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I read that New Years Day is the big day for New Horizons' encounter with Ultima Thule. But that doesn't necessarily mean that there will be pictures of MU69 on the big LED displays in Time Square at 00:01 01-Jan-2019.

There are avoidable delays (press office closures due to government shut-downs) and unavoidable delays (speed of light), schedules (when is the flyby exactly?) and local buffering due to extremely slow data rates from a zillion miles away.

Roughly what time is it likely that some news or data will make it to the general public about any or all of the following:

1. a flyby happened and New Horizons did or may not have survived it


2. a photo or spectrum or some measurement of MU69 itself


3. a deviation of some kind in the trajectory or velocity produced by gravitational deflection by MU69

In simple explanation, we won't able to know what's up with New Horizons right away. The probe will be busy collecting all the science data during the high-speed flyby. Closest approach will be at a distance of 3,500 kilometers at about 05:33 on 1 January UTC, and it’ll happen at a zippy 14.16 kilometers per second.

... As happened at Pluto, New Horizons will not be communicating with Earth during closest approach, because it will be focused on gathering all the science it can during the high-speed flyby. Whenever it does turn back to point at Earth to transmit data it will take more than 6 hours for its data to traverse the distance between us.

However, there would still downlinks from New Horizons around its Jan 1 flyby available. But don't expect it to be either good or punctual¹ :

^{_{Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/Emily Lakdawalla}}

^{WHAT KINDS OF IMAGES OF 2014 MU69 WILL BE AVAILABLE WITHIN DAYS OF THE FLYBY?}

^{The downlinks from New Horizons around its 1 January 2019 flyby of 2014 MU69 will not contain its highest-resolution images. Instead, they will be photos that the team is reasonably confident will contain an image of 2014 MU69.1 Two "failsafe" downlinks are planned for before the closest approach, and three "New York Times" downlinks are planned over the two days after closest approach. These are Rosetta OSIRIS images of comet 67P/Churyumov-Gerasimenko, scaled to be approximately the same size that the New Horizons images of 67P are expected to be, with some processing to add blur and speckle noise (for a variety of reasons, New Horizons LORRI images of MU69 will not look as crisp as Rosetta OSIRIS images of 67P). They are at a phase angle of 10 degrees, similar to the 11-degree phase at which New Horizons will see MU69 from a distance.}

One important caveat: the times reported above are when the images will be downlinked. This is not the same as when they will be published. New Horizons (unlike Curiosity, Opportunity, InSight, solar missions, and formerly Cassini) doesn't push images straight to the Web once they land on Earth. The mission will process them, and the team will write captions, and then NASA will have to vet the captions, and then NASA will publish the images at a time of day that'll maximize news coverage, all of which means it could be up to a day or so after downlink that these images get released.

1. a flyby happened and New Horizons did or may not have survived it

In the Approach phase, which began on 16 August and runs through 24 December (7 days before closest approach). During approach, New Horizons has been taking images for optical navigation and searching for potentially dust-generating hazards like rings or moons. (So far, it has not spotted any.) The in-situ instruments have been busy gathering data on the fields and particles in interplanetary space.

Furthermore, the operation team weighed numerous factors in making its choice to closest approach. The considerations included what is known about MU69’s size, shape and the likelihood of hazards near it, the challenges of navigating close to MU69 while obtaining sharp and well-exposed images, and other spacecraft resources and capabilities.² It's unlikely that New Horizons could not survives the flyby.

2. a photo or spectrum or some measurement of MU69 itself

As said above, New Horizons has been snapping pictures of Ultima Thule to identify any potential hazard. The result so far is clear and safe to approach. Earliest downlinks will be available on Jan 1, the rest will disclosed accordingly during the Departure phase that would lasts one more week after its 2-day period around closest approach, from 3 through 8 January. After that, New Horizons will spend 20 months downlinking all the data, until September 2020.

Regardless of U.S. government shutdown, the show will go on!
^{_{New Horizon flyby of Ultima Thule event timeline. Screenshot retrieved from first reference.}}

Visit the Applied Physics Laboratory's YouTube channel

Reference

Emily Lakdawalla, December 17, 2018, What to Expect When New Horizons Visits 2014 MU69, Ultima Thule And When We Will Get Pictures, The Planetary Society.

² Johns Hopkins University Applied Physics Laboratory (2017), 6 September 2017, New Horizons Files Flight Plan for 2019 Flyby, quoted by New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute (SwRI), Boulder, Colorado.

Emily Lakdawalla, December 27, 2018, New Horizons fast approaching 2014 MU69, Check this blog entry for MU69 photos taken and returned by New Horizons before 1 January, The Planetary Society.

According to this article, "The first images are expected by the evening of January 1, with release planned for January 2. More, higher resolution shots should follow." Evening is presumably that of Johns Hopkins University Applied Physics Laboratory, Eastern Standard Time (UTC-5).

Of particular interest on 2019-01-01 (from the schedule below):

• 0033 EST (0533 UTC) Closest approach
  
  It appears that data will be collected for about 3 hours after this time (note that it will take over 6 hours for any signal to reach Earth and that NH cannot collect and transmit data at the same time)


• 0945-1015 EST (1445-1515 UTC) Live coverage of signal-acquisition


• 1130-1230 EST (1630-1730 UTC) Press briefing: Spacecraft status, latest images and data download schedule

The JHUAPL is largely unaffected by the 3^rd 2018 US government shutdown and will be providing full coverage on their Youtube channel and on the New Horizons website. There will also be live coverage on Twitter @JHUAPL

Keep in mind that we may not get anything close to the quality we got for the Pluto system. Given all the unknowns any images returned may end up being blurry (wrong slew rate) or blank (pointing in the wrong direction).

Schedule of events:
^{Source: Alan Stern / JHUAPL via Twitter, screenshot of this page}