Three months ago, I posted an article explaining what to expect during the flyby. The following is a revised version of the same post, with some errors corrected, the expected sizes of Nix and Hydra updated, and times of press briefings added.
UPDATE July 8: Added newly scheduled July 15 press briefing. UPDATE July 12:Changed schedule of July 13 press briefing. UPDATE July 14: Changed schedule of July 14 evening press briefings.
As New Horizons approaches, every image of Pluto and Charon that each instrument returns will be the best it has ever taken. All of these images will be thrilling to see. But until mid-July, all the images will still be pretty small. When will we get pictures that really answer questions about Pluto? In this blog entry I'll try to explain when we'll get the images that you're hoping for. First, the executive summary:
Closest approach is at 11:49:57 UTC / 07:49:57 EDT / 04:49:57 PDT on Tuesday, July 14, 2015.
New Horizons gets 1.2 million kilometers closer each day.
New Horizons has two cameras.
The Long-Range Reconnaissance Imager (LORRI) has a field of view of 0.29 degrees and a pixel scale of 4.94 microradians and takes black-and-white ("panchromatic") images.
The Ralph Multispectral Visible Imaging Camera (MVIC) has a field of view 5.7 degrees wide and a pixel scale of 19.77 microradians and takes both panchromatic and color images. It has panchromatic, near-IR, red, blue, and methane filters, but no green filter. Color images are usually IR/red/blue.
Today, June 24, is the last day that the orbit of Hydra fit within the LORRI field of view. Images containing Pluto may not contain all the other moons.
Through July 12, New Horizons will take regular LORRI photos of Pluto, Charon, Nix, and Hydra, which will mostly be returned soon after acquisition because they are used for optical navigation.
Pluto will appear larger than the LORRI field of view for less than 24 hours around closest approach.
Since Pluto and Charon rotate slowly (once every 6.4 days), all of the best fully-lit images will show the same hemisphere. The other hemisphere will be imaged at a best resolution of about 38 kilometers per pixel, 3.2 days prior to closest approach.
There are few data downlinks near closest approach, so we will not receive many images in real time. But the ones we get will be great.
The mission has promised to release LORRI images (higher-resolution, black-and-white) in near-real-time, but not MVIC (lower-resolution, color) images.
Only 1% of the science data from the flyby will be returned to Earth during the period around closest approach, including images that the mission has selected for their high science value as well as high public interest. They will be releasing captioned and processed versions as fast as their small team can manage.
The rest of the image data will be downlinked beginning in September, about 2 months after encounter. It will take 10 weeks to download the full data set.
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. 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 other, so-called "low-speed" instruments 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. I asked Kim Ennico for a little more explanation of the "low-speed" distinction, and she said:
SWAP, PEPSSI and SDC are "low-speed" compared to LORRI, Ralph, Alice and REX who are called "high-speed." They are separated in type by the spacecraft bus to which they write their data, the "low speed bus" or the "high speed bus." As an added complication, there is a science mode in Alice which writes to the "low speed bus." We've learned that when we compress and packetize the data for downlink, we have to treat the "high-speed" differently than the "low-speed." We've found you can be most efficient at downloading the "low-speed" data if you do it as a series of playbacks of data from specified mission elapsed time ranges with playback pauses. It made sense to dedicate a period of time to return all the "low-speed data." Plus during the same Juy 20 to September 14 period we can get all the spacecraft data, so if we need to reconstruct the actual pointing of the handful of near-encounter images that came down, we can do so.
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. Since the first time I posted this article, I've had to reduce the apparent sizes of Nix and Hydra by about half to match the new Hubble estimates of their diameters.
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 planetary.org/plutodata 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 will be released on the New Horizons raw image website automatically, are in bold. Automatic release is promised within 48 hours of receipt; lately, the images have been released faster than that. 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!
Sunday, July 12 19:39 UT / 15:39 ET / 12:39 PT: 7.5hr downlink: Final optical navigation images
3 LORRIs of Pluto at 13 km/pix (~185 pixels across disk)
2 LORRIs of Charon at 13 km/pix (~92 pixels across disk)
Monday, July 13 02:23 UT / Sunday, July 12 22:23 ET / 19:23 PT: 4.2hr downlink: Fail Safe A
LEISA and Alice data (no LORRI or MVIC images)
Monday, July 13 06:14 UT / 02:14 ET / Sunday, July 12 23:14 PT: 2.5hr downlink: Fail Safe B
LEISA data (no LORRI or MVIC images)
Monday, July 13 at 10:39 UT / 06:39 ET / 03:39 PT: 1.4hr downlink: Fail Safe C
Monday, July 13 at 16:24 UT / 12:24 ET / 09:24 ET: 3.5hr downlink: Fail Safe D
LORRI Charon at 7.2 km/pix (~170 pixels across disk). Taken 2015-07-13 06:36:57. Range 1.461 million km.
