Development of High Altitude Sprite Imagery Capability - Bruski

Development of High Altitude Sprite Imagery Capability
Shane M. Bruski 1
Department of Astronautics, USAF Academy, CO, 80840, USA
Caleb W. Whitlock. 2
Department of Astronautics, USAF Academy, CO, 80840, USA
Jordan R. Wittman 3
Department of Astronautics, USAF Academy, CO, 80840, USA
The United States Air Force Academy Space Club in conjunction with the USAFA Space Physics and
Atmospheric Research Center is developing the capability to study sprites using a specially constructed
payload box carried aloft by a meteorological sounding balloon. Sprites are electrostatic discharges that
occur in the upper reaches of the mesosphere at altitudes of 50-80 kilometers. The study of sprites is
important to the understanding and eventual prediction of mesospheric weather. The system developed by
the USAFA Space Club uses high-definition, visible spectrum imagery to capture the development and
propagation of sprites. In addition, the payload box carries a flight computer with a data logger to record
GPS sensor information. This system has the ability to conform to multiple mission profiles depending on the
location of the sprites. First, the payload can remain relatively stationary from 24 km to 30 km MSL for 4-6
hours in order to maximize viewing time. This is achieved by developing a radio frequency activated release
system to cut away extra sounding balloons providing free lift. Second, the payload can be carried aloft very
quickly and released on command to fall back to earth under parachute. The system is optimized for quick
turnaround and rapid deployment; it also offers the unique advantage of eliminating atmospheric distortions
because of its extreme altitude.
T
I. Introduction
he purpose of this study is to develop the capability to study the formation of sprites from a high altitude using
sounding balloons. The formation of sprites is of great interest in order to understand and characterize the space
weather environment. The system to image the sprites will be built using largely off the shelf products in order to
minimize the preparation time and minimize the costs. A series of test flights will be conducted that test the
capabilities of the flight hardware. First and foremost will be the method of tracking and recovering the payloads
after launch using the automatic packet reporting system (APRS) and the global positioning system (GPS). Once
that capability is proven, the next test phase will test the imagery equipment and the cut down system at altitude.
Finally, a long duration flight of four to six hours will be conducted at approximately 18-21 km altitude to
demonstrate the ability to remain in a relatively stable position to capture imagery around thunderstorms. To
accomplish these objectives, a flexible integrated balloon and payload system was developed and flown.
II. Tracking and Recovery
To ease cost and complexity issues it is necessary to recover the payload after the mission. A recovery of the
payload in downrange from the launch site requires a system that transmits position and altitude data in real time and
can record the data. Accuracy is paramount which led to the development of a GPS based tracking system utilizing
the automatic packet reporting system (APRS) network already set up for amateur radio operators. This system
developed incorporates the commercial transceiver called the Argent Data VHF Transceiver with integrated Tracker
2 designed to convert the NMEA sentences output by commercial GPS devices and then to send them down to an
amateur radio via serial packets. Two different GPS units were tested to insure redundancy of options. The Garmin®
1
Cadet, Department of Astronautics, USAF Academy, CO 80840, and AIAA Member.
2
Cadet, Department of Astronautics, USAF Academy, CO 80840, and AIAA Member.
3
Cadet, Department of Astronautics, USAF Academy, CO 80840, and AIAA Member.
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18 receiver and the GT-320FW high altitude receiver programmed to work over 25 km were both flight tested and
found to work flawlessly. A terminal node controller (TNC) is then used to translate the packets into the text
formatted readouts of altitude, velocity, position, and battery voltage data which is then recorded onto a computer in
real time using serial port monitoring software. This data is also transmitted to the network of digipeaters set up
throughout the nation which comprise the APRS network. This data is then available live on the website
http://aprs.fi/ and allows people all over the world to see the flight path of the balloon in real time. These also have
the option of a release and forget type of system that does not require a live chase. In flight 5, the APRS system was
critical to finding the payload. More will be discussed in the flight tests and results section.
Since tracking and recovering the payload is required , a redundant system that is completely independent of the
APRS system described above is needed. The SPOT® tracker is a commercial device commonly employed by
hikers and other outdoor enthusiasts based on its rugged design for extreme conditions. It can survive being
underwater, can transmit in low areas where the line of sight APRS system fails, and is extremely resistant to harsh
weather conditions. This system proved to be ideal for the recovery system particularly when the system descends
below about 762 meters or below the horizon of the nearest digipeater tower and the APRS signal is lost.
