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Voyager 1 and 2 Make History

Jan 9, 2019

Image: Design of Voyager 1 & 2 – JPL/NASA
 
Mission Overview
 
The twin Voyager 1 and 2 spacecraft are exploring where nothing from Earth has flown before. Continuing on their more-than-39-year journey since their 1977 launches, they each are much farther away from Earth and the sun than Pluto. In August 2012, Voyager 1 made the historic entry into interstellar space, the region between stars, filled with material ejected by the death of nearby stars millions of years ago. Scientists hope to learn more about this region when Voyager 2, in the “heliosheath" — the outermost layer of the heliosphere where the solar wind is slowed by the pressure of interstellar medium — also reaches interstellar space. Both spacecraft are still sending scientific information about their surroundings through the Deep Space Network, or DSN.
 
The primary mission was the exploration of Jupiter and Saturn. After making a string of discoveries there — such as active volcanoes on Jupiter's moon Io and intricacies of Saturn's rings — the mission was extended. Voyager 2 went on to explore Uranus and Neptune, and is still the only spacecraft to have visited those outer planets. The adventurers' current mission, the Voyager Interstellar Mission (VIM), will explore the outermost edge of the Sun's domain. And beyond.
 
Interstellar Mission
 
The mission objective of the Voyager Interstellar Mission (VIM) is to extend the NASA exploration of the solar system beyond the neighborhood of the outer planets to the outer limits of the Sun's sphere of influence, and possibly beyond.
 
Mission Objective
 
The mission objective of the Voyager Interstellar Mission (VIM) is to extend the NASA exploration of the solar system beyond the neighborhood of the outer planets to the outer limits of the Sun's sphere of influence, and possibly beyond. This extended mission is continuing to characterize the outer solar system environment and search for the heliopause boundary, the outer limits of the Sun's magnetic field and outward flow of the solar wind. Penetration of the heliopause boundary between the solar wind and the interstellar medium will allow measurements to be made of the interstellar fields, particles and waves unaffected by the solar wind.
 
Mission Characteristic
 
The VIM is an extension of the Voyager primary mission that was completed in 1989 with the close flyby of Neptune by the Voyager 2 spacecraft. Neptune was the final outer planet visited by a Voyager spacecraft. Voyager 1 completed its planned close flybys of the Jupiter and Saturn planetary systems while Voyager 2, in addition to its own close flybys of Jupiter and Saturn, completed close flybys of the remaining two gas giants, Uranus and Neptune.
 
At the start of the VIM, the two Voyager spacecraft had been in flight for over 12 years having been launched in August (Voyager 2) and September (Voyager 1), 1977. Voyager 1 was at a distance of approximately 40 AU (Astronomical Unit - mean distance of Earth from the Sun, 150 million kilometers) from the Sun, and Voyager 2 was at a distance of approximately 31 AU.
 
It is appropriate to consider the VIM as three distinct phases: the termination shock, heliosheath exploration, and interstellar exploration phases. The two Voyager spacecraft began the VIM operating in an environment controlled by the Sun's magnetic field with the plasma particles being dominated by those contained in the expanding supersonic solar wind. This is the characteristic environment of the termination shock phase. At some distance from the Sun, the supersonic solar wind is held back from further expansion by the interstellar wind. The first feature encountered by a spacecraft as a result of this interstellar wind/solar wind interaction was the termination shock where the solar wind slows from supersonic to subsonic speed and large changes in plasma flow direction and magnetic field orientation occur.
 
Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year, 35 degrees out of the ecliptic plane to the north, in the general direction of the Solar Apex (the direction of the Sun's motion relative to nearby stars). Voyager 2 is also escaping the solar system at a speed of about 3.3 AU per year, 48 degrees out of the ecliptic plane to the south. To check Voyager 1 and 2’s current distance from the sun, visit the mission status page.
 
