bˈeɪɾə tˈuː mˈʌst biː nˈɑːnnˈɛɡətˌɪv; ˈʌðɚwˌaɪz, ðə ɹˈeɪdɪəs ʌvðɪ ˈɔːɹbɪt wʊd vˈɛɹi ˌɛkspənˈɛnʃəli ɐwˈeɪ fɹʌm ɪts ɪnˈɪʃəl ɹˈeɪdɪəs.
β2 must be non-negative; otherwise, the radius of the orbit would vary exponentially away from its initial radius.