[heidtn]

As someone who works for a space company that was effectively bootstrapped, there are 2 ways I've seen to do it.

1. Government Contracts - this is what my company did. Ground demonstrations to parabola tests to ISS payloads. It's a long hard road and has a lot of NASA bureaucracy, but we just won our first 100MM$ contract and only did one raise 7 years after the company was founded.

2. Build something a big Aerospace company needs - there's a lot of this these days. Company's like Gomspace are building tools for cubesats with minimal startup costs. This is the more independent route, but comes with the challenges of convincing a risk averse industry to use something that hasn't been tested in the correct environment.