PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "T. Farnham; 7 July 2006 " INSTRUMENT_HOST_NAME = "STARDUST" OBJECT = DATA_SET DATA_SET_ID = "SDU-C-SRC-6-GEOMETRY-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "STARDUST DUST COLLECTOR GEOMETRY V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_SET_TERSE_DESC = "Geometry and orientations of the Stardust spacecraft and collection plate during the dust collection phases of the mission." START_TIME = 2000-02-22T01:00:00 STOP_TIME = 2004-01-02T23:00:00 DATA_SET_RELEASE_DATE = 2006-07-07 PRODUCER_FULL_NAME = {"Tony Farnham", "Boris Semenov"} DETAILED_CATALOG_FLAG = "N" DATA_OBJECT_TYPE = "TABLE" ABSTRACT_DESC = "Data set describing the geometry and orientations of the spacecraft and the collector plate during the two interstellar dust collection phases and the Wild 2 encounter." ARCHIVE_STATUS = "ARCHIVED" CITATION_DESC = "Farnham, T.L., Semenov, B., STARDUST DUST COLLECTOR GEOMETRY, SDU-C-SRC-6-GEOMETRY-V1.0, NASA Planetary Data System, 2006." DATA_SET_DESC = " Author ------ The descriptions in this file were written by Tony Farnham using information from the 'Stardust Mission Plan' document (used with permission from the Stardust project). Data Set Overview ================= This data set describes the geometry and orientations of the spacecraft and the collector plate during the two interstellar dust collection phases and the Wild 2 encounter. Dust Sample Collector --------------------- The sample collector was a passive system for collecting dust grains. It consisted of an aluminum grid encasing multiple microporous silica aerogel blocks. The grid array was exposed to a stream of dust particles, which were gradually slowed and captured by the low-density aerogel. The aerogel dissipated the kinetic energy of the particles so they were not destroyed during the collection process. Graded density media was used to give even lower density for the initial impact. The collector grid has two sides, each of which contains separate aerogel blocks. One side of the collector was used to collect samples during the comet encounter and the opposite side was used for interstellar dust collection. Each side of the collector contained a total of 1000 cm^2 of useful collecting area. The collector was housed in the Sample Return Capsule (SRC), a container about a meter in diameter, attached to the Stardust spacecraft along the -x-axis direction. The SRC opened like a clamshell, allowing the collecting grid to be deployed into the dust stream to collect samples. Stowage of the collector was achieved by first folding the collector grid onto the boom via the wrist joint and then folding the boom/collector into the SRC canister via the shoulder joint. At the end of the mission, the SRC detached from the spacecraft and returned to Earth, where the dust samples can be analyzed in detail. In addition to allowing the collector grid to fold up into the SRC, where it was protected, the deployment mechanism was the key for maximizing the amount of time available for the capture of interstellar dust particles. The mechanism allowed the collector to be steered via the wrist joint about the spacecraft y-axis toward the -z-axis. The collector field-of-view remained unobstructed by the SRC backshield for 51 degrees of this motion, half the grid was in shadow at 63 degrees, and all of the grid was in shadow at 75 degrees. (Note that for the shadow definition, the ISP stream is assumed to be incoming perpendicular to the aerogel grid.) It is worth noting that the collector field-of-view would remain completely unobstructed for 65 degrees of the motion should the shoulder joint be used during interstellar dust particle collection. However, usage of the shoulder joint with the collector fully deployed was considered to be an unnecessary risk. The collector was deployed during three separate subphases to obtain dust samples: two periods of Interstellar Particle (ISP) collection and the encounter with Wild 2, where comet samples were obtained. The first ISP collection period lasted from February 22 through May 1, 2000, and the second from August 5 through December 9, 2002. For the collection of comet dust at Wild 2, the collector was deployed on December 24, 2003 and remained deployed until January 2, 2004. Spacecraft Geometry ------------------- ^ +Y | | | _______________ ______________ ______________ | | | ||| | | | solar ||| | | | panel ||| |_______________|_ __________ _|______________||| __| \__________/ | /| | ___ |||| SRC ----->/ | | /HGA\ |||| <---Whipple -------> +X \ | | \___/ |||| Shield \|__| __________ |||| _______________|_/__________\_|______________ | | | ||| | | | solar ||| | | | panel ||| |_______________|______________|______________||| ^ +Z | | High-gain -. | .