Table of Contents
- What is a student BalloonSat?
- How does a BalloonSat differ from a professional scientific balloon payload?
- What are the components in the flight vehicle?
- Are there any weight constraints on the BalloonSat payload?
- Are there any size constraints on the BalloonSat payload?
- How is the payload attached to the vehicle?
- What is a typical BalloonSat flight profile?
- What environmental conditions during flight may affect the payload?
- What is necessary for certifying the payload for flight?
- When and where will the La ACES flight take place?
- How is the vehicle tracked during flight?
- How does flight data get returned from the payload?
- What flight data from the vehicle will be
available for analysis?
A BalloonSat is typically a small student-built device designed to investigate some aerospace related topic that is carried to an altitude around 30 kilometers (~100,000 feet) by a helium filled latex sounding balloon. At this altitude, the BalloonSat is above about 99% of the Earth's atmosphere and is essentially exposed to space. BalloonSats are lightweight (less than 1 kg), compact (1,000 cm3 or less) and inexpensive to construct. Students can use such payloads to investigate science topics in fields such as atmospheric science, remote sensing and cosmic rays, while modeling the systems and processes used to fabricate and operate professional scientific payloads.
Professional scientific payloads are designed to perform state-of-the-art scientific research. In recent years, balloon payloads have investigated the cosmic microwave background radiation, cosmic ray antiprotons, gamma-rays from astrophysical sources, ultra-heavy cosmic rays, solar observations and high energy cosmic rays. These payloads can weight 1,000 kg or more and are carried up to altitudes in excess of 35 km by large volume (>840,000 m3) helium filled balloons. Depending upon launch location, flight duration can be from 10's of hours to greater than 15 days. On launch the flight train from the top of the balloon to the bottom of the payload is taller than the Washington Monument! Flight operations for U.S. balloon payloads are supported by the National Scientific Balloon Facility (NSBF) based in Palestine, Texas, which operates launch sites in New Mexico, Canada, Australia and Antarctica.
The balloon flight vehicle consists of the following from top to bottom: 1) a 2000 gm latex sounding balloon, 2) a Skyangle 60" parachute, 3) a lightweight radio location chirper, 4) the primary GPS receiver - radio transmitter, 5) primary antenna, 6) three to four student BalloonSat payloads, 7) the secondary (backup) GPS receiver - radio transmitted, 8) secondary antenna and 9) a radar reflector. Other details about the flight vehicle can be found on the "ACES-01 Post-Flight Info" page.
To avoid the complications of submitting flight space waivers to the FAA the total weight under the balloon is limited to about 5,400 grams (~12 pounds). Subtracting the weight of the parachute, beacons, antennas and string leaves about 2,500 grams for student BalloonSat payloads. Typically we would like to fly between 4 and 5 student payload, so each payload should be weight constrained to about 500 grams.
In principle, a payload could be any size given that it satisfies the FAA regulation that the weight / size ratio is less than three ounces per square inch on any surface of the package. In practice the larger the payload the heaver it will be until it exceeds the ~500 grams weight constraint. For most purposes, BalloonSats are limited in size to roughly a cube with sides 15 cm to 20 cm long.
The vehicle uses a double string flight train where the strings are separated by about 17 centimeters. These structural strings need to pass through the BalloonSat payload unbroken. Typically the payload will have two plastic soda straws securely glued to payload housing structural members about 16 cm to 18 cm apart, through which the flight train string can pass unimpeded. Securing the payload vertically on the flight train is accomplished by using spring clips both below and above the payload.
A flight will last around 2 1/2 to 3 hours from launch to landing. Initial climb out rates are around 300 meters per minute, but this slows after the balloon passes through the cold tropopause. A maximum altitude of about 30 kilometers is reached after about 1 1/2 to 2 hours, when the latex balloon bursts and the payload begins its descent on the parachute. The parachute descent takes about 45 to 60 minutes. The flight profile for the ACES-01 flight in 2003 can be seen here.
There are three major environmental conditions that the student payload must be able to survive: cold, vacuum and shock. As the vehicle ascends through the atmosphere the air temperature will rapidly decrease to about -40o C to -50o C at the tropopause (~12 to 18 km altitude). After this point the temperature will rise, but will remain below freezing for essentially the rest of the flight. Without proper insulation this "cold soak" will quickly affect payload internals causing humidity to condense and batteries to lose power. Further at 30 km altitude the payload is essentially exposed to the vacuum of space, where sealed components, like closed-cell foam, will expand and potentially burst the payload structure. Finally, while launch is a relatively gentle operation one can expect a slight shock at the initial drop following balloon burst and a larger shock on landing. The parachute is designed to bring the payloads down with a ~4 to 6 m/s rate. The landing shock at this rate is the equivalent to that from a free fall drop of the payload through ~2 meters.
Prior to being allowed to fly, each payload will need to pass a Flight Readiness Review (FRR). This FRR will be conducted by the La ACES management. During the FRR the students will need to provide quantitative evidence that the payload is safe, meets the necessary balloon vehicle interface requirements, and will return valid scientific data as advertised. The FRR will include a written document provided to La ACES management at least two weeks prior to the launch trip and a presentation to take place just prior to integration with the vehicle.
La ACES flight operations will take place at the National Scientific Balloon Facility (NSBF) at Palestine, Texas. We would expect that all groups participating in La ACES will arrive at the NSBF one day prior to launch so that FRR presentations, vehicle integration and pre-launch briefing can take place. The NSBF will provide hanger space, support during launch and flight operations and a tour of the facility. See the ACES-01 Flight Results page for pictures and details about the launch operations at NSBF. The launch trip will be planned for the latter half of May, 2005 (exact dates are to be determined). This is a time when the high altitude winds are in "turn around"; changing from one prevailing direction to the opposite and are at the lowest velocity. Launching during this period of time will keep the balloon vehicle relative close to the launch site throughout the flight.
The La ACES flight vehicle includes two GPS location radio beacons; a primary unit and a backup. (Details about the components included in these beacons can be found on the ACES-01 Post-Flight Information page.) GPS derived latitude, longitude, altitude and time are transmitted to receivers located in the lead chase cars. (This position information is also repeated over the internet.) A laptop computer in the chase is hooked to the receiver and the balloon GPS information is plotted, in real time, on a local map (see the flight path for ACES-01). This allows the chase to follow the balloon while on the road and to locate the landing to within a hundred meters or so.
Other than the GPS position information we generally do not telemeter data from the balloon vehicle. In our experience including telemetry in the BalloonSats adds an unnecessary complication to the already formidable skills and techniques that the students must be able to command in order to develop a successful payload. Instead students write their data to EERAM memory chips on-board their payload controller. Writing and reading these chips is a relative simple operation and, with the large size chips available these days, there is usually no problem with archiving sensor readings throughout the three hour flight. After payload recovery the students download their data to the computers we will have available on the flight line and begin their data analysis.
The flight vehicle team will provide the GPS latitude, longitude, altitude and Universal Time approximately every 30 seconds throughout the flight. This information will be available in either Excel or ASCII text format (see the ACES-01 Tracking team page for an example of these data). To correlate with the vehicle GPS data, a BalloonSat will either need to time stamp its sensor records using a Real-Time Clock or calibrate the readout interval. For example, the ACES-01 FRED experiment used a radioactive source to introduce "spikes" in their data archive at known times. By counting the number of readout records between "spikes" they were able to measure their time interval in seconds and the "spike" immediately prior to launch set their time starting point.