Published: 2017-05-25 12:29:00
Updated: 2017-06-06 15:53:24
Posted May 25
Updated June 6
By Tony Rice
The International Space Station (ISS) will be a little more visible through Saturday morning.
Several times each year, the ISS enters a high-beta period. The Beta Angle, measured between the sun and Earth’s orbit, reached a high of 72 degrees this morning.
Astronauts usually experience a sunrise and sunset on each 90-minute orbit of the Earth. During periods of high-beta angle, the space station is in constant sunlight as it orbits above the sun’s terminator, the line between night and day.
Think of it this way: Picture a track with a bright light in the middle. Now picture an object tied to the end of a rope being swung by a runner circling that track. The light is the sun, the runner is Earth, the track is the orbital plane of Earth, and the object orbiting the runner is the ISS. If the runner swings the rope horizontally, with the plane of track/Earth’s orbit, that’s a low beta angle. The object sees some periods of darkness as it swings into the runner’s shadow. If the runner swings the rope vertically, perpendicular to the plane of track/Earth’s orbit, that’s a high-beta angle. The object is always exposed to light.
Beta angle is an important part of ISS flight controllers planning. While all that sunlight is great for generating power with the station’s massive solar arrays, it presents challenges in keeping the station’s components cool. Controllers must keep the station oriented to provide its own shade on key segments.
Orbiting at just over 250 miles in altitude, ISS is visible to anyone on the ground within a 100-mile wide circle. The closer you are to the center of that circle, the higher in the sky the ISS will reach and the longer it will be visible in the sky. Central North Carolina is at the center of that circle Thursday just after 9 p.m.
Generally, the ISS is visible here on Earth only during the hour or two before or after sunset or sunrise. During high-beta periods, that constant sunlight extends its visibility, even overnight. That provides an unusual number of opportunities to see the station pass overhead as clouds move out later tonight.
The station will be visible:
Thursday, May 25
9:10 p.m. from the SW for over 6 minutes
10:50 p.m. from the NW for 3 minutes (very low pass)
Friday, May 26
3:43 a.m. from the NNW for nearly 6 minutes
5:17 a.m. from the WNW for 5 minutes
9:55 p.m. from the W for 5 minutes
Saturday, May 27
4:28 a.m. from the WSW for 3 minutes
9:03 p.m. from the WSW for 6 minutes
9:49 p.m. from the NW for 2 minutes
The May 25 ground track of the station takes it west of Pinehurst and Carthage, directly over Jordan Lake, directly over the campuses of Cisco and Biogen in RTP, Falls Creek, until it leaves North Carolina directly over the state line at Lake Gaston.
The station will travel from the South Carolina border to the Virginia border in just 41 seconds.
Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on Twitter @rtphokie.