The Mars Exploration Rovers (MER) program posed a significant engineering and technology challenge. Now that the Rovers have operated beyond their original design life of three months by nearly a factor of four it is clear that the challenge was met and far exceeded. A key to the success of MER has been the enhanced power provided by the cruise and Rover solar arrays. 3enefiting from a nearly 50% improvement in cell efficiency compared to the single junction GaAs cells used on Pathfinder, the MER designs were subject to many constraints both in design and in operation. These constraints included limited available panel area, changing illumination levels and temperatures, and variable shadowing, atmospheric conditions and dust accumulation for the rovers. This paper will discuss those constraints and their impact on the design. In addition, flight data will be provided to assess the performance achieved during the mission. INTRODU CTlONFollowing the failure of Mars Climate Orbiter and Mars Polar Lander in December, 1999, and the subsequent failure investigations, a decision for the 2003 launch of the two MER spacecraft (and their Rovers) was made later than optimal. Although some time was gained by basing the design on the successful Pathfinder . mission, requirements differed enough so that the resulting array designs shared some (cruise array) or nothing (Rovers) with the earlier design. Array requirements were dictated by spacecraft power requirements and the operational environments. The major requirements and constraints are discussed below for the m i s e and rover arrays. DESIGN REQUIREMENTS Cruise ArraysThe cruise array substrate 'design was basically that of the Pathfinder design. A large annular fixed array assembled from four equal size quadrants was attached to aluminum struts on the rear side. The cruise array would provide power following launch to charge up the batteries 0-7803-8707-4/05/%20.00 02005 IEEE. and operate the spacecraft ( S K ) during the cruise from Earth to Mars. Since the S/C was spin stabilized and pointed primarily towards the Earth for communication, a maximum array sun off pointing of 40 degrees was required.Due to the cruise array configuration, with the inner portions situated over propellant tanks and the entry module, thereby blocking the radiative view factor to space, cell temperatures would vary across the a m y predominantly radially, with the highest temperatures nearest the center. Superimposed on this was the gradual temperature decrease as the SIC traversed from the orbit of Earth to the orbit of Mars (-1.5AU). The impact of reduced intensity and temperature as the SIC traversed to Mars impacted the array performance by a change in cell current and voltage. Additionally, at Earth it was necessary to allow for any possible unfavorable orientation following launch prior to achieving full attitude control. The result of these requirements meant that an allowable maximum temperature of 9OC might be achieved at I AU falling to -2OC at Mars.In order to take advantage of i...
Jet prop.tSian Laboratoty C&hia Imtitde of Technology 4800 Oak Grove Drive P&m c4 91109 A number of JPL missions, either active or in the p l d g stages, require the accurate LILT flew intensitylow temperatme) clmracte* of tripk-jumtbn solar, Although triple ignetiOn LILT pwloraaanee was reported as recently as 2002, there has been an evolutionary advance in cell technology by both U.S. space cell manufacturers that, for mission design pnrposes, effectively obde&% the earlier data As a d t , JPL M W e d a program to develop a database for the LILT performauce of tbe new high performance t s p k jMction sdnr eel4 apL obtained Emcore Advanced Triple J t i O a CIC assemblies and Spectrdab Ultra Triple JuactiOn CIC assemblies. 'These cells were tested at temperature-intensity ranges designed to cover applicatioas between 1 and 5. 1 8 AU solar distances. 1 MeV deetron irradiatks from 2 5 E14 to 1 El5 w m performed on the d s to evaluate the COBdbiaed effect ol particulde radirdion m d LILT coQdiitio1l8, The e $ k t of IlLT conditions was OBServed to igcnr aq htcrerrse m the variptioe of d l pdomances tBpt at shula4ed 5.18 AU eonditkms the average perfonhance was approximately 3dY0 with the best cells measuring between 32 and 34% efficiency. The 30Ye average efficiency compares with appmximately BY0 average efffifiiency measured on earlier tahobgy t~p k~R S O h U t Z k Nomenclature low intensity, low temperature S h l t cilcuit curretlt maximum power fillfactor o p e n~v o l t a g e maximum power voltage maximum power current airI1.tasszero cell-interconnect-cover advanced triple junction (Emcore) ultra triple junctm (specttoab) astronomical unit (average distance between Earth and sun)
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