MISSION PLAN - PDS Small Bodies Node

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10.0 Appendix B: Unbalanced Attitude Control Force Modeling The STARDUST spacecraft design imparts an unbalanced force, i.e. translational thrust to the spacecraft, every time attitude control burns are executed. This undesirable condition is dictated by the need to prevent contamination of the sample collector. Over the seven year mission, the cumulative ACS activity is estimated to impart tens of meters per second of ∆V. The sum of trajectory correction maneuvers to compensate for the ACS burns could be intolerably large (~40 m/s) unless the ACS effects are accounted for in advance while designing the nominal trajectories. From the navigator’s point of view, the ACS activity is an error source that cannot be ignored in striving to achieve accurate spacecraft delivery at comet and Earth re-entry. This section describes the methods used to model this perturbation source and its incorporation in the trajectory design and maintenance. The ACS perturbation is divided into two categories: 1) almost continually acting ACS limit cycling and 2) less frequent attitude slewing required for communications, maneuvers and special activities. The trajectory optimization program can include the first type of perturbations, but discontinuous second types are too cumbersome to deal with. As a result, the decision has been made to include the latter effect in the navigation tools only in the form of a tabular small forces predict file. This will enable accurate predictions, but will be very slightly off-optimal in the ∆V estimates. 10.1 Limit Cycle Model A mathematical model of the behavior of the attitude control system (ACS) is constructed to compute ACS perturbations to the spacecraft trajectory due to cruise deadbanding or limit cycling. In this model, ACS thruster pulse frequencies are computed consistent with the planned attitude history. The magnitude of the frequency depends on spacecraft mass distribution, thruster characteristics and configuration, mission geometry, and expected solar torques. These pulse frequencies are not incorporated into the trajectory design as individual pulses, but instead, are converted to average perturbative accelerations. The performance of the spacecraft’s hydrazine-blowdown system is modeled according to the manufacturer’s specifications, and the direction of the ACS acceleration is established based on the pre-flight plan for spacecraft attitude. 10.1.1 Spacecraft Attitude History 112
The spacecraft’s trajectory and required cruise attitude history dictates the ACS perturbation due to limit cycling. The main source of attitude offset is the presence of solar torque which depends on the solar range and the spacecraft attitude with respect to the sun. The magnitude of the solar torque and the deadband within which the spacecraft attitude is controlled dictates the frequency at which the ACS thrusters are fired and the corresponding magnitude of the ACS perturbation. The direction of the ACS force, in the case of limit cycling, is parallel to the planned spacecraft +z-axis direction. The forces in the other two axis are assumed to cancel out on average. For the limit cycle model, the cruise spacecraft attitude is divided into four main modes. Table 10.1-1 summarizes these modes and submodes in terms of spacecraft axis alignment. Spacecraft pointing is controlled to within the accuracy established by planned axis deadbands. Each axis is allowed to deviate from the desired pointing direction by the established angular amount. The axis are kept within the desired region by firing the appropriate thruster pair when one of the deadbands is tripped. Table 10.1-2 summarizes the deadband options available. Table 10.1-1 Spacecraft Attitude Options - Limit Cycle Model Option Sub-option First Axis Second Axis 1. Sunpoint 11 +z = -r +y = -r X v 12 +z = -r +y = +r X v 2. Constant off- 21 same as above * sun angle 22 same as above * * followed by a single axis rotation about +y axis 3. Interstellar dust 31 +z = -r +y = -r X ivr collection 32* ,1 +x = ivr +y = -r X ivr 33 +x = ivr +y = -r X ivr * followed by a single axis rotation, angcol amount, about +y axis 4. CIDA 41 +x = -ivr +y = -r X ivr experiment 42* +z = -r +y = -r X ivr * followed by a single axis rotation about +y axis where: +x, +y, +z = spacecraft x, y, z axis unit vectors r, v = spacecraft position and velocity ivr = interstellar particle relative velocity vector (visp - v) angcol = maximum aerogel collector deployment angle Note 1 = option not used in current model due to off-sun angle constraints Table 10.1-2 Spacecraft Deadband Options - Limit Cycle Model Option Deadband Comments 1 x, y, z = 15° Cruise option 1 2 x, y = 2°, z = 10° Near encounter 3 x, y, z = 10° Cruise option 2 It is important to note that the spacecraft attitude for this model is referenced to the orbit plane. During flight, the spacecraft attitude will actually be referenced to the Sun-Earth- Probe plane. This results in slight differences between the modeled and the planned 113
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STARDUST MISSION PLAN February 1, 1
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STARDUST MISSION PLAN Edward A. Hir
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Table of Contents Table of Contents
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10.1.1 Spacecraft Attitude History
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Figure 6.2-1.a Wild-2 Encounter Com
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Table 10.1-3 Spacecraft Attitude Pr
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kg km L L/O Kilogram Kilometer Laun
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Change Log Change Letter Date Affec
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1.0 Introduction 1.1 Purpose The pu
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2.0 Mission Overview 2.1 Mission Ob
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Fairing STARDUST Second Stage Star3
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propulsive maneuvers. To avoid pote
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The STARDUST camera is necessary to
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of-view is smaller, as described in
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Backshell Avionics Deck Parachute C
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Earth Gravity Assist 01/15/01 Earth
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Cruise 2 (Earth-Wild-2) ISP Collect
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2.3.2 Launch Period Strategy 2.3.2.
