Add example of apply_space_motion
Add example of apply_space_motion

larrybradley/astropy,DougBurke/astropy,StuartLittlefair/astropy,astropy/astropy,larrybradley/astropy,astropy/astropy,lpsinger/astropy,saimn/astropy,pllim/astropy,larrybradley/astropy,mhvk/astropy,MSeifert04/astropy,mhvk/astropy,DougBurke/astropy,lpsinger/astropy,saimn/astropy,aleksandr-bakanov/astropy,saimn/astropy,funbaker/astropy,funbaker/astropy,larrybradley/astropy,dhomeier/astropy,mhvk/astropy,aleksandr-bakanov/astropy,MSeifert04/astropy,astropy/astropy,funbaker/astropy,saimn/astropy,aleksandr-bakanov/astropy,astropy/astropy,lpsinger/astropy,stargaser/astropy,dhomeier/astropy,stargaser/astropy,StuartLittlefair/astropy,bsipocz/astropy,DougBurke/astropy,saimn/astropy,bsipocz/astropy,StuartLittlefair/astropy,astropy/astropy,MSeifert04/astropy,pllim/astropy,MSeifert04/astropy,StuartLittlefair/astropy,bsipocz/astropy,mhvk/astropy,lpsinger/astropy,lpsinger/astropy,mhvk/astropy,pllim/astropy,StuartLittlefair/astropy,dhomeier/astropy,bsipocz/astropy,aleksandr-bakanov/astropy,stargaser/astropy,stargaser/astropy,pllim/astropy,larrybradley/astropy,dhomeier/astropy,dhomeier/astropy,funbaker/astropy,DougBurke/astropy,pllim/astropy