Computer Systems

The Flight computer system consists of a Primary Flight System (PFS), a Secondary Flight Computer (SFC), and a telemetry system. Each system handles several functions with some overlap for reliability.

JPEG versions of the schematic and layout. Schematic, PCB Layout
ExpressPCB versions of the schematic and layout. Schematic PCB Layout

Primary Flight Computer

The PFC is a Parallax BS2px and is responsible for reading and recording latitude, longitude, time, altitude, internal capsule temperature, external capsule temperature, and taking pictures. Additional responsibilities include managing memory storage, relay controls, and audible signals. Text Version Stamp Version

The program flow process is simple: Initialize computer system; Check for manual resets; Get GPS data; Parse string and extract pertinent information; Read internal and external temperature; Check memory allocation; Storage information if space available; Evaluate altitude; Determine if picture can be taken; Toggle relay; Start over again. The program has many debugs that I could remove but decided to leave them in so I could watch the process while connected to a PC. I tried to optimize sub procedures and variables based on my coding ability. I am sure a more experienced coder could do better but I am happy with the results.

Secondary Flight Computer

The SFC is a Parallax BS2p24 and is responsible for reading GPS data and displaying this information to an LCD. The LCD is powered during testing and pre-launch activities to verify GPS data acquisition. Additional responsibilities include activating external signal lights when the capsule is below 1000 meters. I used oversized high output LEDS that are setup in a rotating fashion. This way I could maximum the current output without exceeding the Stamps current thresholds. The SFC also provides visual indication that the PFC is working through the use the Primary Flight Computer Active Indicator (PFCAI) light. The PFCAI toggles on and off each time the PFC competes a full cycle of the flight program. Text Version Stamp Version

Parallax software is available on the Parallax download page.

Telemetry System

The indicator and display systems are used during testing, pre-launch, and post-launch activities. Tracking the payload throughout the flight is done via the onboard telemetry system and the vehicle tracking system. All in-flight data and photographs will be stored within the payload until recovery of the capsule, hence the importance of the telemetry system.

The onboard telemetry system is responsible for sending the payloads position back to my PC via amateur radio operating at 144.39 MHz. This is a well established automatic position reporting system (APRS) frequency used by HAM’s in the US. Getting the amateur radio license is easy now since you do not have to know Morse code for a Technician class license.

The Garmin GPS-18 sends native NMEA sentences directly to the APRS device. The OpenTracker converts NMEA sentences to APRS format. The APRS sends the data as audio to the radio and triggers the push-to-talk (PTT) button. The device can transmit other data such as power supply voltage and temperature.

I will be using my laptop PC connected to a Kenwood D700 dual band radio with built in TNC. This allows me to track the balloon on one band while monitoring voice activity in the area on another band. Used in conjunction with UIView-32 and Precision Map I will be able to track the payload in real time and isolate my radio signal from others. This will facilitate the recovery process. I will also use Balloon Track the morning of the launch to predict the flight direction and flight duration of the balloon. I want to stay within a 60-mile radius recovery area. If the prediction software puts the payload outside that range then I reschedule the flight. So far this week the predictions have been within 35 miles of the launch site.  

Power System

Each system has its own single power supply with the exception of the GPS unit. I decided to use the SFC power supply as backup for the GPS to extend its life. If the PFC power supply fails then the relay is deactivated and power is supplied by the SFC power supply. The APRS and radio have their own power supplies and can last for over 24 hours. Between the PFC and SFC the GPS can be powered for 24 hours. This will allow me time to broaden my search area if needed.

Housing Assembly

The housing assembly is divided into 4 sections consisting of an instrumentation platform, an avionics compartment, a battery compartment, and a telemetry compartment. Structural Blueprints To keep the weight down I chose Expanded PVC Plastic sheets that I obtained from Budget Robotics.

The instrumentation platform is where all my bells and whistles are located for easy access. It contains the toggle switches, LCD, and light indicators. In addition, it has my contact information in case someone else finds it before I do. Movie – Instrumentation Panel (7 megs), Structural Blueprints, Label  

The Avionics compartment contains the PFC and SFC. Structural Blueprints  

The battery compartment holds 3 sets of batteries. Each set consist of (6) 1.5 volt AA’s batteries and power the PFC, SFC, and APRS. I already have plans to reduce the power requirements for my next balloon project since this compartment contains almost half the total weight. Structural Blueprints  

The telemetry compartment holds the APRS unit and my modified DL-11 hand held radio. The radio is weak with its 0.3-watt power output and the stock antenna. I replaced the antenna with a 2-meter dipole made from coax cable. This will dramatically increase my transmission range well within my recovery area. Structural Blueprints

Capsule

The capsule consists of the housing assembly and film camera contained in a Styrofoam box and the external antenna. The box is wrapped in a silver space blanket to provide additional warmth and will provide better visibility during the search. I also added an emergency radar reflector for additional visibility. The total weight of the payload is 5.9lbs, which is under the 6 lb FAA limit for a single payload unmanned balloon.

