From: Jet Propulsion Laboratory
Posted: Wednesday, October 23, 2013
UPDATED Oct. 23: Juno exited safe mode on Friday, Oct. 18.
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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