Rendezvous With the Red Planet

LATER this month, on Aug. 24, the American Mars Observer spacecraft will reach its destination. It is equipped to do for Mars what thousands of years of exploration have yet to do for Earth - make a comprehensive mineralogical chart of the entire planet.

As mission science manager Thomas Thorpe notes, Earth still has unexplored areas. But, Dr. Thorpe adds, if Mars Observer successfully completes its main mission, "Mars will be the best-mapped planet in the solar system."

The goal of this long-term study is to understand as much as possible about the Martian geology, terrain, atmosphere, and climate by the time humans go there.

Unlike the essentially national space programs in the past, this will be an internationally coordinated study.

Advanced mission planner Roger Bourke explains that space exploration is so ambitious and costly that "nobody is going to get anywhere if they try to do it on their own."

Thus, Dr. Bourke says: "The era of [national] competition is behind us. Cooperation is ahead of us."

Seen in this perspective, the survey of the Red Planet that Mars Observer is about to make is the start of an exploration adventure that could become a 21st-century epic.

Mission manager Sam Dallas says the spacecraft is reaching Mars in excellent shape. Mr. Dallas, together with Thorpe and Bourke, is at the California Institute of Technology's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. JPL manages the Mars Observer program for the National Aeronautics and Space Administration (NASA).

Once at Mars, the spacecraft will go through a series of maneuvers to reach its proper mapping orbit. It has plenty of rocket fuel to do this. Dallas says controllers saved fuel with precision navigation after a Titan III rocket launched the 2,573-kilogram (5,672-pound) spacecraft from the Kennedy Space Center at Cape Canaveral, Fla., last Sept. 25. They needed only three of four planned course-correction engine firings during the 724-million-kilometer (450-million-mile) journey.

Now, as the spacecraft is about to take its station around another planet at a direct distance of 340 million kilometers (210 million miles) from Earth, its supply of consumables is "right on target," Dallas says.

As now planned, the craft will first enter a long looping "capture" orbit that takes three days to complete. Then, after about 10 days, it will move closer to the planet in a so-called drift orbit with a one-day time period.

Finally, by around Oct. 28, it should have entered its mapping orbit. Here it will circle the planet every 118 minutes at a distance of about 378 kilometers (235 miles) from the surface along a course inclined 93 degrees to the Martian equator. That's as close as it can come without suffering atmospheric drag. School data links

Meanwhile, scientists will have already begun sampling the planet. Dallas says he expects to be taking some data informally by Sept. 14. His main job, however, is to be ready to begin the official mapping mission Dec. 16. His team has to check out every spacecraft system and instrument by then.

Middle-school and high school students can share in the beginnings of this adventure through the Marslink project of the Planetary Society in Pasadena, Calif. This program will provide schools with monthly update packets suggesting activities, images, and lessons. Students will have first-hand Mars Observer data and contact with scientists, according to the society.

Mars is only a little more than half as big as Earth. Yet its surface area is nearly as large as Earth's land area. Mars Observer will chart the whole of this vast landscape once every Martian day, which is 39 minutes longer than an Earth day. Its nominal mission is to do this throughout the four seasons of one Martian year, 687 Earth days. This should give scientists insight into the day-to-day and season-to-season changes of the climate.

The spacecraft has "eyes" that will give a sharper, less distorted view of the planet than has been possible before. A pair of wide-angle cameras can image scenes with two levels of resolution - showing details as small as 7.5 kilometers (4.7 miles) or 240 meters (787 feet) across as desired.

A separate camera, however, can give sharp views of selected targets with details as small as 1.4 meters (4.6 feet). Furthermore, the near-polar orbit will let these cameras look directly down at all parts of the planet. Previous spacecraft in equatorial orbits had only slanting views of polar regions.

A laser altimeter - an instrument never used at Mars before - will chart surface heights with a precision of several meters. Cartographers should be able to use those data together with photo maps to construct three-dimensional topographic charts.

Meanwhile, small gravity-induced accelerations in the spacecraft's orbital speed will allow scientists to map out the gravity field. The gravity map and topographic maps can then be compared in order to look for matches between the shape of the surface and the variations in gravity. The "topo" maps also will show, for the first time, what directions are upstream and downstream in Mars's water-cut channels and lava flows. Measurements and surveys

Mars Observer will track dust and volatile materials. It will try to answer questions of where such materials come from, how they move around, and where they end up. That includes the carbon dioxide "snow" that freezes out of the atmosphere at the winter hemisphere pole and evaporates in the summer.

