Digital Amateur Rocket Tracking System
The Basics
What is DARTS ?
DARTS is an ongoing research project started in the late 1980's by Steve
Bragg, and now funded in part by C2 Technologies. Certain key technologies
developed in association with DARTS are transferred to products at C2,
but DARTS is not currently a product, for rent or for sale.
The goal of DARTS is to develop a tracking capability for non-professional,
high-power sport (amateur) rocketry.
When DARTS is fully functional, it will include these four functions:
real-time range measurement, angle-of-arrival measurement with automatic
ground antenna pointing, telecommand, and telemetry. For the radar
types among my readers, DARTS will be a non-coherent, transponder-augmented,
pulse-time-of-arrival range measurement system with angle tracking and
command/telemetry capability.
Steve Bragg and DARTS team members have achieved success in measuring
range and communicating with hardware onboard rockets, but the auto-track
capability is still in development as of this writing (Fall 1998).
Ranging
DARTS is designed to measure slant range (line-of-sight distance) by sending
pulses from a ground station (Interrogator) to
a Transponder onboard the rocket.
The Transponder will reply back to the ground station after a known (fixed)
interval. The Interrogator then will measure the round-trip time
with a high-speed digital counter. The distance is related to the time-of-flight
by the speed of light.
By making these measurements hundreds of times per second, DARTS will
be able to measure the rocket's slant range with very good accuracy. It
will numerically differentiate the position data with respect to time to
give the rocket's velocity and acceleration.
DARTS does not rely on the reflection from the vehicle's skin, and in
fact the system will reject any such signals by shifting the Transponder's
return signal both in time and in frequency. DARTS uses microwave frequencies
for communication, allowing a narrow pencil-like radio beam, an excellent
"yardstick" for measuring distances to what is essentially a point target.
Angle Tracking
DARTS will automatically keep its antenna pointed at the vehicle, and will
measure the rocket's azimuth and elevation angles with respect to the ground
antenna. Combining this information with the slant range measurements,
DARTS will be able to produce three-dimensional position, velocity, and
acceleration data many times per second.
Angle tracking and measurement gives the rocket's precise direction.
By keeping the antenna pointed directly at the rocket (as close as possible),
a true line-of-sight direction reference is established. DARTS will measure
the antenna azimuth and elevation angles hundreds of times per second,
permitting real-time update of the rocket's 3-D position, velocity, and
acceleration.
Telecommand / Telemetry
DARTS will also have the ability to initiate actions aboard the rocket
via the transponder (e.g., start engines, deploy parachutes, etc.). It
will also be able to send back information (telemetry) from the rocket
such as confirmation of parachute ejection, status of on-board scientific
instrumentation, serial data, etc.
Summary
No other device in the world, existing or planned, compares with DARTS
for high-power rocketry. Current rocket flight parameter measurement
(GPS, altimeters, etc.) give an incomplete picture of rocket performance,
yielding data in only one or two axes. DARTS will give full 3-D flight
data, including position, velocity, acceleration and "jerk" (third deriviative
of position).
Why Develop DARTS ?
"If DARTS is not a commercial product that will generate profit, why develop
it?" A very good question. It think the answer boils down to
two points:
-
Contributions to the experimenter community: DARTS expands the bounds
of what amateur radio experimenters can do, with frequencies and design
concepts that are at the very edge of the experimental envelope.
Also, such a capability does not exist within the mainstream of amateur
(sport) rocketry, so DARTS represents the leading edge in experimental
technologies in that field, too.
-
Technical Challenge / Notoriety: Alright, I admit to being proud
of what I and my team members have been able to do here, our successes
and what we've learned from our failures. I originally took up this
project back in 1989 because it represented a high technical challenge
to me then. Even after I have learned so much and come so far, it
still contains significant technical challenge and opportunity for creative
expression.
What Is Amateur/Sport Rocketry ?
Amateur rockets are similar to the "Estes" models most of had as children,
but an order of magnitude more powerful: an "Estes" 'D' engine delivers
20 Newton- seconds of impulse (thrust x time), an average 'K' engine delivers
2,560 Newton-sec ! With that much power, as you can see, it's quite easy
to lose one.
And, without some sort of flight parameter measurement capability, you
know little about the flight of a $300 engine except that "it went really
high!" Amateur rocket societies such as Tripoli
Rocketry Association know that a system like DARTS would make the difference
between guesswork and real science.
About this Site
I have always considered this website to be a two-way communication medium,
and greatly appreciate comments, advice, criticisms (well-considered and
polite ones), and other feedback.
The organization and layout of this website are intentionally kept as
simple as possible to provide maximum accessibility. While it will never
win a "Top 10% of the Web" award, it should inform in an efficient way.
Any suggestions are welcome.
The DARTS tracking system has evolved through the growth of my experience.
I have arrived at this day through many trials, and many failures. It is
my desire to share these experiences with others, so that others may be
encouraged, and through the help of my readers, we together may achieve
something long-sought-after by the amateur rocket community.
The information on this site is copyrighted by Steven D. Bragg. While
any of it may be copied for educational purposes, proper credit must be
given. Information from this site is not to be used for any commercial
use.
I have tried to keep this site as accessible as possible by avoiding
browser-specific features such as Java (and Javascript), frames, image
maps, and the like. It is not that I am opposed to these things; I simply
want my site to be as accessible as possible. I sometimes browse the site
with text-based Lynx from our Linux system, just to be sure I can do it.
Acknowledgements
Some very nice people at C2
Technologies and Tripoli
Oklahoma Rocket Club have helped me bring this project from a dream
of mine to a reality. Particularly, I'd like to thank
Chris Schuermann and Chris Broyles for believing in the DARTS project enough
to fund it.
Also, Mike Veldman, WD0CTA, has provided some key pieces
of the system and very valuable assistance.
Ellis Nuckolls KC5VMK, Carl Driskill KC5TKD, and Greg
Smith KA5QVV have provided much support in DARTS system testing.
I use LOC
Precision rockets in the testing of DARTS, specifically the Lil' Nuke,
because it shows just how small a rocket you can track!
I also use my Radio Shack
Model 100 laptop as a serial terminal in my testing of the interrogator.
Not available, but still cool! DARTS T-Shirt!
[DARTS Main] [Basics] [FAQ][News][Interrogator][Transponder]
Send comments and suggestions to: ka9mva@qsl.net
basics.htm
This document copyright Steve Bragg, KA9MVA. Updated:
October 02, 1998
