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TERSatMassachusetts
Instituteof Technology
Eric Peters, Danilo Roascio, Leonard Tampkins, Kezi
Cheng
July 1st, 2012
1
Mission Overview
Satellite Goals: - Demonstrate wave-particle interaction
within the inner Van Allen belts - Transmit VLF waves at LEO altitude - Demonstrate science behind potential
radiation remediation technique
SHOT II Goal:- Use VLF wave transmitter to
demonstrate ability to transmit signal to a receiver on the ground
Connection:- Demonstrates payload concept of
operations, tests prototype VLF receiver parts
Mini-demo
2
Stanford VLF group image
SHOT Design Overview
3
Mechanical Results
• Box intact• Thermal isolation between requirements
• Battery performed nominally (i.e., Tbatt > -10 °C)• PA didn’t exceed nominal temperature (i.e., Theatsink < 140 °C)
• Cover slightly open• Several screws didn’t hold components during landing
4
Mechanical Results
Box intact with cover slightly opened
Components broke free of restraints during landing
5
VLF transmitter results – COIL
• Goal: reception from ground of a VLF (17.319 kHz) signal generated by payload
• Problems experienced:
• Lots of VLF noise at launch site
• Self oscillation of LNA amplifier
• No properly keyed signal received at transmission frequency
• Filtering of nearby signals doesn’t show expected keying pattern
• Correlation may reveal something within noise, but in any case the transmission will not be as efficient as expected!
6
VLF transmitter results – PLATES
• Goal: measure on-board the VLF (34.638 kHz) current transferred to plates in correlation with environment
• Data loggers recorded a drop in the plates voltage
7
CURRENT INCREASE?
?
Baloon telemetry
VLF TX – Reasons for Voltage Drop?
• What this could’ve meant:• Increase in current/radiation efficiency at high altitudes
• What this probably means:
• The plates (outside the box, T < -56 °C) cooled through copper cables and circuits to the op-amp input, and somehow influenced it
• Temperatures of 1 MΩ resistor is unlikely to be involved, the transition to/from higher voltage drop is too sudden
• More investigation needed to confirm this theory!
8
Lessons Learned and Future Work
• Better securing of components inside box in future SHOT launches (only for functionality after recovery, no problems in flight)
• VLF transmission with “infinitesimally short” antenna is HARD!
• Focus more on reception equipment for VLF communication:• wideband receiver is not optimal in high noise conditions• tuned amplifier may help reject noise and stabilize operation
• Anything outside the box is cold. This will involve additional precautions on the connections. But can we exploit for our goals the low temperature of the high altitude environment?
• More research needed!
9
Thank you!
Questions? Comments?
10
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