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Background: It is the year 2021 and I am a reclusive and enigmatic billionaire with a flair for the dramatic. I would like a dramatic spotlight to shine down on me on command (at night), so that I can look something like this diagram (without an obnoxious helicopter, plane, or blimp above me):

Spotlight On Person

Specific requirements for the system:

  • Must shine down on me from above. Beam can be slightly angled, but the closer to 90° the better.
  • Radius of the projected spot can be big, but shouldn't exceed 5 meter radius (smaller is better)
  • Color of the light should be white, and the ability to change it would be a bonus
  • The system should work anywhere on Earth, but I am willing to time my dramatic appearances for a satellite to be passing overhead. Launching multiple satellites is also an option.

My solution so far: I think I'd be able to accomplish this by launching a satellite (or a fleet of identical satellites for better coverage) that is equipped with a powerful laser, powerplant/battery, and targeting system. When not in use, the satellite charges its batteries and then when I want to make a dramatic appearance, I feed it my coordinates or use a laser designator to designate my position. Then, the light shines down on me, I impress people, and the laser shuts off again so the satellite can recharge.

Questions:

  • Feasibility. I'm unsure how difficult it would be to maintain beam coherence over such a distance and through the atmosphere. Additionally, I'm unsure how powerful exactly the laser system would need to be and if a satellite can support such a load
  • Price. Approximately how much would a system like this cost in today's US dollars including launch costs. Is \$100 million enough?
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    $\begingroup$ "White" - as perceived by the human vision system, sort of depends on ambient light and what the eye has been adjusted to in the environment. Even Orange can seem "white" if you wait twenty minutes in street-lighting. Could you be spectrum specific, if that's not colorist. $\endgroup$
    – Escaped dental patient.
    Commented Feb 16, 2021 at 17:31
  • $\begingroup$ Is orbit an absolute requirement? You could put a traditional aircraft tens of miles above your head, and I don't think it would attract much more attention than a satellite a couple hundred miles above your head - you wouldn't hear it, and it wouldn't look like much to the naked eye. Orbital approaches are also completely thwarted by cloud cover, but lower altitude solutions could get around that. $\endgroup$
    – Nuclear Hoagie
    Commented Feb 16, 2021 at 17:42
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    $\begingroup$ @Tantalus'touch. Well I'm aware that lasers generally don't come in "white" and those that do are actually a combination out of several lasers, so the specific wavelength isn't important (although probably a cooler white would be better) $\endgroup$
    – Dragongeek
    Commented Feb 16, 2021 at 17:43
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    $\begingroup$ @NuclearHoagie Orbit isn't an absolute requirement however I don't want people to be able to see that that the light is coming from a plane / I want the spotlight to extend further than a human can see. I want to evoke biblical, alien-abduction, or supernatural imagery and if it's possible to do so with a plane, I'd take it into consideration $\endgroup$
    – Dragongeek
    Commented Feb 16, 2021 at 17:47
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    $\begingroup$ I can at the very least say that 100 million will not be enough by a very large margin. $\endgroup$
    – Trioxidane
    Commented Feb 16, 2021 at 17:54

7 Answers 7

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Satellites? Blimps? The Six Million Dollar Man? Drag yourself into the millennium!

You want a drone!

drone spot

Your drone can hover silently above you. It can track your movements via invisible lasers. Cloud cover is not an issue. It can turn on your spotlight from close enough above you that the beam will not diffuse to lame wideness by the time it hits you. The riffraff you wish to address will not be included in your spotlight.

Having an entourage of drones hovering over you at all times has other potential benefits besides dramatic lighting. Drones can come down with leg warmers, or a bottle of Crystal Pepsi or a fresh Cabbage Patch Kid exactly as your needs require. If you are low on soothing tunes you can beckon the tune drone to come closer and serenade you with a little Anne Murray and Neil Diamond.

