Space force

The launch of the Space Force satellite could create a luminous cloud in the night sky this evening

If you’re outside stargazing in the Western Hemisphere tonight and look up at the right time, you might spot something that looks pretty odd to you: a small, circular cloud of light swirling around. will rapidly expand to the apparent size of a full moon, before finally disappearing a few minutes later.

What you just saw was not some weird atmospheric phenomenon, but a fuel dump from a US Space Force (USSF) mission that launched earlier today on a United Launch Alliance (ULA) rocket. ) Atlas V 511 from Space Launch Complex 41 at Cape Canaveral Space Force Station in Florida.

The launch, which took place as scheduled at 2:00 p.m. EST (19:00 GMT), carried two satellites for the USSF’s Space Systems Command (SSC). The mission, called USSF 8, will place the two identical Geosynchronous Space Situational Awareness Program (GSSAP) satellites – GSSAP 5 and GSSAP 6 – directly into a near-geosynchronous orbit approximately 22,300 miles (36,000 kilometers) above from the equator.

Related: The Atlas V rocket launches 2 surveillance satellites for the US Space Force

A United Launch Alliance Atlas V rocket launches two Geosynchronous Space Situational Awareness program satellites for the US Space Force, January 21, 2022.

A United Launch Alliance Atlas V rocket launches two Geosynchronous Space Situational Awareness program satellites for the US Space Force, January 21, 2022. (Image credit: United Launch Alliance)

According to ULA’s flight profile, 6 hours and 35 minutes after launch, the first of the two satellites (GSSAP 5) will be released into its geosynchronous orbit, followed 10 minutes later by the second satellite (GSSAP 6).

The fuel discharge should create a glowing cloud

Seven hours, 11 minutes and 40 seconds after launch, the Centaur second stage will dump its unused (excess) fuel into space. Dumping excess fuel is standard practice for all Centaur booster-assisted launches. This happens after the satellites separate; fuel leaking from a Centaur rocket upper stage.

It turns out that the timing of this event will be perfect to create a celestial spectacle for much of the Western Hemisphere. When the Centaur releases its excess fuel, it will be dark over North and South America. But the Centaur, at an altitude of around 22,300 miles (36,000 km), will be exposed to sunlight, and as such the fuel will reflect sunlight as seen from Earth.

In a Twitter thread, assiduous satellite observer Cees Bassa provided a considerable amount of information regarding the visibility of the fuel dump:

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Bassa likens the fuel dump’s appearance to a “bright nebula, perhaps as big as a full moon in the sky.”

“The cloud should be visible to the naked eye, and with binoculars or telescopes it should be possible to see the cloud growing and changing shape,” Bassa added.

The fuel dump is scheduled for 9:11:40 p.m. EST (6:11:40 p.m. PST). It should suddenly appear to the naked eye as a circular, expanding comet-like cloud about 10-15 degrees west (or right) of the zero-magnitude bluish bright star Rigel in the constellation D ‘Orion. Your clenched fist held at arm’s length is about 10 degrees, so about “a fist or a fist and a half” to the right of Rigel is where the cloud should appear.

Such fuel dumps from satellites have been seen before. On the evening of August 12, 1986, shortly after 10 p.m. EDT (0200 Aug 13 GMT), countless people in the United States and Canada, watching the Perseid meteor shower, were surprised by a discharge of fuel from a Japanese. launch of a satellite that created a luminous cloud.

And on September 1, 2004, the fuel dump from an NRO-1 satellite launched earlier that day was visible from the eastern United States and Canada.

Why dump fuel in space?

Some might ask, what is the need to dump fuel into space? The reason this is done is for safety; to minimize the risk of a vehicle explosion, which in turn would create a large amount of space junk or orbital debris that would then endanger other space vehicles. At such a high altitude, the fuel dissipates quickly and poses no environmental threat to Earth.

Joe Rao is an instructor and guest speaker at New York’s Hayden Planetarium. He writes on astronomy for natural history reviewthe Farmers Almanac and other publications. Follow us on twitter @Spacedotcom and on Facebook.