Flight code validation simulator Page: 3 of 6
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The basic systems required for the rocket
include; Power System, IMU/Attitude Control
System, Flight Sequencer, Fireset, Telemetry System
and Payload. The power system utilizes batteries for
flight and external power supplies via umbilical
cables for ground and pre-launch testing. The
IMU/Attitude Control System and flight sequencer is
contained within the DMARS unit. This system
provides state information of the vehicle for proper
orientation, flight sequencing, and payload release
conditions. The fireset supplies initiation signals to
all ordnance items at the appropriate times and
conditions. Some fireset functions are supplied on a
fixed time basis and others are performed by request
of the flight computer based on the correct states.
The telemetry system combines analog
measurements and digital data streams from the
flight computer and other on board hardware and
sends the data down on a radio frequency (RF) link
to the range ground station for real-time display and
post flight processing.
The IMU is contained in the DMARS,
providing a roll-stabilized platform for strapdown
inertial navigation (see figure 2). The platform
provides 4-axes of gyro information (one redundant)
and 3 axes of accelerometer information. Also, the
SANDAC flight computer, a Motorola 68020, 33
MHz with floating point capability, resides in the
unit with internal communication paths to the
sensors, along with serial, parallel and discrete
communication paths to external electronics and
Telemetry information is provided from the
SANDAC computer via the external parallel port to
a custom programmable Pulse Coded Modulation
(PCM) encoder. This encoder serializes the contents
of a First-In-First-Out (FIFO) at the desired bit rate
and then supplies an interrupt at the desired point for
the computer to refill the FIFO. The serialized data
is both sent out a serial link and also modulated on
the base band of an S-Band Transmitter for RF
I. Rocket System Software
The navigation, guidance and control
(NG&C) software for this vehicle resides in the
SANDAC computer incorporated in the DMARS
(see figure 3). This software is broken down into
three separate functional modules; inertial
navigation, guidance & control, and flight
sequencing. The inertial navigator reads the IMU
sensors and compensates the raw data to provide
correct attitude and position information. The
guidance and control module utilizes the attitude and
position states and acts on them to orient the vehicle
and or modify the motor ignition time to remove the
first stage dispersion in order to force the vehicle to
pass through the desired target position. The flight
sequencer effectively ties all the modules together to
provide for attitude control, guidance and discrete
events at the appropriate times throughout the flight
of the vehicle. These decisions are based on time,
attitude and position states.
The flight code is written in the "C"
language, with assembly language used to
incorporate interrupt service routines and operating
system calls. The VRTX Real-Time Operating
System is utilized for discrete real-time software
control. The code is compiled on a PC using the
Greenhills "C" cross compiler and assembled
utilizing the Quelo Linker and Assembler tool set.
IV. Simulation System Hardware
The simulation system is hosted on a
486/66 MHz PC. The real-time simulation code is
run interrupt driven on an Alacron i860 AT Bus
DSP Board. A custom daughter card was designed to
provide dual port memory addressing and interrupt
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Sims, B.A. Flight code validation simulator, article, August 1, 1995; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc624777/m1/3/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.