Space Exploration, Planetary Landers

With the launch of the first earth-orbiting satellites, the use of unmanned planetary landers, probes, and telescopes came under consideration as a means to chart and explore the solar system. The advantages of such machines became clear immediately, as they represented a short cut in the race between the U.S. and the Soviet Union to dominate this new realm of international competition.

The design and shape of these instruments varied but displayed similar basic requirements: the maximum use of the area within the superstructure for the instruments and the onboard computer, a means to communicate with earth to receive guiding instructions and send back information collected, camera and sensor pods, and an engine and its fuel capable of functioning for several years.

The first ‘‘target’’ was earth’s moon, and both superpowers launched probes beginning in 1958. The first ‘‘wave’’ did not involve landers as such, but machines intended to orbit and perhaps crash on the moon. None of the American Pioneer machines succeeded in this task, but two Soviet Luna spacecrafts came close to earth’s satellite. The U.S. then initiated the Ranger project. Begun in 1959, the first four missions failed outright, but Ranger-7 succeeded in sending back photographs of the lunar surface, which paved the way for the Apollo manned moon landings.

The exploration of Venus also began with the Cold War as background. The peculiarity of Venus’ cloudy atmosphere as well as its impact on human culture dating back to the earliest civilization made it an important target. The Soviet Union first launched probe Venera-1 on 12 February 1961, but the probe failed on its way to Venus.

The U.S. followed suit in summer 1962 with Mariner-1 and Mariner-2. The first failed, but the second one was able to take atmospheric measurements. Several other Venera and Mariner missions followed, all confirming that the planet was completely inhospitable and that the greenhouse effect actually had elevated ambient surface temperature to 430°C. The most recent planetary probe was Magellan, launched in 1989, which mapped most of the planet at high resolution.

Mars drew an equal or even greater interest in its exploration. The Soviet Union reached Mars first, but failed to get any data back from its June 1963 mission. The American Mariner-4 mission flew near the planet in summer 1965, and Mariner- 6 and Mariner-7 further mapped the Mars surface in 1969 in preparation for a landing. None of the probes suggested there was any life on Mars. Exploration nevertheless reached a zenith with the Viking-1 and Viking-2 missions. Launched 10 weeks apart in 1975, both machines took about one year to reach Mars.

Once there, the landers’ missions confirmed the lack of life on Mars due to the high level of ultraviolet radiation that saturates the Martian atmosphere. Although the Viking program ended in November 1976, the probes continued to transmit for another six years. Further planetary probes explored Mars and its satellites. The most successful was the Mars Pathfinder which landed on July 4, 1997, and whose robotic rover, Sojourner, spent 30 days collecting data on the environment and relief of the planet.

The distance between earth and other planets in the solar system has prompted the need for other types of exploration, including solar system probes and space telescopes. The first attempt at surveying outer planets involved the preparation of the Pioneer-10 and Pioneer-11 probes. The first, launched in March 1972, reached the vicinity of Jupiter 21 months later, then pursued a course out of the solar system.

Affixed to its side was a plate with a male and female figure and a series of symbols depicting Voyager’s origins and travel path. The plaque represented an attempt at considering the possibilities in the search for extraterrestrial intelligence (SETI). Although it was elegantly simple, the design was criticized for depicting the female figure in a passive stance whereas the male raises his hand in greeting, and both figures appear to be Caucasian. As for Pioneer-11, it passed near Saturn twice, and in 1990 left the solar system.

Two other American probes, Voyager-1 and Voyager-2, launched in 1977, conducted a planetary tour of the two outermost planets, Uranus and Neptune, and 48 moons. The last investigation of Jupiter was that of the probe Galileo. Although slower than other probes (it used the gravity of planetary bodies to correct its course and increase its speed, also known as the ‘‘slingshot’’ effect), Galileo reached Jupiter in 1995, six years after its launch. It successfully parachuted a probe into the atmosphere that transmitted for 45 minutes before the atmospheric pressure and the planet’s gravity broke it up.

An alternative to expensive probes and the problems of earth-based telescopes (which include visual distortions through the atmosphere) has involved satellite telescopes. Several National Aeronautics and Space Administration (NASA) projects were devoted to this alternative beginning with the Apollo moon missions. The advanced orbiting solar observatory (AOSO), initially scheduled for Apollo moon missions, was turned into the Apollo telescope mount (ATM) and launched aboard the American Skylab space station in 1973. It functioned throughout the station’s manned operations (a total of some six months) and recorded solar activity.

Meanwhile, research into a giant space telescope had begun in the 1960s. The NASA project, which later became known as the Hubble space telescope (HST), capitalized on existing technical knowledge used in the manufacture of spy satellites to order a high-resolution mirror. Although the system underwent several redesigns to fit into a space shuttle bay (instead of the top of a Saturn-V moon rocket as had been initially planned), it was ready for launch in the mid-1980s.

The shuttle Challenger accident of January 1986 delayed the launch date by four years. Once lofted, however, the HST displayed an aberration in its picture resolution. The error, caused by the improper position of one of the mirrors, required a “corrective lens’’ that was installed during a 1993 shuttle-servicing mission. The repair was successful and helped HST uncover new information about black holes.