Imager for Mars Pathfinder (IMP)
The Imager For Mars Pathfinder is a stereo imaging system with color capability provided by a set of selectable filters for each of the two camera channels. It has been developed by a team lead by the University Of Arizona with contributions from the Lockheed Martin Group, Max Planck Institute For Aeronomy in Lindau, Germany, the Technical University Of Braunschweig in Germany and the Ørsted Laboratory, Niels Bohr Institute for Astronomy, Physics and Geophysics in Copenhagen, Denmark. It consists of three physical subassemblies: (1) camera head (with stereo optics, filter wheel, CCD and pre-amp, mechanisms and stepper motors); (2) extendable mast with electronic cabling; and (3) two plug-in electronics cards (CCD data card and power supply/motor drive card) which plug into slots in the Warm Electronics Box within the lander.
Close-Up of the IMP Camera
Head
Azimuth and elevation drives for the camera head are provided by
stepper motors with gear heads, providing a field of regard of ±180 degrees in azimuth
and +83 degrees to -72 degrees in elevation, relative to lander coordinates. The camera
system is mounted at the top of a deployable mast, a continuous longeron, open-lattice
type provided by Able Manufacturing, Inc. When deployed, the mast provides an elevation of
1.0 m above the lander mounting surface.
The focal plane consists of a CCD mounted at the foci of two optical
paths where it is bonded to a small printed wiring board, which in turn is attached by a
short flex cable to the preamplifier board. The CCD is a front-illuminated frame transfer
array with 23 micrometer square pixels. Its image section is divided into two square
frames, one for each half of the stereo FOV's. Each has 256x256 active elements. A 256x512
storage section (identical to the imaging section) is located under a metal mask. The imp
focal plane and electronics are nearly identical copies of the comparable subsystem
employed in the Huygens Probe Descent Imaging Spectroradiometer (DISR), using the Loral
512X512 CCD.
The stereoscopic imager includes two imaging triplets, two fold mirrors
separated by 150 mm for stereo viewing, a 12-space filter wheel in each path, and a fold
prism to place the images side-by-side on the CCD focal plane. Fused silica windows at
each path entrance prevent dust intrusion. the optical triplets are an f/10 design,
stopped down to f/18 with 23-mm effective focal lengths and a 14.4 degree field of view.
The pixel instantaneous field of view is one milliradian. The filter wheel four pairs of
atmospheric filters, two pairs of stero filters, eleven individual geologic filters
(which, when combined with the two pairs of stereo filters, result in thirteen distinct
geologic filters) and one diopter or close-up lens, designed to acquire images of
magnetic, wind-blown dust which adheres to a small magnet located on the IMP tip plate.
Full panoramas of the landing site are acquired during the mission
using the stereo baseline provided by the camera optics. Additionally, monoscopic
panoramas are acquired both prior and subsequent to the mast deployment, yielding
vertically displaced stereo pairs with approximately 80 cm baseline. Images of a
substantial portion of the visible surface are acquired in multispectral images with as
many as eight spectral bands.
IMP Deployed On The Able
Mast
A number of atmospheric imvestigations are carried out
using imp images. aerosol opacity is measured periodically by imaging the Sun through two
narrow-band filters. Dust particles in the atmosphere are characterized by observing
Phobos at night. Water vapor abundance is measured by imaging the Sun through filters in
the water vapor absorption band and in the spectrally adjacent continuum. Images of wind
socks located at several heights above the surrounding terrain are used to assess wind
speed and direction.
A magnetic properties investigation is included as part of the IMP
investigation. A set of magnets of differing field strengths will be mounted to a plate
and attached to the lander. Images taken over the duration of the landed mission are used
to determine the accumulation of magnetic species in the wind-blown dust. Multispectral
images of these accumulations may be used to differentiate among likely magnetic minerals.
The IMP investigation also includes the observation of wind direction
using a small wind sock mounted above a reference grid, and a calibration and reference
target mounted to the lander.