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PICAXE IN SPACE by Clive Seager At 07:10 UTC on November 21st 2013 Kosmotras successfully launched a Dnepr rocket from Dombarovsky Air Base (Russia), carrying the United Arab Emirates’ DubaiSat-2 and 31 other satellites. One of these was not much bigger than a cigarette packet and cost less than $200! A part from the fact that this mission set a new record for the most payloads (32) carried into orbit by a single rocket, one of those satellites, Unisat-5, itself carried internally a number of smaller sub-satellites including four CubeSats and the very first four PocketQube satellites. These were launched almost immediately after Unisat-5 itself was deployed. One of these satellites was controlled by a PICAXE microcontroller. PocketQube is a new class of miniaturised satellites developed by Professor Bob Twiggs, a professor at Morehead State University, Kentucky, USA, who, together with Professor Jordi Puig-Suari designed the larger CubeSat class. PocketQubes use a ‘unit’ size one eighth the size of the previous CubeSat standard – with a ‘1-unit’ length now siliconchip.com.au measuring just 50mm. ‘$50SAT’ as it is affectionately referred to by its developers (its official designation is Eagle 2) is a 1.5 unit, 210g, PocketQube satellite controlled by a PICAXE-40X2 microcontroller. $50SAT has been an international collaborative education project between Professor Bob Twiggs and three radio amateurs, Howie DeFelice, AB2S, Michael Kirkhart, KD8QBA, and Stuart Robinson, GW7HPW. $50SAT was deployed successfully and is now fully operational, orbiting Earth at around 7.5km/s at a distance of around 600km. At the time of writing it is not known if it will be large enough to be accurately tracked by Norad by itself but it can still be tracked fairly reliably using the larger ‘Unisat-5’ it was launched from. February 2014  11 Both sides of the PICAXE and radio motherboard PCB. That’s not much to control a spacecraft, is it! The primary purpose of $50SAT was to create a ‘proof of concept’ that could be used as a cost effective platform for engineering and science students to use for developing real-world skills. The PocketQube form factor has no precision mechanical parts and can be built in a school workshop from locallyobtained 1.5mm sheet aluminium. Professor Twiggs was very keen to support the use of the PICAXE microcontroller as it is very low cost and can be simply programmed in BASIC, without the need for C or assembler programming skills, making it ideal for high school students. $50SAT is comprised of a sheet aluminium cube covered in solar cells. Internally it is quite bare, just two main 40mm x 40mm circuit boards stacked above the battery. The first is the processor/radio board which contains the PICAXE 40X2 microcontroller programmed in PICAXE BASIC, the Hope RFM22B single chip radio transceiver and some peripheral devices such as a DS18B20 temperature sensor. The second board is the power control and monitor board. This board contains four maximum power point controllers, one for each solar array on each side of the spacecraft as well as current monitors for the battery and summed solar power. The battery is an ‘off the shelf’ Klic-7002 lithium ion digital camera battery, charged by the solar panels to a maximum of 3900mV. The $50 nickname was the original budget the development team thought would be the hardware cost. Unfortunately the cost of the high tech triple junction solar cells blew that budget in one hit but you could still build one yourself for around US$200.00 All the circuits, PCB artwork and PICAXE BASIC programs are available on the designer’s website. ute, as well as a fast morse beacon and FSK RTTY. All transmissions from and to $50SAT are at the same frequency, 437.505MHz (but allow up to ±10kHz of Doppler shift). The FSK RTTY sent out by $50SAT is best detected using a ‘Funcube’ USB dongle with a omni-directional antenna but the slow morse should easily be heard using standard amateur radio receivers and has even been heard on lowcost UHF hand-helds. The initial communications requirements at design stage were to: 1. Transmit a slow Morse call sign identity. 2. Provide remote command uplink to turn radio transmissions off (a requirement of all satellites). 3. Operate at a programmable frequency in the 70cm amateur radio band. 4. Include a method of getting data back on solar panel and battery performance. Radio on board The small size of the satellite made it difficult to find a ready-built radio transceiver for communications. There are special radio modems designed for use in CubeSats but they are either not low enough in cost or not small enough for use in the smaller 50mm PocketQube. Therefore the off-the-shelf US$5 Hope RFM22B FSK data transceiver was selected. The RFM22B is based on the Silicon Labs Si4432 device and has a mere 100mW transit power. If you look carefully at the photos you will see Listen in on 70cm $50SAT operates in the 70cm amateur radio band and transmits a slow morse beacon around once a min12  Silicon Chip So you want to build a satellite? Go right ahead: one of the aims of the project was to provide a model for a low-cost satellite which was within the capabilities of high school students. siliconchip.com.au QubeSats Launchers Need to get rid of halogen ceiling lamps?? FORGET HALOGEN GLOBE REPLACEMENTS THIS IS THE BETTER WAY! 4" & 6" Down Lights Unisat 5 with PocketQube launchers. wed As revie HIP SILICON C 3 Feb 201 PocketQube Launchers what that folding dipole antenna is built from – yes, it really is a tape measure purchased from the local hardware store! The ‘FM’ morse is not true FM as such but is generated by the PICAXE microcontroller switching the RFM22 transceiver between two different carriers. The data transmitted includes battery state, idle/receive/ transmit currents, solar charge current and voltage and well as temperature (measured by a common DS18B20 sensor). Summary At the date of writing (late November 2013) the designers are delighted with the performance of the satellite. It is working exactly as designed and is living proof that a working satellite really can be built on a shoestring budget by students using ‘off the shelf’ components such as PICAXE microcontrollers and radio transceivers. Now who do you know who is launching a rocket with room for a (admittedly tiny) extra payload? Congratulations to all those involved. The sky is no longer the limit for back shed tinkerers – space has no limits! SC The Elegantly New DLMM LED Down Lights for office, commercial & residential lighting Elegant single spot emission with Philips DLMi LED Light modules No glaring globes, No unshapely tubes No Mercury, No Lead 6" & 8" direct replacement for 2x18W, 1x26W CFL Elegant alternative to ceramic discharge metal halides 2000Lm & 1100Lm Daylight White, Cool White, Warm White mercury-free $50SAT in its transportation/launch tray. This also gives a good idea of its tiny size! siliconchip.com.au February 2014  13