1 PFP Team Meeting Particles and Fields Package Weekly Team Meeting, SSL January Dave Curtis, PFP PM

2 PFP Team Meeting Thermal Responsibilities PFP Team is responsible for thermal design of PFP boxes –SSL is responsible for PFDPU, SWIA, STATIC, SEP, LPW Booms, and SWEA (with help from CESR) Instrument leads need to work with Thermal Engineer, Chris Smith. PFDPU Mechanical (Donakowski) to work with Chris Smith –MAG team is responsible for MAG sensors –LASP is responsible for EUV –LASP and GSFC provide thermal dissipation of boards in PFDPU, do board-level thermal design (later) for the MAG and LPW boards in the PFDPU

3 PFP Team Meeting Thermal System Design Spacecraft provides each box two thermal sensors and two heater circuits –Harnessed directly to the components –Spacecraft has software-controlled heater controls designed for survival instrument heating –Survival heater power allocation for instruments currently same as normal operational power (except PFDPU). –Redundant heaters can be diode-ORed or run to separate heaters –Temp sensors ate PRTs, provided by the spacecraft. Currently no operational heater power allocated –Survival heater system can be used, but we need a power allocation if we cannot maintain temperature passively –Some boxes will probably need operational heat during eclipse –Thermal Modeling should help determine heater requirements. Nominally all boxes are thermally isolated from the spacecraft –Spacecraft deck is not well controlled (large bus) –As thermal design matures, it may make sense to couple some boxes (such as PFDPU, LPW booms) to the deck to take advantage of larger heat capacity

4 PFP Team Meeting PRT Temp Sensors

5 PFP Team Meeting LM Thermal Presentation There follows a presentation by LM on payload thermal design

6 PFP Team Meeting Payload Thermal Design Approach Payload provides simple thermal model to S/C S/C integrates Payload model into S/C thermal model S/C predicts thermal response of Payload for all S/C design cases S/C generates environments for Payload’s worst cases –Use “Sink Method” to define environments Payload uses environments for Payload thermal design analyses Iterate process

7 PFP Team Meeting Payload Thermal Design Approach Intent of this process is to segregate responsibilities between the S/C & Payload teams while keeping both cognizant of the other’s activities –S/C is responsible for evaluating all phases of the mission & determining which select cases drive the thermal design of the Payload (cases may change as design evolves) –Payload is responsible for the thermal design of the Payload; i.e., develops a design to tolerate the worst case environments –Iterative exchange of model information keeps both parties aware of design evolution

8 PFP Team Meeting Step 1 -- Payload Provides Simple Thermal Model to S/C Simple external geometry –Use rectangles, polygons, disks, cylinders, spheres (or sections of such surfaces) –Include all thermally critical surfaces (e.g., apertures, radiators, MLI blankets) –Suggest using surfaces that are directional in nature Environment on a cylinder is an average of 360 degrees around the circumference Breaking the cylinder into four 90-degree segments allows environments to be defined in four directions (which is useful if a directional radiator needs to be added to the design) Optical properties for all external surfaces –Solar absorptivity (a) & IR emissivity (e) –Ideally two sets: cold case (low a, high e) & hot case (high a, low e) Sets cover range of expected values throughout entire mission Range considers material variations, aging, degradation, etc.

9 PFP Team Meeting Step 1 -- Payload Provides Simple Thermal Model to S/C Thermal network (nodes, capacitance of nodes, conduction & radiation couplings, heat loads) –Include couplings to all external Payload surfaces For MLI, suggest using range for effective emittance to cover performance uncertainty –If internal dissipation drives thermal design, use high value for cold case & low for hot case –Include conduction couplings to simulate mount points to S/C –Include nodes to simulate items of thermal interest (e.g., items having temperature limits) Provide allowable predicted temperature ranges for nodes where applicable –Define heat loads (internal dissipation, heater) on appropriate nodes If heater is thermostatically controlled, define on/off temperatures & heater size These models will evolve with time (keep as small as practical less than 100 nodes) –Initial model may be one internal (lump mass) node with couplings to external geometry –Final versions will be multi-node networks, including many of the features listed above

10 PFP Team Meeting Step 2 – S/C Integrates Payload Model into S/C Thermal Model S/C uses Thermal Desktop software for thermal modeling Payload geometry is inserted into S/C thermal geometrical model Optical properties are inserted into S/C model database –Database is structured to handle two sets of optical properties per surface (hot case & cold case) Payload thermal network is integrated into S/C thermal network –Integrity of conduction & radiation couplings will be maintained during integration Radiation couplings to MLI may be re-structured into “Area x Effective Emittance” to better match S/C model format; these modifications will not alter the conductor value Conduction ties between S/C & Payload may be modified to accommodate the S/C nodal grid (e.g., one conductor may be divided into multiple couplings to multiple S/C nodes); these modifications will not alter the total conductance defined in the Payload model –Internal heat loads are integrated into the S/C model power logic Logic defines component power as a function of state –e.g., off = 0 W, standby = xx W, low power = yy W, high power = zz W Logic defines state as a function of time for each design case Heaters can be modeled as state driven and/or thermostat driven (i.e., on/off vs. temperature) –Variable power vs. temperature logic can be implemented, if required

