Enlisted Information Dominance Warfare Specialist · PDF fileFleet Weather Center Norfolk 1 Enlisted Information Dominance Warfare Specialist (EIDWS) Common Core 115 NAVY SPACE

Fleet Weather Center Norfolk 1

Enlisted Information Dominance

Warfare Specialist (EIDWS)

Common Core

115 NAVY SPACE


• Objectives:

– Describe Space Mission Areas

– Describe the space environment and their effects of communications

– Identify orbits

– Define Apogee and Perigee

– Discuss and locate the 2 main space launch facilities

– Discuss Military Satellite Communications Systems

– Describe GPS

– Discuss Space-based ISR

– Discuss Space situational awareness

– Define Astrometry and Earth Orientation Parameters

– Discuss the role of Precise time

EIDWS Common Core 115 Navy Space



• References:

– Joint Publication 3-14 (JP 3-14)

– NAVEDTRA 14168A

– CJCSINST 6130.01D CJCS Master Positioning, Navigation, and Time Planning (May

08)



• Describe the following Space Mission Areas:

– Space force enhancement : Operations multiply joint force effectiveness by increasing the

combat potential, operational awareness, and providing needed joint force support. There are

five force enhancement missions:

• ISR

• Missile warning

• Environmental monitoring

• Satellite communications

• PNT *

– They provide a critical advantage by reducing confusion inherent in combat situations. Space

force enhancement operations also afford joint commanders access to denied areas and

persistence, which are important characteristics not afforded to air, land, or maritime

capabilities. Space force enhancement functions are often provided by interagency

organizations, commercial organizations, and consortiums.

– Space Support: The space support mission area includes spacelift operations (launching and

deploying satellites), satellite operations (maintaining, sustaining, and rendezvous and

proximity operations), and reconstitution of space forces (replenishing lost or diminished

satellites).

*PTN: Positioning, Navigation, and Timing



• Describe the following Space Mission Areas (cont):

– Space Control:

• Space control provides freedom of action in space for friendly forces, and when directed,

denies it to an adversary. It consists of offensive space control (OSC), defensive space

control (DSC), and SSA.

• Space control enables space superiority through surveying space and terrestrial AOIs (Areo

of Interest) that could impact space activities; protecting the ability to use space; preventing

adversaries from exploiting US, multinational, or neutral space services and capabilities; and

negating the ability of adversaries to exploit space services and capabilities.

• These operations change in nature and intensity as the type of military operations change.

OSC is used to deny adversary freedom of action in space and is based on negation and

offensive prevention measures. DSC is used to protect US space capabilities and is based

on protection and defensive prevention measures.

– Space Force Application: DOD policy defines space force application as combat operations in,

through, and from space to influence the course and outcome of conflict by holding terrestrial

targets at risk. This mission area is incorporated into national space policy as well. Specific

responsibilities can be found in DOD Instruction (DODI) 3100.13, Space Force Application.

Fleet Weather Center Norfolk


• Describe the following entities in the Space environment and how they affect

communications:

– The Sun: The sun has the biggest effect on the space environment. Fueled by nuclear fusion,

the sun combines or ―fuses‖ 600 million tons of hydrogen each second. Two by-products of the

fusion process that impact space systems are:

• Electromagnetic radiation: Substantial amounts of electromagnetic radiation have the

potential to adversely impact radar, communications, and space systems when they are

enhanced and intensified by solar-geophysical phenomena or events.

• Electrically charged particles: The major impact of these particles is over the polar caps,

where the protons have ready access to low altitudes through the funnel-like cusps that are

created by the Earth’s magnetic field lines that terminate at the North and South poles.

These impacts can last from a few hours to several days depending on the intensity of the

flare. Potential impacts include satellite disorientation, physical damage to spacecraft, false

sensor readings, navigation errors, and absorption of HF radio signals.

