That last mission was designated TV-4BU, because it used a remaining test vehicle, which had been upgraded with a new third stage, the Allegheny Ballistics Lab X-248A2 Altair.
Posledná misia mala označenie TV-4BU, pretože použila zostávajúu testovaciu raketu, ktorá mala vylepšený tretí stupeň X-248A2 Altair od firmy Allegheny Ballistics Lab.