NSSDCA ID: 1973-049A-07
Mission Name: Mars 5This investigation comprised two photometers, one (VFM-73) covering the wavelength range 0.32 - 0.70 microns (3200 - 7000 A) and one (ITM-73) covering 0.77 - 0.87 microns (7700 - 8700 A). The objective of the experiment was to photometrically scan the martian surface at various wavelengths from the near-ultraviolet to the near-infrared to determine properties of the rock and regolith.
The VFM-73 polychromatic photometer had two modes, a static mode which would be employed for 150 seconds of each 180 second measurement period, and a scanning mode which lasted 30 seconds. The static mode employed a 1 degree field-of-view of the surface through a 20-mm f/5 objective which was directed parallel to the radiometer, IR-altimeter, and other instruments. The light passes through one of six filters in a filter wheel with effective wavelengths 3200, 3700, 4100, 4900, 5600, and 7000 A. The 3700 A filter is wide-band with a bandwidth of ~300 A. The others are interference filters with bandwidths from 60 A at 3200 A to 100 A at 7000 A. The light then passes through a diaphragm directly into an FEU photomultiplier tube. The measurement time is one second.
In the scanning mode of VFM-73 the light passes through a different objective which swings through a scanning angle of 120 degrees at 6 degrees per second, repeating every 180 seconds, to provide observations of the surface at different phase angles. This mode also had a field-of-view of 1 degree. The light passes through one of two filters, both centered at 7000 A, but one with a bandwidth of 100 A and one at 500 A. The light is then directed to the FEU photomultiplier tube. The instrument has a marker for the coincidence of the scanning objective look direction with the static objective. The output of the photomultiplier tube goes to a circuit operating in either a linear or logarithmic regime, the regime and sensitivity can be controlled by ground command or automatically. With the proper settings, the relative accuracy can be as high as 2%.
The ITM-73 scanning photometer is designed to measure brightness differences in regions adjoining the ground track of the spacecraft. Light from the surface passes through a 20-mm diameter objective lens, which rocks back and forth over a 30 degree angle perpendicular to the spacecraft motion, with a period of 3 seconds. The light passes through a diaphragm which isolates a 0.25 degree angle and then through a filter centered at 8200 A with a bandwidth of about 1000 A. The light then enters an FEU photomultiplier tube. The signal from the tube is conditioned by an automatic gain-control and amplifier device with a long time constant and another amplifier with a short time constant. The signal due to rapid changes in brightness is transmitted in the linear scale, while slow changes are transmitted in a logarithmic scale. The accuracy of the ITM-73 is about 20%.
Questions and comments about this experiment can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. L. V. Ksanfomaliti | Principal Investigator | Institut Kosmicheskich Issledovaniya (IKI) |