orbiter communications. communications windows microwave band signal characteristics orbiter...

Orbiter Orbiter CommunicationsCommunications

Orbiter Communications

Communications Windows Microwave Band Signal Characteristics Orbiter Communications Systems Orbiter S-band Communications Orbiter Ku-band Communications Orbiter UHF Communications Orbiter Audio Communications Orbiter Operational Instrumentation (Telemetry) Orbiter Payload Communications Orbiter Communications Antennas NASA’s Communications Networks

Communications Communications WindowsWindows

Communications - Space

Space communications is limited to the microwave band because of atmospheric attenuation and scattering at most other frequencies

Three windows through the Earth’s atmosphere are found at:

Visible band – not always available because of clouds & rain

Infrared band – too narrow and poor background signature (hot spots looking upward from the ground and downward from space)

Microwave – useful from approximately 1-10 GHz


Communications through more dense atmospheres (Venus, Titan) have only microwave windows

The microwave band has become a standard for space communications

• 1-10 GHz typical through the Earth’s atmosphere

• Much higher frequencies used for space-to-space communications (10-50 GHz) since there is no interfering atmosphere


Most of the Earth’s atmospheric attenuation of microwave signals comes from the oxygen and water molecules

Scattering of electromagnetic radiation is most common from water droplets

Lowest noise band available for Earth-space communications is roughly 1-10 GHz

Microwave BandMicrowave Band

Communications – Microwave Band

Microwave frequencies are defined as 300 MHz–300 GHz1 MHz = 1 Mega Hertz = 1 Million Hertz = 106 Hz1 GHz = 1 Giga Hertz = 1 Billion Hertz = 109 Hz

Common designations for the microwave bands used for spacecraft communications are:

• UHF 300 MHz to 3 GHz• L-band 1-2 GHz• S-band 2-4 GHz *• C-band 4-8 GHz• X-band 8-12.5 GHz• K, Ka, Ku-band 12.5-40 GHz

* Most commonly used space-terrestrial communications band

Communications – Microwave Band

Higher frequency X-band and Ku bands are used in space since there is no atmospheric interference

The higher frequencies also have the advantage of higher data transmission rates which means higher bandwidth• Higher bandwidth offers greater signal density• Higher signal density allows more instruments

and/or data on increasingly complex spacecraft• Newer technology also allows higher signal

density with lower mass and lower power consumption

Signal CharacteristicsSignal Characteristics

Communications – Signals

Signal characteristics

The three fundamental characteristics of the communications signal are

1. Center (or carrier) frequencyFrequency of transmission and reception

2. Signal bandwidthSignal data capacity

3. Modulation and encodingUsed to format the data to make it compatible between the

transmitter and receiver


Center frequency

Orbiter communications covers three different microwave frequency bands• UHF• S-band• Ku-band

Each of the Orbiter's numerous communications systems includes two center frequencies, one to transmit signals and a separate frequency to receive signals simultaneously • Known as duplex communications


Center frequency

Each of the communications system operate on two frequencies called duplex links• Uplink transmission from the ground station that is

received at the spacecraft• Downlink transmission from the spacecraft received at

the ground station

The exception to the duplex link is the Orbiter's S-band command data link• The simpler format called half-duplex allows

transmission and reception, but not simultaneously


Signal bandwidth

Higher frequencies have inherently higher bandwidths unless the design incorporates a smaller bandwidth for lower noise content.

The highest bandwidth in the Orbiter communications links is the highest frequency• High-bandwidth Ku band is used for the TDRSS

satellite link

Lowest frequency link on the Orbiter which is the UHF communications links that carry voice communications and also has the smallest bandwidth


Data and signal modulation

Data and data signals are modulated in two stages

The first stage is data modulation

Data are first encoded for easy digital conversion, transfer and identification

These modulation types include• Pulse code modulation (PCM) – the most common

spacecraft data modulation scheme• Phase modulation (PM)• Phase shift key modulation (PSK)• Pulse amplitude modulation (PAM)


The Orbiter communications system's data modulation is Pulse Code Modulation (PCM)

Analog signals are converted into digital signals by sampling circuits that function at specific levels (8 bit, 24 bit, 32 bit, 64 bit, etc.)


