Data Set Information
DATA_SET_NAME STARDUST DUST COLLECTOR GEOMETRY V1.0
DATA_SET_ID SDU-C-SRC-6-GEOMETRY-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Author------The descriptions in this file were written by Tony Farnham usinginformation from the 'Stardust Mission Plan' document (used withpermission from the Stardust project). Data Set Overview: This data set describes the geometry and orientations of thespacecraft and the collector plate during the two interstellar dustcollection 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 silicaaerogel blocks. The grid array was exposed to a stream of dustparticles, which were gradually slowed and captured by the low-densityaerogel. The aerogel dissipated the kinetic energy of the particlesso they were not destroyed during the collection process. Gradeddensity media was used to give even lower density for the initialimpact. The collector grid has two sides, each of which containsseparate aerogel blocks. One side of the collector was used tocollect samples during the comet encounter and the opposite side wasused for interstellar dust collection. Each side of the collectorcontained a total of 1000 cm^2 of useful collecting area. The collector was housed in the Sample Return Capsule (SRC), acontainer about a meter in diameter, attached to the Stardustspacecraft along the -x-axis direction. The SRC opened like aclamshell, allowing the collecting grid to be deployed into the duststream to collect samples. Stowage of the collector was achieved byfirst folding the collector grid onto the boom via the wrist joint andthen folding the boom/collector into the SRC canister via the shoulderjoint. At the end of the mission, the SRC detached from thespacecraft and returned to Earth, where the dust samples can beanalyzed 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 formaximizing the amount of time available for the capture ofinterstellar dust particles. The mechanism allowed the collector to besteered via the wrist joint about the spacecraft y-axis toward the-z-axis. The collector field-of-view remained unobstructed by the SRCbackshield for 51 degrees of this motion, half the grid was in shadowat 63 degrees, and all of the grid was in shadow at 75 degrees. (Notethat for the shadow definition, the ISP stream is assumed to beincoming perpendicular to the aerogel grid.) It is worth noting thatthe collector field-of-view would remain completely unobstructed for65 degrees of the motion should the shoulder joint be used duringinterstellar dust particle collection. However, usage of the shoulderjoint with the collector fully deployed was considered to be anunnecessary risk. The collector was deployed during three separate subphases to obtaindust samples: two periods of Interstellar Particle (ISP) collectionand the encounter with Wild 2, where comet samples were obtained. Thefirst ISP collection period lasted from February 22 through May 1,2000, and the second from August 5 through December 9, 2002. For thecollection of comet dust at Wild 2, the collector was deployed onDecember 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 madeuse of the fact that the solar system is moving through an environmentof interstellar dust grains. This motion causes the ISPs to appear tostream through interplanetary space in a preferred direction. Theupstream direction for this flow (in ecliptic latitude and longitude)is in the vicinity of (7.7 degrees, 259 degrees), which is the valueadopted for designing the ISP collection. For this direction, the ISPflow 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, thesolar radiation pressure and various other complex processes not wellor easily formulated. If one considers only the simple effects ofsolar gravity and solar pressure, the velocities of ISPs of varioussizes can be calculated easily as a function of beta, where beta isthe ratio of the solar pressure to solar gravity. High beta particles(greater than 1) are believed to be low density, fluffy grains whilelow beta particles (less than 1) are denser and more compact. One toone correspondence between the beta group and the particle size cannotbe made without knowledge of individual particle density, shape andradiative parameters, though assumptions can be made to estimate therange of grain sizes that are likely to be encountered. Typicalresults indicate that grains from 0.1 to a few microns should beexpected. ISP Collection Planning Constraints----------------------------------- A number of constraints were used to guide the planning of the ISPcollection 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 