Tuesday, August 26, 2008

A More Distant Voyager

The Cassini-Huygens mission, a joint undertaking of NASA, the European Space Agency (ESA), the Italian Space Agency (ASI), and several other organizations, was sent on its way October 15, 1997, to investigate Saturn as well as Titan (one of Saturn’s moons). Some scientists believe that Titan might support life or, at least, offer conditions in which life could develop. The mission was named Cassini, in honor of the seventeenth-century French-Italian astronomer Jean Dominique Cassini, who discovered the prominent gap in Saturn’s main rings; and Huygens, after the Dutch scientist Christiaan Huygens, who discovered the Saturn moon Titan in 1655, as well as the rings of Saturn. It recently transmitted dramatic images of Jupiter as it sped past on its way to Saturn.

Mars Observer, Surveyor, and Pathfinder

Mars Observer, launched on September 25, 1992, was to conduct extensive imaging work while orbiting Mars, but contact was lost with the spacecraft on August 22, 1993, as the satellite was establishing an orbit around the red planet. It is possible that a fuel tank exploded, destroying the spacecraft. Mars Global Surveyor was launched on November 7, 1996, and is continuing a long project of (among other things) detailed low-altitude mapping of the Martian surface. Unexpected oscillations in its solar panels while coming into a circular orbit around the planet caused the start of the major surface mapping program to be delayed by almost a year.

Although the Global Surveyor project is extraordinarily ambitious, the public may have been more excited by the mission of the Mars Pathfinder. The craft was launched on December 4, 1996, and landed on Mars the following summer, using a combination parachute and rocket-braking system, as well as an air bag system to ensure a soft, upright landing. A “micro-rover” vehicle was deployed, which began transmitting extraordinary panoramic and close-up pictures of the Martian landscape. It is little wonder that Pathfinder has caused such a stir. We’ve always been fascinated by Mars, which, of all the planets, seems most like Earth and has often been thought of as possibly harboring life—even civilization.

Magellan, Galileo, and Ulysses

More recent U.S. planetary probes have been increasingly ambitious. Magellan was launched in May 1989 and ultimately placed into orbit around Venus. Using high-resolution radar imaging, Magellan produced images of more than 90 percent of the planet, yielding more information about Venus than all other planetary missions combined.
The spacecraft made a dramatic conclusion to its four-year mission when it was commanded to plunge into the planet’s dense atmosphere on October 11, 1994, in order to gain data on the planet’s atmosphere and on the performance of the spacecraft as it descended.
On October 18, 1989, Galileo was launched on a journey to Jupiter and transmitted data on Venus, the earth’s moon, and asteroids before reaching Jupiter on July 13, 1995, and dropping an atmospheric probe, which gathered data on Jupiter’s atmosphere. After an extended analysis of the giant planet, Galileo began a mission to study Jupiter’s moons, beginning with Europa. The so-called Galilean moons were discovered by the mission’s namesake, Galileo Galilei in 1610. The Ulysses probe was delivered into orbit by the shuttle Discovery on October 6, 1990. A joint project of NASA and the European Space Agency (ESA), Ulysses gathers solar data and studies interstellar space as well as the outer regions of our own solar system. Much of the spacecraft’s instrumentation is designed to study x-rays and gamma rays of solar and cosmic origin.

Pioneers and Voyagers

In the fall of 1958, Pioneer 1 was launched into lunar orbit as a dress rehearsal for the planetary probes that followed. The rest of the Pioneer craft probed the inner solar system for planetary information, and Pioneers 10 (1972) and 11 (1973) explored Jupiter and Saturn, the giants at the far end of our solar system. Later, in 1978, Pioneer Venus 1 and Pioneer Venus 2 orbited Venus to make surveys of that planet’s lower atmosphere and, using radar imaging, penetrated thick gaseous clouds in order to reveal the spectacular and forbidding landscape below.

Mariners and Vikings

The U.S. Mariner program launched probes designed to make close approaches to Mars, Venus, and Mercury. Mariner 2 (1962) and Mariner 5 (1967) analyzed the atmosphere of Venus. Mariner 4 (1964) and 6 and 7 (both 1969) photographed the Martian surface, as well as analyzed the planet’s atmosphere. Mariners 6 and 7 also used infrared instruments to create thermal maps of the Martian surface, and, in 1971, Mariner 9, in orbit around Mars, transmitted television pictures of the planetary surface. Mariner 10, launched in 1973, was the first spacecraft to make a close approach to Mercury and photograph its surface.
But even more exciting were the two Viking missions, launched in 1975. The following year, both made successful soft landings on Mars and conducted extensive analysis of the Martian surface.

Thursday, August 14, 2008

The Apollo Missions

The data from the unmanned probes and orbiters was overwhelming in its volume and detail. Some critics continued to argue: Why send human beings? The manned missions clearly captured public attention, beginning with the Soviet Vostok series (1961–1963, including Vostok 6, which carried the first woman into space, Valentina V. Tereshkova) and the U.S. Mercury series (1961–1963). The Mercury series included two suborbital flights and the first U.S. manned flight in orbit, Friendship 7, commanded by John H. Glenn Jr., and launched on February 20, 1962.

(On October 29, 1998, 77-year-old Senator John Glenn boarded the Space Shuttle Discovery and became the oldest man in space. He returned from the mission on November 7.) The U.S. Gemini program came next, twelve two-man spaceflights launched between 1964 and 1967. The Gemini flights were intended very specifically to prepare astronauts for the manned lunar missions by testing their ability to maneuver spacecraft, to develop techniques for orbital rendezvous and docking with another vehicle—essential procedures for the subsequent Apollo Moon-landing program—and to endure long spaceflights. The eight-day Gemini 5 mission, launched August 21, 1965, was the longest spaceflight to that time. The Soviets also developed larger launch vehicles and orbiters. Voskhod 1, launched on October 12, 1964, carried three “cosmonauts” (as the Russians called their astronauts) into Earth orbit.