Passage through the termination shock ended the termination shock phase and began the heliosheath exploration phase. The heliosheath is the outer layer of the bubble the sun blows around itself (the heliosphere). It is still dominated by the Sun’s magnetic field and particles contained in the solar wind. Voyager 1 crossed the termination shock at 94 AU in December 2004 and Voyager 2 crossed at 84 AU in August 2007. After passage through the termination shock, the Voyager team eagerly awaited each spacecraft's passage through the heliopause. which is the outer extent of the Sun's magnetic field and solar wind.
 
In this region, the Sun's influence wanes and the beginning of interstellar space can be sensed. It is where the million-mile-per-hour solar winds slows to about 250,000 miles per hour—the first indication that the wind is nearing the heliopause.
 
On Aug. 25, 2012, Voyager 1 flew beyond the heliopause and entered interstellar space, making it the first human-made object to explore this new territory. At the time, it was at a distance of about 122 AU, or about 11 billion miles (18 billion kilometers) from the sun. This kind of interstellar exploration is the ultimate goal of the Voyager Interstellar Mission. Voyager 2, which is traveling in a different direction from Voyager 1, has not yet crossed the heliopause into interstellar space.
 
The Voyagers have enough electrical power and thruster fuel to keep its current suite of science instruments on until at least 2020. By that time, Voyager 1 will be about 13.8 billion miles (22.1 billion kilometers) from the Sun and Voyager 2 will be 11.4 billion miles (18.4 billion kilometers) away. Eventually, the Voyagers will pass other stars. In about 40,000 years, Voyager 1 will drift within 1.6 light-years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis which is heading toward the constellation Ophiuchus. In about 40,000 years, Voyager 2 will pass 1.7 light-years (9.7 trillion miles) from the star Ross 248 and in about 296,000 years, it will pass 4.3 light-years (25 trillion miles) from Sirius, the brightest star in the sky. The Voyagers are destined—perhaps eternally—to wander the Milky Way.
 
Did You Know?
 
The Voyager Interstellar Mission has the potential for obtaining useful interplanetary, and possibly interstellar, fields, particles, and waves science data until around the year 2020 when the spacecraft's ability to generate adequate electrical power for continued science instrument operation will come to an end.
 
he Voyager mission was officially approved in May 1972. Through the dedicated efforts of many skilled personnel for over three decades, the Voyagers have returned knowledge about the outer planets that had not existed in all of the preceding history of astronomy and planetary science. The Voyager spacecrafts are still performing like champs.
 
It must come as no surprise that there are many remarkable, "gee-whiz" facts associated with the various aspects of the Voyager mission. These tidbits have been summarized below in appropriate categories. Several may seem difficult to believe, but they are all true and accurate.
 
Overall Mission
 
The total cost of the Voyager mission from May 1972 through the Neptune encounter (including launch vehicles, radioactive power source (RTGs), and DSN tracking support) is 865 million dollars. At first, this may sound very expensive, but the fantastic returns are a bargain when we place the costs in the proper perspective. It is important to realize that:
 
on a per-capita basis, this is only 8 cents per U.S. resident per year, or roughly half the cost of one candy bar each year since project inception. the entire cost of Voyager is a fraction of the daily interest on the U.S. national debt.
A total of 11,000 workyears was devoted to the Voyager project through the Neptune encounter. This is equivalent to one-third the amount of effort estimated to complete the great pyramid at Giza to King Cheops.
A total of five trillion bits of scientific data had been returned to Earth by both Voyager spacecraft at the completion of the Neptune encounter. This represents enough bits to fill more than seven thousand music CDs.
 
The sensitivity of our deep-space tracking antennas located around the world is truly amazing. The antennas must capture Voyager information from a signal so weak that the power striking the antenna is only 10 exponent -16 watts (1 part in 10 quadrillion). A modern-day electronic digital watch operates at a power level 20 billion times greater than this feeble level.
 
