PSAS/ SystemRequirements

System Requirements for June 2003 Launch

See also FlightComputerSoftware, FlightComputer, RocketView, and LaunchControl.



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.

Organizational Context

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.

General Description

Product Functions

The 6/2003 LV2 system consists of a solid rocket motor, the vehicle's airframe, ground systems, and avionics.

The requirements for the rocket body are covered by the airframe and propulsion teams and will not be discussed further here.

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.

Similar Systems

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.

User Characteristics

The users of the LV2 system are:

Users are expected to have a significant base of expertise in relevant fields, including C/Unix programming and electrical engineering as necessary.

User Objectives

Each individual volunteer with PSAS has different objectives for a flight of the LV2 system, but several stand out.

General Constraints

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:

  1. Using the Controller-Area Network (CAN) as the primary communications bus between processors in the rocket.
  2. Using PIC microcontrollers for the sensors and other "less intelligent" tasks on the CAN bus.
  3. Using LInux on the FlightComputer in order to perform most computational tasks.
  4. Using 802.11b technology as a telemetry system.

Functional Requirements

Primary Objectives:

Have the avionics system:

  1. Interact with Launch Control Systems to abort or successfully launch.
  2. Record real-time data locally in the system, and send fraction of tha data via the telemetry link.
  3. Measure flight data in order to determine the current state of the flight
  4. Fire the pyrotechnic charges in order to deploy the drogue parachute at apogee.
  5. Fire the pyrotechnic charges in order to deploy the main parachute some distance above the ground.
  6. Convey enough useful information via telemetry to the recovery teams to enable them to track the rocket.

Technical Requirements to meet the primary objective:

Flight Computer:

CAN Nodes:


Other requirements

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.

For the first launch of LV2 in June 2002 the minimum system needed will...

Rough outline of the 6/2003 launch wrt the avionics system:

Before leaving for launch:

T - 1 hour:

T - 10 minutes:

T - 2 minutes:

T - 10 seconds:

T - 0 seconds (Launch Phase):

T + 2 seconds (Boost Phase):

T + 10 seconds (Coast Phase):

T + 60 seconds (Apogee):

T + 61 seconds (drogue Descent Phase):

T + 300 seconds (main descent phase):

T + 360 seconds (recovery stage):

T + 3600 seconds (data recovery):