21 2202238 Ralph CDR Gurule Thermal 070303

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Systems Engineering: 

Systems Engineering Anthony Gurule Thermal Engineering 303 939-4196 agurule@ball.com New Horizons…Shedding Light On Frontier Worlds Ralph Instrument Critical Design Review Aug 5 & 6, 2003

Thermal Subsystem Topics: 

Thermal Subsystem Topics Thermal Design Overview Thermal Subsystem Requirements and Guidelines Changes to Requirements/Implementation Since PDR Process Data Flow Thermal Elastic Analysis Cryoradiator margin philosophy Thermal environments – Pluto encounter Description of thermal model Thermal straps/FP interface Managing Ralph Thermal Gradients Pluto encounter – Operating performance MVIC/LEISA performance operating Warm stage heat map Cold stage heat map Sun “ON” Worst Case Scenario Present thermal design accommodations to provide micrometeoroid protection Present plans for the acquisition of MLI or special optical surface finish Thermal Design Summary

Thermal Design Overview: 

Thermal Design Overview A detailed thermal analysis has been conducted on the current Ralph instrument mechanical design. Predicted thermal performance meets requirements.


    Thermal Requirements 138.1 K (no margin) 151.1 K (margin) (+13 K margin) 91.3 K (no margin) 97.3 K (margin) (+6 K margin)


Thermal Requirements 138.1 K (no margin) 151.1 K (margin) (+13 K margin) 91.3 K (no margin) 97.3 K (margin) (+6 K margin)


Optical bench (Ralph) Ralph shall be maintained to <260 K during normal operation at Pluto Within Ralph optical cavity all surfaces shall be optically black LEISA/MVIC FPAs LEISA electrical loading is 0.005 W MVIC electrical loading is 0.250 W Operating Timeline FPAs shall operate under the timeline described in the proposal During Pluto encounter, both FPA packages shall be “ON” Thermal Guidelines


Changes to Req’ts/Implementation Since PDR There have been some design changes since PDR that effect thermal design. Re-location of spacecraft thermal straps. This moves the maximum gradients from up-n-down to side-ways. Change in the overall optical bench design, thickness. This slightly increases the gradients in the bench. Better definition, since PDR, of the MVIC and LEISA FPA housing packages. PDR level design has been improved with details defined. These detais have been added to the thermal model. Reallocation of materials; I.e., MVIC and LEISA housing flexures made from G-10 to provide more isolation from optical bench and thus lower parasitics. Less parasitics into the system means more temperature margin. LEISA max operating temperature = 100 K Redefintion of spacecraft flexures.

Process Data Flow Thermal Elastic Analysis: 

Generation of surface/radiation model using TSS Generation of thermal math model using SINDA Execute for Non-Op and OP modes. Execute mapping function which takes generated results and converts to IDEAS format. Results are inputted to Structural model as boundary temperatures. Process Data Flow Thermal Elastic Analysis Generate thermal-elastic distortions. Distortions are inputted into optical performance model.

Cryoradiator Margin Philosophy: 

Primary criteria and guidance for passive radiator margin is from MIL-STD-1540C, 15 September 1994, Test Requirements for Launch, Upper-Stage, and Space Vehicles The temperature margin as defined by MIL-STD-1540C was used with some modification Cold stage radiator has a modified margin of 6 K Justification: much of the thermal control design has heritage from SBIRS to Hubble Thermal load margins are consistent with guidelines set by MIL-STD-1540C 138.1 K without margin radiator 91.3 K without margin radiator SBIRS heritage employs similar margin philosophy Cryoradiator Margin Philosophy Modified to HalfWay


Planetary Thermal Environments 40 Rj Worst Case Sun “ON” Scenario At 1 AU Pluto/Charon Encounter Operational 1420 W/m2 49.6 W/m2 0.91 W/m2 T Pluto ~ 55 K Spacecraft Survival Spacecraft Survival

Description of Thermal Model: 

Conductive Contribution from S/C View Factors from Spacecraft Antenna, RTG, S/C Description of Thermal Model 2-Stage Cryoradiator (Cold Stage = LEISA) (Warm Stage = MVIC) Aperture Interior (mirrors, baffles, optical elements painted black) Exterior (2 mil silver teflon) LEISA FPA MVIC FPA Thermal Strap (3) Spacecraft Flexure Painted white Summary of Thermal Nodes Cryoradiator 36 nodes MVIC 110 nodes Ralph 634 nodes Mirrors 101 nodes LEISA thermal 99 nodes Aperture 24 nodes Baffle 12 nodes FP Elec. 6 nodes Misc. 36 nodes Total 1058 nodes

Thermal Straps/FP Interface: 

K1100 thermal strap successfully flown on GFO mission Consists of individual tubes, each containing 10,000 K1100 fibers. End fittings designed to allow maximum, perpendicular heat flow into individual fibers Thermal Straps/FP Interface Design challenges of thermal straps: available length, heat load to move, and relative location of cryogenic radiator to FP assemblies (LEISA and MVIC) Three straps required: 95 K LEISA FP to radiator 150 K MVIC FP to radiator 150 K LEISA shield to radiator K1100 strap made from K1100 fibers Advantages: mechanical compliance with large thermal conductance Disadvantages: moderately expensive, must ensure that heat can get into cross-section of fibers Strap will mount to their respective mounting surface with indium

Managing Ralph Thermal Gradients: 

