Our Lightning Rocket Project

[00:00:06]Lightning, second only to Jason, it's one of the most impressive forces of nature that we have to witness. With the simultaneous ability to form the chemical bonds necessary for life, as well as the sheer power to obliterate it, it's no wonder that this sometimes everyday phenomenon can bring us to awe time and time again.

[00:00:24]But as much as the average weather enthusiast may know about things like storm structure or how to interpret radar, there's a lot about lightning that at least seems elusive. Like what crazy mechanics must be going on in thunderstorms to even make it possible?

[00:00:38]Or why does some lightning seem to jump cloud to cloud while at other times it will strike squarely on the ground? And maybe most importantly for our scientific understanding, how do we learn anything about how lightning works up close and personal if there's no good way of knowing where it's going to strike? Surely there's no way to harness the power of lightning, right?

[00:01:01]So yeah, it turns out that not only can lightning be harnessed, it's been done before in professional settings hundreds of times. And with all that we've learned about doing this in the past 70 odd years, we at Electron Impressions have long been determined to do it ourselves. But before we get to the part of the video where we focus on the work we've been doing and our recent successes, let's first try to build up some intuition of how lightning works, how it can be triggered, the tools that make it all possible, and some of the people who set the stage for our replication efforts today. All right, so first things first, we've got this thing around us at all times called the atmospheric electric field. Under fair weather conditions, this field is positive but fairly weak. This means that for every meter we go up in the atmosphere, the electric potential rises by somewhere around 100 volts relative to ground. Now, you would never notice this for a couple reasons. The first being that since weak conductivity of your shoes and clothing makes you a pretty decent extension of ground, the equipotential lines representing layers of constant atmospheric voltage should warp a good amount around you. And the second more important reason is simply that even if you actually did see this full 200 volts potential drop from head to toe, there's still such a low density of charge carrying ions in the atmosphere to carry that current that you wouldn't feel it anyway. But all this fair weather field pales in comparison to what you see when a thunderstorm approaches over the course of just a few minutes. Ground measured field strength can rocket up to tens of kilts per meter. And not only that, this field can go positive or negative. What entirely determines that strength and polarity of field for anyone unlucky enough to be standing on the ground is the distribution of charge within the thunderstorm. These separated pockets of charge put us pretty close to explaining why lightning occurs. But to understand where that uneven and highly polar distribution of charge is even coming from, we're going to want to zoom in to see what's happening in the updraft.

[00:02:50]Basically, the thermodynamic engine that drives the storm. So looking deep into this representation of an updraft column, we've got a lot of wind moving nearly straight up and fast. At our current elevation of about 5 km, the moisture in the storm has cooled in temperature to become a mix of tiny ice crystals and droplets of super cooled water. That's water that's below freezing, but hasn't actually nucleated on anything to freeze yet. When those droplets do hit larger pieces of ice, though, they freeze onto them and gradually form what we know as grout.

[00:03:20]It's like little tiny pieces of hail.

[00:03:23]Basic kinematics in the drag equation tell us that the smaller ice crystals are much easier for the updraft to carry while the heavier grapple rises more slowly or begins falling relative to the surrounding air. That difference in motion between the two means they are constantly colliding and in the presence of supercooled liquid water. Those rebounding ice grapple collisions result in what is called non-inductive collisional charging. Now, the exact microscopic mechanics behind that charge transfer is still being studied, but the large scale result is well established in laboratory testing. What's observed is that under common mid-level updraft conditions, the grapple acquires negative charge while the smaller ice crystals instead acquire a positive charge. All that said, the sign and efficiency of this can depend strongly on temperature, liquid water content, particle size, and pretty complicated dynamics, which is why this form of charging can even reverse in certain parts of a storm. But generally speaking, the updraft will carry smaller positively charged ice crystals towards the top of the storm and out into the anvil, while the heavier and negatively charged grout pole tends to remain lower or is carried into the precipitation and downdraft. This produces large separated charge reservoirs inside the storm. We could go further and discuss how the subtleties of charging at different levels of the atmosphere can produce a tripolar rather than a simple bipolar structure. But the key takeaway you should have is that storm dynamics can separate charge into regions that are both physically and electrically identifiable. Now once opposing charge reservoirs exist within a storm, the electric field between them can become enormous. But lightning is not simply the entire gap breaking down at once.

