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NASA FUTURE OPERATIONS AT KA-BANDFOR LEO SPACECRAFT SUPPORT

Badri YounesCode 450, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

Tel: (301) 286-5089; Fax: (301) 286-1724; E-mail: badri.younes@gsfc.nasa.gov

David ZilligCode 450, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

Tel: (301) 286-8003; Fax: (301) 286-1724; E-mail: david.j.zillig.1@gsfc.nasa.gov

Anthony ComberiateCode 405, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA

Tel: (301) 286-5678; Fax: (301) 286-1721; E-mail: anthony.comberiate@gsfc.nasa.gov

Mark BurnsStanford Telecommunications, 1761 Business Center Drive, Reston, VA 20190

Tel: (703) 438-8155; Fax: (703) 438-8112; E-mail: mburns@sed.stel.com

Robert ChangStanford Telecommunications, 1761 Business Center Drive, Reston, VA 20190

Tel: (703) 438-8020; Fax: (703) 438-8112; E-Mail: rchang@sed.stel.com

ABSTRACT

S-band, X-band, and Ku-band services currently support the tracking and data acquisition needs ofNASA’s Low Earth Orbiting (LEO) spacecraft. LEO spacecraft can transfer data directly toground stations using S-band and X-band frequencies. LEO spacecraft can also transfer data to theground at S-band and Ku-band frequencies via the Tracking and Data Relay Satellite System(TDRSS) which is part of NASA’s Space Network (SN). With increasing congestion andregulatory issues in these bands combined with growing requirements for higher science data rates,wider bandwidths were allocated at Ka-band for inter-satellite and earth exploration-satelliteservices. In the early 2000s, Ka-band space-to-space link service will be available for LEOspacecraft via NASA’s next generation TDRSS spacecraft (TDRS H,I,J).

This paper addresses three areas related to NASA’s use of Ka-band. First, NASA operations thatcurrently exist at S-, X-, and Ku-bands are discussed and compared to future Ka-band services thatwill be provided by TDRS H,I,J spacecraft. NASA’s move into Ka-band for TDRSS operations isdriven by a number of regulatory and technical issues. For example, increasing congestion in S-band due to new commercial systems may lead to the potential for interference and servicedegradation to TDRSS users. Also, the feasibility of NASA’s continued use of Ku-band isquestionable due to the secondary allocation at the Ku-band frequencies currently used by TDRSS.X-band spectrum crowding and sharing requirements with other organizations have limitedNASA’s use of this band. Ka-band allocations for TDRS H,I,J links are primary on a worldwidebasis allowing user spacecraft to transmit at higher data rates than currently available.

The second topic addressed in this paper is the TDRS H,I,J program in terms of its developmentstatus and capabilities. The purpose of this program is to continue the current TDRSS constellationto 2012, while adding new capabilities such as Ka-band single access (KaSA) services andenhanced S-band multiple access(SMA) services. NASA Space Network operations are discussedin terms of new Ka-band capabilities such as frequency and polarization agility to minimizeinterference and the higher bandwidth available for return links.

This paper concludes with a presentation and analysis of unique operational scenarios that areavailable to LEO spacecraft operating at Ka-band. Overlapping frequency allocations in the 25.5to 27 GHz band for TDRS H,I,J space-to-space and direct space-to-earth communications may

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provide Ka-band LEO spacecraft, using a single antenna, the option of communicating eitherdirectly to a ground station or via TDRS H,I,J. Performance analyses are presented for theseoptions in terms of achievable data rates, and ground and TDRSS contact times. This paper alsoexamines the impact to users operating at Ka-band in terms of available Ka-band technologies.NASA is promoting use of the Ka-band allocation via a web site containing a survey of availableKa-band technology. The web site is: http://ses.stel.com:8080/kaband.

1.0 OVERVIEW OF NASA OPERATIONS

1.1 TDRSS OVERVIEW

Table 1 summarizes TDRS H,I,J services in 2000+ and compares them with existing TDRSSservices. Figure 1 illustrates the TDRS H,I,J spacecraft and TDRSS network elements. TheTDRSS provides tracking (i.e., range and Doppler measurements) and data relay services for earthorbiting spacecraft, aircraft, balloons, and launch vehicles. TDRSS has orbital allocations of 41deg. W, 46 deg. W, 171 deg. W, 174 deg. W, and 275 deg. W. The current TDR spacecraftemploys S-and Ku-band for space-to-space links (SSLs) with a user spacecraft and Ku-band forspace-to-ground links (SGLs) with a ground station located in White Sands, New Mexico. TheTDRS H,I,J spacecraft will add Ka-band user SSLs capability and provide enhanced S-bandmultiple access capabilities. The current TDRSS spacecraft fleet is capable of supporting users ataltitudes only up to 12,000 km due to TDR spacecraft antenna gimbal limits. The new TDRS H,I,Jspacecraft SA antenna will have an outward gimbal limit of 77.5 degrees in the east-west directionwhich will increase the field of view up to geosynchronous orbit. Additional enhancements to theTDRSS network include the construction of a new TDRSS ground terminal at Guam. Thisterminal will be operational in the 4th quarter of 1998. By deploying a TDRS H,I,J above theIndian Ocean (e.g., 275 deg. W), global coverage for KaSA and SSA services will be available toscience spacecraft in the 21st century.