– Solar Wind: The solar wind is a stream of charged particles ejected from the upper atmosphere

of the Sun. It mostly consists of electrons and protons with energies usually between 10 and

100 KeV. These particles can escape the Sun's gravity because of their high kinetic energy and

the high temperature of the corona. The solar wind creates the heliosphere, a vast bubble in the

interstellar medium that surrounds the solar system. Other phenomena include geomagnetic

storms that can knock out power grids on Earth, the aurora (northern and southern lights), and

the plasma tails of comets that always point away from the Sun. This excited state of

atmospheric molecules degrades radar performance in the auroral zones, including ballistic

missile warning radar. It can also adversely affect satellites at altitudes to 600 miles, to include

polar orbiting satellites.




communications (cont):

– Solar Cycle: Solar activity is cyclic in nature, following a 11-year cycle which is called the Solar Cycle.

Generally there is a 4-year rise to a solar maximum, followed by a gradual 7-year decline to solar

minimum.

• Related to this phenomena are geomagnetic storms. Geomagnetic storms are worldwide events that normally

occur on Earth a day or two after a large solar flare erupts on the sun, and have an occurrence frequency that is

directly related to the 11-year solar cycle. Geomagnetic storms are created when a ―gust‖ of the solar wind

compresses the Earth’s magnetic field and are recorded at geomagnetic observatories as a sudden change in

the intensity of the local magnetic field. Since geomagnetic storms greatly hamper communications, it is

fortunate that their effects usually die out within a few days.

– Van Allen Radiation Belts: The Outer and Inner Van Allen Radiation Belts are two concentric, donut-

shaped regions of stable, trapped charged particles that exist because the geomagnetic field near the

Earth is strong and field lines are closed.

• The Inner Belt has a maximum proton density approximately 5,000 km above the Earth’s surface and contains

mostly high-energy protons produced by cosmic ray collisions with the Earth’s upper atmosphere. T

• The Outer Belt has a maximum proton density at an altitude ranging from 16,000 to 20,000 km and contains low

to medium energy electrons and protons whose source is the influx of particles from the magneto-tail during

geomagnetic storms.

• These radiation belts can have serious impact on satellite operations.

– Communications satellites in ―Geosynchronous‖ orbit (35,782 km or 22,235 statute miles altitude)

suffer whenever the Van Allen belt moves inward or outward. Satellites in a semi-synchronous

orbit such as GPS satellites suffer from a variable, high-density particle environment. Both orbits

are particularly vulnerable to the directed motion of charged particles 3-8 that occurs during

geomagnetic storms.

– Space vehicles in low circular orbit (125-130 miles) however, receive an insignificant amount of

radiation from the Van Allen belts.




communications (cont):

– Atmospheric Drag: Another source for space object positioning errors is that of atmospheric

drag on low orbiting objects (less than 1,000-km altitude). Energy deposited in the Earth’s upper

atmosphere by charged particle bombardment heats the atmosphere, causing it to expand

outward over a period of time. This produces more frictional drag on a satellite than expected

and decreases its altitude while increasing its speed. Consequently, the satellite will be some

distance below and ahead of its expected position when a ground radar or optical telescope

attempts to locate it. Conversely, just the opposite conditions result when exceptionally calm

solar and/or geomagnetic conditions cause less atmospheric drag than predicted and the object

is higher and behind its expected location. The consequences of atmospheric drag include:

• Inaccurate satellite locations which can hinder rapid acquisition of SATCOM links for

commanding or data transmission;

• Costly orbit maintenance maneuvers may become necessary;

• De-orbit predictions may become unreliable.



• Identify the following orbits:

• Low Earth Orbit: A satellite is considered to be in a low earth orbit (LEO) at altitudes between

approximately 150 and 800 miles above the Earth's surface. At an altitude of approximately 150

miles, a satellite's period will be about 90 minutes. The Space Shuttle and some scientific

satellites are typically placed in low inclination, low earth circular orbits.

• Medium Earth Orbit: Sometimes called intermediate circular orbit (ICO), is the region of space

around the Earth above low Earth orbit (altitude of 2,000 kilometers (1,243 mi)) and

below geostationary orbit (altitude of 35,786 kilometers (22,236 mi)). The most common use

for satellites in this region is for navigation, such as the GPS(with an altitude of 20,200 kilometers

(12,552 mi)),Glonass (with an altitude of 19,100 kilometers (11,868 mi)) and Galileo(with an altitude

of 23,222 kilometers (14,429 mi)) constellations. Communications satellites that cover the North

and South Pole are also put in MEO. The orbital periods of MEO satellites range from about 2 to

24 hours. Telstar, one of the first and most famous experimental satellites, orbits in MEO. (from

Wikipedia)

• Highly elliptical Orbit: Elliptic orbits of low-altitude perigee and high-altitude apogee (over 35,786

km). They are a kind of high earth orbits. These extremely elongated orbits have the advantage of

long dwell times at a point in the sky during the approach to and descent from apogee. Visibility

near apogee can exceed twelve hours of dwell at apogee with a much shorter and faster-moving

perigee phase. This makes these elliptical orbits useful for communications satellites.



