The NASA Ames Hypervelocity Free Flight Aerodynamics Facility ballistic range is described. The various configurations of the shadowgraph stations are presented. This includes the original stations with film and configurations with two different types of digital cameras. Resolution tests for the 3 shadowgraph station configurations are described. The advantages of the digital cameras are discussed, including the immediate availability of the shadowgraphs. The final shadowgraph station configuration is a mix of 26 Nikon cameras and 6 PI-MAX2 cameras. Two types of trigger light sheet stations are described visible and IR. The two gunpowders used for the NASA Ames 6.251.50 light gas guns are presented. These are the Hercules HC-33-FS powder (no longer available) and the St. Marks Powder WC 886 powder. The results from eight proof shots for the two powders are presented. Both muzzle velocities and piston velocities are 5 9 lower for the new St. Marks WC 886 powder than for the old Hercules HC-33-FS powder (no longer available). The experimental and CFD (computational) piston and muzzle velocities are in good agreement. Shadowgraph-reading software that employs template-matching pattern recognition to locate the ballistic-range model is described. Templates are generated from a 3D solid model of the ballistic-range model. The accuracy of the approach is assessed using a set of computer-generated test images

Bogdanoff, David W.

Cornelison, Charles J.

Perez, Alfredo J.

Wilder, Michael C.

