D Tibbets wrote:To keep it from exploding on impact is relevant, but primarily self destruct of a rocket is triggered either automatically or by a range control officer in order to keep the rocket- intact or in pieces from straying outside of the test/ launch range.
I was wondering about this... it seems to me like detonating the rocket 1000 ft up is more likely to scatter debris outside the range than letting it crash intact. As long as there is no significant horizontal movement, is there no practical way to cut the engines and dump the fuel? Even if the fuel burned when dumped, wouldn't it be a lot more likely to keep everything contained within the range than with an explosion that might send debris flying for miles in any direction?
That's what the FTS does - unzip fuel tank and it consequently ignites. Not as in an explosion where everything detonates as is - more like a pipe bomb where fuel is to surrounding rocket hardware as shrapnel is to pipe bomb explosive charge. AIUI you can see that sequence in this flight's footage: before the fireball happens a white cloud of propellant is visible.
You can do anything you want with laws except make Americans obey them. | What I want to do is to look up S. . . . I call him the Schadenfreudean Man.
Hopefully the test range is large, but I suspect it is much smaller than say- the White Sands test range.Detonating explosives to break up the rocket does three things. a major portion of the fuel will burn up in the air, or disperse (liquid oxygen especially). Secondly, thrust is immediately cut off. This is especially important for solid fuels. Once ignited, it cannot be turned off. Third, breaking the rocket into smaller pieces increases the surface are to mass relationship. Wind resistance will slow the pieces more rapidly than the intact rocket. A good comparison is shotgun birdshot and a slug. The initial velocity and mass may be the same, but the surface area of the spreading birdshot slows much faster than the intact slug or bullet. Any momentum the rocket has built up is more quickly eliminated, again reducing the radius of possible damage. Also, the air resistance consumes a modest to major portion of the KE, less energy once the rocket or pieces reach the ground.
The rocket is not detonated. It is not a detonation. The fuel ignites and the stage loses structural integrity (which is why it breaks up). The stages is "unzipped" so it wont detonate because the open side will not provide any resistance for expanding hot gases when the fuels ignite. This is designed so that debris does not spread over a large area. And that worked as designed. According to SpaceX everything remained inside the boundaries of the testing area.
Not detonated, but unzipped. OK, That is perhaps a better discription. Still it is detonated explosives that does the job of disrupting the structural integrative of the rocket. If the fuel burns, you get a fire ball- what is often called an explosion in the movies, but this is different than a large high explosive blast. Low explosives like gun powder and diesel need confinement to develop high pressure blasts. Solid rockets may be somewhat different? After "unzipping" to eliminate any usefull directional thrust, the solid/ geled fuel spills out and falls to the ground, some or most of it burning along the way. Scattered unburned globs may be scattered all over the debris field. With liquid oxygen the burn rates of even diesel (rocket fuel) will be faster. The explosion of the recent Russian Proton launch demonstrates. I don't know if a self destruct was used, but the rocket started breaking up , possibly due to aerodynamic forces. When it crashed into the ground, there was enough fuel and oxygen so that it provided its own confinement, possibly due to the inertia of the large amount of liquids, and of course the solids. An impressive blast wave was generated.
It sounds like semantics to most people, but the distinction is important and less subtle than it seems.
The aversion to "exploded" is because it refers to something more like what you see on an engineering schematic - "exploded view" of some assembly. Whereas the (only) cause for such a dis-assembly, in the practical context of a rocket, is for propellant combustion to impart that disassembling motion on that "non-exploded" rocket hardware from within said rocket -- as opposed to propellant "exploding" only itself, separately, after the linear FTS charge gives prop tank pressure an almost instantaneous outlet.
It's a completely different situation. An explosive mass and a rocket together as one object, versus the two of them separately even if still proximate. The latter still results in considerable scattering of parts, but inarguably a different situation. That they both look and sound equally like fireworks is deceptive.
You can do anything you want with laws except make Americans obey them. | What I want to do is to look up S. . . . I call him the Schadenfreudean Man.
Seriously???
What does the mechanism of the self-destruct matter?
It exceeded test parameters and was destroyed. Who cares if it was a slingshot or sodium dropped in a bucket?
Silly argument.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)
I think people here are accustomed to a pretty serious level of precision in their communications in general, and it is true that it's not a detonation. A real detonation would mix the propellant and fuel beforehand and then we'd see supersonic combustion through use of a shock wave. Subsonic combustion is deflagration, not detonation. That would make the world's largest air fuel bomb by far. Someone here can do the math but I'd guess it would flatten a very large piece of real estate, probably best compared to a nuclear weapon. It is good to note this is very hard to do and won't happen by accident. Air fuel bombs create carefully planned detonations. You can't really turn a rocket into that kind of bomb by accident.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis
For my part, I find it irritates me that the Main Prog Media keeps the narrative up that the rocket exploded, when what really happened was the rocket was destroyed when it exceeded launch criteria.
Counting the days to commercial fusion. It is not that long now.
My understanding is the auto destruct system also has control of the launch escape system settings on the dragon's integrated thrusters, and it would have the capsule 'escape' from the rest of the rocket as, or just before, the charges that open up the fuel tanks go off.
SpaceX has decided to postpone tomorrow's flight of AsiaSat 6. We are not aware of any issue with Falcon 9, nor the interfaces with the Spacecraft, but have decided to review all potential failure modes and contingencies again. We expect to complete this process in one to two weeks.
The natural question is whether this is related to the test vehicle malfunction at our development facility in Texas last week. After a thorough review, we are confident that there is no direct link. Had the same blocked sensor port problem occurred with an operational Falcon 9, it would have been outvoted by several other sensors. That voting system was not present on the test vehicle.
What we do want to triple-check is whether even highly improbable corner case scenarios have the optimal fault detection and recovery logic. This has already been reviewed by SpaceX and multiple outside agencies, so the most likely outcome is no change. If any changes are made, we will provide as much detail as is allowed under US law.
The previous post seems to explain things well, at least for a preliminary analysis. They cut corners on this test rocket, and therefor had less reserve capacity to handle spurious sensor or other anomalies. As it turned out it bit them. There is a constant tradeoff in the design and operation of rockets as the competing concerns of weight, cost, time, and engineering limits interact. Rockets are impressive examples of Murphy's Law.
