1. G O D D A R D S P A C E F L I G H T C E N T E R 1 SMEX  Lite Modular Solar Array Architecture John W. Lyons

2. GSFC 2 SMEX  Lite Modular Solar Array Architecture Acknowledgement SMEX  Lite Modular Solar Array Development Team: Jim Watzin, SMEX Project Manager Joe Burt, Systems Lead Giulio Rosanova, Mechanical Systems Lead John Lyons, Solar Array Lead

3. GSFC 3 SMEX  Lite Modular Solar Array Architecture Agenda  Introduction  SMEX Program Overview  SMEX  Lite Concept  Why a Modular Solar Array?  Advantages  Disadvantages  Specifications  Design and Development  Verification  SMEX  Lite Missions  Experiment Modules  Conclusions

4. GSFC 4 SMEX  Lite Modular Solar Array Architecture Introduction  Three years between Small Explorer (SMEX) mission definition and launch.  For each SMEX mission to date, the solar array has been the longest-lead item.  Mission-unique solar array procurement requires detailed substrate design well ahead of other spacecraft components.  Every in-house SMEX mission using a mission-unique solar array has encountered problems with I&T schedule.  Separate procurements and qualification programs for each mission increase cost as NRE is repeated for each mission.  Led to development of a modular solar array architecture to allow one panel procurement for multiple missions.

5. GSFC 5 SMEX  Lite Modular Solar Array Architecture GSFC In-House Small Explorer (SMEX) Missions

6. GSFC 6 SMEX  Lite Modular Solar Array Architecture SMEX  Lite Concept  Response to $10M budget for entire S/C  Modular spacecraft configuration  Allows for expansion or contraction of capabilities to support various missions  Allows components to be added or deleted with minimal impact to other subsystems  Concept extended to electronics, sensors, actuators, software, mechanical system, ground support (integration and test and operations) system  Also extended to the solar array

7. GSFC 7 SMEX  Lite Modular Solar Array Architecture Why a Modular Solar Array?  Previous SMEX missions (except for FAST) were similar enough in operating temperature and radiation environment that a standard solar panel module could have been used for all.  Procurement of enough modules for several missions: –Allows array geometry definition to be later in the development flow –Removes the solar array from the critical path of the I&T schedule –Spreads non-recurring costs over several missions rather than paying NRE for each mission  Facilitates inclusion of solar cell/panel experiments SAMPEXFASTSWASTRACE

8. GSFC 8 SMEX  Lite Modular Solar Array Architecture Cost Advantage of Modular Approach In-House GSFC GaAs/Ge Solar Arrays

9. GSFC 9 SMEX  Lite Modular Solar Array Architecture Disadvantages  Maintenance of Inventory (48 flight modules presently in storage)  Solar array not optimized for each mission (But almost, if bus voltage, temperature, radiation requirements are similar)

10. GSFC 10 SMEX  Lite Modular Solar Array Architecture Basic Specifications  Solar panel module sized to provide at least 13.5 watts (normal sun incidence, 80°C, 0.967 AM0) at a maximum-power voltage of +34Vdc at end-of-life over the expected range of SMEXLite environments.  Flight panels shall meet mission requirements after exposure to 5,500 temperature cycles between -80ºC and +110ºC.  Temperature range envelopes expected temperature range of SMEXLite missions.

11. GSFC 11 SMEX  Lite Modular Solar Array Architecture Basic Specifications (Cont.) Charged Particle Radiation  GaAs/Ge solar cells shielded by specified covers and substrate will experience the following maximum 1-Mev electron equivalent fluences and degradations after one year in LEO: Fluence* (e/cm 2 )Degradation (%) Isc:5.02 x 10 12 1.2 Voc: 2.18 x 10 13 2.0 Pmax1.94 x 10 13 3.0 *Includes 1 anomalously large solar flare.

