Arduino space object tracking laser pointer, feasibility?

I’ve been doing a lot a calculus, astronomy, and C++ in my college courses and I want to apply what I’ve learned. My idea is to put a laser on an arm controlled by stepper motors to point out and track things in the sky.

I plan to have 2 stepper motors. One controls the vertical angle of the laser, while the other would horizontally rotate a platform with the other stepper and the laser. This way two motors should be able to point in every direction.

To get it to point at and track celestial bodies I would need to preprogram their orbital parameters as well as Earth’s and the time/location of the laser on Earth.

To track something like the ISS I would need to update the orbital parameters every other day since it moves around so much (orbit decay, maneuvers and the like). I think stars should be the easiest thing to start with.

Parts I think I’ll need to prototype it:
2 steppers, any cheap stepper should do
stepper drivers
A laser pointer
A clamp to hold the laser, platform. I can print these at the local makerspace.
And finally, lots of good math and code

For the final version:
Digital compass, so it knows what way it’s pointed.
A GPS
A display to say what’s being pointed at and some fun facts about that thing
Buttons to enter my location and select an object to point at
A mosfet to switch the laser on/off

Is this feasible? If so, any advice for accomplishing this? Have you seen any projects like this? It’d be nice to have something to go off.

Time is important, but your GPS should be good for that. It will provide accurate time stamps.

If you only need to approximate the object's position in real time it should be doable. Otherwise you will need precision steppers, etc. You will also need some sort of airplane detection, so you don't flash your laser at one.

ChrisTenone: If you only need to approximate the object's position in real time it should be doable. Otherwise you will need precision steppers, etc. You will also need some sort of airplane detection, so you don't flash your laser at one.

I should look into a precision stepper for the vertical axis, but the horizontal one will have a big gear reduction. The platform will be the big gear and I'll print a pinion for the motor. Possibly 11:1 or larger. 1.8 degrees looks like the norm for cheap steppers, so I could get down to 0.16 degrees with that.

Ideally would like to get the angle accurate to the beam divergence, 1.2mrad or 0.069 degrees. I think I could settle for 3.6mrad, 0.21 degrees at most. I think steppers can do half steps, can they do quarter or 16th steps too for greater precision?

edit: typo

I'll make the gear reduction whatever it needs to be so the cheapo motor will match precision with the fancy one.

As for airplane detection, I might need to use my eyeballs and an emergency off switch. I can't think of a way I could do that without a really decent camera and some fancy software.

GustavoMcSavy: ... As for airplane detection, I might need to use my eyeballs and an emergency off switch. I can't think of a way I could do that without a really decent camera and some fancy software.

Be sure you keep a sharp eye out, depending on where you are. It's a felony where I live.

UnoWatt: Legalities and wisdom of this project aside, have you done any calcs on the power requirement of a laser beam to reach that far?

I'm not sure you've ever seen a laser pointer at night. The beam is visible almost until it leaves the atmosphere, even with a cheap 5mw pointer. The dot doesn't need to actually reach the stars for me to see the line pointing in its direction.

As for legality of pointing a laser at the ISS, a 5mw 100% legal laser wouldn't be visible in the slightest to the astronauts. That takes about 1W and even then it's a faint spot of light only as bright as a star. I would clearly see the line from the source, but anyone on the space station or mars for that matter would get a few photons at most.

What a laser beam looks like pointing at the sky

GustavoMcSavy: As for airplane detection, I might need to use my eyeballs and an emergency off switch. I can't think of a way I could do that without a really decent camera and some fancy software.

Surley it should be the other way around, the laser is only on when a handheld switch is kept pressed ?

UnoWatt: Evidently I misunderstood the meaning of "point out" in your opening post. That said to me you want to, well, point out an object by putting a dot on it like I do in class with my laser pointer.

Using a laser (green works best) to 'point out' celestial objects has been the standard teaching technique. The beam does not have to hit the object, and return reflected light. The beam of a sufficiently powerful laser (~10 mW) works in all but the most light polluted environments. My 50mW green laser works splendidly even in midtown, where my school is located.

I remember a calculation for a single mode HeNe laser with a 1 meter cavity pointed at the moon. The circle of light on the moon was about a mile in diameter. So no, we didn't see any light return. However there were experiments that DID bounce lasers off the moon, but these used telescopes (both for transmission and detection - and a LOT more power.)

srnet: Surley it should be the other way around, the laser is only on when a handheld switch is kept pressed ?

Well I can't hold it while stepper motors aim it, but maybe some kind of button on a cable would do. That's a good idea where safety is concerned.

Perhaps a threaded rod driven by a motor would be a good way to get fine resolution.. A shaft encoder could tell you where the pointer is

regards

Allan

ChrisTenone: Using a laser (green works best) to 'point out' celestial objects has been the standard teaching technique. The beam does not have to hit the object, and return reflected light. The beam of a sufficiently powerful laser (~10 mW) works in all but the most light polluted environments. My 50mW green laser works splendidly even in midtown, where my school is located.

