What is the viability of using a computer controlled telescope during the day to track a high altitude balloon? Assuming that we’re receiving realtime GPS coordinates from the balloon payload and knowing the GPS coordinates of the telescope would it be feasible to program the telescope to track it?
-Robert
It would be easy to run some basic math calculations to establish the feasibilty.
Things to take into account
Hmm… It would definitely have to predict the location based on not just on latest location, but also trajectory based on recent updates.
What about optical issues from daylight? I am assuming that ascending to 30km within 90 minutes would not have an issue with curvature of the earth.
Might be fun to try with cheap sounding balloons and a fixed abort altitude for easy recovery.
-Robert
I know the military does optical tracking of items this size and altitude, so I wouldn’t expect that to be an issue if you have optics of sufficient quality and tracking information of sufficient accuracy. It is the latter that I have some doubt of.
GPS altitude reports are notoriously inaccurate, and I suspect would not allow you to place a telescope within the field of view needed to actually see the balloon.
You might try researching FPV antenna tracking setups. Many people use them to keep a high gain antenna pointed at their RC model when doing FPV flight. The only difference is that you would want to mount a telescope to it instead of an antenna. Although, going that route, I would suggest mounting both an antenna and a telescope, in order to get good radio range.
The hardest part would be finding a setup that can handle the weight of a telescope. Usually the antennas people use are pretty small and light, and a couple of standard RC servos are more than enough power to move it. Here is one example.
It works like this - you have a computer onboard the aircraft (APM for example) connected to a GPS receiver and radio transceiver. The aircraft transmits a telemetry stream in real-time with GPS coordinates, airspeed, altitude, etc. Then on the ground, another computer receives this telemetry stream. It also knows it’s own GPS coordinates, so it calculates the pan/tilt angles and moves the tracker to point at the aircraft. Here is a good example of one in action.
The other option would be to buy a motorized telescope, but I have a feeling that would be a whole lot more expensive.
The problem with an FPV setup is that the beam width of a radio antenna is measured in degrees, while the equivalent for an optical setup is measured in seconds at high magnifications (or at best minutes). Optical tracking at these ranges is orders of magnitude more difficult and requires an accurate location.
I strongly suggest doing the basic math on what field of view you get with the magnifications needed at the distances your talking about. I suspect you will find that GPS simply isn’t accurate enough to provide tracking.
Ok, as best as I can get from this: A 1500mm f10 telescope would give me a 0.1 degree field of view showing 53m of the sky at 30,480m (100k ft) away. (This does not account for the telescope eyepiece which can drastically change the magnification) The balloon would have a diameter between 3m to 9m depending on the type and be climbing at maybe 10m/s.
This seems difficult, but not impossible.
Vertical GPS accuracy adds at least another 14 meters of ‘uncertainty’ to the tracking location provided. And it can potentially be much worse then that. I also suggest taking into account eye piece or camera optics, since even a small additional magnification would reduce the field of view below the usable level.
For altitude, APM uses an onboard barometric pressure sensor to get a more accurate fix than GPS altitude.
Barometric sensing of altitude can be very accurate, but as you usually see it, it isnt much better then GPS.
To achieve the accuracy you need a good sensor, decent sample rate, and to follow a slightly complicated calibration procedure right before launch.
Here’s another thought - instead of trying to track it from the ground with a telescope, what about mounting a camera (or multiple cameras) onboard, and transmitting the video back to the ground? If the goal is to simply keep an eye on the status of the balloon, then that might be easier than tracking it with a telescope. There would probably still need to be an antenna tracker on the ground to get ~30km of range, but it wouldn’t be too difficult.
If you have a HAM license (or get someone who is to assist), a 40-50 mile range is easy without antenna tracking.
Adding camera(s) to the payload adds weight for very little gain. A ground based system doesn’t impact the experiment. I don’t “need” to keep an eye on the balloon. It’s more curiosity and cool than anything. Not worth it if it adds weight.
-Robert
I am already planning to include a HAM transmitter, but that will be used for the gps and sensor data.
-Robert
The UTD Space camp group are launching a Balloon next wednesday sometime. If you want practice at this that would be a good opportunity. The Plano Radio club is also going to have a balloon launch in mid July as well.
These would be good folks to talk to, since they have practical experience with this (some of them for decades), and they can provide better guidance.