Action Item Status Manfred Bester THEMIS FDMO Review
Action Item Status Manfred Bester THEMIS FDMO Review Action Item Status − 1 October 5, 2004
Status of Action Items Review Number of RFAs Open RFAs Due Date Mission SRR 3 0 N/A FDMO PDR Peer Review 18 0 N/A Mission PDR 3 0 N/A FDMO CDR Peer Review 18 17 Oct 2004 Mission CDR 2 2 Oct 2004 Note: Only Flight Dynamics and Mission Operations Related RFAs Are Listed and Discussed Below THEMIS FDMO Review Action Item Status − 2 October 5, 2004
Mission SRR RFAs RFA Specific Request Supporting Rationale Reviewer Response Status Rec. 1) Does the spacecraft need to specify a specific circular polarization for the S-band antenna? 2) Need to perform an end-to-end data analysis including data compression, coding, RF link to calculate needed/optimal BER for compressed data. 1) Need to check TDRS Schnurr capability. 2) Compressed data can be/is sensitive to data loss. An endto-end data analysis is required to optimize/select data rate. See detailed response submitted to CLOSED IIRT. Rec. Provide, at the PDR, an optimized ground station acquisition strategy (a week in the life of THEMIS) that meets all nominal requirements. With the addition of 5 satellites, the load on BGS and the use of the USN site must be planned to contain costs. Joyce See detailed response submitted to CLOSED IIRT. Rec. Detail, by the PDR, the processes required for providing orbit determination services for THEMIS including implementation of hardware and software for BGS, training of the operations team, MOC automation plans, metric tracking, data evaluation (for BGS and the USN site), the optimized tracking strategy to achieve the required orbital accuracy and test plans. Capturing and processing Joyce metric tracking data to provide the required orbital products must be planned prudently to contain costs. Several “new” systems need to be implemented, tested and integrated into the MOC. See detailed response submitted to CLOSED IIRT. THEMIS FDMO Review Action Item Status − 3 October 5, 2004
FDMO PDR Peer Review RFAs RFA Recommended Action Rationale Reviewer Response Status 1 Investigate monthly lunar Lunar perturbations can Richon perturbation effects to determine be used to reduce fuel optimal time during month to launch. required if judicious selection of launch date is made. However, lunar perturbations can also increase fuel required by decreasing orbit energy & negatively impacting orbit inclination. The THEMIS team has already CLOSED built tools which allowed investigation of lunar perturbations on orbits P 1, P 2 and P 3 as well as on the LV insertion orbit in order to minimize potential for re-entry on the science orbits, and to maximize the potential for re-entry within 10 years for the LV to adhere to orbital debris requirements. Lunar effects due to different launch dates on the P 3, P 4 and P 5 orbits were found to be very small. 2 Decide on one pre-injection nomenclature for each probe. Should not be names associated with integers 1 -5 since the probes will be numbered Probe 1, Probe 2, etc. post-launch according to their final orbit positions (similar to TDRSS). The team agreed that the pre. CLOSED launch assignment of probe names shall be THEMIS A-E. These names are uniquely related to the CCSDS telemetry and command IDs for each probe bus. Probe constellation IDs P 1 -P 5 are assigned post-launch, once the probes and their instruments have been checked out and the probe placement decision has been made. 3 Resolve time tag issue. THEMIS FDMO Review Currently probes are Richon designated as “Themis 1, Themis-2, …”, “red, green…”, and “A, B, C…”. Multiple names for same probe causes confusion & misidentification of specific probes. Harman Action Item Status − 4 The THEMIS attitude sensor read- CLOSED out timing and attitude determination system is closely modeled after the FAST system which has been operational on orbit for 7. 5 years. October 5, 2004
FDMO PDR Peer Review RFAs RFA Recommended Action Rationale Reviewer Response Status 4 Get initial 3 rd-stage separation states Needed for orbit Richon (attitude & orbit) for each probe from injection analysis. If Boeing. Delta PMA is being done, these states should be available soon. UCB received the nominal launch trajectory ephemeris from KSC. These data are used to perform subsequent studies such as communications coverage and probe re-contact analyses. 5 GMAN modeling issues: define each ‘maneuver mode’ including type of maneuver, which thrusters used, pulsed/continuous, etc. Then determine if GMAN can model maneuver correctly. Richon All anticipated orbit and attitude CLOSED maneuvers have been summarized analyzed. Bob De. Fazio verified that all planned maneuvers can be modeled with GMAN. 6 Determine ground station contact tracking requirements such as pass frequency & duration, number of stations, for maneuver planning & recovery versus regular OD, etc. Richon Mark Beckman performed an OD CLOSED covariance analysis showing the number of passes and arc lengths required to meet THEMIS OD 3 -σ position requirements of 100 km near apogee and 10 km near perigee. In case of the P 1 orbit, the required position accuracy can be achieved with 4 BGS passes taken over a 5. 