• Identify the following orbits (cont):

– Geosynchronous Orbit: A satellite placed in orbit with an average altitude of approximately

19,300 nm will have an average angular velocity exactly equal to that of the Earth's. Stated more

simply, the satellite would have a period approximately equal to one day. This means that it

would take as long for the satellite to complete one revolution around the Earth, as it takes for

the earth to rotate once about its axis. Such an orbit is called a geosynchronous orbit. If a

geosynchronous orbit with an inclination of 0° were perfectly circular, the satellite would appear

to remain stationary in space above the same point on the Earth's surface. This is referred to as

a geostationary orbit. This orbit is predominantly used by relay satellites to provide a

continuous communications capability among ground stations within their very broad field of

view. Some surveillance and warning satellites also use the geostationary orbit. The

geostationary field of view is constant, covering nearly one-third of the Earth's surface with

latitude limitations of approximately 70° North and South of the equator. Effective satellite

communications from a geostationary orbit is not possible at either pole.



• Identify the following orbits (cont):

• Polar Orbit: A low inclination orbit and its latitude limitations, a polar orbit passes over the entire

surface of the Earth. A polar orbit has an inclination of 90° and is usually circular. Due to the ability to

pass over the entire surface of the earth throughout the course of several days, the polar orbit is used

extensively by imagery satellites.



• Define the Apogee and Perigee:

– Apogee: the point in the orbit of an object (as a satellite) orbiting the earth that is at the greatest

distance from the center of the earth.

– Perigee: the point in the orbit of an object (as a satellite) orbiting the earth that is nearest to the

center of the earth.



• Identify the two main space launch facilities in the United States:

• Most U.S. launches take place from one of two complexes: Kennedy Space Center, Cape

Canaveral, Florida, or Vandenberg Air Force Base in California. (according to Ref B, NAVEDTRA

14168A))

– Kennedy Space Center/Cape Canaveral Air Force Station:

• The nation's first space launch on 24 July 1950 used a modified version of a captured World

War II V-2 rocket. Renamed after the death of President John Fitzgerald Kennedy, the

140,000-acre Kennedy Space Center (KSC)is the primary NASA center for the integration,

test, and launch of all of the nation's manned spacecraft and the majority of unmanned

expendable launch vehicles.

• Under an agreement with the U.S. Air Force, NASA shares many of the expendable launch

vehicle and support facilities including the 10,000-mile-long Eastern Test Range

headquartered at the adjacent Cape Canaveral Air Force Station (CCAFS). KSC personnel

also support high inclination NASA launches from the Western Test Range at Vandenberg

AFB California

– Wallops Island, VA:

• The Wallops Flight Facility (WFF) on Wallops Island, VA, (formally Chincoteague Naval Air

Station) is one of the oldest and busiest flight test ranges in the world. Averaging over 300

launches a year, the WFF launches experiments to study the upper atmosphere and space

environment of vehicles ranging in size from small meteorological rockets to the 4 stage

Scout with orbital capability. (According to Ref A, JP 3-14)