NASA Technical Reports Server

National Aeronautics and 
Space Administration
Entry Systems and Technology Division
Ames Research Center
Upgrades and Modifications of the NASA Ames
HFFAF Ballistic Range
David W. Bogdanoff 
AMA Inc., NASA Ames Research Center, Moffett Field, CA, USA
Michael C. Wilder, Charles J. Cornelison
NASA Ames Research Center, Moffett Field, CA, USA
Alfredo J. Perez
Aerodyne Industries, NASA Ames Research Center, Moffett Field, CA, USA
68th Meeting of the Aeroballistic Range Association, 
Monterey, CA, USA, September 17 – 23, 2017
https://ntrs.nasa.gov/search.jsp?R=20180001561 2019-08-30T13:11:11+00:00Z
Overview
• Introduction
• Shadowgraph imaging
• Model detection
• Replacement gunpowder for light gas gun operation
• New hardware for facility systems checks
• Film reading software developments
• Summary and conclusions
268th Meeting of the Aeroballistic Range Association
NASA Ames HFFAF Ballistic Range
• 16 orthogonal shadowgraph stations 1.52 m apart, 22.9 m total length
• Windows – 30 and 38 cm
• Record images with sheet film or cameras
• Shuttering – Kerr cells or gated ICCD cameras
• Pressures – 100 µ to 1 atm
• Gases – air, CO2, N2, Ar, others
• Launchers - 20 to 61 mm powder guns, 170 m/s to 2.0 km/s                              
- 7 to 38 mm two stage light gas guns, 3 to 8 km/s                  
3
•  NASA  Ames HFFAF (Hypervelocity Free Flight Aerodynamics Facility)
68th Meeting of the Aeroballistic Range Association
Shadowgraphs
4
Kerr-cell Shutter
Film Box
Flight Direction
NASA Ames HFFAF Ballistic Range
68th Meeting of the Aeroballistic Range Association
5Shadowgraph Optical Set-up
Shadowgraph Imaging
68th Meeting of the Aeroballistic Range Association
• Only this portion is 
altered for digital 
image recording.
• Sheet film camera set-
up shown here.
North South
Model flight
direction
Shadowgraph Imaging: Recording Methods
• Sheet Film
- High spatial resolution
- Long turn-around (2-3 hours 
to develop images)
- Requires hazardous 
chemicals
• ICCD Camera
- Relatively low spatial 
resolution, high cost
- High temporal resolution 
(gated camera) – No Kerr 
cell shutter required 
• Digital SLR Camera
- High spatial resolution, low 
cost
- Kerr cell shutter required
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(Removed)
7Shadowgraph Imaging: Recording Methods
68th Meeting of the Aeroballistic Range Association
Sheet Film
Digital: Gated ICCD
Digital: SLR / Kerr Cell
Film holder
Dark slide
Kerr cell
Pulse forming network 
8Shadowgraph Imaging: Resolution
68th Meeting of the Aeroballistic Range Association
Detail of Resolution Chart
Line Groups 0 and 1
2.5 mm
(0.098 in)
12.5 mm
(0.492 in)
Spatial resolution of each shadowgraph camera configuration assessed 
from images of a USAF 1951 resolution test chart
Shadowgraph Image of Test Chart
Shadowgraph Imaging: Resolution
• Film, scanned to resolve the film grain, and the digital SLR images all 
resolve elements in group 1 to at least element 3 (results vary station 
to station, shot to shot)
- Line spacing = 2.52 lines/mm
- Bar width = 0.198 mm
• ICCD images resolve element 4 of group 0
- Line spacing = 1.41 lines/mm
- Bar width = 0.355 mm 
68th Meeting of the Aeroballistic Range Association 9
Film Negative Scan
120 pixels/cm
ICCD Camera
38 pixels/cm
Digital SLR Camera
130 pixels/cm
Shadowgraph Imaging: Resolution
• Example images of a typical HFFAF model in flight
- 45o half angle cone 
- 3.3 cm base diameter
- 0.762 cm nose radius
- Flight speed = 2700 m/s
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Film Negative Scan
120 pixels/cm
ICCD Camera
38 pixels/cm
Digital SLR Camera
130 pixels/cm
11
Shadowgraph Imaging
Advantages of new shadowgraph set-up (26 Nikon cameras
and 6 PI-MAX cameras):
• Immediate availability of photos versus 2 – 3 hour wait
for film development
• No digitizing of sheet film photos required (2 – 3 additional 
hours of work)
• No film processing equipment with hazardous media 
to maintain
• 26 out of 32 cameras have high resolution – 6 low
resolution cameras acceptable if each is located between
two high resolution cameras
68th Meeting of the Aeroballistic Range Association
Replacement gunpowder for 1.5” light gas gun
• Original powder was Hercules HC-33-FS – no longer 
available.
• Replacement powder, St. Marks WC 886, found.
• Three proof shots made with new powder – five proof 
shots had been made with old powder
• Gun operating conditions:
- Pump tube length – 18.3 m
- Powder mass – 1.1, 1.5, 2.0 kg
- Hydrogen pressure - 471 kPa
- Piston mass – 21.3 kg
- Break valve rupture pressure – 22.1 MPa
- Projectile – 49 g Lexan slug
- Range pressure – 2.67 kPa
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13
Replacement gunpowder for 1.5” light gas gun
Muzzle velocity versus powder mass for both powders
68th Meeting of the Aeroballistic Range Association
Image-Reading Software Developments 
• Motivation:
- A test was recently conducted of a model 
with a faceted geometry: the Adaptive 
Deployable Entry and Placement 
Technology (ADEPT) Sounding Rocket 
(SR-1) vehicle.
- Unlike blunt conical models typically tested 
in HFFAF, the ADEPT SR-1 profile in 
shadowgraphs appears different vs. roll 
angle and attitude angle normal to the 
image plane.
- Pattern matching using templates 
generated from the CAD model of the 
ballistic-range model could potentially yield 
all attitude angles from a single image.
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• A template matching pattern recognition algorithm was developed for 
determining the position and attitude of a ballistic-range model in 
shadowgraph images.
ADEPT SR-1 Ballistic-Range Model 
ADEPT SR-1 Profiles Rotated 18o