Mission scientists will also be looking for signs of any weak magnetic field. No planetary field has shown up on previous missions. If it can be determined that Mars has no such magnetic field, this would suggest that, unlike Earth, Mars has no fluid electrically conducting core.

Important as such measurements are, however, science manager Thorpe says he expects some of the most exciting science to come from the mineralogical surveys. Scientists will be able to study the planet element by element and mineral by mineral. The spacecraft has an instrument to identify chemical elements by the gamma rays they give off. Elements have unique "signatures" encoded in the way the intensities of the penetrating high-energy rays vary with wave length. Another instrument will detect similarly

unique "signatures" of various minerals, including carbon dioxide and water, by their infrared thermal radiation.

Thorpe explains that Mars Observer can do a better job at this kind of mapping than resource satellites can do for Earth. Earth's atmosphere absorbs or distorts some of the radiation from its surface.

But Mars's largely carbon dioxide atmosphere has an average surface pressure only 0.55 percent of Earth's sea level air pressure. Mars Observer instruments have an essentially unblocked view of the Martian surface unless there's a dust storm.

Because of this, Thorpe says that "there are many [geological] problems we can attack." For example, he notes that the age of rocks can be determined from orbit, just as they are in a laboratory, by measuring the relative abundance of certain radioactive elements and their decay products. The more there is of the decay product, the longer the radioactive clock has been ticking.

This is all part of what Bourke, who is manager for Mars advanced missions at JPL, calls "a comprehensive strategy for exploration of Mars." He explains that the strategy is to characterize Mars "from the outside in."

Mars Observer gives the global overview. Future missions must go to the surface to validate Mars Observer findings by direct sampling and to conduct studies impossible from orbit. Bourke notes, for example, that if Mars once had abundant water, its rocks should contain evidence of this. But rock samples would have to be brought back to Earth for the detailed analysis required. Future missions

The international missions with Russian spacecraft - Mars '94 and Mars '96 - would begin the second phase of exploration. Mars '94 now is scheduled for launch in November 1994. It would arrive at Mars about 11 months later. Besides putting an orbiter around the planet, Mars '94 is to send down two instrumented landers and two ground penetrating probes. Mars '96, to launch in 1996, would deploy a robot rover explorer and a French instrumented balloon. That mission has not yet been fully funded, however.

These missions exemplify the internationalization of Mars exploration. Mars Observer has French-supplied radio equipment to relay data from the Mars '96 balloon, if Mars Observer still is working. This also can be used to relay data from the Mars '94 landers.

Mission manager Dallas says he expects Mars Observer to be viable for at least three 687-day mapping cycles. "We're hoping we're going to be around for Mars '96," he says. However, he adds that "even the Mars '94 [mission] is going to be exciting."

Looking further ahead, the United States is planning to land a network of ground stations that, if the program is approved, could be in place on Mars early in the next century. NASA calls this the Mars Environmental Survey (MESUR).

JPL hopes to test its concepts with a Pathfinder mission using a simple version of the MESUR craft that would also deploy a small robot rover vehicle. It would cost less than $175 million and would launch in November 1996. At this writing, it was in the NASA fiscal 1994 budget. But that budget had not yet been finally passed by Congress. Shared programs

Meanwhile, Frank Schutz, JPL assistant laboratory director for instruments, says he is particularly "excited" about the new international cooperation. Along with France, Finland, Germany, and Russia, JPL has an instrument on board each of the two Mars '94 landers. It will sense chemical activity in Martian soil.

The United States joined the program after the lander design was frozen. Dr. Schutz says JPL engineers couldn't have integrated their instruments into the landers without the help of the other countries. "They're very cooperative, they're first rate people," he says.

Bourke says he, too, is "very optimistic" about the internationalization of Mars exploration. He notes that all the space-faring countries have similar objectives in studying the planet. They include France, Finland, German, Italy, Japan, Russia, the United States, and members of the European Space Agency.

All are spending significant amounts of money on their Mars programs. Yet, Bourke points out, what they want to do at Mars costs more than they individually want to spend.

He adds that, with cold-war rivalry over, "nobody has to prove they're the best in space." Therefore, he explains: "There's much real money being spent. There are shared ambitions."

This is the logic Bourke sees driving these countries to cooperate. Their first formal planning together should come in October when the newly established International Mars Exploration Working Group is to meet in Graz, Austria.

Meanwhile, in a gesture that symbolizes this cooperative spirit, the Planetary Society and the Russian Space Research Institute in Moscow are preparing a record disc to place on the Mars '94 landers. It will encode stories, sounds, and images from the world's science fiction about Mars. It will serve "as a motivation and memento for future explorers there," society president Carl Sagan says.