posted 07-20-2014 06:54 AM               

This week's space cover of the week celebrates summer vacation and vacation trips that ask the perennial vacation trip question, "Are we there yet?" An ESA Philatelic Club cachet cover is shown for the Voyager Program's 35th anniversary of two spacecraft embarking on an incredible journey in space from Earth and through our Solar System, and then 35 years later, departure from our Solar System's heliosheath into interstellar space. This remarkable event is believed to have occurred August 25, 2012, by the Voyager 1 spacecraft. The Lollini cover shown above, coincidentally, was cancelled August 20, 2012, for the 35th anniversary of the Voyager Program's first mission, Voyager 2, launched on August 20, 1977, to the Solar System's outer planets. This Lollini cover is considerably more significant, though, as the departure cover for Voyager 1 from the Solar System's heliosheath into interstellar space only a few days later and is shown with thanks to Tom Steiner.

The Voyager 1 spacecraft is launched after Voyager 2, September 5, 1977, Kennedy Space Center, Florida, on a more direct track to the outer planets of Jupiter and Saturn. The Centennial cover shown is cancelled on Voyager 1's launch date at Cape Canaveral, Florida. A second cancel is applied to the cover for the spacecraft's arrival at the giant outer planet Jupiter and its lunar system, March 5, 1979, and Voyager 1's continuing on to the outer planet Saturn and another large lunar system.

Space Cover #274 – Voyager 1, Are We There Yet?

Here on Earth in the northern hemisphere, it's summer and time to go on vacation, to relax, and take things easy. If you go somewhere with your family or friends, it's also a great time to go somewhere exciting, to see some great sights along the way, and to reinvigorate your spirit of adventure. Our space cover of the week for this week is very much like taking this summer vacation trip in the family car or in a car with your friends. And once in the car on your trip, invariably someone will ask, "Are we there, yet?"

NASA's JPL and Caltech manage the Voyager Program. Bob Rank's Space Voyage cover shown is cancelled on the launch date of Voyager 1 but with a Pasadena, California, cancel. JPL builds both Voyager 1 and 2 and both are outfitted with nuclear power to sustain their long missions to the Solar System's outer planets.

The two Voyager spacecraft are launched September 5, 1977, and August 20, 1977, respectively, to take advantage of a optimal alignment of the planets of our Solar System in late 1977 and a planetary alignment that only occurs only every 175 years. The primary mission for the two Voyager spacecraft is the exploration of outer planets Jupiter and Saturn and their Moon systems.

After making remarkable discoveries on their trip, including active volcanoes on Jupiter's Moon Io and discovery of the intricacies of Saturn's rings and discovering new Moons, NASA/JPL Caltech extended the Voyager Program mission. Voyager 2 launched first but cruising on a less direct, slower journey would explore Jupiter and Saturn but would then be directed to explore the other outer planets of Uranus and Neptune. This would be accomplished in 1989. NASA/JPL Caltech planned that both spacecraft would continue on their journeys over different routes to leave our Solar System and heliosphere and finally enter interstellar space.

Like our summer vacation described earlier, there are surprises along the way. Voyager 1's onboard plasma instrument, measuring the density, temperature and speed of plasma in space, ceased working in 1980 after its planetary flyby of Saturn. So, when Voyager 1 noted the pressure of interstellar space when entering the Solar System's heliosphere in 2004, the Voyager science team didn't have an instrument for the most direct measurement of plasma on Voyager's journey.

Heliosphere is defined as the area outside of the Solar System where the Sun's influence is negligible. It is the exit boundary of the heliosheath, and marks the departure point where interstellar space begins. As a work around to the plasma instrument failure on Voyager 1, testing was changed to monitor the direction of the magnetic field in space received by Voyager 1 to act as a proxy to measure density, temperature, and speed of the plasma to determine the departure point of Voyager into interstellar space.

By August 25, 2012, Voyager 1 entered this new region for good. All the lower energy particles from inside the Solar bubble zipped away, and inside particles decreased by more than a factor of 1,000 compared to the spacecraft entering the heliosphere earlier in its 2004 reading. And, the levels of galactic cosmic rays had jumped to the highest readings of the entire Voyager mission. This would be the anticipated change if Voyager 1 had exited the heliosheath, the demarcation boundary between the heliosphere and interstellar space.

But, are we there yet? The best answer to this nagging question is, "We think we are." But we are still testing with Voyager 1 to make sure this is correct. Two years behind Voyager 1, Voyager 2 will provide a second exit and data set to confirm this is the case.

Voyager Program Chief Scientist Ed Stone of JPL and the California Institute of Technology in Pasadena, California, attempts to verify the answer to this question, "What we can say is Voyager 1 is bathed in matter from other stars." What we can't say is what exact discoveries await Voyager's continued journey. No one was able to predict all of the details that Voyager 1 has seen. So we expect more surprises."

Stone affirms that Voyager 1 is working with a finite nuclear power supply, and has enough power to keep operating the spacecraft's fields and particles science instruments through the year 2020, marking 43 years of continual operation. At that milestone, Voyager Program managers will begin turning off Voyager's scientific instruments one by one to conserve the spacecraft's remaining power, turning off Voyager's last instrument in 2025.

With its scientific instruments turned off, Voyager 1 will continue transmitting engineering data for only a few more years. After that, the spacecraft will be traveling on as Earth's silent ambassador in interstellar space. In an estimated 40,000 years, it will be closer to the star Alpha Centuri, than our own Sun, now seen as just a minute point of light in the Milky Way, our galaxy, as Voyager continues on its remarkable journey.