RAAN to LTAN Converter - LTAN to RAAN Converter
Precise conversion between RAAN (Right Ascension of the Ascending Node) and LTAN (Local Time at Ascending Node). A simple tool to quickly extract LTAN/LTDN or RAAN infomation from a Sun-synchronous orbit.
Conversion:
RAAN: deg
LTAN: UTC
Do you want to extract LTAN from a TLE?
It is very common practice to extract LTAN information from a TLE file that contains RAAN and time information. You can easily calculate the LTAN in UTC by RAAN <-> LTAN Converter. First, extract the TLE epoch from the first line and convert it from YYDOY.FRAC to date and time (below 14/02/2023, 14:50:22 UTC). Second, extract RAAN in degrees from the second line as shown below:
What is RAAN and LTAN? Why do we need a conversion?
RAAN (Right Ascension of the Ascending Node) is a parameter used to describe the orientation of a satellite's orbit around a celestial body, such as the Earth. Specifically, it is the angle between the vernal equinox (the point on the celestial sphere where the ecliptic intersects the celestial equator, defined to be at zero degrees) and the point where the satellite's orbit crosses the Earth's equatorial plane moving from south to north. This angle is measured in the plane of the orbit, and is usually expressed in degrees or radians.
LTAN (Local Time of the Ascending Node) is a related parameter used to describe the timing of a satellite's orbit with respect to the rotation of the Earth. Specifically, it is the time of day (expressed in hours) when the satellite crosses the Earth's equatorial plane moving from south to north. The LTAN is defined such that the satellite will cross the equator at the same local time of day on each orbit.
For Sun-synchronous orbits, the LTAN is chosen to be such that the satellite crosses the equator at the same local solar time on each orbit, which ensures that the satellite is always viewing the Earth under similar lighting conditions. The RAAN and LTAN are related through a simple equation, which takes into account the precession of the satellite's orbit due to the gravitational influence of the Earth and other celestial bodies.
The conversion from RAAN to LTAN, or vice versa, is therefore an essential step in the design of Sun synchronous orbits (SSOs), as it allows the orbit parameters to be selected to achieve a desired local solar time. SSOs are used in a variety of applications, including remote sensing, weather forecasting, and communication, where it is important to have consistent lighting conditions or to maintain a fixed position relative to the Sun.
In remote sensing, for example, SSOs are used to image the Earth's surface with consistent lighting conditions, which allows for accurate comparisons of images taken at different times. In weather forecasting, SSOs are used to gather data on atmospheric conditions at different times of day, which is important for predicting weather patterns. In communication, SSOs are used to maintain a fixed position relative to the Sun, which allows for more efficient use of solar power for spacecraft and reduces the need for complex attitude control systems.