ASCENT
ASCENT 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 ascent and descent 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 ).
ASCENT 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.
ASCENT DATA, NATIONAL WEATHER SERVICE (NWS) METEOROLOGICAL BALLOON
The NWS station at Albany NY, radiosonde station 72518, executed a meteorological balloon release at approximately 6AM on 23FEB, from the Albany airport. The balloon carried a Sippican Mk II radiosonde package, and gathered data on pressure altitude, temperature, dewpoint, and velocity. This data was downloaded from the Integrated Global Radiosonde Archive (IGRA), and the data distilled into the following document. (05MAR - TBD)
albany_23feb_1211z_mod_3.pdf | |
File Size: | 37 kb |
File Type: |
WINDSPEED VS. ALTITUDE
The following three charts illustrate the estimated windspeed vs. altitude, derived from (a) the NWS radiosonde data, (b) the APRS data and (c) the Accutracking data:
(The outliers in the APRS windspeed data near 30,000 m have been suppressed, as they are suspected as in error.) The three plots generally agree with each other, although the increased granularity of the APRS data (roughly every 30 seconds vs. every 60 sec for the cellphone and greater for the radiosonde) better resolves the windspeed, especially the jet-stream-like speeds at 10,000 m altitude. However, the radiosonde data, using a differential GPS measurement, provides a much more accurate estimate of windspeed, so this peak speed might be closer to 70 m/sec near 10,000 m. The APRS data does suggest a similar value.
ASCENT RATE VS. ALTITUDE
The chart that follows illustrates the ascent rate vs. altitude. Only the APRS data is used, since it has the highest granularity and seems to agree well with the other data above.
Several outliers that were > 20 m/sec were suppressed in the plot. The mean ascent rate (excluding outliers) computed from the chart above was 6.3 m/sec. This agreed with the estimated ascent rate computed as (burst-altitude / time-to-burst-altitude), suggesting that the ascent rate data above is accurate.
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. The red entry at 31,221 m is the highest altitude reached.
Examining the ascent rate anew using the GPS data (since the latter updated every 13 seconds) results in the following chart:
Examining the ascent rate anew using the GPS data (since the latter updated every 13 seconds) results in the following chart:
The darker, thicker line are the altitude vs. time points from the GPS log. The light blue line is a linear fit to the data, with the equation for that fitted line shown in red. The slope is 5.1982, or approximately 5.2 m/sec. This does show that the ascent was linear over time and altitude, deviating little from a constant ascent rate. This is however significantly different than the ascent rate estimated from the APRS position reports. The 5.2 m/sec ascent rate better fits the design calculations for the balloon, and will be retained, but the error in the APRS estimate deserves a closer examination.