NASA's Goddard Space Flight Center NASA on Wednesday announced a huge milestone in its $8.7 billion James Webb Space Telescope mission: the completion of the observatory's gigantic golden mirror.

To commemorate the moment, the space agency's Goddard Space Flight Center released a dramatic video about the telescope on YouTube.

"The efforts of thousands of people across the United States, Canada, and Europe, for almost two decades achieved this milestone," the narrator said. "Getting to this point wasn't easy. ... Before astrophysicists' dreams of building Webb could be realized, 10 technologies that did not exist needed to be created and perfected. They were."

The video shows off many of those revolutionary technologies, including lightweight support structures, sensors, and more.

But we noticed that a crucial part of the telescope — about a minute and 30 seconds into the video — is blurred out beyond recognition:

In case that's hard to see, here's a labeled screenshot:

NASA's Goddard Space Flight Center; Business Insider

And let's zoom in on that a bit:

NASA's Goddard Space Flight Center; Business Insider

We provided the first image to Lynn Chandler, a NASA representative for JWST, and asked why the part circled in red was blurred out.

"This technology is proprietary. The government must respect the intellectual property of its industry partners," Chandler told Business Insider in an email.

We then asked which company made the blurred-out part, and requested more details about it and its role in JWST's mission — which, by the way, is to study objects at the edge of the universe and quite possibly the air around Earth-like exoplanets.

"That is the secondary mirror support structure with the secondary mirror on it, which includes details of mirror mounts," Chandler said. "The secondary mirror relays light from the primary mirror and does optical correction."

For reference, below is JWST's secondary mirror with its convex, gold-plated surface. It's a critical part. It takes all of the giant primary mirror's light and focuses it onto a third mirror inside the telescope's housing, which then bounces it into a suite of detectors. Presto, images of the universe.

The blurred-out part on the backside, which you can't see, is noted by the arrow:

NASA/Chris Gunn

NASA declined to tell us which company made the blurred-out part, saying that information is an International Traffic in Arms Regulations issue. (More on this jargon in a moment.)

However, we know Northrop Grumman is the prime contractor that designed the spacecraft, and Ball Aerospace built the secondary mirror.

Lon Rains, a Northrop Grumman representative, declined to comment further and asked us to direct our questions to NASA. Ball Aerospace did not immediately respond.

Wait: Why is a mirror considered a weapon?

NASA Why is the back of a mirror on a taxpayer-funded scientific observatory considered an "arm" that must be regulated?

Probably because of spy satellites.

After all, if your telescope can see as sharply as Hubble, yet resolve objects 10 to 100 times dimmer — as JWST should be able to do — that could be useful for peering down at human activity on Earth. And the US government wants to maintain any edge it can over the militaries of countries like China and Russia.

In fact, if you're working in the US — or for the country — on anything that could be even remotely considered a weapon, including a do-it-yourself spacesuit, you have to make sure it's not on the Department of State's ITAR munitions list. Otherwise you might have to pay up to $1,094,010 and possibly face jail time for each violation.

ITAR experts are common inside companies and agencies that work with space technologies, so one of them at NASA probably reviewed their video and said "this part has to be blurred out" to avoid a violation.

"It's basically caution about space hardware details being released by the US government," Anand Sivaramakrishnan, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland (which works closely with the JWST mission), told Business Insider.

"If I had a piece of space hardware in my room, I may not be allowed to have a foreigner come into my room" per ITAR regulations, Sivaramakrishnan said. "I couldn't let him or her touch it."

What isn't being shown?

NASA's Goddard Space Flight Center Though we're not in the aerospace business, we don't want to violate ITAR — and possibly pay a million dollars.

But we can describe what's back there, generally speaking. (Note: There is a moment in the NASA video that does appear to show the back of the secondary mirror.)

So what is it?

Sivaramakrishnan said it's probably the support structure for the mirror, plus a cluster of motorized actuators that can move it.

You're already familiar with mirror actuators if you've driven a modern car. They're what whir when you fiddle with a side-mirror adjustment knob. But where automobile actuators typically have only two actuators and degrees of freedom — side to side, and up and down — each of JWST's mirrors has six degrees of freedom.

Sivaramakrishnan said the cluster of six actuators is called a hexapod.

"If you take a computer keyboard and hold it in space, it needs six numbers to describe where it is in space," he said. That's up and down, forward and backward, side to side, and a rotational aspect to each one. "So if you want to put a mirror in the exact right location, you have to specify that. And that's a hexapod."

The precision you need in a space telescope in mind-bogglingly precise, though. And JWST has 19 gold-plated mirrors with a hexapod a piece.

Sivaramakrishnan said the tolerance — or error in distance — that the primary mirror of JWST can only be off by 140 nanometers, or just larger than the width of an HIV virus. Any more, and there could be huge problems with the focus and exposure.

The hardware required to do this on JWST is "fancy," he said, and "the details are under restriction."

So if you'd like to find out more, now is as good a time as any to work toward your aerospace engineering degree and get a job at NASA or one of its contractors. Good luck!