ORBITAL LASER VS SNOW

Shoveling snow off your driveway can be a real big pain. Why don’t we just laser it from space instead? Read about whether lasering snow off your driveway from space is a good idea and if it will even work in the first place.

Water is Really Good at Storing Energy

Water has a high specific heat capacity, at about 4184 joules to heat 1kg of it by 1 degree celsius in its liquid form. If we want to melt the snow off our driveway from space with a laser, we’re gonna need to master specific heat capacity and energy transfer. We’re also going to want to pump enough energy into our snow in order to melt it.

So, what is specific heat capacity anyways? Specific heat capacity is how much energy an amount of material needs in order to raise its temperature by some amount of degrees. Water is really good at absorbing a ton of energy without heating up much, which is why there are coastal winds that change direction depending on whether it’s day or night. At day, the ground heats up quickly while the water heats up more slowly, making air rise over land and fall over the water, creating winds blowing towards the land. At night, the wind direction switches as the ground quickly radiates away all its heat and the water becomes warmer than the ground. 

LASER BEAMS COMING DOWN FROM THE SKY TO MELT SNOW THAT ISN'T THERE, BUT I'S SURE IT'S FINE; GRAPHIC BY ELLIOTT CISCO

But it can’t be that simple, of course. There’s a few catches; the specific heat capacity of a material is different depending on whether it’s gas, solid, liquid, or other form. There is also a certain amount of energy required to change a material’s state. For water, heating up 1kg of it in its solid form (ice, aka the snow we want to melt) takes 2093 joules per celsius. To transform from solid to liquid, 1kg of water then needs another 333,550 joules of energy, which is its latent heat of fusion. During this change, the temperature of the water will not increase until it fully changes form back into either ice or into liquid water.

How much energy is in a joule anyways? A typical LED light bulb uses 10 watts, which is conveniently 10 joules worth of energy per second. To transform one gram of 0°C ice into liquid water would take 333.55 joules, and if the LED light bulb is perfectly efficient, it would take it about 33 seconds to do so. This also assumes that once the water melts, it completely stops absorbing energy from the bulb (which would not happen in real life).

Big, Big, Big Lasers

In order to direct our energy at the target (snow), we’ll be using lasers to focus all the energy onto one spot. A typical laser pointer uses 5 milliwatts, or 5/1000th’s of a watt. This, obviously, is way too little. It would take about 18 and a half hours to turn one gram of 0°C ice into water with a 5mW laser pointer, assuming perfect efficiency. Thankfully, more powerful lasers exist.

With a 10 watt laser, we can get the same ~33 seconds to melt 1 gram of 0^oC ice into liquid water that we had with our LED, assuming perfect efficiency. 10 watt lasers are typically used to automatically apply designs onto wood by burning it a bit, and a 10 watt laser being shined into your eye would have similarly fiery consequences (DO NOT SHINE A 10 WATT LASER INTO YOUR EYE!!!). 

Now, we could just keep on increasing the wattage of our laser and calculating the stats, but we need a goal. Let's say that each driveway needs to take 1 minute to melt, because there’s going to be a lot of driveways and there’s probably not going to be many laser satellites. How many kilograms of snow are going to be on each driveway though? Let's say that each driveway will be 36 square meters in area. Let’s also say that snowfall on our identically sized driveways is 600 centimeters deep whenever we need to blast it with the orbital laser. The density of our snow will be a pretty heavily packed 25 kilograms per cubic meter as well. This should give us a pretty accurate amount of snow for a somewhat realistic, pretty snowy day. Now we calculate the  total volume of our theoretical driveway, being 21.6 meters cubed; using the density of our theoretical snow, we get a weight of 540 kilograms worth of ice that we need to melt in one minute. Using this, we can then calculate the minimum power our laser will need to be in order to melt 540 kilograms of ice in a minute (also assuming perfect efficiency, at least for now).

How many Watts do we need in order to melt 540 kilos of 0°C ice in a minute? Well, if Watt is an average adult male, the heat from his body will output about 100 joules each second, with a wattage of 100 Watts. No, wait, watts, not Watts. So our Watt(s) with a wattage of 100 watts will need to melt 540 kilos of 0^oC ice in a minute, which will need 180,117,000 joules of energy to melt. In 60 seconds, one Watt with their 100 watts of wattage can output 6000 joules. From this, we find that we will need 30,019 and a half Watts, or 30,020 Watts if we don’t agree with two half Watts walking around afterwards.

