The Venerean nuclear ramjet

I know this sounds like a porno title but hear me out.

In Venerean conditions a ramjet requires hundreds of megawatts to superheat the air, so (at 458 * area wattage) we're still not solar-powering this thing.

But nuclear Pluto emits little "waste heat" since all the hotness is for blasting back compressed air coming at us from the front. When it's not running, it flies with the flotilla or is floated in the clouds, and is loaded there; it is assisted into its Mach 3-6 run by single-use thrust, either chemical rockets or some battery-powered aeroplane. At first...

Once aloft the ramjet circles the 40075 km equator - rather, the 40515 km 70km-altitude circle - at Mach 3. 40515000 / (3*315) = 42873 seconds. So an even twelve hours. More likely half that, at Mach 4.5.