Data and signal modulation

The second modulation stage is signal modulation

Data that are communicated between spacecraft and ground stations are handled at a much lower frequency than the 2-3 GHz frequency used to transmit and receive the signals

Therefore, the data must be mixed with the carrier (center) frequency that is in the 2-3 GHz frequency range

The two types of Orbiter RF signal modulation are FM frequency modulation) and PM (phase modulation)


Following the two modulation stages in the transmitter and two demodulation stages in the receiver, the signal output from the receiver will be approximately the same as the signal input into the transmitter

The difference in the two signals is a function of the quality of the transmitter and receiver, and the influence of external and internal noise

Reproduced signal quality is determined by the communications system design

Orbiter Communications Orbiter Communications SystemsSystems


UHF Voice Duplex and

simplex

S-band Data, voice Duplex

Ku-band Video, data Duplex

Orbiter Communications Data Types

TelemetryDownlink data of the Orbiter's operating conditions and configurations, systems, payloads and crew biotelemetry measurements

CommandUplink data directed to the Orbiter systems to perform functional or configuration changes

Rendezvous and trackingOnboard radar and communications system for tracking and performing rendezvous with orbiting satellites/spacecraft

Video Video imaging is used onboard, or relayed to ground from the crew cabin or on EVA activities, or from the payload bay, or from the remote manipulator arm

Voice communicationsIntracommunications between the flight crew members, and between the flight crew and ground

DocumentationPrinted data from the Orbiter's thermal impulse printer system

Orbiter Communications Data Types

The Orbiter communications system frequency bands include:

1. S-band • PM (Phase Modulation) • FM (Frequency Modulation) • Payload

2. Ku-band• TDRSS data & video communications • Rendezvous radar

3. UHF voice• Ground • EVA

Note:Voice communications are also available through the military TACAN unit

Other frequencies are used for the Orbiter's navigation subsystems and include C-band for the radar altimeter, L-band for the GPS and TACAN units, and Ku-band for the MSBLS landing system

Orbiter S-band Orbiter S-band CommunicationsCommunications


S-band S-band communications are the most versatile of the

Orbiter's communications bands

Payload data, telemetry, commands, voice, and some video are handled with the multiple S-band units

The versatile functions of the S-band communications include two modulation types

• Phase modulation (PM)

• Frequency modulation (FM)


S-band

The Orbiter's S-band communications are used for

• Inter-Orbiter communications

• TDRS satellite uplink and downlink

• Payload communications

• Telemetry to/from ground

• Video and audio to/from ground

• DoD payloads (discontinued)


S-band PM

The Orbiter's S-band Phase Modulation unit is the primary communications system which provides a duplex link between the Orbiter and ground, either through the STDN stations or through the TDRSS relay satellite

S-band PM is the most versatile of the Shuttle's communications modes, providing communication channels for four primary functions


S-band PM

• Command channel - used to send commands from ground control to the Orbiter

• Voice channel - used for one-way and two-way voice communications between ground and Orbiter. Also used for the thermal impulse printer system

• Telemetry channel - carries real-time Orbiter and payload operational telemetry data to ground

• Turnaround tone ranging channel - used to aid in tracking the orbiter

A precise RF carrier is transmitted to the Orbiter for timing and Doppler measurements


S-band PM

S-band PM uplink • The Orbiter's S-band duplex forward (up) link operates

through the STDN or TDRS• Carrier frequency is at either 2.106.4 MHz (primary) or

2.041.9 MHz (secondary) for the NASA networks

S-band PM downlink• The S-band duplex return (down) link also operates through

the STDN or TDRSS• Phase modulation center carrier frequency is at 2.287.5 MHz

(primary) or 2217.5 MHz (secondary)

S-band PM Department of Defense S-band link (discontinued)


Transponders

Dual S-band PM transponders operate as multipurpose, multi mode transmitter/receivers• Each can simultaneously transmit and receive, or

transmit only, or receive only, although only one transponder operates at one time

• Transponders allow commands, telemetry and voice data through the communications network

The S-band transponders provide coherent (stable, timed) measurements on the PM up and down links for two-way Doppler data for spacecraft velocity data, and two-way tone ranging for spacecraft slant-range distance data