I remember a calculation for a single mode HeNe laser with a 1 meter cavity pointed at the moon. The circle of light on the moon was about a mile in diameter. So no, we didn't see any light return. However there were experiments that DID bounce lasers off the moon, but these used telescopes (both for transmission and detection - and a LOT more power.)

It looks like I still cannot get it - you point at the moon and make 1 mile wide beam that hit the moon but you have so little energy you cannot detect the returned light. How you know you are pointing on the moon? You had some detector on the moon? Or you are just looking at the beam and guessing if it points in the right direction? If so why you need huge laser instead of simple pointer?

Did you look at the link in reply #6?

Smajdalf:
It looks like I still cannot get it - you point at the moon and make 1 mile wide beam that hit the moon but you have so little energy you cannot detect the returned light. How you know you are pointing on the moon? You had some detector on the moon? Or you are just looking at the beam and guessing if it points in the right direction? If so why you need huge laser instead of simple pointer?

As implied by Mike, the beam makes a bright line pointing into the sky. You can follow the line to whatever object you are pointing at.

I did not do the laser on the moon experiment! NASA or a NASA funded lab did. It involved a retro-reflector placed on the moon by astronauts in the 1970s.

This assumes one believes that humans landed on the moon. If not, well then, it’s just magic.

An interesting question is why the beams (shown in the link to reply #6) seem to end. At least part of the explanation has to do with the layer of light-reflecting particles that form the "planetary boundary layer", which is of varying thickness. But other factors, such as trigonometry, etc. must come into play.

That makes the problem of making an automated pointer much more difficult, because you have to know where the "end" of the beam appears to the observer.

As for identifying stars and especially tracking moving objects, the Arduino does not have the floating point precision or clock speed required for this.

http://www.laserpointersafety.com/aviationfacts/whybeamsseemtoend.html

jremington: An interesting question is why the beams (shown in the link to reply #6) seem to end. At least part of the explanation has to do with the layer of light-reflecting particles that form the "planetary boundary layer", which is of varying thickness. But other factors, such as trigonometry, etc. must come into play.

That makes the problem of making an automated pointer much more difficult, because you have to know where the "end" of the beam appears to the observer.

As for identifying stars and especially tracking moving objects, the Arduino does not have the floating point precision or clock speed required for this.

http://www.laserpointersafety.com/aviationfacts/whybeamsseemtoend.html

Thanks for the link!

As an aside: when I point a laser horizontally over the ocean from an elevation of 10 meters or so above the sea level, the beam also seems to disappear after a relatively short distance (relative to the apparent distance of the horizon.) Possibly due to scattering (much more aerosol water over the ocean)?

For backyard astronomy, the beam does not need to be pointed very precisely. For tracking that could be used for measurement or communication, I agree, the Arduino is not powerful or fast enough. But for casual observing, you just want people to look in the right direction.

However, if one has access to a "goto" type telescope mount, you can just tape a laser pointer to the barrel of the scope. No Arduino needed, with plenty of precision.

As an aside: when I point a laser horizontally over the ocean from an elevation of 10 meters or so above the sea level, the beam also seems to disappear after a relatively short distance (relative to the apparent distance of the horizon.)

That is why I mentioned that other factors must come into play. The explanation in the link is obviously incomplete, but I have not been able to find one that satisfactorily explains all of the factors.

Big gears, lots of teeth, worm gear. Since you supposedly learned calculus, hopefully you know some trig to get your resolution of angles down.

jremington:
That is why I mentioned that other factors must come into play. The explanation in the link is obviously incomplete, but I have not been able to find one that satisfactorily explains all of the factors.

Right?

I’d like to be able to see beam from the side as it passes over the water. Unfortunately perpendicular scattering is much dimmer than backscatter. It gives me a warm fuzzy that such simple phenomenon is so difficult to characterize. Maybe low cost science is still a thing!

People do use laser beams to map particulates and gas density very high in the atmosphere, but they use sensitive detectors. So, at least some of the explanation has to do with the sensitivity of the eye.

There is a lot more on the topic here: http://calgary.rasc.ca/atmosphere.htm

Plenty of room for high cost science!

It's all high cost now!

Being a scientist in Michael Faraday's time would have been fun. You could do a simple experiment with a candle and a pane of glass, then have a Sunday afternoon public lecture and demonstration. At a cost of 2 or 3 dollars.

I work on the third floor of a building that is about 15 miles from "South Mountain". I was able to aim a home-made argon laser at the mountain, measure the total output at the laser, and drive to a picnic site on the mountain and measure the light there (I used an interference filter to select the laser's light.) The data was not very good, but it could have been worked up into a science-on-the-cheap project.

But most of my work involves instruments that cost many thousands of dollars, and a handful of technicians, interns, and students.