5 -day arc. Some of the orbit fine tuning maneuvers require a delta V of 30 -50 cm/s. An adequate pre-maneuver orbit solution can be obtained by collecting two-way Doppler data from three different ground stations, e. g. Berkeley, Wallops Island Santiago. Further analyses are under way. THEMIS FDMO Review Several questions regarding whether GMAN can be used to model finite maneuvers in all maneuver configurations. Action Item Status − 5 CLOSED October 5, 2004
FDMO PDR Peer Review RFAs RFA Recommended Action Rationale Reviewer Response Status 7 Determine UCB station capabilities Mission depends heavily Richon including support for perigee passes. on UCB antenna for tracking. Need to know if orbit determination constraints can be met. Two-way Doppler tracking CLOSED capabilities of the Berkeley Ground Station were demonstrated with equipment on loan from Wallops Flight Facility. The 1 -σ error of range rate measurements is expected to be 3. 5 mm/s in a 10 -s integration time. Due to the low orbital inclination the maximum azimuth and elevation rates during a pass support will be less than 0. 5 deg/s. The Berkeley Ground Station is capable of tracking with maximum azimuth and elevation rates of 8. 0 and 3. 0 deg/s, respectively. 8 ITOS-to-MSASS interface code to be Harman used provided to UCB. successfully for other mission. Richon UCB will provide interface code to extract attitude sensor data from ITOS and reformat these to be compatible with MSASS/MTASS input. 9 Real-time attitude determination - is this a requirement? If so, which software? Possibly use MTASS with modifications. Harman Real-time attitude determination is CLOSED required for maneuver support. A ground-based real-time ADS will be implemented, based upon the quaternions that are derived from sun sensor and IRU data and are propagated on-board, and are in turn sent to the ground. THEMIS FDMO Review Action Item Status − 6 CLOSED October 5, 2004
FDMO PDR Peer Review RFAs RFA Recommended Action 10 Multi-satellite critical operations: need to have at least two prime workstations supporting, plus at least one hot back-up for emergencies. 11 MSASS is not capable of performing magnetometer alignment. Determine if UCB needs to acquire MTASS in addition to MSASS for this function. 12 Include pre-launch operations (Simulation planning & support, launch preparations) in future FD&MO reviews. 13 Provide access to latest mission information to peer panel at least two weeks before review. THEMIS FDMO Review Rationale Reviewer Normally one has one Richon prime and one back-up for any critical operation for a single-satellite mission. UCB will have to be able to support multiple satellites with critical operations. Ensure resource requirements are identified & included in planning. Response Status The ground systems design CLOSED includes at least 10 ITOS workstations, including a designated prime and back-up for each probe. Furthermore, any of these workstations can be assigned to any probe. In addition, two ITOS workstations will be connected to the Closed IONet for communications via TDRSS with one probe at a time. Harman UCB will obtain ADS which CLOSED includes both MSASS and MTASS. A software usage agreement is in the process of being finalized. Richon Pre-launch operations and simulations including green card exercises were included in the MPDR presentations already and will be presented in more detail in upcoming reviews. Richon The review team will receive most CLOSED recent mission documentation at least two weeks prior to future peer reviews. Action Item Status − 7 CLOSED October 5, 2004
FDMO PDR Peer Review RFAs RFA Recommended Action Rationale Reviewer Response Status 14 Maneuver calibration procedures need to be documented. Each orbit & attitude Richon maneuver should be analyzed post-maneuver for efficiency & accuracy. Results should be applied to future maneuver planning. Also needed for bookkeeping of fuel used. The UCB team has received CLOSED sample procedures from GSFC FDAB and from Swales for EO-1 maneuver planning and execution. Applicable elements of these procedures will be incorporated into the THEMIS procedures. 15 Document who is responsible for fuel -used bookkeeping (propulsion engineer or Flight Dynamics Engineer or other FOT member). One entity should have Richon responsibility for this function. It is particularly critical at the end of life when probes must perform a controlled reentry. A dedicated member of the CLOSED THEMIS flight dynamics team, namely the propulsion engineer will be responsible for bookkeeping the fuel usage. 16 Institute Command Authorization Meetings (CAMs) for all orbit & attitude maneuvers. Requires participation & ‘signoff’ from all relevant subsystems & systems (FOT, flight dynamics, thermal, power, C&DH, scientists, etc. ). Best practices. Reduces Richon risk. Command Authorization Meetings CLOSED (CAMs) will be held prior to any critical command operation, including execution of orbit and attitude maneuvers as well as critical instrument operations such as boom deployment or HV turn-on. Such meetings are common practice already with all missions currently operated by UCB, i. e. FAST, RHESSI and CHIPSAT. THEMIS FDMO Review Action Item Status − 8 October 5, 2004