Voyager Spacecraft
 
Each Voyager spacecraft comprises 65,000 individual parts. Many of these parts have a large number of "equivalent" smaller parts such as transistors. One computer memory alone contains over one million equivalent electronic parts, with each spacecraft containing some five million equivalent parts. Since a color TV set contains about 2500 equivalent parts, each Voyager has the equivalent electronic circuit complexity of some 2000 color TV sets.
 
Like the HAL computer aboard the ship Discovery from the famous science fiction story 2001: A Space Odyssey, each Voyager is equipped with computer programming for autonomous fault protection. The Voyager system is one of the most sophisticated ever designed for a deep-space probe. There are seven top-level fault protection routines, each capable of covering a multitude of possible failures. The spacecraft can place itself in a safe state in a matter of only seconds or minutes, an ability that is critical for its survival when round-trip communication times for Earth stretch to several hours as the spacecraft journeys to the remote outer solar system.
 
Both Voyagers were specifically designed and protected to withstand the large radiation dosage during the Jupiter swing-by. This was accomplished by selecting radiation-hardened parts and by shielding very sensitive parts. An unprotected human passenger riding aboard Voyager 1 during its Jupiter encounter would have received a radiation dose equal to one thousand times the lethal level.
 
The Voyager spacecraft can point its scientific instruments on the scan platform to an accuracy of better than one-tenth of a degree. This is comparable to bowling strike-after-strike ad infinitum, assuming that you must hit within one inch of the strike pocket every time. Such precision is necessary to properly center the narrow-angle picture whose square field-of-view would be equivalent to the width of a bowling pin.
 
To avoid smearing in Voyager's television pictures, spacecraft angular rates must be extremely small to hold the cameras as steady as possible during the exposure time. Each spacecraft is so steady that angular rates are typically 15 times slower than the motion of a clock's hour hand. But even this was not steady enough at Neptune, where light levels are 900 times fainter than those on Earth. Spacecraft engineers devised ways to make Voyager 30 times steadier than the hour hand on a clock.
 
The electronics and heaters aboard each nearly one-ton Voyager spacecraft can operate on only 400 watts of power, or roughly one-fourth that used by an average residential home in the western United States.
 
A set of small thrusters provides Voyager with the capability for attitude control and trajectory correction. Each of these tiny assemblies has a thrust of only three ounces. In the absence of friction, on a level road, it would take nearly six hours to accelerate a large car up to a speed of 48 km/h (30 mph) using one of the thrusters.
 
The Voyager scan platform can be moved about two axes of rotation. A thumb-sized motor in the gear train drive assembly (which turns 9000 revolutions for each single revolution of the scan platform) will have rotated five million revolutions from launch through the Neptune encounter. This is equivalent to the number of automobile crankshaft revolutions during a trip of 2725 km (1700 mi), about the distance from Boston,MA to Dallas,TX.
 
The Voyager gyroscopes can detect spacecraft angular motion as little as one ten-thousandth of a degree. The Sun's apparent motion in our sky moves over 40 times that amount in just one second.
 
The tape recorder aboard each Voyager has been designed to record and playback a great deal of scientific data. The tape head should not begin to wear out until the tape has been moved back and forth through a distance comparable to that across the United States. Imagine playing a two-hour video cassette on your home VCR once a day for the next 33 years, without a failure.
 
The Voyager magnetometers are mounted on a frail, spindly, fiberglass boom that was unfurled from a two-foot-long can shortly after the spacecraft left Earth. After the boom telescoped and rotated out of the cannister to an extension of nearly 13 meters (43 feet), the orientations of the magnetometer sensors were controlled to an accuracy better than two degrees.
 
Navigation
 
Each Voyager used the enormous gravity field of Jupiter to be hurled on to Saturn, experiencing a Sun-relative speed increase of roughly 35,700 mph. As total energy within the solar system must be conserved, Jupiter was initially slowed in its solar orbit---but by only one foot per trillion years. Additional gravity-assist swing-bys of Saturn and Uranus were necessary for Voyager 2 to complete its Grand Tour flight to Neptune, reducing the trip time by nearly twenty years when compared to the unassisted Earth-to-Neptune route.
 
