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Emily LakdawallaMarch 10, 2015

What to expect when you're expecting a flyby: Planning your July around New Horizons' Pluto pictures

Note: A revised version of this post, "What to expect when you're expecting a flyby: Planning your July around New Horizons' Pluto Pictures (version 2)," is now available. Please go there for the most accurate information.

New Horizons is now closer to Pluto than the Sun is to Earth: 1 astronomical unit, or 150 million kilometers. A tiny course correction burn steered them closer to their goal today. As New Horizons begins to approach Pluto, there's a single question everybody keeps asking me: when will we get the first pictures? The trivial answer to that question is that we already have them. But as exciting as it is to know that New Horizons has sighted Pluto, a teeny dot wobbling among stars is not what people mean when they ask about New Horizons' pictures. What people want, of course, is the portrait photo, the one we're going to be seeing on magazine covers and in textbooks for years to come.

As New Horizons approaches, every image of Pluto and Charon that each instrument returns will be the best it has ever taken. They will be thrilling to see. But until mid-July, all the images will still be pretty small. In the days leading up to the July 14 flyby, with only one exception, all of the images that we will receive of Pluto and Charon will be lower-resolution than the best Ceres pictures we have received from Dawn to date.

Approaching Ceres

NASA / JPL / UCLA / MPS / DLR / IDA / collage by Emily Lakdawalla

Approaching a dwarf planet

These Dawn images of Ceres have similar quality to the best images that we will receive from New Horizons at Pluto through July 13, the day before the flyby. Only one image that New Horizons will return before the flyby will be higher-resolution than these.

In this blog entry I'll try to explain when we'll get the images that you're hoping for. First, the executive summary:

It's hard to get data from Pluto

Data will arrive on Earth in a series of downlinks. Downlink sessions can last as long as about 8 hours, but are usually somewhat shorter. Whenever New Horizons is downlinking data, it can't take new photos, so the downlinks get shorter and less frequent as the spacecraft gets close to the time of the flyby, when it concentrates on collecting as much data as possible. Because data downlinks are slow, there will be much less data downlinked than New Horizons has stored on board. After data is downlinked, it must be processed before posting online. How long that will take is not yet known.

On Sunday, July 12, New Horizons will transmit the last of its optical navigation data. These images will have lower resolution than the images we have already received from Dawn at Ceres. Then, on Sunday and Monday, July 12 and 13, there will be a series of four "Fail Safe" downlinks. These are designed to return a minimum set of data from all instruments, just in case New Horizons does not survive the flyby. A last downlink ending overnight Monday July 13, called "E-Health 1," will include one last pre-closest approach photo of Pluto.

Then there is a nail-biting 24-hour period of waiting while New Horizons concentrates on flyby science and does not communicate with Earth, followed by the much-anticipated beep of the "Phone Home" downlink on Tuesday night, July 14. Following closest approach, on Wednesday and Thursday, July 15 and 16, there will be a series of "First Look" downlinks containing a sampling of key science data. Another batch of data will arrive in the "Early High Priority" downlinks over the subsequent weekend, July 17-20. Then there will be a hiatus of 8 weeks before New Horizons turns to systematically downlinking all its data. Almost all image data returned during the week around closest approach will be lossily compressed -- they will show JPEG compression artifacts. Only the optical navigation images are losslessly compressed.

The transmission of the High Priority data set will be complete on July 20, and then image transmission will pause. For nearly two months, until September 14, New Horizons will switch to near-real-time downlinking of data from instruments that generate low data volumes (like SWAP and PEPSSI) while it transmits just housekeeping information for all of the rest of the data. No new images will arrive on the ground during this time.

On September 14, New Horizons will begin downlinking a "browse" version of the entire Pluto data set, in which all images will be lossily compressed. It will take about 10 weeks to get that data set to the ground. There will be compression artifacts, but we'll see the entire data set. Then, around November 16, New Horizons will begin to downlink the entire science data set losslessly compressed. It will take a year to complete that process.

