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#180
by
Kabloona
on 05 Aug, 2019 18:42
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Page 8 of the attached pdf
For the reentry-descent phase of flight, the measurements were made on land with the majority
acquired in the state of California and about 25 percent in the state of Florida. The measured
boom signatures were generally N-wave in character, similar to those observed from supersonic
aircraft, with amplitudes ranging from about 0.10 psf from the vehicle at about 243,000 feet altitude
to a maximum of 2.32 psf just prior to landing. Signature periods, however, were much
greater than those observed on aircraft being on the order of about 0.40 second to about 2.5 seconds.
Predictions of the magnitude of sonic booms and ground footprints for Mach numbers to
about 6.0 compared favorably with measurements.
So a SS landing produce twice as much overpressure in Titusville. whether that translates to twice as loud or 10x as loud i don't know.
A little Googling gives some links to NASA studies on perceived loudness of sonic booms. It seems that the shape of the wave has a large effect on the perceived loudness of the boom, and the shape of the wave depends on the geometry of the vehicle, etc. So two different vehicles can produce sonic booms of differing perceived loudness, even though the peak overpressure of the wave is the same. Then trying to predict the perceived loudness of Starship booms as compared to Shuttle booms is probably impossible given the unknowns of wave shape differences and the subjectivity of human loudness perception.
So while peak overpressure maps may be useful for a general assessment of the sonic footpring over a large geographic area, it's probably impossible to predict how many people in, say, Orlando are going to find Starship booms "very annoying," which is apparently a term of art in these sorts of studies.
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#181
by
Orbiter
on 05 Aug, 2019 21:13
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#182
by
Star One
on 05 Aug, 2019 21:38
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He does namecheck this forum at the end recommending people visit the forum.
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#183
by
InfraNut2
on 05 Aug, 2019 21:39
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When I try to download the document, access is blocked with the following message:
Web Page Blocked!
The page cannot be displayed. Please contact the administrator for additional information.
URL: netspublic.grc.nasa.gov/main/20190801_Final_DRAFT_EA_SpaceX_Starship.pdf
Client IP: --redacted--
Attack ID: 20000008
Has the server interpreted a high number of downloads or high bandwidth use for this file as a DoS attack and blocked it?
Anyone else have the same problem?
Does anyone know of another downloadable copy of this?
Hope someone can help me get a copy to satisfy my curiosity...
-- "InfraNut2"
(I thought this was open public info anyway...? BTW: I am located in the allied (NATO) country Norway, but I do not think country has anything to do with it, since that would be pretty meaningless in these days when many use VPNs, proxies and such)
Link works for me just now.
Copy of report attached
Thanks AnalogMan !!!
Now I finally got the report.
(Original site still blocked for me...)
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#184
by
Dave G
on 05 Aug, 2019 21:54
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... worst case SpaceX needs to position a drone ship some miles off the coast for Starship to land, this is the advantage of a VTVL, it can land pretty much anywhere.
As I understand it, in order for BFR to meet it's operating cost targets, it must be fully and
rapidly reusable.
Launching from land and landing at sea wouldn't satisfy the second part of that requirement, as this would involve:
- shipping it back to a sea port
- bringing it from vertical to horizontal
- trucking from the sea port back to the launch pad (is this even possible with a 10 meter diameter and fins?)
- bringing it back to vertical
That's why they want to land Starship right back at the launch pad, as requested in the Draft EA.
If the sonic boom issue is a show stopper, it may be cheaper for them to move the whole launch pad offshore.
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#185
by
Lars-J
on 05 Aug, 2019 22:03
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Yep. They must have some detailed plans for an offshore launch and landing platform. (anchored or floating)
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#186
by
Norm38
on 05 Aug, 2019 22:27
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The sonic boom thing is starting to worry me.
Isn't this what killed the Concorde?
If they'd been able to offer super-sonic domestic flights, e.g. New York to L.A., they may have been profitable.
In any case, governments banning Concord super-sonic flights over land due to sonic booms has set a precedent.
Breaking that precedent could prove difficult.
This could be a serious issue for landing orbital Starship missions in Florida and Texas.
First, times have changed, and Florida has experience with sonic booms. The general public no longer believes that this is a sonic boom:
Ahh, it’s the 6pm Starship back from the Moon!
Second, the Concorde wasn’t economical. A few extra hours costs way less, and that travel was still possible.
There is no space travel without a sonic boom. So either regional governments come to terms with that, or spaceports relocate. But it’s no big deal, so nothing to sweat over.
