The Good ERTS

For the past three months, a strange moth-shaped satellite has been orbiting the earth in a nearly perfect polar orbit some 560 miles high. Sweeping down from the Arctic to Antarctica and back again every 103 minutes, the 1,965-lb. spacecraft has been taking as many as 752 pictures of the earth every day; each shot covers a 115-by-115-mile square. Unlike U.S. and Soviet spy satellites, which are on the lookout for military sites, the mission of NASA's first Earth Resources Technology Satellite (ERTS-1) is purely scientific. A direct spin-off of the space agency's active new interest in its home planet, ERTS is now returning dramatically revealing views of the earth.

Equipped with two separate systems of sensors, the experimental satellite "sees" its subject in three different colors: near infra-red (beyond the range of human vision), green and red. Transmitted separately back to earth, these colors can be combined to produce eerie multicolor photographs that are highly informative. ERTS owes its perceptive ability to the fact that every object, living or inanimate, emits, absorbs or reflects light in a highly characteristic way. Such spectral "signatures" are especially distinctive in infrared. ERTS, for instance, uses its infra-red sensors not only to identify crops in an area but also to tell something about their development and health.

Along with its eye for color, ERTS has another useful capability. Because of the timing of its polar orbit, the satellite passes over the same spot on earth at almost precisely the same hour every 18 days. Lighting conditions at each site are thus unchanged (except for the slow seasonal drift in the angle of the sun and possibly different cloud cover). As a result, there is little difference in shadows from one picture to the next, and ERTS can quickly spot any changes in terrestrial features since its last visit.

Wild Gyrations. The satellite's twin sensing systems have already proved their worth. Last month, ERTS suffered a mysterious power surge that temporarily affected the stabilizing jets and caused wild gyrations. To protect the satellite's three RCA vidicon cameras (which make up one of the sensing systems), controllers at NASA'S Goddard Space Flight Center shut the cameras down until they could locate the problem and send new instructions to the satellite's computer. Meanwhile, the other system, a multispectral scanner built by Hughes Aircraft Co., was fully able to take up the observational slack.

Since its launch from Vandenberg Air Force Base last July, the $112 million spacecraft has sent back more than 53,000 pictures of the earth. The photographic deluge is now being examined by more than 300 scientists, whose disciplines range from agriculture to volcanology. Says ERTS's scientific chief, Dr. Arch Park: "We're pleased and enthusiastic."

The scientists have every reason to be happy. In photographs of the U.S. West, for example, geologists discovered previously unknown faults in California's Monterey region. They also spotted remnants of an old volcano near Reno, Nev., that seems to be undergoing gradual uplifting by subterranean forces. In Oklahoma, scientists detected timber that had been harmed by exposure to the powerful chemical defoliant 245-T as part of a field-clearing effort; earlier observations by plane had failed to spot the damage. Off Cape Cod, the satellite quickly showed oceanographers what changes currents are causing in the topography of the ocean floor. ERTS has even displayed skills as a space-age divining rod. One scientist reports that by looking for unusually lush vegetation in photographs of Florida, he was able to locate an area surprisingly rich in ground water.

These findings probably are only a small sampling of things to come. Before ERTS finishes its year-long mission next summer, the General Electric-built satellite is expected to turn up a host of other new information about the earth in fields as widely different as cartography, urban planning, hydrology, seismology and ecology. Indeed, the space agency is so pleased with its highflying surveyor that it is already pressing ahead with plans to launch a second ERTS in November 1973.

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From the time it began sending back its remarkably clear pictures of Mars a year ago, Mariner 9 has made one startling discovery after another. Across millions of miles of space, it has transmitted shots of Martian volcanoes that may still be active, curious winding channels that could have been carved by torrents of water, possible tracks left by glaciers, sands whipped by winds of hundreds of miles an hour and other tantalizing features that point to previously unsuspected geological, chemical and perhaps biological processes on the red planet. Indeed, the flight of the windmill-shaped spacecraft drastically changed the image of Mars. Says Cornell Astronomer Carl Sagan, one of Mariner's principal scientists: "We have accumulated more information about Mars from the single mission of Mariner than from all previous observations in history."

Now, after its 698th pass around the planet, Mariner's mission has finally come to an end. Because the precious supply of attitude-controlling nitrogen gas has been exhausted, the spacecraft can no longer point its antenna toward earth for radio transmissions back to Caltech's Jet Propulsion Laboratory. As a result, Mariner's final 15 pictures remained locked on board. But scientists are hardly disappointed. Exceeding its expected working life of 90 days by eight months, Mariner yielded a total of 7,329 photographs, covering the entire surface of Mars as well as its tiny moonlets, Phobos and Deimos. Indeed, even as Mariner lapsed into silence, NASA scientists were studying its photographs to select possible sites for the unmanned Viking spacecraft, which is scheduled to land on the red planet in 1976.

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