[00:04:54]Instead, the first steps of a discharge are believed to begin inside a much smaller region between reservoirs where the field is locally intense. Under this extreme field, electrons can start to accelerate into air molecules, freeing additional electrons. And as this builds like an avalanche, ionizing increasing volumes of gas to become hot and conductive, it can develop into a birectional leader. While the negative end of this leader will try to propagate into positive charge, its positive end will propagate into negative charge. And if both ends remain inside the same cloud, we call the result intracloud lightning. When that channel instead connects charge pulled up in two different clouds, we call it intercloud or cloudtocloud lighting. But the ground is also an enormous charge reservoir. If one leader end can keep propagating downward through a favorable electric field, the flash can become cloud to ground lightning. This is where it can get really interesting and there are two distinct varieties. In positive cloud to ground lightning, a positive leader originating from near a region of positive charge, for example, an updraft base, descends toward ground and eventually connects with an upward propagating negative leader. Positive leaders can also originate from an upper positive charge reservoir, sometimes as the result of a long horizontal intracloud discharge. And in this particular case where a positive cloud to ground strike gains access to a large upper positive reservoir, it can sustain much larger charge transfer. That is one reason some, but not all, positive flashes can be especially energetic and support long continuous currents. But the far more familiar case is negative cloud to ground lightning. Here, a branched negative leader progresses downward in jagged steps. And as it approaches, the field intensifies at grounded objects, launching several short upward positive leaders. One of them, in our case one beginning at the corner of this building, wins the race and completes the conductive path to ground, sending up a return stroke through the now conductive channel. This can happen several times, sometimes far more, and with much longer duration than positive cloud strikes, which almost always conclude at the end of a single continuous stroke. Now, you can imagine that the difficult part for anyone trying to study this is that a natural leader may begin at almost any favorable location inside a huge evolving storm.

[00:07:01]We can cover the ground with instruments as much as we want and still walk away with no guarantee that a lightning strike will occur close enough to get any real measurement. But if we deliberately lift a grounded conductor into that strong field with something, say a rocket with trailing wire, we can rapidly alter the equipotential landscape and create cloud to ground initiation at a time and place of our choosing. And the biggest advantage that this rocket triggering has over something like a tall building is that while nearby charges can help screen or partially shield a stationary object from the most extreme theoretical field predicted by the pan equation, a rapidly introduced wire has little time to induce these alterations. And with higher resulting field, rockets send up strike initiating leaders a lot more consistently. Now, you might have noticed that in this animation, rocket triggering is only something I've shown attempted underneath the negatively charged region. This is no coincidence.

[00:07:50]Decades of prior work by professional atmospheric scientists like Morris Newman, Pier Hubert, Martin Uman, Vladimir Rockov, and others dating as far back as the 1960s have conclusively shown that the chances of initiating a cloud to ground strike through rocket triggering are astronomically higher when launching from ground into a negatively charged region. And not only that, these people have shown the importance of the surrounding negative fields magnitude. The harsh reality is a rocket that makes it sufficiently high enough to normally get a strike might still be unable to unless it has a strong enough electric field to act as motivation. Only through the sheer number of launches that have been done in the past 70 years do we know what this threshold ground measured field is roughly at least as a roundabout function of the rocket's apogee. Now that's all well and good, but you must be thinking this is a whole lot of talk about electric fields and why they're important. How could you even try to measure something like the electric field between the ground and an intangible object like the sky? Sure, you can measure the electric field between two known electrodes like across this battery just by knowing the voltage across and dividing by the separation.

[00:08:54]But there's an awful lot of separation to account for between the ground and cloud embedded pockets of charge. Well, there's a pretty elegant solution to all this called the electric field mill.

[00:09:05]I'll save the finer details for a future video where I go over how we make our very own printed ones for use in stormchasing. But the core function is to directly calculate electric field strength and polarity all while acting as a semi-stationary device on the ground. And aside from making for a really cool gadget to throw outside during a thunderstorm and watch as massive charges jump around in the sky, those researchers realized pretty early on that a tool like this could be used to time the launch of their rockets, specifically to time the launch for a period when the overhead charges were strongly negative. And that's still how they do it. Professional research labs have employed a wide range of rocket designs and spooling methods over the years, but they've remained pretty constant in their use of electric field mills, which unfortunately are both commercially immobile and incredibly expensive. Wait, $3,000 for a field mill? This isn't $3,000.

[00:10:01]watch our future video.

[00:10:06]And this brings us back to our Lightning Rocket project. Since 2020, this has been an on-again off-again project for us, largely left on the back burner until the past year and a half when we fully committed towards making this all happen. This has involved a lot of iterating on rocket, spool, wire, ignition, winding, and most recently fieldmill design. But we've come a long way and have a pretty decent amount to show for it. Now, progress is all well and good, but have we gotten a strike so far this season?

[00:10:32]>> Record.

[00:10:36]There it goes.

[00:10:39]Holy.

[00:10:40]>> We got it. [screaming] Yo, >> it worked.

[00:10:44]>> We got it. We got it. Let's go.

[00:10:50][laughter and gasps] We got it. No way.

[00:11:56]Now, there's so much more that went into making this happen that we've decided to put out a follow-up video in about 2 weeks from now. If we get another strike before then, you'll be sure to find it there, along with a whole bunch of other information regarding the process we went through to develop a working system. In the meantime, all of this behind the scenes footage is currently out on our Patreon for anyone interested. Thank you so much for watching and we'll catch you guys in the next