What was the source of the glow trailing the missile the Navy tested?

November 8, 2015 11:36 AM

Like a lot of Californians, I saw this light in the sky last night. The Navy has revealed that it was testing a Trident-launched missile, so that part of the mystery is resolved. But why did it look like that?

As seen in the link, the missile was trailed by a cone of bright white light and a longer, narrower, dimmer plume of blue light, which persisted for several minutes. I'm curious to know what's going on in and around an unarmed missile that would generate those two glows, and what was left of the missile when the glow died out. (Also -- out of morbid curiosity -- when Armageddon comes and somebody sets up us the bomb, if it arrives at night, will it look like this?)

Informed answers only, please (to the extent that anyone can give an informed answer about a matter with some classified aspects) -- it's a tempting question to speculate wildly on, but I don't want it to get deleted as chatfilter. Also, I wish to stress that my interest in this is not conspiracy theory-driven.

posted by aws17576 to Science & Nature (12 answers total)

Best answer: Pretty simple, really. The sun was below the horizon for you, but not for the rocket once it got up high enough to drop the first stage and launch the second. The exhaust plume from the rocket at that height caught the setting sun and lit up in the dark sky.
posted by JoeZydeco at 11:44 AM on November 8, 2015 [4 favorites]

I saw it, too, here in L.A. Pity it wasn't as dramatic as some displays I've witnessed in the past. The part that had me mystified at the time is that it didn't look like it had come from Vandenburg AFB, where these events usually come from. But dusk launches, lit by the setting sun, in fairly clear weather often produce otherworldly displays, so fantastic, I'm surprised they don't create much more stir than they do.
posted by 2N2222 at 11:58 AM on November 8, 2015 [2 favorites]

And, regarding OMG ARMAGEDDON, an incoming missile will be out of propellant and entering the local atmosphere on gravity alone so you won't see much of anything with the naked eye. If you do, you'll have at most a few seconds to think about it.
posted by JoeZydeco at 11:59 AM on November 8, 2015

Certainly the distance above the horizon and exhaust plume per the above is exactly correct. Another potential contributing factor is the moisture content of the air. If the humidity at the altitude the missile was flying is relatively high that may tend to further diffuse the light from the motor's exhaust.
posted by Emperor SnooKloze at 12:41 PM on November 8, 2015 [2 favorites]

Response by poster: The sun was below the horizon for you, but not for the rocket once it got up high enough to drop the first stage and launch the second. The exhaust plume from the rocket at that height caught the setting sun and lit up in the dark sky.

Hmm, anyone know how high up and/or how far offshore this thing was? It came by well past the end of nautical twilight where I am (SF Bay Area). If it had been overhead, it would have had to be more than 90 miles up to get direct light from the sun, but I suppose it could have been farther to the west than I thought. I saw it in the southwestern sky, seemingly moving from SE to NW and not noticeably changing in intensity.

Supposing reflected sunlight was the only source of the glow, can anyone comment on the bluish tint of the longer plume? Normally the last colors one sees at sunset are at the red end of the spectrum (due to refraction, I believe).
posted by aws17576 at 12:54 PM on November 8, 2015 [1 favorite]

Best answer: The Trident II can get up to 1200 km in altitude, which helps it travel farther (high sub-orbital space). The submarine it was fired from was somewhere off the coast of Southern California (the dark blue parts off San Diego most likely) on this map) at it headed northward (hence the need to reroute landings and take offs coming in and out of LAX this week). They can self-destruct it or aim an unarmed missile at a target, but I haven't seen them say which they were doing here.
posted by cecic at 1:28 PM on November 8, 2015

I don't know if this will help, but about 15 years ago, I was in Orlando when a space shuttle launched after dark, at about 9:30p if memory serves. That's about 50 miles distance. This was a scheduled launch, so scads of people were out to watch it.

The light from the rocket was incredibly bright. At first it was like a tiny sun, which is to say, the light emanated from a single point. But as it ascended, it looked much more like the photo in your link.

Which is only to say (guess) that atmospheric conditions and distance probably play a part in what is seen on the ground.
posted by Short Attention Sp at 5:07 PM on November 8, 2015

Best answer: If it was a Navy SLBM, it was probably being fired towards Kwajalein, the atoll in the US Marshall Islands where the US government has the Ronald Reagan Ballistic Missile Defense Test Site, formerly the Kwajalein Missile Range. The military keeps loads of equipment for spotting and getting positions on incoming missile warheads from Navy SLBMs and Airforce ICBMs. I remember reading about it in a National Geographic in the 1990s-- the islands have closed-circuit television networks for everyone, and when there's a missile inbound, they let all the civilians known by flashing a message on the TV, so they can all head out to the beach and watch the MIRVs (Multiple Independent Reentry Vehicles-- each one is a ceramic cone containing guidance and, in this case, instruments where the warhead normally goes) come in. It's pretty cool looking when all they do is re-enter and splash down, as opposed to hosing everyone's skin and retinas with searing UV light before the massive blast wave hits. The military watches everything around with many radars and sonar, and I think they try to recover the MIRVs. So that's my guess as to where it's going.

