PocketQube Radio Ramblings

As PocketQube's are pretty new on the space scene, there isn't much in the way of  COTS hardware available. You can now purchase the bus structures and ground integration jigs from PocketQube Shop , but it takes a few more components to get a fully functioning satellite!

One important area to consider is comms. How am I going to communicate with the satellite, and how is it going to communicate with the ground? For now I'll just talk about the space to ground segment hardware. I won't include discussions about licensing as that's for another time.  The spacecraft is going to need a radio and an antenna, along with sufficient power to enable the signal to reach the ground.

Out of the 4 PQ "veterans" in space, at least 2 ($50Sat and T-LogoQube) are known to have used the HopeRF RFM22B radio module. This is a tiny 16x16mm RF tranceiver module, that is capable of +20dBm output (That's 100mW for those that haven't googled it yet), in the UHF frequency range. It is based on the Silicon Labs Si4432 Radio IC. Despite the seemingly limited power output, some of the data types can be detected almost horizon to horizon - approx 2900km range! Data packets can also be decoded at up to 900km with just a 10db gain Yagi and a LNA. Not bad for a sub $25 radio module!!!!!
Compare this to Cubesat Radio systems that cost well over $5000. GomSpace sell one for 8000 EUR with a 3W transmitter. Clyde-Space have one for $8600 , with 500mW to 2W RF output.

There's a thread on the DIYsats forum here about this and other HopeRF radio modules.

So where to from here?

So the RFM22B is a proven performer for PocketQubes. Its low power requirements make it a good choice, but it does have some limitations. The data rate used by $50Sat is 1kbps. This is fine if your payload isn't very data intensive. But what are the alternatives? Here's a few areas I am looking into.

HopeRF make another module  - RFM23BP. This is similar to the RFM22B, except the power output is 500mW. The higher power should allow higher data rates. The issue with this module is the higher electrical power requirements, which can affect how the PQ power subsystem is designed.

Still on the HopeRF parts list is the RFM69HCW. This module appears similar in specification to the RFM22B, but is based on the Silicon Labs Si4463 module. Now Silicon Labs state that the Si4432 shouldn't be used for new designs, although I don't think they intended their parts to be used in space! The Si4463/RFM69HCW uses an new API style approach to programming. While touted as being simpler and more efficient, testing from the $50Sat team has so far proved otherwise.

Silicon Labs also state that a low cost external FET can be used to boost the output to 27dBm/500mW.

Testing would need to be conducted to validate this approach.

Another HopeRF product is the RFM26W . While similar again, it is described as a device that "operates as a time division duplexing (TDD) transceiver where the device alternately transmits and receives data packets."

On to the RFM96W and the RFM98W. These are based on Semtech IC's, probably the SX1276 . These have the capability of using a patented LoRa modem, which can potentially increase the devices sensitivity, and therefore link budget. Further investigation is required as this ic has duty cycle limits, and whether the LoRa function works when the radio isn't configured for spread spectrum usage.

Then there's the HM-TRP. These are possibly most commonly used in the 3D Robotics Wireless Data Module. These also have 100mW/20dBm output, but operate as a simple transparent FSK transceiver - meaning that you just feed it UART data and it converts it to RF.

Another option could be to use a FEM ( Front End Module) in conjunction with the RFM22B. RFMD make a module - RFFM6403 . This is a 1W Power amplifier, but it can also operate in Bypass mode if required. It can also be a LNA for the receiver. This part is brand new and is available now in a reel, or later in March if you need single items. Definitely worth evaluating.

Other alternatives are pre-made modules from Radiometrix. They have some compact VHF / UHF transceivers. ( maybe not as cheap as $25 though).

Then there's 2.4ghz modules........ I haven't looked that far into this, but given my intention to use a USB SDR Dongle as a groundstation, that's out of their frequency range ( although I did find an interesting article recently using some cheap hardware as a down-converter. See here for info)

Conclusion

The only conclusion so far is that I really need to get my Amateur radio license and start doing some testing! I've purchased some of the HopeRF modules for testing, and have made the rookie mistake of buying the bare modules, sans breakout board. Half pitch pins don't fit in normal breadboards!

Fortunately bare breakout boards for the RFM22B are available from Modtronics in Australia. Others should take my advice and get populated boards such as those from Modtronics or from Sparkfun in USA. 

As for the other modules, if you have any skills in KiCad, you can design a basic breakout and get the boards manufactured relatively cheaply from places such as Seeedstudio or Itead Studio. 

I'll let you know how I get along!

New DIY Space Forum

A new Forum has been started by a fellow DIY Space enthusiast.
The url is http://diysats.com
Its a place where people of all skill and knowledge level can discuss anything related to DIY Space.

Please register and join in the ever expanding community of space enthusiasts!

How do I start to build a PocketQube?

So, you think the idea of building your own Sputnik seems pretty cool. I don't know if it's a good pick-up line at parties, but as far as personal achievement goes, it's up there. But where to start?

Disclaimer: I'm not an expert, or even qualified to give financial advice...This post is just to give potential people or teams a place to start and spur imagination and further exploration.

Back to the story. If you've got to the point of thinking that you're capable of building a satellite, you probably got at least some knowledge about what's involved. Yes? No ? I'm not going to write this "Choose your own Adventure" style, so I'll start with some basics.

