Orbital insertion is just a few hours away now! Here is the timeline, in Central Daylight Time (UT -5). Note that times given account for the Jupiter-Earth lightspeed transit time for signals, so events are listed as controllers would find out about them,
20:13 – Juno begins transmitting status tones in lieu of full telemetry; while oriented for the burn, Juno cannot point its dish antenna directly at Earth, and so these status tones are all the team will have to go on.
20:16-20:37 – Juno transitions to JOI attitude; the spacecraft will be slowly moving itself into the correct orientation for the insertion burn; it’s spin-stabilized, so it can’t just reorient the way many other spacecraft can; its spinning like a top, so it needs to sort of wobble its way into the desired orientation. As of the time I write this, Juno should be wrapping this up.
21:41 – Switch to the toroidal low-gain antenna, as the high-gain antenna is no longer pointing at Earth; this antenna is located on the back of the spacecraft and is less directional
21:45 – Nutation dampening; nutation is the wobbling you see in a child’s top as it spins down; at this point, Juno is dampening out the wobble caused by the precession into JOI attitude
21:50-21:53 – Final tweaks to Juno’s orientation
21:56 – Spin up from 2 RPM to 5 RPM, to hold the spacecraft steady during the burn
22:01 – Juno is spun up and ready to go!
22:18 – Insertion burn begins!!! Juno’s main engine burns a combination of hydrazine and nitrogen tetroxide, and will consume 7,900 kg of propellant over the 35-minute burn.
22:53 – Burn complete. Mission controllers will be listening for a specific status tone, as well as for an expected amount of Doppler shift that would indicate the desired change in velocity was acheived.
22:55-23:00 – Juno spins back down to 2 RPM.
23:07 – Juno begins precessing back to sun-pointing attitude. This is vital not only for proper pointing of the medium- and high- gain antennas, but also for solar power generation; Juno has been on batteries for most of this sequence.
23:11 – Juno is now pointing close enough to the sun for the medium-gain beam to reach us; the status tones will now end.
23:16 – Juno is locked back on the Sun.
23:36 – Detailed telemetry downlink begins.
Tomorrow, more detailed data will come down over the high-gain antenna, and once they are safely in Jupiter orbit they will switch on the science payloads. July 13 there is an optional trajectory correction maneuver scheduled; on August 27 the spacecraft will see its first perijove after turning on instruments; and on October 19 there is an orbital reduction scheduled to reduce the orbital period to a mere 14 days. The nominal mission is slated to late to February 20, 2018, and end with a daredevil plunge into Jupiter’s atmosphere.
So . . . the encounter is underway! Keep your fingers crossed for another couple of hours!