There have been times I've planned a manned orbital, for instance, but when I go to assemble it the hardware isn't quite ready and I'd like to fly an unmanned orbital instead. That would be a really handy option, but . . . is it realistic? Can a manned mission be changed to a dummy one at short notice like that, or do dummy missions require substantial preparation as dummy missions (to fine-tune the automation, etc.)? Does anyone know? (I wouldn't want to do this if it's not a realistic option.)