Are Ionospheric Scramjets possible?

[Apollo19]

I was doing some Wikipedia browsing, and I came across the concept of Scramjets for spaceplanes. The highest estimate for a top speed of a scramjet in atmosphere is Mach 25, which is approximately orbital velocity. The ionosphere contains high levels of O, so would it be possible to fly a scramjet aircraft in it (at approx. 100km)?

 

[mfb]

High fraction does not mean high amount - the ionosphere is extremely thin. You don't get much oxygen there, and not much lift. You need a very high speed to counter this. 100km is at the Kármán line, where the required flight speed reaches the orbital speed - your "plane" becomes a satellite.

 

[Apollo19]

Thanks. Thing is that at Mach 25, surely even though it is very thin, you are taking in some? Do you know if such a scramjet would work, even if it had very low thrust? And for the sake of the theory, assume that there is no drag.

 

[mfb]

I'm sure you can burn something, but airplanes are always a quantitative problem.
The air is thin, but at that speed drag is relevant.