A view of the equinox from mission control
As the Sun passes directly over the equator, the lines marking day and night on the large world map in NASA's Mission Control Center are straight for a moment. Equal amounts of sunlight are shining on the northern and southern hemispheres.
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The March equinox made itself known to flight controllers on the big screens in NASA's Mission Control Center (MCC) in Houston on Thursday. The position of the International Space Station (ISS) is marked on a world map along with the Sun and the solar terminator, or the line the ISS enters the Earth's shadow.
Note the yellow dot marking the Sun's position over the equator and the line between day and night are straight and parallel. This happens only twice each year, on equinox. That dot will move northward and the terminator line more curvy as spring turns to summer. By September 22, the Sun will be back over the equator and the terminator lines will again be vertical on this map.
The Sun's position and where the station will pass from day to night is particularly important to the flight controller at the SPARTAN (Station Power Articulation and Thermal Control) position. Sunlight means power for the station's huge solar arrays but it also means increased heat that must be dissipated.
Reading the MCC map
- The sub-solar position is marked with a yellow dot
- The red vertical lines mark the solar terminator or the where day turns to night and vice versa.
- The position of the ISS is shown here in south of Africa, the white egg shape around it indicates where the ISS is above the horizon, also known as it's footprint.
- The swooping white lines show the path of the ISS including the previous, current and next orbits. The square brackets on these lines indicate where ISS will be passing from night into day or day into night.
- SAA: South Atlantic Anomaly, an area where the Earth's magnetic field is considerably weaker. Radiation levels increase as the ISS passes through this area. During periods of high solar activity, astronauts will move to more protected areas of the station as they fly through the SAA.
- T171W, T046W, T275W: Tracking Data Relay Satellites (TDRS), NASA geosynchronous satellites are used for voice, video and data communications
- STPB, DJS, ULD, USK, PPK: Russian Ground communications stations
- LAT, LON, & ALT: ISS's current position: 45.9 S, 51.7 W Altitude: 235.2 miles
- INC 51.7: this is in inclination of the orbit to the equator in degrees. Think of it this way, a satellite orbits directly over the equator has an inclination of 0, one that orbits over the poles has an inclination of 90. 51.7 was chosen for the ISS because it passes over mission control centers in Houston and Moscow and gives access to the most scientifically interesting areas of the Earth from space. It also prevents low beta angles (read on)
- D/N: time to the next pass from day to night (32 minutes, 7 seconds here)
- BETA 48.2: this ia the beta angle or the angle of the ISS's orbit to the Sun. When this number is above 60, the station can be in constant sunlight, which makes the SPARTAN controller's job more interesting.
Other acronyms in the photos
- MET: Mission Elapsed Time
- EXP-62: Expedition 62, the current 6 month long mission
- 61S, 74P, DREW, NG-13, SPX-20 METs: Time docked for the Soyuz crew capsule and the Progress, Cygnus, and SpaceX cargo capsules
- GMT: Greenwich Mean Time
- OBT: On Board Time
- FD: Flight Director
- LOS: Loss of signal
- FE: Flight Engineer, one of the astronauts aboard the ISS
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