Tej yam ntxwv ntawm lub zog ntawm planetary
(1) Lub hnub iav, lub ntiaj teb cov kab thiab lub nplhaib sib npaug yog concentric, uas yog, tig ib ncig ib txoj kab ntau. Qhov no tuaj yeem tshem tawm cov khoom sib txuas rau theem nrab thiab cov theem nrab xws li cov neeg siv hauv cov ntawv tsav nkoj;
(2) Tag nrho cov qeeb ib txwm nrog mesh sib, thiab tsis tas yuav qis rau cov iav thaum hloov, yog li cov kev sib txhuam thiab hnav yog me thiab lub neej ua haujlwm ntev;
(3) Cov qauv yog yooj yim thiab compact, thiab nws cov load yog muab faib rau ntau tus hniav uas muaj zog;
(4) Muaj ntau lub iav muaj pes tsawg.