Data Format

Of all the telemetry transmitted by TVNSP nearcraft, two types of data are transmitted as a part of the nearcraft's status. They are the nearcraft's health data and GPS position data. This report explains the layout of these two types of data. Using this report you will be able to interpret TVNSP nearcraft status telemetry

Nearcraft Health Data is broken into eight bus channels. Data from each bus channel is prefixed with the symbol, B-CHn, where n is an integer representing the bus' channel. For example, bus channel two has a prefix symbol of B-CH2. Following the bus channel prefix symbol is the value of that bus channel. The value consists of a decimal representation of a twelve bit, unsigned integer. So values for each bus channel span the range from 0 to 4095, inclusive. In the case of temperature data, the values represent the temperature in tenths of a Kelvin. See the end of this report for an explanation of the Kelvin temperature scale. In the case of voltage data, the number represents the voltage in hundredths of a volt. Note that voltages pass through a voltage divider before being digitized. Barometric pressure data, bus channel one, is a voltage data, but is used in relative mode. That is, the pressure at the start of a mission is compared to pressure throughout the flight. Here are the eight bus channels and the health data they represent.

	Channel 1: Cabin Air Pressure
	Channel 2: Auxiliary Voltage
	Channel 3: CC/PS Voltage
	Channel 4: CC/PS Temperature
	Channel 5: Not Used At This Time
	Channel 6: Battery Temperature
	Channel 7: Cabin Temperature
	Channel 8: Servo Voltage

Two GPS NMEA sentences are used as GPS position data, the GGA and RMC sentences. The GGA sentence is used to determine the nearcraft's position in three dimensional space. The RMC sentence is used to determine the nearcraft's velocity about the horizontal plane. Post-flight analysis determines the ascent and descent rates of the nearcraft from the GGA sentence. Here is the format of the GGA and RMC sentences.

Recommended Minimum Specific GPS/Transit Data (RMC)

$GPRMC,hhmmss.ss,a,ddmm.mmmm,N,dddmm.mmmm,W,z.z,y.y,ddmmyy,d.d*CC

	hhmmss.ss - time
	a - status (A=Valid, V = Invalid)
	ddmm.mmmm,N - latitude
	dddmm.mmmm,W - longitude
	z.z - speed over ground
	y.y - heading, true north
	ddmmyy - UTC time of fix
	d.d - magnetic variation
	v - variation sense
	CC - checksum

GPS Fix Data (GGA)

$GPGGA,hhmmss.ss,ddmm.mmmm,N,dddmm.mmmm,W,q,ss,y.y,a.a,M,g.g,M,t. t,iiii*CC

	hhmmss.ss - UTC time of fix
	ddmm.mmmm,N - latitude
	dddmm.mmmm,W - longitude
	q - GPS quality (0 -gps not available, 1-gps available, 2 - differential fix available)
	ss - number of satellites being used (must be at least four for a three dimensional fix)
	y.y - DHOP (dilution of horizontal position)
	a.a,M - antenna height in meters
	g.g,M - geoidal separation in meters
	t.t - age of differential data
	iiii - differential reference station ID
	CC - checksum

The Kelvin Temperature Scale

Each unit in the Kelvin scale is equal to each degree in the Celsius scale. Where the Celsius scale begins at the freezing point of water, the Kelvin scale begins at absolute zero, the lowest possible temperature. Absolute zero is -273 deg C, or 273 deg below the freezing point of water. To convert Kelvins to degrees Celsius, add 273 to the temperature in Kelvins. Use any method you're comfortable with for converting degrees Celsius into degrees Fahrenheit.

One final note, there are no degrees in the Kelvin scale. The proper way to say 12 K is to say, twelve Kelvins. Don't say twelve degrees Kelvin, if you want to be strictly correct.