Ausroc III Telemetry System =========================== Steven S. Pietrobon Small World Communications 6 First Avenue Payneham South SA 5070 Australia Email: steven@sworld.com.au 10 September 1999 Ausroc III is a liquid fueled sub-orbital sounding rocket being developed by the Australian Space Research Institute. An important part of any rocket is the telemetry system. The telemetry system gathers various information on the state of the rocket, such as temperatures, pressures, valve positions, tank levels, stresses, etc. and transmits this information to the ground. The design of the Telemetry system was assigned to the University of South Australia in 1991. After several student projects, a practical telemetry system was developed in 1994 [1-3]. The three parts of the system are the Signal Conditioning Module (SCM), Data Acquisition Module (DAM), and Telemetry Encoder Unit (TEU). The SCM performs the task of converting sensor signals, e.g., from thermocouples, strain gauges, level sensors, potentiometers, etc. to a standard -5 Volt to +5 Volt range. The SCM was implemented on a 100x160 mm Eurocard sized board, with a small daughter board for thermocouple conditioning. Each SCM board could condition up to eight signals. A calibration board was also constructed. The DAM performs the task of converting and combining the analog signals from the SCM boards into a single digital signal. The DAM can accept either 16 analog signals or 15 analog signals and 12 digital signals. A 12-bit analog to digital converter is used. The DAM was implemented on a 100x160 mm Eurocard sized board. The TEU performs the task of combining the digital signals from the DAMs into a single high speed digital stream for transmission to the ground. Up to 16 DAMs can be accessed for a total of 256 sensors. The TEU can also access up to 256 12-bit words from the Flight Computer via a dual-port RAM. The TEU can also send the sensor data to the Flight Computer via the dual-port RAM. The TEU was implemented on a 100x160 mm Eurocard sized board. After payload separation from the rocket, the TEU switches over to send payload data to the ground. The DAMs and TEU are connected together with two RS485 twisted pair lines. One line sends a clock signal from the TEU to the DAMs at a frequency of 2 MHz. The other line is a shared data bus. The access the data from the DAMs, the TEU sends an 11-bit word down the data bus, and then tri-states the bus. The first two bits are a high and a low, followed by eight address bits, and then a final parity check bit. All the DAMs receive this data. The first four bits of the address selects one of 16 DAMs. The next four address bits selects one of 16 sensor signals. If the DAM is configured to accept digital signals, then sensor address 0 selects the digital signals (1 bit for each digital signal). Once a DAM recognises its address with the correct parity, it holds the data bus low. The DAM then starts the analog to digital conversion process which takes 22.6 microseconds. The DAM then transmits 15 bits to the data bus, and then tri-states the bus. The first two bits are two highs, followed by the 12 data bits, and then a final parity check bit. Once the TEU has received this data, it forces the bus low, ready for transmission of the next address. The TEU buffers the data and transmits the 12 bit data and parity bit at 250 kbit/s. The initial design had 54 13-bit words in each minor frame and 16 minor frames in each major frame. The first two words in each minor frame are for synchronisation. The third word is the major frame count (from 0 to 4095 with one parity bit) and the fourth word is the minor frame count (from 0 to 15 with one parity bit). The telemetry system is now being designed for flight by Small World Communications. The initial designs used Xilinx XC3000 field programmable gate arrays (FPGA) in plastic leaded chip carrier (PLCC) packages. These designs have now been translated into Xilinx Spartan FPGAs using quad flat packages (QFP) which are less prone to vibration damage. The DAM uses a MAX122 A/D converter which is relatively expensive. Much cheaper A/D's are available, but they have 0 to 5 Volt inputs and different control logic. This would imply that the DAM control logic and SCM output buffer would have to be redesigned. The TEU design was unusable and was redesigned with a number of improvements. The three erasable read only memories (EPROM) have been replaced with a single EPROM and the two dual-port RAMs have been replaced with a single dual-port RAM. The frame structure was also changed to 24 13-bit words per minor frame and 20 minor frames per frame. The data rate was also decreased to 31.2 kbit/s to match the required sampling rates of the system. The TEU, DAM, and power supply conditioners are now expected to be on one 233x160 mm Eurocard. Only one board will have the TEU. The SCM will also be on one 233x160 mm Eurocard, being able to condition up to 16 sensors. Daughter boards will not be used, since the large board size will allow up to eight temperature sensors to be used. The first Ausroc III vehicles are expected to have five sensor conditioner units throughout the rocket, accessing up to 70 sensors. Table 1 lists a possible telemetry sensor list. References ========== [1] V. Rose, "Ausroc III Signal Conditioning Module," Uni. of S.A., ASRI report 94-7, 1994. [2] T. Ziersch, "Ausroc III Data Acquisition Module," Uni. of S.A., ASRI report 94-8, 1994. [3] D. Mullins, "Ausroc III Telemetry Encoder," Uni. of S.A., ASRI report 94-9, 1994. Table 1: Ausroc III Telemetry Sensor List ========================================= Range Frequency Location Qty Sensor Type Required (Hz) ------------------------------------------------------------------------- Sensor Conditioning Unit 1 (inside Boattail) Motor 1 Pressure 0-7 MPa 100 Motor 1 'K' type TC 0-500 C 100 Gimbal System 2 LVDT actuator displ. 0±40 mm 100 Propellant Valves 2 Valve position 0-90 deg 100 Propellant Valves 2 Flow meters 0-15 L/s 100 Aft Support Structure 2 CEA strain gauges ±5 % strain 10 Aft Support Structure 2 'K' type TC 0-500 C 10 Boattail Fairing 2 CEA strain gauges ±5 % strain 10 Boattail Fairing 2 'K' type TC 0-500 C 10 Sensor Conditioning Unit 2 (inside Intertank 1) Kerosene Tank 1 Pressure 0-7 MPa 10 Kerosene Tank 1 Level sensor 0-2 m 10 Kerosene Tank 6 CEA strain gauges ±5 % strain 10 Kerosene Tank 2 'K' type TC 0-500 C 10 Intertank 1 2 CEA strain gauges ±5 % strain 10 Intertank 1 2 'K' type TC 0-500 C 10 Spare Channels 2 Sensor Conditioning Unit 3 (inside Intertank 2) LOX Tank 1 Pressure 0-7 MPa 10 LOX Tank 1 Level sensor 0-2.5 m 10 LOX Tank 6 CEA strain gauges ±5 % strain 10 (2 x Rosettes) LOX Tank 2 'K' type TC -200 to 300 C 10 Intertank 2 2 CEA strain gauges ±5 % strain 10 Intertank 2 2 'K' type TC 0-500 C 10 Helium Tank 2 'K' type TC -200 to 300 C 10 Sensor Conditioning Unit 4 (inside Payload Fairing) Helium Tank 1 Pressure 0-34 MPa 10 Roll Thruster Reg. 1 Pressure 0-7 MPa 10 Helium Tank 6 CEA strain gauges ±5 % strain 10 (2 x Rosettes) Payload Fairing 2 CEA strain gauges ±5 % strain 10 Payload Fairing 2 'K' type TC 0-500 C 10 Nose Cone 2 CEA strain gauges ±5 % strain 10 Nose Cone 2 'K' type TC 0-1000 C 10 Sensor Condition Unit 5 (inside Nose Cone) Nose Cone 4 'K' type TC 0-1300 C 10 Nose Cone 4 W / Re TC 0-3000 C 10 Spare Channels 8 ------------------------------------------------------------------- Total 70 Flight Computer: This will produce a digital output and will include information such as position, attitude, control commands, and system status. TC = Thermocouple temperature measuring device.