In contrast with the first -- which formally began in 1957 with the launch of Sputnik, the first artificial satellite, by the former Soviet Union and touched off a desperate and largely secret race for space supremacy between Russia and the United States -- this new, potentially golden era of exploration has been signaled by two distinctly positive developments.
First, on Jan. 14, President George W. Bush ordered a fundamental redirection of U.S. space policy, requiring NASA to phase out the space shuttle program and the bulk of its involvement in the International Space Station. Instead, the agency will pursue a long-term plan to return humans to the moon -- to stay -- and to push out into the solar system.
Second, on March 23, the Opportunity rover, which as of that day had spent exactly two Earth months exploring the Martian surface, transmitted data back to mission controllers indicating the planet once held a large body of liquid water -- perhaps an ocean.
Opportunity's discovery represented a historic moment in space expeditions. Up until the time the rover actually observed the clear signs that water had flowed on Mars, the solar system contained only one proven home for lakes, rivers and oceans. Now, there is at least one more planet that can provide water for astronauts in the future -- and there is unconfirmed evidence of several more.
As a result, NASA is preparing to launch a new race of advanced robots in the coming decade on missions to locations much farther out in the solar system.
The first of the probes will enter service in 2008 with a mission to orbit the moon and image its surface features. Eventually, however, the spacecraft under design will follow the Voyager and Galileo spacecraft to continue studying the frozen worlds orbiting the planet Jupiter.
In the mid 1990s, Galileo found evidence that oceans of liquid water might lay beneath thick sheets of ice on Europa, Callisto and Ganymede -- three of the giant planet's four largest moons.
The Jovian probe will be called the Jupiter Icy Moons Orbiter, or JiMo, and will be carried to the Galilean moons -- so named because they were discovered by Italian astronomer Galileo Galilei in 1610 -- by a new version of today's Atlas or Delta space boosters. They also will be fueled by a compact but powerful nuclear reactor that would drive the probe's experiments and, in smaller versions, energize separate probes launched from the mothership.
The idea behind JiMo is to flight-test new technologies that eventually would be aimed at closer targets, such as moon landings. The mission is part of the NASA's new building-block strategy for space exploration, according to NASA space architect Gary Martin.
"Mars is not a stopping point," Martin said. "Some of our studies looked at what the next location past Mars would be."
NASA identified Jupiter's Galilean moons because they, as Mars once did, may harbor liquid water. Using its new powerplant, JiMo would be able to visit those frozen worlds for years at a time, changing its orbit when necessary to investigate newly discovered and interesting features located by its onboard imaging systems.
The reactor's sustained power generation also would make it possible for JiMo to send down space probes that could function as mini-submersibles, plunging into and burrowing through the frozen ice fields to dive deeply into the alien oceans. The space subs then would transmit back their discoveries -- possibly including images -- to JiMo in orbit, which would relay the data back to mission controllers on Earth.
"What are some promising scientifically driven exploration locations?" Martin asked. "You can change the whole way you do science because you can circle each of the icy moons of Jupiter, but you also have the power when you are done doing the science around one (moon) you can go on to the other."
Eventually, the reactor system, called Prometheus, that will be test-flown aboard JiMo will be used to help power astronaut base camps on the moon's surface.
"These are building blocks," Martin explained.
Meanwhile, NASA on Thursday approved an extended mission for Opportunity and its twin, Spirit, giving them up to five more months of tasks. The Mars Exploration Rovers, as they are known officially, are wrapping up their primary mission assignments, which were supposed to last 90 days.
"Given the rovers' tremendous success, the project submitted a proposal for extending the mission, and we have approved it," said Orlando Figueroa, Mars Exploration Program director at NASA Headquarters in Washington.
The rovers actually have made their missions a bit more than simple extensions -- they figure to become part of the story of the century.
Phil Berardelli is UPI's Science & Technology Editor. E-mail email@example.com