Sonic flight without the boom

> Seeing how the discussion has been much about the physics of supersonic
> shockwaves, does anyone know how NASA performed this sonic boom
> attenuation?
> 
> http://spaceflightnow.com/news/n0309/06supersonic/

To me it looks like they are doing several things. First, at the nose they 
are bringing the expansion waves as close as possible to the compression 
(bow) wave. The lower conic section of the nose is bullet shaped. 
Initially, creating a stronger shock wave, immediately followed by 
expansion waves. Essentially, separating the air with a compression wave 
(the easy part, increasing pressure gradient), followed by a broad area of 
expansion waves (the hard part, decreasing pressure gradient) to turn the 
flow back parallel to the velocity vector. Creating as small a hole in the 
air as possible. 
 
There is a reason bullets are the shaped the way they are. The supersonic 
areodynamicist seem to be rediscovering this. 
 
Second, has to do with paying attention to the Area Rule. Once the hole in 
the air is made, don't make it any bigger. Keep the cross-sectional area 
(or disturbance in the air) along the longitudinal axis a constant. So, the 
area of the pelican bow is decreased at the wing. Decreasing the cross 
sectional area of the pelican bow, while the wings are increasing the cross 
sectional area. The decreasing area of the pelican bow is creating 
expansion waves, while the increasing area of the wing is creating 
compression waves, the net effect being zero further from the aircraft. 
This again brings the compression waves and expansion waves as close 
together as possible, in this case, right on top of one another. This way 
the additional frontal area of the wing, isn't additional area, and doesn't 
contribute to the sonic boom. 
 
Even though the modified F-5 is longer and has more early frontal area, it 
seems to have the same (or less) drag as the unmodified F-5.
 
http://www.dfrc.nasa.gov/Gallery/Photo/F-15B/Medium/EC03-0229-6.jpg 
 
http://www.dfrc.nasa.gov/Gallery/Photo/F-15B/Medium/EC03-0210-1.jpg 
 
http://www.dfrc.nasa.gov/Gallery/Photo/F-15B/Medium/EC03-0210-5.jpg 
 
http://sonicbooms.org/News/F5SSBD_PressConf.htm 
 
This URL shows a nice plot comparing the sonic booms of the modified F-5 
compared to the unmodified F-5. It's interesting that the effect of the 
nose occurs in the first 16 milliseconds. 0.016 seconds X 1360 fps (Mach 
1.36) velocity, which equals the first 22 feet of the aircraft. 
Essentially, 30% of the initial shock wave is dissipated by the expansion 
waves generated in the first 22 feet. 
 
Also, interesting is the effect on the Wake shock that is following the 
aircraft. It's magnitude is slightly reduced, but the main effect seems to 
be that it is moved closer to the tail of the aircraft. The modified longer 
aircraft is plowing a 3.5% smaller hole in the air than unmodified version. 
I'd be surprised if the modified aircraft doesn't have a slightly higher 
top end. 
 
In URL sonicbooms, it says "The flight tests showed that by designing the 
body and wing of the aircraft to a specific shape, the pressure waves can 
be kept from merging.", would be better described as "the bow shock 
pressure wave can be slightly dissipated with a closely placed expansion 
fan (waves)."

Because the Wake shock is generated by the air filling in the hole behind 
the aircraft, there isn't as much that can be done about it, except to 
reduce the size of the hole the aircraft is boring in the sky. Note that on 
the modified F-5 the second Wake shock is larger in magnitude than the 
truncated Bow shock.

Craig Fink