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    $\begingroup$ Absolutely this. You avoid the problem of all that atmosphere scattering light between a satellite and the Earth's surface. $\endgroup$
    – Sal
    Commented Feb 16, 2021 at 22:01
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    $\begingroup$ I've seen people play with commercial and custom-made drones, and while they're not noisy, they're not completely silent either. You should either make a special breed of drones (shouldn't be too hard), or/and make it float quite high above. Also, don't forget that batteries don't last long on them, so make sure you have some spares for 24/24 coverage :). $\endgroup$
    – Tortliena - inactive
    Commented Feb 17, 2021 at 9:24
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    $\begingroup$ @Tortliena maybe steal the wing design from owls, and use a mini-glider instead of a 'copter? Extra bonus, a pair of orbiting spotlights will look more awesome than a single static one. Another extra bonus: Robotic owl familiar will rack up tons of style points, even in full daylight. $\endgroup$
    – John Dvorak
    Commented Feb 17, 2021 at 9:37
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    $\begingroup$ @Sobrique - my cursory research suggests it is battery life. The really bright lights are hungry and eat the battery in 10 minutes. But I am sure a savvy engineer could rig an alternator to generate electricity off of the drone engine. $\endgroup$
    – Willk
    Commented Feb 17, 2021 at 21:53
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    $\begingroup$ I don't think a drone would fulfill all my requirements. First, there's the technical: a spotlight consumes an enormous amount of energy and is rather heavy (so a single drone would need to be extremely beefy to carry it), and I want the imagery of a single beam piercing down from the heavens--people should be able to see the beam all the way up until it disappears from sight like spotlights in Vegas. $\endgroup$
    – Dragongeek
    Commented Feb 18, 2021 at 8:17
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It is quite doable, but highly unlikely in the stated budget of \$100m

First: the light.

  1. You will need a laser, for the required beam collimation.(to keep the spot size small enough)
  2. You will need multiple lasers to combine, to form a suitably aesthetically pleasing visible white light color.
  3. You will need lasers of sufficient power.
  4. You will need a power source for the lasers.
  5. You will need targeting systems capable of suitable aim. Include all control systems in this requirement.
  6. The light source needs to hang around long enough for your speech, without visibly distorting. This means multiple sources trading off the work, or a much stronger source further out.
  7. You will need some means to get the thing launched.

#1 About the best we can do with a powerful laser, through the Earth's atmosphere, is the sort of thing used for the Lunar Laser Ranging experiment which is quite capable of lighting up a 6.5km spot on the moon. Taken in reverse, a satellite at 400km distance can illuminate a 7m spot on earth. Problem #1 is solved.

#2 Trivial, just RGB your lasers.

#3 We need a good spotlight. For an audience. An impressive but not blinding spotlight. I'll accept MolbOrg's comment above for this. 200Kw Satellite laser power, delivering 20Kw ground power, giving 1/2 daylight illumination over the 7m diameter spot.

#4 200Kw consumption is a bit much, that is three times as much solar power as the ISS. Plus, you want the light at night, when a low satellite is likely to be in Earth's shadow. So a modest solar panel for recharging a rather hefty battery pack. Um... 200Kw for 3 minutes would require... one Tesla battery pack. Although the unaltered form will not like that discharge rate!

#5 NO problem. We have spy satellites and ground mappers quite capable of keeping a camera pointed at the ground accurately enough to allow long(-ish) exposure photos. Doing the same with lasers is no problem. You even have a very visual feedback system for targeting.

#6 This is a problem. Due to the relatively low orbit of your satellites, they are zooming horizon-to-horizon in under 10 minutes. To maintain a spot at all, max about 8 minutes window. To maintain a spot without obviously having a rapidly moving source, you need to have your Sat way further out(thus needing much more coherent lasers), or.. you need to shine the spot simultaneously from multiple sats.

#7 If we can keep the mass under 10 tons, a single Falcon9 can hoist it.