The Voyager delivery accuracy at Neptune of 100 km (62 mi), divided by the trip distance or arc length traveled of 7,128,603,456 km (4,429,508,700 mi), is equivalent to the feat of sinking a 3630 km (2260 mi) golf putt, assuming that the golfer can make a few illegal fine adjustments while the ball is rolling across this incredibly long green.
 
Voyager's fuel efficiency (in terms of mpg) is quite impressive. Even though most of the launch vehicle's 700 ton weight is due to rocket fuel, Voyager 2's great travel distance of 7.1 billion km (4.4 billion mi) from launch to Neptune resultsed in a fuel economy of about 13,000 km per liter (30,000 mi per gallon). As Voyager 2 streaked by Neptune and coasts out of the solar system, this fuel economy just got better and better!
 
Science
 
The resolution of the Voyager narrow-angle television cameras is sharp enough to read a newspaper headline at a distance of 1 km (0.62 mi).
 
Pele, the largest of the volcanoes seen on Jupiter's moon Io, is throwing sulfur and sulfur-dioxide products to heights 30 times that of Mount Everest, and the fallout zone covers an area the size of France. The eruption of Mount St. Helens was but a tiny hiccup in comparison (admittedly, Io's surface-level gravity is some six times weaker than that of Earth).
 
The smooth water-ice surface of Jupiter's moon Europa may hide an ocean beneath, but some scientists believe any past oceans have turned to slush or ice. In 2010: Odyssey Two, Arthur C. Clarke wraps his story around the possibility of life developing within the oceans of Europa.
 
The rings of Saturn appeared to the Voyagers as a dazzling necklace of 10,000 strands. Trillions of ice particles and car-sized bergs race along each of the million-kilometer-long tracks, with the traffic flow orchestrated by the combined gravitational tugs of Saturn, a retinue of moons and moonlets, and even nearby ring particles. The rings of Saturn are so thin in proportion to their 171,000 km (106,000 mi) width that, if a full-scale model were to be built with the thickness of a phonograph record the model would have to measure four miles from its inner edge to its outer rim. An intricate tapestry of ring-particle patterns is created by many complex dynamic interactions that have spawned new theories of wave and particle motion.
 
Saturn's largest moon Titan was seen as a strange world with its dense atmosphere and variety of hydrocarbons that slowly fall upon seas of ethane and methane. To some scientists, Titan, with its principally nitrogen atmosphere, seemed like a small Earth whose evolution had long ago been halted by the arrival of its ice age, perhaps deep-freezing a few organic relics beneath its present surface.
 
The rings of Uranus are so dark that Voyager's challenge of taking their picture was comparable to the task of photographing a pile of charcoal briquettes at the foot of a Christmas tree, illuminated only by a 1 watt bulb at the top of the tree, using ASA-64 film. And Neptune light levels will be less than half those at Uranus.
 
The Future
 
Through the ages, astronomers have argued without agreeing on where the solar system ends. One opinion is that the boundary is where the Sun’s gravity no longer dominates – a point beyond the planets and beyond the Oort Cloud. This boundary is roughly about halfway to the nearest star, Proxima Centauri. Traveling at speeds of over 35,000 miles per hour, it will take the Voyagers nearly 40,000 years, and they will have traveled a distance of about two light years to reach this rather indistinct boundary.
 
But there is a more definitive and unambiguous frontier, which the Voyagers will approach and pass through. This is the heliopause, which is the boundary area between the solar and the interstellar wind. When Voyager 1 crosses the solar wind termination shock, it will have entered into the heliosheath, the turbulent region leading up to the heliopause. When the Voyagers cross the heliopause, hopefully while the spacecraft are still able to send science data to Earth, they will be in interstellar space even though they will still be a very long way from the “edge of the solar system”. Once Voyager is in interstellar space, it will be immersed in matter that came from explosions of nearby stars. So, in a sense, one could consider the heliopause as the final frontier.
 