What to expect, when

Here is a graphical summary of all of the LORRI data that New Horizons is expected to downlink in the two weeks surrounding closest approach. I used Voyager images of Jupiter and Saturn moons to stand in for Pluto, Charon, Nix, and Hydra: Ganymede for Pluto, Tethys and Rhea for Charon, and Janus and Hyperion for Nix and Hydra. Don't take the comparisons between the moons and Kuiper belt objects too literally -- this comparison is just meant to give you a sense of the scope of the near-encounter data set at a glance.

Simulation of the New Horizons Pluto flyby LORRI data set

Voyager images: NASA/JPL. Chart by Emily Lakdawalla.

Simulation of the New Horizons Pluto flyby LORRI data set
In the two weeks surrounding New Horizons' flyby of Pluto, only 1% of the science data that it acquires will be downlinked to Earth. This chart uses Voyager images of Jupiter's and Saturn's moons to stand in for the images that New Horizons' highest-resolution camera, LORRI, is expected to downlink in the summer of 2015. Visit for futher explanation.

Following is a complete list of all the planned downlinks of image data during the highest-intensity period around closest approach. The times given are planned downlink end times. Downlinks containing LORRI images, which should be released automatically, are in bold. It is not yet known how long it will take the pipeline to run that will send these images to the Web. When I find out more precisely how long it will usually take to generate images from the raw data, I will update this post. Also, the times and ranges of the images may change by as many as 7 minutes and 6000 kilometers as navigators update their knowledge of Pluto's position; I will update this post as necessary. Therefore, I do not recommend the copying and reposting of this text, because it will become out of date!

Note: A revised version of this post, "What to expect when you're expecting a flyby: Planning your July around New Horizons' Pluto Pictures (version 2)," is now available. Please go there for the most accurate information.

Sunday, July 12 19:40 UT / 15:40 ET / 12:40 PT: 7hr 5m downlink: Final optical navigation images

Monday, July 13 02:24 UT / Sunday, July 12 22:24 ET / 19:24 PT: 4hr 13m downlink: Fail Safe A

Monday, July 13 06:15 UT / 02:15 ET / Sunday, July 12 23:15 PT: 2hr 30m downlink: Fail Safe B

Monday, July 13 at 10:40 UT / 06:40 ET / 03:40 PT: 1hr 14m downlink: Fail Safe C

Monday, July 13 at 16:25 UT / 12:25 ET / 09:25 ET: 3hr 30m downlink: Fail Safe D

Tuesday, July 14 at 03:15 UT / Monday, July 13 at 23:15 ET / 20:15 PT: 52m downlink: E-Health 1

Wednesday, July 15 at 00:09 UT / Tuesday, July 14 at 21:09 ET / 18:09 PT: 17m downlink: Phone home

Wednesday, July 15 at 10:00 UT / 07:00 ET / 04:00 PT: 1hr 29m downlink: First Look A

Wednesday, July 15 at 19:25 UT / 15:25 ET / 12:25 PT: 6hr 54m downlink: First Look B

Thursday, July 16 at 04:24 UT / 00:24 ET / Wednesday, July 15 at 21:24 PT: 1hr 50m downlink: First Look C

Thursday, July 16 at 07:24 UT / 03:24 ET / 00:24 PT: 1hr 52m downlink: First Look D

Thursday, July 16 at 13:23 UT / 09:23 ET / 06:23 PT: 4hr 15m downlink: First Look E

Friday, July 17 at 16:33 UT / 12:33 ET / 09:33 UT: 3hr 15m downlink: High Priority A

Saturday, July 18 at 10:30 UT / 06:30 ET / 03:30 PT: 4hr 36m downlink: High Priority B

For the rest of Saturday and Sunday, downlinks include REX and LEISA data, with no LORRI or MVIC data.

Monday, July 20 at 16:03 UT / 12:03 ET / 09:03 PT: 3hr 15m downlink: High Priority G

After that, we must wait for September, when the downlink of the full data set will begin. But there will be plenty to explore in this first taste of the New Horizons data!

For even more detail on the images that will be acquired and downlinked during the near-encounter phase, you may enjoy this New Horizons team "Playbook".

Many thanks to Alan Stern and Kim Ennico for helpful comments!

Read more: New Horizons, Pluto, Charon, mission status, Pluto's small moons

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
Read more articles by Emily Lakdawalla

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