Mars Global Surveyor
Mars Orbiter Camera
MOC Focus Test Images
MGS MOC Release No. MOC2-83, 10 March 1999
Observations during the first week of March 1999 were mostly aimed at
acquiring quantitative and qualitative information about the
Mars Orbiter Camera (MOC) in
the environment in which it was originally designed to operate. Chief
among the "calibration" data were measurements of the camera's focus, which
is very sensitive to temperature because the magnification is so high. Using
heaters around the rim (outer portion) and hub (inner portion) of the
primary mirror to minutely change the shape of the mirror, pictures were
taken of stars--which are "point sources" for accurate measurement--and of
the north polar cap and
polar dune field
for comparison between the theoretical quality of the image and the
practical quality.
Two representative focus conditions are shown here.
In each frame, the upper left corner of the left-hand image is shown
enlarged 2-fold on the right. The star Omega 2 Scorpius is shown for
comparison; its oblong shape is an indication of how far and in what
direction focus lies. The closer to a symmetric "circle," the closer to
focus. A comparison of the enlargements shows that subtle features are
better discriminated in the image at 0.35 W hub (lower picture)
than at 0.66 W rim (upper picture),
indicating that heating of the inner portion of the mirror moves the
camera closer to focus. The two MOC images show similar surfaces on
the permanent north polar ice cap at nearly 1.5 meters (5 feet) per
pixel. Each image (left side) shows an area about 578 meters (631 yards) wide;
illumination is from the upper right.
Malin Space Science Systems and the California Institute of
Technology built the MOC using spare hardware from the Mars Observer
mission. MSSS operates the camera from its facilities in San Diego,
CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project
operates the Mars Global Surveyor spacecraft with its industrial
partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA
and Denver, CO.
To MSSS Home Page
Contact: info@msss.com
