There was a press briefing this morning on the upcoming flyby of Mercury by MESSENGER. Closest approach happens Monday, October 6, at 08:40 UTC. It's the spacecraft's second of three flybys before eventually entering orbit in March of 2011. Here's the high points of the briefing and the plans for the encounter. Below, I've got a detailed timeline focusing mostly on the imaging plans.
They targeted the flyby not with rocket firings but instead by using solar sailing. MESSENGER is the first spacecraft to intentionally shift its trajectory (rather than just its attitude) using solar sailing techniques. Neat.
During this encounter, the sunlit hemisphere of Mercury is basically the same as the nightside hemisphere of Mercury in the last encounter, meaning that MESSENGER will be seeing pretty nearly all of the terrain that it didn't see during the first encounter.
The terrain it will see includes a large chunk of Mercury that's never been seen up close by a spacecraft before, 30% of the whole surface, an area equivalent to the land area of South America.
The imaging campaign is pretty familiar, similar to that for the previous encounter. There's not so much imaging on the inbound leg of the flyby because Mercury will be a fairly thin crescent to MESSENGER. There are many mosaics and a movie planned for the outbound leg.
The first data will start hitting the ground shortly before 06:00 UTC on Tuesday. It'll take several days to get all the images to Earth.
I'm told we'll see daily image releases beginning Tuesday and continuing for the next week or two. Sadly, this is not one of the missions that has chosen to release all of their image data right away.
ere's a nice graphic that illustrates how this flyby will fill in a goodly chunk of the remaining gaps in our maps of Mercury:
NASA / JHUAPL / CIW
Science plans for MESSENGER's second Mercury flyby, October 6, 2008
This map of Mercury includes all of the spacecraft image data taken to date. In 1975 and 1976, Mariner 10 acquired images of about 40 percent of Mercury, covering much of the hemisphere from 180 to 360 degrees east longitude. During MESSENGER's January 2008 flyby, approximately another 20 percent of the planet was revealed in regions west of the Mariner 10 coverage. During the October 2008 flyby, MESSENGER will fill in much of the remaining terrain on the hemisphere opposite the Mariner 10 hemisphere, and will also fill in the gore crossing the northeastern portion of the Mariner 10 map (purple areas). The red and blue lines indicate the ground tracks of the Mercury Laser Altimeter data from the two MESSENGER flybys.
And here's the science timeline. As they did last time, the MESSENGER team has prepared a really cool Web-based application, the "Mercury Flyby Dynamic Visualization," where you can see exactly where the cameras are looking, when, throughout the close part of the encounter. Thanks to the team for that and for the planning document they sent me detailing the science plans, which I translated into this timeline.
Spacecraft time (UTC)
Time with respect to closest approach (hh:mm)
Oct 3 03:30
Optical Navigation image #1 As it approaches Mercury, MESSENGER will take a series of eight optical navigation images.
Optical Navigation image #2
Start continuous Deep-Space Network (DSN) coverage of encounter. As Earth rotates, antennae at the three DSN stations at Goldstone, California; Canberra, Australia; and Madrid, Spain will continuously monitor MESSENGER's radio signal.
Oct 4 04:00
Optical Navigation image #3
Optical Navigation image #4
Optical Navigation image #5
Oct 5 04:00
Optical Navigation image #6
Optical Navigation image #7
Optical Navigation image #8
Turn to start encounter imaging sequence; beacon-only tracking of satellite begins To image Mercury, MESSENGER has to rotate, and will no longer be able to point its high-gain antenna at Earth. From this point until many hours after the flyby, Earth will not receive data from MESSENGER, but still will be able to listen for a MESSENGER's beacon signal.
Begin scans of Mercury solar tail with MASCS MESSENGER performed similar observations during its first flyby, but these observations begin at more than three times farther away from Mercury. They run for more than nine hours, while imaging continues.
Oct 6 04:10
Start approach scattered light sequence using wide-angle camera The sequence includes 84 images of Mercury.
Wide-angle camera full-color image (5 km/pixel) From a distance of about 27,000 kilometers (18,000 miles), Mercury will nearly fill the wide-angle camera frame. The view will be of a slender crescent of Mercury, with less of the surface sunlit than was the case for the approach crescent image of the first flyby. Dynamic visualization >
Narrow-angle camera approach mosaic (~450 m/pixel) Now only 16,000 kilometers (10,000 miles) from Mercury, MESSENGER will capture a 4-by-11 mosaic of the thin crescent. Dynamic visualization >
Eclipse entry For 17 minutes, MESSENGER will be hidden from the Sun.
