X-Ray Calorimeter Systems Engineering Brian Ottens Martha Chu Feb 17, 2011
Total Instrument Rack-up(no contingency included) Still preliminary as of noon Feb 29
Driving Philosophy (From Customer Presentation A. Ptak et al) • How much IXO science is possible at lower cost points for a NASA X-ray mission? I really love X-ray science but it makes me cry to see the pricetag Still, even as we cut waste and inefficiency, this budget freeze will also require us to make some tough choices.
Big Picture • Major science areas (from customer presentation A. Ptak et al): • Galaxies and black hole evolution • Large scale structure • Matter under extreme conditions • Life cycle of matter and energy • Single instrument on the spacecraft • Lifetime & Environment: 3 years @ L2 • Closest in-house analog: ASTRO-H • Similar IDL customer: Con-X in 2008 • Mostly served as a reference for current study and not a biasing force for estimates
Fixed Technical Parameters • Boundary conditions and noteworthy engineering assumptions used for the study: • Furnished mirror assembly used to acquire signal. • Alignment budget and execution outside scope of XMS functionality. • Retain competitive marketplace for cryocooler procurement. • 100% margin on cryogenic power at this stage of development. Margin held in cryo subsystem. • Market for specific engineering products at time of procurement is comparable to today. • Use TDM scheme from customer-furnished FPA information. • 1060 TES array • Availability and integrity requirement for science data quantified at the “medium” level: • 5% ADR maintenance acceptable (regeneration 2 hrs per 42 hrs) • 1% calibration acceptable (15 min per day) • Infrequent Single Event Upsets (SEU) acceptable • Reliability: • Assume 0.8 Ps required for entire mission • Allocate 0.9 Ps requirement against instrument. Begin with single string and apply redundancy to meet 0.9 • Data from only half the detector array is required for mission success. • No distinction between loss at the array vs loss in the electronics. • Mostly standard engineering resources from S/C (discussed in detail later in presentation)
Summary of Trades Considered and Changes Implemented • Testability vscryocooler power • Filter Wheel and Electronics Box Placement • Software vs firmware vs firmware + software • After seeing preliminary MEB CPU quotes, this trade was halted for insufficient value. • Blanketing vs sunshade • Targeted reliability improvements • Very limited redundancy implemented: heater circuits, flight mechanisms, cryocooler drive electronics • Configurations showing more redundancy are occasionally presented as alternates • Off-the-shelf cards are believed to have the ability to drive 2 windings, with unknown failure isolation between the 2 drive circuits. Solution – 2 cards are baselined. • Majority of detector data is “parallel-chain” - each chain handles data from half the array. Losing one chain doesn’t take out the other. • # of ADR stages • Currently holding a 3-stage unit, similar to Astro-H. • Flying limited amounts of GSE to lower test durations • # of Thermal cases and environments to analyze (discussed later)
Early Orbit Operations (Notional) Cruise XMS Warm Checks, Door Actuation, & Cooldown Critical Mission System Checks S/C Outgassing (XMS OFF) XMS Cold Checks Off XMS Calibration Reserve Science Ops @ L2 5% ADR unavailability and 1% to calibrate. Notionally 2hr/42 hr for ADR and 15min/day for calibration. Launch Day 91 Day 81 Day TBD Day 21 Day 71 Solar panels deployed & comm link established (Declared as Day 1) Arrive at L2 (Day 100)
From Athena PDD Best value for thermal analysis – “Full power,” “half power,” and Launch Phase (no power) cases. Cruise and L2 environments.
