Development of critical parameterEstimator models for space batteries

Abstract

In the space battery arena there is a continuous drive towards newlinedesigning and producing lighter more robust reliable longer lasting cycle newlinelife and calendar life higher energy density batteries with smart battery newlinemanagement system Power requirement and life time requirement of the newlinesatellites are also increasing Traditionally Nickel Cadmium and Nickel newlineHydrogen batteries were used in space applications Significant improvements newlinehave been made in NiCd and NiH2 batteries to meet the need and they have newlinereached their technological limit Cadmium has been the object of growing newlineconcern among environmentalists These trends dictate use of Lithiumion newlinebatteries which satisfy most of the space battery requirements including high newlineenergy density longer life low self discharge etc newlineTypical Low Earth Orbit LEO spacecrafts batteries have to newlineundergo 15 charge discharge cycles in a day The pattern will repeat year after newlineyear There will be roughly 5500 cycles in a year The life time of the newlinebatteries in LEO will be 5 to 8 years Since larger number of cycles involved newlinethe allowed Depth of Discharge DOD will be generally 205 Lower newlinethe DOD longer the cycle life The discharge will be for 35 minutes and the newlinecharge duration will be around 65 minutes In LEO orbits the batteries are newlineused continuously without rest newlineThough the number of charge discharge cycles is less in Geo newlinesynchronous orbit GEO the life time is 15 to 20 years There will be two newlineeclipse seasons in a year extending for 45 days each During solstices periods newlinethe battery is dormant Even during the 45 days eclipse the eclipse duration newlineincreases from 10 minutes to a maximum of 72 minutes and falls back again newlineIn a 15 year period the batteries will undergo a maximum of 1350 charge newlinedischarge cycles So we go for DOD of 60 to 80 in GEO In GEO newlinespacecrafts battery degrades both due to cycling as well as storage when the newlinebatteries are not at all used newline newline newline newline newline newline newline newline newline