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Stardust-NExT: A Mission At Tempel 1 After Deep Impact!

A General View of Comet Tempel 1 as Seen by the Stardust-NExT Mission on February 14th, 2011. picture courtesy of site 'Amateur Astronomy' based on a picture NASA/JPL-Caltech/Cornell

NASA's Stardust-NExT mission successfully encountered the Tempel 1 comet on February 14th, by 8:40 p.m. PST (11:40 p.m. EST), at a distance of approximately 111 miles (178 km)! The Stardust-NExT mission was a transformation of the Stardust mission, a NASA's mission which had launched by early 1999 and had successfully passed close to comet Wild 2 in January 2004, collecting cometary dust as it eventually came by Earth to release a sample-ladden capsule in January 2006. NASA then, since the summer of 2007 had extended the craft mission under the name Stardust-NExT, to a second flyby of comet Tempel 1, by Feb. 14, 2011, while is was to be returning from a close approach to the Sun and as the comet had been the object of the Deep Impact mission in 2005 which had had a load impacting at the surface. After that passage at Tempel 1, the Stardust craft should keep imaging until no longer of value and eventually be plugged off by March or April 2011. Comet 9P/Tempel is a periodic comet discovered by Wilhelm Tempel on April 3, 1867 orbit of which lies between the orbits of Mars and Jupiter as it belongs to the Jupiter-family comets, which are comets orbital periods are varying because of close approaches with the planet Jupiter. Comet Tempel 1 nucleus is elongated and irregular, with a size 4.7-3 miles (7.6-4.9 kilometer) and its rotation period of about 41.9 hours. Pictures from the Deep Impact impact are showing that the nucleus is featuring several regions of distinct morphology, suggesting considerable variation in exposed materials, geologic processes and ages. Dozen apparently circular features, ranging from 131 to 1,312 feet (40 to 400m) are extant. Whether such features are impact craters or sublimation pits remains uncertain. Smooth surface regions were also spotted and located in gravitational lows, reminiscent of the plateau seen on comet Borrelly, but the surroundings are different. There is circumstantial evidence that the smooth deposits may be associated with either recent or currently active regions on the nucleus

How did The Flyby Occurred?

Animated Sequence of Stardust-NExT Mission at Comet Tempel 1 on February 14th, 2011. Comet's Nucleus at Closest is by 111 Miles (178 km) Away Only!. animation courtesy of site 'Amateur Astronomy' based on pictures NASA/JPL-Caltech/Cornell

As the mission proceded with trajectory correction maneuvers to focus the target better, it eventually was running by about 24,000 mph (38,600 km/h) during its approach to comet Tempel 1. During the encounter phase, the spacecraft carried out many operations in short order as that was done automatically, the spacecraft being too far away, on the other side of the Sun relative to the Earth, to receive timely updates from Earth. That included turning the spacecraft to point its protective shields between it and the anticipated direction from which cometary particles would approach. Then, 4 minutes to closest, the craft began science imaging of the comet's nucleus. The mission memory was limited to 72 high-resolution images taken through a imaging sequence running for about 8 minutes. The imaging was most closely spaced around the time of closest approach for best-resolution coverage of Tempel 1's nucleus. Spacecraft's navigation camera took the job as it was a amalgam of spare flight-ready hardware left over from previous NASA missions, the Voyager, Galileo and Cassini ones. Each image took about 15 minutes to transmit as the craft had turned on its automatic navigation system in preparation to the flyby. Once the flyby performed, beginning by about 10 p.m. PST (1 a.m. EST on Feb. 15), Stardust turned to point its high-gain antenna at Earth and started downlinking data worth 468 kilobytes and images. 10 hours in total were needed to complete the transmission

Science

thumbnail to Four Views of Comet Tempel 1 During the Flyby by The Stardust-NExT Mission on February 14th, 2011. Two Image at Center are The Closest Approach Images as Taken at 3 Seconds Before and 3 Seconds After the Closest Passage Respectively

click to Four Views of Comet Tempel 1 During the Flyby by The Stardust-NExT Mission on February 14th, 2011. Two Image at Center are The Closest Approach Images as Taken at 3 Seconds Before and 3 Seconds After the Closest Passage Respectively. picture courtesy of site 'Amateur Astronomy' based on a picture NASA/JPL-Caltech/Cornell