11 PFP Team Meeting Step 3 – S/C Predicts Thermal Response of Payload for All S/C Design Cases Multiple S/C design cases are defined to bound all thermal aspects of the mission, from an overall S/C perspective –Consider all mission phases (e.g., launch, initial acquisition, cruise, MOI, Mapping) –Consider all mission operations (e.g., normal modes, safe modes) –Define worst cold & hot conditions for each phase / operation Allow for use of hot / cold parameters (e.g., optical properties, MLI effective emissivity) Cases evolve with time –Initially, those cases assumed most pertinent to overall thermal design are considered Cover bulk of mission –Cases assumed less pertinent are added as design evolves Make certain “assumption” regarding pertinence is valid Payload unique cases can be added (as required) to handle thermal design issues

12 PFP Team Meeting Step 4 – S/C Generates Environments for Payload’s Worst Cases Payload temperatures & heater power requirements are predicted for all S/C design cases Worst cases (hot & cold) for a Payload are defined based S/C model predictions –Maximum temperatures for critical nodes define hot cases –Minimum temperatures for critical nodes &/or maximum heater power usage define cold cases –As a minimum, one hot & one cold case are defined Multiple hot &/or cold cases can be processed, if required Worst case environments are delivered to Payload using the “Sink Method” –“Sink Method” uses sink (or boundary) nodes to define the effective environment seen by Payload external surfaces & to define the mounting interface with the S/C One sink is defined per each external surface in the Payload model One S/C mount point sink is defined (typically one is adequate; more are possible, if required) –Temperature profiles for each sink define a Payload design environment Details regarding the “Sink Method” are provided later in this presentation Payload temperatures predicted for worst cases are included with environment deliveries –Allows Payload to cross check “Sink Method” using simple Payload model

13 PFP Team Meeting Step 5 – Payload Uses Environments for Payload Thermal Design Analyses Payload integrates appropriate sinks (boundary nodes) into Payload thermal model Payload integrates appropriate logic to set sink temperatures in Payload thermal model –Sink temperatures may be constants or functions of time Payload develops an appropriate thermal design to tolerate the defined worst case environments Payload thermal model used for design may differ from the simple Payload model given to S/C –External geometry & optical properties must match simple version for “Sink Method” to be accurate A technique for estimating impacts of optical property changes is included in the “Sink Method” description – this allows Payload to evaluate external design options without having to request updated sink information for each possible option –Internal network need not match simple version & is typically more complex Payload updates simple model to incorporate design changes Payload delivers updated simple model to S/C

14 PFP Team Meeting Step 6 – Iterate Process S/C incorporates all simple Payload model updates into the S/C thermal model S/C evaluates updated Payload model against all S/C design cases –Determine if design modifications cause creation of more severe or different hot / cold cases –Changes to worst case definitions will spawn another iteration If Payload model updates alter the external geometry &/or optical properties, new environments will be generated & returned to Payload for another iteration Iterations continue until Payload thermal design is complete –When Payload meets all requirements under all S/C (& Payload unique) design cases

15 PFP Team Meeting Payload Thermal Environments – Sink Method Payload in Spacecraft (S/C) Thermal ModelPayload Thermal Model Using Sink Method Payload -- Absorbs heat from environment (e.g., sun, planet, reflections from S/C) -- Radiates to space -- Thermally coupled to S/C by m conduction paths ( ) n radiation paths ( ) Define external environment using sinks -- One conduction sink ( ) Typically adequate, more if required -- N radiation sinks ( ) One for each external surface Sink temperature includes effects of environmental heating, view to space & views to S/C 1 m 2 n 1 2 Environmental Heating Space Payload S/C (N external surfaces) 1 2 N C Payload (N external surfaces)

16 PFP Team Meeting Payload Thermal Environments – Sink Method, Conduction Payload in Spacecraft (S/C) Thermal ModelPayload Thermal Model Using Sink Method Number of conduction couplings between Payload & S/C determined by Payload model network & S/C model node grid at interface location -- Payload model defines quantity of couplings exiting Payload model & conductance of each coupling -- Payload model couplings are attached to appropriate node(s) in S/C model -- Total conductance same in both models, i.e., C = c1 + c2 + ….. + cm m 1 Payload S/C (N external surfaces) C Payload (N external surfaces) c1 c2 cm P/L C 2 T C Conduction sink is modeled as boundary node in Payload thermal model Temperature of sink ( ) is defined for each analysis case -- Minimum of two cases (worst case cold & worst case hot) -- Constant or function of time, depending upon case T C