Table 1 - TDRS Spacecraft Capabilities Comparison

Service WSC & TDRS A-GCapabilities(4)

WSC & TDRS H,I,JCapabilities

S-Band Forward 300 kbps; EIRP = 48.5 dBW 300 kbps; EIRP = 48.5 dBW

Return 6 Mbps; G/T = 8.5 dB/K 6 Mbps; G/T = 8.5 dB/K

Single Ku-Band Forward 25 Mbps(5); EIRP = 48.5 dBW 25 Mbps(5); EIRP = 49 dBW

Access Return 300 Mbps; G/T = 26.5 dB/K 300 Mbps; G/T = 26.5 dB/K

Ka-Band Forward N/A 25 Mbps(5); EIRP = 63 dBW

Return N/A 300 Mbps/800 Mbps(1);

G/T = 26.5 dB/K

Number of Links

2 SSA/TDRS; 12 SSA/WSC2 KuSA/TDRS; 12 KuSA/WSC

2 SSA/TDRS; 12 SSA/WSC2 KuSA/TDRS; 12 KuSA/WSC2 KaSA/TDRS; 8 KaSA/WSC(2)

Multiple Access Forward 1/TDRS @ 10kbps; 4/WSC 2/TDRS(3) @ 300 kbps; 4/WSC

Return 5/TDRS @ 100 kbps; 20/WSC 6/TDRS(1) @ 3 Mbps; 20/WSCUser Tracking Range, 1&2 way Doppler Range, 1&2 way Doppler

(No Ka-band Tracking)NOTES: (1) Spacecraft only; (2) Ku- or Ka-band; (3) 1/TDRS at WSC; (4) For user data

configurations, see 530-SNUG, Space Network Users’ Guide; (5) WSC currentconfiguration supports 7 Mbps.

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1.2 NASA X-BAND OPERATIONS

In addition to its Space Network, NASA also operates S-band and X-band ground based trackingstations located throughout the world. These stations provide launch and on-orbit tracking anddata acquisition support for NASA approved missions including launch and landing support for theSpace Shuttle.Two new multi-mission ground stations have recently been implemented by NASA to support theEarth Observing System (EOS) polar orbiting spacecraft missions and other NASA approvedmissions. The Earth Observation System (EOS) Polar Ground Station (EPGS) Project wasengineered and constructed by NASA/GSFC in concert with the Norwegian Space Center. Theproject currently consists of two high latitude stations, one at Poker Flats, Alaska, the other atSvalbard, Norway.

Figure 1 - TDRS H,I,J Spacecraft with TDRSS Network Elements

The systems are designed to provide TT&C (S-band) and high rate science data capture (X-band)primarily for the EOS AM-1, LANDSAT-7, and QuikSCAT missions. These stations willeventually be augmented with more capability to serve as a multi-mission resource for the growingfleet of NASA’s polar orbiting science spacecraft. The stations are now undergoing engineeringtests and will be operational by mid-1998.Each of these stations will provide receive capability for X-band science data at rates up to 150Mbps, receive capability for S-band telemetry from 1 kbps to 524 kbps, and command capabilityfor S-band at 2 kbps. The station will be remotely operated using the Monitor and ControlSubsystem, which provides the mechanism for gathering status parameters from the remote site RFand baseband data equipment. It also issues equipment set-up commands to establish varioussystem support configurations based on a locally stored schedule of support requirements.

