A strobe light on the ISS

[halman]

What would happen if a small strobe light, that fired every five seconds or so, were mounted on the International Space Station? Would it be more visible to people who don't normally look at the sky, day or night? Would we be able to see where it was even when it was in shadow? To my mind, publicizing the International Space Station is the best bang we are going to get for our buck, or our butt. When it is pointed out to people, they are mesmerized, seeing something that looks like a star sliding across the sky. I am sure that many people have noticed it, and not known what it was.

Mounting a strobe light on the ISS couldn't be that expensive, probably only about 500,000 dollars or so. But the Public Relations we could earn with it might be enormous. When people start to ask, "What is that flashing light that goes across the sky?", they can be told what it is, and that there are people up there right now. Bringing attention to our first (for Americans. not the Russians,) outpost in space, our first real effort at space exploration, is essential to getting public support for spending on the space program, because we can say that is where we are learning to live and work in space.

What the space program needs is enough money to do things right, not cheaply. Even a tiny fraction of the defense budget, diverted to defending the future though exploring space, would have a tremendous impact on our ability to maintain our presence off-planet.

 

[halman]

Moments ago, it occurred to me that school children could donate their change to an ISS Strobe Light Fund, just like they did for the Hubble Space Telescope. Only this time, they could see with their own eyes the blinking light going across the sky, and know that they helped put it there. Television programs from the ISS should be a priority, for consumption in grade schools. We want those little kids talking about space with their parents, informing them, and challenging them.

 

[Mee_n_Mac]

What would happen if a small strobe light, that fired every five seconds or so, were mounted on the International Space Station? Would it be more visible to people who don't normally look at the sky, day or night? Would we be able to see where it was even when it was in shadow? To my mind, publicizing the International Space Station is the best bang we are going to get for our buck, or our butt. When it is pointed out to people, they are mesmerized, seeing something that looks like a star sliding across the sky. I am sure that many people have noticed it, and not known what it was.

Mounting a strobe light on the ISS couldn't be that expensive, probably only about 500,000 dollars or so. But the Public Relations we could earn with it might be enormous. When people start to ask, "What is that flashing light that goes across the sky?", they can be told what it is, and that there are people up there right now. Bringing attention to our first (for Americans. not the Russians,) outpost in space, our first real effort at space exploration, is essential to getting public support for spending on the space program, because we can say that is where we are learning to live and work in space.

What the space program needs is enough money to do things right, not cheaply. Even a tiny fraction of the defense budget, diverted to defending the future though exploring space, would have a tremendous impact on our ability to maintain our presence off-planet.

I doubt the ISS has the power to spare to run the kind of strobe it would take to be appreciable. The ISS is already incredibly bright at mag -2.0* on some passes. How bright do you want the strobe to be ? Do you want to see it strobing during a pass as aforementioned or just when the ISS is not illuminated by the Sun ? If the latter what's the minimum magnitude you desire ? In any case I think that's going to be one powerful strobe.


*I read that theorectically it can attain -4.7 but I don't know I've ever seen it that illuminated.

 

[MeteorWayne]

A stobe would be pretty superfluous considering how bright it already is. I belive a good pass now is as bright as magnitude -2.5. That would be the 5th brightest object in the sky, after the Sun, Moon, Venus, and the brief Iridium flares. I don't think you could reasonably power a strobe brighter than that as Mee_n_Mac said. The ISS also occasionally flares with reflections from the solar panels. The brightest I have evr seen was about mag -3, but that was two solar arrays ago. So the - 4.7 or -5 that has been reported seems resonable if you catch a reflection off of 3 or 4 arrays. That's brighter than Venus.

 

[halman]

I'm not sure if it was the ISS, but I saw something about that magnitude one morning. But the ISS goes over many times when I can't see it because it is in shadow, and I have watched it go from a -2.4 to invisible over my house several times. I was not suggesting a strobe that would rival the brightness of the reflected sunlight, but something larger than anti-collision lights on aircraft. A five second duty cycle would allow for low-level recharging, so the power requirements would not be be great.

It just seems to me that a small flashing light moving at speed across the sky might get people's attention better than a steady, bright light moving across the sky. In either case, the station would be very noticeable. Which is publicity for the space program, something which NASA can't buy.

