The Mars Surveyor '98 Lander Descent Imager (Mars Descent Imager, or MARDI) consists of optics, a focal plane assembly (FPA), Data Acquisition System (DAS) electronics, and a power supply, developed under Planetary Instrument Definition and Development Program (PIDDP) funding. It is characterized by small physical size (~5 X 5 X 9 cm, <500 gm), low power requirements (<3 W, including power supply losses), and high science performance (1000 X 1000 pixel, low noise images acquired every 2 seconds, and ultimate resolution better than 1 cm/pixel). Depending on available data storage and computational resources, MARDI will acquire 8 to 16 images, spanning three orders of magnitude in scale, during the roughly 70-80 seconds between aeroshell jettison and spacecraft touchdown. Mission operations and coordination of data return benefits greatly from use of facilities and personnel at Malin Space Science Systems (MSSS) shared with the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) operations effort. These shared resources not only greatly reduce operations cost and complexity, but permit extremely rapid data return (<12 hr, depending on landing site location), as MOC data resources can be allocated to return these descent images through the use of the Mars Relay.
Moreover, descent imaging systems provide a crucial link between orbiter and lander observations. They provide context for the lander data as a function of scale (resolution) and area. No other form of observation provides such context.
The Mars Surveyor '98 Announcement of Opportunity uses a common theme--volatiles and the long-term evolution of the martian climate--to focus mission science objectives. MARDI addresses this theme not by measurement of a particular elemental isotope or molecular species, but by searching for landforms representative of surface processes that reflect the martian environment, by providing other instruments the ability to reject or accept their own measurements based on the general and specific geologic context of those observations, and by linking orbiter observations to those made by the lander.
The primary contributions of descent imaging to climate studies will be through serendipitous observation of primary and/or secondary landforms that show the action of environmentally-specific processes (e.g., channeling, patterned ground, etc.), and through the constraints placed on relative age relationships of features seen at the landing site (e.g., features imaged at resolutions between millimeters and meters are likely to reflect surface processes that operate on timescales of a few years to a few hundreds of millions of years).
The Mars Surveyor Program Science Definition Team (MSPSDT) differed from the Mars Science Working Group (MSWG) in its view of descent imaging. The MSPSDT believed that descent imaging, while important, was likely to cost too much in payload resources (in particular, dollars, mass, and power) to be included in each of their illustrative payloads, although they did include it in one as an example. In contrast, the MSWG has previously acknowledged the importance of descent imaging by including it in every Mars surface mission scenario it has recommended. The two positions are reconciled by this proposal, which meets the science and observational goals of the MSWG within one-eighth to one-half of the resources contemplated by the MSPSDT.
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