SP-425 The Martian Landscape


Uplink and Downlink


[28] After the excitement of the first days, our work fell into a regular pattern. Each of the more than 40 persons on the Imaging Team was specially trained to carry out a specific task. All those months of tests began to pay dividends.

The principal division of work was between "uplink," preparing commands for new pictures to be telemetered to the Lander, and "downlink," processing the pictures that had been returned to Earth.

The uplinkers had the most demanding and tedious job. A new command load had to be prepared and certified approximately every two days. In one sense, the requirements for change in our preprogrammed sequence were less than we had imagined. The cameras were working perfectly; there was no need to switch pictures from a faulty photosensor. Indeed, even the estimated exposure settings, the so called gains and offsets, were generally correct. The entire martian scene was of equal interest so the strategy of complete coverage displayed in the preprogrammed sequence was appropriate for the actual mission.

Most changes in pictures were dictated not by us, but requested by others. Scientists and engineers alike were reluctant to conduct spacecraft operations without a picture to document the event. For example, on sol 2, the sampler arm jammed in an intermediate position because the arm had not extended far enough to release a locking pin. Although the corrective procedure was relatively straightforward, it was decided that no further commands would be issued until we acquired a picture of the sampler arm in its stalled position. A last minute camera sequence was prepared; the resulting picture documented the suspected failure mode.

Throughout the mission, sampler arms on both Landers proved to be prima donnas. Several times they unexpectedly stalled in the middle of sample acquisition sequences. Each time, a disabling permanent failure was feared-a disastrous event since the key scientific instruments inside the Lander depended on the sampler arm to provide martian soil. However, a new sequence of commands always brought the sampler arms back to life. This oft repeated sequence of failure despair success elation imparted a Hollywood movie like aura to the mission-it also heightened the impression of an "intelligent" robot on Mars.

The requirement to monitor the progress of the sampler arm with repeated pictures had some peripheral benefits. Our ability to generate commands for new picture sequences on very short notice was verified. As some of us had expected, the burdensome series of meetings and time consuming cross checks could be abbreviated. With the feasibility of late commands verified by these Lander health pictures, it was relatively easy to persuade managers that the same techniques could be used to update science sequences.

Pictures were required not only to certify the condition of the Lander; they were also necessary to document each sample sequence. First the candidate area had to be stereoscopically imaged to locate rocks and slopes that might endanger the sampler arm. Special computer driven equipment, constructed by one of our Science Team members, Sid Liebes, was used for rapid construction of topographic profiles. Then a series of pictures was required during the sampling operation to document each event: successful deployment of the arm, digging of the hole, delivery of the sample to the inlet ports on the upper deck of the spacecraft. These were extraordinarily difficult sequences to plan since the pictures had to be precisely timed to intersperse with the sampler operations.

The downlink activity was equally demanding. Each time a transmission occurred from Lander to Earth, either directly or through the Orbiter relay, a team of two or three persons monitored the incoming data, made preliminary adjustments, and transferred the data to magnetic tape, suitable for further processing. As each picture was assembled on the screen you were the first to view this part of Mars. It took no unusual flight of fancy to imagine yourself on the martian surface. The effect was heightened during those downlinks late at night or early in the morning when the flight operations building was deserted, with only a skeleton crew to monitor spacecraft operation and to catalog the data returning to Earth.

Once the raw data had been received in the FOVLIP area (i.e., First Order Viking Lander Imaging Processing- Viking acronyms numbered in the thousands, and some conversations seemed to be in a foreign tongue), it was passed on to the Image Processing Laboratory where the pictures were enhanced to produce the best possible image. Although this procedure appears questionable, it is in fact entirely appropriate. No detail is introduced into the scene that was not, in fact, recorded by the cameras. Since the raw imaging data were generally of high quality, enhancement was usually limited to restoring lines of data that had been misplaced during transmission, improving picture contrast, and adding labels and marginal scales.

Superimposed on the uplink and downlink tasks was a constant succession of science meetings and press conferences. Scientific data were coming in so rapidly that keeping abreast of each new finding was a hopeless task. We had little time even to study the pictures we had taken. No sooner was one sequence planned and acquired, than we were in the midst of the next one. Although the frenzied activity of the first few days subsided, the operation of the mission continued with around the clock activity that consumed all our resources.