1.NASA Headquarters, Washington DC

2.NASA Johnson Space Center, Houston Texas, Center,

Houston Texas

3.NASA White Sands Test Facility, White Sands, New Mexico

4.NASA Kennedy Space Center, Cape Canaveral, Florida,

is responsible for assembly, pre-flight testing, launch, and

landing recovery of the Space Shuttle

5.NASA Marshall Space Flight Center, Huntsville, Alabama

6.NASA Michoud Assembly Facility, East New Orleans,

Louisiana

7.NASA Slidell Computer Complex, Slidell, Louisiana,

8.NASA Stennis Space Center, Bay St. Louis, Mississippi

9.NASA Goddard Space Flight Center, Greenbelt, Maryland

10. Wallops Flight Facility, Wallops Island, Virginia, a GSFC

field installation, is responsible for launching small rockets

with scientific payloads

11.Space Telescope Science Institute, Baltimore, Maryland

12.NASA National Scientific Balloon Facility, Palestine, Texas

13.NASA Jet Propulsion Laboratory, Pasadena, California

14. NASA Langley Research Center, Hampton, Virginia

15.NASA Lewis Research Center, Cleveland, Ohio

16.NASA Ames Research Center, Moffett Field, California

17. NASA Ames-Dryden Flight Research Facility, Edwards Air

Force Base, California

18. Vandenberg AFB, California


• Identify the two main space launch facilities in the

United States (cont):



• Discuss the following Military Satellite Communication Systems:

– Navy UHF Follow-on (UFO):The Navy has procured a new constellation of satellites to replace

the aging FLTSATs: the UHF Follow-On (UFO). The UFO features higher power transmitters

designed to improve service, reliability, and dependability. The UFO satellites are mixed with the

FLTSATCOM legacy system.

• The UFO-4 through –9 spacecraft contain an EHF communications payload with enhanced

antijam telemetry, command, broadcast, and fleet interconnectivity. There are 39 channels

available up to UFO-4. The EHF payload provides an additional 11 channels, for a total of 50

channels on UFO-4 through -9. Nine UFO spacecraft are currently operational on orbit.

• The Navy has ordered a total of 10 satellites. Current planning includes the launch of UFO-

10, and as new satellites are planned and built, they will be incorporated into the future

architecture. UFO–8 and 9 mark the first two of potentially three spacecraft configured with

a GBS payload. Adapted from commercial direct-to-home television technology, GBS

provides highspeed, wideband broadcast signals (receive-only) to warfighters in all

branches of the military, on land, at sea, and in the air. UFO-9 is positioned over the Atlantic

Ocean, and UFO 8 is located over the Pacific Ocean. When UFO-10 is launched over the

Indian Ocean in 1999, the Defense Department will have near-global GBS coverage.



• Discuss the following Military Satellite Communication Systems (cont):

– Defense Satellite Communications System (DSCS):

• The DSCS is a high capacity, SHF satellite based subsystem of the Defense Communications

System (DCS). The DCS provides worldwide, jam-resistant, secure voice and high data rate

communications for command and control, crises management, and intelligence data

transfer service between the National Command Authority, Joint Chiefs of Staff (NCA/JCS)

and the Unified Commanders-in-Chief (CINC). It also provides communications among the

CINCs and their component forces, and from early warning sites to operations centers.

• Currently all active and reserve satellites are DSCS III, first launched in 1982. They provide

increased survivability and capability as well as greater antenna performance and flexibility

over DSCS II, launched in 1971. DSCS III provides global coverage 70N to 70S with a primary

constellation consisting of five satellites.

• DSCS supports the Ground Mobile Force Satellite Communications (GMFSC) program, wide-

band data relay for surveillance and intelligence, Navy Fleet communications, and other

selected users. It provides tactical communications through the GMFSC Program. GMF

(Ground Mobile Forces) terminals increase the range of and decrease the need for terrestrial

relays while providing for faster system setup and disassembly. The GMF terminals also

increase capacity/capability in support of tactical operations during all phases of conflict.

Systems that utilize DSCS include:

– Global Command and Control System (GCCS)

– Joint Deployable Intelligence Support System (JDISS)

– Joint Worldwide Intelligence Communications System (JWICS)

– Contingency TACS Automated Planning System (CTAPS)

– Secure Telephone (STEL)

– Joint Maritime Commanders Information System (JMCIS)



• Discuss the following Military Satellite Communication Systems (cont):

– Global Broadcast System (GBS): The Global Broadcast Service (GBS) is derived from

commercial direct broadcast technology and uses high-powered transponders to provide HDR

wideband simplex broadcast signals into 1-meter or smaller antennas and sophisticated receiver

suites. As aforementioned, GBS is incorporated in UFO 8, 9, and will be included eventually in

UFO-10. GBS will be fully operational by mid-1999, and will be integrated into the current

MILSATCOM architecture. The GBS payload will revolutionize satellite communications by

providing high-volume data and video information products to military tactical terminals. Naval

Space Command has been designated the manager for GBS on UFO satellites and ensures the

GBS payload is optimally configured to support the Joint user community. GBS promises to

enable dominant battlefield knowledge, which will contribute to future success in military

operations.