Complete scans of Mercury solar tail with MASCS; start night exospheric observation As MESSENGER gets close to Mercury, MASCS will switch from studying Mercury's "tail" to studying its atmosphere, looking for the telltale ultraviolet glow of different gases.
Start spacecraft slew sequence to point instrument deck at planet
Start firing MLA laser at Mercury The laser will be ranging to Mercury's surface throughout closest approach, gathering a topographic profile. Closest approach happens on the night side of Mercury, so MESSENGER cannot take images of the areas being measured by the laser altimeter, but these areas were imaged both by Mariner 10 and by MESSENGER during its January flyby. Dynamic visualization >
Closest approach to Mercury MESSENGER will pass within 200 kilometers of the surface, firing its laser all the time.
Start dayside surface scan with MASCS The multipurpose MASCS switches targets again, this time from the atmosphere to spectroscopic study of the composition of the rocks on the surface.
Combined wide-angle camera imaging, MLA laser ranging, and MASCS spectral studies As MESSENGER flies across the terminator into the Sun over Mercury's equator, it will simultaneously gather color images with its wide-angle camera, laser ranging with the laser altimeter, and spectral analysis, building up a coordinated data set. Dynamic visualization >
Complete Mercury surface laser ranging In the 10 minutes since the flyby, MESSENGER will have receded to nearly 10 times its closest approach altitude, too far for the laser altimeter to "see" the surface. Wide-angle camera imaging and MASCS spectroscopy continue. Dynamic visualization >
Start dayside low-exospheric observation sequence with MASCS
Narrow-angle camera high-resolution departure mosaic #1, equatorial image strip (100-150 m/pixel) It will take 35 narrow-angle image frames, captured at a rate of one every five seconds, to march across the sunlit portion of Mercury's equator as MESSENGER recedes from 3,600 to 4,500 kilometers (2,200 to 2,800 miles) above Mercury. MASCS will simultaneously observe the surface. Dynamic visualization >
Start dayside high-exospheric observation sequence with MASCS
Narrow-angle camera departure mosaic #2, northern hemisphere (150-300 m/pixel) 162 frames will be necessary to cover Mercury's northern hemisphere, nearly fully lit by the Sun. The western two-thirds of the mosaic covers terrain previously imaged by Mariner 10, but the Mariner 10 data included a large "gore" of no imaging data cutting across the map; this mosaic will fill in that gore. Dynamic visualization >
Wide-angle camera departure color mosaic #2 (2.2-3 km/pixel) A 3x3 mosaic will be shot through all of the wide-angle camera's color filters. Dynamic visualization >
Wide-angle camera calibration imaging (3.2 km/pixel)
Begin narrow-angle camera departure movie Narrow-angle camera images will be taken over the next 15 hours as MESSENGER recedes from the flyby.
Wide-angle camera departure shot #5 (32 km/pixel)
Oct 7 04:38
End narrow-angle camera departure movie
Wide-angle camera departure shot #6 (67 km/pixel)
Turn to Earth to regain radio contact
Begin data playback
Complete playback of high-priority images Selected images have been marked for early playback. Likely candidates include inbound and outbound wide-angle camera images that encompass all of Mercury in a single frame, providing the context images for all of the higher-resolution shots.
Complete playback of all high-priority non-imaging science data through 21 hours after closest approach
Complete playback of all medium-priority non-imaging science data through 2 hours and 20 minutes after closest approach
Oct 8 11:05
Complete playback of all high-priority non-imaging data through 46 hours 35 minutes after closest approach and all image data through 47 minutes after closest approach This includes the first two narrow-angle camera mosaics, of the equator and northern hemisphere, and the full-globe wide-angle camera mosaic.
End continuous DSN coverage for encounter
Oct 9 01:05
Start additional DSN 70-meter coverage for data playback
Complete playback of all high-priority non-imaging data through 64 hours 15 minutes after CA and all image data through 1 hour 40 minutes after CA. No additional medium-priority data played back. This will include all of the narrow-angle camera mosaics and the closest single-frame wide-angle camera departure view.
For context, you may want to check out the following stories on the first flyby: