If you have the ability to put together a team that can raise a few hundred million in venture capital to go after a few big government contracts, then maybe. There's a reason why some markets are dominated by essentially two major players.

Not sure where the $70 billion valuation comes from either, but if you add together the market capitalization of Boeing, Lockheed Martin and SpaceX you're still under $100 billion. Boeing and Lockheed Martin also make other stuff.