Block Diagram Subassembly Filter wheel, MXRS, & Mechanism MXRS HV Drive (redundant) Aperture Door w/ redundant release X-rays Aperture Cylinder & op htr (S/C one-time actuation) Flying-GSE µvalve filters Vent door (not required for mission success) 50 mK Microcalorimeter SQUID readout amplifiers Antico detector Ground servicing ports FPA ADR Stage 1 Calorimeter Front End Elec (FEE) (Parallel chains for each half of the FPA) Calorimeter Digital Electronics & Event Processing (DEEP) 0.6-1.0 K Science Data 4K SQUIDs & termination resistors ADR Stage 2 (0.6K) Op Htrs Subassy ADR Control Electronics (ADRC) ADR Stage 3 (1.3K) 4.5 K • Main Electronic Box • LVPS • Power Switching & Distribution (PDU) • Single Board Computer (SBC) • Digital I/O • Housekeeping (analog input) • FW Stepper Drive 18 K (1/3 of blanket mass here) 75 K (2/3 of blanket mass here) 260-300 K S/C C&DH Cryostat cold head Cryocooler S/C Power Cryocooler Drive Electronics Cryocooler Drive Electronics Heat Pipe to radiator Cryocooler Compressors LHP condenser Multiple Locations S/C furnished survival power Redundant
Concerns and System Level Risks • Risk of cryocooler loss in the event of power interruption. There is experience with a Japanese cryocooler on ISS where power was removed and some contamination migrated to an unwanted area (and caused failure). There is no data to support a risk for any US cooler, but since the consequences are so high, the presenter recommends researching further and/or implementing process controls to avoid on-orbit issues. • The customer-furnished diagram detailing authority to transition instrument modes may be misleading. Multiple opinions in the IDL felt that a ground command and the instrument processor should have unlimited authority to transition instrument states (unless it’s a short-term hazard). This may simply be a representation error. • Technology readiness concerns are in-family with normal mission-enabling technology developments. This will be familiar to decision making authorities but possibly not comforting. • A post-study-week analysis on micrometorite damage to the optical train may require light design changes (such as spare filters in the filter wheel). • An “no-ETU other than MEB, SpaceCube & I/O, & FW mechanism” approach has some risks and must be actively managed. Risk is detailed in later slides.
Risks of a No-ETU* Plan*Except MEB, Spacecube, & FW mechanism • The recommendations are presented to inform the customer on the risk of implementing a no-ETU plan and using that informed state to actively manage the risk. • Assumptions: • Mission-enabling technology (the FPA and critical interfacing equipment) is separately developed in a stand-alone TRL maturation campaign. • Complex equipment identified as very high heritage remains at that amount of heritage • For example, no major changes in the ADR (from Astro-H) are assumed. • Sufficient simulators and GSE are available as test equipment during the bench testing campaign (S/C simulators, cold heads, flight electronics aren’t needed for the FPA TRL campaign, etc) • A standard set of interfaces between the S/C and instrument are implemented • Standard data exchange protocols, clean power specifications, conducted EMI requirements, etc • The overall mission risk posture has some flexibility and there’s a need to employ this risk • For example, if the “price to get selected” had room to implement an ETU, why wouldn’t you do it? • This approach is implemented early (at SRR or earlier). • Availability of sufficient flight-spare parts. • “Empty” housings can be fit-checked onto the S/C as early as possible • A GOLD rule waiver would have to be submitted for deviations to providing FSW an “ETU Flight Data System” • The IDL consensus is that this is defined as the Single Board Computer (SBC) and digital I/O cards only • Milestones where cost-risk is disproportionally high: • First CPT of the instrument • Instrument thermal performance test • Instrument EMI/EMC qualification • Other environmental qualification (general risk) • Resolving certain issues such as handling damage
Notional I&T Flow and Specific Risks(Yellow color indicates cost-risk is disproportionally high) • Specifically perceived risks • Given that the instrument baseline CPT is defined as flight configuration, then slips in subassembly delivery may create large “marching army” costs while waiting for the all-flight configuration. • Mitigations: • Have replacement equipment available to substitute for missing flight equipment so CPT-like testing can begin and common “bugs” in scripts and equipment can be identified. Specifically, train operators and have GSE available to I&T. • Select low-risk suppliers who can confidently go straight from EDU to flight, especially in electronic cards. • Given that some bugs in the baseline CPT may require white wires, have some reliability workarounds to this non-ideal state. For example, flight redundancy makes accepting a lot of white wires easier. ADR build & subassy test FPA build & subassy test Cryostat Assembly Cold head build & subassy test Flight Instrument baseline CPT Flight Instrument Environmental Pack & Ship Cryostat structure fab Stuff flight boxes & bench test PC board build & bench test PC board build & bench test PC board build & bench test Approx 6 boxes Approx 1 doz boards
Specifically Perceived Risks of No-ETU*(cont’d 2/3) • Environmental qualification • Given that the flight test may be the first time the instrument sees the flight shielding and flight cabling, then the risk of EMI/EMC issue is noteworthy. • Mitigations: • Systems engineering should keep extra mass for shielding and filters going into EMI/EMC testing. • Any shielding that is employed should be robust. • The design should be cognizant of EMI/EMC concerns. • Given that the cryostat has some ability to mispoint (independent of the mounting deck) and thermal pointing deviations are very difficult to “patch up,” then significant pointing issues will require lengthy fixes. • Mitigations: • Systems engineer will have to hold more margin than usual against this problem (IDL Lead SE’s recommendation: 100% margin until test data is presented). • Systems engineer will have to devise and keep workarounds available to solve this type of issue. Examples – operational heaters, blanketing, etc. • Given that there is no intermediate build from EDU to flight, then significant design or assembly errors have to be corrected before proceeding to the next milestone for its use (note: there are some exceptions to this but they are few). • Mitigations: • Consider levying a requirement on the mission-enabling TRL 6 unit that it be as flight like as possible (or even the flight design). • (repeated from previous page) Select low-risk suppliers who can confidently go straight from EDU to flight, especially in electronic cards. • Consider what risk can be addressed in EDU equipment, even though it may not be flyable • Examples – thermal air cycling, pyroshock, conducted EMI testing, etc.
