BalloonSatellite

BalloonSatellite about goals data link Packet Radio Cell Phone Modem data collection Platform Small System Testing Initial Testing Eggbeater antenna Design

Stumble It!

about

Since 2005 or so I've been toying with the idea of sending a camera system to 100K ft and see what I can see. This is in no way a novel project and there have been many successful missions by weirdos just like me. This is a long term project that won't be launched until 2008 at the earliest.

This is in no way a novel project:

• Make Balloon
• Make Balloon Test
• [[][Other One]]
• [[][Yet Another One]]

goals

data link

A major goal of this project is to maintain a data link with the satellite for telemetry as well as envinronmental data collection. The satellite will cost enough that I don't want to lose it but if I do I would like to have collected at least some data from it. Ideally I want to download images from the onboard cameras over this link. They would have to be scaled down to accomodate the low baud rate I expect but it should be possible to download 10K to 30K images in a few minutes.

Packet Radio

Seems to be the way to go. Packetized, long distance links, proven technology. Slow data rates 1200 baud likely, 9600 baud at best.

• TNC-X - PIC based lightweight, low power TNC

Cell Phone Modem

Would a cell phone stay connected at 100K ft? Spark Fun sells some cheap, light, cellular radios.

I'm thinking a cell phone/cellular module would make a good backup system to locate the payload after it returns to earth. Either an SMS from the phone with the last known GPS coordinates or somehow use triangluation from the cell phone call (can non-super fed types do that?)

data collection

The second major goal of this project is to photograph the black of space. Since I'm sending a pretty powerful computer that high up I might as well gather some other data. Of course I need some sort of tracking so I'll probably go with GPS.

• Digital Images
• Temperature
• Altitude or pressure
• Latitude/Longitude via GPS

This camera pretty much handles all of the picture taking requirements and simplifies a lot of the design for me. In addition I can still download images remotely by switching the camera UART to the highspeed downlink radio UART. The plan is to download thumbnails (for their smaller size) and then selectively download the high res images that look the best. Of course all of the images will be spooled on board (SD card probably) for later recovery.

Platform

This main computer may be a BlackfinOne SBC which wil be responsible for overall system control, data collection, and communication back to earth. I am trying to keep the weight and size down though so I may fall back on a few 8-bit systems working together rather than one monolithic controller. The camera system described above takes care of most of the visual data collection so the rest of the system as well as managing the camera should be fairly straightforward with 8-bit procs. I'd like to keep everything as simple as possible as well as critical system redundency to make it more robust and increase the chances of success.

Small System Testing

To ensure success there are a lot of systems to test out as well as recovery mock-ups to practice finding the payload. In addition I plan on mocking up small, tethered tests and possibly some small 'throw away' tests.

• WeatherStation - Similar systems to what the balloon would use so a good starting point

Initial Testing

This initial test system will only go up to about 500 ft or 1000 ft on a tether. Here I can test data links, photo retrieval and practice with yagi to maintain a data link from as far away as possible. The big drawback is I am using a different radio (zigbee 60mW, not 900MHz 1W), different camera system, and not using telemetry and using the same radio for the uplink and downlink. I will be able to get some nice pics from 500ft though and will learn some of the issues I'll run into with the big system.

Test System
Part	Price
ZigBee Radio - 1mi range	2x $32
Eggbeater Antenna	make
Avronics mainboard	in stock
VGA Camera used in AVRcam	$50
I2C thermometer (DS75 -55C to 125C)	in stock
Pressure Sensor
SD Socket, SD card
500' - 1000' kite string
Batteries
Skybuster Balloon

Questions

• Is it worth developing all of the software to use the VGA camera if its not going to be used in the final balloon? No but since most of it is done put it to some use.
• Can I steal most of the code from the AVRcam? yes but probably not worth it. Without RAM the C3088 is too slow unless it is very stable for many seconds

Eggbeater antenna Design

According to this site the circumfernce of each loop is defined as C = 299.8/f where f is in MHz.

C = 299.8/(2.4*1000) = 0.125m

The second loop needs to be 90 deg out of phase from the first so this is done with a timing delay by directly feeding the first loop and feeding the second loop through a trace of the correct length to delay the signal enough. Velocity factor is avaliable in most handbooks (coax is RG-62). Again see the above page for the details. The values for velocity factor seem to be between 0.66 and 0.8 so that means: 0.020m <= L <= 0.025m. I need to follow up on this to be sure it's a valid assumption.

L = 0.25*(velocity factor)*299.8/f (Mhz)

-- ChristopherPepe - 07 Jan 2007