Re: Stereo in space

[P3D Gregory J. Wageman <gjw@xxxxxxxxxx>]

John R. writes;

>The Mars Pathfinder mission that they're trying to launch again tonight
>(Tuesday night) incorporates stereo imaging in the lander part, or in the
>rover, or in both (I haven't had time to find the Web page yet.) The rover
>uses a laser scanning system to detect obstacles, so I'm not sure whether it
>has an imager as well.

We watched that launch "live" on NASA TV courtesy of our local cable
company.  The Web page is at URL http://mpfwww.jpl.nasa.gov/  Here's
a relevent excerpt about the 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 Xrsted Laboratory, Niels Bohr Institute
 for Astronomy, Physics and Geophysics in Copenhagen, Denmark. It consists
 of three physical subassemblies: (1) camera head (with stereo optics, fil
 er 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.

 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."


(The typos are theirs.)

        -Greg W.


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