How did Shepard's and Grissom's speeds compare with orbital velocity?

Question

As is often said here and in XKCD, an orbit isn't merely high up... it's also going fast. The first two American astronauts -- Alan Shepard and Gus Grissom -- did indeed get "high up" enough to qualify as being in space (well above the Karman line). But their flights were "sub-orbital", and they fell back down before making it all the way around the Earth. Let's see if they were "going fast."

1. What was the maximum speed each achieved by Shepard and Grissom? (You may use whatever units are convenient.)

2. What speed would they have needed to acheive orbit?

3. In percent, how did their maximum speeds compare to orbital velocity?

For further reading:

• Could it be possible to launch a rocket from a balloon?
• What use could be getting to space just for a bit?
• How can Yuri Gagarin's Vostok 1 flight be considered to have been orbital, since he did not go all the way around Earth?

Answer 1

The Post Flight Mission Report for Grissom's flight compares key parameters for the two manned suborbital missions (Shepard's MR-3 and Grissom's MR-4):

The corresponding document for John Glenn's orbital flight gives its orbital velocity.

Assuming the Glenn number is inertial velocity, the percentages are 28.7% and 29.5%.

In metric figures, MR-3 reached 2252 m/s, MR-4 2310 m/s, and Glenn's MA-6 7842 m/s.