There was some awfully interesting scenery showing up in the southern hemisphere, and this was a chance to see it close-up. By August 5, the craft had snapped an additional thirty-three close-encounter images and left Mars. As it sped away, it followed a similar program to Mariner 6's, adding observations of a small comet to its dance card.
After the first tantalizing twenty-plus low-res images from Mariner 4, Mariners 6 and 7 were a smash. A total of 201 images were sent home, with fifty-nine of these being close-encounter images. These images covered about 20 percent of the Martian surface. Ultraviolet and infrared data were acquired from the planet, and the atmospheric pressure was further refined to about 7 millibars. The south polar cap revealed itself to be composed primarily of carbon dioxide after all (a thick layer of water ice would be identified below this over thirty years later).
The missions sent back enough information to allow for future planning of missions like Mariners 8 and 9, as well as early thinking about the Viking mission. Surface composition, atmospheric density, and ambient temperatures were tracked andstudied. The mass of Mars was refined and lots more experience was gained in deep-space flight and control. Atmospheric data showed large amounts of dust present, as well as water and carbon dioxide clouds, and finally, the atmospheric pressure measurements of Mariner 4 were confirmed.
All in all, these Mariners accomplished about all that could be done in a fast flyby. It was time to try something much more challenging: send a craft into orbit around Mars.
I n his own words, Bruce Murray was “drafted…reluctantly!” to work on Mariner 4 fresh out of grad school, but in the end, his collaboration with people like Robert Leighton resulted in not only a stellar career but also a fascinating path through deep-space exploration. 1 Arriving at Caltech as a young man, he blossomed within the Mariner program and eventually headed off to spearhead Mariner 10 to Mercury—a single-spacecraft, low-cost, and high-risk mission that would be a precursor of “faster, better, cheaper” at JPL. In time he became the director of JPL, then retired to continue evaluating the massive data dumps from the Viking missions that had been stored and largely uninvestigated. Never a shy man, Murray is not one to mince words, and when he takes on a fight, his opponents had best be prepared to defend themselves…even if that opposition is NASA. Such an event occurred early in his career, as Mariners 6 and 7 were being designed.
“Mariners 6 and 7 were to be carbon copies of Mariner 4, and we had a long struggle with JPL and NASA to upgrade them with greater information capacity. This was the principal theme I played: to increase the amount of data to be returned, which was easy to do. For example, on Mariner 4…the telecommunications channel to return the data…only returned eight bits per second. That's like a teletype…It could have returned much more, and Mariners 6 and 7 would have been a similarly conservative design. But I, in particular, had a real battle with them. I had to learn aboutthe electrical engineering, I had to learn about the communications, I had to figure out all this stuff. I realized what was happening was that the engineers were protecting themselves. They put tremendous safety margins in so that if anything went wrong they would still be able to get the signals back. But they paid for that with poorer signals. By choosing to get one-hundredth of what they could get back, they were much more certain of getting it done. It was really a sociological and psychological problem once you understood the technical principles. And that led to a long battle. Mariners 6 and 7, in fact, had sixteen thousand bits per second instead of eight bits per second. It was a factor of increase of two thousand, as a so-called engineering experiment.”
The term engineering experiment was accurate to a point but
After the first tantalizing twenty-plus low-res images from Mariner 4, Mariners 6 and 7 were a smash. A total of 201 images were sent home, with fifty-nine of these being close-encounter images. These images covered about 20 percent of the Martian surface. Ultraviolet and infrared data were acquired from the planet, and the atmospheric pressure was further refined to about 7 millibars. The south polar cap revealed itself to be composed primarily of carbon dioxide after all (a thick layer of water ice would be identified below this over thirty years later).
The missions sent back enough information to allow for future planning of missions like Mariners 8 and 9, as well as early thinking about the Viking mission. Surface composition, atmospheric density, and ambient temperatures were tracked andstudied. The mass of Mars was refined and lots more experience was gained in deep-space flight and control. Atmospheric data showed large amounts of dust present, as well as water and carbon dioxide clouds, and finally, the atmospheric pressure measurements of Mariner 4 were confirmed.
All in all, these Mariners accomplished about all that could be done in a fast flyby. It was time to try something much more challenging: send a craft into orbit around Mars.
I n his own words, Bruce Murray was “drafted…reluctantly!” to work on Mariner 4 fresh out of grad school, but in the end, his collaboration with people like Robert Leighton resulted in not only a stellar career but also a fascinating path through deep-space exploration. 1 Arriving at Caltech as a young man, he blossomed within the Mariner program and eventually headed off to spearhead Mariner 10 to Mercury—a single-spacecraft, low-cost, and high-risk mission that would be a precursor of “faster, better, cheaper” at JPL. In time he became the director of JPL, then retired to continue evaluating the massive data dumps from the Viking missions that had been stored and largely uninvestigated. Never a shy man, Murray is not one to mince words, and when he takes on a fight, his opponents had best be prepared to defend themselves…even if that opposition is NASA. Such an event occurred early in his career, as Mariners 6 and 7 were being designed.
“Mariners 6 and 7 were to be carbon copies of Mariner 4, and we had a long struggle with JPL and NASA to upgrade them with greater information capacity. This was the principal theme I played: to increase the amount of data to be returned, which was easy to do. For example, on Mariner 4…the telecommunications channel to return the data…only returned eight bits per second. That's like a teletype…It could have returned much more, and Mariners 6 and 7 would have been a similarly conservative design. But I, in particular, had a real battle with them. I had to learn aboutthe electrical engineering, I had to learn about the communications, I had to figure out all this stuff. I realized what was happening was that the engineers were protecting themselves. They put tremendous safety margins in so that if anything went wrong they would still be able to get the signals back. But they paid for that with poorer signals. By choosing to get one-hundredth of what they could get back, they were much more certain of getting it done. It was really a sociological and psychological problem once you understood the technical principles. And that led to a long battle. Mariners 6 and 7, in fact, had sixteen thousand bits per second instead of eight bits per second. It was a factor of increase of two thousand, as a so-called engineering experiment.”
The term engineering experiment was accurate to a point but
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