System Testing

My wife and I got up before dawn and set out to perform multiple tests on HAPB and verify launch procedures. We learned that 2 people can definitely launch a balloon with little effort. Setting up the launch site was a snap. Sandy had to drive back to the house to get the cotton gloves that I left off our list. While she was gone, I realized that I also forgot the balloon. When she returned we had a good laugh and continued with the testing. Filling the balloon much easier and faster then we expected. It only took 12 minutes to put 200 cubic feet of helium into the balloon.

I verified that that the telemetry system was working before attaching the payload. We attached the payload and let loose the balloon. We allowed the balloon to rise to 150 feet above our position. I verified the PC software was tracking the system correctly then we lowered the balloon and prepared for the drop test. Movie - Skyward (16 Megs)

We removed the electronics for the drop test. If the chute and capsule could not survive a 100 foot drop, then there is no point in ruining the electronics. We replaced the electronics with an equivalent amount of weight inside the capsule and pulled the release pin. The capsule landed square without any damage. The payload dropped at a rate of ~1200 feet/minute, which is equivalent to 11.5 mph. The test was successful.   Movie – Drop Testing  (5 Megs)

Launch Day (08-26-2006)

We got up around 5 in the morning and set out to the launch air field. We had a typical Texas summer morning. 85 degrees and a light hot breeze. I decided to launch from the taxi way instead of the actually air field. It was closer to the road and easier to get things moved from the car to the launch site. Movie - Prelaunch (8 Megs)

The test setup we did earlier in the week really helped make things move smooth. One item we didn't use during the test was sissle cord which is used for the load line. That is the line that runs from the balloon to the parachute. To be exempt from FAA regulations the balloon load line must be less then 50 feet and break with a force of 50 lbs. or less. Sissle cord meets that requirement. Working with sissle cord can be nerve racking since it breaks easily. After attaching one end to the balloon and the other end to the parachute we started to let the balloon rise. There were a couple of times we thought it was going to break and lose the balloon before we even got the payload off the ground. But after a few tense moments we were ready to launch the HAPB-1.

At 7:28am we let HAPB-1 fly Movie - Launch (24 Megs)

Seconds after releasing the payload my wife realized we had one big program - I forgot to turn on the camera!!!!!!!!!!! After 10 months of working on this project how in the world could I forget to do that. The whole purpose was to take pictures. I wasn't happy to say the least. I had turned it on during the closeout procedure but turned it off again to save battery power while checking on the received telemetry data. I didn't think about it again. So now the close out procedure has been modified to prevent that from happening on the next flight. We weren't going to get any pictures during this flight but we still needed to recovery HAPB-1 if we wanted a HAPB-2. Besides, I am not the first to mess up a camera. Al Bean on Apollo 12 pointed the first color TV camera at the sun, then hit it with a hammer. No pictures of men walking on the moon that mission - or so the story goes.

I was shooting for 100,000 feet and came really close. My onboard data had the capsule at 98,500 feet, however, I found some erroneous data had been captured so I decided to use what UIView-32 recorded as the official altitude of 97,116 feet. The charts below represent some of the data that was captured over the course of the flight.

Altitude	Flight Path
Ascent -Descent Profile	Capsule Temperature

3D Graphics (Provided by Google Earth Plus)

Google KML files: Part 1, Part 2

Recovery

The recovery itself was worth all the work. While Sandy was driving, I was watching for updates and comparing our position to that of the balloon. There were a couple of times during the chase that I wasn't sure if we were going in the right direction. The predictions had the landing site 17 miles up range a couple of days before. As the weekend grew closer it was predicting about 38 miles north-west of our launch site. If you ever plan to launch a balloon, there is a great online site that is a must for predictions: Near Space Ventures

When the capsule was only a mile above the earth we really got excited. Sandy had been driving the back roads like an old pro (AKA maniac) and was trying to get us to the landing zone in time to see HAPB-1 land. At 2235 feet we thought we saw her. A white slender stream falling from the sky. But HAPB-1 was silver with gold. What we were really watching was a piece of the balloon that had detached from the rest of the payload. Meanwhile, HAPB-1 was landing behind us. All we had to do was turn around and we would have probably seen her land.

HAPB had actually landed 1/4 mile east of us but we had to go a mile or 2 to get over to the right road. For a while the last transmission was from 2235 feet. While getting the handheld GPS ready I heard HAPB-1 call again. This time her altitude was only 1228 feet. The same altitude as us. I punched in the coordinates and found that she was only a tenth of a mile away. We tried to find the local owner of the land that we were about to trespass on but a big barking german shepard changed our minds. We had to climb under some barbwire but we were 500 feet and closing. Then I spotted her laying in the grass, in a pile of fire ants, beeping and waiting for us to pick her up and take her home. Movie - Recovery (15 Megs).

Damage Assessment

After getting back to the truck I looked over the capsule and noticed that the it made it through the flight without any damage. Inside, the payload feet had made impressions into the styrofoam from the landing but nothing else seemed to be wrong. Movie - Assessment (11 Megs). I did notice some moisture on the instrumentation platform and I believe I suffered some minor damage to the EEPROM resisters due to the moisture. I will have reduce the number of the hand warmer in my next launch which should eliminate the problem.

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