▁mirror ▁trans it ▁teles cope . ▁FM ▁Radio ▁waves ▁can ▁detect ▁de br is , ▁after ▁reflect ing ▁off ▁them ▁onto ▁a ▁receiver . ▁Opt ical ▁tracking ▁may ▁be ▁a ▁useful ▁early - warning ▁system ▁on ▁space craft . ▁ ▁The ▁U . S . ▁Str ateg ic ▁Command ▁keeps ▁a ▁catalog ▁of ▁known ▁orb ital ▁objects , ▁using ▁ground - based ▁rad ar ▁and ▁teles cop es , ▁and ▁a ▁space - based ▁teles cope ▁( origin ally ▁to ▁distinguish ▁from ▁host ile ▁miss iles ). ▁The ▁ 2 0 0 9 ▁edition ▁listed ▁about ▁ 1 9 , 0 0 0 ▁objects . ▁Other ▁data ▁come ▁from ▁the ▁E SA ▁Space ▁Deb ris ▁T eles cope , ▁T I RA , ▁the ▁Gold stone , ▁Hay stack , ▁and ▁E IS CAT ▁rad ars ▁and ▁the ▁Cob ra ▁D ane ▁ph ased ▁array ▁rad ar , ▁to ▁be ▁used ▁in ▁de br is - environment ▁models ▁like ▁the ▁E SA ▁Meteor oid ▁and ▁Space ▁Deb ris ▁Terr est rial ▁Environment ▁Reference ▁( MA ST ER ). ▁ ▁Me asure ment ▁in ▁space ▁▁ ▁Return ed ▁space ▁hardware ▁is ▁a ▁valuable ▁source ▁of ▁information ▁on ▁the ▁direction al ▁distribution ▁and ▁composition ▁of ▁the ▁( sub - mill imet re ) ▁de br is ▁flux . ▁The ▁L DEF ▁satellite ▁deployed ▁by ▁mission ▁ST S - 4 1 - C ▁Ch allen ger ▁and ▁retrieved ▁by ▁ST S - 3 2 ▁Columbia ▁spent ▁ 6 8 ▁months ▁in ▁orbit ▁to ▁gather ▁de br