Nose Into Page Nose Out of Page
Image Reading: Template Generation
68th Meeting of the Aeroballistic Range Association 15
• 3D CAD Model at a Given Attitude 
- Attitude angles (pitch, yaw, and roll) 
measured about the center of gravity 
(CG) 
- CG located at the CAD origin
Side-View Template
x-z (Pitch) Plane
Top-View Template
x-y (Yaw) Plane
• Cross correlation of image and template
- The maximum value of the cross-correlation coefficient matrix, Cmax, is 
maximized when the template attitude matches the attitude of the model in 
the shadowgraph image
- Location of Cmax determines CG location of the model
Image Reading: Template Matching
68th Meeting of the Aeroballistic Range Association 16
Shadowgraph Image Template
Cmax = 0.98
xCG
zCG
Cross-Correlation Matrix
C
Image Reading: Attitude Determination
• Find in-plane template 
angle that best 
matched the image
- Strongest cross 
correlation occurs when 
the template attitude 
matches the attitude of 
the model in the 
shadowgraph image
• Perform search 
iteratively on both side 
and top view 
shadowgraph images
68th Meeting of the Aeroballistic Range Association 17
Cmax vs. Template In-Plane Angle
Image Reading: Attitude Determination
• Out-of-plane template 
angle effects Cmax, but 
has small impact on in-
plane angle match
- Consequently, it is 
possible in this example 
to determine both in-
plane and out-of-plane 
angles from one image
68th Meeting of the Aeroballistic Range Association 18
Cmax vs. Template Out-of-Plane Angle
Image Reading: Attitude Determination
• Roll angle can also be 
determined for certain 
model geometries, 
however, 
• Cmax is less sensitive 
to template roll angle
- Roll results in small 
changes to the model 
profile
• Multiple peaks occur 
- Axial symmetry of this 
model
• User verification of roll 
angle is required
68th Meeting of the Aeroballistic Range Association 19
Cmax vs. Template Roll Angle
Image Reading: Example Result
68th Meeting of the Aeroballistic Range Association 20
Top ViewSide View
Image Reading: Evaluation
• Computer-generated 
“shadowgraph” images were used 
to evaluate the accuracy of the 
image reading software
- 160 orthogonal image pairs generated
- Model position and attitude drawn from 
uniformly-distributed random numbers
- CG location rounded to nearest pixel 
when creating the images (expected 
accuracy is therefore no better than 1 
pixel)
68th Meeting of the Aeroballistic Range Association 21
+x
+z
5 in (127 mm)
+θ
5 in 
(127 mm)
+x
+y
-ψ
Side View
Top View
Image Reading: Evaluation
• A second set of images included 
image distortions representative 
of HFFAF images
- A 2nd order curvature
 Horizontal lines curve down range
 Vertical lines curve up
- Images were smoothed to soften the 
edges of the model and wires
- Speckle noise was added
- Images were randomly-rotated 
between ±2 deg to represent 
misalignment of sensor-plane axes 
with tunnel axes
- The same positions and attitudes 
were used in both sets
68th Meeting of the Aeroballistic Range Association 22
Exaggerated illustration of 
typical image distortions
Image Reading: Evaluation
CG location
• Histograms of the 
difference between 
measured and actual 
position is shown for the 
down-range position
- Normal distributions for Un-
Distorted Images
- Distribution of errors slightly 
skewed in direction of 
distortion for distorted 
images
- Larger standard deviation is 
proportional to degree of 
distortion
• Similar results were 
obtained for the cross-
range positions, y and z
68th Meeting of the Aeroballistic Range Association 23
Down Range (x) Measurement Error
x (meas) – x (actual)
(pixels)
-0.36 -0.27 -0.18 -0.09 0 0.09 0.18 0.27 0.36
(mm)
Image Reading: Evaluation
68th Meeting of the Aeroballistic Range Association 24
Model Attitude
• Pitch and yaw (not 
shown) angle 
measurements were 
minimally effected by 
image distortion
- Mean and standard deviation 
unaffected by the distortions 
applied (3σ ~ 0.5 deg)
- However, more cases 
deviated from the actual 
angle with distortions applied
Pitch Angle Measurement Error
θ (meas) – θ (actual), deg
Image Reading: Evaluation
68th Meeting of the Aeroballistic Range Association 25
Un-distorted Images
Distorted Images
Roll Angle
• The unique geometry of 
the ADEPT model allows 
roll-angle identification by 
this method
• The uncertainty is larger 
than for pitch or yaw since 
the model profile variations 
are small with roll
• The correct angle was 
more frequently found for 
un-distorted images, 
however, the error for 
misidentified roll angles 
was much larger
- Possibly due to pixilation of the 
un-distorted images
Roll Angle Measurement Error
φ (meas) – φ (actual), deg
Summary and Conclusions
Several recent upgrades, updates, and hardware evaluations at 
the NASA Ames HFFAF ballistic range were discussed
Conversion to digital shadowgraph imaging:
• Current configuration:
- 26 digital SLR cameras equipped with heritage Kerr-cell shutters
 Resolution approaches the film-grain resolution of the standard sheet film
 Camera cost is low
- 6 gated ICCD cameras
 Lower resolution, but Kerr cell not required
 Camera cost is high
• Advantages of digital imaging:
- Immediate availability of images for evaluation (vs ~3 hours for film)
- No need for film-processing chemicals and equipment
- No need for film scanning (an additional 2-3 hours)
68th Meeting of the Aeroballistic Range Association 26
Summary and Conclusions
Replacement Gun Powder:
• The heritage powder (Hercules HC-33-FS) used in the 
Ames 1.5” light gas gun is no longer available
• A replacement powder (St. Marks WC 886 ) was identified
• Proof shots were performed for expected muzzle 
velocities between 3 km/s and 5 km/s
