// ORBITAL LOGISTICS AND PROPULSION TERM
Semimajor Axis
Half of the longest diameter of an elliptical orbit, representing the average distance of an orbiting object from its primary body.
TECHNICAL DEFINITION
The semimajor axis (a) is half the longest diameter of an elliptical orbit, representing the average distance of an orbiting body from its primary focus, and is a fundamental orbital element that determines the orbital period according to Kepler's Third Law.
BACKGROUND
The Quasi-Zenith Satellite System (QZSS) , also known as Michibiki , is a regional navigation satellite system (RNSS) and a satellite-based augmentation system (SBAS) developed by the Japanese government to enhance the United States-operated Global Positioning System (GPS) in the Asia-Oceania regions, with a focus on Japan. The goal of QZSS is to provide highly precise and stable positioning services in the Asia-Oceania region, compatible with GPS. Four-satellite QZSS services were available on a trial basis as of 12 January 2018, and officially started on 1 November 2018. A satellite navigation system independent of GPS is planned for 2023 with seven satellites. In May 2023 it was announced that the system would expand to eleven satellites.
READ MORE ON WIKIPEDIASYNONYMS & ALIASES
- Orbital radius (average)
- major axis half
- 'a' parameter
USAGE NOTE
The semimajor axis is a key parameter used to define the size and energy of an orbit.
DEVELOPERS
Organizations developing technology related to Semimajor Axis.
Developer of the Systems Tool Kit (STK), a leading physics-based software platform used for mission design and orbital analysis. The software allows engineers to define, model, and manipulate orbital elements, including the semimajor axis, to plan spacecraft trajectories.
Operates a global network of phased-array radars for tracking objects and providing space situational awareness (SSA) services for Low Earth Orbit (LEO). Their core technology calculates and catalogs the precise orbital elements, including the semimajor axis, of satellites and debris.
Provides the FreeFlyer commercial off-the-shelf (COTS) software for astrodynamics. This tool is used by satellite operators for mission design, analysis, and flight dynamics, all of which are fundamentally based on calculating and predicting orbital parameters like the semimajor axis.
Specializes in Space Domain Awareness (SDA) by operating a large global network of optical telescopes to track space objects, particularly in geosynchronous orbit (GEO). Their technology focuses on precisely determining and predicting orbital states, of which the semimajor axis is a key component.
A launch service and spacecraft systems provider. Their Photon spacecraft and Electron kick stage are designed for precise orbital insertion and in-space maneuvers, directly controlling the final semimajor axis and other orbital elements for customer payloads.
As the operator of the Starlink megaconstellation, SpaceX's technology is heavily reliant on the precise management of orbital elements. Their systems perform constant station-keeping and orbit-raising maneuvers, which directly involve changing the semimajor axis of thousands of satellites.
Develops orbital transfer vehicles (OTVs) designed to provide in-space transportation. Their service is to move satellites from a launch vehicle's drop-off orbit to their final operational orbit, a process that is fundamentally about changing the orbit's size by altering its semimajor axis.
Provides satellite ground systems, including command and control (C2) software. This technology is used by satellite operators to monitor and maintain the health and position of their spacecraft, which includes managing and adjusting orbital parameters like the semimajor axis.