12. GSFC 12 SMEX  Lite Modular Solar Array Architecture SMEX  Lite Solar Panel Module 4 x 4 cm GaAs/Ge single-junction solar cells with 10-mil-thick CMX covers (18.5% eff. @ 28° C, 1Sun AM0) 1 string of 50 series cells per module, shunt tap 20 cells below positive terminal Parallel redundant blocking diodes on back of module Substrates: Al honeycomb, graphite composite facesheets, Kapton insulator, approx. 21.0 cm x 43.0 cm x 1.90 cm Sized to provide 13.5 watts at 35 volts at 80°C, 0.967 AM0, 1-MeV electron equivalent fluence for Pmax of 5x10 13 e/cm 2 Avg. Module Mass Substrate:140 gm Add-on: 172 gm Total: 312 gm

13. GSFC 13 SMEX  Lite Modular Solar Array Architecture Modular Solar Array Frame Unpopulated WIRE Solar Panel Composite Frame (Above Right) Bonding a SMEX  Lite Module to WIRE Solar Panel Frame (Below)

14. GSFC 14 SMEX  Lite Modular Solar Array Architecture Modular Solar Array Wiring Back Side of Triana Solar Array Wing SMEX  Lite Solar Array Block Diagram

15. GSFC 15 SMEX  Lite Modular Solar Array Architecture Development of Modular Array  Procure test modules from array vendor  Assemble test modules into a portion of a panel (small frame)  Perform acoustic, vibration, thermal cycling on assembled wing to qualify approach  Procure flight modules, assemble into panels  Thermal vacuum test at wing level, acoustic, random vibration on spacecraft

16. GSFC 16 SMEX  Lite Modular Solar Array Architecture Verification  Module (at vendor) –Electrical Measurement, Visual Inspection, 8 thermal vacuum cycles -85ºC to +115ºC, Incoming testing at GSFC  Qual Array –Assemble 2 to 5 modules into a qual panel, Electrical Measurement, Visual Inspection, Acoustic, Random Vibration, 5,500 rapid thermal cycles -90ºC to +120ºC  Flight Panels (at GSFC) –Assemble modules into panels, Electrical Measurement, Visual Inspection, 8 Thermal Vacuum cycles -85ºC to + 115ºC, bakeout, Acoustic (On S/C), Random vibration (on S/C)

17. GSFC 17 SMEX  Lite Modular Solar Array Architecture Missions Using SMEX  Lite Modular Solar Arrays 540 km, 97° inclination, four-month full-sun mission 2 Wings, 1 Panel per wing, 9 modules per panel 180 watts EOL solar array power 16 GaAs/Ge modules, 2 experiment modules SMEX  Lite Solar Array, but not Modular Spacecraft Bus Light-Concentrating Photovoltaic (LCP) experiment module Triple-Junction solar cell experiment module Launched 3/4/99 WIRE (Wide-Field Infrared Explorer) Mission: Detect and measure properties of “Starburst” galaxies Primary mission failed due to premature opening of IR telescope lid, venting of solid hydrogen coolant Subsequently used for astroseismology investigations and as a test bed

18. GSFC 18 SMEX  Lite Modular Solar Array Architecture Missions Using SMEX  Lite Modular Solar Arrays (Cont) Earth-Sun L1 Orbit 2-5 year mission 2 Wings, 2 panels per wing 10 modules per inboard panel, 8 modules per outboard panel 500 watts EOL solar array power First mission to use modular spacecraft bus Completed Integration and Testing In storage awaiting shuttle launch opportunity Mission: Measure radiant power emitted by sun-lit side of earth Measure ozone and cloud coverage Measure solar wind and magnetic field characteristics TRIANA

19. GSFC 19 SMEX  Lite Modular Solar Array Architecture WIRE Solar Panels With Experiments WIRE -X Panel with LCP Module GaAs solar cells Mini-trough reflector for each cell Performed successfully in orbit Reported at 2000 IECEC WIRE +X Panel with Triple- Junction Module 21.7% efficient, 1 Sun AM0, 28°C 2 strings of 2 x 4 cm solar cells Performed as predicted in orbit Reported at 1999 AIAA Space Technology Conference

20. GSFC 20 SMEX  Lite Modular Solar Array Architecture Triana Solar Panels Integrated to Spacecraft

21. GSFC 21 SMEX  Lite Modular Solar Array Architecture Conclusions  SMEX  Lite Solar Array is flying on WIRE spacecraft –Will fly on Triana spacecraft  Advantages: Cost, Schedule, Technology Experiments  Disadvantages: Not optimized for each mission, cost of maintaining inventory  After the WIRE mission, SMEX project converted to Principal- Investigator mode, in-house SMEX project office closed.