth the transition. However, the Reagan Administration cut the Board in 1982. A subsequent bill, the Omnibus Trade and Competitiveness Act of 1988, recognized that international competitiveness required that the U.S. begin to adopt the metric system and required the federal government to use it for business-related activities. However, adoption by the rest of us is still voluntary. Thus, the two systems continue to coexist.

When the preachers of my youth tried to get us to convert, they were always quick to point out our sinful nature. Our degraded selves must not be allowed to supplant the glorious selves that God intended. Likewise, the miserable failure of the MCO mission should have been enough to get Americans to the see the error of our ways. We took our first step down the metric aisle years ago, but we've become the worst kind of backsliders. We are clinging to a way of life that is destructive to us, isolates us from the world around us, and can no longer be justified. A conversion is needed.