Mike's Telemetry Roundup

ed note: While this is directed at EOSS-49, the telemetry format is standardized over most flights.

EOSS-49 APRS Beacon GPS and Telemetry Format

Mike Manes, W5VSI
Pres. Edge of Sciences, Inc.
Tel: 303-979-4899
manes@attglobal.net

17 April 01

EOSS-49 Balloon Flight:

The EOSS APRS Module will accompany the CU Space Grant cubesats on the EOSS-49 high altitude balloon.  Launch will occur on Sat 21 April at 0900 MDST, with a rain date of Sun 22 April.

A decision to launch on schedule or delay to Sunday will be made by 8:30 PM Fri 4/20, and Messrs Kohler and Lund will be notified either way by telephone.  The on-air meeting where that decision will be made will be held on the 147.225 repeater at 8 PM.

The launch site and ground station setup will begin at 0700 on Fatton Ranch near Windsor, CO.  Directions to the launch site can be found at www.eoss.org.  The balloon is expected to burst between 85,000 and 95,000 ft above sea level, well in to the stratosphere, and at the edge of space.

EOSS APRS beacon:

This beacon will transmit in the blind on 144.430 MHz using a 350 mW FM transmitter and standard 1200 baud AX.25 packet UI protocol.  A sample of the logged downlink data is appended.

Each telemetry record comprises two lines of ASCII text, and each record is separated by a blank line.

The first line of each record is generated by the ground station and shows the callsign of the station sending the data (W5VSI-11 is the APRS beacon, but others may appear in the log) and the time and date of receipt, per the ground station computer clock.  Although there may be some fixed error in the time measurement, there is no more than 5 sec delay between the time the telemetered measurement is taken and the time of receipt at the ground.  Note that the format of the time and date field may differ from the appended sample, but it's simple to decipher.

The second line contains the telemetered data in comma-delimited ASCII fields and terminated with a <CR-LF>.  For this beacon, there are four record types denoted by the first 2 or three characters of the first field.  Those identifiers are three NMEA GPS record types, all beginning with "$GP", and the EOSS on-board telemetry records which begin with "T#".  In addition, there will be a text message beaconed from time to time which may be ignored:

W5VSI-11>BEACON [171943T APR 01]: <UI>:
EOSS-49 / CU SGC Cubesats, Windsor CO - ATV on 426.26 MHz.

All records, except $GPGSV (satellites in view) are downlinked once per minute.  Since AX.25 protocol uses CRC to ensure data integrity, there is excellent confidence that the logged data is error-free. However, records received with "bit hits" that corrupt the CRC simply will not appear in the log. Thus it is likely that some records will be missing.  The time tags may be used to detect these events.

Although EOSS uses the NMEA data for tracking the balloon, the NMEA data is likely to be of little interest, with one exception:

$GPGGA,013552,3934.0777,N,10503.7657,W,1,07,1.06,1678.9,M,-20.9,M,,*79
^^^^^^

The 10th field on the $GPGGA record contains the balloon MSL altitude in meters; this may be useful as an independent variable to correlate with other telemetry variables, such as barometric pressure or air temperature.  This field will be null ",," if fewer than four GPS birds are locked in.

In addition, the 2nd field of all the NMEA records contains time of day in UTC.  Since the on-board GPS is set to report only every 20 sec, the NMEA data may be received up to 25 sec late.

Onboard telemetry format:

The format of the onboard telemetry record is:

T#fff,an0,an1,an2,an3,an5,bbbbbbbb

where,

T# is the telemetry record identifier,

fff is a telemetry frame counter which increments after each telemetry frame is transmitted,

anx are decimal representations of 8-bit ADC conversions of analog voltage signals using a full-scale reference, Vref. Thus 000 represents 0.00 V and 255 represents 255/256 x Vref.  Note that Vref may is not particularly temperature stable, but an1 contains a stable voltage reference which may be used to back out Vref for the other
measurements.

an0 represents battery voltage, Vbat:

        Vbat, V  = an1 / 10 (no Vref correction need be applied).

an1 is a stable 2.460 volt reference used for determining Vref:

        Vref, V = 2.460 V x (256/an1).

an2 is the as-yet uncalibrated output of an absolute barometric pressure sensor, Vbaro:

        Vbaro, V = an1 x (Vref/256).

an3 is the beacon's internal air temperature, Tin:

        Tin, K =  an3 x (Vref/256) x 100.0

an5 is the outside air temperature, Text:

        Text, K =  an5 x (Vref/256) x 100.0

Note: deg C = deg K - 273.

bbbbbbbb is a binary representation of irrelevant internal logic states and may ignored.

