First distance test

The team has completed the first distance test of our equipment and achieved a range of around 500m. Whilst this clearly is a long way short of the required range, we were still reasonably satisfied. I can almost hear your cries of "Why?". There were a number of known issues with our set-up on this first test - these include:

1. Using only a helical antenna on tranmitter, which we already knew to be very poor. To make matters worse, it's not even electrically the correct length due to the way we have connected it to the prototype board. This will not be an issue on the flight as we will either be sending a whip or half-wave dipole (properly connected!). Tests on these types will be run shortly.

2. Our transmitter was well inside a building surrounded by computer equipment - the helical antenna taped to a laptop screen. The building has metal walls, ceilings and floors - unrealistic for our flight, seeing as the transmitter will have clear line of sight and be in clear air.

3. I was holding the dipole incorrectly. This was partly down to the fact I'd forgotten our transmitter wasn't actually in flight. Future tests will ensure it is being held correctly.

4. We're still on prototype boards. Both circuits are far from ideal even on the breadboard - to assist a little with this, I'm hoping to knock up the production version of the receiver over the weekend. The transmitter needs to stay on a prototype board for now - but it might be worth a bit of a shuffle to ensure we aren't causing interference.

With this in mind, we hope to get much further next time.

A better kind of antenna

No testing occured yesterday - instead parts for a better antenna were purchased. We couldn't link up our coathanger version due to lack of the appropriate connecting cable (50 ohm coax). Andy got hold of some last night and Phil bought a 5mm diameter aluminium rod. By cutting this at the appropriate length and sticking it in some 'choc-block' we end up with, what should be, a very good half-wave dipole. We hope to test in the next few hours.

What's next?

As far as we've come, there's still a long way to go. Tomorrow, (or as I write this, later today), we will be conducting the first round of range tests.
These tests, using our prototype receiver and transmitter, will give us our first chance to see what the units are capable of. Part of tomorrows plan involves making a half-wave dipole antenna to go on our receiver, which is essentially just some coathangers cut to the correct length for our centre frequency. Confirming range is an important step to qualifing our hardware for flight - theres little point in putting all this extra weight on board if we lose the signal before the balloon loses GSM. Lets hope for some good results...

Assuming we get the results we require, the next stage will be to purchase a suitable GPS receiver. Some research has already been undertaken in this area, so we are reasonably familiar with what will (and what won't) do the job. Once again, its no easy task. We have many contraints that consumers normally wouldn't think twice about including weight, power use, minimum baud rate and ability to customize NMEA data. Just to make make things that extra bit harder, we also need a device which implements COCOM aka ITAR restrictions properly. Every GPS receiver sold in world has a restriction built-in to prevent a 'home-brew' cruise missile. The exact implementation should shut down the GPS device should it exceed 60,000ft AND be moving at greater than 999 knots. Unfortunately, most GPS developers code their firmware with 'OR' instead of 'AND' - no doubt assuming neither are very likely anyway. The upshot of all this being that as our balloon will be going above 60,000ft, we need to make sure that our device doesn't bug out or we'll never see our payload again!

Still, lets get through tomorrows testing first....

Balloon update

After a successful radio test, what better way to round off the day than to find that our balloon has been dropped off.

Radio Update

Quick update: the radio equipment has been tested and works!

Assembly

This evening was assembly time. Here you can see both prototypes (almost) fully assembled. Andy has purchased the outstanding DIL socket to be installed tomorrow.

Communication: Proof of concept 1

As you will have seen from a previous post, the method for getting telemetry back from the HAB is as follows:

GPS Device -> Conversion to radio data -> Transmission -> (Radio) -> Reception -> Conversion to serial data -> PC -> Google Earth & Internet

Theres a lot going on here and each stage needs careful testing. The very first proofs of concept are:

(1) Plugging in a GPS device and capturing the raw data with hyperterminal
(2) Connecting two computers with a null modem cable and using hyperterminal, (and the settings we expect to be using in our application), send raw data between the machines.

Both of these we would expect to work; there really is no reason whatsoever that it wouldn't. However, in the interest of being thorough the tests needed to be done. You'll be unsurprised to hear that we had no problems whatsoever.

The next task is to assemble the transmitter and receiver modules. Once assembly is complete, we will can retest (2) from above, this time wirelessly. We'll start with the Tx and Rx next to each other and should that work, we'll begin distance testing.

Power & Weight

Zephyrus 1's balloon doesn't have much lifting power. To achieve a satisfactory altitude, the maximum payload weight is just 580 grams. Working to such contraints isn't easy and every gram counts. At the same time, our avionics are going to be demanding on power. Running just a GPS chip alone draws 100mA. That might not sound like a lot, but it'll drain a 9v PP3 battery in about 2 hours. To make matters worse our expected drain is closer to 300mA which will kill it in just minutes.

After finding that the PP3 battery performs so badly, especially under load, it has been decided that AAA size batteries will power our GPS receiver and radio gear. We'll also be using Lithium batteries rather than alkalines as they provide better longevity in high drain applications and as an added bonus they are also significantly lighter. An average AAA battery weighs in at 12 grams - whereas the Lithium counterpart is just 7.6 grams (Energizer L92). Since we need 4 to power our telemetry package thats a saving of close to 18 grams.

