This is a two-part question: a) We know Apollo 1 burned up on the launch pad during a live test, but was there a full, unmanned test like Artemis 1 will undergo? b) Whatever tests Apollo endured, wouldn’t the Apollo design be locked down at some point? So, why did Apollo 13 experience a design change leading to the Apollo 13 crisis? In short, if it ain’t broke, why fix it?
They did do several unmanned tests of the hardware.
As for the design changes, the point was, Apollo 1 was broke, so they did have to fix it.
Apollo 13 didn’t have a design change from the other manned Apollo craft (save for Apollo 1). The problem, such as it was, was always there. It was after Apollo 13 that the CSM was changed so that a single failure wouldn’t cause complete loss of fuel cells, and they added an extra oxygen tank on the other side of the SM.
I believe the Apollo hardware was upgraded throughout the program - there were several “blocks” of spacecraft that had certain changes, similar to what’s done with airplanes.
There were several versions of the lunar modules. The earliest ones were supposedly too heavy to land, while the later models could carry heavier loads (including the rovers) to the surface.
I’d have to do actual research to be more precise.
In hindsight, we know they broke things by changing things… but they thought they were fixing it.
There was a problem ( electromagnetic interference ) and solution with the wiring to the Oxygen tank’s “shelf”, the compartment that holds the various tubes and wires in place , and holds its weight while accelerating, that meant that the Oxygen shelf for oxygen tank 2, taken from CSM106 - Apollo 10’s - and once modified it was put into CSM109 for Apollo 13. This is possibly a trigger for the Apollo 13 event, maybe not. Was that electromagnetic interference worth fixing ? Maybe it wasn’t so serious ?
Logs noted that the problematic shelf was dropped while removing it, but only 5cm, a few inches, and not damaging … This just highlights its not easy to remove and install the thing, there may have been other unlogged incidents… such as inadvertently loosening the filler tube fitting, and then not tightening it back up properly… ? Trying to fix things can break things, was it worth it ?
So they should test very well after a change… but they didn’t test it well enough - they threw it into CSM109, Apollo 13, leaving it there without testing.
We know it wasn’t tested… Because during Apollo 13’s Countdown Demonstration Test in March, they detected the subject oxygen tank was not emptying via the filler tube… Ok , who needs to empty the oxygen via the filler tube ??? Was that correct thinking ? No ! Its a dramatic change, they didnt even know why it wasn’t emptying. They didn’t think “Our filler tube might have a serious flaw … we need to KNOW FOR SURE it does not .” It didn’t occur to them that it was acting like the valve on a football, a tube that opens under the inflow, but squashes closed when held against its aperture. When it wasn’t meant to do that, it could could crack and let all the gas out to space ??? But no they didnt even find out WHY … yet the ground equipment had no problem, and so the problem was probably there in the filler tube, where it could be folded by the gas pressure …
What they did was use a workaround, I don’t know its been determined if this had been tested before,
but they used the heater to speed up draining of the oxygen via the inhabitable spaces of the CSM…
Instead of pumping liquid oxygen out, they boiled it in the tank., using the heater that is there to ensure the flow rate is is at the maximum needed on space.
Why bother doing this work around ? Well ok, they wanted to get the CSM to the standard starting point, so as to not test out the unusual situation. But which was less risky, boiling off the O2 , or just leaving it there until actual lift off ? Well ok, they might have thought the 2nd filling would be a test of its reliability… if the tank could be filled, that would test it was really just a temporary problem, like ice due to the rapid depressurisation… In hindsight we can say that it probably had the football valve effect going on.
But there had been another change, though back in 1965, that on the ground, they had changed from using the 28 volts that would be used in space, to 65 Volts, so that the flow of oxygen out was faster. but the increased power wasn’t available in space… But, they left the thermostat in use , as being one rated for 28 volts ONLY, neglecting that specification had changed… So right there, why make a change ? Its only testing the equipment works, why not just test it for a short time and not test it to fully empty ? But they needed to fix the ability to empty the oxygen out, so they wanted to be able to more rapidly cycle the oxygen in and out… eg for safety after the Apollo 1 incident, they wanted to be sure to not have pure O2 …
They had plenty of time to test it out, they made the change in 1965… with the problem from it occurring in 1970. But they left the thermostat problem there and they were cooking their electrical wires… this may have been the reason they had detected “electromagnetic interference”… the short circuits from the cooked wires… but they didn’t test the “fixed” device thoroughly, they just followed instruction and then ticked the box … without testing, they left it broken for the Apollo thirteen launch pad test. Broken i a different way perhaps, but perhaps broken in the same way too.
So they had their reasons for the lesser changes,but they did make a serious mistake in not diagnosing the cause of the inability to empty the O2 via the filler tube… they flew with an UNKNOWN change.