You've got as far as deciding on a form factor for the satellite. PocketQube. Now, what size PocketQube are you going to build? If you know anything about getting things into space, it's not exactly cheap, and the cost is based on mass. The bigger the chassis, the larger the mass. So a 1P PocketQube is the smallest in the range, and you can go up from there, generally in .5P increments, up to 2.5P. PocketQube Shop can provide a range of off-the-shelf hardware. Or you can build it from scratch like Wren . Depends on the skills you or your team possess. You just need to ensure it complies with the PocketQube Standards.

Next. Subsystems.

There's a few critical systems you'll need to have. While they can be separate, and often are in cubesats, they may need to be integrated for a PocketQube. But as far as design goes you'll need to think about the following:
Power ( Generation and storage)
Command and Data Handling ( CDH)
Attitude Determination and Control Subsystem ( ADCS)
Communication
Payload
Thermal
Structure
Software

Now you're going to have to "hit the books", both literally and metaphorically. Each subsystem can be considered a specialist area, and there are many books on each one. Pocketqube's haven't been around for a while, so there's nothing currently written that's specific to the platform.
At the cheaper end of the scale ( less than $8), there are general books such as "DIY Satellite Platforms" by Sandy Antunes. The other end of the scale has textbooks like the "Handbook of Satellite Applications" that costs $850.
Or you could use the internet. The Cubesat standard has gone through the same progression that the PocketQube standard will undoubtedly go through. There are presentations from Cubesat Developers Workshops  . There are peer-reviewed publications . There are hundreds of PhD Thesis that can be Googled.

At the end of the day, you'll need to apply what you learn and build your satellite. There's not yet a complete turnkey COTS solution for Pocketqubes, so you'll have to roll up your sleeves! You'll need to understand each of the subsystems and devise a way to integrate them all. You'll learn things like "Link Budget" and that Lithium Polymer batteries won't charge in temperatures below 0C, and many other intricacies of building a satellite.

Testing. Do what the $50Sat team did and breadboard your satellite. At early stages, you don't need to have the final circuit board designed. You don't need the space rated solar cells for testing your control and radio code. When you get close to finalising these things, make 1 or more engineering models so you can test mechanical systems like antenna deployment.

There's definitely alot to learn if you're an amateur like me, but it's achievable. The cost of the hardware isn't exorbitant, and you just need the dedication and enthusiasm ( ok, and aptitude) to build your own satellite.

What or Who is OzQube-1?

OzQube-1 is the name for a pico-satellite that is proposed to be designed and built as a DIY project, by a space enthusiast. It is going to be based on the PocketQube form factor. This means that it is very small as far as satellites go ( as small as 5cm³), and will not use expensive hardware.

Inspiration for this satellite came from Kickstarter, where I contributed to a project called Pocketqubeshop.com. This project showed me that it was possible to build a satellite for less than the cost of a TV. ( Launching it is another thing I'll go into another time). The Kickstarter campaign coincided with the first launch of several satellites using the Pocketqube form factor. The highlight for me was the $50sat , or Eagle2. This is a Pocketqube that was built for around $250 in parts* ( the original plan was for $50, but they opted for higher cost solar cells). This little bird has proven to be a solid, reliable platform, providing radio telemetry to radio amateurs around the world. It was a collaborative education project between Professor Bob Twiggs, ( the inventor of the cubesat and Pocketqube standards), Morehead State University in USA, and 3 radio amateurs. Have a look at the links page for more on $50sat.

It is the intention that OzQube-1 follows a similar path. The beacon and basic telemetry will be using the amateur radio bands, with an aim to make it accessible to anyone with a USB Software Defined Radio (aka USB DVB-T dongle from eBay) , some free software, and an antenna.

Now I am not an engineer, or someone that has had previous experience with building hardware for space. I'm currently an IT Professional, but I am definitely an amateur when it comes to the other skill areas required for building this craft, so I'll be learning a lot along the way. I have tinkered a bit with various mechanical and electronic systems, so I'm not completely in the dark about the challenge that lies ahead.

In addition to the amateur radio part of the craft, I've yet to formalise a plan for the main onboard computer that will function as the Command and Data Handling System, or any potential payload. I'll have more in future posts!

Naming the Baby

Like with a newborn, a name is something that parents approach in different ways. Some go through the pregnancy trying to decide on a name they like. Some have a name picked out in advance, well before conception. Some wait till the baby is born before they decide on a name.

Having never been involved with the build of an actual satellite before, I was not sure what to do. I've only just decided to build a proof of concept "engineering model" PocketQube. I'm not sure what it's purpose is yet. I'm not even sure if it's something I'm capable of building. I don't know if I'll have the resources to progress the idea past a certain point.

BUT, I'll give it a shot! So while I'm formulating a plan for this endeavour, I thought it would be better if I gave it a name, so that my obsession can have a focus. ( plus it gives my wife a specific thing to refer to, rather than call me Space Geek)

I've experienced naming children, so surely this couldn't be too far removed?

So what does one do in this day and age? Well.... I emailed people and Googled names.
Being a relatively new standard, there aren't many birds flying yet, so there's not alot of risk in having the same name as an existing PocketQube. I looked at names of CubeSat's. I looked at Australia's involvement in the space industry ( didn't have to look far, but it eliminated Aussat from the list of potential names)

After all that, I wanted something simple, that referred to 2 things - Australia and PocketQubes.

The result:

OzQube-1

(Because it could be the first of many!)

New Blog - Hooray!!!!!

I finally decided to make a home for my new obsession. After taking a vigorous "interest" in space related activities, thanks to Kickstarter and other goings on in the world like the endeavours of Curiosity and Space-X.

So, "Hello Blog World"!