Could a nuclear weapon be seen from space?

[The Disintegrator]

More precisely, could a ground burst nuclear weapon detonation (let's go with the Trinity test of 20kt) be spotted from low earth orbit (say on the ISS at about 410km above the surface) by the naked human eye? Would it be something you would have to know where to be looking, or would it be bright enough to catch your eye? If not, would a larger weapon of say 300kt used in a 2.2km high air burst be visible? Would the answer change significantly if it were an overcast day as opposed to a sunny day?

I've scoured Yahoo Answers and other sources but haven't really found much besides conjecture, and proof that seems to just point to satellites being able to pick up the flashes. Does anyone have any suggestions on how to figure this one out without just guessing?

Thanks.

[bilateralrope]

I think a better question to ask is what would be the smallest explosion that would be visible from space ?

Two variables that would affect the answer are time of day and cloud cover.

I have no idea how to go about answering the question.

[Adam Reynolds]

The short answer is that it is going to be extremely dependent on environmental conditions. My quick search indicates that roughly 35% of the energy is converted to thermal energy, part of which is released as visual light. I'm not sure there is really an easy answer here. It also depends a great deal on the position of whatever is looking for said flash.

It is powerful enough to cause flash blindness in individuals, which is why the scientists involved in the Manhattan project, with the apparent exception of Richard Feynman(he recognized that the visual light wouldn't do any real damage and viewed it through a car windshield that would block the UV light), all wore welding goggles. He was 20 miles away, while the closest group was only 6 miles away with their heads down and thus obviously saw nothing. No one else in his group actually saw anything due to their glasses. This might actually be a way to answer your question. If you could determine how much protection low grade welding goggles offer, that would allow you to have a rough estimate what level of brightness the explosion had. I don't think there actually was any real data on this specific question.

I also believe there was work done on this issue for bomber crews though I have no idea about it. Perhaps Sea Skimmer might have something on this.

As for the satellite comment, early warning satellites can see ballistic missiles launch. That isn't a very good indication on what the ISS can see.

[Purple]

IIRC bomber crews had ways of covering the glass in their cockpits so as to make them non transparent completely and just flying blind once they dropped the bomb. They also wore eye patches so that if they lost one eye to a surprise nuke they'd have another. Not making this up.

[SpottedKitty]

As for the satellite comment, early warning satellites can see ballistic missiles launch.

I thought what they actually detected was the heat trace of a rocket launch. And it's quite plausible for weather conditions to make a smallish nuke detonation hard to spot from orbit. In fact, from what I remember reading, the most reliable detection method in the early days was actually ground-based — seismometers. The mini-earthquake signature of a bomb going off is apparently distinctive; it was used to confirm many of the early USSR test shots, and I think it might still be in use today as a backup for whatever the modern satellite detection system uses.

[Terralthra]

Lightning bolts are easily visible from the ISS through thick cumulonimbus clouds. Even a small nuclear weapon detonated above ground would be even easier to see.

[Prometheus Unbound]

Lightning bolts are easily visible from the ISS through thick cumulonimbus clouds. Even a small nuclear weapon detonated above ground would be even easier to see.

Lightning happens at the top of clouds too - I don't think think the ISS can see lightning that's hitting the ground,below clouds...

[Terralthra]

It totally can. Images of lightning seen from space are easily found with a simple web search. Some bolts are above the clouds, others are visibly blurred by the cloud above them.

[Broomstick]

The mini-earthquake signature of a bomb going off is apparently distinctive; it was used to confirm many of the early USSR test shots, and I think it might still be in use today as a backup for whatever the modern satellite detection system uses.

If I recall, seismometers were part of what was used to confirm the North Korea nuclear tests, which are fairly recent. Seismometers can also detect underground tests, which satellite viewing can't.

[dragon]

depending on the orbit.
An example is the human eye's resolution at 0.6 arcmin
link

The ISS is at an altitude of 173 miles, so at that resolution, the unaided human eye can resolve an object 159 feet wide. There are individual buildings larger than that.

