NOVA HAB: Design

Schematic

I've finalized my schematic in PCB Artist:

I moved to a digital copy now as my paper copy has started too look like spaghetti with so many changes as I've developed it. The one big item removed from the schematic is the digital camera. An unsuccessful attempt was made to dis-assemble a Canon digital camera and high-jack the power/capture switch and so I will instead have a GoPro camera capturing an HD video of the entire flight.

Payload

I opted for a payload container that would allow for easy construction and would give on impact with the earth. After a quick run to the grocery store, I grabbed this styrofoam cooler. Additionally, since styrofoam is very permeable, I felt comfortable leaving my GPS and GSM module antennas inside the container.

Per FAA requirements, a high-altitude weather balloon project have a reflector and so I assembled the reflector shown above with 90 degree angles.

(3) The balloon envelope is equipped with a radar reflective device(s) or material that will present an echo to surface radar operating in the 200 MHz to 2700 MHz frequency range.

In addition to the reflector device requirement, it is required to keep the payload within weight specifications:

(4) (ii) Carries a payload package that weighs more than six pounds;

(iii) Carries a payload, of two or more packages, that weighs more than 12 pounds;

Currently, the payload stands at 3.3 lbs without the camera. With the GoPro camera and mounting attached, I should have a final payload weight less than 4 lbs.

Balloon

The latex balloon chosen was manufactured by Kaymont, from what I've gathered, they seem to be the king manufacturer for meteorological balloons. I opted for the larger 1200 gram balloon. Unfortunately Helium prices are on the very high side at $90 for a 150cu. ft. I'm anticipating using most of this for the flight with a 3.5 lbs payload.

Ground Antenna

A 900 MHz 12 dBi Yagi Antenna was purchased to be used for tracking from the ground. The transceiver units purchased came with 4 dBi antennas and have a range of up to 20 miles, but I opted to get the directional antenna with hopes that I can track the payload throughout the flight.

Testing on the ground without line-of-site, I was able to achieve over a thousand feet. This performance was expected with a normal urban environment, but it doesn't provide much for gauging how well the radio communications will perform line-of-site at great distances. Unfortunately, this is the best I can do where I live, the true test will be launch day.

Descent System

The parachute will be tucked into a 1.5" PVC and deployed by the micro-controller. Similar to a model rocket launch, the parachute will be deployed with a small amount of gunpowder, ignited by a nichrome wire (much like that in a toaster oven). I am using two 1.5V D batteries supply about 3 Amps, heating the nichrome wire and igniting the gunpowder in a couple of seconds to launch the chute.