Organizing a rendezvous of all the Watts in the world to melt tons of ice aside, we’ll need a 3,001,950 watt laser for this, assuming that the laser is perfectly efficient (we’ll deal with efficiency later). A quick google search to see if there’s any three million watt lasers on the market and... nope. Turns out no one wants people to sell what are essentially OSHA and civilian safety violations waiting to happen.

So if we can’t just buy our way to victory, we’re gonna have to do it IKEA style and buy our way to victory (some assembly required). Aka: build our own 3 million watt laser. But before we do that, we need to make sure that 3 million watts is really all we need.

Blasting Through the Atmosphere

Unfortunately, for our epic space laser satellite of doom to work, it has to actually hit the snow with a laser. Between our average suburban driveway and our satellite is, notably: other satellites, clouds, air, civilian air transport, birds, and objects overhanging above the driveway. If we want to avoid other satellites, we’ll just have to put ours lower. Unlike birds, civilian air transport (specifically the citizens inside), and other pretty much legally non-existent things, we can’t ignore satellites. They either have big companies or countries backing them up legally, and some things could seriously break if the wrong thing is destroyed. An avoidance system would result in delays; putting our satellite lower not only prevents any chance of our laser hitting other satellites but also reduces the amount of atmosphere we’ll have to pierce through (though not by very much). This will put our satellite in low earth orbit, at an elevation of about 400 kilometers.

Now, we only have to deal with the atmosphere. If we can figure out the upper limits of how much energy the atmosphere can block, we can figure out how much additional power we need for our laser to still fit within our requirements. There are a few parameters here: the wavelength of the electromagnetic waves we’ll be blasting at the snow (think: what color the light will be), cloudiness, whatever’s in the air, etc.

This actually presents quite a particular problem. We need a wavelength that is both good at transferring heat to snow and good at piercing through the atmosphere. After perusing the interwebs for a considerable amount of time looking for a graph that would show the wavelength of light in relation to how much heat was transferred to ice from space down to earth, nothing was found. It is for this reason that I will just pick the wavelength 1.57µm which, according to the European Space Agency, has the lowest reflectance in snow. This wavelength is also in the infrared range, which means it should be pretty good at transferring heat. 

So, when the laser travels through the atmosphere, it will lose some energy due to the air in the way. The wavelength of light is one of the main factors that determines how much energy our laser will lose, and thankfully for us, infrared light just so happens to not be absorbed by the atmosphere much. It’s still something though, and because our satellite will move about 177 kilometers in the time it will take for it to melt a driveway, the resistance will not be the same throughout (if the satellite is moving, the laser cannot be aimed perfectly down and cannot always take the shortest path through the atmosphere). If we are to be more realistic, conditions will not always be perfect either, as things such as clouds, moisture, and wind can all change energy loss. Due to this, we’ll just assume a 75% energy loss on our laser due to traveling through the atmosphere. 

This percent loss is likely to be highly inaccurate, with it possibly being too low. It was based off of a research paper found available on Current Optics and Photonics, which aimed a 1.57µm laser high into the atmosphere and observed significant energy level drops, at a 77% drop in the worst conditions. Due to them not aiming the laser all the way through the atmosphere, we’ll use 75% as an average. This means our minimum laser wattage is now a whopping 12,007,800 watts!

Our First Victi- I Mean Customer

At this point, we’re basically done. All the investors have pitched in, we’ve done about the bare minimum of work to guarantee this thing’s safety, and the public pressure is on. After expending a large quantity of money to design and launch our satellite, we’re finally ready to use it. Sent up to space alongside the laser satellite is a very small nuclear reactor to produce the required amount of energy to fire, although we never told the public about that part due to the concern of potential concerns.

After some time, a willing participant from Tiffin, Iowa decides they want to doom their neighborho- I mean bring in new ideas with open arms, and purchases their package. After the satellite’s orbit lines up with a good time to fire, everything is ready.

It’s a relatively clear winter day. Students mill about within the nearby CCA high school. The satellite takes aim. Before it lies a driveway with about the specified amount of snow on it, just asking to be removed. The satellite is about to line up. Time marches forward.

Just as abruptly as investors' stocks are about to tank, the laser fires. An invisible beam of 12 million joules hammers Earth’s atmosphere every second. At first, not much happens. 