– WGS (Wideband Global SATCOM system): A satellite communications system planned for use

in partnership by the United States Department of Defense (DoD) and the Australian Department

of Defense. The system is composed of the Space Segment satellites, the Terminal Segment

users and the Control Segment operators. DoD wideband satellite communication services are

currently provided by a combination of the existing Defense Satellite Communications System

(DSCS) and Global Broadcast Service (GBS) satellites.

– "A single WGS spacecraft has as much bandwidth as the entire existing DSCS

constellation.‖



• Describe the Global Positioning System (GPS):

– A space-based global navigation satellite system that provides reliable location and time information in

all weather and at all times and anywhere on or near the Earth when and where there is an unobstructed

line of sight to four or more GPS satellites. It is maintained by the United States government and is freely

accessible by anyone with a GPS receiver. GPS was created and realized by the Department of Defense

and was originally run with 24 satellites. It was established in 1973 to overcome the limitations of

previous navigation systems.

– Advantages of GPS include:

• Accuracy. The GPS constellation provides continuous global service. Accuracy of the service is provided by

the type of receiver used, the number of satellites in view, and the geometric configuration of those satellites.

• Accessibility. Because GPS equipment is passive, it is capable of providing continuous real-time information.

Any authorized user with a keyed PPS receiver has access to the most precise PNT information. However,

commercial user equipment cannot receive and process the PPS information and is limited to the SPS signal.

• Graceful Degradation. Each GPS satellite can store information on board for up to 60 days. In the event the GPS

constellation cannot be updated, accuracy will gradually degrade. The rate of degradation is very slow in the

first few days but increases with time. This allows GPS to be used for several days even if the update

capabilities are interrupted.

• Common Grid. The default navigation grid used by the GPS is the World Geodetic System 1984 (WGS-84). WGS-

84 can be easily converted to any grid reference using the terminal device.

• Jamming. Space-based navigation systems (e.g., GPS) are resistant to some types of jamming. The use of GPS

encryption (like a more robust military code [MCode]) and nulling antennas/filters, as well as the correct

placement of GPS receivers on various platforms, improves jamming resistance. Tactical measures employed

by joint forces decrease vulnerability from ground-based jamming (such as placing a hand-held receiver at the

bottom of a foxhole).

• Anti-Spoofing (A/S). With the precise capability provided by the GPS, a logical concern is that an adversary

could generate false signals to mislead an authorized user with respect to position or timing information. A/S

technology is designed to mitigate receiver confusion that could be caused by intentionally misleading

transmissions



• Describe the advantages and disadvantages of Space-based ISR.

– Advantages:

• The prime advantage of space-based ISR capabilities is their potential to provide systematic

and focused coverage of AOIs, sometimes without detection, from sanction.

• Often, the product of a space or terrestrial capability can enhance accuracy and shorten

reaction times to the user by cueing another space system to survey an AOI. Likewise, a

space-based capability may be used to cue a terrestrial-based system for more precise

location, discrimination, and targeting.

• ISR systems also enhance planning capabilities by providing updated information regarding

terrain and adversary force dispositions. Space-based imagery, in particular, supports the

full range of military intelligence activities including indications and warning, current

intelligence, order of battle, scientific and technical intelligence assessments, targeting, and

combat assessments. Imagery is also used to conduct mission planning and rehearsal.

– Limitations:

• In addition to the access limitations and a predictable overflight schedule dictated by the

satellite orbit, satellite systems may be affected by a variety of atmospheric disturbances

such as fog, smoke, electrical storms, and precipitation and clouds, which affect the ability

of imaging systems to detect adversary activity, missile launches, and battle damage.

• Other limiting factors include: priority conflicts; tasking, processing, exploitation, and

dissemination limitations; and low numbers of assets.



• Discuss space situational awareness (SSA).

– Is fundamental to conducting space operations. The requisite current and predictive knowledge

of the space environment and the operational environment upon which space operations depend

– including physical, virtual, and human domains – as well as all factors, activities, and events of

friendly and adversary space forces across the spectrum of conflict.

