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1
This thing is really more similar to a capsule than a hypersonic glide vehicle, except it's not passively stable in the belly flop direction. The brakerons give it active stability along with maneuverability and it has a much lower ballistic coefficient than any capsule flown to date. A bloody brilliant design. I wonder if they'll adopt it for the BFB as well.

As others have mentioned on the discussion thread, I think the "sky-diving" BFS is the most impressive and under-appreciated part of the BFR design evolution.  It'll go down as one of the quintessential, SpaceX/Elon innovations.  We'll know its historical status if it's successful, and if it's copied by other providers.

But, BFB doesn't need this radical redesign.  It won't reach orbit, just like F9 S1, so no need for anything other than re-implementing the F9 S1 scheme on a much bigger booster.

Did you see the video and picture a few lines above? The technique was thought of in the 60's.

Didn't see the video first time around being at work and having YouTube blocked.  I did watch afterward and the idea is definitely similar in design, but not in purpose.  What I would intuit though is that everyone thinks of aero-surfaces as a means to aid in a typical airplane-like reentry (now and in the 60's.)  For example, before the 2018 BFS reveal, when Elon leaked the images of BFR with the fins-brakerons, absolutely no one was thinking "sky diver".  Everyone was still thinking "space plane" or "shuttle 2.0".

That model in the vertical wind tunnel is not doing an airplane-like reentry. It's doing exactly what Elon was talking about. NASA gets credit for the original invention, SpaceX gets credit for attempting to scale it up it to a functioning spacecraft. There's plenty of credit to go around for everyone. It's the perfect example of how the public/private partnership should work.

For that matter, I remember an episode of Battlestar Galactica where the Galactica does a skydive-like reentry over the camp where the humans are being held prisoner. Maybe Elon was inspired by that 😁
2
This thing is really more similar to a capsule than a hypersonic glide vehicle, except it's not passively stable in the belly flop direction. The brakerons give it active stability along with maneuverability and it has a much lower ballistic coefficient than any capsule flown to date. A bloody brilliant design. I wonder if they'll adopt it for the BFB as well.

As others have mentioned on the discussion thread, I think the "sky-diving" BFS is the most impressive and under-appreciated part of the BFR design evolution.  It'll go down as one of the quintessential, SpaceX/Elon innovations.  We'll know its historical status if it's successful, and if it's copied by other providers.

But, BFB doesn't need this radical redesign.  It won't reach orbit, just like F9 S1, so no need for anything other than re-implementing the F9 S1 scheme on a much bigger booster.

Did you see the video and picture a few lines above? The technique was thought of in the 60's.

Didn't see the video first time around being at work and having YouTube blocked.  I did watch afterward and the idea is definitely similar in design, but not in purpose.  What I would intuit though is that everyone thinks of aero-surfaces as a means to aid in a typical airplane-like reentry (now and in the 60's.)  For example, before the 2018 BFS reveal, when Elon leaked the images of BFR with the fins-brakerons, absolutely no one was thinking "sky diver".  Everyone was still thinking "space plane" or "shuttle 2.0".
Yeah Musk was visibly chuckling as he explained that the horizontal stabilizer looking thing was actually only a leg, and they made it look like a fin because it looked better....

(Which is a stretch of course since symmetry helps during ascent...  But still...)

He is very proud of having come up with a unique solution based on first principles and "asking the right questions".

I'm hoping they had time to follow this route far enough to know there aren't any show stoppers hiding in the details.

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ABCD: Always Be Counting Down
He was talking about the "top fin" that it was not a vertical stabilizer...
Yeah meant vertical...

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ABCD: Always Be Counting Down

3
This thing is really more similar to a capsule than a hypersonic glide vehicle, except it's not passively stable in the belly flop direction. The brakerons give it active stability along with maneuverability and it has a much lower ballistic coefficient than any capsule flown to date. A bloody brilliant design. I wonder if they'll adopt it for the BFB as well.

As others have mentioned on the discussion thread, I think the "sky-diving" BFS is the most impressive and under-appreciated part of the BFR design evolution.  It'll go down as one of the quintessential, SpaceX/Elon innovations.  We'll know its historical status if it's successful, and if it's copied by other providers.

But, BFB doesn't need this radical redesign.  It won't reach orbit, just like F9 S1, so no need for anything other than re-implementing the F9 S1 scheme on a much bigger booster.

Did you see the video and picture a few lines above? The technique was thought of in the 60's.

Didn't see the video first time around being at work and having YouTube blocked.  I did watch afterward and the idea is definitely similar in design, but not in purpose.  What I would intuit though is that everyone thinks of aero-surfaces as a means to aid in a typical airplane-like reentry (now and in the 60's.)  For example, before the 2018 BFS reveal, when Elon leaked the images of BFR with the fins-brakerons, absolutely no one was thinking "sky diver".  Everyone was still thinking "space plane" or "shuttle 2.0".
Yeah Musk was visibly chuckling as he explained that the horizontal stabilizer looking thing was actually only a leg, and they made it look like a fin because it looked better....

(Which is a stretch of course since symmetry helps during ascent...  But still...)