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#187
by
Llian Rhydderch
on 05 Aug, 2019 23:09
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"SpaceX plans to launch the Starship/Super Heavy up to 24 times per year from LC-39A. A static fire test would be conducted on each stage prior to each launch."
Yes, but it also says:
"The Starship and Super Heavy would exceed the lift capabilities of the Falcon Heavy. Due to the higher lift capability, Starship/Super Heavy could launch more payloads and reduce the overall launch cadence when compared to Falcon 9 and Falcon Heavy. This would increase the cost effectiveness of the space industry."
Sounds like STS, or Titan IV, or EELV. Fewer launches, more stuff on each. Initial claims of cost-effectiveness that didn't pan out in those cases.
- Ed Kyle
The incentives are entirely different. The results that emerge will be as well.
One would not expect the outcome of government-procured launch systems from a oligopolistic gvmt contractor space industry to ever be close to comparable to what will emerge from a private company spending their own resources to design an orbital launch system.
I'm not arguing with your history of missed promises with "STS, or Titan IV, or EELV. Fewer launches, more stuff on each. Initial claims of cost-effectiveness that didn't pan out..." Am just pointing out that any comparison of outcomes with entirely different incentive structures will be fraught.
SpaceX has been re-writing the rules of the game with their novel innovation, rapid tech advancement, and rather drastic cost reductions for over a decade now. They've clearly demonstrated the ability to out-innovate and radically cost-reduce the legacy way of doing spaceflight technology development.
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#188
by
DigitalMan
on 05 Aug, 2019 23:54
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The sonic boom thing is starting to worry me.
Isn't this what killed the Concorde?
If they'd been able to offer super-sonic domestic flights, e.g. New York to L.A., they may have been profitable.
In any case, governments banning Concord super-sonic flights over land due to sonic booms has set a precedent.
Breaking that precedent could prove difficult.
This could be a serious issue for landing orbital Starship missions in Florida and Texas.
First, times have changed, and Florida has experience with sonic booms. The general public no longer believes that this is a sonic boom:
Ahh, it’s the 6pm Starship back from the Moon!
Second, the Concorde wasn’t economical. A few extra hours costs way less, and that travel was still possible.
There is no space travel without a sonic boom. So either regional governments come to terms with that, or spaceports relocate. But it’s no big deal, so nothing to sweat over.
The funny thing is, that shuttle information posted above made me LESS concerned rather than more after looking at it closely.
Another thing is, we get daily thunderstorms that probably make much more substantial noise. Sometimes in the middle of the night. Last week I saw 2 lightning strikes not 50 feet away from my back door within 20 minutes of each other as I was looking out the window.
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#189
by
RobLynn
on 06 Aug, 2019 00:22
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As I understand it, in order for BFR to meet it's operating cost targets, it must be fully and rapidly reusable.
Launching from land and landing at sea wouldn't satisfy the second part of that requirement, as this would involve:
- shipping it back to a sea port
- bringing it from vertical to horizontal
- trucking from the sea port back to the launch pad (is this even possible with a 10 meter diameter and fins?)
- bringing it back to vertical
Or more simply utilise two identical launch/landing ships (probably catamaran for stability and speed given low mass) that can cruise a SH back from 1000km downrange in 24 hours, and do launch far enough off coast that range safety and environmental compliance issues are minimised. SH and starship launch from one and land on other.
Ships are cheap to build - about $2/kg so such ships are likely to only cost a few $10's of million each. Possibly cheaper than building a land based launch tower.
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#190
by
su27k
on 06 Aug, 2019 02:54
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... worst case SpaceX needs to position a drone ship some miles off the coast for Starship to land, this is the advantage of a VTVL, it can land pretty much anywhere.
As I understand it, in order for BFR to meet it's operating cost targets, it must be fully and rapidly reusable.
Launching from land and landing at sea wouldn't satisfy the second part of that requirement, as this would involve:
- shipping it back to a sea port
- bringing it from vertical to horizontal
- trucking from the sea port back to the launch pad (is this even possible with a 10 meter diameter and fins?)
- bringing it back to vertical
That's why they want to land Starship right back at the launch pad, as requested in the Draft EA.
If the sonic boom issue is a show stopper, it may be cheaper for them to move the whole launch pad offshore.
The cost is much more complicated, if we're talking about marginal cost of launch, I don't think a boat trip will add much to it. What the offshore landing will do is limiting their launch rate, but in this EA the launch rate is already limited to 24 per year, and the downrange landing of SH will be limiting the launch rate too, so landing Starship offshore wouldn't change the equation.
