RockSat 2010
Team CajunSat
Mark Roberts
Dr. Andy Hollerman
Department of Physics
University of Louisiana at Lafayette
Lafayette, Louisiana 70504
U N IVE R S ITY
OF
LOUISIANA
L a f a y e t t e
June 23, 2010
RockSat Objectives
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•
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Graduate student Mark Roberts
decided to design and build an
improved Geiger counter from the
component that could detect cosmic
rays from high altitude or near Earth
space.
We decided to participate in both the
LASPACE HASP 2009 and RockSat
programs for this payload.
Mark will use his work on these
projects for his Master’s degree
research.
Functional Block Diagram
GPS
Batteries
Lithium 9 Volt
Power
Data
G-switch
Power
Subsystem
Geiger Circuit
X/Y
Accelerometer
Port
Sensors
RBF
Z
Accelerometer
Flash
Memory
AVR
PCB
AVR
Microcontroller
Temperature &
Pressure
Sensor
Temperature
PCB
Systems Layout: Electronics Plate
OSL
Badge
G-Switch
GPS
OSL
Badge
Batteries
Temp
PCB
Z
Accelerometer
Micro-controller
Geiger Counter
Subsystems Layout
Micro Controller Board
Geiger-Mueller Tubes
LND 72118
LND 7134
LND 72118
Dead Time (µs)
70
Gamma
Sensitivity
45
(CPS/MR/HR)
LND 7134
Dead Time (µs)
Gamma
Sensitivity
(CPS/MR/HR)
Tube
Capacitance (pF)
Tube Capacitance
(pF)
3
45
7.5
3
What is Dead Time?
Dead Time : The minimum time between detectable pulses will be less than the recovery
time. This is the pulse resolving time.
Non-paralyzable dead-time: is defined as an event that occurs during this period is not
counted nor does it influence the ability of the tube to respond to later events.
Paralyzable dead time (resolve time): is the time duration between the end of the nonparalyzable dead time and a resolving point at which a pulse larger than the discriminator
level can be developed.
8
Split Source Method to determine Dead Time
A split radiation source is nothing more than a radioactive source that is split into
two pieces.
The source as a hole is considered to be the combined sources of N1 and N2
therefore I will call it NC . N1 is the left side of the split source for me; making N2
the right side of NC.
Counts are taken from N1, N2, and NC sources with the same time duration. Then
the dead time of the system can be calculated by
N1  N 2  NC
T
2 N1 N 2
[seconds]
I made my own split source with some Uranyl Acetate
that was laying around which happens to contain
Uranium 238! =o)
Geiger Plateaus
10
Geiger Counter
11
Geiger Counter
900
850
800
Voltage (V)
750
700
650
600
550
500
450
-3.2
-2.1
-1
0.1
1.2
2.3
3.4 4.5 5.6
Time (sec)
6.7
7.8
8.9
10
11.1 12
-4
x 10
Structure Subsystem
We have already milled the platforms. Also all structure
hardware (standoffs, bolts/nuts) has been received.
Air tight chamber for static port
Also have Polyethylene tubing
(1/4’’ x .170’’ x 25 ft) fitted with a
¼’’ OD x ¼” NPT connector.
The Stay Puft Test
The average off the shelf Marshmallow is a foam object with
closed wall air cells within the foam.
By placing a Marshmallow in a Vacuum the walls will expand
with reduction of pressure; when air is allowed back into the
chamber the walls collapse hence the marshmallow rapidly
deflates to a shriveled state from it’s original form.
The Stay Puft Test is to demonstrate the effectiveness of the air tight containers'
constructed. One marshmallow is placed inside the air tight container and then
placed into the vacuum chamber along with another marshmallow.
Other Tests performed…
Shock/Stress
Testing
Cold Test
Heat Test
15
Integrated Payload
16
Conclusions
• Launch the RockSat Geiger counter payload on June 24,
2010 at the NASA WFF.
• Continue working with students to develop payloads for high
altitude balloons and rockets:
- Recruit new outstanding graduate and undergraduate
students (available $17.5k/yr Master’s degree fellowship).
• Begin outreach into the physics and engineering of rocket
flight to local K-12 schools.
• Write winning proposals to continue efforts into the future:
- NASA EPSCoR Louisiana State Submission - Spring 2010
(subcontractor to Louisiana Tech University - $115k/yr).
• Continue training students with the motto “walk before you
run...”.
Acknowledgements
•
Drs. Greg Guzik and John Wefel at Louisiana State University for all
their help in the development of our LaACES and HASP payloads.
•
Other travel and related funding was provided by the State of
Louisiana Board of Regents using the Space Grant Program.
•
Colorado Space Grant and RockSat for providing this oppurtunity.
Questions???
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