See, that is the mistaken assumption right there. They don't have time. We
can reach space but since it doesn't pay very well, we don't use that ability much. Remember the previous space race? That was purely for
bragging rights. But if we know hostile aliens are in space and killing them resolves an existential threat? Dragons deploying armed satellites bigger and more heavily armed than their ships are going to be planned within hours and launched within weeks. Steely Eyed Missile Men with fifty cups of coffee are going to start working up designs for surface-to-space missiles immediately. The amount of budget redirected to stopping the aliens would be utterly staggering as every nation on Earth shifts to total war footing and all their excess is channeled straight into defending earth.
We'd go from a cottage industry hand-making small runabouts to building
Liberty Ships.