FDMO PDR Peer Review RFAs RFA Recommended Action Rationale Reviewer Response Status 17 Provide MAP Anomalous Forces technical paper to UCB. Outgassing of Richon instruments & other hardware may introduce anomalous forces creating torques on probes). UCB received a copy of the MAP anomalous force paper. 18 Provide JON/WBS to Code 595 for THEMIS support. Code 595 flight Richon dynamics engineers cannot support THEMIS without charge number. GNCD has received a JON for CLOSED support of THEMIS flight dynamics work. THEMIS FDMO Review Action Item Status − 9 CLOSED October 5, 2004
Mission PDR RFAs RFA Specific Request Supporting Rationale Reviewer Response Status 15 Detail the roles of GSFC flight dynamics support to THEMIS mission operations. This shall include use of GSFC tools (GTDS, GMAN, etc. ) and configuration management of these tools and GSFC personnel support during Phases C/D and E. Significant new capabilities Joyce are required of UCB to support this mission including orbit determination and maneuver planning and maneuver operation. See detailed response submitted to CLOSED IIRT. 16 Document the criteria for selection of probes for their operational orbits (designation as P 1, P 2, P 3, P 4, P 5) to prepare for the initial conjunction observations. Discuss potential probe anomaly scenarios and nonnominal instrument complements that may be part of this selection process. Define the team members and positions that will support the PI in the probe placement decision. The selection process should Joyce be well defined to enable the team to optimally implement the probe placements to prepare for the initial prime science observing season. See detailed response submitted to CLOSED IIRT. THEMIS FDMO Review Action Item Status − 10 October 5, 2004
Mission PDR RFAs RFA 30 Specific Request Supporting Rationale Reviewer Consider adding a requirement to Without this information being Killough upload the Probe numerical P# to the embedded in the downlink Probe once it is (re-) positioned in its packets, the science team will orbit, and a requirement to include have to have some additional the P# in all telemetry packets table in order to correctly (extension to secondary header? ? ). interpret the results. Having it An additional benefit of this is that embedded in the data avoids the on-board P# could be coupled any possibility of confusion. with a P# embedded in uplink While the CCSDS S/C ID commands, which could cross-check ensures that a Probe doesn’t to make sure the ground ops team process a command not didn’t inadvertently uplink a intended for it, it doesn’t do maneuver command to the wrong that in terms of the Probe probe. orbit position. What is probably a very small investment in adding this information to telemetry and command formats now might save a lot of headache (and maybe heartache) later. THEMIS FDMO Review Action Item Status − 11 Response Status See detailed response submitted to CLOSED IIRT. October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern 1 The previously discussed support by GSFC to train UCB/THEMIS personnel in the use of GTDS for end-to-end orbit determination operations has not been implemented. This training is vital to the development of this key mission function. THEMIS FDMO Review Recommended Action Reviewer 1. An agreement between Joyce appropriate GSFC and UCB/THEMIS personnel should document the required orbit determination training and the technical personnel to support the training. 