The Stardust-NExT craft flew by another angle the Deep Impact had, allowing for more territories seen on the nucleus. It also had like a mission to study the coma, or comet's atmosphere. Engineering telemetry downlinked after closest approach indicates the spacecraft flew through waves of disintegrating cometary particles, including a dozen impacts that penetrated more than one layer of its protective shielding. Instead of having a little stream of uniform particles coming out, debris apparently came out in chunks and crumbled

thumbnail to A Before-and-After Comparison of The Part of Comet
Tempel 1 that Was hit By the NASA's Deep Impact Spacecraft Impactor as The Left-Hand Image was Obtained by Deep Impact in 2005 and The Right-Hand Image Showing Arrows Identifying the Rim of the Deep Impact Impactor Crater

thumbnail to A Other Before-and-After Comparison of The Part of Comet
Tempel 1 that Was hit By the NASA's Deep Impact Spacecraft Impactor Showing, in Succession, From Left to Right the Impact Area Before Impact, as Highlighted with a Red Circle, the Area After Impact (With a Indication of Sunlight Incidence and Selected Features), and The Accurate Spot of The Impact. White Arrow is The Impactor's Trajectory

click to First Picture (Left) is Showing A Before-and-After Comparison of The Part of Comet Tempel 1 that Was hit By the NASA's Deep Impact Spacecraft Impactor as The Left-Hand Image was Obtained by Deep Impact in 2005 and The Right-Hand Image Showing Arrows Identifying the Rim of the Deep Impact Impactor Crater, as Second Picture (Right) is A Other Before-and-After Comparison of The Part of Comet Tempel 1 that Was hit By the NASA's Deep Impact Spacecraft Impactor Showing, in Succession, From Left to Right the Impact Area Before Impact, as Highlighted with a Red Circle, the Area After Impact (With a Indication of Sunlight Incidence and Selected Features), and The Accurate Spot of The Impact. White Arrow is The Impactor's Trajectory. picture courtesy of site 'Amateur Astronomy' based on a picture NASA/JPL-Caltech/University of Maryland/Cornell (left) and on a picture NASA/JPL-Caltech/Cornell/Univ. of Maryland (right)

On the side of the nucleus of comet Tempel 1 the flyby revealed territories that had never been seen before. Three terraces of different elevations are visible, with dark, banded scarps, or slopes, separating them. The widest of the banded slopes is about 1 miles (2 km). The lowest terrace has two circular features that are about 500 ft (150 m) in diameter. Such configuration likely hint to layers coating the nucleus, a observation Deep Impact already had done for the other side of the comet. Pictures released also allow to check changes in the surface of comet Tempel 1 which likely might be due to that, between the two visits, the comet made one trip around the Sun. Changes are caused by a erosion with is caused by volatile substances evaporating away from the comet. In a region highlighted with a smooth terrain at a higher elevation than the more textured surface around it, with prominent white cliffs showing the limit, the cliffs have been seen eroded by as much as 66 to 100 ft (20 to 30m) in some places as depressions have merged together over time, also from erosion. White cliffs or deposits are also seen on other images taken during the flyby which likely are related to the cometary nucleus activity when exposed to Sun's heat. As far as the scar of the 2005 Deep Impact mission's collision with Tempel 1 is concerned, it is also worth the science as images returned are showing a crater with a small, brighter mound in the center as some of the ejecta likely went up and came right back down. On how subdued the crater looks like, scientists think that that cometary nucleus is fragile and weak. The impact crater is estimated to be 500 ft (150 m) wide

thumbnail to Terraces Seen At Comet Tempel 1 by the Stardust-NExT Mission, With a Spatial Resolution of About 50 ft (15 m) per pixel

