The direct blast and thermal effects were factored into the selection of observation site, as is the flydown hazard for vehicle termination or propulsive failure in the first few tens of seconds of flight. However, unbeknownst to analysts at the time, inversion layers in the atmosphere can reflect and even amplify the shock in a phenomenon called distance focusing overpressure, so the shock experienced four or five miles away may be more intense than only two or three. The sustained acoustic vibration, however, attenuates proportional to the square of distance.
Although water is a good sound conduction medium for sources that are in direct contact or submerged in the water, it effectively reflects most of the sound an energy from a source tht is outside the water. The massive change in density and viscosity between air and water makes it an extremely effective acoustic barrier, hence why when you duck your head under water you cannot hear anything being said outside the water.
As for mobile launchers, the transporter/erector/launcher (TEL) is aligned to a known reference using a theodolite or geodolite, the launch vehicle is erected (and in the case of liquid propellant vehicles like the ‘Scud’ family of boosters, fueled), and then the launch crew preps and arms the missile and runs like hell upwind before the launch officer fires the missile remotely. The plume experienced by the vehicle during launch usually doesn’t last long enough to do serious damage, although I have seen the inch-thick windows on a TEL crazed due to the vibration environment. If a launch vehicle actually exploded or caught fire and failed to launch, the TEL would be completely destroyed. And I do mean completely, as in a twisted, melted wreck of a truck.
I suspect that was where I was for the Apollo XVII launch, which took place at night. I don’t remember it being particularly loud, and I dislike loud noises. The most impressive thing was seeing ignition significantly before hearing it.
I saw a launch of a much smaller rocket (maybe a Titan, or whatever’s one size down from a Titan) to put the Spitzer Space Telescope into orbit, and the sound was distinctive and very loud, but I mainly remember it sounding more like natural phenomenon than something artificial. That is, it sounded like thunder or being really close to a waterfall, something primal like that.
There is a lot of smoke from the plume, but I see nothing to indicate the TEL would be damaged beyond repair. The plume from a solid propellant motor would be hot (>2000 K past the exit plane) but the vehicle is moving so quickly tha the TEL is only exposed for a period of around one second. American LGM-30G ‘Minuteman’ and LGM-118A ‘Peacekeeper’ missiles launch from silos (and in the case of Peacekeeper Rail Garrison, were planned to be launched from a railcar platform) which are reloadable with minimal refurbishment, including all of the mechanical structures which are no more delicate than a heavily built transporter.
The plume of a liquid rocket engine or solid propellant motor does less damage than most people imagine, and most of what is done is due to acoustic effects rather than thermal. I mean, I wouldn’t park my car behind one, but a TEL with a thick steel body and thermal protection should easily be serviceable for tens of launches.
Decibel is a relative measure of intensity or power, proportional to the log of the ratio to some reference. Broadband acoustic phenomena are generally specified in terms of sound pressure level (SPL). L[SUB]P[/SUB] = 9.2 dB[SUB]SPL[/SUB] would barely be audible; less than leaves rustling in the distance.
The audio track on that video clearly shows clipping of the acoustic signal at maximum amplitude. And one of the things that cannot be conveyed by any video or recorded audio track–unless you have a very expensive and extremely bitchin’ stereo system–is the subsonic component which vigorously shakes your sinus cavity and parietal pleura in a way only The Rolling Stones could do prior to 1970.
Well you are right in this compilation of Russian ICBM rocket launches you see a Topol launch beginning at 1:45 and you can later see that the cannister is still standing as the smoke clears momentarily. You also see a SS-24 railcar launch although you cannot tell that whether the launcher is still there. I will also say that some of the Russian launch control equipment looks kind of outdated
But that raises another question. I know that one of the advantages of a cold launching from silos (such as the SS-18 in the above video) is that the missile clears the silo before ignition, unlike the hot launch technique employed by the Miniteman with ignition within the silo, which destroys the silo. Why would the silo be destroyed in such a situation when a mobile TEL would not be…is it because of the enclosed space>
As an aside, why do solid fuel motors produce such conspicious smoke trails, in the above video, the SS-18 and SS-19 engines produce much less smoke than the Topol or SS-24.
I don’t know where you get the notion that Minuteman silos are destroyed during launch, but it isn’t true. There are Minuteman test silos at Vandenberg Air Force Base that have been used to launch tens of test flights. They do require refurbishment between flights (washout, replacement of umbilicals, inspection and repair of seismic suspension system, new spray-on foam insulation) but the basic structure of the silo is not damaged by the launch.
The advantages of cold launch are thus: one, it allows you to launch a large booster from a small silo without having to make consideration for plume expansion and overpressure (i.e. it allowed refitting the much larger diameter Peacekeeper into existing Minuteman II silos); the booster does not have to see the aggressive launch environment in the silo and ground acoustic field; the booster is more survivable in the case of a near strike during launch (a Minuteman flying out of the silo during a blast would be sheared by the blast, a Peacekeeper would accept the shear load on the pads, and once in the air, would just be pushed sideways); and it does allow reuse of the silo with minimal refurbishment. The downsides are the aggressive ejection load (comparable to a staging event, but on the full L/D of the booster); the need to correctly time ignition in order to recover command authority of the booster; design and maintenance of a separate launch eject gas system.
The reason solid propellant motors produce dense white and brown clouds of smoke is because they are full of particulates. Not only do solid propellants form more dense combustion products, but most contain a significant amount of “loaded solids”, e.g. aluminum, zinc, iron, et cetera to increase combustion temperature and control the burn rate. Combustion products from many storable liquid fuel propellants such as RP-1 and nitrogen tetroxide tend to be brown, but less dense so they clear more quickly. Chemically ‘clean’ propellants such as hydrogen peroxide and ethyl alcohol, and cryogenic propellants like liquid hydrogen and liquid oxygen, tend to give relatively colorless plumes (usually faint blue or yellow, depending on the oxidizer to fuel ratio). Although this gives poorer thermodynamic efficiency (the dense products act less like an ideal gas and do not expand well in the expanding nozzle region) they provide higher specific thrust and are denser to store, which is why many medium, heavy, and super-heavy lift vehicles use strap-on solid propellant boosters at launch; this allows them to get off the launch pad and up to speed faster, wasting less energy on “gravity drag” (i.e. the energy you have to expend just to stay aloft before reaching orbital speed) even though they are not as propulsively efficient in terms of specific impulse.
Cool. Not being familiar with ballistic missile launches, all I could think of were Shuttle and Apollo launches, and their exhaust color–and then this paragraph swum up. Thanks.
Note that a lot of the vapor you see at Saturn V and STS launches is actually steam from the water-filled flame trench that is heated by the exhaust. This is done intentionally to dampen the acoustic environment during the first few, slow seconds of ignition and liftoff.
