John Glenn's Mercury mission

[Peter B]

Okay, not the reality of Apollo, but something that's been sort of sitting at the back of my mind...

Early in his flight, Glenn was informed that he was Go for at least seven orbits, and Glenn repeats that back to the Capcom. Obviously, thanks to the heat shield issue, the mission was terminated at three orbits.

But if he was cleared for at least seven orbits, what was the actual intention for the mission's duration? Did mission planners have a particular duration in mind, or were they going to keep going as long as the consumables would last?

[Sus_pilot]

I think they were referring to the fact that the launch and subsequent orbit was high enough to avoid atmospheric drag for at least that long, so an early landing would not be an issue. 

I think...

[Bob B.]

According to the Mercury-Atlas 6 News Release, January 21, 1962...

FLIGHT DURATION - Depending on literally thousands of variables, the Mercury Operations Director (Manned Spacecraft Center Associate Director Walter C. Williams) may elect a one, two, or three-orbit mission.  That decision will be made only minutes before launch and may be changed at any time during the mission.  Recovery after one full orbit is planned for about 500 miles east of Bermuda; after two orbits, some 500 miles south of Bermuda; three orbits, about 800 miles southeast of Cape Canaveral, Fla.  Each orbit takes about 90 minutes, carrying the craft between 100 and 150 miles altitude, 32 degrees north and south of the equator.

If the mission ends after one or two, the astronaut will be moved to the Kindley Air Force Base Hospital in Bermuda for a 48-hour rest and debriefing.  If the mission goes a full three orbits, he will be flown to Grand Turk Island (Bahamas) for a similar operation before being returned to the mainland.

[bknight]

The original mission was for a maximum of three orbits, as was Scott Carpenter's.  Longer duration missions were Wally Schirra with 6 orbits and finally Gordon Coopers 22 mission that had a lot of problems during the last few orbits.

Edit: Number of Cooper's orbits, I was remembering 34 HOURS