Our camera will also be powered by Lithium batteries (probably Energizer L91) as they weigh just 14 grams compared with 23 for alkalines. Since the A560 takes two AA's we will be saving another 18 grams here.

Simply changing from alkaline to Lithium batteries will shave a massive 36 grams off of our payload and come the final weigh-in that could be vital.

5v regulation

We need perfect 5v regulation to our circuit. I've put together the prototype and it works perfectly. As you can see from the photo, you can't do much better than that.

Prototyping

I'm now testing our components whilst waiting for the remaining parts to arrive. As you can see, these LEDs work fine ;-)

Components...

An order has now been placed for a ton of components from RS. This mixed bag of resistors, transistors and capacitors will be the supporting cast in our transmitter and receiver PCBs.

I've come up with a design for a voltage regulator module which will break off +5V and +3.3V rails - whether it will work is a different matter...

Telemetry Update

Somewhat unexpectedly, it would appear that we are making headway on the ability to receive telemetry for at least part, if not all, of Zephyrus 1's journey.

Andy has located transmitter and receiver circuit diagrams which use a chip to encode and decode serial data. This will allow us to connect a GPS device and send its data wirelessly to a computer. We are now pricing components and checking weight constraints.

The next step is to build prototype devices - which will involve butchering one of Phil's GPS devices.

Balloon ordered

The balloon that will lift Zephyrus 1 is now on its way from the USA. The 300 gram balloon has a burst altitude of nearly 70,000 feet and can carry a payload of upto 660 grams when filled with Hydrogen. Since our balloon will be filled with Helium (as we'd quite like to live to launch a second balloon) we're capping our payload at around 500 grams.

Telemetry

Currently the team are investigating the possibility of getting telemetry from our HAB, which is much more difficult than it might sound. Mainly this is down to transmission output power limitations which are enforced in the UK. The small areas of the radio spectrum that are licence exempt require output power to be 10mW or less (on the European mainland that limitation is 100mW).
It is not beyond our capability to be able to send and receive a signal at that distance even with this, somewhat over-the-top, restriction - however it is unlikely that any telemetry hardware will make it onto this first flight. Instead development will continue with the radio hardware as it is something we would like on subsequent flights.

More avionics testing...

An important test of our avionics equipment is the freezer test. The device must run continously for at least 120 minutes with 25 of those being in the freezer.

I have carried out the simulation personally and am pleased to report that the unit passed. The unit obviously lost signal during its time in the freezer, but immediately began returning positional data when removed. I allowed the device to run for some 90 minutes afterward and no problems were detected.

Somewhat impressively the device was not charged after the previous test that Andy ran, so battery life is thankfully not a concern either.

These results convince me that our choice of tracking technology is correct and am confident that it will allow us to locate and retrieve our payload.

Photo/Video System

The team were divided over whether we should be taking just photos or taking video as well. Taking two cameras was obviously an option but adds a lot in weight (and cost). Thankfully it turns out that there is a single camera solution in the Canon PowerShot A560.

For a compact it's a very decent piece of hardware, but the real treat is in an aftermarket firmware which will allow us to run a script on it. This script will potentially be set-up to take a photo every minute, with say 10-15 seconds of video in-between.

Andy directed the eBay 'sniping' operation to win us the Canon A560 a little earlier today with just 3 seconds remaining on the clock. Sorry Bidder 7...

Avionics: Tracking

Once our HAB has been released, we will have no control over where it goes nor can we visually track it. So, if we ever want to see our payload again there needs to be a way of finding out where it has landed. Thats where the tracking component of our avionics come in.

Several different methods have been employed by other teams which vary in complexity, starting from a device which sends texts of its GPS position all the way up to RF modems that provide a constant stream of GPS data back to a base station.

Our solution is a Windows Mobile device running GPS tracking software. The software on the phone gets its location from the inbuilt GPSOne Qualcomm chipset which then sends this data over GPRS to a server. The server translates the data and displays the real time position on Google Maps/Earth.

We don't expect a signal above 3000 feet but we are really more interested in its position once it lands.

Andy tested the device on Thursday by taking the unit on a trip into the countryside. His test proved that even if it loses a GSM signal for a prolonged period - once it regains it the device resumes returning positional data.

Foam drying out...

The foam shell is continuing to dry... An 'off-cut' of the material seems very promising. It would appear to be light, strong and very flexible.

Avionics bay

The 'Avionics bay', if you can call it that, is obviously very important. We need to protect our equipment from the harsh conditions of 'near space' and survive a heavy landing whilst allowing us to take photos and being light enough for our balloon to lift.

Phil is working on a prototype(pictured), made out of expanding foam, which hopefully will meet all the criteria.

Zephyrus. The High Altitude Balloon project.

It seems that everyone is jumping on the bandwagon to get a snap of the third rock from space these days. During our regularly scheduled coffee and a whinge a number of us at work decided to join the party and to finally prove that the Earth isn't flat.

To get 'out there' we need a balloon. A big balloon. We also need a payload of gadgets to track it and to snap us some photos. Most importantly, we need to give the project a name. And we have one.

Zephyrus, meaning "west wind" is the name for our project to go into the stratosphere and beyond...