– It includes components of ISR; environmental monitoring, analysis, and reporting; and warning

functions. SSA leverages space surveillance, collection, and processing of space intelligence

data; synthesis of the status of US and cooperative satellite systems; collection of US, allied,

and coalition space readiness; and analysis of the space domain.

– It also incorporates the use of intelligence sources to provide insight into adversary use of

space capabilities and their threats to our space capabilities while in turn contributing to the

JFC’s (Joint Force Commander) ability to understand enemy intent



• Discuss space situational awareness (SSA)(cont).

– SSA supports the following key objectives:

• (1) Ensure space operations and spaceflight safety. SSA provides the infrastructure that

ensures that US space operators understand the conditions that could adversely impact

successful space operations and spaceflight safety (i.e., collision avoidance).

• (2) Implement international treaties and agreements. SSA is a means by which compliance,

via attribution, can be verified and by which violations can be detected.

• (3) Protect space capabilities. The ability of the US to monitor all space activity enables

protection of space capabilities, helps deter others from initiating attacks against space and

terrestrial capabilities, and assures allies of continuing US support during times of peace,

crisis, and conflict.

• (4) Protect military operations and national interests. SSA supports and enhances military

operations.



• Discuss space situational awareness (SSA) (cont).

– Components of space situational awareness include:

• (1) Intelligence. For SSA, intelligence provides the characterization and analysis of foreign

(adversary and third-party) space capabilities, to include adversary or third party use of US,

or commercial space capabilities to their advantage and intent. Characterization includes,

but is not limited to, how forces and assets operate, their impact upon military operations,

and their vulnerabilities and strengths. Intelligence analysis of all elements of space systems

is required to determine threats and vulnerabilities of foreign space capabilities. It primarily

supports the characterization and analysis of space capabilities in preparation for targeting

or protection. Reliable, timely, and accurate intelligence also supports assessment.

• (2) Surveillance. Space surveillance is the systematic and continuous observation and

information collection on all man-made objects orbiting the Earth. Surveillance contributes

to orbital safety, indications and warning of space events, initial indications of where threats

may be located, and assessment. Space events include satellite maneuvers, anticipated and

unanticipated launches, reentries, and mission impacting space weather. Surveillance data,

for example, is used to produce the satellite catalog — the fused product that provides the

location of on-orbit satellites as well as man-made space debris. Information from the

satellite catalog is used by predictive orbital analysis tools to anticipate satellite threats and

mission opportunities for friendly, adversary, and third party-assets.

• (3) Reconnaissance. Reconnaissance provides the detailed characterization of a specific

object needed to analyze and assess the operational environment. Space reconnaissance

supports targeting and post-strike assessment. Reconnaissance data, for example, may

come from an unmanned aircraft system (UAS) providing visual images of a mobile satellite

ground station to aid in the planning of a strike against that ground station. Assets that

perform reconnaissance may also conduct surveillance.



• Discuss space situational awareness (SSA) (cont).

– Components of space situational awareness include (cont):

• (4) Environmental Monitoring. Environmental monitoring includes the characterization,

analysis, and prediction of space weather (e.g., solar conditions), terrestrial weather near

important ground nodes, and natural phenomena (e.g., interplanetary objects, such as

meteoroids and asteroids) in space. This environmental information must be accurate and

timely to protect space systems and support space control planning and execution.

Predictions of natural environmental effects should be synchronized with military

commanders’ COAs (Course of Action) to enhance military effectiveness. Environmental

monitoring, analysis, and prediction are critical in space control and space force

enhancement operations. Natural phenomena, such as solar activity and lightning, can

interfere with space systems. Operators must be able to differentiate between natural

phenomena interference and an intentional attack on a space system in order to formulate

an appropriate response.

• (5) Space Common Operational Picture. The space common operational picture (COP) is a

subset of the overall COP that aggregates information about space and terrestrial weather

that could impact space systems; the blue space picture showing US, allied, and civilian

space capabilities; the red/grey space picture showing adversary and neutral space

capabilities; and space debris tracking. SSA provides the relevant space information needed

in planning, execution, and assessment. Combining multiple sources of information into a

COP is essential for SSA. Likewise, C2 (Command and Control) and reporting processes

enhance SSA by providing feedback on the status/readiness of forces and insight on how

integrated space capabilities are contributing to military operations. Fusion of SSA

information occurs at several levels, but is crucial at the C2 nodes. Multiple C2 nodes will

often require SSA information, making unity of effort for SSA activities essential.



