DARTS measures slant range (line-of-sight distance) by sending pulses from a ground station (Interrogator) to a Transponder onboard the rocket. The Transponder replies back to the ground station after a known (fixed) interval. The Interrogator measures the round-trip time with a high-speed digital counter. As shown in the illustration at left, the distance is related to the time-of-flight by the speed of light.
By making these measurements hundreds of times per second, DARTS is able to measure the rocket's slant range with very good accuracy. Position is numerically differentiated 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 rejects 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.
DARTS also has the ability to initiate actions aboard the rocket via the transponder (e.g., start engines, deploy parachutes, etc.). It can also send back information from the rocket such as confirmation of parachute ejection, status of on-board scientific instrumentation, serial data, etc.
For the radar types among my readers, DARTS is
a noncoherent, transponder-augmented pulse time-of-arrival range measurement
system with angle tracking and command/telemetry capability.
DARTS automatically keeps its antenna pointed at the vehicle, and measures the rocket's azimuth and elevation angles with respect to the ground antenna. Combining this information with the slant range measurements, DARTS produces three-dimensional position, velocity, and acceleration data many times each 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 measures 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
No other device in the world 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 gives full 3-D flight data, including position, velocity, acceleration and "jerk" (third deriviative of position).
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 makes the difference
between guesswork and real science.
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 the present solution 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. Certain portions of the DARTS system are copyrighted by C2 Technologies, Inc.
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.
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.
The DARTS site is listed on:[AeroPac Rocketry][Tripoli OK Rocketry]
Check out the DARTS T-Shirt!