 

[MeteorWayne]

I still don't think it would work. Can you do some calcs to see how many candlepower it would need to be to be seen from the surface of the earth? There are dozens of satellites that flash at magnitude +1 and brighter with even shorter periods, and you never hear of anyone noticing them, except for satellite and meteor observers. The general public certainly doesn't or they would be common UFO reports, or questions here in Ask the Astronomer or The Unexplained. Almost none are from flashers, most are Iridiums, or the ISS without lights, or NOSS. So that's not bight enough. To create a mag -2 flash would require a lot of light. And you can't use a focused beam or any location would only see one flash.

 

[halman]

I have watched the anti-collision lights on airliners when they are still many miles away, and those are not that powerful. A single flash is hard to catch, whereas a steadily blinking light is very noticeable, even if it is fairly weak. The light will not be dispersed until the last 2 or 3 miles of its journey, if I am not mistaken, and I have seen headlights from many times that distance. A strobe as bright as a car head light is very common, being used on broadcast towers all over the place. I am not looking to distract drivers of vehicles or pilots, just to grab the attention of anyone who happens to be looking at a fairly dark area of the sky when the ISS is going by.

Once people notice something odd up there, they will begin watching more closely, possibly seeing the ISS in sunlight next, which definitely should get their attention. The more people who know that we are actually doing something in space, the more people there will be who would support increasing the funding for doing things in space. The ISS passes over every part of the world during the course of a few weeks. so it potentially could be seen by most of humanity in a matter of months, if people were looking for it. That kind of advertising is hard to beat.

 

[MeteorWayne]

OK, let work the problem a little. Lets say you are seeing airline lights (which are focused beams BTW) from 10 miles away. The ISS orbits at about 215 miles, so thats more than 20 times distant. That means to get that same brightness it will require a light source 400 times as bright. In adddition, it can't be focused (or any one spot will only see one flash), and it has to pass through at least 60 miles of atmosphere if directly overhead, and as much as 600 miles of atmposphere near the horizon. So near the horizon, it would need to be more than 8000 times as bright to be seen, from overhead maybe 600 to 800 times as bright.

I'll have to look at what kind of bright strobes are availbale...


PS, you should be doing this work, not me It's your idea!! :lol:

 

[Mee_n_Mac]

PS, you should be doing this work, not me It's your idea!! :lol:

Yeah !

I was going to figure out what intensity would be required to make a strobe be mag 0 at the ISS distances and what it would require for power and then I thought .... hey it's not my idea !

 

[halman]

MeteorWayne,

The airline lights that I am referring to are the wingtip strobes, which are not focused, because I can watch them approach, pass over, move away. I am only about 100 miles from Seattle-Tacoma International, and it is not unusual to be able to see three airliners heading there along a flight lane. (At night, in good seeing conditions.) They are several miles in altitude, and probably 30 miles or more away, because it takes more than a minute before they pass overhead.

Against a dark background, even a fairly weak light source is visible for long distances.

Hey, c'mon folks, I am talking about publicizing space exploration here! You ought to be supporting me, not shooting me down. I know that there is a way that this could be done, at a reasonable cost, I just don't know what it is. And yes, I do know about the inverse-square law, and the effects of atmosphere upon light. This thing doesn't have to be blinding, just visible.

 

[MeteorWayne]

MeteorWayne,

The airline lights that I am referring to are the wingtip strobes, which are not focused, because I can watch them approach, pass over, move away. I am only about 100 miles from Seattle-Tacoma International, and it is not unusual to be able to see three airliners heading there along a flight lane. (At night, in good seeing conditions.) They are several miles in altitude, and probably 30 miles or more away, because it takes more than a minute before they pass overhead.

Against a dark background, even a fairly weak light source is visible for long distances.

Hey, c'mon folks, I am talking about publicizing space exploration here! You ought to be supporting me, not shooting me down. I know that there is a way that this could be done, at a reasonable cost, I just don't know what it is. And yes, I do know about the inverse-square law, and the effects of atmosphere upon light. This thing doesn't have to be blinding, just visible.

Hey we're not trying to shoot you down (poor choice of words, hope homeland security isn't listening ), just asking you to show (not even prove) the feasability.

As I said, even regular +1 magnitude flashes from satellites every night are not noticed by the public.
"Just visible" ain't enough, because no one notices what's up there already. Just being visbile is not enough.
It would have to be stunningly bright.

