Artificial Star Laser Controller for Telescope Calibration

Ground and space-based telescopes are often calibrated using a network of “standard stars” that are used as reference points. Currently, astronomers use the star “Vega’ as a reference point for calibration; however, modern methods such as the use of an artificial star are needed to increase the accuracy of the calibration. The goal of this project is to design a high precision laser controller to be flown on a spacecraft, which will provide a reliable and accurate laser light source to serve as an artificial star reference point for telescope calibration. Given the intended use of this laser controller, its error must be extremely low. Otherwise, fluctuations in the laser may cause improper calibration of the telescopes. This project aims for a percent error of less than 0.25% for the controller. Factors that can cause fluctuations in the laser output are temperature as well as the current supplied to it. In this project, a laser mockup design was created with thermistors and current sensors used to research the laser’s performance under different operating conditions. After designing and printing the laser mockup printed circuit board (PCB), preliminary results suggest that thermoelectric cooling (TEC) can properly maintain the temperature of the mockup to avoid fluctuation. Applications of this project arise in a variety of scientific fields. This laser controller will be used to calibrate telescopes that detect and analyze exoplanets and black holes, including the GMU telescope.

Hi everybody my name is Lina and I am a junior electrical engineering student here at GMU, and I’m presenting my project which is creating an artificial star laser controller to calibrate telescopes.

So starting off by talking about how telescopes are calibrated, what you need
is a reference star. Basically this is a base of all your measurements, and what you do is you can measure the light coming out from the Star and then you
can compare it to what is known for the reference star. So if they match, then your telescope is calibrated properly, and if they don’t match you can adjust
your settings.

So currently all SI traceable astronomical measurements are based on
measurements from one star named Vega that were taken in the 1970s which is a pretty long time ago. With modern astrophysics you need a
lot more precision and accuracy, so NASA and NIST need a new method to calibrate their telescopes so that way they can have more accurate measurements. Some other methods that you can use to calibrate a telescope is using an artificial star which is basically a very strong laser that’s also very
precise, and this way you can use it to act as a reference star instead of using
an actual star so this way you can control the light intensity. The goal of my project is creating a very high precision laser controller that will be flown on the spacecraft and will act as an artificial star to calibrate telescopes, and my goal is to have a very low percent error less than 0.25 percent. So here’s a block diagram of my full system so we have the laser driver which is supplying current to the laser itself and then we have the TEC controller
which is used as thermoelectric cooling which will control the temperature and keep it steady for the laser. Then we have two ADCs and then we have it all connected to a Raspberry Pi.
Taking a closer look at the laser driver, it has five volt DC power and
then it has these inputs so you can control the levels of the light intensity of the laser and current level. Then it has all these outputs that we’re going to track.
It’s the same thing with the TEC controller, so we have the temperature setting, the voltage setting, and then we have all of these outputs that will
tell us it’s working properly and that will sense the temperature and the
current.
Here’s a photo of my first prototype that I’ve been testing. This one has
the laser mock-up on it, so the two diodes right here and then it has a fan,
a heat sink, and then it has the TEC module which will maintain a steady
temperature right underneath the heat sink, and you can kind of see it in the
side view but the two wires here the red one and the black one are for the TEC. Maintaining steady temperature is really important to keeping the error
low so I designed a quick experiment to make sure that the TEC was working
properly. So the way the TEC works is that it can either heat or cool depending on the direction of the current, so if your current is forward then it’s heating and if your current is reversed then it’s cooling. I had three trials with three different current levels 0.25, 0.5, and 0.75 A, and then I tested how well the TEC worked for all of them.
Basically I measured how long it took for the temperature to peak and then I
measured the maximum and the minimum temperatures for each one as you can see it here in the plots. For the first trial with 0.25 amps we have the temperature increasing up until about 30 degrees Celsius where it peaked,
and then I turned off the supply at 100 seconds which is when the peak time was, and then you can see it cool back down to room temperature. Then for reverse current, the orange one, it does the same thing but this time it’s cooling and then heating back up. For trial two it looks about the same, but the temperature time was a lot faster at 60 seconds this time versus
100 from before and the peaks are also a lot taller. Same thing for trial three with 0.75 amps, so this time peak temperature is at 58 seconds and the maximum and the minimum temperatures are a lot higher
than they were before.
Basically that tells us that TEC works properly and you can control the amount of current to control how fast you want it to heat up or what your
temperature is desired to be. Right now what I’m still working on is putting everything together and interfacing it with Raspberry Pi. I’m working on doing breakout boards like this one that you can see here, that will make
sure each chip is working properly before I put them all together.
Finally some applications of my project are calibrating NASA and NIST telescopes as well as the GMU telescope. They can also use this for dark
matter calculations and finding new exoplanets and black holes.
Thank you so much for watching!