1 ), ▁pp .   3 5 7 ▁– ▁ 3 6 0 . ▁ ▁Donald ▁K ess ler ▁and ▁Bur ton ▁Cour - Pal ais ▁( K ess ler ▁ 1 9 7 8 ), ▁" Coll ision ▁Fre quency ▁of ▁Art ific ial ▁Sat ell ites : ▁The ▁Cre ation ▁of ▁a ▁Deb ris ▁B elt " ▁Journal ▁of ▁Ge oph ys ical ▁Research , ▁Volume ▁ 8 1 , ▁Number ▁A 6 ▁( 1 ▁June ▁ 1 9 7 8 ), ▁pp .   2 6 3 7 – 2 6 4 6 . ▁ ▁Donald ▁K ess ler ▁and ▁Phill ip ▁An z - M ead or , ▁" C rit ical ▁Number ▁of ▁Space craft ▁in ▁Low ▁Earth ▁Or bit : ▁Using ▁Fragment ation ▁Data ▁to ▁E valu ate ▁the ▁St ability ▁of ▁the ▁Or b ital ▁Deb ris ▁Environment ", ▁Pres ented ▁and ▁the ▁Third ▁European ▁Conference ▁on ▁Space ▁Deb ris , ▁March ▁ 2 0 0 1 . ▁ ▁( Te chn ical ), ▁" Or b ital ▁Deb ris : ▁A ▁Techn ical ▁Ass ess ment " ▁National ▁Academy ▁of ▁Sciences , ▁ 1 9 9 5 . ▁. ▁ ▁Jim ▁Sche fter , ▁" The ▁G row ing ▁Per il ▁of ▁Space ▁Deb ris " ▁Popular ▁Science , ▁July ▁ 1 9 8 2 , ▁pp .   4 8 ▁– ▁ 5 1 . ▁ ▁Further ▁reading ▁▁▁ ▁" What ▁is ▁Or b ital ▁Deb ris ? ", ▁Center ▁for ▁Or b ital