This document will describe the relationship between the goals of the Portland State Aerospace Society and the avionics system for the June 2003 LV2 avionics system (hence forth "system").
This document is intended for developers of the electrical and software systems of the LV2 avionics package which is scehduled to fly in June 2003. This document is maintained by the PSAS avionics team (with leads by Larry Leach, Jamey Sharp, James Perkins and Andrew Greenberg).
The system requirements gathering process should produce a list of features which must necessarily be implemented to achieve the goals of the PSAS, and should organize those features by priority and difficulty.
The PSAS vision is to put "Nanosatellites into Orbit". The rationale for this vision is that solving the problem of reaching orbit requires solving many smaller, yet interesting, problems.
A significant problem which must be solved to achieve orbit is that of guidance. A rocket must be able to modify its trajectory in-flight to enter an orbital trajectory.
All activities of the PSAS are limited by funding, and so an additional goal for all aspects of the project is to find the cheapest way to build a rocket. As all work done by group members is on a volunteer basis, plans must allow for constraints on volunteers' time as well.
The 6/2003 LV2 system consists of a solid rocket motor, the vehicle's airframe, ground systems, and avionics.
The requirements for launching the rocket are discussed in LaunchControl and are included in this document by reference.
The requirements for monitoring the rocket's telemetry are discussed in RocketView and are included in this document by reference.
Sounding rockets, such as the Black Brant, use similar avionics systems, so information about their design decisions may be beneficial in the development of PSAS products.
Systems making extensive use of the CAN bus for data are found primarily in automotive applications.
The users of the LV2 system are:
- Students and members of the PSAS team
- Any outside group using this vehicle as the basis for their small sounding rocket project.
Users are expected to have a significant base of expertise in relevant fields, including C/Unix programming and electrical engineering as necessary.
Each individual volunteer with PSAS has different objectives for a flight of the LV2 system, but several stand out.
- collect data from as many sensors as possible, given resource constraints
- develop algorithms for processing of sensor data: InertialNavigation
- deliver data, processed if possible or raw otherwise, to the ground during flight
- FUTURE: control parts of the flight autonomously, leading eventually to closed-loop trajectory control
The LV2 avionics system has the technical constraints that were included for various reasons over the course of the LV0, LV1 and LV2 projects. Theae include:
- Using the Controller-Area Network (CAN) as the primary communications bus between processors in the rocket.
- Using PIC microcontrollers for the sensors and other "less intelligent" tasks on the CAN bus.
- Using LInux on the FlightComputer in order to perform most computational tasks.
- Using 802.11b technology as a telemetry system.
Have the avionics system:
- Interact with Launch Control Systems to abort or successfully launch.
- Record real-time data locally in the system, and send fraction of tha data via the telemetry link.
- Measure flight data in order to determine the current state of the flight
- Fire the pyrotechnic charges in order to deploy the drogue parachute at apogee.
- Fire the pyrotechnic charges in order to deploy the main parachute some distance above the ground.
- Convey enough useful information via telemetry to the recovery teams to enable them to track the rocket.
Technical Requirements to meet the primary objective:
- Data stream logging
- Analyze data stream
- CAN-message based Flight state machine
- Communication channel tests
- GPS Node transmitting LAT/LON/ALT
- IMU Node transmitting acceleration state
- ATV system sending 1.3GHz carrier at >1W with overlay of flight computer state and GPS data
- Power Node providing power for entire flightl
Display telemetry on the ground
- Independent uplink node which can fire pyrotechnics wo/main system
- Antenna system (slots or patches)
- umbilical system in Launch Tower
- Flexible 2m system
These should be edited into a coherent whole, because they express a variety of important aspects of the system.
The flight computer controlling LV2 has some important duties.
- monitor pre-launch status, and be capable of aborting a launch if certain conditions are met.
- report on the progress of the flight thru the boost phase, into coast, parachute ejection, descent and recovery.
- collect data from all available sensors, such as GPS, IMU, pressure, temperature, and magnetometer
- filter and re-transmit relevant data to a remote ground station for storage and analysis
- act as a mechanism for seperating the vehicle's nosecone and deploying the recovery parachutes at apogee.
- in future, guide the LV2 rocket during powered flight
- communication with the CAN bus to control on-board components handling large amounts of data throughput (@ 32 measurements per second)
- passing control codes out to the CAN bus to control components
- receiving control codes from the 802.11b data link
- sending data out to the 802.1b data link
- run in a real-time setting
- communicate with the Ground Computer at a high data rate
- be capable of firing the igniters for the Solid Rocket moters of LV2
- be capable of passing data from the following sensors to the ground
- Altimiter (pressure)
- 6 Degree of Freedom Inertial Measurment Unit
- battery status
- Ignitor status
- Recovery system status
- be capable of integrating IMU data with GPS data to determine the current course and speed of LV2.
- be capable of controlling the future steering system of LV2.
- be capable of detecting apogee of LV2
- be capable of triggering the recovery system at apogee
- run in a real-time operating system (RTLinux)
For the first launch of LV2 in June 2002 the minimum system needed will...
- detect launch
- detect apogee
- activate the recovery system
- downlink GPS and acccellerometer data to teh ground computer.
- change the rate of sampling from the GPS and accellerometer.
- detect touchdown.
- broadcast a location signal upon touchdown
- use WiFi in the Ham Radio 50cm band for COMMS
Rough outline of the 6/2003 launch wrt the avionics system:
Before leaving for launch:
- Swap out and check new battery pack.
- Power up system via umbilical
- Do a systems check (?) and final checkout (communications, sensors, antennas, etc)
- Shut down system.
- Give avionics module to airframe team.
T - 1 hour:
- Airframe team mounts rocket to launch tower
- connect umbilical cord (no power)
T - 10 minutes:
- Power up umnbilical cord to boot up rocket
- Do preliminary system checkout
- Test communication systems
- Ramp up systems to full power
- Arm pyrotechnics
- Arm flight computer for launch
- arm launch tower (motor igniters)
T - 2 minutes:
- Turn off umbilical power
- monitor systems - any failure OR warning aborts launch
- begin countdown
T - 10 seconds:
- Final countdown
- FC asked to turn on RocketReady
- If FC status ok, assert RocketReady
- RocketReady cleared on any warning or failure.
- Begin monitoring for launch detect.
T - 0 seconds (Launch Phase):
- Motor igniter fired.
- Launch detect by umbilical cord removal, Z accelerometer, GPS, and pressure.
T + 2 seconds (Boost Phase):
- Monitor all sensors
- motor burnout detect: Z accelerometer, GPS and pressure
T + 10 seconds (Coast Phase):
- Monitor all sensors
- software arm pyrotechnics
- apogee detect (IMU, GPS, and pressure)
T + 60 seconds (Apogee):
- Fire drogue pyrotechnics
- Monitor for confirmation of drogue. Keep firing until drogue confirmed by GPS and pressure velocity mesaurements
T + 61 seconds (drogue Descent Phase):
- Shutdown unecessary systems
- monitor altitude and position
T + 300 seconds (main descent phase):
- At 2,000ft AGL, fire main parachute
- continue monitor and sending altitude and position
T + 360 seconds (recovery stage):
- Shut down all systems but ATV beacon
- Wait for recovery - shut down on recovery
T + 3600 seconds (data recovery):
- Reboot system, extract raw data