2. A training plan as part of an overall orbit determination operations schedule is to be provided one month prior to MOR. Action Item Status − 12 Response Status Following recommendations of the OPEN GNCD Branch Head and the FDF Operations Director, UCB is now planning on contracting directly with AI Solutions to obtain mission critical training of the THEMIS Flight Dynamics Team in GTDS based orbit determination. GNCD FDAB/FDF will not participate in the orbit determination training. A statement of work and a request for quotation will be submitted to AI Solutions shortly. AI Solutions already has developed material for suitable GTDS training courses that are applicable. As part of the statement of work, AI Solutions will also be contracted to provide assistance with configuring GTDS for THEMIS orbit determination at the Berkeley Mission Operations and Flight Dynamics Center. Details of the training plan and the corresponding implementation schedule with various milestones are outlined in THEMIS FDMO CDR Peer Review RFA Reponses. October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern 2 There may be no documented requirement that an updated postinjection vector be provided to the THEMIS Project based on Boeing Delta Redundant Inertial Measurement System data. This data is required to maintain communications with the probes until an accurate orbit determination is available. It is even more important in the event of a non-nominal injection. THEMIS FDMO Review Recommended Action Reviewer The Project should pursue Joyce levying this requirement with additional details provided by GSFC/FDF on Boeing prior to the MOR. Action Item Status − 13 Response Status Requirements for delivery of real- OPEN time telemetry as well as second stage burn modeling from Boeing to GSFC/FDF to generate state vector updates are outlined in the Delta (NASA) Launch Vehicle PSLA (451 -PSLA-Delta (NASA)). Only guidance data from the second stage are available. In the absence of a navigation system on the third stage, a post-insertion state vector for the THEMIS probes will be generated by GSFC/FDF based on observed second-stage guidance data and a predicted nominal thirdstage performance. GSFC/FDF support for THEMIS for the first 48 hours of the mission is documented in the THEMIS PSLA (451 -PSLATHEMIS). October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern 3 Currently, the mission design work centers on the evolution of Keplerian elements. However, it has been claimed that despite their individual motions the line of apsides of each orbit remains constant for 1 st order. A set of plots showing the right ascension and declination of the line of apsides is suggested to support this claim and to clarify the reasons for selecting a constant right ascension of perigee (RAP). 4 A ΔV budget with allocations to account for daily / time-of-day launch window and ELV dispersions was not presented and may not be available as of this date. A complete ΔV budget is needed to determine how stable the current design is. A technical approach and Schiff schedule should be drafted as soon as possible and be submitted for a review at MOR. THEMIS FDMO Review Recommended Action Reviewer Schiff Action Item Status − 14 Response Status The annual RAP drifts for all five OPEN probes during T 1 and D 1 are summarized in Table 3 -1. Launch RAP is equal to launch RAAN for an APER of 0 deg. The plots shown in Figures 3 -1 through 3 -5 in THEMIS FDMO CDR Peer Review RFA Reponses show the evolution of the line of apsides, i. e. the declination of apogee versus right ascension of apogee (black traces) for each of the five probes for tail season 1 (21 -Oct-2006 – 22 -Apr-2007). In addition, the plots also show the development of the inclination (blue traces), APER (green traces) and RAP = RAAN + APER (red traces). The ΔV budget accounting for launch window and ELV dispersions is available, but was not presented at the peer review. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. OPEN October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern 5 On Slide 7 of the Propellant Budget, four ΔV inefficiencies were considered. However, these inefficiencies are all associated with the geometry of the thruster, either in the body frame (i. e. misalignment) or inertially (rotational impulse loss sin(η/2) / (η/2), the beta inefficiency, and finite arc losses). However, performance loss is not considered. THEMIS FDMO Review Recommended Action The project should take a specific position on an Isp inefficiency which, if considered, will lower the overall ΔV capability of the spacecraft. Consider the rocket equation: ΔV = g Isp ln (mi / mf) Reviewer Schiff A change in Isp of δIsp will cause a change in ΔV. If the Project decides against considering this possible inefficiency then they should be clear on all ΔV budgets that such an inefficiency is not being used. Action Item Status − 15 Response Status The THEMIS thruster performance OPEN is known to be very repeatable with a 3 -σ variance of 2. 8% based on 26 firings of test thrusters over the last 3 years. Therefore a 2. 8% Isp inefficiency is carried in the maneuver calculator spreadsheet. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern 6 Clarify requirements in mission for close approach/debris per NASA Safety Standard 1740. 14 and NASA Policy Directive 8710. 3 B. NASA satellites are required to provide predicted ephemeris to Cheyenne Mountain for every orbit-changing maneuver of >1 km, and for launch and early orbit operations. Review NSS 1740. 14 & NPD Richon 8710. 