Transponders

Doppler and ranging signals are available for tracking while in line-of-sight from the NASA Spaceflight and Tracking Data Network (STDN) ground stations during launch, lift-off, ascent, or landing, or when it is in view of Space-Ground Link System (SGLS) ground stations• The third tracking dimension comes from the

ground station's antenna elevation and azimuth• The two-way Doppler function operates through

the TDRSS, but the two-way ranging does not


S-band FM

The Orbiter's S-band FM system is used exclusively to downlink telemetry data from as many as seven different sources• Limited to one source at a time

S-band FM downlink operates at a center frequency of 2.250 MHz and is available through the STDN or Air Force ground stations• S-band FM downlink does not operate through the

TDRSS system


S-band FM selection


S-band FM

The S-band FM telemetry data sources include :• Real-time SSME data from the engine interface units

from prelaunch through MECO (ME)• Real-time video (TV) • Operations recorder dumps of high- or low-data-rate

telemetry at 1.024 kbps (OPS RCDR) • Payload recorder at 25.5 kbps or 1.024 kbps (PL

RCDR) • Payload analog at 300 Hertz or 4 MHz (PL ANLG) • Payload digital data at 200 bps or 5 Mbps (PL DIGITAL) • DoD data at 16 kbps or 256 kbps in real time or 128

kbps or 1.024 kbps of playback (DOD)

Orbiter Ku-band Orbiter Ku-band CommunicationsCommunications


Ku-band

The Orbiter's Ku-band system is a dual-function unit• Communications system• Tracking/rendezvous radar system• Not available simultaneously

Ku-band high-frequency, high-bandwidth unit operates from 15.250 MHz to 17.250 MHz, with carrier frequencies of 13.755 GHz from the TDRSS (return/uplink) and 15.003 GHz from the Orbiter (forward/downlink)• Being increased to 22.5 to 27.5 GHz for new TDRSS

capabilities

Ku-band can be used for TDRSS space-to-space communications since there is no atmospheric interference that effects space-to-ground links


Ku-band

Ku-band frequencies are roughly six times higher than the Orbiter's S-band center frequency which offers a much larger bandwidth• Advantages of the Ku-band link are found in its

high-bandwidth video capability which is extremely limited in S-band

Because the Ku-band antenna is located in the payload bay, the system can only be operated while on orbit and while the payload bay doors are open


Ku-band unit

The 1-meter single antenna can be rotated 360o in roll and 162o in pitch

Some pointing positions can be blocked by the Orbiter depending on its attitude and orbit position with respect to the TDRS satellites

Pointing for TDRSS communications or for the radar tracking can be made manually, or are automated using the General Purpose Computer's background SM software


Ku-band block schematic


Ku-Band rendezvous radar

The Orbiter's Ku-band rendezvous radar functions as a traditional radar• Uses skin reflections and signal path timing for

distance measurements

It also has transponder capability • Tracks other spacecraft or payloads in orbit by

the identification of their unique signal reply• Like aircraft, transponder coding offers a much

better return signal which increases target identification distance and improves range accuracy, provided the spacecraft has a compatible transponder


Ku-Band rendezvous radar

Manual or automated search routines are available to gimbal the Ku-band antenna to search for orbital hardware

Rendezvous radar identification is a function of the radar sensitivity, and the range, reflective cross section, surface reflectivity, and the transponder performance

Ku-band radar range is approximately:• 30.5 m to 27.8 km (100' to 15 nm) for passive

(reflection) targets• 30.5 m to 555 km (100' to 300 nm) for active

(active transponder) targets

Orbiter CommunicationsOrbiter Communications

Ku-band radar and communications switchesKu-band radar and communications switches

Orbiter UHF Orbiter UHF CommunicationsCommunications


UHF band

Voice communications between crew members on the Orbiter, and launch control and mission control personnel is backed up with the narrow-band UHF communications system

Orbiter's UHF system is used as primary EVA crew communications between the cabin crew

UHF can also be used in the half-duplex or simplex mode for communications through the STDN or SGLS ground stations

UHF communications may also be used for voice communications during approach and landing through the TACAN


UHF band

UHF can be used as a two-way audio link with the Shuttle Training Aircraft during launch

UHF signals (uplink and downlink) are routed through the external UHF antenna on the Orbiter's bottom forward fuselage

UHF voice communications are available through:• Cabin-EVA link • Airlock-EVA link • TDRS (backup) • STDN and SGLS (simplex, backup) • TACAN (backup)


UHF EVA operations

UHF duplex communications employed on Orbiter EVA includes the following features:

• Biotelemetry and suit data transmitted to Orbiter at 296.8 MHz

• Biomedical data are replaced with suit telemetry data every 2 minutes for 15 seconds

• Audio transmit frequency is 259.7 MHz for EVA-A astronaut and 279.0 MHz for EVA-B astronaut

• Receive frequencies are 259.7 (A) and 279.0 MHz (B)

• Airlock communications are available through the airlock antenna


UHF-band schematic

Orbiter Audio Orbiter Audio CommunicationsCommunications


Audio Communications

Voice communications between crew members and ground are furnished by the S-band, UHF and Ku-band links

Multiple audio links provide near-continuous communications between ground and Orbiter crew• Interrupted during the Zone of Exclusion (ZOE)

region that is dictated by the TDRSS orbit coverage

• Communications as well as navigation signals are also interrupted during the during the high-temperature phase of reentry


Audio Communications

Audio on the Orbiter is transferred between communications points by the Audio Distribution System (ADS) which integrates the signal sources for distribution throughout the Orbiter, and the S-band and Ku-band links with ground

Audio communications are available on the following links:• Downlink to launch control and mission control are through

the Ku-band and the S-band links• Interconnect with launch control and mission control on the

launch pad are made through the T-0 launch umbilical panel

• TACAN

Orbiter CommunicationsAudio communications schematic

Orbiter Operational Orbiter Operational InstrumentationInstrumentation

Vehicle TelemetryVehicle Telemetry


Orbiter Operational Instrumentation (OI) system

Orbiter systems are closely monitored by the instrumentation system which consists of• Sensors, or transducers• Signal conditioners that bring sensor voltages/currents to

digital circuitry levels on the MDM inputs• Multiplexer/Demultiplexers (MDMs)• Pulse Code Modulation Master Units (PCMMUs)• Operational recorders• Payload recorders• Master timing equipment• Onboard checkout equipment

The OI system monitors more than 3,000 parameters for processing and display, either through downlink telemetry or onboard readouts


Orbiter Operational Instrumentation (OI) system

Operational instrumentation data begins with the sensor acquisition• Weak transducer signals are converted into digital

logic levels for input into the Mulitplexer/Demultiplexers for initial processing

Instrumentation data are then transferred to the Pulse Code Modulation Master Unit for data formatting

Data are then routed to the Network Signal Processor• There the data are interleaved with audio, video, and

other telemetry for transmission through the S-band and Ku-band downlinks, and the operational recorders for later downlink


Simplified block diagram of the Orbiter Instrumentation System


Orbiter instrumentation system component characteristics

Orbiter Payload Orbiter Payload CommunicationsCommunications


Payload Communication System (PCS)

The Payload Communication System (PCS) is used to transfer data to and from Orbiter's various payloads• Transferred over hardwire lines or on dedicated S-

band payload data links

Payload patch panel in the flight deck is used to direct payload data in one or more paths

Data from the payloads can be routed directly to the downlink without processing, or through the Pulse Code Modulation Master Unit and processing• Data can also be recorded for later downlink


Payload Communication System (PCS)

PCS is also used to activate, deactivate, and check out attached and deployed payloads

S-band payload data are transferred through a hemispherical antenna located on the upper forward section of the Orbiter

The link can be used for communications with attached and free-floating payloads


Payload data flow schematic

Orbiter Communications Orbiter Communications AntennasAntennas


Orbiter antennas

Except for the Ku-band system, the antennas on the Orbiter are placed on the vehicle exterior, but protected from the extreme heat of reentry by the surface insulation

A wide variety of antenna designs on the Orbiter are matched to the operating frequency and directional requirements

Antennas include • S-band• Ku-band deployable antenna (radar & communications)• UHF• L-band antennas for the TACAN and GPS systems• C-band antennas for the radar altimeter• Ku-band antennas for the MSBLS landing system


Orbiter antennas

S-band antennas are designed to cover either a broad-beam 180o and placed on the top and bottom of the vehicle, or a narrower 90o beam and placed on four points around the Orbiter• Both provide a full 360o coverage

Broad-beam antennas used for the S-band FM communications, called hemisphere antennas, are located on the top and bottom of the forward fuselage


