▁Soviet ▁Union ▁made ▁most ▁of ▁their ▁launch es ▁in ▁the ▁ 1 9 7 0 s ▁and ▁ 1 9 8 0 s . ▁ ▁High er ▁alt itudes ▁ ▁At ▁higher ▁alt itudes , ▁where ▁air ▁drag ▁is ▁less ▁significant , ▁orb ital ▁decay ▁takes ▁longer . ▁S light ▁atmos pher ic ▁drag , ▁lun ar ▁perturb ations , ▁Earth ' s ▁gravity ▁perturb ations , ▁solar ▁wind ▁and ▁solar ▁radiation ▁pressure ▁can ▁gradually ▁bring ▁de br is ▁down ▁to ▁lower ▁alt itudes ▁( where ▁it ▁dec ays ), ▁but ▁at ▁very ▁high ▁alt itudes ▁this ▁may ▁take ▁mill enn ia . ▁Although ▁high - alt itude ▁or bits ▁are ▁less ▁commonly ▁used ▁than ▁LE O ▁and ▁the ▁on set ▁of ▁the ▁problem ▁is ▁slower , ▁the ▁numbers ▁progress ▁toward ▁the ▁critical ▁threshold ▁more ▁quickly . ▁ ▁Many ▁communic ations ▁sat ell ites ▁are ▁in ▁ge ost ation ary ▁or bits ▁( GE O ), ▁clust ering ▁over ▁specific ▁targets ▁and ▁sharing ▁the ▁same ▁orb ital ▁path . ▁Although ▁veloc ities ▁are ▁low ▁between ▁G E O ▁objects , ▁when ▁a ▁satellite ▁becomes ▁der el ict ▁( such ▁as ▁Tel star ▁ 4 0 1 ) ▁it ▁assumes ▁a ▁ge os ynchronous ▁orbit ; ▁its ▁orb ital ▁incl ination ▁increases ▁about ▁. 8 ° ▁and ▁its ▁speed ▁increases ▁about ▁ ▁per ▁year . ▁Imp act ▁velocity ▁pe aks ▁at ▁about ▁. ▁Or b ital ▁perturb ations ▁cause ▁longitude ▁dr ift ▁of ▁the ▁in oper able ▁space craft ▁and ▁pre cess ion ▁of