thumbnail to Terrain Changes at Comet Tempel 1 Between the Deep Impact Mission in 2005 and the Stardust-NExT Mission in 2011. Smooth Terrain at a Higher Elevation Than Textured Surface Aside as Cliffs Eroded Back to The Left or Other Changes Seen Too

click to Terraces Seen At Comet Tempel 1 by the Stardust-NExT Mission, With a Spatial Resolution of About 50 ft (15 m) per pixel (left) and to Terrain Changes at Comet Tempel 1 Between the Deep Impact Mission in 2005 and the Stardust-NExT Mission in 2011. Smooth Terrain at a Higher Elevation Than Textured Surface Aside as Cliffs Eroded Back to The Left or Other Changes Seen Too (right). pictures courtesy of site 'Amateur Astronomy' based on a picture NASA/JPL-Caltech/Cornell (left) and NASA/JPL-Caltech/University of Maryland/Cornell (right)

The Stardust-NExT Mission Trajectory and Phases

A Illustration of The Stardust-NExT Mission Trajectory. picture site 'Amateur Astronomy based on a picture NASA

The trajectory of the Stardust-NExT mission, like illustrated by image above, consisted of four loops of the Sun in two separate orbits. Loops 1 and 2 represent the orbit the spacecraft like was left in after the sample return on Jan. 15, 2006. The Earth gravity assist on Jan. 14, 2009 placed the spacecraft in the final heliocentric orbit (Loops 3 and 4) intercepting Tempel 1 on Feb. 14, 2011 (39 days after the comet’s perihelion)

The Stardust-NExT Mission was featuring a certain number of phases like described below

Cruise 1 Phase. That first mission phase began in August 2007 as characterized by mission planning on the ground, as minimal interaction with the spacecraft in flight occurred averaging approximately one short contact with the spacecraft every four weeks to update navigation and spacecraft health. Two trajectory correction maneuvers were performed the one on Sept. 19, 2007 placing the spacecraft on a trajectory for an Earth flyby in January 2009
Earth Gravity Assist Phase. Activities turned high then with that second phase, approximately three-month-long phase. Two trajectory correction maneuvers were performed during this phase. Stardust made its closest approach to Earth on Jan. 14, 2009. At its closest point to Earth, the spacecraft was about 5600 miles (9,100 km) over the California/Mexico border south of San Diego and traveling at a speed of approximately 22,400 miles per hour (36,000 km/h). The result of that Earth flyby was to place the mission in a new heliocentric orbit that would result in a flyby of Tempel 1
Cruise 2 Phase. Like Cruise 1, Cruise 2 was a maintenance period requiring one contact with the spacecraft every four weeks only. Also during Cruise Phase 2, the Stardust spacecraft executed the largest trajectory correction maneuver of the extended mission. On Feb. 17, 2010, with the spacecraft on the opposite side of the solar system and beyond the orbit of Mars, the rockets fired for 22 minutes and 53 seconds, changing the spacecraft's speed by 54 miles per hour (24 meters per second). The burn adjusted the time of the spacecraft’s encounter to maximize the possibility of the spacecraft capturing high-resolution images of desired surface features of the comet
Approach Phase. Beginning at encounter-minus-60 days, this phase characterized by the beginning of optical navigation of comet Tempel 1 from the spacecraft's onboard camera, NavCam, frequent spacecraft systems checks and tests, and trajectory correction maneuvers to refine Stardust's trajectory. All of these maneuvers are geared toward the most fuel-efficient refinement of the spacecraft's path toward comet Tempel 1. Six hours after a last trajectory correction maneuver (encounter-minus-42 hours), the spacecraft took its final set of approach-phase Optical Navigation (OpNav) images and downlink them to Earth. Mission navigators analyzed these images for the latest on the location of the comet and made their final recommendations on whether or not a final maneuver for this phase should be performed to move the spacecraft away from the comet. This would be done if the projected flyby distance is too close
Encounter Phase The Encounter Phase began at 24 hours before the time of closest approach and concluded 24 hours after the time of closest approach. The first critical milestone occurs at encounter-minus-24 hours. That is when the Stardust-NExT mission team begins uplinking the set of commands that will carry the spacecraft through its encounter with Tempel 1. At encounter-minus-18-hours, engineers will have the last scheduled opportunity for a final trajectory correction maneuver prior to encounter. This maneuver would only be executed if mission navigators indicate the spacecraft could pass closer to the comet's nucleus than planned. The information used in the decision of whether to execute the maneuver or not is based on the data previously taken in the final set of OpNav images. Regardless of whether or not this maneuver is executed, no further maneuvers are scheduled
Flyby. Then the flyby occurs like detailed in the table below
Departure Phase. The Departure Phase for the Stardust-NExT encounter begins at encounter-plus-2-days. The spacecraft will begin imaging the comet as it recedes into the distance. This departure-phase imaging begins at encounter-plus-2-days with one image every 5 minutes. From encounter-plus-4-days to encounter-plus-10-days, a science image of the comet will be taken every 12 minutes. Mission operations will end with spacecraft decommissioning several weeks after encounter, and the project will end after data analysis and programmatic closeout

