Ten days after leaving Earth in the nose of an Atlas 5 launcher, the Jupiter-bound Juno spacecraft is flying straight and true, allowing NASA managers to cancel a planned rocket burn to aim the probe toward the next waypoint on its five-year journey to the solar system's largest planet.
The decision to call off the clean-up maneuver later this month will move forward initial testing of Juno's suite of scientific instruments, according to Jan Chodas, the mission's project manager at the Jet Propulsion Laboratory in Pasadena, Calif.
"Because we canceled TCM 1, we will start the instrument low voltage checkouts earlier and perform them at a more leisurely pace," Chodas said.
One of Juno's sensors, a plasma and radio experiment named Waves, was activated and deployed its antennas Aug. 9, according to Chodas. Waves will measure plasma and radio activity in Jupiter's auroras.
Chodas said the remaining instruments, including a radiometer, magnetometer, particle detector, and infrared and ultraviolet payloads, will be checked out between Aug. 22 and Sept. 2.
A series of high-voltage tests before the end of the year will verify full functionality of all the instruments.
On its way to the biggest planet in the solar system -- Jupiter, NASA's Juno spacecraft took time to capture its home planet and its natural satellite -- the moon.
"This is a remarkable sight people get to see all too rarely," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. "This view of our planet shows how Earth looks from the outside, illustrating a special perspective of our role and place in the universe. We see a humbling yet beautiful view of ourselves."
The Jupiter-bound Juno spacecraft was supposed to have completed the second of two critical engine firings Tuesday to aim for a gravity sling shot past Earth next year, but managers put off the burn to analyze pressure readings aboard the probe.
The first "deep space maneuver" occurred last Thursday, Aug. 30, more than 300 million miles from home, to begin fine-tuning the craft's course to intercept Earth. The Leros-1b main engine was fired for 29 minutes and 39 seconds, changing Juno's velocity by about 770 mph while consuming around 829 pounds of fuel.
It was an accurate maneuver and navigators reported it was a success. But subsequent reviews of telemetry revealed one of the propellant pressures within the spacecraft's propulsion system was higher than expected. Juno's controllers opted to scrub Tuesday's burn and take an extra 10 days to examine the pressure increase and consider mitigation options, NASA said in a statement.
The upcoming burn, targeting a similar duration and speed change as the first, is rescheduled for Sept. 14 with no impact to the mission.
On a side note, I'd love to know how they calculate which path to take, when to fly by Earth, how close the flyby should be, etc... - I suppose computer simulations are used.
The name of Juno's trajectory to Jupiter is formally known as '2+ dV-EGA'. EGA stands for Earth Gravity Assist and the 2+ specifies the timing of that flyby occurring a little more than two years into the mission. dV indicates that Juno utilizes a hyperbolic excess velocity leveraging trajectory. This trajectory is attractive because it features a short flight time to Jupiter while saving launch energy costs.
"Juno's odometer just clicked over to 9.464 astronomical units," said Juno Principal Investigator Scott Bolton, of the Southwest Research Institute in San Antonio. "The team is looking forward, preparing for the day we enter orbit around the most massive planet in our solar system."
Nope. The spacecraft flies over the poles of Jupiter in a highly elliptical orbit, so there is no chance for Juno's orbit to intersect a moon and get close. The spacecraft's camera is relatively wide angle and not a telescope like New Horizon's LORRI. So Juno is not designed to observe the moons, period. The instruments may indirectly study Io through its interaction with Jupiter's magnetic field, but that's about it.Now, I haven't read all the mission details yet, but is this craft going to do close flybys of any of the moons?
More: Juno @ IoAbout 40 megabytes of Junocam data can be sent back to Earth on each orbit; depending on the exact size of each image and the amount of data compression, somewhere between 10-100 images will be taken. A very common question about Junocam is whether it will be able to image Jupiter's moons, especially volcanically active Io. In theory, Junocam can image them, but unless there is a serendipitously close approach, they will never be more than a few pixels across. For example, if Io were directly above Juno it would be at a distance of about 345,000 kilometers and resolution would be 232 kilometers per pixel, so the whole satellite would only be about 16 pixels across. The other moons will be even farther away.
Junocam has a wide field of view, covering about 70 degrees around a line perpedicular to the spacecraft's spin axis by a full 360 degrees around the spin axis. As such the resolution is low -- the instantaneous field of view (the angle one pixel subtends) is 673 microradians. (For comparison, Dawn's Framing Camera has am IFOV of 94 microradians, and Cassini's Narrow-Angle Camera is 6 microradians.) The Junocam resolution thus ranges from about 3 km/pixel at closest approach to about 1800 km/pixel at apojove, when the planet will only be about 75 pixels across. For the two hours around closest approach, Junocam will achieve better resolution than Cassini did during its Jupiter flyby.
Main Space Science Systems built the camera and says it is "derived from the MSL MARDI instrument", not something that would take high resolution photos of distant moons.The biggest encumbrance to performing Io science with Juno is the low spatial resolution of the imagers on-board and their longevity in Jupiter's radiation environment. The best encounter of Io by Juno will occur on September 24, 2017 at a distance of 139,470 km. If Juno were to target Io at this time, JunoCAM's pixel resolution would be 111 km/pixel while for JIRAM it would be 35 km/pixel. So Juno's best images of Io would be on part with what New Horizons's RALPH instrument acquired, despite the order of magnitude improvement in distance. Another issue to keep in mind is that JunoCAM may not last much beyond the 7th orbit due to the high radiation environment at Jupiter. The closest approach during this time is on orbit 7 on December 24, 2016 at distance of 311,050 km. The projected pixel scale for this encounter would be 78 km/pixel for JIRAM and 249 km/pixel for JunoCAM.
NASA’s Jupiter-bound Juno spacecraft will perform a close flyby of Earth on Oct. 9, 2013. The time of closest approach is approximately 19:21 UTC (3:21 pm U.S. Eastern time). During the flyby Juno will come to within 347 miles (559 kilometers) of Earth.
Map showing Juno’s ground track during the Earth flyby. Credit: NASA/JPL-Caltech
The geometry of Juno’s Earth flyby near the rime of closest approach. Credit: NASA/JPL-Caltech