- Muzzle velocities were 5 – 9% lower (for the same powder mass) 
for the replacement powder
- Difference in performance of the powders easily compensated for 
by increasing powder load of new powder ~10%
- Additional evaluations are planned
68th Meeting of the Aeroballistic Range Association 27
Summary and Conclusions
Shadowgraph-reading software:
• Shadowgraph-reading software that employs template-
matching pattern recognition was developed
- For the case studied, 3σ measurement accuracy was 
±0.3 mm in position
±0.6o for pitch and yaw 
±1.8o, for roll angle, however user verification of roll angle was 
required
68th Meeting of the Aeroballistic Range Association 28
Summary and Conclusions
(Discussed in the full paper, but not presented here)
Model detection:
• An off-the-shelf, solid-state, model detection system was retro-
fitted to the HFFAF at 3 stations to evaluate as a potential 
replacement for the heritage vacuum-tube technology
- New system is more susceptible to spurious triggers (early and/or late 
detection) when the projectile is self-luminous (typical for speed > 3 
km/s)
- New system functions well for lower-speed shots
- No further evaluations currently planned
System check hardware: 
• A high-velocity rifle is used to check model-detection and 
shadowgraph imaging systems
• Updated from 0.220” Swift rifle to a 0.204” Ruger 
- Ammunition for the heritage rifle became difficult to obtain
- No impact to facility operations have been found
68th Meeting of the Aeroballistic Range Association 29
National Aeronautics and 
Space Administration
Ames Research Center
Entry Systems and Technology Division
68th Meeting of the Aeroballistic Range Association 31
Backup
32
Shadowgraph optical set-up – spark gap, 
collimating mirror and side station window – this 
portion of set-up always remains unchanged
Shadowgraphs
68th Meeting of the Aeroballistic Range Association
33
Shadowgraph optical set-up – focussing mirror 
and film box. Kerr cell is behind film box.
Shadowgraphs
68th Meeting of the Aeroballistic Range Association
34
Model Detection
Off-the-Shelf Infrared Model Detection System
68th Meeting of the Aeroballistic Range Association
35
Model Detection
Standard Custom Visible Light Model Detection System
Phototube
68th Meeting of the Aeroballistic Range Association
Model Detection
Tests are underway to investigate the use of a commercially-
available infrared (IR) model detection system as a replacement 
for the custom-designed and built visible-light photobeam system 
• Standard system
- Light sheet source: Visible light from halogen lamp collimated by strip 
mirror
- Light detection: Phototube
• Off-the-Shelf system
- Light sheet source: Row of IR LEDs
- Light detection: Row of IR phototransistors
• Results:
- IR system found to be more likely to trigger at erroneous times with 
self luminous models (e.g. hypersonic tests with radiating bow shock)
- Three IR systems implemented; on account of above issue, no more 
planned at this time
68th Meeting of the Aeroballistic Range Association 36
37
Shadowgraph Imaging
Sheet film/camera comparisons
68th Meeting of the Aeroballistic Range Association
38
Replacement gunpowder for 1.5” light gas gun
• Original powder was Hercules HC-33-FS – no longer
available.
• Replacement powder, St. Marks WC 886, found.
68th Meeting of the Aeroballistic Range Association
39
Replacement gunpowder / New hardware
• To check out the shadowgraph stations, in the past
a 0.220” rifle with 0.220” Swift ammunition was used.
• It was becoming harder to obtain the Swift ammunition,
so a switch to a 0.204” Ruger rifle was made.
68th Meeting of the Aeroballistic Range Association
Replacement gunpowder
•  Muzzle velocities were 5 – 9% lower with the new
powder than with the old powder
•  This can easily be compensated for by increasing
the powder load with the new powder by ~10%
New hardware
Image Reading: Coordinate System
• Position of the center of gravity 
(CG) of the model measured 
relative to the reference wire origin
68th Meeting of the Aeroballistic Range Association 40
• The in-plane attitude measured  
relative to the reference wires
• Roll angle typically determined with 
reference pins on the model
5 in 
(127 mm)
Taut wires (4x)
Top View
yCG
+ψ
(yaw angle)5 in (127 mm)
Plumb 
wires (4x)
Catenary 
wires (2x)
xCG
zCG
+θ (pitch angle)
Side View
Image Reading: Evaluation
CG location
• Residual error (i.e., difference between 
measured and the actual position) plotted as 
histograms for the 160 image pairs
• Normal distributions for Un-Distorted Images
• Distribution of errors slightly skewed in 
direction of distortion for distorted images
68th Meeting of the Aeroballistic Range Association 41
Un-Distorted Images
x y z
Mean error 1.07 pix0.10 mm
1.00 pix
0.09 mm
-1.04 pix
-0.10 mm
3σ 1.01 pix0.09 mm
1.06 pix
0.10 mm
1.16 pix
0.11 mm
Distorted Images
Mean error 1.68 pix0.16 mm
0.60 pix
0.05 mm
-0.53 pix
-0.05 mm
3σ 2.79 pix0.27 mm
2.93 pix
0.27 mm
3.28 pix
0.30 mm
Image Reading: Evaluation
68th Meeting of the Aeroballistic Range Association 42
Un-distorted Images
Distorted Images
Un-Distorted Images
Pitch (θ) Yaw (ψ) Roll (φ)
Mean error 0.004o 0.002o 0.69o
3σ 0.51o 0.31o 11.34o
Distorted Images
Mean error 0.003o 0.009o -0.04o
3σ 0.64o 0.59o 1.79o
Model Attitude
• Pitch and yaw angle measurements were 
minimally effected by image distortion 
• For roll angle (automated results without user 
verification), the correct angle was more 
frequently found for un-distorted images, 
however, the error for misidentified roll angles 
was much larger (reason TBD)


Upgrades and Modifications of the NASA Ames HFFAF Ballistic Range

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