On title: correct notation is “AN/TVS-3” in ALL CAPS, as used in the original article. This “AN/“ prefixed system is called JETDS, used to identify electronic gears in US military.
Examples include AN/PVS-14(nightvision goggles), AN/ALR-67(V)3 (airplane RWR), AN/PRC-152(walkie talkie radio).
According to the Wp the the world's most powerful searchlight today is 7 times more powerful. The beam in Luxor Hotel in Las Vegas has 39 7 kW xenon lamps to produce of beam of about 9.129 billion candela, 13 million lumen.
"The brightness emanating from the Luxor lamp room is about twice that which emanates from an equal area of the sun's surface (about 95,000,000 cd/ft2 versus 45,000,000 cd/ft2)."
Consider also the vortex water-wall arc lamp, in which the cooling water (deionized, so that it is a very poor conductor) runs inside the quartz tube. It is swirled so that there is a gas-filled space along the axis, through which the electric current flows[1]. I have seen powers up to 100MW mentioned.
I recall reading somewhere that David Letterman wanted to use one on his show to melt a small car, but the manufacturer thought it frivolous and did not cooperate.
> Soldiers were told that these searchlights could cause sunburns from over a mile away.
I was skeptical at first, but according to the wiki article about xenon arc lights, they actually produce quite a bit of UV light - the spikes are even higher than visible light.
You can actually generate UV with very low voltage if you have the right semiconductors. That we regularly deal with tens/hundreds of volts without incident is quite astonishing.
> Initially, NASA underestimated the electromechanical interference (EMI) projected by the light and the Apollo computers crashed when the beams were aimed at the rockets on the launch pads.
Not wanting to ruin a good story, but I find this unlikely. If it were true I would think the military would be more interested in using them as weapons for electronic warfare than search lights. More likely the lights were interfering with radio links like telemetry or voice. Or maybe they were just not conforming to some EMI guidelines NASA was using at the time and were modified as a safety precaution.
There's a little more detail about the Apollo situation on a post [1] by Neal Strickberger on Candlepower Forum:
"Chicken wire! Turns out this was added for the Apollo program, when they used the TVS-3s to light the pad. A 20kW short-arc fed with 400Hz 3phase fullwave rectified unfiltered power produces lots of RFI at 1200Hz harmonics, and when nice and focused with a reflector it was enough to shut down the capsule. So they made a Faraday cage."
Optical people are rolling their eyes at the size of reflector required for 1200 Hz.
BEST hope possible to make the story true would be clear glass semiconductors can detect incoming light so MAYBE germanium glass tube diodes hanging out in the air could get confused, although why a moon rocket would have bare unprotected glass semiconductors on the outside is a mystery.
_harmonics_ means more than just the first odd harmonic.
With 20 kilowatts flowing it's very believable that the comb reaches quite a ways up the spectrum. And the radiator doesn't have to be tremendously efficient or focused with that kind of input power to produce significant effects in unintentional receivers. Also remember that wiring harnesses in spacecraft are probably very long, so will be good receivers at many frequencies reaching quite low.
It's not hard to crash computers with stuff like this. I remember in college someone built a tesla coil in one of the lab rooms that would crash people's phones.
Kind of a fun story that's related. A friend of mine ran a machine shop in the early 2000s that had the world's largest plasma cutter. Apparently one afternoon the police and FAA showed up to investigate their property. The plasma cutter was generating enough interference to cause computer problems at IAH airport and on landing planes (their shop was in the flight path of the aiport.) Allegedly it had taken the FAA months to figure out where it was coming from due to the fact the plasma cutter was typically only running for a few minutes at a time.
It makes sense. Every arc is an impulse and that's wideband noise. (The FFT of a spark is basically a horizontal line.) The earliest radios were spark gap transmitters.
But sparks and arcs aren't impulses. They're much more interesting than that spectrally, including with significant peaks and harmonic components. These properties are things that protection equipment can use to detect and localize faults.
This is very cool (or hot as the case may be), but I'm not exactly sure why being visible from space is stressed so much. The astronauts onboard the ISS don't look down at nothingness when they're on the night side of the world. Plenty of lights can be seen which aren't billion candlepower arc lamps.
From the ISS, the very smallest blobs you can see are 100 meters wide. There are very many large blocks of lights that can be seen from space. But to see a single light, it has to give a significant boost to the average brightness of an area larger than a football field. That's not very easy.
The size of area is not too relevant. The angular size of stars is very close to zero, yet we see them with naked eyes because they deliver sufficient energy flow. Pretty sure you can do that with just a few watts laser with size measured in millimeters, if you focus it well enough onto the ISS.
The area and angular size of the light itself doesn't matter.
But I'm talking about the angular size of the smallest detail a human eye can perceive, which does matter a lot.
Anything smaller than one arc minute might as well be a point source. A star is smaller than an arc minute. A light viewed from space is smaller than an arc minute. But either way, that "point source" has to be bright enough to light up the entire arc minute to stand out from its surroundings.
