In the 1960s a GRAND PLANETARY TOUR to study the outer planets was proposed. It was an ambitious plan to send unmanned probes to the outer planets of the outer solar system. The Grand Tour could exploit a rare, unusual and favorable alignment of the planets Jupiter, Saturn, Uranus, Neptune and Pluto. This planetary alignment would occur in the late 1970s and would not occur again for 175 years. This special alignment of these planets, could allow a probe to be sent to Jupiter and use that planet as a gravitational slingshot to extend its trajectory to the other planets further out in the Solar System. Gravity assist would enable a single probe to visit the four gas giants….Jupiter, Saturn, Uranus, and Neptune….while requiring a minimal amount of propellant and a shorter travel time between planets. The NASA space probes Voyager 1 and Voyager 2 have been exploring our solar system to the outer planets for more than 34 years. Many of the scientists now working on the Voyager project weren’t even born when the probes were launched in the 1970s. Originally, the Voyager probes were designed as part of the Mariner program. Voyager 1 was called Mariner 11 and Voyager 2 was called Mariner 12. The program progressed, however, and the name was changed to Voyager. Voyager 2 was actually launched first on August 20, 1977 and Voyager 1 followed 2 weeks later on September 5, 1977 and was sent on a faster, longer, and more circular trajectory. Remote control programming was used to endow the Voyagers with greater capabilities than they had when they left the earth, enabling their 2 planet mission to become a 4 planet mission. Voyager 1 could have been sent to Pluto after Saturn, but instead was sent on a trajectory which brought it close to Titan, Saturn’s planet sized moon, eliminating the Pluto flyby. Voyager 2’s trajectory could not be bent to bring the probe by Pluto after the Neptune flyby in 1989. Eventually, Voyager 1 and Voyager 2 explored all the giant outer planets of our solar system, 48 of their moons, and the unique systems of rings and magnetic fields that those planets possess. On December 19, 1977 Voyager 2 entered the asteroid belt. Nine days later, Voyager 1 traveling at a greater speed overtook Voyager 2. In June of 1977, the primary radio receiver failed on Voyager 2 and the mission since then on has been flown using the backup receiver. By 1998, both spacecraft had shown signs of a lessening power supply. Voyager’s signals are transmitted by a 20-watt radio transmitter and are so faint that the amount of power reaching NASA’s antennas is 20 billion times smaller than the power of a digital watch battery. February 17: Voyager 1 passed Pioneer 10 to become the most distant human-made object in outer space. In 2002, the then 25-year-old Voyager 1 was more than 8 billion miles away from Earth. Radio signals required 12 hours to reach the probe. NASA sent commands to activate a spare sun sensor and star tracker to help the craft locate its position. Voyager 1 was leaving the Solar System, rising above the ecliptic plane at an angle of about 35 degrees, at a speed of 39,000 per hour. Voyager 2 was also leaving the Solar System diving below the ecliptic plane at an angle of about 48 degrees at a speed of 35,000 per hour. Both spacecraft continue to study ultraviolet sources among the stars, and the fields and particles instruments aboard the Voyagers will continue to search for the boundary between the Sun’s influence and interstellar space. The Voyager spacecraft are expected to return valuable data for two or three more decades. Communications will be maintained until the Voyagers’ nuclear power sources can no longer supply enough electrical energy to power critical subsystems…estimated to be sometime in 2020. On August 1,Voyager 1 reported that the solar wind speed appeared to slow down. Voyager may have crossed the Solar System “termination shock.” On April 15 2004,Voyager 2 detected a shock wave from the October 2003 solar storms, experienced here on Earth. Voyager 2 measured its speed, composition, temperature and magnetism. On January 5 2005, after 10,000 days and 7 billion miles away from Earth, Voyager 2 held and still holds the record of travelling to more planets than any other man-made object in history. January 21: Also after 10,000 days and 9 billion miles from Earth, in a dark, and cold area at the very edge of our Solar System, Voyager 1 held and still holds the record as the explorer from Earth that has traveled farthest from home. It was more than 100 times farther from the Sun than the Earth. The Infrared Spectrometer and Radiometer heater was turned off to save power on Voyager 1 on December 7, 2011. The heater was used to keep the UVS (or Ultra Violet Spectrometer) warm. The UVS temperature has dropped to below the measurement limits of the sensor; however, UVS is still operating. Scientists expect to continue to receive data from the UVS until mid-2013, at which time the instrument will be turned off to save power. There are several other instruments that continue to work. So where are the Voyagers now? Our entire solar system – every planet, asteroid, spacecraft, and life form belonging to our solar system – sits inside a gargantuan bubble of gas about four times wider than the orbit of Neptune..… and our sun is responsible for this. The sun blows the bubble by means of the solar wind. Astronomers call the bubble itself the Heliosphere and its outer membrane is the Heliosheath. The Heliosheath is important to humans because it helps protect us from galactic cosmic rays. Galactic cosmic rays are subatomic particles accelerated to nearly light speed by supernovas and black holes. Cosmic rays can penetrate flesh and damage DNA, so scientists need to learn as much as possible about the Heliosheath. Voyager 1 is currently located about 12 billion miles from Earth. It has crossed the Termination Shock, and is now inside the Heliosheath. Voyager tells us that we are in a stagnation region where the wind of charged particles streaming out from our sun has calmed. It is showing that what is outside this region is pushing back. The Heliosheath is 3 to 4 billion miles thick, and the Voyagers will be inside it for another 10 years or more before crossing the Heliopause and into inter stellar space. Voyager 2 is currently located about 10 billion miles from Earth also in the Heliosheath.
Voyager 1 will be the first to pass through the HELIOPAUSE, which is the boundary area between the solar and the interstellar wind. Recent data from Voyager has shown this boundary NOT to be smooth but frothy and bubbly…..and the bubbles are GIGANTIC. Both Voyagers continue exploring where nothing from Earth has flown before. In the more than 34 years since their launch, they each are much farther away from Earth and the Sun than Pluto. Each of the Voyager probes is famously equipped with a Golden Record, literally, a gold-coated copper phonograph record containing photographs, sounds, and salutations from the Earth. Said Carl Sagan at the time…..”A billion years from now, when everything on Earth we’ve ever made has crumbled into dust, when the continents have changed beyond recognition and our species is unimaginably altered or extinct, the Voyager record will speak for us”. The discs will be there in the event that sometime in the distant future, Voyager encounters alien life or some future human life. Barring any serious spacecraft subsystem failures, or they crash into something we cannot yet calculate, the Voyagers may survive until the early twenty-first century, about 2025, when diminishing power and hydrazine levels will prevent further operation. Were it not for these dwindling consumables and the possibility of losing lock on the faint Sun, our tracking antennas could continue to “talk” with the Voyagers for another century or two!
