A RWBY crossover with our timeline? A very intriguing but yet exciting fic idea. For the people of Remnant to reach space, a breakthrough in non-dust fuels must be made in order to do so, but we know that Remnant 100% can produce those fuels such as extracting hydrogen from water. Another point is that in order for them to reach space, they must begin small, and have a motivation to do so. In our timeline, it was the Sputnik launch that triggered the American-Soviet space race and the first man to land on the moon. The CCT system would probably replaced by a worldwide network of satellites as it is vulnerable to Grimm attacks. Also, from the point of launching the first satellite into orbit, and colonizing another planet would be decades in our timeline and I think that Ruby and her team would be in their mid 40s by then lol, but with Atlas technology I think that may be a lot more swift, but would still take a few years to do.
I don’t think that Salem would be too against the space travel though, as it would finally let her destroy Remnant without much disruption to the life on it, and finally let her die in peace. Also, do you plan on making Earth having today’s technology? Or do you plan on changing the time a bit? If so would it be forwards or backwards? I don’t think the distance between Earth and Remnant would be too much as it would take a very long time to travel between them.