24th May, 2005

Voyager home page

NASA's Voyager 1 spacecraft has entered the solar system's final frontier, a vast, turbulent expanse where the Sun's influence ends and the solar wind crashes into the thin gas between stars.

This still shows the locations of Voyagers 1 and 2. Voyager 1 is traveling a lot and has crossed into the heliosheath, the region where interstellar gas and solar wind start to mix. Click on the image for movie or download color print resolution still and black & white still. Credit: NASA/Walt Feimer

"Voyager has entered the final lap on its race to the edge of interstellar space, as it begins exploring the solar system's final frontier," said Dr. Edward Stone, Voyager project scientist at the California Institute of Technology in Pasadena. Caltech manages NASA's Jet Propulsion Laboratory in Pasadena, which built and operates Voyager 1 and its twin, Voyager 2.

Starting with a view of our Milky Way galaxy, the orange gas in the animation represents the interstellar medium. The bow shock is created because the heliosphere is moving through like a boat through the water, crashing through the interstellar gases. The bow shock in front of the moving heliosphere is similar to the one observed by the Hubble Space Telescope. Click for animation. Credit: NASA/Walt Feimer

In November 2003, the Voyager team announced it was seeing events unlike any encountered before in the mission's then 26-year history. The team believed the unusual events indicated Voyager 1 was approaching a strange region of space, likely the beginning of this new frontier called the termination shock region. There was controversy at that time over whether Voyager 1 had indeed encountered the termination shock or was just getting close.

We don't know the exact location of the termination shock and changes in the solar wind cause it to expand, contract, and ripple like a plate underwater. Water spreads out over the plate in a relatively smooth flow but has a rough edge where the water slows down abruptly and piles up. The edge is like the termination shock, and as the water flow changes, the shape and size of the rough edge change. Credit: NASA/ESA

"The consensus of the team now is that Voyager 1, at 8.7 billion miles from the Sun, has at last entered the heliosheath, the region beyond the termination shock," said Dr. John Richardson from MIT, Principal Investigator of the Voyager plasma science investigation.

The termination shock is where the solar wind, a thin stream of electrically charged gas blowing continuously outward from the Sun, is slowed by pressure from gas between the stars. At the termination shock, the solar wind slows abruptly from its average speed of 300 to 700 km per second (700,000 - 1,500,000 miles per hour) and becomes denser and hotter.

The Hubble Space Telescope imaged this view in February 1995. The arcing, graceful structure is actually a bow shock about half a light-year across, created from the wind from the star L.L. Orionis colliding with the Orion Nebula flow. For more information on this image, see HubbleSite . Click on the image for a very large version. Credit: NASA, The Hubble Heritage Team (STScI/AURA)

The strongest evidence that Voyager 1 has passed through the termination shock into the slower, denser wind beyond is its measurement of an increase in the strength of the magnetic field carried by the solar wind and the inferred decrease in its speed. Physically, this must happen whenever the solar wind slows down, as it does at the termination shock. Consider a highway with moderate traffic. If something makes the drivers slow down, say a puddle of water, the cars pile up - their density increases. In the same way, the density (intensity) of the magnetic field carried by the solar wind will increase if the solar wind slows down. In December 2004, Voyager 1 observed the magnetic field strength increasing by a factor of two and a half, as expected when the solar wind slows down. The magnetic field has remained at these high levels from December until now. An increase in the magnetic field intensity of about 1.7 times was seen at the time of the event announced in 2003.


The Voyagers are identical but on different flight paths. Voyager 1 is about 8.7 billion miles from the Sun and traveling at a speed of 3.6 AU per year while Voyager 2 is about 6.5 billion miles away and moving at about 3.3 AU per year. One 'AU' equals the distance between the Sun and Earth, or 93 million miles. In July 2004 scientists used Voyagers to track a solar blast to the edges of the solar system. Credit: NASA/Walt Feimer

"Voyager's observations over the past few years show that the termination shock is far more complicated than anyone thought," said Dr. Eric Christian, Discipline Scientist for the Sun-Solar System Connection research program at NASA Headquarters, Washington, DC.

For their original missions to Jupiter and Saturn, the Voyagers were destined for regions of space far from the Sun, so each was equipped with three radioisotope thermoelectric generators to produce electrical power for the spacecraft systems and instruments. Still operating in remote, cold and dark conditions 27 years later, the Voyagers could last until 2020.