However, Kwaj is a pretty long shot for a sub-launched ballistic missile, 5000 miles for a missile that with a secret range said to be around or in excess of 3000 nm, and Kwaj is WSW of San Diego-- I see the claim above that it was headed North, and I don't know of other test ranges, but the southern coast and Aleutian chain of Alaska are within 3000nm of San Diego.

But I don't doubt that something that high over SD would be visible from LA. Perhaps you've heard of the 2009 Norwegian Spiral Anomaly, in which everyone in the eastern half of Norway could see a strange and beautiful luminous spiral-with-a-tail in the sky. It was an Russian SLBM that had failed and was tumbling end-over-end above the atmosphere hundreds of miles away.

Also worth noting that molecules of this and that in the atmosphere can be excited electrically to the point that they emit light. I don't have a good sense of how this works, but I've heard of it being referred to as a common source of light pollution for astronomers. It might just be that all the free electrons zinging around the earth all day are causing the particles of the exhaust to absorb energy and give it off as light, or some such thing.

Bluish tint might be due to the sunlight being partly filtered by the Earth's atmosphere further to the west of the rocket, or because the light was being filtered by the air as it came towards the eyes of LA denizens. If it was excitation light rather than reflected sunlight, the light would be emitted in specific colors depending on the energy of excitation and which molecules. I don't knwo enough about the chemicals of rocket exhaust, but whatever they are, their emission spectra are probably something easily found if they are not too exotic.
posted by Sunburnt at 6:57 PM on November 8, 2015 [2 favorites]

Best answer: Phil Plait (the Bad Astronomer) did a nice write up of the event.

100% conspiracy-free :)
posted by tillei at 7:30 PM on November 8, 2015 [1 favorite]

Best answer: I did some calculations using this Distance-to-Horizon calculator and this Sun Position Calculator.

The idea I had in mind is that as the rocket goes up, it can see a horizon that's farther and farther away. If the rocket was 100miles up, it sees a horizon that's almost 900 miles away from the spot on the surface directly below the rocket. At 200miles up, it's 1200 miles. If we pick the spot on the rocket's horizon due west (or in any case, due sun-ward), and if there was an observer standing on the ocean at that point, then I think that if the sun is up in the sky for the observer, than the rocket is in sunlight, albeit a sunlight that is passing through the atmosphere and back out again.

From there I had to guess, eyeball distances, and check. I knew from playing around with google earth the other day that SD to Kwaj was 5000 miles, so I could eyeball about 1/5th that distance as being the spot where the rocket sees the sun rising over its (the rocket's) horizon. Since the rocket went up around 6PM PST, and the rocket sees further and further west, until a time to sees the sun appear to rise in the west. Eyeballing it wasn't great, though, but I could use a calculator, thus:

The sun would be up at 6PM PST at a longitude that's about 132W, and that works out to a distance of 890 miles, which is coincidentally the distance the rocket can see (within a very small error) at 100 miles of altitude. So, the rocket was at 100 miles of altitude when it passed into sunlight and become visible. That number could be lower depending on how far west it had travelled.

With a few more variables filled in, one could probably work out the altitude of the staging event (the blast of gas) which will go into that person's country's Naval Intelligence and Strategic Defense database somewhere.
posted by Sunburnt at 3:00 PM on November 9, 2015

Just a followup; I have since read that the range for the Trident II missile is at or greater than 5000nm, rather than the 3000nm number above (which I was told, over 20 years ago, while touring one of the silo rooms on an Ohio-class "boomer" (missile submarine)). 5000nm certainly puts Kwajalein's missile range within, erm, range.
posted by Sunburnt at 3:53 PM on November 18, 2015

As seen in the link, the missile was trailed by a cone of bright white light and a longer, narrower, dimmer plume of blue light, which persisted for several minutes. I'm curious to know what's going on in and around an unarmed missile that would generate those two glows

This is an extremely interesting question. I think it has very little to do with the sun; the launch was so bright because of the sun, but that does not play a role in the two plumes.

I have a strong suspicion that the narrow blue plume was the exhaust from the gas generator that powers the thrust vectoring on the rocket. For example. in the Shuttle SRB, the rocket exhaust was vectored by a hydraulically-powered nozzle, and that hydraulic power came from burning hydrazine to drive a pump, after which the exhaust was expelled. I cannot find a description of how the Trident D5 thrust vectoring is powered, but the principle is likely the same in using some alternative combustion path. Exhaust that exits at lower pressure will form a much narrower plume than the main propulsion exhaust, and either a different propellant or incomplete combustion could give it a different color.
posted by kiltedtaco at 10:28 AM on November 29, 2015