Under the question SN11 was launched in fog. Why not wait for better conditions? I wrote the comment:

armchair totally unsupported theory: the fog presented an opportunity to test the emergency self-destruct system without the accompanying spectacular videos that would echo around the internet years later when they started putting large groups of people in it.

Question: Are rocket self-destruct systems ever flight-tested/flight-proven?

In other words, the self-destruct system of a rocket in flight is intentionally triggered specifically to see what happens.

There are several things that have to work right for this system to perform reliably, including procedures, communications, certainty that propulsion stops, and possibly (I don't know) that the rocket breaks up in to several non-aerodynamic pieces. My thinking there is that if stopping propulsion was the only goal then small pyrotechnic guillotines on the fuel lines would be sufficient.

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    $\begingroup$ Do you mean the system as a whole, or portions of it? $\endgroup$ Apr 1 '21 at 1:32
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    $\begingroup$ As now written, I am unaware of any such test. The piece-parts, sure, they were tested and qualified. I was always jealous of those guys! $\endgroup$ Apr 1 '21 at 1:37
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    $\begingroup$ My understanding is that flight termination systems are specifically designed to open the tankage widely, so that the propellants can mix and burn (relatively) safely, up in the air, instead of doing so at ground level. (The term "unzipping" is often used.) Breaking into high-drag sections (hence with low terminal velocity) is probably a desirable and unavoidable side effect of doing so. $\endgroup$ Apr 1 '21 at 1:41
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    $\begingroup$ @RussellBorogove supposedly the Proton FTS just shuts off the engines. Whee! $\endgroup$ Apr 1 '21 at 1:50
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    $\begingroup$ @OrganicMarble a separate and very interesting question could ask about what exactly various destruct systems are designed to accomplish and how it differs. I hesitate to ask myself because someone will just comment "Obviously, to destruct itself". This question is about complete end-to-end testing of the system. These days I doubt it, but I'm going to add the history tag because a lot of stuff that is understood now wasn't in the past. $\endgroup$
    – uhoh
    Apr 1 '21 at 2:18

Project Highwater

SA-2 and SA-3 were test flights of of the Saturn I booster. Their S-I first stage launched normally, then the remaining fuel was detonated after engine cutoff:

The S-IB Stage Propellant Dispersion System (PDS) will sever each of the nine propellant tanks and disperse the propellants if flight termination becomes necessary. Two exploding bridgewire (EBW) firing units, a safety and arming device (S&A), two EBW detonators, Primacord, and flexible linear-shaped charges (FLSC) make up the PDS (figure 4-72). Primacord assemblies interconnect the FLSC to detonators in the S&A device. The EBW firing units interface with the PDS detonators and the secure range safety command system. If flight termination becomes necessary, the range safety command system (Section 1) will provide signals to arm (charge the EBW high voltage storage capacitor) and trigger the firing units, which deliver high-energy electrical pulses to the EBW detonators in the S&A device (figure 4-73). Explosive leads in the S&A device rotor propogate the detonator explosion to the Primacord and subsequently to the FLSC assemblies. The FLSC assemblies rupture the propellant tanks allowing the propellants to disperse radially from the stage and burn rather than explode. The burning propellants result in only a fractional amount of the theoretical yield if the vehicle should explode. The reliability of Saturn propellant dispersion systems was demonstrated during the flights of SA-2 and SA-3. After S-IB stage engine cutoff a destruct command destroyed the vehicle to release water ballast contained in the dummy upper stage (Project Highwater).

source, p. 4-59

These flights also had dummy second and third stages filled with water, which was intended as an experiment called Project Highwater. The self-destruct systems were successful.

April 25 [1962]

The Saturn SA-2 first stage booster was launched successfully from Cape Canaveral. The rocket was blown up intentionally and on schedule about 2.5 minutes after liftoff at an altitude of 65 miles, dumping the water ballast from the dummy second and third stages into the upper atmosphere. The experiment, Project Highwater, produced a massive ice cloud and lightning-like effects. The eight clustered H-1 engines in the first stage produced 1.3 million pounds of thrust and the maximum speed attained by the booster was 3,750 miles per hour. Modifications to decrease the slight fuel sloshing encountered near the end of the previous flight test were successful.

November 16 [1962]

Saturn-Apollo 3 (Saturn C-1, later called Saturn I) was launched from the Atlantic Missile Range. Upper stages of the launch vehicle were filled with 23000 gallons of water to simulate the weight of live stages. At its peak altitude of 167 kilometers (104 miles), four minutes 53 seconds after launch, the rocket was detonated by explosives upon command from earth. The water was released into the ionosphere, forming a massive cloud of ice particles several miles in diameter. By this experiment, known as "Project Highwater," scientists had hoped to obtain data on atmospheric physics, but poor telemetry made the results questionable. The flight was the third straight success for the Saturn C-1 and the first with maximum fuel on board.

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    $\begingroup$ This is great, thanks! I was certain that somebody sometime in the early days must have said "Aw c'mon, can't we try it at least once? It needs to be 'tested' right?" $\endgroup$
    – uhoh
    Apr 1 '21 at 4:28
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    $\begingroup$ @OrganicMarble bah! an explodey Rick-roil. The real ka-blooies of SA2 and SA3 $\endgroup$ Apr 1 '21 at 8:57
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    $\begingroup$ @uhoh Given that these were ubernerds playing with incredibly fancy toys (and getting paid to do it!), I imagine that it was one part "we need to test the entire TTS and LES to validate ascent abort modes producing LOV meet RSO and MFCO specifications without an accompanying LOC" and one part "let's blow stuff up". $\endgroup$ Apr 20 '21 at 15:02

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