Going for the whole moon: the Lunar Observer would study what other spacecraft missed

Science News, April 28, 1990 by Jonathan Eberhart

Going for the Whole Moon

The stampede to the moon began in January 1959 with the Soviet Union's Luna 1 probe, which missed its objective by 6,000 kilometers. Two months later came the U.S. Pioneer 4, which passed 10 times as far away. In spite of early failures, the space race was on, and more than five dozen spacecraft have since made the trip, most of them taking pictures and a few carrying astronauts and returning with moonrocks. It might thus seem that the moos is well known by now -- yet in a sense, all of these missions wore blinders.

Spacecraft photographing the moon from orbit have been able to observe only narrow strips, in large part because most orbits have been angled to pass only slightly above or below the lunar equator. Furthermore, the orbits of different spacecraft often do not overlap, so when scientists want to compare different kinds of measurements gathered during separate missions, the date often reveal little more than individual "postage stamps," marking the only spots on the surface where the various orbital paths cross.

Similarly, scientists know little about variations in the lunar gravitational feld -- necessary for figuring out where the moon's mass is concentrated -- and about the moon's surface composition, because few spacecraft have followed orbits tilted enough to carry them over the higher latitutes near the lunar poles.

In 1974, scientists began advocating a solution to this knowledge gap, in the form of an unmanned spacecraft called the Lunar Polar Orbiter. Carrying instruments similar to those aboard the Apollo craft and other missions, it would have gone into an orbit tilted about 90[degrees] to the moon's spin axis, so that the whole lunar surface would have passed beneath it. the Apollo program had wound down by that time, however, and a polar moon-orbiter atttracted little support, even when some scientists noted that this single mission could expand all the Apollo-era "postage stamps" into global maps. The Lunar Polar Orbiter lost out to a considerably more intriguing plan called the Jupiter Orbiter and Probe. The twin spacecraft, renamed Voyagers 1 and 2, took advantage of a rare alignment of the outer planets to visit Jupiter, Saturn, Uranus and Neptune during an enormously successful 12-year mission.

Now NASA wants to give the moon another look. Its 1991 budget request, now under consideration by Congress, seeks $15 milliont o begin developing a $500-million-plus polar orbiting mission called the Lunar Observer.

Why now? Space agency officials cite several reports in recent years -- including one by then-astronaut Sally Ride and another by the National Space Commission -- proposing a permanently inhabited lunar outpost and human exploration of MArs as objects for NASA's focus. In addition, President Bush included both objectives as part of a "Human Exploration Initiative" proposed last July.

Indeed, many space enthusiasts see the Lunar Observer as testing the commitment of the administration, Congress and the nation to the idea of sending humans to the moon once again. While the craft could carry out its mission without obligating the United States to an inhabited lunar installation, building such a base early in the 21st century requires something like the Lunar Observer as a preparatory step.

NASA's plans for the envisioned moon base call for building habitats and an oxygen plant as well as developing new construction technologies to use in the inhospitable lunar environment. Before any of these projects got underway, however, the Lunar Observer would lay the groundwork, providing key facts about potential sites for the outpost. NASA officials see the lunar craft as similar in design to another unmanned spacecraft called the Mars Observer, scheduled for launch in 1992.

Some Lunar Observer proponents, however, worry about whether continued scientific investigation of the moon would win enough support to get the mission started were it not for the added enticement of the more costly human visits that might follow. "The Human Exploration Initiative is what is driving this mission right now," says Douglas Nash, a development-flight project scientist for the craft at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "The assumption is that we're going to send human beings back to the moon. The odds are that except for Bush's initiative, it [the Lunar Observer] wouldn't get off the ground at this time."

Cost estimates for the mission run from $500 million to $700 million, plus the cost of launching the craft with an expendable rocket instead of the space shuttle, says Kerry Nock, the project's science-mission design manager at JPL. Nash, Nock and others express hope that the Lunar Observer will head moonward in seven or eight years in the form of two identical spacecraft, each perhaps deploying a small "subsatellite" to help with some of the planned experiments. Using two craft, Nash says, would keep the data flowing, complete the mission more quickly and allow the option of doing some things differently with the second craft.