• Define the following:

– Astrometry: The branch of astronomy that relates to precise measurements and explanations of

the positions and movements of stars and other celestial bodies. Although once thought of as

an esoteric field with little useful application for the future, the information obtained by

astrometric measurements is now very important in contemporary research into the kinematics

and physical origin of our Solar System and our Galaxy, the Milky Way.



• Define the following (cont):

– Earth Orientation Parameters: The Earth’s rotation is not even. Any motion in/on the Earth

causes a slowdown or speedup of the rotation, or a change of rotation axis. Most of them can be

ignored, but movements of very large mass, like sea current or tide can produce discernible

changes and cause error to very precise astronomical observations. The Earth Orientation

Parameters (EOP) is fitted to describe such irregularities. Technically, they provide the rotation

of the ITRS to the ICRS, or vice versa, as a function of time.

• COMPONENTS:

– Universal time. Universal time (UT1)stands for the earth rotation, which performs

one revolution in about 24h. The earth rotation is uneven, so UT is not linear with

respect to atom time. It is practically proportional to the sidereal time, which is

also a direct measure of earth rotation. The excess revolution time is called

length of day (LOD).

– Coordinates of the pole. Due to the very slow pole motion of the earth, the

Celestial Ephemeris Pole (CEP, or celestial pole) does not stick still on surface of

earth. The Celestial Ephemeris Pole is calculated with past observation data, and

is somehow averaged, so it differs from the instantaneous rotation axis by quasi-

diurnal terms, which are as small as under 0.01". In setting up a coordinate

system, a static terrestrial point called the IERS Reference Pole, or IRP, is used as

origin; the x-axis is in the direction of IRM, the IERS Reference Meridian; the y-

axis is in the direction 90 degrees West longitude. x and y are the coordinates of

the CEP relative to the IRP.

– Celestial pole offsets. Celestial pole offsets are described in the IAU Precession

and Nutation models. The observed differences with respect to the conventional

celestial pole position defined by the models are monitored and reported by the

IERS.



• Discuss the role of precise time in the following:

– Global Positioning System: The US Navy, through the US Naval Observatory (USNO), is

responsible for establishing and maintaining the astronomical reference frame(s) for celestial

navigation and orientation of space systems. The USNO provides star catalogs, Earth orientation

parameters, almanacs, software products, and data services to meet DOD operational needs for

navigation. The US Navy, through the USNO, is also responsible for deriving and maintaining

standards for Precise Time and Time Interval (PTTI) and ensuring uniformity in PTTI operations.

Coordinated Universal Time (UTC) (USNO), as determined by the Master Clock at USNO, is the

DOD time standard. The output of the Master Clock is the reference for the master control of

GPS.

– Geo-location:

*PTN: Positioning, Navigation, Timing



• Discuss the role of precise time in the following:

– Network synchronization:

• US Naval Observatory is the sole provider to the defense community of precise time and

astrometry (PTA) for communications, weapon targeting and navigation. They are critical to

PNT* infrastructure. 4 key enablers by USNO include: (FROM NAVO 2025)

– Time - maintain master clock and disseminates precise time and time intervals.

– Astrometry – determines fundamental positions motions and distances of

celestial objects. Maintains the astronomical reference frame.

– Earth Orientation – rotation and orientation of Earth’s sphere impacting

navigation, astronomy, geodesy, communications and time keeping.

– Astronomical Data Products – Nautical, Air, and Astronomical Almanacs

– Directly support ISR as the reference for guidance systems and to navigate and

orient space-based platforms

– Earth Orientation and Precise Time are key enablers for GPS and ISR platforms

– USNO’s Precise Time references provides standards for satellite and other

communication systems.

*PTN: Positioning, Navigation, Timing



Questions??

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Enlisted Information Dominance Warfare Specialist · PDF fileFleet Weather Center Norfolk 1 Enlisted Information Dominance Warfare Specialist (EIDWS) Common Core 115 NAVY SPACE