The Making of the Mars Polar Lander Mars Descent Imager (MARDI)

MARDI in the MSSS cleanroom, January 1998.
CLICK HERE for larger image (1.2 MBytes).

MARDI, not much bigger than a pocket knife, consists of a stack of circuit boards and aluminum housings mated with a wide angle lens. The picture above shows the MARDI flight instrument, just after it was completed at Malin Space Science Systems (San Diego, California) and just before it was delivered to Lockheed Martin Astronautics (Denver, Colorado) for integration with the Mars Polar Lander (MPL) spacecraft.

At the back of the camera (above) are the mounting feet--these are used to bolt the camera to the spacecraft. Forward of the feet are a stack of three printed circuit boards, separated by pieces of aluminum housing and cabled together by means of flexible printed circuit board cables. The foremost of these three boards connects by means of another flex cable to a fourth board, the focal plane assembly (which is not visible). The focal plane board carries an electronically shuttered charge coupled device (CCD) detector. This CCD converts the image projected onto it by the lens to an electrical signal. That lens has a conical sunshade, to prevent direct illumination of the front element of the lens by the Sun. MARDI interfaces with the spacecraft by means of two cables, one for power and temperature telemetry, the other for transfering commands to and data from the camera.

MARDI flight unit data acquisition system
circuit board, October 1997.

The key to reducing the mass and power required for the instrument was to take advantage of the tremendous advances that have occurred over the last ten years in electronics. This reduces both the size and number of electronic components necessary in the design, which reduces the mass and power required. This picture shows the MARDI flight data acquisition system (DAS) board. The board is 7 cm (2.75 in) long and 5.7 cm (2.25 in) wide. The largest component is the digital signal processor, which controls all instrument functions. The other components provide the circuitry to transmit to and receive data from the spacecraft. This and the other MARDI boards were integrated with the aluminum housing which provides at least 0.15 in. of radiation shielding.

MARDI flight unit focus test, December 1997.
The three rectangles on the wall are bar targets.
The bottom target has a spacing below the Nyquist
frequency of the MARDI detector, so the bars are
aliased to a lower spatial frequency. Note that this
image only covers part of the MARDI field of view.

After integrating the electronics with the housing, the next step in the MARDI assembly is to mate the electronics with the optics and then focus the camera. The distance between the lens and CCD detector is metered by a small spacer ring at the back of the lens. To focus MARDI, a series of images of a set of bar targets were acquired with different thickness of shims in place of the focus spacer ring. The image from the best focus position is shown in this figure. The test targets are the three vertically stripped rectangles near the center of the image. The upper two targets show the system has good contrast down to its limiting resolution. The bars on the bottom test target are below the size the camera can resolve at that distance.

Mars Descent Imager onboard MPL during final cleaning.
Click Here for "life-size" image (1.3 MByte).

After MARDI was focused, it was put through a series of environmental and calibration tests before being delivered for integration with the MPL spacecraft. Environmental tests include (1) heating and cooling the camera to temperatures it will encounter in space and on Mars, and (2) shaking the camera to simulate the launch of the MPL spacecraft. Once delivered to Lockheed Martin Astronautics in Denver, Colorado, the instrument was bolted to the lower side of the spacecraft, as shown here. At this location on the MPL lander, the camera will be able to "see" the landing site during descent.

MARDI picture taken after integration with the spacecraft
at Lockheed Martin Astronautics. MARDI is looking at the floor.
The location of test points, numbered one through five, were determined
by theodolite. Click Here for higher-resolution view (575 Kbytes).

After MARDI was integrated with the spacecraft, it was necessary to measure where it was pointed relative to the spacecraft. Five precision measured test points were surveyed in on the floor beneath the spacecraft, within the MARDI field of view. MARDI took an image of those points, which are seen numbered in the picture above. Knowing were the points are relative to the lander and in the MARDI image will allow location of surface features on Mars in MARDI images relative to the lander.

MARDI was aboard when MPL was launched January 3, 1999.

The Mars Polar Lander, with MARDI aboard, was launched from Florida on January 3, 1999. The scheduled date for MARDI's entire mission--to acquire images of the landing site during terminal descent of the Mars Polar Lander--is December 3, 1999.

©1999 Malin Space Science Systems, Inc.