Fantastic journey

Science World, Oct 6, 1997

NASA is back in deep space, exploring the solar system with new spacecraft that are smaller, smarter, and a lot less expensive.

Is there ice at the bottom of a dark crater at the Moon's south pole? The possibility of finding water on Earth's barren satellite has scientists dreaming of lunar colonies. Speaking of water, what caused the devastating floods that long ago swept the surface of Mars? The Red Planet is now cold and dusty, but two or three billion years ago, it might have resembled Earth.

These are some of the questions scientists at the National Aeronautics and Space Administration (NASA) hope to answer in the coming decade. NASA is launching a new generation of unmanned spacecraft to explore the Moon, Mars, and Saturn.

Astronauts regularly orbit Earth in the space shuttle, but piloted missions to the Moon ended 25 years ago--due in part to their tremendous expense. NASA hopes to send a piloted spacecraft to Mars as early as 2011 (the round-trip would take almost two years and cost about $20 billion). A piloted mission to Saturn would take almost 14 years round trip, not counting research time.

Instead of sending astronauts on interplanetary missions, the agency is concentrating on cost-effective missions involving robotic spacecraft that orbit or land on planets and moons. NASA scientists have outfitted the new spacecraft (also called space probes) with powerful communications systems, and flight engineers have refined navigational techniques. This makes for better missions that provide more data. Most probes never return to Earth, another cost savings.

"Some of these missions only took about two years of planning from start to launch," says NASA program manager Scott Hubbard. That's a big improvement from earlier probes, which often took more than a decade (and hundreds of millions of dollars) to build and launch!

Here's a short list of NASA's latest spacecraft, all of which are doing more with less. Read on and become the space-suavest teen for light-years around!

Mars Global Surveyor

Destination: Mars Launched: Nov. 7, 1996 Scheduled Arrival: Sept. 1997

Global Surveyor will orbit Mars for two years, photographing and mapping the planet's entire surface. These images could help scientists locate dried-up lake beds and other areas that once might have contained life.

Global Surveyor will transmit photographs and other data via the Deep Space Network (DSN), the largest communications network in the world. DSN consists of nine enormous antennas (up to 64 meters, or 210 feet, in diameter) located in California, Spain, and Australia. The sites are scattered around the world so spacecraft can always send a direct signal to Earth.

Interplanetary communication has been a vexing problem for NASA. Because probes operate on frugal power, they must broadcast signals to Earth on as little as 20 watts of power, according to Wayne Lee, NASA design engineer. That's one-third the power used by an average light bulb! By the time a spacecraft's signal reaches Earth from, say, Neptune, it registers one millionth of one billionth of a watt! Amazingly, DSN's giant dish antennas can "hear" these faint whispers from deep space.

Lunar Prospector

Destination: Moon Scheduled Launch: Oct. 1997 Scheduled Arrival: Oct. 1997

Could humans ever move to the Moon? The solar-powered Lunar Prospector will undertake a year-long "low polar orbit" (only 100 km, or 62 miles, from the surface) around the Moon to find out. The spacecraft will chart the lunar surface and look for volcanoes, signs of lunar quakes and polar ice. One of its instruments, a neutron spectrometer, is capable of locating a cup of water in a cubic yard of soil.

Cassini

Destination: Saturn Scheduled Launch: Oct. 6,1997 Scheduled Arrival: June 2004

Cassini, at 5,630 kg (6.2 tons) the second-largest interplanetary spacecraft ever launched, will travel more than 3.5 billion km (2.2 billion miles) to reach Saturn. This will be a truly fantastic journey, considering that NASA engineers will purposely launch Cassini in the wrong direction, toward Venus, not Saturn.

Why? NASA engineers have devised an ingenious flight plan to minimize the spacecraft's use of fuel. Over 50 percent of Cassini's weight is liquid fuel, most of which the spacecraft will use during a 90-minute "burn" to slow its speed as it nears; Saturn. But Cassini could not reach its destination without help from natural physical forces.

All spacecraft require tiniest (the force provided by a rocket engine) to overcome Earth's gravity (the force that tries to pull the rocket back to the ground). As the craft escapes Earth's gravitational field, however, it enters the Sun's gravitational field. The Sun pulls the craft into orbit, and this orbit carries it on its journey--just as the Earth orbits the Sun.

In the case of Cassini, engineers will place the probe into an orbit around the Sun that will take it very close to Venus and Earth. The gravitational fields of these planets will pull on the spacecraft as it passes them, causing it to increase its speed, a phenomenon called gravity assist. NASA engineers liken gravity assist to a person running next to a merry-go-round. If that person grabs hold of the merry-go-round for a short time, he will run faster until he lets go. In the same way, Cassini will "grab hold" of Venus and Earth until it gains enough momentum (speed) to whip off into space in a new trajectory (path) toward Saturn.