S-Band Phased Array forMultiple-Access (MA) service

1 Fwd, 5 Rtn Links for F1-F72 Fwd, 6 Rtn Links for TDRS H,I,JField of View (Primary):+ 10.5 Deg. Conical

❏❏

1 of 2 Single Access (SA) AntennasS & Ku-Band for F1-F7S, Ku, & Ka-Band for TDRS H,I,JField of View (Primary):

❏

❏+ 22.5 Deg. E-W+ 31.0 Deg. N-S

TDRSSGroundStation

NASA andCustomerGround

Operations

Primary site atWhite Sands, NM - STGT - WSGTU

❏

Additional Guam siteunder construction forIndian Ocean coverage

❏

Space-Ground Link

Fwd: 14.6-15.225 GHzRtn: 13.4-14.05 GHz

❏

❏

Forward Space-Space Link:S-Band: 2025-2120 MHzKu-Band: 13.775 GHzKa-band: 22.55 23.55 GHz

Extended Field of View❏ + 77.5 Deg. (outward E-W)- 22.5 Deg. (inward E-W)+ 31.0 Deg. N-S

TDRS Constellation275° W, 174° W,171° W, 46° W,41° W

❏

Return Space-Space LinkS-Band: 2200-2300 MHzKu-Band: 15.0034 GHzKa-Band: 25.2534 to 27.4784 GHz (225 MHz Channel),25.545 to 27.185 GHz (650 MHz Channel)in 25 MHz steps

07/01/97 TR97086\RC2723

S-Band Phased Array forMultiple-Access (MA) service

1 Fwd, 5 Rtn Links for F1-F72 Fwd, 6 Rtn Links for TDRS H,I,JField of View (Primary):+ 10.5 Deg. Conical

o

o

1 of 2 Single Access (SA) Antennas

S & Ku-Band for F1-F7S, Ku, & Ka-Band for TDRS H,I,JField of View (Primary):

o

o+ 22.5 Deg. E-W+ 31.0 Deg. N-S

TDRSSGroundStation

NASA andCustomerGround

Operations

Primary site atWhite Sands, NM - STGT - WSGTU

o

Additional Guam siteunder construction forIndian Ocean coverage

o

Space-Ground Link

Fwd: 14.6-15.225 GHzRtn: 13.4-14.05 GHz

o

o

Forward Space-Space Link:

S-Band: 2025-2120 MHzKu-Band: 13.775 GHzKa-band: 22.55 23.55 GHz

Extended Field of Viewo + 77.5 Deg. (outward E-W)- 22.5 Deg. (inward E-W)+ 31.0 Deg. N-S

TDRS Constellation

275° W, 174° W,171° W, 46° W,41° W

o

Return Space-Space Link

S-Band: 2200-2300 MHzKu-Band: 15.0034 GHzKa-Band: 25.2534 to 27.4784 GHz (225 MHz Channel),25.545 to 27.185 GHz (650 MHz Channel)in 25 MHz steps

07/01/97 TR97086\RC2723

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2.0 TDRS H,I,J DESIGN SUMMARY

Table 2 highlights the key TDRS H,I,J spacecraft design features. TDRS H,I,J will provide singleaccess and multiple access service to LEO user spacecraft at S-band, Ku-band and Ka-band. Thenew spacecraft include two 15-ft. mechanically steerable single access spring-back antennas withS, Ku, Ka-band feeds. These antennas can simultaneously support S/Ku-band or S/Ka-bandservice. A separate transmit and receive S-band multiple access phase array patch antennaprovides increased EIRP and G/T performance. TDRS H,I,J will use the existing Ku-bandfrequency plan for the space-to-ground link (SGL).

SSA and KuSA Backward Compatibility: The new spacecraft design will ensure all existing S-band single access(SSA) and Ku-band single access (KuSA) service requirements are met. Thiswill allow TDRSS to maintain services continuity for existing users such as Hubble SpaceTelescope (HST) and Shuttle.TT&C Link: The S-band TT&C link is supported with forward and aft omni spacecraft antennas(4-pi steradian coverage). These antennas will support launch, transfer orbit and on-orbitemergency operations. The Ku-band TT&C link, via the SGL antenna, will support on orbitnormal operations. In order to allow collocation of up to two TDRSS spacecraft, each T&C linkwill support two command and telemetry frequency pairs. Collocation will be possible betweenthe existing TDRS fleet and TDRS H,I,J spacecraft, and between TDRS H,I,J spacecraft.

Table 2 - TDRS H,I,J Spacecraft Summary

Launch Readiness Date July 1999, January 2000, July 2000Mission Life 12 years for payload, 15 years for consumablesOrbit Geosynchronous (E-W, ± 0.1 deg., N-S, ± 7 deg.)Launch Vehicle ATLAS-IIA, augmented by internal propulsion on S/CLaunch Site Eastern Test RangeSpacecraft Characteristics:

Dry Weight ~ 3300 lb.Wet Weight ~ 7000 lb.Dimensions 68.8 x 45.7 ft (27.7 ft. stowed length)Telecommunication Services Ka-, Ku-, and S-BandPropulsion Liquid Bi-propellantAttitude Control 3-axis Sun/Earth referencePower Solar array and batteriesThermal Passive, augmented by electric heatersGround System Controlled by ground stations at the WSC