3 B to determine requirements applicable to THEMIS. Incorporate into procedures and analysis. Requirements for close approach OPEN and orbital debris generation are addressed in the THEMIS Final Orbital Debris Report (CDRL #37) which was submitted by the Project for review by NASA HQ, GSFC and KSC. UCB will work with Adrienne Davis at GSFC/FDF to prepare the required paperwork to notify Do. D about THEMIS orbit maneuvers in accordance with NPD 8710. 3 B, Section 5. b. 7. Notification of Do. D will be part of the operations procedures. 7 Need verification / QC of trajectory design and maneuver plan for all probes. Currently one person (Frey) doing all analysis. Need capability for targeting and optimizing trajectory design. Free. Flyer (AI Solutions) can do this. Contract with GSFC, AI Richon Solutions, other trajectory design group to verify trajectory design and maneuver plan. If switch from GMAN to Free. Flyer, AI Solutions is logical choice. A consulting contract will be set up OPEN between UCB and AI Solutions to verify GMAN/Free. Flyer compatibility. UCB purchased a Free. Flyer Engineer run-time license in the meantime. AI Solutions will likely be contracted by the Explorer’s Office to independently verify key scenarios in the THEMIS mission design. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. THEMIS FDMO Review Recommended Action Reviewer Action Item Status − 16 Response Status October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern 8 There is a requirement for use of MSASS and MTASS for attitude determination. As of now, there is no formal agreement between GSFC/FDAB for any requirement or modifications to software, delivery of software, version (CM) for software, or testing to meet launch schedule. THEMIS FDMO Review Recommended Action Agreement on requirements for software, delivery schedules, versions and testing needs to be done as soon as possible with GSFC/FDAB. Resource (funding) to make any modifications or do testing needs to be agreed upon. Reviewer Hoge Action Item Status − 17 Response Status The requirements document for the OPEN THEMIS Real-time Attitude Determination System (RTADS) which includes MSASS and MTASS are in the draft stage and are currently reviewed by UCB and Swales. Once the review at UCB and Swales is completed (target date: October 8, 2004), the document will be submitted to GSFC/GNCD for review and comments. GNCD has agreed to provide upgrade of MSASS including new nutation estimation utility. This upgrade is already covered as an institutionally funded activity. This task covers the transfer of the upgraded software and a small level of consultation for its use. It is assumed UCB has experience in the use of MSASS for the FAST mission. October 5, 2004
FDMO CDR Peer Review RFAs RFA 9 Statement of Concern Recommended Action Version of GTDS software is planned Determine effort for testing for upgrade to latest version. and verification of software. GSFC/FDF maintains only an HP Implement a CM process for version of software. A Solaris version GTDS software if one does is used for THEMIS operations and not exist. Work with analysis. When updated version is GSFC/FDF for software delivered will need to be compiled upgrade via under Solaris. This will require time Commercialization Office at and resources to compile and test GSFC. software that may not be in schedule. Additionally, CM process for upgrade is not clear. THEMIS FDMO Reviewer Hoge Action Item Status − 18 Response Status UCB currently uses GTDS version OPEN 96. 03 Delta 4, 09/11/1997 (HP-UX V 10. 2 source code, compiled under Solaris). FDF currently uses version 2002. 01 for operations. A new version 2003. 01 will be available in October 2004. UCB has been working with the GSFC Commercialization Office to obtain a transfer license for version 2003. 01. A preliminary 90 -day license has been granted already. Upon delivery, version 2003. 01 will be installed under a dedicated flight dynamics operations account at UCB and placed under SCCS version control. Subsequently the source code will be compiled under Solaris. Upon compilation, a series of tests will be performed to compare state vector propagation results against test cases and ephemeris files generated with the same version of the code at GSFC. Also, the new version will be compared against the version that is currently used at UCB for THEMIS mission design work. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. October 5, 2004
