Before the "Other World" business starts up Waldo is a hard sf story. I enjoyed reading the description of Waldo's free-fall habitat; given the lack of the computerization, I think it still holds up.
Heinlein was noted for doing his homework in the settings of his stories. For example, the orbital parameters of Waldo's home are consistent with physics. But what are we to make of this discussion about which spacecraft to take up to "Wheelchair"?
I'll have you there in three shakes. That tub of yours probably won't do over five hundred, and Wheelchair must be all of twenty-five thousand miles up.
What can the 500 refer to? The discussion is in English units; surely Heinlein didn't think a craft capable of 500 mph could make it into orbit?