17 PFP Team Meeting Payload Thermal Environments – Sink Method, Radiation Payload in Spacecraft (S/C) Thermal ModelPayload Thermal Model Using Sink Method External geometry of Payload inserted in S/C geometrical thermal model -- Geometry & optical properties coordinated with Payload thermal analyst -- Geometry consists of simple surface types (e.g., polygons, cylinders, cones) -- Simulates all critical thermal surfaces (e.g., apertures, radiators, MLI enclosures) S/C thermal model calculates environmental heating & all radiation couplings Radiation sink temperature is derived for each Payload surface using S/C thermal model results 1 2 n Environmental Heating Space Payload S/C (N external surfaces) 1 2 N Payload (N external surfaces) T 1 T 2 T N Radiation sink is modeled as boundary node in Payload thermal model -- One sink per each external surface Temperature of sink ( ) is defined for each analysis case -- Minimum of two cases (worst case cold & worst case hot) -- Constant or function of time, depending upon case Radiation coupling from surface to sink is A e -- A = area of external surface i -- e = emissivity of external surface i T i i i i i 1 1 A e 2 2 N N

18 PFP Team Meeting Radiation Sink Derivation Surface T s T i A e i i Radiant energy into surface Equivalent Sink ModelSystem Model 1 j n Space Surface T 1 T j T n T i Environmental Heating, Q i T sp G n G j G 1 G = ( F A ) ij i j G sp Q = Q + S ( F A ) s T - T iinijij j = 1 4 i j = n, sp 4 Q = A e s T - T iins 4 i 4 i Equate equations & expand terms Q + S ( F A ) s T - S ( F A ) s T = A e s T - A e s T iijij j = 1 4 i j = n, sp 4 is 4 i 4 iiji j = 1 j = n, sp ii S ( F A ) s T = A e s T j = 1 i j = n, sp 4 i 4 ijiii By definitionTherefore Q + S ( F A ) s T = A e s T iijij j = 1 4 j = n, sp is 4 i Solve for sink temperature T = + S ( F A ) T ijij j = 1 4 j = n, sp s 0.25 s i Q A e ii 1

19 PFP Team Meeting Radiation Sink Temperature Adjustment for Optical Property Change Sink temperature is a function of environmental heating (Q) Q T = + S ( F A ) T ijj j = 1 4 j = n, sp s 0.25 sA e 1 Revised Optical PropertiesBase Case Surface T s T A e a/e Surface s T ’ A e’ a’/e’ T ’ Environmental heating is a function of surface optical properties & incident heat rates ij Assume: F ~ e F ij Then, s Q = A ( a q + e q ) ir s 1 T = q + q + S F T ijj j = 1 4 j = n, sp s 0.25 sir a e Sink temperature for revised optical properties can be estimated as follows: s 1 T ’ = - q + T 4 s 0.25 s a’ e’ a e s Use of total absorbed solar heating rates to update sink temperatures for revised optical properties: To allow sink temperature modifications for optical property updates, total absorbed solar heating rates ( aq + aq ) are provided along with sink temperatures ( T ) solalb s s 1 T ’ = - + T 4 s 0.25 a’ e’ a e s solalb aq + aq a

20 PFP Team Meeting Typical Mounting for Payload Sensors Payload is responsible for thermal design of Sensor –Radiators sized for worst case hot environment (1 Au solar environment around earth 1389 W/m^2) In some cases, Aperture is sufficient to radiate internal heat and rest of sensor is blanketed –Heaters sized for worst case cold environment (deep space radiation environment - eclipse) Sensors are thermally isolated from structure with G10 standoffs –Typical values for #10 bolt with 0.25” G10 under sensor foot and 0.063” G10 under bolt head G = W/C per bolt –Structure temperatures will be above -50C in the cold case and less that 50C in hot case S/C Deck or APP platform, inches thick Typically -50C to +50C G10/G11 isolator, NAS /0.50 inch total thick inch OD, inch ID k G10 = W/mK Sensor mounting foot G10 isolating washer, inch thick inch OD, inch ID k G10 = W/mK #10 Ti bolt (0.19 inch major diameter) k Ti = 7.14 W/mK Metallic washer, inch thick

21 PFP Team Meeting Electronic Box Thermal Control Option 1 - Payload is responsible for thermal design of box –Radiators sized for worst case hot environment (1 Au solar environment around earth 1389 W/m^2) –Heaters sized for worst case cold environment (deep space radiation environment - eclipse) –Boxes could be thermally isolated from structure with G10 standoffs –Typical values for #10 bolt with 0.25” G10 under sensor foot and 0.063” G10 under bolt head G = W/C per bolt –Structure temperatures will be above -50C in the cold case and less that 50C in hot case Option 2 – S/C is responsible for Thermal control of Box –In cases where boxes are mounted inside the external thermal blankets or if there is a heater power savings for system, S/C will be responsible for controlling the box to the ERD limits –In this condition, the box could be installed so internal heat is either conducted and radiated into the MLI enclosure, or radiated off an external radiator on the opposite side of the structure –Heaters and sensors would be installed by the S/C to maintain lower temperature limits