Man made things that can be seen from the ISS

1. The Great Pyramids at Giza

Some squinting may be required to spy Egypt’s greatest monuments in this picture snapped by astronaut Nicole Stott. If you’re really lost, look for a pair of triangular shadows near the center…

2. Bridges


Long bridges crossing over straits stick out like a sore thumb. However, identifying them can be a pain. Last year, astronaut Chris Hadfield caught a glimpse of what he thought was the Golden Gate, but may have really been a less-glamorous bay area counterpart.
3. Lonely Desert Roads

Chris Hadfield, via Universe Today

As Hadfield explains, desert highways look like “straight human [lines] drawn onto incredibly rough terrain," making them rather noticeable.
4. Cities at Night


Space-bound explorers have taken hundreds of nocturnal photos over various urban centers. Here’s a helpful interactive gallery. Go look up a metro area near you.
5. The Greenhouses of Almería


A sprawling sea of plastic greenhouses covers over 64,000 acres in southeastern Spain. Tons of fruits and veggies (tomatoes, cucumbers, peppers, etc.) are produced here, generating $1.5 billon in revenue every year.
Kinda, Sorta, Not Really Visible: The Great Wall of China

link

[Prometheus Unbound]

It totally can. Images of lightning seen from space are easily found with a simple web search. Some bolts are above the clouds, others are visibly blurred by the cloud above them.

Oh a flash, sure - sorry I thought you meant the bolts themselves. My bad.


Are you sure they can see them at the bottom of the clouds? Sometimes we don't see them at the top but can hear them, when we're on the ground. Some of those clouds can be 20-40km high I think?

[Terralthra]

Here's a photograph taken of Starfish Prime, a 1.4 megaton device. The photo is taken from 1400 km away, through heavy cloud cover.

[SpottedKitty]

The mini-earthquake signature of a bomb going off is apparently distinctive; it was used to confirm many of the early USSR test shots, and I think it might still be in use today as a backup for whatever the modern satellite detection system uses.

If I recall, seismometers were part of what was used to confirm the North Korea nuclear tests, which are fairly recent. Seismometers can also detect underground tests, which satellite viewing can't.

I actually didn't mean visible-light detection for satellites — I'm sure I remember reading that at least one system detects the electromagnetic pulse. That'll work for line-of-sight to the detonation, whether it's airburst, groundburst, or even underground. All you need is enough satellites so that all the line-of-sight zones overlap.

As an aside, about the NK test shots — didn't the seismograph data also prove at least one of them fizzled?

[Sea Skimmer]

GPS satellites host the USNDS system, which replaced an earlier more basic system, which detects space and atmospheric nuclear blasts with visual flash sensors, several bands of EMP sensor, an X-ray sensor, the later only relevant to explosions in space itself, and several forms of charged particle detectors also primarily but not completely intended for detecting bursts in space. USNDS is supposed to detect any nuclear explosion which is not underwater or underground, the later being covered by a world wide network of seismic sensors.

Estimating yield of underground blasts is iffy because the size of the cavity they are exploded in can have a huge variation on the transmitted shock. One North Korean test is thought to have failed but nobody can be sure of that. In fact it probably is possible to conceal a ~15kt underground nuclear test, as its been estimated in certain kinds of rock a 600 foot diameter cavern would actually be able to contain the blast without collapsing after being pumped down to near vacuum. However it would in turn be nearly impossible to conceal the enormous amount of evacuation required to build such a cavern. Electromagentic effects may or may not be detectable for underground bursts, that depends on local ground conditions, depth and yield.

As for the original question, you could indeed see a Horoshima sized bomb from space. However the fireball of a yield that small lasts less then 1 second and the flash is just that, a flash. If you were not looking at the spot it is very unlikely you would notice it with the naked eye, and the grazing angle would limit the area over which it could be seen. Much higher yield weapons would be far more noticeable.

Are you sure they can see them at the bottom of the clouds? Sometimes we don't see them at the top but can hear them, when we're on the ground. Some of those clouds can be 20-40km high I think?

Tsar Bomba's cloud rose to over 60km after being exploded at about 6.4km height, but in contrast the 15 Megaton castle bravo test detonated at sea level rose to about 60,000 feet. Most megaton range bombs pushed the cloud up to around 50,000ft. The lower the burst the more material mass and wind to move in more material mass exists to cool the cloud as it rises and thus limit its height. Of course as can be seen in the near space tests, if you go high enough you cease to get anything that looks like a normal mushroom cloud at all. You would always get at least a small cloud from a nuke though even in deep space, because of its own mass being vaporized.

I thought what they actually detected was the heat trace of a rocket launch.

Yes its a form of thermal imaging that detects the booster plume. However they will actually pick up much smaller sources of heat, and this has to be filtered out by software, such as B-52 strikes and aircraft afterburners igniting, and that was with the 1980s models. Much better satellites are now in orbit, and a test program exists with several satellites in orbit which have FLIR sensors good enough to thermally track actual ICBM warheads in flight.

[jwl]

Considering it is possible for you to see the ISS from ground level with the naked eye, and nuclear explosions are considerably more big and obvious than the ISS... of course you can see nuclear explosions from the ISS with your naked eye.