The only thing your eye perceives is the total light coming from that arc minute. Which is the same as saying you have to bring up the average brightness of that arc minute.
And an arc minute's area, viewed from low orbit, is somewhat bigger than a football field.
> Pretty sure you can do that with just a few watts laser with size measured in millimeters, if you focus it well enough onto the ISS.
Yeah but that's a laser. This is a white light. Much more difficult and impressive.
> And an arc minute's area, viewed from low orbit, is somewhat bigger than a football field.
This means if you take a point light designed to light a football field (football fields do have these light sources), and direct it into space instead of the ground, will be visible from low orbit.
> This means if you take a point light designed to light a football field (football fields do have these light sources), and direct it into space instead of the ground, will be visible from low orbit.
A point light designed to light up an entire football field should work, yes.
What football field has single lights that powerful? Normally you have many flood arrays with a dozen or more lights each.
> People did it with less powerful light sources:
Cool! So that's somewhere around one kilowatt, significantly easier to do.
Though notably it's still a spotlight. I wonder how many watts of flood light you would need.
> Normally you have many flood arrays with a dozen or more lights each.
I was thinking about a single array, from the orbit it’s pretty close to a point source.
> I wonder how many watts of flood light you would need.
I don’t know about efficiency of that military equipment (need beam angle to compute), but I would expect with modern white LEDs you don’t need that many watts, they’re very efficient at converting electricity to light. You would probably still want liquid cooling for them, though.
In the parent article, the author talks about obtaining replacement bulbs - Since this is an arc lamp, there's no filament to burn out.
Does anyone know the failure modes of an arc lamp? Do the electrodes wear out / erode? Is repair even possible for something like this or is it essentially remanufacturing the entire thing because of the capsule enclosing everything?
Unfortunately not repairable. Failure modes:
cathode melts, gap gets larger, unstable arc;
anode melts or cracks, possible catastrophic failure;
seals (uranium glass) to tungsten leak, xenon bleeds out;
envelope fractures, catastrophic failure!
In some cases electrodes vaporize and plate the inside of the envelope.
Details at https://www.sqpuv.com/PDFs/TroubleshootingGuide.pdf
Searchlights work by focusing light from a source to infinity. Physics dictates that small light sources focus better. Getting searchlight-level brightness from an LED source will require an LED array, which will be too big to focus effectively.
LEDs make excellent floodlights, but if you want reach, xenon discharge lamps are still the best option.
If anyone wants to dive into physics behind the reasons why you can't efficiently collimate light from a large emitter like a LED array, this Stack Exchange answer [1] and the Wikipedia article about etendue [2] is a good start.
There was a very interesting article about how you can't focus 100's of magnifying glasses using light from the moon to start a fire, probably similar in principles?
LED car headlights do use this principle; it does have some applications.
However, the diameter of each LED optic would need to at least equal the diameter of the single optic used for a point source light. The result would be an enormous searchlight with a very broad beam.
I can't find any solid information on the quantitative light output of the AN/TVS-3, but xenon arc lamps typically produce 30 lumens per watt. Therefore, the 20KW AN/TVS-3 should produce around 600,000 lumens.
Readily available high-power LEDs are capable of 1700 lumens, so equaling the AN/TVS-3 would take--as a very rough ballpark that does not take into account the different light distribution between LEDs and discharge lamps--350 LEDs and optics. The AN/TVS-3 uses 30" optics, so those optics would also need to be at least 30" in diameter.
350 30" optics is a lot more like a wall of light than a searchlight. Aiming that many separate optics would also be a nightmare.
What I'm not sure of is if the lumins/watt rating is given for the light output or the power input.
The input power rating is 450 Amps * 200 Volts * 1.732 = 155880 electrical watts. That's nearly 7.75 times as much electrical power as light output. That makes sense since the peak efficiency is about 7.3 for a xenon arc lamp.
Why does the optic need the same diameter? For gathering all of the light, with a mirror at least, I think you could place a smaller optic closer to the light and still capture the same fraction of the light?
I probably am missing something about optics though.
The ability of an optical system (a lens, mirror, or combination) to collimate the output of a light source into a narrowly diverging beam is directly proportional to the diameter of the optical system's final element and inversely proportional to the size of the light source.
Bigger optics = less beam divergence = more useful range.
This is a function of the diffraction limit[0] and is a property of physics.
If you want to match the beam divergence of a 30" optical system, you have to use 30" optics; there are no shortcuts.
I know that we can create very large virtual apertures for receiving signals by using arrays of many receivers. The basic diffraction physics presume a single source, so it isn't totally obvious that they generalize to a multi-source system.
I can, however, imagine that a multi source system would require in-phase light sources to kind of mimic a phased-array receiver on the send side.
Examples include AN/PVS-14(nightvision goggles), AN/ALR-67(V)3 (airplane RWR), AN/PRC-152(walkie talkie radio).