DESCENT
DESCENT DATA, CELL PHONE TRACKING SYSTEM
The accompanying PDF file is extracted from a spreadsheet analysis of the Boost Mobile / Accutracking data gathered from the flight. Both descent and ascent data is combined into one spreadsheet.
accutrack_results.pdf | |
File Size: | 60 kb |
File Type: |
(Email the team if you require the source document: it was developed in iWork Numbers, but can exported into an Excel file.)
Note that for the accutracking data, there is a data gap above roughly 15,000 m. Also, some position reports were received without an altitude.
For this data and the APRS data to follow, a word on the calculations.
Time change (seconds) on a row is the difference between the time for that row and the time of the prior row.
N-S change (m) on a row is derived from the change in latitude between that row and the prior row. The estimate, valid for small changes, is derived from the approximation: 1 minute latitude = 1 NM (nautical mile) (or 1852 m).
W-E change (m) on a row is derived from the change in longitude between that row and the prior row. The estimate, valid for small changes, is derived from the approximation: 1 minute longitude = 1 NM * cos(latitude).
W-E speed and N-S speed is estimated as W-E change/time change, and N-S change / time change.
Change in altitude is the difference in altitude between the current row and the prior row.
Ascent / descent rate is the change in altitude / time change for that row.
Wind speed is the estimated wind speed in the horizontal plane, assuming that the change in balloon position between two rows is due to wind at that altitude, and that the altitude change is small enough to be neglected. It is estimated trigonometrically from the W-E speed and the N-S speed: the wind speed is the length of the hypotenuse of the triangle formed with these former two values as legs of the triangle.
Wind direction, that is, the direction that the wind is moving towards as an CW angle from true North (vs. where it is blowing from, which is meteorological convention), is estimated from that same triangle above, as the inverse tangent of the (N-S speed / W-E speed ).
Note that for the accutracking data, there is a data gap above roughly 15,000 m. Also, some position reports were received without an altitude.
For this data and the APRS data to follow, a word on the calculations.
Time change (seconds) on a row is the difference between the time for that row and the time of the prior row.
N-S change (m) on a row is derived from the change in latitude between that row and the prior row. The estimate, valid for small changes, is derived from the approximation: 1 minute latitude = 1 NM (nautical mile) (or 1852 m).
W-E change (m) on a row is derived from the change in longitude between that row and the prior row. The estimate, valid for small changes, is derived from the approximation: 1 minute longitude = 1 NM * cos(latitude).
W-E speed and N-S speed is estimated as W-E change/time change, and N-S change / time change.
Change in altitude is the difference in altitude between the current row and the prior row.
Ascent / descent rate is the change in altitude / time change for that row.
Wind speed is the estimated wind speed in the horizontal plane, assuming that the change in balloon position between two rows is due to wind at that altitude, and that the altitude change is small enough to be neglected. It is estimated trigonometrically from the W-E speed and the N-S speed: the wind speed is the length of the hypotenuse of the triangle formed with these former two values as legs of the triangle.
Wind direction, that is, the direction that the wind is moving towards as an CW angle from true North (vs. where it is blowing from, which is meteorological convention), is estimated from that same triangle above, as the inverse tangent of the (N-S speed / W-E speed ).
DESCENT DATA, APRS RADIO TRACKING SYSTEM
The accompanying PDF file is extracted from a spreadsheet analysis of the APRS radio data gathered from the flight. Both ascent and descent data is combined into one spreadsheet. Two PDF file options are provided: the -01 option places the large spreadsheet into one page; the -02 option places the spreadsheet into individual pages, much as you would see in 'print preview' mode.
aprs_results_01.pdf | |
File Size: | 122 kb |
File Type: |
aprs_results_02.pdf | |
File Size: | 133 kb |
File Type: |
(Email the team if you require the source document: it was developed in iWork Numbers, but can exported into an Excel file.)
Note that for the APRS data, there was ambiguity between (a) the BigRedBee APRS radio reporting altitude in m, (b) the aprs.fi website displaying the altitude in feet, and (c) the aprs.fi download erroneously converting the data into m, when it already was in m. As such, the FALSE altitude column is that provided by aprs.fi, which was converted into true values in the TRUE column.
Note that for the APRS data, there was ambiguity between (a) the BigRedBee APRS radio reporting altitude in m, (b) the aprs.fi website displaying the altitude in feet, and (c) the aprs.fi download erroneously converting the data into m, when it already was in m. As such, the FALSE altitude column is that provided by aprs.fi, which was converted into true values in the TRUE column.
DESCENT RATE VS. ALTITUDE
The following chart illustrates the descent rate vs. altitude.
The descent rate in general followed the air density vs. altitude for the atmosphere: in the thin air, the descent rate was high, slowing as the spacecraft reached lower altitudes and denser air. The descent rate stabilised at approximately 11 m/sec near the ground. This was higher than the expected 9.8 m/sec for this class of parachute and spacecraft weight.
RAW GPS DATA FROM BigRedBee APRS RADIO
The BigRedBee can be programmed to log GPS fixes to internal 1Mbit flash memory. Since the spacecraft was recovered, this was extracted and analysed. The raw data, formatted for readability and placed into an Excel chart. Additional columns unique to the GPS include the number of GPS satellites in-view when the fix was computed, and the time to compute each fix.
23feb_brb_gps.xls | |
File Size: | 167 kb |
File Type: | xls |
The data in the file was color-coded for viewing. The first three entries in purple show the BigRedBee flying at incredibly high altitude and speed over North Africa: this is assumedly erroneous data written to flash at power-up. The next set of entries in grey are valid fixes, but the spacecraft is still on the ground at the launch site, turned on but waiting for launch, or back on the ground at landing. The remaining entries in black are of the flight.
Examining the descent rate anew using the GPS data (since the latter updated every 13 seconds) results in the following chart:
Examining the descent rate anew using the GPS data (since the latter updated every 13 seconds) results in the following chart:
The series of dots are the altitude vs. elapsed time points from the GPS log. From this, the descent rate vs. altitude can be estimated, as shown: