TERSatMassachusetts

Instituteof Technology

Eric Peters, Danilo Roascio, Leonard Tampkins, Kezi

Cheng

July 1st, 2012

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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

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Stanford VLF group image

SHOT Design Overview

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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

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Mechanical Results

Box intact with cover slightly opened

Components broke free of restraints during landing

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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!

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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

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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!

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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!

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Thank you!

Questions? Comments?

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