  There are currently no experiments, either satellite or ground-based, that
are sensitive to astrophysical gamma-rays at energies between 20 and 250 GeV.
We are developing the Solar Tower Atmospheric Cherenkov Effect Experiment
(STACEE) to explore this energy range. STACEE will use heliostat mirrors at a
solar research facility to collect Cherenkov light from extensive air showers
produced by high energy gamma-rays. Here we report on the results of prototype
test work at the solar facility of Sandia National Laboratories (Albuquerque,
NM). The work demonstrates that the facility is suitable for use as an
astrophysical observatory. In addition, using a full scale prototype of part of
STACEE, we detected atmospheric Cherenkov radiation at energies lower than any
other ground-based experiment to date.