A Timeline of Flyby of Mission Stardust-NExT at Comet Tempel 1
encounter-minus-16 hours any final modifications or refinements to the existing flyby commands are uploaded. This is the final scheduled two-way communications with the spacecraft until after encounter

encounter-minus-3 hours the spacecraft turns on the Comet and Interstellar Dust Analyzer instrument

encounter-minus-1 hour the Encounter Phase enters its "critical sequence." This sequence is characterized by the spacecraft carrying out many important milestones. The first milestone of this sequence occurs at encounter-minus-one hour, when the spacecraft turns to place its protective Whipple Shields in the ram direction -- that is the spacecraft puts its shields between it and the anticipated direction cometary particles would approach. This maneuver places the spacecraft in an attitude that does not allow the high-gain antenna to point at Earth. As a result, there will not be any high-rate communications between the spacecraft and ground during this critical phase

encounter-minus-30 minutes the spacecraft initiatesits AutoNav program. AutoNav allows the onboard navigation system to assist camera pointing by adjusting the angle of the NavCam's scan mirror. It also provides information to the spacecraft's attitude system on the magnitude of a roll that the spacecraft performs at five minutes before closest approach. The role is designed to correct any out-of-plane error and thus keep the comet's nucleus in the camera's field of view

encounter-minus-20 minutes the Dust Flux Monitor instrument is turned on

encounter-minus-5 minutes the spacecraft initiates a "roll-to-comet point." This approximately 40-second long rolling maneuver places the spacecraft in an attitude that optimizes the NavCam's ability to keep Tempel 1's nucleus in its field of view

encounter-minus-4 minutes the science imaging begins. The nominal imaging sequence runs from encounter-minus-4 minutes to encounter-plus-4 minutes. The spacecraft's onboard memory is limited to 72 high-resolution images, so the fastest possible NavCam imaging frequency is used around closest approach for best-resolution coverage. From encounter-minus-4 minutes to encounter-minus-2 minutes-and-24 seconds, 12 frames are taken (one every 8 seconds). From encounter-minus-2-minutes-and-24 seconds to encounter-plus-2-minutes-and-30 seconds, 48 frames are taken (one every 6 seconds). From encounter-plus-2-minutes-and-38 seconds to encounter-plus-3-minutes-and-50-seconds, 12 frames are taken (one every 8 seconds)

encounter! the spacecraft is expected to be approximately 200 kilometers (124 miles) from the comet's nucleus

encounter-plus-1-minute-and-36-seconds AutoNav has completed operations and is turned off

encounter-plus-4 minutes high-resolution science imaging is complete

encounter-plus-20 minutes the Dust Flux Monitor instrument is turned off

encounter-plus-60 minutes the spacecraft performs an attitude change to point its high-gain antenna at Earth

encounter-plus-3 hours the Comet and Interstellar Dust Analyzer instrument is turned off. This completes the collection of science data during the Encounter Phase of the Tempel 1 flyby. A total of 720 megabytes of data, including 72 high-resolution images, are stored for playback

encounter-plus-3-hours-and-38-minutes the Madrid dish of NASA's Deep Space Network begins to receive the playback of science data collected during encounter. Five selected NavCam images are returned first. NExT, data from the two other instruments are downlinked. Finally, the remaining 67 high-resolution images taken during encounter are downlinked. To ensure all images and science instruments data have been collected, the science data from encounter will be downlinked in its entirety up to three times during the NExT two days