 

[CalliArcale]

halman, most of the folks here are engineers and other nerds. This sort of reaction is instinctual, and should not be taken as an indictment of the concept. It's just what first comes to mind for us.

My first thought is that the strobe would only be meaningful when the ISS is in darkness, but most of the time when there are unlit passes, it is very late at night -- late enough that few people will be willing to go out and look for it anyway. (Certainly not a good time for schoolchildren.) The most popular viewing times, twilight, will also be the times when it's already pretty darn bright.

I have a different idea. A satellite in low Earth orbit that essentially acts as a disco ball -- several reflectors, then allowed to tumble (or set spinning for stability purposes). It wouldn't work if mounted to the ISS, but its flashing light would keep working even after the probe's own electronics fail, because it would just be reflecting sunlight. It might be something to add to the next tiny university satellite.

 

[silylene]

Let's say the strobe was a green laser, pointed downwards at the surface, and this laser had a 1 milliradian dispersal (same as a laser diode pen). Let's further assume we want the green light to be very noticable - so noticable, it is 'annoying' but not visually damaging. The FAA has defined an 'annoyance glare' level = 5E-6 watts/cm2


Based upon this, and assuming the ISS is orbiting at a 400km altitude, I calculate a 6.5 kW green laser would be required to generate a bright enough light to create a very noticable 'annoyance glare'. The spot size on earth's surface would be about 405m in diameter.

Each pair of solar power wings on the ISS generates 32.8 kW, for a total of 131 kW (ignoring the smaller backup solar wings).

Therefore, to operate a continuous green laser on the ISS bright enough to be very annoyingly noticable (even in daylight) on the earth's surface would require about 5% of the electrical generating capability of the ISS.

A laser 1/100 as bright (still very bright) would require only about 0.05% of the ISS's generating capability.

Of course, this bright green light would be visible only to people lucky (?) enough to be inside of the 405m diameter spot.

 

[tanstaafl76]

Epileptic astronomers may have some concerns!

 

[Mee_n_Mac]

Let's say the strobe was a green laser, pointed downwards at the surface, and this laser had a 1 milliradian dispersal (same as a laser diode pen). Let's further assume we want the green light to be very noticable - so noticable, it is 'annoying' but not visually damaging. The FAA has defined an 'annoyance glare' level = 5E-6 watts/cm2


Based upon this, and assuming the ISS is orbiting at a 400km altitude, I calculate a 6.5 kW green laser would be required to generate a bright enough light to create a very noticable 'annoyance glare'. The spot size on earth's surface would be about 405m in diameter.

Each pair of solar power wings on the ISS generates 32.8 kW, for a total of 131 kW (ignoring the smaller backup solar wings).

Therefore, to operate a continuous green laser on the ISS bright enough to be very annoyingly noticable (even in daylight) on the earth's surface would require about 5% of the electrical generating capability of the ISS.

A laser 1/100 as bright (still very bright) would require only about 0.05% of the ISS's generating capability.

Of course, this bright green light would be visible only to people lucky (?) enough to be inside of the 405m diameter spot.

Nice ! I'd only say that I think your 6.5 kW is optical output power. The input power will be several times as large. I'm not sure what the efficiency of a strobe or laser for this usage might be, let's SWAG 20% ??? So to get 6.5 kW out you'll need to put in about 32.5 kW. Then there's the atmosphere to contend with.

 

[silylene]

Good point on efficiency.

Now if you wanted simply a bright laser, as opposed to an annoyingly bright laser, (0.01x), then only a ~300 W laser would be required (20% efficiency).

I was assuming a perfectly clear atmosphere. Green light is highly transmitted, as you know.

(By the way, the ISS makes approximately just enough power to run a laser bright enough to blind anyone who looked upwards. I didn't add that to my original calculations.)

 

[halman]

I would be thrilled with a 1000 watt strobe, which I believe would be visible as a 1 or 2 magnitude star. I don't expect it to be bright enough to catch your attention, simply visible if you happen to be looking at it. Because it might make some people wonder, "What is that?" To stimulate people's curiosity is all that we could hope for, just as seeing the station in daylight surely does. A flash every 5 seconds is going to distinguish the station from an airplane, yet will be frequent enough to track.

By charging up a capacitor bank during daylight, the strobe could be used without drawing down the station's batteries.