FDMO CDR Peer Review RFAs RFA 10 Statement of Concern Recommended Action Reviewer Given flexibility and priority of data Identify statistics and metric Crouse available from day to day of the and include in operations plan mission, is there a science data to monitor performance. collection statistic that can be agreed upon as a measure of mission success? THEMIS FDMO Review Action Item Status − 19 Response Status Conjunction science data up to 750 OPEN Mbits per orbit collected during the wedding season (February 21 ± 2 months) and during the dayside season (August 21 ± 2 months) are considered mission critical, and 100% recovery will be attempted. In addition, up to 40 Mbits of data collected in slow survey mode during radiation belt crossings of each orbit are to be recovered at the 100% level also. Also, all probe state-of-health and engineering data are to be recovered at the 100% level. Other data are of lesser importance. Statistics will be generated against the above metrics. October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern Recommended Action Reviewer Response Status 11 Understand implications (if any) of the NISN mission operations voice enhancement activity. Review Project Management Crouse Plan from NISN and identify impact (schedule, cost, etc. ). The THEMIS Network Operations OPEN Manager (John Ervin) states there is no problem with UCB’s SCAMA system w. r. t. planned voice system upgrades at GSFC. 12 Current analysis uses 50% penumbra to determine eclipse. What impact is there for penumbra less than 50% on both power and thermal? Look at eclipses defined as Crouse 100% (umbra) from beginning of penumbra to end of penumbra. Evaluate recharge period as well. A refined shadow analysis has OPEN been performed to determine the penumbra and umbra durations for all encountered shadows throughout the mission. A Power Management Tool (PMT) is currently under development at Swales. Additional analyses will be performed when the development of this tool has been completed. The PMT will be available to the THEMIS Flight Operations Team to manage the probe power budgets during on-orbit operations. Swales has performed a begin-oflife, end-of-life and worst case power analysis, showing that the power system will not experience lockout, and battery performance meets our current worst case requirements at EOL. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. THEMIS FDMO Review Action Item Status − 20 October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern Recommended Action Reviewer Response Status 13 Are maneuvers needed specifically to calibrate the gyros? Will maneuvers already in the orbit plan be enough to calibrate the gyros? A study is needed to see if the Ottenstein gyros can be calibrated sufficiently through the nominal course of maneuvers. Is there enough observability of the attitude about these maneuvers plus enough maneuvering about different axes? Can bias, scale factor and misalignment be solved? If there are errors in these, how much attitude error will there be and will this be more than the knowledge requirement for maneuvers? The Inertial Reference Units (IRUs) OPEN a. k. a. gyros are calibrated as a byproduct of already planned-for maneuvers. Swales has performed an analysis showing that special maneuvers to calibrate the gyros are not required. 14 The health-and-safety check of THEMIS B is currently scheduled during shadow without any check before ATS load in sunlight. Insert a 10 -minute delay in BGS acquisition health-andsafety checks so all five probes are in sunlight. A 10 -minute delay was inserted into OPEN the L&EO timeline so that all probes are in sunlight during the first set of AGO and BGS passes. THEMIS FDMO Review Ottenstein Action Item Status − 21 October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern 15 It appears that more attitude analysis is needed to prepare for the mission. The presentation does not show enough analysis yet. THEMIS FDMO Review Recommended Action Reviewer Response Status 1. Derived requirements. Ottenstein Are thermal or instrument constraints which will derive requirements on attitude determination or control? Are there Sun angles to be avoided? Consider the problem of the EFI on POLAR at certain Sun angles and determine whether such a problem will apply to THEMIS. Determine what the range of Sun angles is during the mission. Quote from Prof. Mozer, EFI PI: OPEN “The only Sun angle problem with EFI occurs when SPB spheres pass through the spacecraft shadow. This puts a large glitch in the sphere output signal. THEMIS is planning for this. ” The nominal range of angles between the spin axis and the direction toward the Sun is 80 -100 deg for all probes. 2. Torque analysis. How much change to gravity gradient, solar radiation pressure and dipole moment torques affect the attitude and Sun angle per orbit and over the course of a month? With all booms deployed, the THEMIS probes carry an angular momentum of 829. 4 N m s, which provides a huge “gyroscopic stiffness”. Gravity-gradient (GG) torques cause a maximum spin axis tilt of 0. 038 deg per orbit. Torques due to solar radiation pressure cause a worst case tipping of 0. 064 deg per month. Magnetic moments cause a worst case tipping of the spin axis by 0. 037 deg per month. