SPACECRAFT SYSTEMS
SPACECRAFT (CAPSULE, JACKET, PARACHUTE, RIGGING)
The shell was constructed from Corning Foamular Insulpink XPS extruded styrene insulation, R-value 7.5, wall thickness 3.8 cm. This was cut into pieces and hot-glued into place to form a rectangular shell closed on 5 sides; a separate lid slid in to close the 6th side. Outer dimensions were 21.6 cm x 21.6 cm x 33.0 cm with the lid in place. This shell then displaced a volume of approximately 7.9 liters; assuming a weight of water of 1000 gm/liter, the shell would experience a buoyant force of 7960 gm, more than enough to keep it afloat even with the weight of the subsystems and parachute. (This was a consideration, given the proximity of the ocean, and the numerous lakes and rivers near the landing site.)
An outer abrasion jacket, which also served as the attach points for the parachute rigging, was constructed of nylon, and an opening flap above secured with sewn-on Velco strips. Four attach points consisted of loops of Dacron tape sewn to the jacket, with slip rings attached to the loops. The jacket and capsule survived the mission without damage.
Rigging consisted of Dacron line, attached to the parachute risers, and held to shape via attachment to a 8in plastic needlepoint loop, based on Paul Verhage's design. The rigging survived the mission without damage.
The parachute was a Rocketman 36in parachute. The risers, normally sewn together at their apex, were detached, formed into separate riser lines, and attached to the rigging via brass swivels. The parachute possessed a loop sewn to the top of the canopy, to which the balloon line was attached. The parachute survived the mission without damage.
The capsule, jacket, and rigging weighed in at approximately 440 gm. The parachute weighed in at approximately 120 gm.
An outer abrasion jacket, which also served as the attach points for the parachute rigging, was constructed of nylon, and an opening flap above secured with sewn-on Velco strips. Four attach points consisted of loops of Dacron tape sewn to the jacket, with slip rings attached to the loops. The jacket and capsule survived the mission without damage.
Rigging consisted of Dacron line, attached to the parachute risers, and held to shape via attachment to a 8in plastic needlepoint loop, based on Paul Verhage's design. The rigging survived the mission without damage.
The parachute was a Rocketman 36in parachute. The risers, normally sewn together at their apex, were detached, formed into separate riser lines, and attached to the rigging via brass swivels. The parachute possessed a loop sewn to the top of the canopy, to which the balloon line was attached. The parachute survived the mission without damage.
The capsule, jacket, and rigging weighed in at approximately 440 gm. The parachute weighed in at approximately 120 gm.
APRS RADIO SYSTEM
The BigRedBee 2m HP APRS radio ('BRB') was received housed in a Pelican 1010 case, and a dual-band 140MHz/440MHz monopole whip antenna was provided. The radio was removed from the case, and the attached AA battery pack (6 AA batteries in a plastic enclosure) set aside. Standing alone, the resultant radio weight was approximately 130 gm.
An external battery pack was constructed from a Kingmax Lithium-polymer 7.4V, 1000 mA-hr battery. Battery weight and cabling was approximately 110 gm.
The BRB was specified as drawing 100 mA in idle mode, and 2000 mA when transmitting at 5 W. The APRS packets are 1200 Baud FSK with a packet transmit duration <1 sec. The BRB has flexibility in transmit power depending on the voltage supplied: supplied voltage levels between 4.0 Vdc and 7.5 Vdc produce RF transmit powers between 1 W and 5 W. The battery was chosen to provide at least 4 hours of continuous operation with the APRS radio transmitting every 30 seconds. During this mission, the BRB was activated at approximately 1:33 PM EST, and continued transmitting at 30 sec intervals until approximately 11:21 PM EST, a duration of 9hr 48min! The BRB reported telemetry alongside position/altitude on the APRS packets, to include sampled voltage. The resultant voltage vs. time plot derived from the telemetry:
An external battery pack was constructed from a Kingmax Lithium-polymer 7.4V, 1000 mA-hr battery. Battery weight and cabling was approximately 110 gm.
The BRB was specified as drawing 100 mA in idle mode, and 2000 mA when transmitting at 5 W. The APRS packets are 1200 Baud FSK with a packet transmit duration <1 sec. The BRB has flexibility in transmit power depending on the voltage supplied: supplied voltage levels between 4.0 Vdc and 7.5 Vdc produce RF transmit powers between 1 W and 5 W. The battery was chosen to provide at least 4 hours of continuous operation with the APRS radio transmitting every 30 seconds. During this mission, the BRB was activated at approximately 1:33 PM EST, and continued transmitting at 30 sec intervals until approximately 11:21 PM EST, a duration of 9hr 48min! The BRB reported telemetry alongside position/altitude on the APRS packets, to include sampled voltage. The resultant voltage vs. time plot derived from the telemetry:
The curve shows the discharge profile expected of Li-ion batteries, maintaining a nearly flat voltage through the majority of its discharge until reaching a cutoff, where the voltage then drops dramatically. From this curve, it is expected that the BRB transmitted APRS packets at 5W RF power for at least the 8 hours. Note that the BRB has a low-voltage shutoff circuit to prevent damage to the Li-ion polymer battery should the battery voltage drop below 3V.