What are they doing with all of that power, anyway? That would be a pretty big coffeemaker.

 

[tadpoletriker]

Would a 1000 watt strobe flashing for 1/1000 of a second every five seconds consume on the order of 1 watt of power?
If it were close to overhead, with the atmosphere thinning with altitude, might the the net effect be the less than that from an aircraft at 30 miles range and closer to the ground?

JohnB

 

[tampaDreamer]

Great discussion. One thing I'd like to mention, it's the strobing that would make this noticable more then the brightness. If you flashed it on for a fraction of a section every 1-2 seconds, once word got out, even people who don't know squat about astronomy would see the blinking green light and know it was the ISS.

Now what about this.. lets say we expand our laser to have a 1000 or 2000 mile diameter. Instead of targeting the path of the ISS it could be made to target the northern hemisphere. Or perhaps its targeting could be changed.. optimize for new england one month, optimize for southern usa/europe another month, etc. Of course I have no idea the combinations that would work for this based on the path of the ISS.

This could work!

keep going!

 

[MeteorWayne]

I hope you realize the idea of intentionally creating more light pollution makes me sick

And I'm still waiting for some hard numbers to show that this is even feasible. There's a lot of "I think it will be +1 or +2" and a lack of calculated facts

 

[halman]

tampaDreamer,

Whoa! I don't want to consume the entire output of the station's solar arrays just to let people know that it is there! Just a little flashing light traveling across the night sky to pique their curiosity. like MeteorWayne says, there is enough light pollution already.

As far as calculating the brightness, what standard of receptivity will we use? I don't even know what light intensity is calibrated in anymore, having grown up with 'foot-candles'. I might be completely wrong in my assumptions, which is not uncommon, but my experience argues that I have a good chance of being right. All I care about is doing whatever I can to raise awareness of space exploration. I already drag people outside to watch the ISS pass over, talk about space all the time, and post blogs about how space exploration is our only long term hope of survival. This seemed like a fairly easy way to get 20 or 30 more people interested.

 

[MeteorWayne]

The real question is then, is the effort and expense worth it to attract 20 or 30 more people?

You accomplish far more (as I do) by dragging your neighbors out to watch the ISS pass overhead. If each of us here did that, we'd have thousands of people interested

 

[halman]

Actually, I think that the numbers would be a bit higher, I was just being sarcastic. And you are right. Dragging the neighbors, your roommates, your folks, the boss , anybody, out to see the ISS go by will help the cause. Explain that there are 3 people living up there right now, going around the Earth at 17,500 miles per hour. When the station suddenly fades out, tell whoever that it just went into the Earth's shadow, it didn't blow up. (See! This is where the strobe light comes in.)

For those of you who don't know when the ISS is visible, you can look it up at a neat site called 'Heavens Above,' which can be found here:

http://www.heavens-above.com/

You log in, type in your zip code, postal code, or whatever, and it comes back with a list of times the station will be visible from your location, as well as expected magnitudes, transit durations, etcetera.

What is really special is when the shuttle is close to the station, because then you get to see two bright stars zipping across the sky.

 

[Mee_n_Mac]

And I'm still waiting for some hard numbers to show that this is even feasible. There's a lot of "I think it will be +1 or +2" and a lack of calculated facts

Aaaah maaannnn that's the kinda challenge I just can't resist ! :lol:

OK, mebbe if the wife lets me have the time tomorrow and between beers I'll do some groundwork but someone will have to supply some parameters. The biggies are how wide a swath do we want our strobe to be seen from and just how bright is bright enough (magnitude-wise). Otherwise I'd just extend Sylene's example. My guesses are a 1/sec blink rate would be enough to make people noticing the ISS say "hey, that's the ISS. I can tell by it's strobe". I'd opine that a mere mag 1 (let alone 2) would get make any difference in getting people to notice the ISS. It's already much brighter than that on it's "good" passes and still people aren't making it general watercooler talk (unless you happen to work at NASA).

 

[aphh]

OK, let work the problem a little. Lets say you are seeing airline lights (which are focused beams BTW) from 10 miles away. The ISS orbits at about 215 miles, so thats more than 20 times distant. That means to get that same brightness it will require a light source 400 times as bright.

That is true. Intensity of electromagnetic radiation drops or increases in the square of the distance.