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. Action Item Status − 22 October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern Recommended Action Reviewer 3. Nutation damping. How quickly will nutation be damped after a maneuver and separation? If it does not damp as expected, are there contingency plans to actively damp it? THEMIS FDMO Review Action Item Status − 23 Response Status The dominant source of nutation damping is fuel slosh. A 1 st linear model plot of damping versus tank fill is shown below. Nutation damping is being confirmed by detailed models at both Swales and UCB. Nutation Time Constant (NTC) results from simulations (presented at Mission CDR) were obtained using pendulum models for slosh with analytical parameters (mass, length, hinge point, residual mass and location) and empirical parameters (damping) from SLOSH software (Dodge). The dimensionless time constants (DTC) from these simulation results are greater than three times the DTC from empirical Neer-Salvatore scaling (Hubert 2003) for comparable cases (same inertia ratio & fill fraction). Therefore, the results are considered conservative. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. There are no plans to actively damp nutation. October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern THEMIS FDMO Review Recommended Action Reviewer Response Status 4. Shadow analysis. How will long shadow periods affect the attitude of the spacecraft? Will there be perturbations to contraction of the booms? How will the shadows affect the ability to perform attitude determination? Are maneuvers planned with respect to knowledge of the shadows? How are gyros affected? How is the system affected by not having a Sun pulse during the shadows? Data from WIND, POLAR and FAST of spin rate changes near eclipse may be of use. The wire boom cables are a multiconductor construction designed for low CTE (< 1 ppm/ C). The thermal mass is ~10 x WIND / IMAGE / DE 1 wires, while the CTE is 20 x lower, which makes shadow troubles almost benign. A plot of the POLAR spin period during a two-hour shadow is shown below. Attitude determination during shadows will be based on FGM data for near-earth shadows. Otherwise, attitude determination will not be performed during shadows. The probe attitude vector is assumed to be inertially stable. Maneuvers are planned to be performed outside of shadows. During shadows the probes generate artificial sun pulses for onboard timing purposes. 5. Attitude error budget. How was the 1 deg science error budget obtained? How stringent is it? What elements of error go into the budget? The 1 deg science attitude budget requirement is derived from the minimum science requirement to measure the magnetic field (to within 10% or 1 n. T, whichever is larger. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. Action Item Status − 24 October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern THEMIS FDMO Review Recommended Action Reviewer Response Status 6. MSASS training. If a copy of MSASS using Sun and FGM is available before the version with the Kalman filter, this should be used with FAST data to see how well Sun and magnetometer agree with Sun and Earth for training with use of FGM data. The THEMIS team is looking into using FAST Sun sensor and magnetometer data to test MSASS. Furthermore, the Kalman filter MSASS version of MSASS with magnetometer and MSSS should be compared to the Sun and Earth data version with data from FAST. 7. MSASS studies. At each planned attitude examine observability for Sun sensor and magnetometer. Generate simulated data (Matlab can probably generate this to go directly to the DA system). One group should generate the data while another group should determine the attitude with an a priori knowledge of no better than 5 deg or so. Generate clean data first, but at proper bin size, then later include noise and misalignments and offsets that can be expected. The THEMIS team wishes to thank the reviewer for this excellent suggestion. Action Item Status − 25 October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern Recommended Action Reviewer 8. Magnetometer observations are critically affected by timing errors. How will offsets in time be communicated to the attitude determination team? Will additional MSASS development be needed? Note that analysis with Matlab for magnetometer only attitude solutions for a spinning spacecraft (FAST and IMAGE) was made for GSFC in the past and these studies should be examined. THEMIS FDMO Review Action Item Status − 26 Response Status Flux gate magnetometer data are time tagged by the IDPU with an accuracy that is negligible with respect to the clock drift. The latter can be as large as ± 500 ms/day. However, the probe clock will be adjusted periodically to an accuracy of a few milliseconds with respect to UTC. If such a clock adjustment is performed just prior to a critical attitude determination event near perigee, the clock offset may be kept below 10 -20 ms. At a spin rate of 20 rpm this timing error translates into an attitude error of 1. 2 – 2. 4 deg, which is less than the 5 deg requirement for maneuver operations. A modification of MSASS may not be required to take clock offsets into account. October 5, 2004
