Here is a 21 f-stop comparison (−10 to +10) of ISO 100 black and white film with a digital (Nikon D750 full-frame 24 megapixel CMOS) sensor. The same lens and neutral density filter were used for each set of images.
The extraordinary tolerance of photographic film to overexposure (“overexposure latitude”) explains why bright rocket exhaust plumes do not wash out the entire image on NASA’s vintage engineering film cameras as opposed to today’s digital video. It’s also why when using a digital camera, you should set the exposure so the bright end of the image histogram isn’t clipped by the dynamic range of the sensor.
Note than an overexposure of 10 f-stops means the film is receiving 2^{10}=1024 times as much light as the optimum exposure, and yet a (somewhat) usable image is still produced. At the same time, the limited underexposure latitude of film means that when shooting film you should “expose for the shadows” to preserve detail in darker parts of the scene, counting on the tolerance for overexposure to handle the bright parts.
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After releasing the video in the main post, the creator, Paul Shillito, learned from a viewer that NASA continues to use film cameras for engineering photography of the Space Launch System. As noted, film can handle the dynamic range of brightness which video cannot. These films were taken at high speed, providing slow-motion views of the liftoff and ascent of the rocket. NASA did not make these films public until an enterprising self-described “spaceflight nerd” filed a Freedom of Information Act request, whereupon NASA published video of all the engineering camera views of the launch, which you can download from this index page of “Artemis High Speed Film”. These video files are huge—gigabytes in size—so think about where you’re going to put them and how long they’ll take to download before you click that button. There are about eight hours of video, some shot at 100 frames per second, and all videos are silent.
Paul Shillito has prepared an 8 minute “highlight reel” from this material, sped up in some cases, set to Gustav Holst’s The Planets. These are the only images of the Artemis I launch I’ve seen in which the glare from the solid rocket boosters does not wash out detail from the rest of the vehicle. In the close-ups of the engine bay of the first stage booster, note how flame is dancing around the heat shields protecting the four RS-25 engines as the solid rockets burn nearby.
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It looks like liftoff is powered only by the SRB’s. Is this possible?
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It could be done, as the solid rocket boosters (SRBs) produce 75% of the total thrust at liftoff, 1490 tonnes each, 2980 tonnes total, which is more than the total weight of the vehicle, 2610 tonnes. But they don’t do that. The four RS-25 liquid engines are lit in the final seconds of the countdown and only after they are confirmed to be running stably and approaching full thrust are the SRBs lit and hold-down bolts blown. If you look at the detailed views of ignition and liftoff in the video, you can see the blue shock cones from the liquid engines between the SRBs. Liquid hydrogen burns with an almost transparent flame, so it isn’t immediately apparent when seen next to the brilliant SRB exhaust plumes.
There are multiple reasons for starting the liquid engines first, and on the pad. First, it allows detecting any problems with one or more engines which might affect flight. It’s a lot cheaper to cut off the engines before liftoff and fix the problem than to lose a mission when an engine fails to air-start on the way to orbit. Second, the extra thrust from the liquid engines, 758 tonnes, increases the thrust to weight ratio and makes the rocket ascend more rapidly, decreasing gravity losses which would consume more fuel with no benefit. Finally, since the liquid engines are never restarted during the mission, it allows all of the complex and heavy equipment required to start the engines to be on the ground, where it can be reused from flight to flight.
These reasons are why most rockets with solid boosters start the liquid core engines on the launch pad. That’s most, but not all—the Titan III lifted off using only its SRBs and lit the core stage engines just before jettisoning the boosters. But the Titan used hypergolic-fueled engines which are much simpler to start and, having been designed as an ICBM, already had the gear to start them on board.
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