The VHF antenna was external to the capsule, oriented vertically on the lid. (The GPS receiver was inside the capsule.) The distance to the radio horizon vs. altitude, using a simple model, is shown:
The VHF antenna was external to the capsule, oriented vertically on the lid. (The GPS receiver was inside the capsule.) The distance to the radio horizon vs. altitude, using a simple model, is shown:
This shows that, at a burst altitude of 30km (30,000 m), a distant APRS station on the ground, could hear the APRS transmitter on the spacecraft if that station is as far as 700 km (435 mi) away.
The RF free-space path loss at 144MHz is shown:
The RF free-space path loss at 144MHz is shown:
This shows that for a distance of 700 km, the RF signal would decrease by 132 dB. This is a logarithmic ratio; translated into power, this means that the 5 Watt APRS transmission from the spacecraft, or 37 dBm, would decrease to -95 dBm, or 0.0003 nanoWatts at a distance of 700 km. This is within the minimum discernable signal level of a good APRS receiver, assuming certain conditions.
The APRS packet data displayed on aprs.fi was downloaded, distilled, formatted, and placed into a spreadsheet, provided here:
The APRS packet data displayed on aprs.fi was downloaded, distilled, formatted, and placed into a spreadsheet, provided here:
aprs_formatted.xls | |
File Size: | 370 kb |
File Type: | xls |
Analysing the path data, that is, the path from spacecraft APRS transmitter to ground APRS receivers, show the longest paths, which occurred near the burst altitude:
Two long reception paths are shown.
The path on the right from the spacecraft near burst altitude (near 30km) shows APRS packets received by ground station VE2SBR-3, 465 km away. This station is located at 46.9782 deg N, 72.1418W, in Riviere-a-Pierre, Canada (NW of Quebec City).
The path on the left from the spacecraft near burst altitude shows APRS packets received by ground station WD4HDL-1, 675 km away. This station is located at 38.7342N, 77.8358W in Warrenton, Virginia USA. This was very close to the radio horizon, an impressive span.
The path on the right from the spacecraft near burst altitude (near 30km) shows APRS packets received by ground station VE2SBR-3, 465 km away. This station is located at 46.9782 deg N, 72.1418W, in Riviere-a-Pierre, Canada (NW of Quebec City).
The path on the left from the spacecraft near burst altitude shows APRS packets received by ground station WD4HDL-1, 675 km away. This station is located at 38.7342N, 77.8358W in Warrenton, Virginia USA. This was very close to the radio horizon, an impressive span.
CELL PHONE SYSTEM
A Sanyo Innuendo cellphone, vended by Boost Mobile, was used as a secondary radio tracking system. The phone was loaded with an applet provided by Accutracking.com, which automatically reported phone-derived position/altitude to the Accutracking network via cellular data connection.
The phone's standard battery was used: this was a Li-ion battery SCP-38LBPS, a 3.7Vdc, 880 mA-hr battery.
The phone was activated at 11:14 AM EST on 23FEB, programmed to report position once every 60 seconds. The last position report, #732, was received at 12:58 AM EST on 24FEB, for a total time on of 13 hr 44 min.
The phone's standard battery was used: this was a Li-ion battery SCP-38LBPS, a 3.7Vdc, 880 mA-hr battery.
The phone was activated at 11:14 AM EST on 23FEB, programmed to report position once every 60 seconds. The last position report, #732, was received at 12:58 AM EST on 24FEB, for a total time on of 13 hr 44 min.
CAMERA SYSTEM
A Canon SD1100 camera was used to take static pictures during the flight. The camera was modified to autoboot the CHDK firmware, and to execute an intervalometer script, automatically taking pictures every 20 seconds, until either the power failed, or the internal memory was filled. The internal memory was an SD card, 2GB in capacity, formatted as FAT16. Standing alone, the camera weighed in at approximately 130 gm.
The internal battery was removed, and the camera was wired to an external battery, an LP-805060 3.7B 2700 mA-hr battery. With cabling and adapter, the battery weighed in at approximately 50 gm.
The camera was activated at 1:30 PM EST on 23FEB. The last photo was taken at 4:24 PM EST on 23FEB, at which time the SD card memory was full. A total of 1041 photos were taken. The camera is a 3264 x 2448 pixel (8 Megapixel) model. Photo sizes were variable, ranging from 2.1MB to 4.7MB: the typical photo size of photos taken during the ascent and descent was 2.4MB.
The internal battery was removed, and the camera was wired to an external battery, an LP-805060 3.7B 2700 mA-hr battery. With cabling and adapter, the battery weighed in at approximately 50 gm.
The camera was activated at 1:30 PM EST on 23FEB. The last photo was taken at 4:24 PM EST on 23FEB, at which time the SD card memory was full. A total of 1041 photos were taken. The camera is a 3264 x 2448 pixel (8 Megapixel) model. Photo sizes were variable, ranging from 2.1MB to 4.7MB: the typical photo size of photos taken during the ascent and descent was 2.4MB.