Happy Independence Day! Juno orbital insertion timeline

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!


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