Considering that Space X have just announced that their BFR can take anyone anywhere in the world in under 1 hour, that would be enormous speed, does this rocket not produce sonic boom? If not is it because of its shape and that it does not have wings? Will it ever be allowed to fly across the US above the oceans and anywhere at those speeds considering again sonic boom?
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asked Sep 29, 2017 at 14:45
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7$\begingroup$ hundreds of satellites cross the oceans and continents at this moment, at enormous speeds. Yet nobody complains about sonic booms. $\endgroup$– DeltaLima ♦Commented Sep 29, 2017 at 14:53
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6$\begingroup$ Why worry about sonic booms? Consider the launch noise. Then figure that when you launch from anywhere the noise would be acceptable (KFC or Vandenberg, in the US), it would likely take you as long or longer to get there and board the rocket, than it would to go directly to your destination. $\endgroup$– jamesqfCommented Sep 29, 2017 at 18:09
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6$\begingroup$ @jamesqf I don't know about you, but I can get to KSC much faster than I can get to, say, Hong Kong. And, like most of the world's population, I can get to KFC much faster than to either of those locations. :) $\endgroup$– reirabCommented Sep 29, 2017 at 18:28
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$\begingroup$ Please tell me this stands for Big F***** Rocket. (reference: doom.wikia.com/wiki/BFG9000) $\endgroup$– Peter CordesCommented Sep 29, 2017 at 21:18
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5$\begingroup$ @PeterCordes Technically it stands for Big Falcon Rocket, but yes, it was deliberately chosen for the similar sound. en.wikipedia.org/wiki/BFR_(rocket) $\endgroup$– Chris HayesCommented Sep 29, 2017 at 21:22
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3 Answers
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The only way to get anything that far that quickly is to send it into space, and that's exactly what Musk is suggesting. The BFR will launch a passenger carrying spacecraft out of the atmosphere and into a sub-orbital path, it will re-enter the atmosphere close to its destination. Rockets launch pretty much straight up and a sonic boom would have to compete with the rocket itself on noise. Once above the atmosphere there is no sonic boom because there is no air.
On re-entry all spacecraft create a sonic boom, for most of the re-entry this is inaudible from the ground because the air is extremely thin, once in the lower atmosphere it gets louder. By the time the spacecraft gets low enough to create a really big sonic boom it's usually at a subsonic speed and would not make any boom at all. The shuttle and Apollo spacecraft both created sonic booms on re-entry, that's covered in this Space SE Question.
So, are sonic booms a problem in this idea? It depends, the space shuttle re-entered over the continental US many times and it never bothered anyone, but if it was happening a few times a day it might be a problem. You could get around that for the most part by re-entering over sparsely populated areas or the ocean.
More likely it's not the sonic booms that people won't want from a noise perspective, but the launches.
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Since the rocket will be traveling through space, there will be no noise on the ground during cruise.
As pointed by @DeltaLima in the comments, a lot of satellites are crossing the sky above us at this very moment. Since there is no air in space, no sound can be heard, especially from that distance.
The only noisy parts will be the takeoff and landing, but with carefully selected location, this shouldn't be a problem.
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2$\begingroup$ Landing presumably won't be supersonic, so booms shouldn't be an issue there. 'Takeoff' (i.e. launch) will be noisy regardless of the boom. $\endgroup$– reirabCommented Sep 29, 2017 at 18:26
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$\begingroup$ @reirab landing is subsonic, but part of approach is supersonic. $\endgroup$ Commented Sep 29, 2017 at 22:01
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$\begingroup$ @ChrisStratton True, but, if it's anything like the Space Shuttle, that part of the approach will be too high to matter. Not sure about SpaceX's rocket, but the Space Shuttle descended extremely quickly. It was like piloting a brick. $\endgroup$– reirabCommented Sep 30, 2017 at 13:52
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1$\begingroup$ "a carefully selected location" for takeoff would have to be far from a densely populated area. Which pretty much defeats the point of "getting quickly from A to B". You would first have to get from your area of population to A which is "far from civilization". Seems like a pretty deep flaw in the plan. I hope they have thought this through. $\endgroup$– FlorisCommented Sep 30, 2017 at 18:39
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I doubt it. Sonic boom/s may well occur but likely (or could be specifically planned by routing etc) to occur in upper atmosphere/away from population centers.
The rocket seems planned to take off from an island or floating structure (judging by the graphics, which showed a ferry to the launch site), which could easily be tens of miles away from land if that were an issue. That distance might be enough to mitigate a lot of the launch noise.
As for landing, it's probably possible to come into landing along such a trajectory as to not be near a city when excessive noise will be produced, either by coming in over the ocean (in the graphic's example) or even by 's'turning around populated areas, shedding speed in the same trajectory (the space shuttle bled off speed this way, I believe).
Note that military craft produce booms frequently (although AFAIK they try to limit proximity to populated areas), as does any orbital (and most suborbital, although not so many of those fly these days) rocket, and Concorde produced booms. So:
Will it ever be allowed to fly across the US above the oceans and anywhere at those speeds
I don't see potential booms impacting whether it is allowed at all. Where it is permitted to be routed/produce booms, and how frequently, are open questions.
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$\begingroup$ The US banned commercial supersonic aircraft flying across land in the US specifically because of the Concorde, so in theory any supersonic "aircraft" produced by Space X flying above the US would also be prohibited if not by the same rule, by the same concerns. However it's a rocket and not an aircraft and so doesn't make the same sonic booms. Perhaps more importantly this shouldn't also be an issue because it's made by a US company, not a foreign one, and Boeing has no plans to make it's own competing version. $\endgroup$ Commented Sep 30, 2017 at 0:38
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$\begingroup$ Rules can be changed. NASA has been working on technologies to minimise sonic boom related disturbance as part of its research into hypersonic aircraft, so there's some mitigation possibilities there too. $\endgroup$ Commented Sep 30, 2017 at 2:20
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$\begingroup$ Yes, I explained why I think the rules would be changed if necessary. $\endgroup$ Commented Sep 30, 2017 at 2:29
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$\begingroup$ @RossRidge Those rules only apply if you're flying in U.S. national airspace. Rockets don't do that, except during launch. Completely different sets of rules involved. $\endgroup$– reirabCommented Sep 30, 2017 at 14:05
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$\begingroup$ @reirab Yes, as I said "it's a rocket and not an aircraft". $\endgroup$ Commented Sep 30, 2017 at 14:27