Subsystem Overview

Sapling uses a HopeRF UHF LoRa radio module. LoRa is a relatively new low power, long range, low bitrate radio modulation technique. It uses a chirp spread spectrum modulation scheme and is especially useful because signals can be demodulated even below the noise floor.

Sapling possesses a deployable omnidirectional tape spring v-dipole antenna. The antennas are made of standard tape measures, which are both soldered and screwed to the Z+ face of the satellite. The radiation patterns are shown in figures below

Horizontal Radiation Pattern

Vertical Radiation Pattern

Sapling will interface with the ever-growing TinyGS network, an open network of over 1200 active amateur ground stations worldwide, for telemetry. Those interested in listening for Sapling, including students at partner institutions, are encouraged to build their own ground station and join the TinyGS community at tinygs.com. Sapling will be commanded via the Durand ground station on Stanford’s Campus.

Beacon Contents

The beacon packet which Sapling Giganteum will transmit every 60 seconds while in idle mode or every 60 minutes while in low power mode is around 50 bytes and contains the following:

<aside> 📻 callsign

state_machine.current_state (boolean)

radio.tx_power

solar_charging (boolean)

enable_rf.value (boolean), whether or not the LDO for the radio is enabled

gc.mem_free (amount of free memory in the SAMD chip)

boot count

of messages received from a ground station that pass CRC and verification

of messages received that fail to pass CRC

uncaught exceptions

batt_voltage,

system_voltage,

system_current,

batt_temp

radio.rssi (on last message received)

radio.snr (on last message received)

ambient light sensor values packet as 12 bit ints, ranging from 0-40k lux, from all 6 faces

16bit magnetomer readings in 3 axes

16bit gyroscope readings in 3 axis

imu temperature

16 bit int lat

16 bit int lon

16 bit int altitude

GPS time as seconds from epoch (configured as march 1st)

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Communications System Requirements

Communications Requirements