-- Solar panels Antenna \ / \. / ________________ __.'_`._______ _______/______||| __|--------------|||| ||| /| | |||| SRC -----> / | | Spacecraft |||| <---Whipple -------> +X \ | | Bus |||| Shield \|__|______________|||| Interstellar Particle (ISP) Streams ----------------------------------- For collecting interstellar dust particles, the Stardust project made use of the fact that the solar system is moving through an environment of interstellar dust grains. This motion causes the ISPs to appear to stream through interplanetary space in a preferred direction. The upstream direction for this flow (in ecliptic latitude and longitude) is in the vicinity of (7.7 degrees, 259 degrees), which is the value adopted for designing the ISP collection. For this direction, the ISP flow has a speed of 26 km/sec relative to the solar system. The flight paths of ISPs are modified by the gravity of the sun, the solar radiation pressure and various other complex processes not well or easily formulated. If one considers only the simple effects of solar gravity and solar pressure, the velocities of ISPs of various sizes can be calculated easily as a function of beta, where beta is the ratio of the solar pressure to solar gravity. High beta particles (greater than 1) are believed to be low density, fluffy grains while low beta particles (less than 1) are denser and more compact. One to one correspondence between the beta group and the particle size cannot be made without knowledge of individual particle density, shape and radiative parameters, though assumptions can be made to estimate the range of grain sizes that are likely to be encountered. Typical results indicate that grains from 0.1 to a few microns should be expected. ISP Collection Planning Constraints ----------------------------------- A number of constraints were used to guide the planning of the ISP collection phases. o Larger particles are preferred for laboratory analysis. As such, the best orientation for the collection of interstellar particles is one that tracks the beta=1 particle. Optimization for these grains means that solar radiation pressure balances solar graivity, and so the trajectories of the dust are largely unaffected by passage through the solar system. o The collector pointing strategy should be consistent throughout the collection periods. If this is attained, then it is expected that the tracks left in the aerogel will reveal inertial direction information of the collected particles. o Low impact velocities (less than 25 km/s) are required to assure higher chance of successful capture of the particles. o Collection of interplanetary particles is to be avoided to prevent corruption of the interstellar dust sample. Interplanetary particles are assumed to have a velocity of 50 km/s and to be traveling radially outward from the sun. This constraint can be relaxed to allow for communications, TCMs, and spacecraft deadbanding. o Contamination of the interstellar sample by plume impingement (rocket exhaust from the spacecraft) is to be kept to a minimum. As such, no collection is permitted during DSMs (or TCMs > 20 m/s), but allowed during other TCMs. o Collection is allowed with as much as half of the collector grid in the SRC backshell 'shadow' if required to lengthen the collection periods. ISP Collection Strategy ----------------------- Interstellar dust collection was concentrated in the part of the spacecraft's trajectory where the interstellar dust impact velocity was relatively low (e.g., the spacecraft was moving in roughly the same direction as the dust stream) For this configuration, the dust was overtaking the spacecraft from behind, which allowed the ISPs to be collected on the back side of the dust collector. Given the passive nature of the collection instrument and the uncertainty in the direction of the interstellar stream (as large as 30 degrees), stringent attitude control was unnecessary, and the optimum periods for collecting ISPs corresponded well to the inbound portions of the cruise phases. Collection was performed only during the first two orbits, resulting in 201 days of total collection time. Collection was not performed on the third loop to avoid contamination of the cometary samples collected during the encounter with Wild-2. In addition to the science constraints described above, a number of spacecraft constraints were imposed for the planning