$50SAT - MO76

Eagle2

21st November 2013, 07:11. Dombarovsky air base

$50SAT,128,,162,,,54,3,,21,140,87,,102,,3723,*70

Howie DeFelice AB2S Systems Engineer in commercial VSAT

Michael Kirkhart KD8QBA Electronics engineer, hardware hacker, amateur radio operator

Stuart Robinson – GW7HPW Computer Network Support

Professor Robert Twiggs Professor of Space Science

The Team

The PocketQube Concept

Pioneered by Professor Twiggs

Smaller satellites, lower launch costs

Based on 50mm cube format

The PocketQube Concept

Simple to build

Bring the construction within the remit

of schools and colleges

Off the shelf commercial components

What's a PICAXE?

PICAXE – based on PIC micro controller

Easy to understand

Easy to program

On board firmware

Morse Beacon

Low power

Minimum Requirements

Report on battery and charge

Can be turned off remotely

Would other radios fit in a 50mm cube?

Direct modulation mode

Packet handler

Frequency agile

Minimum distance required - 600kM

100mW FSK 1-2kM range

RFM22B

Caerphilly to Machen – 8km

Cardiff to Mendips

40km

Uplink Budget Calculation

I estimate the threshold level to receive consistent packets to be about 18 dBm TX power for the 40 Km link.The estimated signal strength at the receive end of the 40Km link would be -99 dBm. The typical BER performance for an FSK demodulator for a BER of 10E-6 is about 15 dB Eb/N0, which should be roughly equivalent to S/N. Assuming that this is the case, that would make our estimated sensitivity or Minimum Discernible Signal, MDS) -99dBm - 15 dB = -114 dBm. That's about 7 dB below spec, but the data still had some assumptions involved. Given the circumstances of the test the only conclusion I would make is that things are probably pretty close to optimum. The one piece of missing information is RFM22 noise figure. For a space application this is the most important factor in evaluating link performance because it adds directly to the MDS: MDS = -174(dBm/Hz) + 10 Log BW (Hz) + NF (the BW here refers to the pre-detection bandwidth, 15 KHz for a typical FM receiver) Making the assumption of a 15 KHz bandwith and backing into the previously assumed MDS of -114 dBm would give us a NF of 18 dB. However, we need to remember that this testing was done with the antenna as the signal source so this NF number includes the NF of the antenna, in this case an almost isotropic source. With that in mind, the 18 dB number is reasonable and is useful when evaluating the in orbit performance of the receiver. Using a system noise figure of 18 dB and a required S/N of 15 dB, I recalculated the required uplink power at about 5 deg elevation and overhead. At 5 deg elevation, a slant range of about 2600 Km, you would need an EIRP of 55 dBm, or 36W into a 10 dBi beam. At 90 deg elevation (overhead) you need an EIRP of 28 dBm or less than a watt into an omni. Based on this, I think we have a viable communications link over most of the pass.

Uplink Budget Calculation

in Summary

At 5 deg elevation, a slant range of about

2600 Km, you would need an EIRP of 55

dBm, or 36W into a 10 dBi beam.

Based on this, we have a viable communications link over most of the pass.

At 90 deg elevation (overhead) you need an

EIRP of 28 dBm or less than a watt into an omni.

Design of $50SAT

Do the minimum to prove the concept

Watchdog and latch up protection

RFM22B

PICAXE 40X2

40mm boards

Philosophy – you can’t add simple

$50SAT Clean Room Facility

Development Model

Prototype PCBs

Current monitor

4 sets of TASC solar cells

Construction of $50SAT

4 x LTC3105 MPPT and charger board

Solar power

Battery

and

RFM22

Monitoring & Reporting

EEPROM corruption

Flash corruption test

Voltages

Currents

Detect the RFM22B 'smart' restart issue

SEU RAM check

Communications

FSK RTTY

1Kbps data telemetry

Fast Morse data – 120WPM

Encoded the charge and battery volts

Morse callsigns – 5

The Flight Model Build

Michael Kirkhart

Command Uplink

Meanwhile.....

Software errors, despite all the testing !

Pointing the solar panels at the Sun !

Spin fading ?

Battery – well not really

What we got wrong

Time below 0C – much longer than expected

Open source and public

FSK RTTY

Digital telemetry – viable satellite comms

Kept it simple

Amount of testing

It Worked !

What we got right

Professor Twiggs

Finally - Thanks to:

Morehead University

GAUSS Group - University Roma

PE0SAT LW2DTZ ST2NH DK3WN JA0CAW PE2G PY4ZBZ

VE3HEO LW2DTZ LU4EOU WB2AOZ EU1XX N1AIA

EA1JM Ozqube-1 JA0CAW IW0HLG VK2XV

M5AKA

Chantal Cappelletti, Universidade de Brasília

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