Voyager's interstellar mission

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. As of July 2003, Voyager 1 was at a distance of 13.3 Billion Kilometers (88 AU) from the sun and Voyager 2 at a distance of 10.6 Billion kilometers (70 AU). Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year, 35 degrees out of the ecliptic plan 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. Both Voyagers are headed towards the outer boundary of the solar system in search of the heliopause, the region where the Sun's influence wanes and the beginning of interstellar space can be sensed. The heliopause has never been reached by any spacecraft; the Voyagers may be the first to pass through this region, which is thought to exist somewhere from 8 to 14 billion miles from the Sun. Sometime in the next 5 years, the two spacecraft should cross an area known as the termination shock. This 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. The Voyagers should cross the heliopause 10 to 20 years after reaching the termination shock. The Voyagers have enough electrical power and thruster fuel to operate at least until 2020. By that time, Voyager 1 will be 12.4 billion miles (19.9 billion KM) from the Sun and Voyager 2 will be 10.5 billion miles (16.9 billion KM) 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. In some 296,000 years, Voyager 2 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. For current distances, check: Mission Weekly Reports 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, and are still 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 will be held back from further expansion by the interstellar wind. The first feature to be encountered by a spacecraft as a result of this interstellar wind/solar wind interaction will be 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. Passage through the termination shock ends the termination shock phase and begins the heliosheath exploration phase. While the exact location of the termination shock is not known, it is very possible that Voyager 1 will complete the termination shock phase of the mission between the years 2001 and 2003 when the spacecraft will be between 80 and 90 AU from the Sun. Most of the current estimates place the termination shock at around 85 ± 5 AU. After passage through the termination shock, the spacecraft will be operating in the heliosheath environment which is still dominated by the Sun's magnetic field and particles contained in the solar wind. The heliosheath exploration phase ends with passage through the heliopause which is the outer extent of the Sun's magnetic field and solar wind. The thickness of the heliosheath is uncertain and could be tens of AU thick taking several years to traverse. Passage through the heliopause begins the interstellar exploration phase with the spacecraft operating in an interstellar wind dominated environment. This interstellar exploration is the ultimate goal of the Voyager Interstellar Mission.

Voyagers last status report

Week Ending  September 10, 2004

Command Transmission & Verification Operations

Voyager 1 command operations consisted of the uplink of a command loss timer reset on 09/08 [DOY 252/2000z].  The spacecraft received the command .

Voyager 2 command operations consisted of the uplink of seven bracketed command loss timer resets sent on five-minute centers using 0.5 Hz steps on 09/10 [DOY 254/1552z].  The spacecraft received four of the seven commands sent

Sequence Generation Operations

Continue sequence development  of CCSL A053.

Data Return Operations

Voyager 1 Data Processing and Operations:

There were 87.8 hours of DSN scheduled support for Voyager 1 of which 5.2 hours were large aperture coverage.   There were no real-time or schedule changes or significant outages during the period.

Science instrument performance was nominal for all activities during this period.  One frame of GS-4 data was recorded this week.  A second frame of GS-4 data was recorded on day 254.  The EDR backlog is 2 days.

Voyager 2 Data Processing and Operations:

There were 54.8 hours of DSN scheduled support for Voyager 2 of which 54.8 hours were large aperture coverage.   There were no real-time or schedule changes or significant outages during the period.

Science instrument performance was nominal for all activities during this period.  One frame of GS-4 data was recorded  this week.  The PRA receiver recovered from it's 90 th POR event on September 7.  Twenty-six frames of GS-4 data were played back on September 8.  The EDR backlog is 2 days.

Flight System Performance

Voyager 1 performance was nominal during this report period. Activity included turning on the BC gyros on 9/8 (DOY 252).

Voyager 2 performance was nominal during this report period.  Activities included switching to X-Band high power on 9/7 (DOY 252), DTR playback on 9/8 (DOY 252) and a switch from the AC to BC gyros on 9/10 (DOY 254).

PROPELLANT/POWER CONSUMABLES STATUS AS OF THIS REPORT

RANGE, VELOCITY AND ROUND TRIP LIGHT TIME AS OF 09/10/2004