1.1. Introduction to Investigation
    1.2. Rationale/Relationship to AO

1.1. Introduction to Investigation

This investigation proposes to fabricate, test, calibrate, and deliver a descent imaging experiment for the Mars Surveyor '98 Lander mission, scheduled for launch in December, 1998. It further proposes to support Mars Surveyor '98 mission operations, to acquire, process, and archive the imaging data, and to provide scientific analyses of the images acquired.

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.

1.2. Rationale/Relationship to AO

Among the most dramatic images returned from space over the past forty years have been those transmitted by the Ranger spacecraft, and those filmed by the Apollo astronauts, during their descents to the lunar surface. These missions not only provided impressive views of the Moon, they did so in particularly memorable ways. In addition to unambiguously telling where a spacecraft has landed, images acquired during descent to a planet's surface provide the public with a visual perspective of spectacular, often breathtaking, beauty and excitement. The process of acquiring such images is simple, and the results easily understood by all who see them. Descent imaging provides tangible results for early release to the public, and engenders a sense of "being there" not usually available with planetary missions.

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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