The overall objective of space situational awareness (SSA) is to know the location of every object orbiting the Earth, to know why it is there, what it is doing now, and predict what it will be doing in the future.It is the ability to track and understand what exactly is in orbit from either space or from the ground. This capability is needed to protect the extensive U.S. investment in space assets for weather, reconnaissance, navigation, and communications. These systems represent hundreds of billions of dollars worth of public and private investment and play a key role in the national economy, U.S. prosperity, and wealth creation.
Satellites from every nation naturally cluster in preferred orbits: Low Earth Orbit (LEO) for weather and reconnaissance, Medium Earth Orbit (MEO) for cellular telephone communication and navigation, Geostationary Orbit (GEO) for Global Positioning Systems (GPS) and communications, as well as Highly Elliptical Orbits (HEO) or Molniya Orbits for communications services and other uses at high northern latitudes. These preferred orbits are littered with spent rockets, dead satellites, and thousands of other bits of debris that are hazards to space operations. By charting and tracking, SSA helps protect space assets and ensure safe operations by providing warnings of potential hazards (natural or manmade, intentional or unintentional) in a manner timely enough to allow preventive actions to be taken.
The greatest challenge to SSA is the existence of totally unknown RSOs in space. These are natural objects like meteorites, debris from launch vehicles, or debris broken off from already orbiting assets. The proliferation of debris in space constitutes one of the primary threats to safe operation of spacecraft. This debris can range in size from the smallest particles to large objects such as rocket bodies. Given the high relative velocities (up to 16 km/sec) in potential collisions in space, even small debris (e.g., < 1cm diameter) can cause significant damage. Most of the 17,000 or so objects greater than 10 cm in diameter are regularly tracked and cataloged by the United States Air Force (USAF). However, there are more than 200,000 objects between 1 cm and 10 cm in diameter that remain largely untracked because of the difficulty in observing them. These objects propose a potential threat to U.S. space assets and the number continues to grow. Recent large jumps in debris have been caused by the destruction of the Chinese satellite in 2007, and the collision between the spent Russian Cosmos 2251 satellite and the Iridium 33 satellite in 2009. For safety and security, these objects must be detected, identified, and assessed without the benefit of any pre-conditional information such as cues or guidance.