This EA is just to get them started, it's not some 10 years plan, it's what they'll do at the moment. The EA's purpose is not to be the be all and end all plan for everything Starship, it's what they need to get this thing flying in the next 2 years. They can re-assess the situation after Starship starts flying, who knows what will happen then, maybe the sonic boom wouldn't be as loud or the public wouldn't be as skittish, like I said, we'll see.
While I would like to see they working on offshore launch platform too, and I hope ASoG is such a platform, that is probably for another thread.
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#191
by
Dave G
on 06 Aug, 2019 10:52
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... Starship is going to be significantly louder than Space Shuttle by a factor of 2 or 3, if I refer to the overpressure map below that I found here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110011322.pdf
I agree.
Comparing the sonic boom maps, it seems sonic booms for Starship will be much worse than the Space Shuttle.
Maybe I'm wired differently, but when I see a potential issue, I embrace it as a problem to be solved or worked around. If it turns out to be a non-issue, I'm pleasantly surprised. If not, at least I understand the issue fully.
To be clear, I'm not saying sonic booms are a definite show-stopper, only that it's a potential issue, so it's worth understanding more about it.
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#192
by
Dave G
on 06 Aug, 2019 11:18
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... the blue / light green are for sound levels that you probably won't notice unless you are listening for it.
The
Draft Environmental Assessment section on sonic booms says exactly the opposite.
In general, booms in the 0.2 to 0.3 psf range could be heard by someone who is expecting it and listening
for it, but usually would not be noticed. Booms of 0.5 psf are more likely to be noticed, and booms of 1.0
psf are certain to be noticed.
The light-blue lines represent
1.0 psf, and includes about 1/3 of Florida, including Tampa, Clearwater, etc.
The green lines represent
2.0 psf, twice what the EA says is "certain to be noticed", and includes the entire Orlando metro area.
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#193
by
DigitalMan
on 06 Aug, 2019 12:09
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Once again,
Don't get the idea that we don't have daily loud noises in the form of thunderstorms. Starship noise seems irrelevant.
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#194
by
Dave G
on 06 Aug, 2019 12:22
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Don't get the idea that we don't have daily loud noises in the form of thunderstorms.
Good point.
Starship noise seems irrelevant.
Have to disagree here. The
Draft EA includes 42 pages on sonic booms, so it seems relevant to this thread.
As I said, it's possible that sonic booms will end up being a non-issue, but that's yet to be determined.
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#195
by
Star One
on 06 Aug, 2019 13:30
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Once again,
Don't get the idea that we don't have daily loud noises in the form of thunderstorms. Starship noise seems irrelevant.
I hardly think you have thunderstorms 365 days a year.
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#196
by
DigitalMan
on 06 Aug, 2019 13:36
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Once again,
Don't get the idea that we don't have daily loud noises in the form of thunderstorms. Starship noise seems irrelevant.
I hardly think you have thunderstorms 365 days a year.
Pretty close to that. Besides, you aren't suggesting there are going to be more launches than there are thunderstorms, are you?
edit: I did a google and it shows we get more than 100 per year. I guess it only FEELS like we get them every day.
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#197
by
waveney
on 06 Aug, 2019 13:48
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Once again,
Don't get the idea that we don't have daily loud noises in the form of thunderstorms. Starship noise seems irrelevant.
I hardly think you have thunderstorms 365 days a year.
Pretty close to that. Besides, you aren't suggesting there are going to be more launches than there are thunderstorms, are you?
edit: I did a google and it shows we get more than 100 per year. I guess it only FEELS like we get them every day.
Agree - In the past I often worked in North Orlando - in the summer you could set your watch by the afternoon thunderstorm - always 4:15 (for about half an hour)
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#198
by
RoboGoofers
on 06 Aug, 2019 14:07
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I believe one of the main complaints about sonic booms is that they come out of the blue. thunderstorms are usually obvious and predictable.
Someone in another thread mentioned the reaction to the starlink visibility and SpaceX's reponse. At least in that case some old lady didn't have a hummel figurine shaken off a shelf in her curio cabinet. So whatever you might think is a non-issue, there are plenty of other people out there that will loudly complain.
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#199
by
DigitalMan
on 06 Aug, 2019 14:19
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Just as some consider the thunderstorm talk valueless now you know how I feel about the noise 'concerns'. People die regularly due to thunderstorms. Regardless, based on comments, I will consider this discussion vector exhausted.
On another note, I saw posts on another thread about potential measures to mitigate the severity of sonic shock exposed to land. I wonder whether SpaceX will make an effort to test some possible mitigations as part of the Starship mark 1 & 2 test regime?