FDMO CDR Peer Review RFAs RFA Statement of Concern Recommended Action Reviewer Response Status 16 TDRSS SSA support is baselined. TDRS HIJ SMA services may be able to support telemetry and command have greater availability. UCB/SSL should investigate use of SMA services from TDRS HIJ and that Doppler rates at perigee passes are within TDRSS limits. Gramling Code 451 performed a link analysis OPEN for TDRSS, showing that only TDRSS SSA mode is feasible. In addition, the GN style THEMIS transponder is not compatible with SMA mode in terms of RF frequency and modulation. The maximum range rates between the THEMIS probes and TDRSS are 10. 5 km/s and 2. 4 m/s 2 near perigee of the insertion orbit. The maximum rates that TDRSS can support are 12. 0 km/s and 15. 0 m/s 2, respectively. 17 There may not be sufficient tracking data (from more than one station) to allow for post-launch orbit determination (may not have adequate acquisition data). There may be a time gap in the timeline at 02: 15 to 03: 50 MET where another ground station, preferably Santiago, to get two-way Doppler data. Or, can second set of round-robins (starting at 04: 00 MET) be done through another ground station? Look at timeline to see if Gramling another station could be brought up to get additional Doppler data sooner after launch. Develop timeline for early orbit solution updates and determine OD support and station requirements. Timeline should go through the first apogee maneuvers (perigee raising) for all five probes and include time after maneuvers to do OD. Once the probes have been OPEN maneuvered to a Sun normal attitude, one pass set per day scheduled for support by the Berkeley Ground Station has been shifted over to the Wallops Ground Station to allow for optimal tracking data acquisition for early orbit determination. See detailed response in THEMIS FDMO CDR Peer Review RFA Reponses. 18 Is there a requirement for a back-up If yes, pre-launch testing MOC? would be required. THEMIS FDMO Review Hoge Action Item Status − 27 According to the Mission Manager (Frank Snow), a back-up MOC is not required for THEMIS. CLOSED October 5, 2004
Mission CDR RFAs RFA 3 Specific Request Supporting Rationale Revisit TDRS link margin to Current forward link margin establish sufficient forward link (1. 6 d. B) is not sufficient at margin and ensure any new CDR. operational constraints are included in the operations plan. THEMIS FDMO Reviewer Schnurr Action Item Status − 28 Response Status The TDRSS link budget has been OPEN revisited an effort has been made to find ways to improve the forward link margin. On the probe side, the receiver G/T performance is fixed. The modulation index cannot be increased because the resulting lower RF carrier signal level would impact receiver lock performance negatively. There are no hidden losses on the TDRSS side that are too pessimistic. The TDRS-to-probe range cannot be restricted to retain optimum coverage for monitoring orbit insertion and maneuvers. However, by far the largest variation in forward link margin is due to the probe attitude in combination with a non-omni directional probe antenna pattern. The only way to increase the forward link margin from 1. 6 to 3. 0 d. B would be by restricting the attitude angles, and correspondingly maneuver scenarios such that the forward link margin is 3. 0 d. B or larger during critical operations. The constraint analysis depends very strongly on the details of the probe antenna pattern, and we need to wait until a radiation pattern of a high-fidelity engineering model can be obtained from the manufacturer – New Mexico State University / Physical Sciences Laboratory (NMSU/PSL), presumably by end of September 2004. October 5, 2004
Mission CDR RFAs RFA Specific Request Rec Project should provide periodic mission design/propellant budgeting oversight to help assure propellant usage is being best used to satisfy science mission, contingency operations, extended mission and end-of-life operations requirements and objections. THEMIS FDMO Review Supporting Rationale Reviewer Delta V is a critical resource Ford which needs considerable attention through the design cycle through mission operations. Action Item Status − 29 Response Status The Explorer’s Office has initiated a task OPEN to independently verify UCB’s mission design work, including verification of the delta V budget. The UCB Flight Dynamics Team provides insight into their mission design and propellant budgeting details in various reviews focusing on flight dynamics and mission operations. October 5, 2004
- Slides: 29