III. Still and Video Imagery Capture
The still and video imagery capturing system is designed to operate in a harsh environment for extended periods
of time and still take high quality images in the visible spectrum of its surroundings. Since a development from
scratch would prove to be extremely time demanding, the continued use of off the shelf commercial items was the
route chosen. A 5 megapixel Nikon P2® digital still camera that was programmed to take photos every minute was
used on flights one and two. This was to prove the feasibility of taking a commercial camera not designed to operate
in extreme conditions such as a near vacuum and prove it will operate correctly. In addition, during flight two, a
thunderstorm was seen in one of the still photos taken by the Nikon P2® and was later determined to be over 700
miles distant in Texas thus proving the advantage of a high altitude camera platform. On flights three and four, a
high definition GoPro Hero Naked® camera was carried aboard to test the feasibility and quality of video imagery
with that system. In future flights, it is planned that four HD Hero® cameras will be carried aloft to capture as much
of the sky as possible. Two cameras will be pointed up each at 45 degrees from the horizontal, one pointed straight
out, and finally one pointed straight down. From flight three, it was determined that from an altitude of 30.480 km
with the camera pointed straight down at the ground a 350 km viewing radius was theoretically possible. This results
in a 3801,000 square km viewing area in which to view lightning activity below the balloon.
IV. The Comparison of Flight Prediction Software
Before every flight, a set of two commonly used flight prediction software programs found online were used to
predict where the balloons were to fly. The models used were Balltrack Online developed by Near Space
Adventures and Balloon Trajectory developed by the University of Wyoming. The true value of these models lies in
predicting the landing site of the balloon. However, these models have different methods of calculating the flight
trajectories based on the inputs they require. Therefore, by looking at where the balloons actually landed and where
they were predicted to land gives an estimate of which model tends to be more accurate and which parameter causes
them to become inaccurate. The inputs to both models are found below in figures 1 and 2.
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Figure 1. Balltrack Online Input Parameter Example
Figure 2. Balloon Trajectory Input Parameter Example
In summary, it was found that Balltrack Online was the most accurate program of the two models so long as
good information was input. A more detailed comparison of the actual versus the predicted landing sites lies on the
appendices. In order to be accurate, the Balltrack Online model required accurate ascent and descent rate
information whereas the Balloon Trajectory automatically input those values.
V. Flight Tests and Results
Four flight tests have been conducted thus far. They have all served to test the tracking system and to develop a
comprehensive set of launch procedures that will ensure the most successful flights possible. Each of the four flights
is summarized below.
A. Flight One
Flight one was a test flight to evaluate the performance of a still camera at above 18 km and to test the Garmin®
18 GPS above that altitude as well. A secondary payload of a meteorological weather sonde was carried for the
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United States Air Force Academy’s Meteorology Department. The flight reached a maximum altitude of 31 km and
landed approximately 88 km north and east of the launch location. The unit was recovered successfully with the help
of a last second SPOT® tracker unit from a local high school.
B. Flight Two
Flight two was a test of the SPOT® tracker at high altitudes, a new payload box, and a new parachute. The
balloon flight was a launch and forgets mission since no live data was being sent down to the ground. The flight
landed approximately 125 miles north and east of its launch location. The balloon was recovered at 11 pm in zero
light conditions.
C. Flight Three
Flight three served as a test of the HD GoPro Hero Naked® video camera. The camera was pointed straight
down to demonstrate that position for future flights. The flight also demonstrated the necessity of having a
redundant tracking system as the APRS feed was lost when the balloon was approximately 762 meters in altitude.
The SPOT® tracker successfully sent its position to the tracking website 170 miles from the launch site. The balloon
was in the air for over four hours which contributed to the extreme distance the balloon landed from the launch site.
A unusual wind pattern at 30 km was identified. Winds usually are calm at 30 km however, on this occasion the
balloon picked up speed reaching a maximum velocity of 104.60 km per hour at 31 km in altitude.
D. Flight Four
Flight four served as a test for a new GPS receiver unit and to demonstrate a new flight profile used to track
balloons near thunderstorms. This flight was unique in that it used almost exactly the same materials as the last
flight to demonstrate rapid reuse and low turnaround time. A more accurate method of measuring lift was developed
to guarantee a short flight. 4.54 kg of weights were tied to the bottom of the balloon which was then filled until they
could be lifted off the ground. Approximate lift was 11 pounds at launch. At about 35 minutes into the flight and at
an altitude of 17 km extreme turbulence was encountered. This combined with a small amount of ice buildup on the
cord connecting the parachute to the payload box led to the payload box separating from the balloon and parachute.
The payload box survived a free fall from 17 km to impact at almost 112.63 km per hour with little to no damage.
