The mount on the top of the 747 (the Shuttle Carrier Aircraft) for the drop tests was very similar to the one used throughout the program for ferry flight. The major difference was that the legs on the forward support strut for the drop tests were 13 feet long instead of the normal 8.5 feet long used for ferry flight, and included a fairing/drag strut on ...
For a rocket or spacecraft not to be reused, pyrotechnics should be more reliable, less weight and less components. No need for pressure tanks, regulators, hoses, valves and pistons. Redundant detonators are easy and were used with success. Redundant valves are more difficult and increase weight.
There are decades of experience using pyrotechnics with ...
For Apollo: more nuts than bolts, but vastly more non-threaded connectors
Table I of Apollo Experience Report: Spacecraft Pyrotechnic Systems, NASA Tech Note D-7141, lists all of the pyrotechnics above the Saturn booster (e.g. the CSM, LM, escape tower, etc.). Of the more than 210 pyrotechnic devices, 8 were nuts and 4 were bolts:
4 frangible nuts held the ...
I found a document about that theme:
Apollo Spacecraft & Saturn V Launch Vehicle Pyrotechnics / Explosive Devices
More than 210 pyrotechnic devices per Apollo Mission.
All devices required high reliability and safety
Most devices were classified as either crew safety critical or mission critical.
When complete system redundancy was ...
It's nuts to the shuttle, 16 to 9
Launchpad to stack connections
4 bolts with frangible nuts held each Solid Rocket Booster (SRB) to the pad.
Each solid rocket booster has four hold-down posts that fit into corresponding support posts on the mobile launcher platform. Hold-down bolts hold the SRB and launcher platform posts together. Each bolt has a nut at ...
Source: Apollo Experience Report: Spacecraft Pyrotechnic Systems
LES = launch escape system (carries the CM away during an abort)
CM = command module (the main crew compartment)
SM = service module (uncrewed compartment with engines, equipment, and fluids)
LM = lunar module (lands on the moon)
SLA = spacecraft lunar-module adapter (conical part ...
#22 - explosive bolt for opening the top cover
As you can see in the diagram, the explosive bolt (#22) is in a comfortable environment inside the capsule, protected by thermal insulation (#11).
I know of at least one NASA pyrotechnic failure, although it was arguably not really the fault of the pyros themselves. It occurred on the Skylab 1 launch in 1973, the then-unmanned space station itself on a modified Saturn V. The interstage ring between the first and second stage failed to detach from the second stage because the linear shaped charge (LSC) ...
Sometimes they can do their job a little too well, or blow out some stuff when they're not supposed to, but I've never heard of one failing. They are normally used in a redundant pair fired close to simultaneously where either one will do the trick. The electronics firing them are also redundant. If your pyro fails to do its job, I'll be willing to bet 20:1 ...