Costs:
A single Falcon9 flight will easily hoist 10 tons to a 400km orbit of your choice for you, costing \$65m.
If you use mostly off-the-shelf tech, you should be able to shoehorn in the needed power, control and laser systems for \$35m
Be generous, and assume you are not charged for ground control facilities.

Yes, you could lob a single such Spotlight Satellite for your use with a budget of \$100.

But. It would not quite fulfill your requirement unless you set up a constellation of many such sats. Which will, of course, break your budget.
You would need to time your speech down to the second. You would need to limit your speech to under 8 minutes, better under 3 minutes to avoid your round bright spot turning into a fuzzy ellipse of much greater size.
And it will be obvious to observers that the light is coming from a moving source.

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    $\begingroup$ I suspect the collimation would be further helped by the laser beam only getting scattered by the atmosphere at the end of its path, whereas when aiming at the Moon you have scattering at the start. $\endgroup$
    – Lars H
    Commented Feb 17, 2021 at 16:28
  • $\begingroup$ tesla pack it let's say 80kwh, so it should last for more than 3 minutes, half discharge gets us 1/5 of a hour $\endgroup$
    – MolbOrg
    Commented Feb 17, 2021 at 17:40
  • $\begingroup$ Hybrid LiPo/supercap solutions can probably help with the discharge rate, but at the expense of higher mass... so more expensive. And for a less obviously moving light a higher orbit would work. $\endgroup$
    – Corey
    Commented Feb 18, 2021 at 4:57
  • $\begingroup$ Just nitpicking, but it is small k for the SI unit prefix "kilo" for 10³, a capital W for SI unit watt, and not the other way round. - It is a bit misleading, though, that all the prefixes for fractions of a unit are lower case and almost all prefixes for multiples of a unit are upper case, with the exception of the first three, including kilo... $\endgroup$
    – I'm with Monica
    Commented Feb 18, 2021 at 12:10
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Let me compound on L. Dutch's answer. You can solve the color problem by using multiple lasers instead of one. You can also solve the problem with orbital speeds by having the satellites in a very high orbit - having 96 satellites in geostationary orbit should allow you to have a nice spotlight effect as long as you don't stray from the equator. Otherwise you would need thousands of satellites in geosynchronous orbit.

Keep in mind that though there is no official cost for a geostationary spot, they are given at a first-come, first serve basis. In the 80's some companies were launching satellites to geostationary orbits and renting the satellites for a few million dollars per year each. I imagine that the price would have skyrocketed by now, pun intended.

Also keep in mind that you will have things resembling pillars or light, not spotlight cones. This is due to the immense distances involved.

Last but not least, I don't know how to calculate the size of satellites you would need for this. I imagine it could be like ICESat-2, a satellite that shoots lasers at Earth:

ATLAS [Law's note: this stands for "Advanced Topographic Laser Altimeter System"] emits visible laser pulses at 532 nm wavelength. As ICESat-2 orbits, ATLAS generates six beams arranged in three pairs in order to better determine the surface's slope and provide more ground coverage. Its predecessor, ICESat, had only one laser beam. The greater number of lasers allows for improved coverage of Earth's surface. Each beam pair is 3.3 km (2.1 mi) apart across the beam track, and each beam in a pair is separated by 2.5 km (1.6 mi) along the beam track. The laser array is rotated 2 degrees from the satellite's ground track so that a beam pair track is separated by about 90 m (300 ft). The laser pulse rate combined with satellite speed results in ATLAS taking an elevation measurement every 70 cm (28 in) along the satellite's ground path.

The laser fires at a rate of 10 kHz. Each pulse sends out about 200 trillion photons, almost all of which are dispersed or deflected as the pulse travels to Earth's surface and bounces back to the satellite. About a dozen photons from each pulse return to the instrument (...)

As you see, you'd probably need something orders of magnitude bigger than ICESat-2 (which was a payload of about 298kg), and capable of much tighter focus.