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Table 2.3-2 Baseline Mission Parame
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Table 2.3-2 Baseline Mission Parame
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*B plane angle (deg) -41.051 -40.96
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2.3.2.2 ∆V Budget The total ∆V
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Accumulation of Radiation with Time
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Table 2.3-4 STARDUST Alternate-2 Mi
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calculations will require more deta
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10 17 10 16 10 15 10 14 10 13 Fluen
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8 10 flare, no shielding 6 10 4 10
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The orbit of comet Wild-2 was drast
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• Dust density = Nucleus density
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2.4.4 Interstellar Dust Science Pla
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Launch Initial Acquisition TCM-1 Ac
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Stage II ignition t=277.5 s h=66.4
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Special ‘coming-off-theperiscope
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phases are very similar to the stan
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presented in tables contained in Ap
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Figure 4.2-4.b. Beta Meteoriod Impa
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180 Off-SEP & ORBIT normal angle (d
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2/6 launch Events Attitude 74 days
Page 80 and 81: yaw, while continuing to meet solar
Page 82 and 83: Time Image Description images pixel
Page 84 and 85: (EGA-60d to +30d) TCM 4 (EGA-60 d)
Page 86 and 87: 6.0 Wild-2 Encounter Phase (E-100 t
Page 88 and 89: the installation of the HGA. The su
Page 90 and 91: Date Sept-03 Oct-03 Nov-03 Dec-03 J
Page 92 and 93: Coma images will be acquired primar
Page 94 and 95: mirror via a simple one dimension t
Page 96 and 97: The cross track error corresponds t
Page 98 and 99: 14 12 10 24 km 3 sigma distance 1 s
Page 100 and 101: All 34-m HEF except selective 70-m
Page 102 and 103: SRC Entry / Descent Atmospheric Ent
Page 104 and 105: Two TCM’s are planned within this
Page 106 and 107: It is important to note that, other
Page 108 and 109: 8.0 Planetary Protection The object
Page 110 and 111: Earth-Probe Range Sun-Earth-Probe A
Page 112 and 113: 9.1 Mission Data Set (cont) 14.00 E
Page 114 and 115: 14.00 MOON-PROBE RANGE Launch Phase
Page 116 and 117: 180.00 SUN-EARTH-PROBE ANGLE EGA Ph
Page 118 and 119: 180.00 SUN-PROBE-MOON ANGLE EGA Pha
Page 120 and 121: 180.00 SUN- WILD-2 -PROBE ANGLE Enc
Page 122 and 123: Cone & Clock Angles of Wild-2 Cone
Page 124 and 125: 180 Cone & Clock Angles of Sun 180
Page 126 and 127: 9.4 Wild-2 Encounter Data Set (cont
Page 128 and 129: 16.00 MOON-PROBE RANGE Return Phase
Page 132 and 133: spacecraft attitude when the spacec
Page 134 and 135: Time From Launch Off-sun Angle (deg
Page 136 and 137: Acceleration (1E-11 km/s/s) 12 10 8
Page 138 and 139: +z, yaw +y, pitch +x, roll Figure 1
Page 140 and 141: ** vectors evaluated at the time of
Page 142 and 143: Rgt Ascen (deg) [eme'2000] 360 300
Page 144 and 145: Table 10.2-6 Communications Schedul
Page 146 and 147: Table 10.2-6 Communications Schedul
Page 148 and 149: 031228 19180 0 031229 19180 0 03123
Page 150 and 151: TRAJECTORY CORRECTION MANEUVERS EVE
Page 152 and 153: 2453509.10737773 50518. 143437. 229
Page 154 and 155: 50204. 3437. 2189.12 outb SEP = 3 d
Page 156 and 157: Table 12-1 ISP #1 Collection Period
Page 158 and 159: Table 12-2 ISP #2 Collection Period
Page 160 and 161: Table 12-4 ISP #2 Spacecraft Attitu
Page 162 and 163: Table 12-5 CIDA #1 Collection Perio
Page 164 and 165: Table 12-6 CIDA #2 Collection Perio
Page 166 and 167: 908.000 41.659 20.000 9.272 175.100
Page 168 and 169: Table 12-8 CIDA #1 Spacecraft Attit
Page 170 and 171: Table 12-9 CIDA #2 Spacecraft Attit
Page 172 and 173: Table 12-11 CIDA #3 Solar Conjuncti
Page 174 and 175: 13.0 Appendix E: PRD Traceability M
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