Night Glider mode (or "XVV Night Glider mode") is one of the procedures for orienting the
solar arrays on the
International Space Station
The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...
.
Normally the
photovoltaic
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...
solar arrays of the space station track the sun. However, one of the main causes of
orbital decay
Orbital decay is a gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods. These orbiting bodies can be a planet and its satellite, a star and any object orbiting it, or ...
on the space station is that the area of the solar arrays, brushing against the thin residual atmosphere at orbital altitude, results in a small amount of
aerodynamic drag
In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding ...
. The drag can be lowered by orienting the solar arrays in "sun slicer" mode, where they fly edge-on to the orbital direction, rather than tracking the sun, however, this orientation reduces the power produced. The "night glider" mode is a hybrid orientation,
[G. Landis and C-Y Lu, "Solar Array Orientation Options for a Space Station in Low Earth Orbit", ''Journal of Propulsion and Power, Vol. 7'' No. 1, 123-125 (1991).] where the solar arrays track the sun during the period when the space station is illuminated, are rotated edge-on to the orbital direction when it enters in the Earth's shadow, and then are returned to their tracking position when the station re-enters sunlight. This reduces the average drag on the station's solar arrays by about 30 percent, with no reduction in power.
Use of night-glider mode had been proposed at NASA Lewis early in the space station's history,
but was only implemented in 2003, after the
Space Shuttle Columbia disaster
The Space Shuttle ''Columbia'' disaster was a fatal accident in the United States space program that occurred on February 1, 2003. During the STS-107 mission, Space Shuttle ''Columbia'' disintegrated as it reentered the atmosphere over Te ...
, when the ability of the
Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program n ...
to bring propellant to the station for orbital maintenance was removed while the
Space Shuttle program
The Space Shuttle program was the fourth human spaceflight program carried out by the U.S. National Aeronautics and Space Administration (NASA), which accomplished routine transportation for Earth-to-orbit crew and cargo from 1981 to 2011. I ...
went through a period of redesign. The implementation of drag-reducing flight modes of the space station resulted in saving about 1,000 kg of orbital-maintenance propellant per year.
[Lindy Fortenberry, Kathy Laurini, John-David F. Bartoe, and Bill Gerstenmaier, NASA Johnson Space Center, "Continuing the Journey on the International Space Station," paper IAC-03-T.1.02, 54th IAF Congress, Bremen Germany (2003)]
A different operational mode, ''sun slicer'' drag-reduction, is also sometimes used; in sun slicer mode, the arrays are oriented edge-on to the direction of travel for the full orbit. In this mode, the drag is minimized, however, the power output is reduced from the full power available. Operationally, it is sometimes desirable to orient the solar arrays to produce the opposite effect, and maximize the drag on the arrays. This may be done, for example, to reduce the space station orbital altitude in order to reduce the amount of fuel required for the shuttle to reach the space station. Choosing which solar array orientation mode is used is a function of ISS operations ("mission control").
See also
*
Electrical system of the International Space Station
References
{{Reflist
External links
*A tutorial on space station operation fundamentals: J. Bacon,
Space Flight 101'' (2006), pp. 81–92. See NAS
Scientific and Technical Aerospace Report V. 44, issue 21, p. 12 (2006).
*Overview of night-glider mode: NASA Glenn Research Center, "Change in Solar Array Orientation Successfully Reduced ISS Propellant Usage,"
Research and Technology 2006', NASA TM-2007-214479, pp. 118–119 (2007).
International Space Station (ISS) power supply information at Aviation Spectator
International Space Station