Going Mainstream - GPS Declassified: From Smart Bombs to Smartphones - page 143

networks but also personal computers and countless devices with embedded
computer chips. Predictions ranged from the inconvenient—stalled cars, stuck
elevators, and power blackouts—to the apocalyptic—chaos in the streets, planes
falling from the sky, and nuclear missiles launching themselves. 156 Govern-
ments and corporations spent more than $250 billion worldwide on software
and hardware fixes in the last few years leading up to the rollover. 157
In this charged environment, news reports trumpeted a similar but unre-
lated potential problem for gps receivers at midnight on August 21-22, 1999.
“Coming Satellite Adjustment a y2k 'Dress Rehearsal,'” announced the Globe
and Mail (Toronto, Canada). 158 “gps Users May Want to Dust Off Compasses,”
advised the Washington Times . 159 “Date Flaw Could Sink Navigation Systems,”
warned Computing magazine. 160 However, the gps “end-of-week” rollover was
neither a flaw nor unexpected; it is an integral part of the way gps marks time.
gps does not operate on a 365-day year. The largest unit of time in the gps sys-
tem is one week, or 604,800 seconds. 161 Starting at week zero, the first one
pegged initially to midnight (Greenwich mean time), January 5-6, 1980, the
system operates for 1,024 weeks, about twenty years, and then rolls over like
an odometer to week zero again. This provides a continuous time scale, unlike
Coordinated Universal Time (utc), maintained by the U.S. Naval Observa-
tory, which periodically adds leap seconds to adjust for the earth's rotation in
the same way that leap years adjust the calendar for the earth's orbit. There is
nothing significant about the 1,024-week cycle. It results from the scheme used
to represent each week in ten-digit binary code—zeros and ones—in the stream
of digital signals gps satellites transmit to receivers. 162 In a ten-digit sequence
the number of unique combinations of zeroes and ones is 1,024—two raised
to the tenth power (2 10 ).
The rollover had no effect on the gps satellites themselves but put at risk
receivers built before 1993, when manufacturers adopted new specifications
designed to accommodate it. 163 Nevertheless, gps hardware makers, which
analysts estimated to make up a $4.4 billion industry in 1998, perceived sig-
nificant liability issues and issued public warnings. 164 Trimble Navigation
warned consumers on its website to avoid using gps devices during the week
before the rollover, calling such use “potentially hazardous.” 165 Federal agen-
cies from the Department of Transportation to the Consumer Product Safety
Commission issued advisories referring consumers to the U.S. Coast Guard
Navigation Center's website or a toll-free y2k hotline (888-usa- 4y2k, later
acquired by a savvy telemarketer) for inquiries about devices or manufactur-