As of Oct. 17, Juno was approximately 4.4 million miles (7.1 million
kilometers) from Earth. The one-way radio signal travel time between
Earth and Juno is currently about 24 seconds. Juno is currently
traveling at a velocity of about 23.6 miles (38 kilometers) per second
relative to the sun. Velocity relative to Earth is about 6.5 miles (10.4
kilometers) per second. Juno has now traveled 1.01 billion miles (1.63
billion kilometers, or 10.9 AU) since launch.
Juno’s Earth flyby gravity assist was completed on Oct. 9. Several
Juno science instruments made planned observations during the approach
to Earth, including the Advanced Stellar Compass, JunoCam and Waves.
These observations provided a useful opportunity to test the instruments
during a close planetary encounter and ensure that they work as
designed. The main goal of the flyby -- to give the spacecraft the boost
it needed in order to reach Jupiter – was accomplished successfully,
and the spacecraft is in good health and responding to ground
controllers.
Soon after its closest approach to Earth, the spacecraft initiated
the first of two "safe modes" that have occurred since the flyby. Safe
mode is a state that the spacecraft may enter if its onboard computer
perceives conditions on the spacecraft are not as expected. Onboard
Juno, the safe mode turned off instruments and a few
non-critical spacecraft components, and pointed the spacecraft toward
the sun to ensure the solar arrays received power. The likely cause of
the safe mode was an incorrect setting for a fault protection trigger
for the spacecraft's battery. During the eclipse, the solar cells, as
expected, were not generating electricity, and the spacecraft was
drawing on the battery supply. When the voltage dropped below this fault
protection trigger, the spacecraft initiated the safe mode sequence.
The spacecraft acted as expected during the transition into and while in
safe mode. The spacecraft exited the safe mode on Oct. 12.
The spacecraft entered the safe mode configuration again on Sunday
evening (10/13/13). When the spacecraft's onboard computer transitioned
from the Earth flyby sequence to the cruise sequence, a component
called the stellar reference unit remained in the Earth flyby
configuration. When the spacecraft's computer saw the draw on
electricity was slightly greater than expected, it did as it was
programmed to do and initiated a safe mode event.
Navigation has confirmed that Juno's current trajectory is
"near-perfect" vs. planned. The mission team is in two-way
communications with the spacecraft and it is operating as expected, and
designed for, in safe mode. They expect to exit safe mode sometime next
week.
Juno will arrive at Jupiter on July 4, 2016, at 7:29 p.m. PDT (10:29 p.m. EDT).
Juno was launched on Aug. 5, 2011. Once in orbit around Jupiter, the
spacecraft will circle the planet 33 times, from pole to pole, and use
its collection of eight science instruments to probe beneath the gas
giant's obscuring cloud cover. Juno's science team will learn about
Jupiter's origins, structure, atmosphere and magnetosphere, and look for
a potential solid planetary core.
Juno's name comes from Greek and Roman mythology. The god Jupiter
drew a veil of clouds around himself to hide his mischief, and his wife,
the goddess Juno, was able to peer through the clouds and reveal
Jupiter's true nature.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Juno
mission for the principal investigator, Scott Bolton, of Southwest
Research Institute in San Antonio. The Juno mission is part of the New
Frontiers Program managed at NASA's Marshall Space Flight Center in
Huntsville, Ala. Lockheed Martin Space Systems, Denver, built the
spacecraft. JPL is a division of the California Institute of Technology
in Pasadena.
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