A Timeline of Flyby of Mission Stardust-NExT at Comet Tempel 1
encounter-minus-16 hours	any final modifications or refinements to the existing flyby commands are uploaded. This is the final scheduled two-way communications with the spacecraft until after encounter
encounter-minus-3 hours	the spacecraft turns on the Comet and Interstellar Dust Analyzer instrument
encounter-minus-1 hour	the Encounter Phase enters its "critical sequence." This sequence is characterized by the spacecraft carrying out many important milestones. The first milestone of this sequence occurs at encounter-minus-one hour, when the spacecraft turns to place its protective Whipple Shields in the ram direction -- that is the spacecraft puts its shields between it and the anticipated direction cometary particles would approach. This maneuver places the spacecraft in an attitude that does not allow the high-gain antenna to point at Earth. As a result, there will not be any high-rate communications between the spacecraft and ground during this critical phase
encounter-minus-30 minutes	the spacecraft initiatesits AutoNav program. AutoNav allows the onboard navigation system to assist camera pointing by adjusting the angle of the NavCam's scan mirror. It also provides information to the spacecraft's attitude system on the magnitude of a roll that the spacecraft performs at five minutes before closest approach. The role is designed to correct any out-of-plane error and thus keep the comet's nucleus in the camera's field of view
encounter-minus-20 minutes	the Dust Flux Monitor instrument is turned on
encounter-minus-5 minutes	the spacecraft initiates a "roll-to-comet point." This approximately 40-second long rolling maneuver places the spacecraft in an attitude that optimizes the NavCam's ability to keep Tempel 1's nucleus in its field of view
encounter-minus-4 minutes	the science imaging begins. The nominal imaging sequence runs from encounter-minus-4 minutes to encounter-plus-4 minutes. The spacecraft's onboard memory is limited to 72 high-resolution images, so the fastest possible NavCam imaging frequency is used around closest approach for best-resolution coverage. From encounter-minus-4 minutes to encounter-minus-2 minutes-and-24 seconds, 12 frames are taken (one every 8 seconds). From encounter-minus-2-minutes-and-24 seconds to encounter-plus-2-minutes-and-30 seconds, 48 frames are taken (one every 6 seconds). From encounter-plus-2-minutes-and-38 seconds to encounter-plus-3-minutes-and-50-seconds, 12 frames are taken (one every 8 seconds)
encounter!	the spacecraft is expected to be approximately 200 kilometers (124 miles) from the comet's nucleus
encounter-plus-1-minute-and-36-seconds	AutoNav has completed operations and is turned off
encounter-plus-4 minutes	high-resolution science imaging is complete
encounter-plus-20 minutes	the Dust Flux Monitor instrument is turned off
encounter-plus-60 minutes	the spacecraft performs an attitude change to point its high-gain antenna at Earth
encounter-plus-3 hours	the Comet and Interstellar Dust Analyzer instrument is turned off. This completes the collection of science data during the Encounter Phase of the Tempel 1 flyby. A total of 720 megabytes of data, including 72 high-resolution images, are stored for playback
encounter-plus-3-hours-and-38-minutes	the Madrid dish of NASA's Deep Space Network begins to receive the playback of science data collected during encounter. Five selected NavCam images are returned first. NExT, data from the two other instruments are downlinked. Finally, the remaining 67 high-resolution images taken during encounter are downlinked. To ensure all images and science instruments data have been collected, the science data from encounter will be downlinked in its entirety up to three times during the NExT two days

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