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USSTRATCOM Space Control and Space Surveillance

USSTRATCOM’s space control mission includes: surveillance of space, protection of US and friendly space systems, prevention of an adversary’s ability to use space systems and services for purposes hostile to US national security interests, and direct support to battle management, command, control, communications, and intelligence.  The space control mission is conducted by USSTRATCOM’s Joint Functional Component Command for Space (JFCC-Space).

JFCC-Space, through its Joint Space Operations Center (JSpOC), detects, tracks, and identifies all man-made objects in Earth orbit.  Crews work around the clock constantly tracking these objects.  They task the Space Surveillance Network (SSN), a worldwide network of 29 space surveillance sensors (radar and optical telescopes, both military and civilian) to observe the objects.  The crews use computers to match sensor observations to the more than 22,000 man-made orbiting objects and update the position of each one.  These updates form the Space Catalog, a comprehensive listing of the numbers, types, and orbits of man-made objects in space.

Space surveillance involves detecting, tracking, cataloging and identifying man-made objects orbiting Earth, which include active/inactive satellites, spent rocket bodies, debris, and fragments. Space surveillance accomplishes the following:

  • Analyze new space launches and evaluate orbital insertion
  • Detect new man-made objects in space
  • Chart present position of space objects and plot their anticipated orbital paths
  • Produce and maintain current orbital data of man-made space objects in a space catalog
  • Inform NASA and other government entities if objects may interfere with the orbits of the Space Shuttle, the International Space Station, and operational satellite platforms
  • Predict when and where a decaying space object will re-enter the Earth's atmosphere
  • Prevent a returning space object, which to radar looks like a missile, from triggering a false alarm in missile-attack warning sensors of the U.S. and other countries
  • Determine which country owns a re-entering space object
  • Predict surface impacts of re-entering objects and notify the Federal Emergency Management Agency and Public Safety Canada if an object may make landfall in North America or Hawaii

SSN Sensors
The SSN uses a "predictive" technique to monitor space objects, i.e., it spot checks them rather than tracking them continually.  This technique is used because of the limits of the SSN (number of sensors, geographic distribution, capability, and availability).  Below is a brief description of each type of sensor.

Phased-array radars can maintain tracks on multiple satellites simultaneously and scan large areas of space in a fraction of a second.  These radars have no moving mechanical parts to limit the speed of the radar scan - the radar energy is steered electronically.  A detection antenna transmits radar energy into space in the shape of a large fan.  When a satellite intersects the fan, energy is reflected back to the detection antenna, where the location of the satellite is computed.  Two examples of these radars include Cavalier AFS in North Dakota and Eglin AFB in Florida.

Conventional radars use moveable tracking antennas or fixed detection and tracking antennas.  A tracking antenna steers a narrow beam of energy toward a satellite and uses the returned energy to compute the location of the satellite and to follow the satellite's motion to collect more data.  These include radars include the Altair complex at the Reagan Test Site in the Kwajalein Atoll and the Haystack Millstone facility at the Massachusetts Institute of Technology.

Electro-Optical Sensors consist of telescopes linked to video cameras and computers.  The video cameras feed their space pictures into a nearby computer that drives a display scope.  The image is transposed into electrical impulses and recorded on magnetic tape.  This is the same process used by video cameras.  Thus, the image can be recorded and analyzed in real-time.

Space Based Space Surveillance (SBSS) satellite is the follow-on to the Midcourse Space Experiment (MSX) satellite.  SBSS satellite provides the only space-based sensor in the U.S. Air Force SSN with the ability to detect debris, spacecraft or other distant space objects without interference from weather, atmosphere or time of day.  SBSS satellite uses a visible sensor mounted on an agile, two-axis gimbal, which allows ground operators to quickly move the camera between targets without having to expend time and fuel to reposition the entire spacecraft. 

Ground-Based Electro-Optical Deep Space Surveillance sites assigned to Air Force Space Command (AFSPC) play a vital role in tracking deep space objects.  Between 3,900 and 4,100 objects, including geostationary communications satellites, are in deep space orbits more than 22,500 miles from Earth.

The SSN sensors are categorized as dedicated (those with the primary mission of performing space surveillance) or contributing and collateral sensors (those with a primary mission other than space surveillance).  Combined, these types of sensors take between 380,000 to 420,000 observations each day. 

Joint Space Operations Center (JSpOC)

The JSpOC’s Space Situational Awareness (SSA) Operations Team, along with the Advanced Operations Branch; maintain a current computerized catalog of all Earth-orbiting man-made objects, charts preset positions, plots future orbital paths, and forecasts times and general location for significant man-made objects reentering the Earth’s atmosphere.