thespacecraft's trajectory where the interstellar dust impact velocitywas relatively low (e.g., the spacecraft was moving in roughly thesame direction as the dust stream) For this configuration, the dustwas overtaking the spacecraft from behind, which allowed the ISPs tobe collected on the back side of the dust collector. Given the passive nature of the collection instrument and theuncertainty in the direction of the interstellar stream (as large as30 degrees), stringent attitude control was unnecessary, and theoptimum periods for collecting ISPs corresponded well to the inboundportions of the cruise phases. Collection was performed only duringthe first two orbits, resulting in 201 days of total collection time.Collection was not performed on the third loop to avoid contaminationof the cometary samples collected during the encounter with Wild-2. In addition to the science constraints described above, a number ofspacecraft constraints were imposed for the planning of interstellardust science. The following spacecraft guidelines apply to the designof 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 collectorthat was maintained inside the SRC and deployed during the ISPcollection subphases. As previously stated, the collection subphasesare defined via the previously discussed constraints. The off-sunangle and beta meteoroid constraints in conjunction with the aerogelcollector deployment geometry were the primary geometric factors thatdefined the start and end of each collection period. Each ISP collection period was established using two differentstrategies for tracking the spacecraft relative to the ISP velocityvector. The first strategy was implemented during the first part ofeach collection period and involved taking advantage of the deploymentmotion (about the wrist joint) of the aerogel grid to track the motionof the ISP stream in the spacecraft x-z axis plane. The out-of-planecomponent of the ISP stream was tracked by yawing (yaw is a rotationabout the z-axis) the spacecraft sufficiently to place the s/crelative ISP stream in the x-z axis plane. The +z-axis of thespacecraft, and as a result the solar panels, remained oriented towardthe sun. Once the aerogel grid wrist was fully extended it could no longer be usedto track the ISP stream and the second strategy was invoked. The secondstrategy involved pointing the spacecraft -x-axis toward the incomingISP stream. With the grid wrist fully extended, the vector normal tothe grid surface was parallel to the spacecraft x-axis. The strategy wasimplemented until the off-sun angle was such that the beta meteoriodconstraint was violated, which typically occured prior to reaching powerrelated off-sun angle constraints. Both of these strategies were consistent with the above stated off-sunangle limits. As previously stated, the maximum allowable'center-of-deadband' off-sun angles, given 15 degrees deadbands, are 0degrees and 20 degrees, respectively. The aerogel grid deploymentgeometry allows collection to start much earlier than would bepossible by a simple off-sun pointing strategy, especially in light ofthe 0 degrees +x-axis-to-sun off-sun angle constraint. Comet Dust Collection--------------------- For the comet encounter sub-phase, the dust collector was fullydeployed nine days before closest approach. The spacecraft's attitudewas such that the +x-axis was aligned with the spacecraft's velocityvector (relative to the comet). This oriented the collector so thatit was perpendicular to the incoming dust, which would impinge on thefront side of the grid. About five hours after the closest approachto comet Wild 2, the collector was stowed, where it remained protecteduntil 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) \______/ \______/
DATA_SET_RELEASE_DATE 2006-07-07T00:00:00.000Z
START_TIME 2000-02-22T01:00:00.000Z
STOP_TIME 2004-01-02T11:00:00.000Z
MISSION_NAME STARDUST
MISSION_START_DATE 1999-02-07T12:00:00.000Z
MISSION_STOP_DATE 2006-01-16T12:00:00.000Z
TARGET_NAME 81P/WILD 2 (1978 A2)
UNKNOWN
TARGET_TYPE COMET
UNKNOWN
INSTRUMENT_HOST_ID SDU
INSTRUMENT_NAME SAMPLE RETURN CAPSULE
INSTRUMENT_ID SRC
INSTRUMENT_TYPE DUST SAMPLE COLLECTOR
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE The geometry configurations listed in this data set were derived from SPICE kernals for the Stardust spacecraft.
CITATION_DESCRIPTION Farnham, T.L., Semenov, B., STARDUST DUST COLLECTOR GEOMETRY, SDU-C-SRC-6-GEOMETRY-V1.0, NASA Planetary Data System, 2006.
ABSTRACT_TEXT 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.
PRODUCER_FULL_NAME Tony Farnham
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