What's the minimum airspeed of and unladen 747?

An empty cargo 747-200F with near empty tanks stalls at about 85-90 KIAS or so -

I have no idea how heavy a space shuttle is...

At low altitude, at 15,000 ft mentioned by Rachel -

I would expect these guys to be at 300 KIAS...

Rather slow for a 747 - Vmo (red line) being 383 KIAS -

.

African or European.

Shuttle carrier (developed from -100): Mach 0.6, 397 knots, or 457 miles per hour if you prefer. That's its typical cruise speed. That's because it can only safely fly at 15,000 ft when carrying the shuttle.

The typical cruise speed of an unladen -100 is Mach 0.84, 481 knots or 555 miles per hour if you prefer.

A typical commerical 747 is a -400 and cruises at Mach 0.85, 493 knots or 576 miles per hour. A -400ER (extended range) is able to cruise at Mach 0.855.

A typical commercial 747 will cruise at anything between 35,000 ft and 41,000 ft - thinner air (higher altitudes) generally means a higher airspeed (I believe).

I assume these are pretty much the minimum accepted airspeeds when the aircraft is at its typical cruising altitude. The airspeed will gradually get slower as the aircraft starts to descend.