Since the launch of Sputnik in 1957, over 38,000 man-made objects have been catalogued, many of which have since re-entered the atmosphere. Currently, the JSpOC tracks more than 22,000 man-made objects orbiting Earth that are 10 centimeters or larger.  About five percent of those being tracked are functioning payloads or satellites, eight percent are rocket bodies, and about 87 percent are fragmentation and inactive satellites.

The JSpOC protection mission consists of conducting laser clearing procedures, analyzing intentional threat, and collision avoidance. The JSpOC compiles information on hostile events that could directly or indirectly threaten U.S. or allied space assets. This information is analyzed to determine potential impacts on assets so that timely warnings and recommendations for suitable countermeasures can be made.

On a routine basis, JSpOC conducts collision avoidance analysis for the Space Shuttle and the International Space Station (ISS).  During shuttle missions, the center computes possible close approaches of other orbiting objects with the shuttle's flight path.  The JSpOC constructs a theoretical box around a high interest object, (e.g. the Space Shuttle) and projects the flight path several days in advance. If any of the catalogued objects intersects this theoretical box, the JSpOC forwards the analysis to the NASA.  NASA makes the determination whether or not to change the flight path of the shuttle. NASA offers to the general public on its website, the opportunity to track various satellites.  Click here to go to NASA's J-Track

The 614th Air and Space Operations Center, Detachment 1 (614 AOC/Det 1) provides the site and personnel to provide a geographically separate backup to JSpOC’s SSA Operations.  The 614 AOC/Det 1 would take over SSA operations in the event the space control mission at the JSpOC could not function.  This capability is exercised frequently.

Re-entry Assessment and Space Surveillance

Re-entry Assessment describes the operational procedures by which USSTRATCOM predicts the time and location of atmospheric reentry and potential ground impact) of decaying man-made objects in space.  Current capabilities limit the ability to predict within a 30-minute, 6,000-mile window when and where a particular object should re-enter the Earth's upper atmosphere and outline a potential surface impact area.

Objects are tracked throughout their orbit life, with the results posted in the Space Catalog.  When an object appears to be re-entering within seven days, orbital analysts in the JSpOC will increase sensor tasking (monitoring) and begin to project a refined re-entry time and location.  At the four-day point, a monitor run is accomplished three times a day.  Messages indicating the calculated re-entry time and location are transmitted to forward users and customers at the four-, three-, two- and one-day points.  Starting at the 24-hour point, the object is monitored at the highest level of scrutiny, with processing at the 12, six and two-hour points.  Again, ground traces and messages are transmitted.  The object is monitored throughout re-entry.

Graphic depicting typical re-entry path
The graphic above depicts the reentry of a typical satellite in a low Earth orbit. Figures may change depending on the orbital characteristics of space vehicles.

Re-entry Assessment is an "inexact science."  It is virtually impossible to precisely predict where and when space debris will impact due to limitations in the tracking system as well as environmental factors that can influence debris.  Most of USSTRATCOM's space-tracking radars are located in the Northern Hemisphere, making continuous orbit coverage impossible.  Consequently, a returning satellite could be outside sensor coverage for several hours.

Also, environmental factors acting on an object's orbit could include variations in the gravitational field of the landmass and ocean areas, solar radiation pressure, and atmospheric drag.  Objects re-entering may skip off the Earth's atmosphere, much as a stone skipped across a pond, causing it to impact much further away than originally forecast.

Graphic depicting how reentry items may break up when they hit the atmosphere.

USSTRATCOM will verify that an object has re-entered by using a process of "No Show" sensor reports verifying the object is no longer in orbit.  Once it is determined not to be in orbit, sensor tasking ends and the object is deleted from the "Active "tracking mission of the surveillance network.

The chances of someone being struck by a re-entering object are slight.  The great majority of objects that re-enter disintegrate due to the intense heat created by re-entry into the Earth's atmosphere.  Only a small percentage of objects ever re-enter over land since water comprises 75 percent of the Earth's surface.  Additionally, only about 25 percent of the Earth's landmass is actually inhabited.  If the object is forecast to make landfall in North America or Hawaii, the JSpOC will notify the Federal Emergency Management Agency and/or Public Safety Canada.

Since tracking began with Sputnik, more than 22,000 man-made objects the Department of Defense tracked have re-entered the Earth's atmosphere.  The Department of Defense has tracked over 38,000 objects in its space catalog. 

USSTRATCOM maintains historical orbital data on objects even after they have re-entered the Earth's atmosphere.  Unless an object is actually found and returned to NASA or any other agency, USSTRATCOM would have no knowledge of objects that have survived re-entry.

Current as of May 2012

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