Comments on: Space Station Solstice

By: astronomy round-up: 27 July 2012 | Jennifer Willis

astronomy round-up: 27 July 2012 | Jennifer Willis — Fri, 27 Jul 2012 16:05:49 +0000

[...] Space Station Solstice [...]

By: realta fuar

realta fuar — Fri, 27 Jul 2012 01:37:02 +0000

Thanks Carlos! As usual, some of the B.A.’s readers know more about a subject than the B.A. Aren’t “educational” blogs generally supposed to work in the other direction? . This is presumably good for the B.A.; for his readers, I’m not so sure as most people don’t read the comments for any blog.

By: MadScientist

MadScientist — Wed, 25 Jul 2012 23:55:20 +0000

That provides such a beautiful example of Rayleigh scattering as well.

By: Nathan

Nathan — Wed, 25 Jul 2012 21:31:37 +0000

Back when I started following the Shuttle I would frequently hear about how certain time periods were blacked out for launch window “due to high beta angle.”

This situation where the orbital plane of the ISS results in nearly continuous daylight was difficult for me to visual first. Phil’s diagram is nice but I also found an ISS flash app on NASAs site that gives a nice animated visual guide.

As a bonus it explains the flight orientations of the ISS during these periods too (XVV, XPH, and YVV). YVV is the orientation/attitude flown during high beta angle and is informally known as Barbecue.

http://spaceflight.nasa.gov/station/flash/start.swf

By: Carlos

Carlos — Wed, 25 Jul 2012 18:20:53 +0000

@Grizzly (#6) – No there is no period of constant night. The satellite is always going around the earth, and sooner or later it must come back “in front” of the earth on the sunlit side. Imagine the earth with its shadow (umbra) cone projecting behind it, away from the sun. The shadow moves up and down 24 degrees with the season due to the tilt of the earth’s axis. Now take a hula hoop wich represents the orbit. You can rotate it up and down (inclination) and around the earth’s axis (right ascension of the ascending node, RAAN, if you must know). Under some rotations the entire hoop is outside of the umbra cone – much like the diagram Phil drew. However, it is impossible for the entire hoop to be INSIDE of the umbra cone, which is what is required for a period of constant night. According to my handy SMAD book (Space Mission Analysis and Design) the longest eclipse (night) period for a satellite at space station altitude is a little over 36 minutes. This is regardless of inclination or RAAN. This happens when the orbit (hula hoop) crosses right through the middle of the umbra cone.

By: Grizzly

Grizzly — Wed, 25 Jul 2012 17:59:52 +0000

Okay, another stupid question here. But given the orbital mechanics, if a period of constant daylight is possible, the opposite must also occur. Are there extended periods of “night” and how often do they occur?

By: Jonathan Lubin

Jonathan Lubin — Wed, 25 Jul 2012 17:15:56 +0000

I like how you at times can see Crescent Earth beneath you — terminator is visibly curved.

By: Phil Plait

Phil Plait — Wed, 25 Jul 2012 15:21:46 +0000

Good point, Carlos (#1) – I didn’t know the orbital plane precessed that much!

By: Pete Jackson

Pete Jackson — Wed, 25 Jul 2012 14:51:42 +0000

Watching the slow approach and departure of the Sun from the Earth’s limb gave me an idea. Would the ISS not be a good platform to observe for small bodies orbiting the Sun within the orbit of Mercury, as well as objects approaching the Earth from the sunward direction (otherwise very hard to detect). It would seem relatively easy to mount, with a mount that compensates for the ISS’ orbital motion, a fast large-aperture camera, and fire away towards the directions near the Sun when it is below, but close, to the Earth’s limb. I would anticipate very short exposures that are later stacked.

By: Jake

Jake — Wed, 25 Jul 2012 14:23:52 +0000

I’m sure this is out there, but you probably know the answer quicker. Is the orbital alignment consistant? Is the south end of the orbit always facing the sun, and the north end away? Or does the orbit “precess” around the earth?

NM, Carlos answered while I was reading and posting. Thanks Carlos.