I think that the lack of the crusades would seriously hinder the technological development of Europe. Many new inventions were learned in the crusades, and it is not like the crusades signifigantly hurt Arab scientific learning.
You are aware that the Catholic church was pretty much the sole custodian of scientific knowledge in the dark ages right? Without the church, chances are Europe would be just emerging from the Dark Ages now.
Although the graph is very Euro-centric it does bring up a good point: The dark ages really left Europe in the crapper for a while. If the Roman Empire never falls (probably due to the fact that there is no Christianity around) it will continue to advance although certainly not at the speed the graph suggests.
The crusades only brought scientific advancement to the West because they were the keepers of what the Roman Empire had left behind. With the Roman Empire around there will be competition between both most probably resulting in faster scientific advancement.
Also yes the Catholic Church was the sole custodian of scientific knowledge for a very long time. Without it Europe would be emerging of the dark ages right about now. But had it not been there in the first place there would be no dark ages therefore scientific halt. I know it is a bit of a paradox but its true.
I think that with out the fall of the Roman Empire but still keeping enough enemies / rivals around it for competition. Space could have been reached in the 1700s.
However Rome has a few disadvantages that it needs to get around. Fist and foremost a better numerical system: theirs suck. That was one important thing the crusade brought.
Though it all depends on the drive for exploration that develops.
The other question is, what is the latest possible Space Discovery, once again with a POD pre 1800s and post 1800s