Specifically Perceived Risks of No-ETU*(cont’d 3/3) • Resolving issues such as those resulting from handling damage • Given that there may be significant differences between the EDU and Flight equipment, than unavailability of the flight equipment will either halt that activity or require a substitute unit. • Mitigations: • Many of the mitigations against the baseline CPT delay are applicable here. • Minimize exposure to handling damage (optimize # of moves) and enforce discipline on I&T team. • Given that repair efforts have a disproportionately high probability of occurrence, than a “servicable” cryostat assembly should be prioritized. • Mitigations: • Add extra volume to access individual components with minimal disassembly. • Hold extra cryo margin to allow for unforeseen attachments and connections between cryo zones. • Minimize permanently fixed connections such as welding and epoxies.
Non-Obvious Spacecraft Needs • Instrument mounting deck • After installing onto that furnished deck, kevlar and thermal blanketing • Alignment with collector optics assumed S/C responsibility and not covered in IDL study • Aperture and vent door mechanism power • Radiation monitor used to safe instrument • Numerous power services – possibly some with very high availability requirements • 2 data buses (high and low rate) • Real estate on the anti-sun side for thermal radiators • And/or some structure to position the radiator for views of the cold sink • Survival heater power • Currently estimated at 365W (avg) and can be lowered with $$ for thermal equipment or heat exchanges with S/C • Sufficient memory for science data • 1pps time signal with 100 usec accuracy The presenter recommends bringing the detailed list from the final report to any MDL study or any discussions on S/C procurement requirements.
Top-Level* Mass Summary Still preliminary as of noon Feb 29 *this listing does not include all subassemblies, please refer to the final mass model (MEL) for a full summary
Mass Summary By Subsystem Still preliminary as of noon Feb 29
Instrument Power Summary Spacecraft Power Bus Requirement * The one-time use items are short duration and do not factor into instrument power demand ^Survival heater power at 70% duty cycle results in a slightly higher peak (approx 930W).
Data Rates* Average Data Rate: • Assume Count Rate ~ 500 counts/sec (for ~10milli-Crab source) • Assume ~10 bits each for positions X and Y position on the Array • Signal ~ 52 bits (energy, time stamp, rise time, event type/grade, & anti-co) • Average Data rate ~ [(52 + 10+ 10) bits/count ] x (500 counts/sec) ~ 36,000bps (x2 for 100% margin) • Average Data Rate ~ 72Kbps (with 100% margin) Peak Data Rate: • Maximum count rate capability ~ 15,000counts/sec (ie. 80% throughput and full energy resolution) • Assume 4-bits (16 pixels) each for positions X and Y at center of the Array • Signal ~ 52 bits (energy, time stamp, rise time, event type/grade, & anti-co) • Peak Data Rate ~ [(52 + 8)bits/count ] x 15000 counts/sec) ~ 900,000bps (x2 for 100% margin) • Peak Data Rate ~ 1.8Mbps *Data rates are dominated by the science data stream, and engineering telemetry is accounted for by the higher-than-normal margin values.