Example:

W5VSI-11>BEACON [210856T APR 01]: <UI>:
T#003,084,126,164,152,153,00111110

This data was received from the EOSS beacon, W5VSI-11, at 0856 MDST on 21 April as the 2nd telemetry frame since last power-up. Vbatt = 8.4V, Vref = 4.998 V, Vbaro = 3.202 V, Tin = 296.8 K (23.8 C) and Text = 298.7 K (25.7 C).

The nearest GPS altitude beacon was:

$GPGGA,155552,3934.0777,N,10503.7657,W,1,06,1.06,1684.2,M,-20.9,M,,*73

taken at 15:55:52 UTC, or 08:55:52 MDST as 1684.2 meters or 5524 ft.

Related files:

This page in plain text minus the graphics and formatting

The full log file of EOSS 49

Sample telemetry log:

full log file linked above

W5VSI-11>GPS,GATE,GATE,WIDE [171927T APR 01]: <UI>:
$GPGGA,,,,,,0,00,,,,,,,*66
W5VSI-11>BEACON [171934T APR 01]: <UI>:
T#001,084,126,164,152,153,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171934T APR 01]: <UI>:
$GPRMC,013450,V,3933.8954,N,10503.3960,W,0.000,0.0,180401,10.6,E*4A
W5VSI-11>GPS,GATE,GATE,WIDE [171934T APR 01]: <UI>:
$GPGGA,,,,,,0,06,,,,,,,*60
W5VSI-11>BEACON [171935T APR 01]: <UI>:
T#002,084,126,164,152,152,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171935T APR 01]: <UI>:
$GPRMC,013550,A,3934.0777,N,10503.7657,W,0.000,0.0,180401,10.6,E*53
W5VSI-11>GPS,GATE,GATE,WIDE [171935T APR 01]: <UI>:
$GPGGA,013552,3934.0777,N,10503.7657,W,1,07,1.06,1678.9,M,-20.9,M,,*79
W5VSI-11>BEACON [171936T APR 01]: <UI>:
T#003,084,126,164,152,152,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171936T APR 01]: <UI>:
$GPRMC,013650,A,3934.0777,N,10503.7657,W,0.000,0.0,180401,10.6,E*50
W5VSI-11>GPS,GATE,GATE,WIDE [171936T APR 01]: <UI>:
$GPGGA,013652,3934.0777,N,10503.7657,W,1,06,1.06,1684.2,M,-20.9,M,,*73
W5VSI-11>BEACON [171939T APR 01]: <UI>:
T#005,085,126,164,151,151,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171939T APR 01]: <UI>:
$GPRMC,013850,A,3934.0777,N,10503.7657,W,0.000,0.0,180401,10.6,E*5E
W5VSI-11>GPS,GATE,GATE,WIDE [171939T APR 01]: <UI>:
$GPGGA,013852,3934.0777,N,10503.7657,W,1,06,1.07,1682.5,M,-20.9,M,,*7D
W5VSI-11>EOSS [171939T APR 01]: <UI>:
$GPGSA,A,3,18,21,15,23,29,09,,,,,,,2.34,1.07,2.08*06
W5VSI-11>BEACON [171940T APR 01]: <UI>:
T#007,086,126,164,151,151,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171940T APR 01]: <UI>:
$GPRMC,014050,A,3934.0777,N,10503.7657,W,0.000,0.0,180401,10.6,E*51
W5VSI-11>GPS,GATE,GATE,WIDE [171940T APR 01]: <UI>:
$GPGGA,014052,3934.0777,N,10503.7657,W,1,05,1.19,1687.1,M,-20.9,M,,*7F
W5VSI-11>BEACON [171941T APR 01]: <UI>:
T#008,086,126,165,151,151,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171941T APR 01]: <UI>:
$GPRMC,014150,A,3934.0777,N,10503.7657,W,0.000,0.0,180401,10.6,E*50
W5VSI-11>BEACON [171942T APR 01]: <UI>:
T#009,086,126,164,151,151,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171942T APR 01]: <UI>:
$GPRMC,014250,A,3934.0777,N,10503.7657,W,0.000,0.0,180401,10.6,E*53
W5VSI-11>GPS,GATE,GATE,WIDE [171942T APR 01]: <UI>:
$GPGGA,014252,3934.0777,N,10503.7657,W,1,06,1.20,1688.2,M,-20.9,M,,*78
W5VSI-11>BEACON [171943T APR 01]: <UI>:
EOSS-49 / CU SGC Cubesats, Windsor CO - ATV on 426.26 MHz.
W5VSI-11>BEACON [171943T APR 01]: <UI>:
T#010,086,126,164,151,151,00111110
W5VSI-11>GPS,GATE,GATE,WIDE [171943T APR 01]: <UI>:
$GPRMC,014350,A,3934.0777,N,10503.7657,W,0.000,0.0,180401,10.6,E*52