The U.S. Apollo lunar missions not only made up the most complex space exploration program ever conceived, but were perhaps the most elaborate scientific and technological venture in the history of humankind. Today, even if we had the desire, we no longer have the launch vehicles required to bring astronauts to the moon. According to the mission plan, a Saturn V multistage booster (rocket) would lift the 3-man Apollo spacecraft on its 21⁄4-day voyage to the moon, leaving behind the launch stages in pieces as it left the earth. After its journey, the small remaining piece of the initially launched craft would become a satellite of the moon, and the Lunar Module, with two men aboard, would separate from the orbiting Command Module and land on the moon. After a period of exploration on the lunar surface, the astronauts would climb back into the Lunar Module, lift off, and dock with the orbiting Command Module, which would fire its rockets to leave its lunar orbit and carry the three astronauts back to Earth.

After several preliminary missions, including Earth- and Moon-orbital flights, Apollo 11 was launched on July 16, 1969. On board were Neil A. Armstrong, Edwin E. “Buzz” Aldrin Jr., and Michael Collins. While in lunar orbit, Armstrong and Aldrin entered the Lunar Module, separated from the Command Module, and landed on the Moon, July 20, 8:17 P.M. Greenwich Mean Time.

“That’s one small step for [a] man,” Armstrong declared, “one giant leap for mankind.” And perhaps that sentence expressed the rationale for the effort, which went beyond strictly scientific objectives and spoke of and to the human spirit. Not that science was neglected. During their stay of 21 hours and 36 minutes, the astronauts collected lunar soil and moon rocks and set up solar-wind

Apollo 12 landed on the Moon on November 19, but Apollo 13, launched April 11, 1970, had to be aborted because of an explosion, and the astronauts, as recounted in a recent film through their great skill, resourcefulness, and courage, barely escaped death.

Apollo 14 (launched January 31, 1971), Apollo 15 (July 26, 1971), Apollo 16 (April 16, 1972), and Apollo 17 (December 7, 1972) all made successful lunar landings. Budgetary constraints, declining public interest, and the improving capabilities of unmanned missions eventually brought an end to the Apollo missions.

Lunar Probes

There were voices raised in protest, both in the political and scientific communities. Why try to put men on the moon, when unmanned probes could tell as much or more—and accomplish the mission with far less expense and danger?
The Russians had successfully launched the first lunar probe, Luna 2, on September 12, 1959, targeting and hitting the moon with it. Luna 3, launched the following month, on October 4, 1959, made the first circumnavigation of the moon
and transmitted back to Earth civilization’s first photographs of the Moon’s mysterious far side.
Another Soviet lunar first would come on January 31, 1966, when Luna 9 made a successful lunar soft landing—as opposed to a destructive impact.
In 1961, the United States launched the first of the Ranger series of nine unmanned lunar probes, hitting the moon with Ranger 4 in 1962 and orbiting it, with Rangers 7, 8, and 9, during 1964–1965. These last three missions generated some 17,000 high-resolution photographs of the lunar surface, not only valuable as astronomy, but indispensable as a prelanding survey.
From 1966 to 1968, seven Surveyor probes made lunar landings (not all successful), took photographs, sampled the lunar soil, and performed environmental analysis. Surveyor 6 (launched on November 7, 1967) landed on the lunar surface, took photographs, then lifted off, moved eight feet, landed again, and took more photographs. It was the first successful lift-off from an extraterrestrial body. The Lunar Orbiter series, five orbital missions launched during 1966–1967, mapped much of the lunar surface in 1,950 wide-angle and high-resolution photographs. These images were used to select the five primary landing sites for the manned Apollo missions.

JFK’s Challenge

On May 5, 1961, about three weeks after the Russians put a man into a single orbit, U.S. Navy commander Alan B. Shephard was launched on a 15-minute suborbital flight into space. Americans were proud of this achievement, to be sure, but the Soviets had clearly upstaged it. Just 20 days later, on May 25, President John F. Kennedy spoke to Congress: “I believe this nation should commit itself to achieving the goal, before the decade is out, of landing a man on the moon and returning him safely to Earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space, and none will be so difficult or expensive to accomplish.”

First Observatories in Space

In 1962, the United States launched its first extraterrestrial observatory, the Orbiting Solar Observatory (OSO). It was the first of a series of solar observatories, designed to gather and transmit such data as the frequency and energy of solar electromagnetic radiation in ultraviolet, x-ray, and gamma ray regions of the spectrum—all regions to which our atmosphere is partially or totally opaque.

The Early Explorers

The first space satellite the United States sent into orbit was Explorer 1, launched on January 31, 1958. While the satellite didn’t beat Sputnik 1 into space, it accomplished considerably more than the Soviet probe. Explorer 1 carried equipment that discovered the innermost of the Van Allen radiation belts, two zones of charged particles that surround the earth. By 1975, when the Explorer series of missions ended, 55 satellites had been launched, including Explorer 38 (July 4, 1968), which detected galactic radio sources, and Explorer 53 (May 7, 1975), which investigated x-ray emission inside and beyond the Milky Way.

Satellites and Probes

Astronomers and other scientists were not always enthusiastically supportive of the manned space program, many of them feeling that it stole both public attention and government funding away from more useful data-gathering missions that could be carried out much more efficiently and inexpensively by unmanned satellites and probes. There is much truth to this sentiment. However, at least in the 1960s, unmanned exploratory missions continued to have high priority, and did not really suffer from the parallel development of the manned space program.