Humans on Mars by 1970

[iancampbell]

As far as the use of Orion pulse craft in OA, the Cybiota use them - they aren't particularly bothered by EMP effects since they mostly use biotechology in their civilisation, such as it is.
http://www.orionsarm.com/eg-article/480d35f9a8ecd

Perhaps some of the lost and isolated colonies that were cut off by the Version War and other major events, like the Oracle War and the Gehenna event, were forced back to a 20th century level of technology; a quick and dirty way to get back into an interplanetary stage of development would be to use boom-boom ships into orbit.

Yup. One possible reason why ground-launched Orion might get developed is because either the resources for being nice about it no longer exist (say, if we spend too long getting off this rock and resources get depleted) or if we really need quick-and-dirty. The former was explored in the Poul Anderson novel "Orion Shall Rise" and the latter in "Footfall".

As for EMP effects - well, probably so. An easy way to avoid that problem is to launch from somewhere a long way from anywhere - maybe a dedicated floating platform, itself EMP-hardened, in the middle of an ocean.

I suppose that the point is really this: Until we get more advanced technology, the best way of getting large loads into orbit is to use nuclear technology of some sort, simply because of the huge mass/energy ratio available - and the only way to use that which we have right now is uncontrolled, i.e. bombs.