We know that oxygen is the "king" of oxidizers:
- non-toxic (unlike fluorine)
- only an oxidizer (potassium nitrate, for example, comes with K and N which aren't what we want)
- no need for catalysis ($H_2O_2$)
But with all that being said, we still have to contain it inside a very cold tank (90K) or a very pressurized one (so very heavy…).
With all that in mind, would it be a good idea to use nitrogen dioxide ($NO_2$) and/or dinitrogen tetroxide($N_2O_4$) to stabilize the $O_2$? (I mean raising its boiling point.) It would reduce the need for cooling machines (not cheap) while letting the mix be a good oxidizer.
EDIT 1 : As Organic Marble pointed out it seems that $N_2O_4$ could replace $NO_2$ in the question. But because $NO_2$ and $N_2O_4$ are always in chemical equilibrium, filling a tank with one of them is, I guess, filling it with both of them ?
And if any of you think of another good oxidizer that would do the trick, feel free to share the idea!