Solar Energy and Zoë power Life in the Atacama 2005 Science & Technology Workshop January 6-7, 2005 James Teza Carnegie Mellon University

Life in the Atacama 2005 Science/Technology Workshop 1NASA Ames Research Center / Carnegie Mellon Zoë Power in 2004 Advanced Triple Junction solar array Cell efficiency 23.3%, system efficiency 21.7% Area 2.4 m 2 Batteries Lead acid (used to Oct 14) 1000 Wh Li polymer (Oct 14 through 18) total 3k Wh Power management and distribution (PMAD) system Monitored of power system parameters bus voltages and currents solar input currents load currents (locomotion and hotel) Load switching hardware in place but not operational Acquired insolation data at weather station

Life in the Atacama 2005 Science/Technology Workshop 2NASA Ames Research Center / Carnegie Mellon SOLAR ARRAY 1 Zoë power system - overview MPPT 1 BATTERY 1 AND CONTROLLER LOCOMOTION (FRONT) SOLAR ARRAY 2 MPPT 2 BATTERY 2 AND CONTROLLER LOCOMOTION (REAR) HOTEL DC/DC COMPUTING SCIENCE INSTRUMENTATION SENSORS COMM PMAD CONTROL & LOGGING PMAD SWITCHING

Life in the Atacama 2005 Science/Technology Workshop 3NASA Ames Research Center / Carnegie Mellon Do we have enough energy available? Weather station logged solar radiation data each minute Sensor Thermopile, spectral range: 305 to 2800 nm Data logged to disk within station Station located within about 10 km of science site B, 20 km of site C

Life in the Atacama 2005 Science/Technology Workshop 4NASA Ames Research Center / Carnegie Mellon Solar flux – Atacama - September 34567Sol

Life in the Atacama 2005 Science/Technology Workshop 5NASA Ames Research Center / Carnegie Mellon Solar flux – Atacama - October Sol 10Sol 11 Sol 14 Sol 13 Sol 12

Life in the Atacama 2005 Science/Technology Workshop 6NASA Ames Research Center / Carnegie Mellon Solar energy in Atacama Available solar energy per day for flat collector using logged data Average: 2.52 x 10 7 J per day (period 9/8/04 through 10/9/04) Sol Sol

Life in the Atacama 2005 Science/Technology Workshop 7NASA Ames Research Center / Carnegie Mellon Available electrical energy on Zoë Calculations based on logged data ATJ panel area 2.4 m 2, Cell efficiency – 23.3%, MPPT efficiency – 97% Array network efficiency (diode) – 96% Average: 1.35 x 10 7 J per day (period 9/8/04 through 10/9/04) Sol Sol

Life in the Atacama 2005 Science/Technology Workshop 8NASA Ames Research Center / Carnegie Mellon Zoë electrical load energy – logged data

Life in the Atacama 2005 Science/Technology Workshop 9NASA Ames Research Center / Carnegie Mellon Solar input energy from array – logged data

Life in the Atacama 2005 Science/Technology Workshop 10NASA Ames Research Center / Carnegie Mellon Energy balance – logged data

Life in the Atacama 2005 Science/Technology Workshop 11NASA Ames Research Center / Carnegie Mellon Energy required per day Average Power (W) Time per day (h) Energy per day (Wh) Energy per Day (MJ) Locomotion Hotel Spectrometer FI Hibernation (estimate) Total15.0 Issue: Available electrical power on Zoë marginal for expected locomotion and science loads

Life in the Atacama 2005 Science/Technology Workshop 12NASA Ames Research Center / Carnegie Mellon Issues with logged data Weather station data contained gaps Spectral mismatch of solar sensors and solar cells Spectral response of ATJ cells about 450 to 1600 nm Thermopile data from the weather station may over estimate available insolation PMAD data log contained gaps Start of day charging was typically not logged PMAD time stamps incorrect Initial PMAD logs (before site C) corrupt

Life in the Atacama 2005 Science/Technology Workshop 13NASA Ames Research Center / Carnegie Mellon 2004 results Positive ATJ solar arrays performed as expected Lithum polymer batteries appeared to perform well - typically ended day at 60 to 77 % of full charge Negative Power available marginal for expected loads (computing and FI) PC104 stacks not as robust as hoped PMAD, weather station and state estimator all experienced faults Electrical system several faults Softstart relay failure at start of mission PMAD problems during Site B – faulty connection PMAD logging not automatic – missing data PMAD switching not implemented – hardware exists (mostly) but not software PMAD power backup – implementation faulty and unreliable Li polymer cell balance is critical for extended operation

Life in the Atacama 2005 Science/Technology Workshop 14NASA Ames Research Center / Carnegie Mellon 2005 Issues Power switching required to fulfill objectives Complete PMAD hardware implementation PMAD Software design Robust system - extensive testing Consider lower power options – if any Mission scheduling to maximize insolation and minimize load Li battery testing and spares Better battery model for planning extended operation