Location of trim heaters used to further decrease gradient Managing Ralph Thermal Gradients To improve the thermal gradients within Ralph, trim heaters are an integral part of the thermal control design for the bench. Additional heater power will balance out the thermal gradients in the x,y,z directions

Pluto Encounter Optical Bench Performance: 

Ralph – Active Thermal Control By using active methods (trim heaters) thermal gradients are maintained within requirement of 3K. Absolute bench temperature 240 K. Power levels: 0.175 W, 0.175 W, 0.15 W Pluto Encounter DTy = 1.8 K DTx = 1.2 K DTz = 1.1 K Pluto Encounter Optical Bench Performance

MVIC/LEISA Performance Operating: 

Pluto Encounter LEISA and MVIC meet their operational temperature requirements (with trim heaters) LEISA FPA 91.3 K without margin 97.3 K with margin (+6 K) MVIC FPA 138.1 K without margin 151.1 K with margin (+13 K) MVIC/LEISA Performance Operating Cryoradiator – cold stage 90.3 K without margin 96.3 K with margin (+6 K) Cryoradiator – warm stage 125.4 K without margin 138.4 K with margin (+13 K) Ralph 220 K without margin 234 K with margin (+14 K) Without Margin With Margin LEISA 27 mW 349 mW (30%) MVIC 505 mW 749 mW (48%)

Warm Stage Heat Map @ Pluto - Operational: 

Space 0.505 W Cold Radiator MLI/Supports 0.0737 W Ralph Supports 0.0742 W Orbital/Surroundings 0.0026 W 0.5959 W 0.094 W FPA Parasitics Electrical Loading 0.3459 W 0.250 W Space Spacecraft Surroundings Orbital Ralph MLI/Supports FPA Parasitics Electrical Loading LEISA Thermal Loading Warm Stage Heat Map @ Pluto - Operational

Cold Stage Heat Map @ Pluto - Operational: 

Space 0.2691 W Warm Radiator MLI/Supports 0.0737 W Surroundings 0.0023 W 0.193 W Orbital 0.0001 W Electrical Loading 0.005 W FPA Parasitics 0.188 W Space Spacecraft Surroundings Orbital Warm Radiator MLI/Supports FPA Parasitics Electrical Loading Cold Stage Heat Map @ Pluto - Operational

Sun “ON” Radiator Worst Case Scenario: 

Sun “ON” Radiator Sun “ON” Radiator Worst Case Scenario Assumptions Used Spacecraft pointing error occurs sometime after launch Distance from the Sun is about 1 AU System has undergone a checkout. Ralph is in a quasi-steady state condition Spacecraft has stopped spinning When pointing error occurs, the Sun is normal to the radiating surface Radiator surface painted white Failure mechanisms: 1) maximum temp of the FP assemblies before bonding or detector failure is 323 K with 15 K margin. 2) radiator honeycomb panels at 338 K, with margin. 3) white paint at 338 K, with margin LEISA MVIC LEISA MVIC 323K - FP Failure 338K - H/C-Paint Failure

Sun “ON” Aperture Worst Case Scenario - FPAs: 

Sun “ON” Aperture Direct Normal Sun Loading onto LEISA/MVIC Based on Loading Full Sun 1368 W/m2 Primary Mirror 0.53 W Secondary Mirror 0.48 W Tertiary Mirror 0.44 W Dichroic 0.53 W Filter 0.53 W CCD (LEISA/MVIC) 1.02 W/2.66 W * Worst-case loading profile * Sun spot size = 25.34 mm2 Sun “ON” Aperture Worst Case Scenario - FPAs MVIC LEISA 323 K - FP Failure 338 K - H/C-Paint Failure


Sun “ON” Aperture Worst Case Scenario – MVIC Filters Problem Statement : Filter requires black masking to minimize ghosting Filter only weakly thermally coupled to holder as net A/L is very small Filter reaches >700K in <1 min Mitigation analysis: Install reflective strip on sun-side of filter to reflect impinging sun, OR Install long pass filter on aperture window. Filter Filter/CCD Holder CCD SUN Assumptions to Analysis: Filter – fused silica 66mm x 15.1mm x 1mm Filter – black strips 1mm wide, 95%a, 95% e Goal: Filter – non-black, 25%a, 95% e <410K in 10 minutes Assume no contact-worst case 2.5” aperture opening, Sun = 5.86mm diameter Radiates to surroundings (~300K) Initial Analysis


Present Thermal Design Accommodations to Provide Micrometeoroid Protection Micrometeoroid impact analysis conducted by Dr. Alan Stern, dated 19 June 2003. Fractional area damage on the radiator is on the order of << 1%. Based on conservative assumptions that the radiator faces the ram direction 100% of the time and that the typical dust impact speed is 20 km/sec. Thus the radiator meteoroid damage can be considered negligible. Thus no need to incorporate unique micrometeoroid protection in the MLI blankets.


Plans for Acquisition of MLI or Special Optical Surface Finish Based on the results from the Micrometeoroid Impact Analysis there is no need to incorporate unique micrometeoroid protection in the MLI blankets. However, to ensure a robust MLI design, Beta Cloth will be used as the inside layer of the exterior MLI Blankets. Baselined for other programs including Deep Impact.


Thermal Design Summary A detailed thermal analysis has been conducted on the current Ralph instrument mechanical design. Predicted thermal performance meets requirements. Future Work Work with Mechanical Engineer to finalize design Update model as needed Pursue MLI and thermal strap design

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