On Feb 10, 7:56*pm, Brian Thorn wrote:
On 2012-02-10 09:15:13 +0000, Yeechang Lee said:

In retrospect we know that the O-ring issue that destroyed Challenger
was inevitable. It had almost happened in earlier flights and would
likely have happened on some winter day sooner or later. That said,
let's say it doesn't ever happen. Maybe because it's diagnosed, or
NASA and Thiokol listen to Boisjoly and require a certain outside
temperature for launches, or NASA just never schedules a launch on
that cold a day.

The relatively simple joint heaters would have been enough to resume
flying while the field joint was redesigned, I think.

NASA flew nine shuttle flights in 1985,

…and came 15 seconds away from a tenth on December 18, 1985.

In calender year terms, Brian. They actually flew 10 missions within a
one year span from STS-51-C launched on January 24, 1985 to STS-61-C
which launched January 12, 1986. Had STS-51-L not been delayed by
STS-61-C, it would have been 11 in 12 months, and Challenger would
have been launched in warmer weather, thus a launch failure would not
likely have occurred.

Also along similar thinking; Discovery, which launched four times in
1985, actually had launched six times in a one year period from first
flight on August 30, 1984 to it's last pre-Challenger flight on August
27, 1985. So theoretically you could have orbiters doing 4-6 flights a
year, if dedicated OPFs were available. Say one OPF at Vandenburg, and
three at KSC, which allows all four vehicles to be processed
simultaneously. That means between 12 and 18 flights a year, if ET and
SRB production and processing permits it. Atlantis between STS-51-J
and and STS-61-B had demonstrated a 55 day turnaround between flights
(45 days minus the days lost by ferrying Atlantis between Edwards and
KSC), so ramping up to 7 flights for one orbiter was theoretically
doable back then. Columbia probably would never be able to manage more
than 4-5 flights a year given her history of being chronically
stricken with technical issues compared to the other orbiters.

a rate it would never hit
again although it flew eight per year several times in the
1990s. Without losing Challenger, how many flights could NASA have
expected to have flown a year?

If Challenger had not been destroyed (say, the windshear did not cause
the leak to reopen at altitude), and the severe damage of the o-rings
was found after SRB recovery, this should have been sufficient for
Thiokol's engineers to effectively force a moratorium on Shuttle
launches until the joint heaters could be implemented, resuming flying
say in 1987. During that time, the Shuttle program could well have
caught its breath and built up a stockpile of spare parts that would
have made meeting the flight rate somewhat easier (this was done after
Challenger.) I think realistically the program would have topped out
around 15-16 per year, 12 from KSC and 3 or 4 from SLC-6.

Agreed, though SLC-6 would have likely put a huge damper on things for
a while once the actual fueled testing of Columbia at that facility
revealed the flaws there.

*I understand it was contemplating
perhaps two dozen a year with the four shuttles; was such a pace
feasible?

No. External Tank production would probably have peaked around 18 per
year. Michoud could handle *a little more, but I doubt they would have
really pushed that hard. They'd have reduced the flight rate to keep
things under control.

They'd have had no choice, looking back on it. There were other
technical issues that would have forced delays or flight rate
reduction or caused a catastrophic loss.

*If not that many, a dozen? 15?

Probably, if they funded a third OPF at KSC (without sacrificing SLC-6.)

Would the agency order a
fifth shuttle with such demand?

No, they would have backed out of the commercial market anyway,
relieving pressure on the 24-per-year goal. Arianespace would have
taken more commercial payloads regardless of Challenger.

Why? STS had huge cargo capacity for most of the then existing
satellite classes. Just load up a bunch of satellites into one mission
as was done for STS-41-D.
-Mike