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    $\begingroup$ U can extend a litle bit with power estimates, and laser pumping efficiencies, with ligthspot around 500-700-900 W per square meter we need something like 20kW total, optimistic 10percent pumping gets us something around 200kW in space. LiPo power density, solar panels 1-2 kW solar panels is enough, so i guess it fits in few tons easily, lasers another few maybe, so suprisingly there is a potencial for one falcon launch. To OP - Elon is that u?! $\endgroup$
    – MolbOrg
    Commented Feb 16, 2021 at 21:08
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Why no blimp?!? It's quiet, practically invisible, it can follow you and you can decide whether you want to be mysteriously backlit or resplendently front-lit just by moving it around. They are relatively cheap so instead of having one, you could have one in every city you needed it in and it could come down during the day to re-charge. Everybody else is basically right about the LED lasers, but with a blimp, you'd have options - Collimated light doesn't necessarily need to be mono-(or bi- or tri-)chromatic. If you're worried about somebody noticing it, remember - all of the lighting technology has shrunk impressively over the last many years. If a blimp with a 10 m diameter is at 32,000 feet, it'll appear about the same size as a dime at 30 feet.

You could automate the whole thing by having GPS sensors on the blimp and the billionaire's phone constantly adjusting both the target of the beam and the origin!

Geo-stationary orbit is hugely expensive to get to and you will never be able to adjust the location. If you have a presentation in New York, the angle will be very different from when you're in LA and forget about Shanghai. You'd need to provide all the required power either with solar cells or a nuclear powered Peltier junction. From the back of the envelope, this option would cost 100 times what the blimp cost and it would offer less functionality - not a choice a self-made billionaire would make.

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    $\begingroup$ I'd like to add that high-altitude balloons are very much a cheap alternative to satellites in the real world. There are various concepts for using high altitude balloons to provide internet access to remote locations in a similar fashion to satellite internet access. So our dramatic billionaire might be involved in one of those projects and have balloons to spare. $\endgroup$
    – Ruadhan
    Commented Feb 18, 2021 at 9:33
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A few tweaks might be required, but the Soviet Union did something like this in their Znamya project.

Basically, they put some reflectors in the sky. In the initial test, they provided light over multiple square miles that had a luminosity 5 or 10 times the moon.

So just some additional engineering, and it should work!

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  • $\begingroup$ Since this relies on reflected sunlight, I think this only works at times when the satellite is illuminated but the ground is not, which limits the use of the system to just before dawn or just after dusk. There's no way you could get a perpendicular spotlight shining down at midnight using this (perhaps unless you're at a very extreme latitude). $\endgroup$
    – Nuclear Hoagie
    Commented Feb 17, 2021 at 13:48
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    $\begingroup$ @NuclearHoagie You could chain together mirrors from several satellites, and create a loop of light around the earth... maybe? $\endgroup$
    – Onyz
    Commented Feb 17, 2021 at 16:19
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    $\begingroup$ @NuclearHoagie, that depends on the altitude. The only part of space where your satellite isn't illuminated by the sun is in the umbra of Earth, and close to Earth that is about Earth-sized, but at geosynchronic orbit distance its angular size is fairly small. $\endgroup$
    – Lars H
    Commented Feb 17, 2021 at 16:24
  • $\begingroup$ @LarsH Good point. By my calculation, the angular size of the umbra at geosynchronous altitude is about 20 degrees, putting the reflecting satellite entirely out of commission for only about an hour a night. Although, the brightness will get progressively worse as you enter the penumbra, and you'll have issues focusing non-collimated light at that distance. $\endgroup$
    – Nuclear Hoagie
    Commented Feb 17, 2021 at 16:58
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    $\begingroup$ @NuclearHoagie, in addition Earth's axial tilt helps. I remember that back in the 1990's a certain TV channel had to stop broadcast for maybe an hour after midnight, because (as it was explained) their satellite would then be passing through the umbra — presumably it didn't have enough batteries to keep the transmitter going. BUT this only happened a couple of days around each equinox (which made it noticeable as a deviation from the normal schedule). Most of the year the satellite passed "above" or "below" the umbra, rather than through. $\endgroup$
    – Lars H
    Commented Feb 17, 2021 at 21:41
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Not feasible in the way you propose it.