Block Diagram for Costing Subassembly Purchase/Build Key: RFI Vendor Estimate Vendor Build Purchased Filter wheel & Mechanism Grass Roots Goddard In-House Build MXS MXS HV Drive Aperture Door w/ redundant release X-rays Op Heater Flying-GSE µvalve filters Vent door (not required for mission success) Aperture Cylinder (inclds filters) 50 mK Microcalorimeter SQUID readout amplifiers Calorimeter Digital Electronics & Event Antico detector Ground servicing ports FPA ADR Stage 1 Calorimeter Front End Elec (FEE) Processing (DEEP) 0.6-1.0 K 4K SQUIDs & termination resistors ADR Stage 2 (0.6K) Subassy ADR Control Electronics (ADRC) ADR Stage 3 (1.3K) 4.5 K • Main Electronic Box • LVPS • Power Switching & Distribution (PDU) • Single Board Computer (SBC) • Digital I/O • Housekeeping (analog input) • FW Stepper Drive 18 K 75 K 260-300 K Cryostat cold head Cryocooler Cryocooler Drive Electronics Cryocooler Drive Electronics Heat Pipe to radiator Cryocooler Compressors Redundant
Cost Assumptions • FPGA firmware will be costed using a pre-defined costing scheme in the electrical presentation • Flight S/W will be costed using SEER-SEM based on lines of code • Instrument Level Considerations • Ground Support Equipment (GSE) - 5% of Estimated Instrument Hardware Cost to Estimate • Environmental Testing - 5% of Estimated Instrument Hardware Cost • Engineering Test Unit (ETU) – we will document 2 cases • 10% wrap for estimated cost of ETUs • A 2nd case will show an ETU only for the hardware req’d to comply with Gold Rules: • Where an ETU is req’d for FSW testing (pre and post flight): • DEEP Box: SpaceCube processor board and digital I/O board • MEB: although a partial MEB may be sufficient, our cost was only provided at a fully integrated level, so we have costed an ETU for the entire assembly • Where an ETU is req’d for mechanism lifecycle testing: filter wheel & filter wheel control electronics (this was identified after the study concluded upon review of Gold Rules) • Flight Spares - 10% of Estimated Instrument Hardware Cost • Instrument to S/C Bus Integration & Test - 5% Estimated Instrument Hardware Cost. Typically Included in WBS 10.0
Cost Assumptions • Unique purchased items and Pass Thrus: • ADR Assembly Grass roots • ADR Electronics Grass roots • Cryocooler + Electronics RFI Vendor Estimate • FPA Assembly Grass roots • SpaceCube Grass roots • Main Electronics Box Vendor Purchased Item • X-Ray Calibration Source +HVPS Vendor Purchased Price if possible • Filters Grass Roots
Conclusion and Path Forward • A preliminary set of resources for the 2012 X-ray Calorimeter concept was generated and is in-family with prior efforts (after scaling for complexity). • A limited set of additional equipment was needed to meet ps requirement. • A modest but sufficient set of GSE that flies was included to aid testability. • The baseline engineering data set is sufficient to continue the path to costing exercises. • Few major risks were identified and there appear to be possibilities to reduce them with further development. • Instrument specific S/C needs are slightly above “basic,” but with the exception of cryocooler power availability, don’t appear to drive costs (see recommendation next page). • A high-value approach to thermal analysis provides information without excess costs.
Recommendations for Future Work • Consider whether a different type of door (for example sliding o-ring valve) could reduce the standoff distance of the cryostat. • Work with ADR supplier to model magnetic disturbances for potentially sensitive components. • Review results for micrometeorite damage to the the optical train. Small design changes may be required. • Align some small differences between cryocooler RFI responses and expected use of cryocooler. For an RFI this is fine, but for the RFP prioritize firm requirements as much as possible • Determine how large of a risk the cryocooler is to restart. If this is truly a risk, the presenter believes one will have a difficult time passing a design review without an engineering mitigation (such as a S/C uninterruptable power supply). • Consider the trades and options put forward to reduce heater power – (1) louvres, (2) Loop Heat Pipes (LHPs), or (3) allow for warm-up time between standby and science mode so standby heaters don’t have to run so much.
Detailed Operating Modes • Constraints: • Strongly prefer not to turn cooler off (preferred but not prohibited) • Too warm – contamination • Mitigate with sun avoidance pointing • Too cold – freezes and won’t restart • Mitigate with contam control on the ground • Accommodate emergency conditions on spacecraft • Protect against solar radiation events • Notified by S/C furnished radiation sensor • Especially protect the high voltage • Modes • OFF* – no power anywhere • EMERGENCY* – Only HK & Digital • SURVIVAL/COOLDOWN – Cryocooler, HK, + Digital • STANDBY – Ready for observation but not taking detector data • REGENERATE –ADRs dump their heat • INITIALIZE • CALIBRATION • OBSERVE * Indicates cryocooler is off