Explaining The Amazing Rocket Trail Over LA

alloyed scott manley here and this as you might've guessed is the Falcon 9 load launched out of Vandenberg on Friday I've had a ton of people asking me about this because of course rocket launches don't usually look like that or do thee so first up this video here is from Doug Ellison who you may remember was the guy that got me the tour of JPL and showed me all the awesome behind-the-scenes stuff and narrated a couple of videos this is from his drone he's down of course in SoCal and yeah it seems that he had the best view because not only did he understand that a rocket launch was gonna happen but he put a camera in place and got the whole event from start to finish now the launch time of the Falcon 9 was a 5:27 p.m. had II an instantaneous window because they were trying to line it up with the required orbits for iridium now the launch time was really important because it meant that it launched in darkness but as it got high enough it would launch into the bright Sun so Vandenberg's about 160 miles to the west of the location and a few seconds after launch you can see the rocket and its trail now the trail is darker than the sky behind it so this is a an occlusion trail it's basically blocking out the light and that's how we're gonna see it but as the rocket gets higher up the reverse is gonna happen the sky is gonna be darker and the rocket trail is gonna be much brighter because it's gonna be catching the Sun which is over the horizon but as the trail high enough it can actually illuminate the trail directly and there's also this nice moment where the trail goes dark and that's presumably because there's a cloud layer further out which is blocking the Sun so the Sun isn't illuminating this section of the trail anyway as it gets higher up a second thing is happening the atmospheric pressure is dropping down and that means that the rocket trail is starting to expand further and further now if you go back to my video on rocket nozzle design you'll remember that the rocket exhaust comes out at a specific pressure and at sea level at launch this pressure is generally law and the atmospheric pressure so you have an over expanded nozzle and the exhaust gets pinched down as you go higher up the pressure starts to match the exterior pressure now as you get to very high altitudes the nozzle becomes under expanded and the exhaust trail expands a great deal after leaving the engine and of course it's good to match the size of your exhaust nozzle to the ambient pressure outside that's why the first stage of the Falcon rocket has nine engines with small engine bells and the second stage has one engine with one very wide engine bell it's much easier to actually see this air exhaust expansion happening if you look at all videos specifically from the East Coast where they have really good launch tracking cameras this is obviously much faster than regular speed but you can see how the exhaust is just expanding out into the atmosphere now the lower atmosphere is also a bit more turbulent you can see here there is actually a kink starting to form in the trail there that's very common because the winds were art different altitudes can be doing going different directions and frequently rocket trails will take on a very erratic look minutes after launch this is a daytime trail from a shuttle launch and it does look like it's gone crazy gone out of control but paradoxically if a rocket really did fly that erratically on launch it would probably be terminated by the flights a bara system before it reached the altitude where the Sun was able to illuminate it the shuttle trail is much denser than the Falcon 9 because it has these at big solid rocket boosters and they tend to produce a lot more smoke a lot more particulate matter whereas the Falcon 9 is using kerosene and liquid oxygen so its main products are going to be carbon dioxide and water of course you're gonna get a lot of other chemicals but those are the main constituents I gather that most of the visible trail is from the water of freezing out in forming tiny ice crystals and with the next section of the video shows the staging and you'll see that the trail is again still pretty rough at this point that then it transitions to this much smoother formation and that's basically the transition between having nine engines all kind of competing with each other to a single engine the one engine to rule them all but I also want to zoom in to these little puffs that are happening in the trail so what's happened is a rocket has staged this is a first stage using its attitude control thrusters and of course these puffs of gas come out they're not as high-energy as the main exhaust because the main exhaust has a higher exhaust velocity these little puffs are coming from cold gas attitude control thrusters they're basically a pressurized tank of gas that's allowed to expand through a nozzle now some of their SpaceX Watchers got some better views but this one is especially interesting because you can see the two fairings coming off and they appear to be using some sort of reaction control thrusters to control their attitude so so while SpaceX weren't gonna recover the booster in this particular case it is clear that they're working on experiments to recover their fairings and that might explain the new mr. grabby claws ship lots of speculation at this time but a lot of people think that they're gonna string a net between there and use it to soft land fairings because the fairings take a really long time to build and cost a bit five million dollars each you can actually get a pretty good idea of how big those payload fairing ZAR because Elon of course posted this image of his Tesla Roadster getting ready to write the Falcon Heavy I think it's also worth mentioning that as we get into the upper atmosphere the because the atmosphere gets so thin the engine trail becomes dominant and so the turbulence of the atmosphere essentially goes away or high up there's a lot less difference in the air flows as there are lower down so that's why the trail expands in such a clean you know clean manner it shows this kind of fish head shape anyway by this point in the launch most people in LA were saying what the hell and calling 911 or alien invasions but I mean yeah look the whole reason this is so visible is because it launched in the dark into the sunlight and so you could see a lot of features which would normally be blocked by the blue sky would normally overpower any of this detail and if it launched at night it wouldn't be illuminated so there is a short window of about half an hour before sunrise half an hour after sunset where rocket launches can look absolutely spectacular and of course it was launching south so people in LA were seeing the complete trail Sayid on one last feature worth showing was the booster basically coming back down to earth even although there was no plan to recover the booster they did perform a reentry burn as usual presumably doing their usual experiments to make sure that you know things worked as I understand it there wasn't really the pressure to recover this booster because it's an older block for design and you know the new hotness is coming in they don't need any of their old and busted stuff so yeah thanks to Doug for his video thanks to SpaceX for making an awesome launch and I hope you can do this again in the future when I get a chance I'm Scott Manley fly safe [Music]

Channel: Scott Manley

Views: 265,271

Keywords: spacex, rocket, falcon, iridium, LA, drone, fairing, landing, UFO, not aliens, not armageddon

Id: CJ6nn8fZOmc

Length: 7min 43sec (463 seconds)

Published: Sun Dec 24 2017