Color of the light should be white: laser are monochromatic, with a few nm bandwidth. Below you can see a qualitative comparison between the spectrum of a laser and the spectrum of a LED. To make it appear white as perceived by the human eye, you would need to cover the whole visible spectrum, which makes for about 500, 1 nm wide bands. Even using 3 colors to emulate white, you would still need about 150 lasers. Good luck finding a laser for each wavelength with a tuning of 1 nm. I have seen PhD being made on tunable lasers, but not in the range of powers you are interested in. And I am not mentioning the difficulty of compensating for the different diffraction of each wavelength.

enter image description here

Beam can be slightly angled, but the closer to 90° the better.: a satellite normally circles the whole planet in about 90 minutes. It covers one degree around the vertical of a given spot for 7 hundreds of a second. Spy satellites can get that sort of control, but they don't aim for an object the size of a watermelon (with all the due respect for your head), though they can resolve it in their images.

equipped with a powerful laser: last but not least, what makes you think that it is smart to stand under the shine of a laser powerful enough to shine through more than 100 km of atmosphere? Unless your goal is to impress the bystanders with the laser burns that you will get.

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    $\begingroup$ The color problem could be solved by using three lasers instead one, no? $\endgroup$
    – The Square-Cube Law
    Commented Feb 16, 2021 at 18:52
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    $\begingroup$ @Alexander, spotlights used in theaters are hot enough to keep the performer warm if not sweaty. And they are not hundred kilometers above their head. $\endgroup$
    – L.Dutch ♦
    Commented Feb 16, 2021 at 19:57
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    $\begingroup$ "To make it appear white as perceived by the human eye, you would need to cover the whole visible spectrum" - surprised anyone using computer devices is capable to write such thing, while rigth at the moment u reading that comment u are looking at RGB screen which physically incapable to cover whole spectrum, nor it has to as human eyes are incapable to percieve it, as they have mostly 3 ligth detecting rhodopsines for red green blue, it is not impossible to have more thre are animals with 12, but we work on 3. And all colors we distinguish are combinations of intensities of those. $\endgroup$
    – MolbOrg
    Commented Feb 16, 2021 at 20:50
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    $\begingroup$ @L.Dutch - Reinstate Monica my objection was to "laser burns". Our desired level of Illuminance may get the target a little warm, but nowhere near the level of burning. $\endgroup$
    – Alexander
    Commented Feb 16, 2021 at 21:17
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    $\begingroup$ If the laser is still dangerously powerful when it hits he ground, just turn it down some. There will certainly be a sweet spot between being powerful enough to injure and being too dim to see. You just need a laser that's tuned to shine through X km of atmosphere, and no more - it can't be both so powerful that it burns skin and also so dim that you can't reduce the power. $\endgroup$
    – Nuclear Hoagie
    Commented Feb 17, 2021 at 13:40
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Stage spotlights

Another solution that could accomplish this on a budget is simple stage lights. You can purchase a semi-decent stage spotlight for around $100. You have \$100 million available, so you could buy a million of them (or slightly less to account for the price of installation). But let's say you just buy 100 lights, that should way more than enough. You can then use the rest of the money to employ teams of electricians and lighting technicians so that whenever you know or think you're going to be somewhere, you send them in advance to install spotlights onto the side of buildings or whatever. If you know you're not coming back to a location for a while, they can then remove them and move them elsewhere as needed.

Benefits over other suggestions are:

  • Way easier and cheaper than satellites and not subject to cloud cover
  • Not as noisy as drones, little to no risk of being shot down or stolen
  • Supports local economy wherever you go, provides jobs for electricians
  • Can also work for indoor appearances
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