Orbiter antennas

90o S-band PM antennas are called quadrature antennas because they provide a full 360o coverage with four antennas at four quadrant points• Two at the top and two at the bottom of the

forward fuselage

UHF and S-band payload communications antennas are also placed on the forward fuselage beneath HRSI or LRSI/FRSI surface tiles/blankets• Like the S-band FM and PM antennas

Orbiter CommunicationsAntenna placement - forward fuselage


Antenna placement including navigation signals

NASA’s Communications NASA’s Communications NetworksNetworks


NASA communications networks

NASA's space communications network is called the Spaceflight Tracking and Data Network (STDN)

The STDN consists of the following: Ground station network (GN) originally established for the

Mercury program

Space network (SN) that consists of the TDRSS satellites and the ground station in White Sands, New Mexico

A network link system called the NASA Communications Network (NASCOM)• NASCOM is an amalgamation of national and international

communications channels that interconnect the NASA and USAF launch and control sites, control centers, tracking sites, and support functions and locations.


NASA communications networks

NASA's primary mission launch and control sites at the Kennedy Space Center and the Johnson Space Center are but two of the main centers that manage mission data on NASCOM.

The primary network switching center at the Goddard Space Flight Center (GSFC) directs worldwide network operations including those at other communications and mission centers located at the Jet Propulsion Lab in Pasadena, California, and the three Deep Space Network sites

Additional network facilities and support are provided by the Air Force communications centers at Cape Canaveral, Florida and Vandenberg AFB, California


TDRSS – Tracking and Data Relay Satellite System

NASA's Tracking and Data Relay Satellite System was developed to overcome the spotty communications coverage by NASA's STDN ground tracking stations used for manned spacecraft missions and orbiting satellites

The Mercury-era ground station network offered only partial communications service, and had to be manned continuously because of the many satellites that were in orbit at any one time


The final design configuration for NASA's space-based communications network employed two satellites in geostationary orbit with a fixed ground station link• This arrangement provided coverage for at least

85% of low Earth orbit spacecraft• A third geostationary spacecraft designed to

serve as a spare is also used to relay data between the two active communications satellites and the fixed ground station through a Ku-band link

Orbiter CommunicationsTDRSS satellite placement


TDRSS

Ku-band is used for the ground-satellite link located at White Sands

Ku-band has marginal all-weather propagation through the atmosphere in moderate-to-heavy precipitation

White Sands, New Mexico was selected for the ground site because of its high annual clear day average and its low precipitation climate• White Sands site is also Federal land established

originally for flight tests, and the launch and tests of suborbital rockets


TDRSS satellites

TDRSS satellites support data relay communications on two primary bands, the S-band and the Ku-band

Telemetry and command data that supports the TDRS satellites from the ground station is available in C-band on a separate antenna and receiver/transmitter system

The S-band and Ku-band communications are carried by two sets of antennas partitioned in frequency and accessibility

Two types of data access are available• SA – single access• MA – multiple access


TDRSS satellites

SA – single access Ku-band service on the TDRS is carried through two 4.9 m

(16') graphite steerable parabolic reflector antennas

Data use on the Ku-band antennas is dedicated to specified users, and includes spacecraft tracking and ranging information• Normally allocated to high-bandwidth users such as the

ISS, HST, Landsat satellites, and when in orbit, the Space Shuttle

Each of the two parabolic antennas has two access frequencies• Ku-band• S-band


TDRSS satellites

MA - multiple access S-band multi-access antennas available for up to

20 users

Multi-user S-band service called MA includes 30 helical antennas that are not steerable

Does not provide tracking or ranging information

Orbiter Communications TDRSS satellite


TDRSS Ground Station

The TDRSS ground element includes the dual-redundant ground station links and the data distribution and control network

Ground operations also include the TDRS satellite control and maintenance operations that support the spacecraft and maintain their orbital position


Two separate communications installations are collocated at the site• Both have duplicate

network data handling and services

Cacique, the name for the first White Sands Ground Station was completed in 1978

Danzante was completed in 1991

TDRSS CoverageGeometric coverage of the typical circular

LEO orbit is greater than 88% as shown

TDRSS Coverage and Zone of Exclusion (ZOE)

TDRS Spacecraft TDRS Spacecraft PayloadPayload

•17.4 m span including solar arrays

•14 m from SA antenna edge to antenna edge

•2,270 kg (5,000 lb) at launch

•Minimum expected lifetime is 10 years on-orbit

•Built by TRW

The EndThe End

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