MVIC Pluto and Charon color at 28 km/pix (~86 and ~43 pixels across disk). Taken 2015-07-13 07:37:55. Range 1.406 & 1.418 million km. - Can be used to colorize LORRI Charon image in same downlink; less good for colorizing later Pluto image because of 12.5-hour time difference, during which Pluto will rotate about 30 degrees
This downlink also includes Alice, LEISA, PEPSSI, and SWAP data.
Tuesday, July 14 at 03:15 UT / Monday, July 13 at 23:15 ET / 20:15 PT: 0.9hr downlink: E-Health 1
LORRI Pluto at 3.8 kilometers per pixel (~630 pixels across disk). Taken 2015-07-13 20:17:28. Range 768,000 km. - The best single-frame photo of Pluto that will be available during encounter period
No science data, just a brief burst of telemetry confirming that the spacecraft survived the flyby. The communications pass should begin July 15 00:53 UT / July 14 20:53 ET / 17:53 PT. According to the NASA media schedule, the mission team on Earth should receive the signal by 01:02 UT / 21:02 ET / 18:02 PT.
Wednesday, July 15 at 19:25 UT / 15:25 ET / 12:25 PT: 6.9hr downlink: First Look B
LORRI Nix at 3.0 km/pix (~9x19 pixels across disk). Taken 2015-07-13 23:19:16. Range 590,000 km. - The best photo of Nix that will be available during encounter period; LORRI's best will be 10 times higher-resolution
3 frames on Pluto from high-resolution LORRI mosaic at 0.4 km/pix (Pluto will fill all 3 frames, each frame ~410 km wide). Taken 2015-07-14 10:10:15. Range 77,000 km. - The highest-resolution images of Pluto that will be available during encounter period
Alice, LEISA, REX, and SWAP data
Thursday, July 16 at 04:23 UT / 00:23 ET / Wednesday, July 15 at 21:23 PT: 1.9hr downlink: First Look C
PEPSSI data (no LORRI or MVIC images)
Thursday, July 16 at 07:23 UT / 03:23 ET / 00:23 PT: 1.9hr downlink: First Look D
3 frames on Charon from high-resolution LORRI mosaic at 0.38 km/pix (Charon will fill frame, each frame ~390 km wide). Taken 2015-07-14 10:23:47. Range 79,000 km. - The highest-resolution images of Charon that will be available during encounter period
PEPSSI and SWAP data
Thursday, July 16 at 13:22 UT / 09:22 ET / 06:22 PT: 4.3hr downlink: First Look E
MVIC Pluto and Charon color at 5.0 km/pix (~480 and ~240 pixels across disks). Taken 2015-07-14 06:49:08. Range 254,000 and 269,000 km. - Color portrait of Pluto & Charon in same image
Friday, July 17 at 16:32 UT / 12:32 ET / 09:32 UT: 3.3hr downlink: High Priority A
LORRI Hydra at 1.2 km/pix (~48x28 pixels across disk). Taken 2015-07-14 07:39:28. Range 231,000 km. - The best-resolution well-lit photo of Hydra in the data set (there will be a higher-resolution one taken of a crescent Hydra)
1 frame on Pluto from 2x2 LORRI mosaic at 2.2 km/pix. Taken 2015-07-14 02:49:47. Range 444,000 km. - Will show Pluto filling a corner of image
Saturday, July 18 at 10:29 UT / 06:29 ET / 03:29 PT: 4.6hr downlink: High Priority B
LORRI Pluto at 1.8 km/pix (Pluto will fill frame). Taken 2015-07-14 19:06:24. Range 360,000 km. - A departure crescent shot of Pluto
MVIC Nix color at 3.1 km/pix (~18x8 pixels across disk). Taken 2015-07-14 08:02:39. Range 165,000 km. - The best color image of Nix that will be available during encounter period; may be used for stereo with image returned in First Look B
For the rest of Saturday and Sunday, downlinks include REX and LEISA data, with no LORRI or MVIC data.
Monday, July 20 at 16:20 UT / 12:20 ET / 09:20 PT: 3.3hr downlink: High Priority G
4 frames on Pluto from high-resolution LORRI mosaic at 0.4 km/pix (Pluto will fill all 4 frames, each frame ~410 km wide). Taken 2015-07-14 10:10:15. Range 77,000 km. - Adds to high-resolution mosaic that began downlinking Wednesday in First Look B
Following that, no images will be returned until September 14, at which point we will gradually get the entire image data set.