Barring any serious spacecraft subsystem failures, the Voyagers may survive until the early twenty-first century (~ 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!
 
Fast Facts
 
Launch: Voyager 2 launched on August 20, 1977, from Cape Canaveral, Florida aboard a Titan-Centaur rocket. On September 5, Voyager 1 launched, also from Cape Canaveral aboard a Titan-Centaur rocket.
 
Launch
 
Voyager 2 launched on August 20, 1977, from Cape Canaveral, Florida aboard a Titan-Centaur rocket. On September 5, Voyager 1 launched, also from Cape Canaveral aboard a Titan-Centaur rocket.
 
Planetary Tour
 
Between them, Voyager 1 and 2 explored all the giant planets of our outer solar system, Jupiter, Saturn, Uranus and Neptune; 48 of their moons; and the unique system of rings and magnetic fields those planets possess.
 
Closest approach to Jupiter occurred on March 5, 1979 for Voyager 1; July 9, 1979 for Voyager 2.
 
Closest approach to Saturn occurred on November 12, 1980 for Voyager 1; August 25, 1981 for Voyager 2.
 
Closest approach to Uranus occurred on January 24, 1986 by Voyager 2.
 
Closest approach to Neptune occurred on August 25, 1989 by Voyager 2.
 
Most Distant Spacecraft
 
The Voyager spacecraft are the third and fourth human spacecraft to fly beyond all the planets in our solar system. Pioneers 10 and 11 preceded Voyager in outstripping the gravitational attraction of the Sun but on February 17, 1998, Voyager 1 passed Pioneer 10 to become the most distant human-made object in space.
 
The Golden Record
 
Both Voyager spacecrafts carry a greeting to any form of life, should that be encountered. The message is carried by a phonograph record - -a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth. The contents of the record were selected for NASA by a committee chaired by Carl Sagan of Cornell University. Dr. Sagan and his associates assembled 115 images and a variety of natural sounds. To this they added musical selections from different cultures and eras, and spoken greetings from Earth-people in fifty-five languages.
 
Present Status
 
As of August 2017, Voyager 1 was at a distance of 20.8 billion kilometers (139.3 AU) from the Sun.
 
Voyager 2 was at a distance of 17.2 billion kilometers (115    AU).
Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year.
Voyager 2 is escaping the solar system at a speed of about 3.3 AU per year.
 
There are currently five science investigation teams participating in the Interstellar Mission. They are:
 
1. Magnetic field investigation
2. Low energy charged particle investigation
3. Cosmic ray investigation
4. Plasma Investigation (Voyager 2 only)
5. Plasma wave investigation
 
Five instruments onboard the Voyagers directly support the five science investigations. The five instruments are:
 
1. Magnetic field instrument (MAG)
2. Low energy charged particle instrument (LECP)
3. Cosmic ray instrument (CRS)
4. Plasma instrument (PLS)
5. Plasma wave instrument (PWS)
 
One other instrument is collecting data but does not have official science investigation associated with it:
 
6. Ultraviolet spectrometer subsystem (UVS), Voyager 1 only
 
Termination Shock
 
Voyager 1 crossed the termination shock in December 2004 at about 94 AU from the Sun while Voyager 2 crossed it in August 2007 at about 84 AU. Both spacecraft are now exploring the Heliosheath.
 
The Heliosphere
 
The heliosphere is a bubble around the sun created by the outward flow of the solar wind from the sun and the opposing inward flow of the interstellar wind. That heliosphere is the region influenced by the dynamic properties of the sun that are carried in the solar wind--such as magnetic fields, energetic particles and solar wind plasma. The heliopause marks the end of the heliosphere and the beginning of interstellar space. Voyager 1, which is traveling up away from the plane of the planets, entered interstellar space on Aug. 25, 2012. Voyager 2, which is headed away from the sun beneath the plane of the planets, is expected to pass beyond the enter interstellar space in the coming years.


 


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