Notes from my laptop, pardon the mess. This is one of two documents (so far) developed for the high altitude balloon project that Thom and I are working on in St. Louis. For the todo list check out http://spacepunk.org/content/high-altitude-balloon-project-todo-list
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Introduction
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The goals of this project are to gain experience
in the development of near-space craft and the
communication systems that are critical to their
missions.
Goals
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- Reach Stratospheric altitude
- Communications with ground
- WiFi for live video
- APRS for GPS becon
- Recorded HD video for later retrevial
- Alternative power
- Solar
- Wind
- Survive
- Battery life
- Payload
- GPS System
Long term goals/brainstorm
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- Research into potential launch platform for
rocketry projects and eventual orbital applications.
- Life of balloon at high altitude, potential
long-term platform
- Floating public wifi into a secret
but awesome web server?
- Long distance private network relay
This project can be broken down into two parts. first an
aerodynamic portion involved in getting the payload to the
desired altitude and keeping it there, then second part of a
technological payload that will transmit data back down to
a desired base station.
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Payload
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The technological portion could be anything. In the first launch
we will stick to the bare minimum of:
+ GPS receiver to locate craft
+ Radio transmitter to broadcast GPS location data
using APRS, to be decoded on the ground
+ Omnidirectional antenna for APRS transmission
+ High-Definition camera. Potentially Canon HF series,
for it's solid state storage technology. [1]
+ Video encoding hardware for live transmission of HD
source.
+ High-bandwidth (relative to APRS) connection to ground
station. [2]
+ Directional antenna for WiFi signal transmission
There are a number of technological ideas we'd like to add in
subsequent launches:
+ A tighter directional antenna to more efficently apply
power towards a higher gain in a specific direction
+ Stepping motors to use as servos to control the
directional antenna
+ Research high-definition live video for this
+ Deployment of estes rocket, perhaps something to LEO
Some technological challenges have been discussed. Perhaps we
may wish to stray from using a directional antenna on a baloon
based aircraft. We could not guarentee its stability in keeping
a lock without perhaps an expensive gyroscope.
Regarding specific implementations of hardware, there are several
known options.
+ Parallax BASIC Stamp
+ Arduino
+ BeagleBoard
+ Gumstix
+ Roll-your-own
These various solutions each have their pros and cos. We will
discuss these based on preliminary research (wikipedia and
company websites).
-Parallax BASIC Stamp
I have one of these laying around. Programmed in BASIC. Too slow
for video or data transmission, maybe useful in GPS broadcast.
What about
-Arduino-
Runs an 8-bit Atmel AVR, but many have been implemented using
higher-end Atmel chips. Code would be written in C and is all
'embedded' code. Probably not powerful enough for video decoding
and transmission.
-BeagleBoard
This actually has a video chip onboard that supposedly processes
720p. C64x.
Would need USB WiFi dongle. Estimated $40. SD Card interface
a possiblity, though.
Questions:
+ Is the SVideo port an input, for possible use of pulling
in the SD video? [Answer: NO]
+ Cost against the Gumstix.
+ Weight, power usage, tempreature operating range while
handling video.
Advantages:
Downsides: Video AND WiFi over USB interface. Could be avoided
-Overo
Similar to the BeagleBoard, in that it uses the same processor,
but doesn't have the onboard TI video processor.
Overo Water is comparable to BeagleBoard: $169, no networking,
has C64x and "Camera In". No details on "Camera In" yet.
Overo Fire has wifi and a port for an EXTERNAL ANTENNA.
Fire costs $219. Assuming no Camera In, USB board is ~$40,
bringing us to $260.
Advantages: Seperate WiFi and USB interfaces
Downsides: Expensive
.................
[1] It's unknown how a traditional tape-based video technology
will react to -20C tempreatures at 20 miles in altitude.
[2] Transmission does not have to be in high definition.
Preliminary research shows Sweedish attempts were able to
keep a WiFi signal with an average thruput of ~64Kbps
.................
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Aerodynamics
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Simply put, aerodynamics are currently the weak point of the
project. [1] This we plan to change. However, in theory this
project is rather straightforward: get something high up and
allow it to survive descent if needed.
The aeronautics of this project have several design goals:
+ Enter the stratosphere. This is 7mi through 30mi.
The baloons we've looked at are expected to hit
twenty
+ Allow for the payload to survive its descent. Probably
using a parachute of some kind.
There are several ideas we'd like to add into future launches
in this aspect as well
+ Multi-baloon craft. For greater payloads
+ Rocket launch platform
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[1] As of 7/17/09.
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Resources
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http://diydrones.com
military surplus stores for balloons
http://beagleboard.com
sanguino.cc
Antennas by Kraus
zigbee
