tions across the continental U.S. (see
Figure 1). DARPA selected readily ac-
cessible public sites where the balloons
would be visible from nearby roads,
each staffed by a DARPA agent who
would issue a certificate validating each
balloon location. While general infor-
mation about the Challenge (such as
date and time of the deployment, with
a picture of a balloon) had already been
distributed, some details were not an-
nounced (such as DARPA’s banner on
each balloon and an attendant at each
balloon issuing certificates). Teams
submitted their guesses to a DARPA
Web site and were given feedback as to
which balloons had been identified cor-
rectly. While the balloons were sched-
uled to be taken down at 5:00 p.m. local
time, DARPA was prepared to re-deploy
them a second day and leave the sub-
mission process open for up to a week
until a team identified all 10.