of interstellar dust science. The following spacecraft guidelines apply to the design of these experiments: o Off-sun angles of the +z-axis are limited to 15 degrees (absolute) when pointing the +x-axis (whipple shields) toward the sun and 35 degrees (absolute) when pointing the -x-axis (SRC) toward the sun. Assume 15 degrees deadbands during ISP collection and CIDA periods, such that, maximum 'center-of-deadband' off-sun limits are 0 degrees and 20 degrees, respectively. o Off-Earth angles are limited such that Earth must always be kept within one of the low gain antenna fields-of-view. o The aerogel grid is to be deployed only once per ISP collection period. o Science periods should avoid conflicts with other mission phases (Launch, EGA, Encounter) and key geometrical events (solar conjunction). ISP Collection Subphases ------------------------ Capture of ISPs was accomplished via the passive aerogel collector that was maintained inside the SRC and deployed during the ISP collection subphases. As previously stated, the collection subphases are defined via the previously discussed constraints. The off-sun angle and beta meteoroid constraints in conjunction with the aerogel collector deployment geometry were the primary geometric factors that defined the start and end of each collection period. Each ISP collection period was established using two different strategies for tracking the spacecraft relative to the ISP velocity vector. The first strategy was implemented during the first part of each collection period and involved taking advantage of the deployment motion (about the wrist joint) of the aerogel grid to track the motion of the ISP stream in the spacecraft x-z axis plane. The out-of-plane component of the ISP stream was tracked by yawing (yaw is a rotation about the z-axis) the spacecraft sufficiently to place the s/c relative ISP stream in the x-z axis plane. The +z-axis of the spacecraft, and as a result the solar panels, remained oriented toward the sun. Once the aerogel grid wrist was fully extended it could no longer be used to track the ISP stream and the second strategy was invoked. The second strategy involved pointing the spacecraft -x-axis toward the incoming ISP stream. With the grid wrist fully extended, the vector normal to the grid surface was parallel to the spacecraft x-axis. The strategy was implemented until the off-sun angle was such that the beta meteoriod constraint was violated, which typically occured prior to reaching power related off-sun angle constraints. Both of these strategies were consistent with the above stated off-sun angle limits. As previously stated, the maximum allowable 'center-of-deadband' off-sun angles, given 15 degrees deadbands, are 0 degrees and 20 degrees, respectively. The aerogel grid deployment geometry allows collection to start much earlier than would be possible by a simple off-sun pointing strategy, especially in light of the 0 degrees +x-axis-to-sun off-sun angle constraint. Comet Dust Collection --------------------- For the comet encounter sub-phase, the dust collector was fully deployed nine days before closest approach. The spacecraft's attitude was such that the +x-axis was aligned with the spacecraft's velocity vector (relative to the comet). This oriented the collector so that it was perpendicular to the incoming dust, which would impinge on the front side of the grid. About five hours after the closest approach to comet Wild 2, the collector was stowed, where it remained protected until it was opened after returning to the Earth . Collector Deployed Configurations --------------------------------- Collector fully extended Collector steered into (comet encounter and ISP stream ISP tracking strategy 2) (ISP tracking strategy 1) || \\ Collector Grid ----> || \\ || \\ Wrist ------> o o | | | | | _____ | _____ Shoulder -----> o| | o| | | | | | | SRC | | | /`._ | | /`._ | | \ `._ | | \ `._ | | Heatshield ---> \ `.|_____| \ `.|_____| (open) \______/ \______/ " CONFIDENCE_LEVEL_NOTE = "The geometry configurations listed in this data set were derived from SPICE kernals for the Stardust spacecraft. " END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_MISSION MISSION_NAME = "STARDUST" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_TARGET TARGET_NAME = "81P/WILD 2 (1978 A2)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = "INTERSTELLAR_PARTICLES" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = "SDU" INSTRUMENT_ID = "SRC" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "N/A" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END