192
3 A Brief History of Space Flight
3.6.5 Debates on Voyager-1
Since it was shown by analyzing the measurement data that the speed of the solar
wind had slowed down to subsonic speed, scientists at the Applied Physics Laboratory
of Johns Hopkins University considered that the Voyager-1 entered the termination
shock region in February 2003. However, some other scientists expressed doubt
because the solar-wind detector onboard of the Voyager-1 ceased functioning in
1990, which meant that the termination shock detection would have to be inferred
from the data from the other instruments onboard [14, 15]. On May 25, 2005, in
a scientific session at the American Geophysical Union meeting in New Orleans,
Edward C. Stone, as a project scientist for the Voyager program, presented evidence
that the Voyager-1 crossed the termination shock on December 15, 2004, at a distance
of 94 AU away from the Sun. At the same month, a NASA press release said that the
consensus was that the Voyager-1 was then in the heliosheath.
On December 13, 2010, the Voyager-1 was at the distance of about 116 AU away
from the Sun, when it was confirmed that the Voyager-1 had passed the reach of
the radial outward flow of the solar wind as measured by the Low Energy Charged
Particle device. It is suspected that the solar wind at this distance turns sideways
due to the interstellar wind pushing against the heliosphere. In fact, the solar wind
detection onboard of the Voyager-1 had been consistently at zero since June 2010,
which also provided a conclusive evidence for the event.
In March 2011, to measure the sideways motion of the solar wind at the location of
the Voyager-1 in space, the spacecraft’s orientation and attitude was changed by the
command from the ground control center. Based on a test roll done in February, the
spacecraft’s ability to maneuver and reorient itself had been verified. The spacecraft’s
course was not changed, while the spacecraft rotated 70 degrees counterclockwise
with respect to the Earth to detect the solar wind. Since taking the family portrait
photograph of the planets in 1991, it was the first time that the spacecraft had done any
major maneuvering. After the first roll, the Voyager-1 had no problem in reorienting
itself with Alpha Centauri, its guide star, and resumed sending transmissions back
to the Earth. It was expected that the Voyager-1 entered into the interstellar space at
any time. At this time, although the Voyager-2 was still detecting outward flow of
the solar wind, it could be estimated that the Voyager-2 would experience the same
environment as the Voyager-1 in the following months or years. On May 21, 2011,
the Voyager-1 was at 12.44° declination, 17.163-h right ascension and 34.9° ecliptic
latitude, located in the constellation of Ophiuchus as observed from the Earth. On
December 1, 2011, a veteran scientist of the Voyager Program at the University of
Arizona in Tucson, Bill R. Sandel reported that the Voyager-1 had detected the first
Lyman-alpha radiation originating from the Milky Way. The Lyman-alpha radiation
from other galaxies had been detected previously, but the radiation from the Milky
Way was not detectable due to the interference from the Sun. On December 5,
2011, the NASA announced that the Voyager-1 had entered a new region referred
to as “cosmic purgatory”. Within the stagnation region whose inner edge is at the
distance of about 113 AU away from the Sun, the charged particles streaming from
3 A Brief History of Space Flight
3.6.5 Debates on Voyager-1
Since it was shown by analyzing the measurement data that the speed of the solar
wind had slowed down to subsonic speed, scientists at the Applied Physics Laboratory
of Johns Hopkins University considered that the Voyager-1 entered the termination
shock region in February 2003. However, some other scientists expressed doubt
because the solar-wind detector onboard of the Voyager-1 ceased functioning in
1990, which meant that the termination shock detection would have to be inferred
from the data from the other instruments onboard [14, 15]. On May 25, 2005, in
a scientific session at the American Geophysical Union meeting in New Orleans,
Edward C. Stone, as a project scientist for the Voyager program, presented evidence
that the Voyager-1 crossed the termination shock on December 15, 2004, at a distance
of 94 AU away from the Sun. At the same month, a NASA press release said that the
consensus was that the Voyager-1 was then in the heliosheath.
On December 13, 2010, the Voyager-1 was at the distance of about 116 AU away
from the Sun, when it was confirmed that the Voyager-1 had passed the reach of
the radial outward flow of the solar wind as measured by the Low Energy Charged
Particle device. It is suspected that the solar wind at this distance turns sideways
due to the interstellar wind pushing against the heliosphere. In fact, the solar wind
detection onboard of the Voyager-1 had been consistently at zero since June 2010,
which also provided a conclusive evidence for the event.
In March 2011, to measure the sideways motion of the solar wind at the location of
the Voyager-1 in space, the spacecraft’s orientation and attitude was changed by the
command from the ground control center. Based on a test roll done in February, the
spacecraft’s ability to maneuver and reorient itself had been verified. The spacecraft’s
course was not changed, while the spacecraft rotated 70 degrees counterclockwise
with respect to the Earth to detect the solar wind. Since taking the family portrait
photograph of the planets in 1991, it was the first time that the spacecraft had done any
major maneuvering. After the first roll, the Voyager-1 had no problem in reorienting
itself with Alpha Centauri, its guide star, and resumed sending transmissions back
to the Earth. It was expected that the Voyager-1 entered into the interstellar space at
any time. At this time, although the Voyager-2 was still detecting outward flow of
the solar wind, it could be estimated that the Voyager-2 would experience the same
environment as the Voyager-1 in the following months or years. On May 21, 2011,
the Voyager-1 was at 12.44° declination, 17.163-h right ascension and 34.9° ecliptic
latitude, located in the constellation of Ophiuchus as observed from the Earth. On
December 1, 2011, a veteran scientist of the Voyager Program at the University of
Arizona in Tucson, Bill R. Sandel reported that the Voyager-1 had detected the first
Lyman-alpha radiation originating from the Milky Way. The Lyman-alpha radiation
from other galaxies had been detected previously, but the radiation from the Milky
Way was not detectable due to the interference from the Sun. On December 5,
2011, the NASA announced that the Voyager-1 had entered a new region referred
to as “cosmic purgatory”. Within the stagnation region whose inner edge is at the
distance of about 113 AU away from the Sun, the charged particles streaming from