He is very proud of having come up with a unique solution based on first principles and "asking the right questions".

I'm hoping they had time to follow this route far enough to know there aren't any show stoppers hiding in the details.

-----
ABCD: Always Be Counting Down
He was talking about the "top fin" that it was not a vertical stabilizer...
4
SpaceX BFR - Earth to Deep Space / Re: BFS Engineering Thread
« Last post by eriblo on Today at 03:39 PM »
..."quick an dirty math getting 3.3 MNm and 1.7 MW per rear brake"...

The vehicle isn't going to enter at 90 degree angle of attack with brakes extended straight out, ever. For one thing, that would be a ballistic entry, which is a Very Bad Idea at those velocities. Also, 6 g is too high, even for an upper bound. Entry heating goes with deceleration rate (and a 300 second entry at 6 g is almost 18 km/s) so there's no reason to decelerate that fast unless the vehicle can't generate enough lift to decelerate slower - and I see no reason to believe that is the case here. The simulation shows an average deceleration of about 1.7 g. I'd consider 3-4 g a better upper bound.

The torque estimation is very sensitive to the actual drag coefficient, which varies significantly with extension angle, vehicle angle of attack, and velocity. The projected area of the fin also varies with extension angle and vehicle angle of attack. The power estimation is very sensitive to the necessary angular rate of change of the brakes. If you change each of those values to other entirely reasonable guesses, the power requirement drops by more than 10 times - which suggests this really isn't a problem you can get a good handle on with a BOTE calculation.
Agree with all of the above*, which is why I expressed surprise at getting close to Elon's "1 MN". However, the actual quote is:
Quote from: Elon, Private lunar mission presentation.
It requires an enormous amount of force to move those wings, it's in the mega-Newton class of force.
If this is interpreted as "actuator force" being in the MN range you get the order of magnitude reduction I would expect from all of the points brought up (hinge is less than 1 m in diameter so torque will be < 0.5 MNm per 1 MN of "force to move the wing"). Would hopefully move the problem down a few notches to merely "rocket science hard" :)

*I ill note though that the 6 g is "The Word of Elon" (presentation Q&A in with regard to a direct lunar reentry). I guess he might just be quoting Apollo numbers despite the much lower ballistic coefficient of the BFS...
5
This thing is really more similar to a capsule than a hypersonic glide vehicle, except it's not passively stable in the belly flop direction. The brakerons give it active stability along with maneuverability and it has a much lower ballistic coefficient than any capsule flown to date. A bloody brilliant design. I wonder if they'll adopt it for the BFB as well.

As others have mentioned on the discussion thread, I think the "sky-diving" BFS is the most impressive and under-appreciated part of the BFR design evolution.  It'll go down as one of the quintessential, SpaceX/Elon innovations.  We'll know its historical status if it's successful, and if it's copied by other providers.

But, BFB doesn't need this radical redesign.  It won't reach orbit, just like F9 S1, so no need for anything other than re-implementing the F9 S1 scheme on a much bigger booster.

Did you see the video and picture a few lines above? The technique was thought of in the 60's.

Didn't see the video first time around being at work and having YouTube blocked.  I did watch afterward and the idea is definitely similar in design, but not in purpose.  What I would intuit though is that everyone thinks of aero-surfaces as a means to aid in a typical airplane-like reentry (now and in the 60's.)  For example, before the 2018 BFS reveal, when Elon leaked the images of BFR with the fins-brakerons, absolutely no one was thinking "sky diver".  Everyone was still thinking "space plane" or "shuttle 2.0".
Yeah Musk was visibly chuckling as he explained that the horizontal stabilizer looking thing was actually only a leg, and they made it look like a fin because it looked better....

(Which is a stretch of course since symmetry helps during ascent...  But still...)

He is very proud of having come up with a unique solution based on first principles and "asking the right questions".

I'm hoping they had time to follow this route far enough to know there aren't any show stoppers hiding in the details.

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ABCD: Always Be Counting Down

6
Depends on how high above ground level your eyes are. A quick & dirty distance to the horizon (ignoring atmospheric distortion & rocket height) is

(eye height is above ground level, so include platforms)

SQRT(eye height in feet/0.5736) = miles

Metric formula,

SQRT(eye height in cm/6.752) = km
7
Cross-post re: clarification of launch window:
http://www.launchphotography.com/Delta_4_Atlas_5_Falcon_9_Launch_Viewing.html
Quote
The next United Launch Alliance Atlas 5 rocket from Cape Canaveral, flying with the maximum five SRBs, will launch AEHF-4 for the US Air Force on October 17 at 12:15am EDT. The launch window stretches two hours to 2:15am EDT.
04:15 - 06:15 UTC

EDT = UTC - 4 hours
9
Space Science Coverage / Re: JAXA Hayabusa2 Mission : General Thread
« Last post by meekGee on Today at 03:18 PM »
Should be "Samples collected from the surface of a world beyond Earth's moon".

Japan did that first.

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ABCD: Always Be Counting Down

10
If SpaceX is in the process of constructing a launch pad offshore, how would we know? How far out would it need to be to be for the construction to be invisible from the viewing areas on shore?
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