Over at CCA high school, some students notice an intense warmth coming from the window. That’s called innovation, kids! Moving on. Please ignore any combustion of skin that may be occurring.

After the first few seconds have passed, a beam of glowing air is now visible, and our customer’s house catches on fire. As the air gets warmer and warmer, a convection current starts to create a strong upwards draft, sucking up small pieces of trash and debris that catch fire as soon as they enter the beam. After about 40 seconds, the beam is white-hot and everything around the area the laser is hitting starts to combust. The suction effect from the convection current is so strong that the shingles from the house start to fly off, as wind speeds reach tornado levels. At this point, the snow has been blown away up into the convection current and has been dispersed into the air, while the driveway becomes the next target for the laser (we never programmed a failsafe for if the snow gets removed faster than we thought).

Eventually, the laser stops firing, the only initial noticeable change is that it’s radiating much less warmth. The convection current remains for quite a bit longer and the area around the beam tries to equalize its temperature. What remains? The equivalent of a small-scale nuclear wasteland, without the lingering radiation. Everything around where the laser hit has been vacuumed into the atmosphere, and will probably fall down at some point. Depending on where our customer is, students inside CCAHS may feel on a scale from uncomfortably warm to dead.

So, what even really went on? Let’s rewind to the start of the barrage.

Surprisingly, as the laser slams the atmosphere, the ozone layer remains mostly unaffected (as the infrared radiation does not affect it much). What is affected though, is all the greenhouse gases in the atmosphere. Before the beam can even reach the ground, 9 million of the 12 million joules per second are eaten up by the atmosphere alone. 

Our 36 square meters of driveway have about 360 kilograms of air on top them, and according to Ohio University, air only needs about a joule per gram to heat up by 1° Celsius. This means that every second, our 9 million joules are heating up the pillar of air above the driveway about 25°C. If you are unaware, room temperature is typically around 25° C, and 100° C is the temperature at which water boils. This has some... adverse side effects, but at least the snow is melting. The 3 million joules being blasted at the snow only results in about 5% being reflected away.

You may be wondering: would the extra heat from the warm air vaporize the snow? Now, to take 0° C liquid water and heat it with 3 million joules per second would result in the vaporization of the water after about 75 seconds. Normally, the laser would melt the snow after 60 seconds. While this might be sped up slightly by the small amount of air touching the snow, I highly doubt that the water would vaporize in the 60 seconds the laser fires simply due to air’s low density and energy stored in heat. It’s not like this would even have the chance to happen anyways, considering the snow gets vacuumed up into the beam once the convection gets going.

About 30 seconds into the operation, the air temperature reaches about 750° C. This, in an unfortunate strike of luck (also known as guaranteed chance), results in our prized customer’s house spontaneously combusting. In fact, basically everything nearby the laser catches on fire. 

While the laser itself may not be visible to the human eye (or at least what’s left of it after it boils away), the heat waves from the laser sure are. Actually, the air would be glowing a bright orange. When the laser first started firing, it was completely invisible. But as it fired longer, the air (being heated up to about 1000 degrees) started to glow red, then orange, and shifting to white. As previously mentioned, a huge convection current is also created due to the heat as super hot air rises, in what could only be a bird’s dream. Wind speeds reach as much as 50 meters a second, as if a huge vacuum cleaner is annihilating the area surrounding the laser. What a success!

The Aftermath (We Already Did the Math, and We’re Cooked)

Now, besides the imminent legal and physical destruction of us for creating a weapon of mass destruction, a terrible problem has occurred in our satellite. Due to the... more than understated overlook of potential safety issues with our device, a heating error in the satellite has caused it to break apart enough to create a leak in the nuclear reactor. Cesium-137 is now leaking out of the reactor and into the atmosphere, which we’re convinced will be very healthy for the general population.

Overall, we managed to create a laser that is probably better at solving the housing crisis by removing unaffordable buildings than removing snow off driveways. We’re also certain that our calculations are off, as the person working on this article is not the most well versed in physics and such. While we wait to be debunked and for the U.S. military to come obliterate us, we decided to get counsel from a local professional. After asking them if a 12 million watt laser would be a good idea, they replied it  sounds like a “great idea”. We’ll be sure to use this evidence in court to defend our actions.

As the military closes in on us and cesium dust fills the sky, the lesson learned is: no, we can not use orbital lasers to reasonably melt snow off our driveways. How unfortunate.