Again, this flight demonstrated a need for a redundant tracking system as the violent force of the impact caused the
SPOT tracker to turn off. The box was located using previous data points to calculate descent rate and then
combined with the winds that day to draw a probability circle to where it landed. The system was still transmitting
its position 24 hours later which was picked up by HAM radio and when entered into a handheld GPS led straight to
its recovery site.
VI. Future Test Flights
Two final test flights remain before the system is considered operational. The first test will demonstrate the
ability of the system to successfully cut the balloon away from the parachute using a HAM radio to send a signal to
a receiver onboard the balloon. This signal will be in the form of a coded sequence of numbers that will be read by a
DTMF (dual tone multi-frequency) board and will activate a relay switch. This switch will allow current to flow
through a nichrome wire wrapped around the nylon cord connecting the balloon to the parachute. With the current
flow, the wire will heat up and melt through the string in a matter of seconds. In all previous flights, the balloons
have failed to shred as they are designed to do at altitude. They remain mostly intact as 2-3 kg of dead weight above
the parachute causing it to only partially inflate enter into a fast than expected fall. The cut down system will allow a
precise maximum altitude and a more predictable landing site. Finally the second test flight that remains will serve
as a test of the high altitude long duration flight at a relatively stable position. Through previous flights and the
advice of the USAF Academy Meteorology Department, a region at approximately 18-21 km has been found to
contain winds that are below 16.09 km per hour. This altitude is ideal for long duration flights as it is high enough to
be above most of the atmospheric distortion and out of the winds. Should this region not prove to be calm, the flight
will continue to rise until a calm region is found. At launch, the flight will consist of two balloons connected
separately to the payload box. The large main balloon will be filled to the point where its lift exactly matches the
weight of the payload and the system will be neutrally buoyant. The second smaller balloon will simply to provide
the lift needed to get the system up to the desired altitude. A separate cut down device will be connected to each of
the balloons and at that desired altitude, the balloon providing the free lift will be cut away and the system will
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ecome neutrally buoyant. After 4-6 hours, the main balloon will be cut away as helium will begin to diffuse
through the walls of the balloon and the system begins to sink. This flight will be the final flight before the system
becomes operational and long duration flights studying sprites are possible. Finally, a new spring scale was acquired
to allow precise measurements of lift which will enable a more accurate relation between ascent rate and the amount
of helium in the balloon.
Appendix A
Balloon Ground Tracks and GPS Coordinates
Figure A1.Balloon Trajectory Forecast for Flight One
Figure A2. Balltrack Online Forecast Flight One*
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Figure A3. Balloon One’s Actual Landing Site
Figure A4. Flight Two Balloon Trajectory Prediction
Figure A5. Flight Two Balltrack Online Prediction*
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Figure A6. Flight Two SPOT Tracker Coordinates Actual
Figure A7. Flight Three Balloon Trajectory Prediction
Figure A8. Flight Three Balltrack Online Prediction*
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Figure A9. Flight Three SPOT Tracker Coordinates Actual
Figure A10. Flight Three APRS Data Google Maps Actual
In summary, the Ball Track Online outperformed the Balloon Trajectory for landing accuracy on two of the three
flight tests. The Ball Track Online software was found to be more flexible and more able to take into account the
changes in the balloon parameters. Those parameters included the ascent rate and the descent rate neither of which
could be input into the Balloon Trajectory. These two parameters are absolutely critical for the duration the balloon
is in the air as they determine how long the balloon will remain in the winds aloft. Consequently, these parameters
determine how far the winds will push the balloon. Although the Ball Track Online was found to be more accurate,
the practice of comparing the two models will still be continued. If they agree on direction, then it can be concluded
the weather data going into them will yield a valid flight path of the balloon and their results can be trusted.
*Note that the blue line is the balloon’s ascent and the red is the descent
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Appendix B
Flight Imagery
Figure B1. Flight Configuration
Figure B2. Thunderstorm Located in Texas
700 miles From Launch Site
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Figure B3. HD Video Camera View Looking
Straight Down from 100,000 Feet
Acknowledgments
A great deal of faith has been placed in us by the Space Club’s advisor; Dr. Ken Siegenthaler who was has
continually encouraged us to expand our horizons. Without him, this project would never have lifted off the ground.
A special thanks also goes to Dr. Geoff Mcharg who supports these endeavors as we work towards imaging high
altitude sprites. We also want to thank Mr. John Clark for his advice and help with the electronics.
References
Website
1 Glahn, Rick von, “Balloon Related Programs”, URL: http://www.eoss.org/balsoft.htm [cited 06 March 2011].
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