New Ka-Band Single Access (KaSA) Link: TDRS H,I,J spacecraft will include space-to-spacelinks (SSL) using Ka-band frequencies where NASA has primary allocation. The new KaSAservice will offer frequency agility and LHCP/RHCP selectability to minimize interference. Thenew KaSA service will share the existing Ku-band SGL frequency spectrum and existing groundterminal KuSA communication equipment to provide user service. Ka-band TWT amplifiers with15 watts of output power will be used on the TDRS spacecraft to achieve a forward link EIRP of63 dBW. High electron mobility transistor(HEMT) LNAs with a noise figure of 2.8 dB will beused to achieve a return link G/T of 26.5 dBi/°K (with TDRS autotrack and USAT axial ratio of1.0 dB).The spacecraft design will include KaSA autotrack capability to enhance KaSA antenna pointingaccuracy. The autotrack capability is similar to current TDRS F1-F7 long loop design used forKuSA service. Azimuth and elevation error signals amplitude modulate the KaSA return signalfor transmission to the ground. The ground will recover the error signals and generates antennapointing commands for transmission to the spacecraft on-board computer via command link.KaSA autotrack will use constant rate pull-in based on sign information of the error signals toaccomplish antenna acquisition. Within KaSA antenna primary field-of-view (N-S +/- 31 deg., E-W +/-22.5 deg.), the spacecraft will be able to achieve KaSA autotrack with G/T greater than 26.5dB/K in less than 10 seconds. The spacecraft will also include one 650 MHz KaSA return channelcapable of supporting data rates up to 800 Mbps. The current SGL downlink will be capable of

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accommodating this wideband channel. NASA will be able to accommodate customer data ratesup to 800 Mb/s with SQPSK modulation by adding new ground receivers at the WSC.Note that there are limitations on maximum customer spacecraft velocity. The current KuSAservice is capable of supporting free-flight spacecraft with maximum velocities up to 12 km/sec.TDRS H,I,J KuSA service will also support this spacecraft velocity, however, KaSA will only becapable of supporting spacecraft velocities up to 6.7 km/s. This limitation can be overcome bymodifying ground receivers to allow greater Doppler frequencies on the return link.SMA Link: TDRS H,I,J S-band Multiple Access (SMA) design will use phased array antennas thatinclude 15 patch elements for forward service and 36 patch elements for return service. Thespacecraft will support two SMA forward link services with an EIRP of 34 dBW or one SMAforward link service with an EIRP of 44 dBW. The spacecraft will also support up to 6 return userlink services with a G/T greater than 4.5 dB/K within the specified FOV. Because the TDRS H,I,Jspacecraft uses on-board beamforming, the MAR service will use only 6 of the existing 30 F1-F7SGL downlink frequencies to minimize the ground terminal impact. The maximum data rate forTDRS H,I,J MAR service will be 3Mb/s. These new features will make SMA performance closeto SSA performance. The increased EIRP and G/T performance will offer both weight and powerbenefits to future TDRSS S-band customers. It also will reduce the single access antenna loadingfor SSA customers.Spacecraft Operations: TDRS H,I,J design will include the following on-board functions to supportthe TDRSS mission:

1) SA antenna control: The ground terminal will upload “steering” information to the spacecrafton-board computer (OBC) in terms of user spacecraft ephemeris (azimuth and elevationangle timeline). The on-board computer will generate SA gimbal commands based onupload steering information, body attitude error and autotrack errors (autotrack only). TheOBC will issue gimbal commands to steer the SA antenna.

2) SMA phase array antenna control: The ground terminal will upload “steering” information tospacecraft on-board computer (OBC) in terms of azimuth and elevation angle timeline. Theon-board computer will generate MA amplitude and phase commands based on uploadsteering information and body attitude error. The OBC will issue the amplitude and phasecontrol command to the on-board beamforming network.

3) Antenna Control from Ground Terminal: The ground terminal will also be capable ofpointing both SA and SMA antenna manually.

4) Momentum management: The spacecraft will perform roll/yaw momentum dumping by solartacking with thruster backup

Ground Terminal Modification: The ground terminal will include: new TT&C software anddisplays to accommodate TDRS H,I,J spacecraft; modification of ground hardware for new SMAon-board beamforming; ground hardware modifications to accommodate new T&C link commandand telemetry frequencies. Figure 3 illustrates the ground modifications for new SMA services.

3.0 KA-BAND OPERATIONS CONCEPT

3.1 SYSTEM ARCHITECTURE

Figure 2 illustrates an architecture for dual TDRSS/direct-to-ground Ka-band communications.This architecture provides users with the flexibility of using either TDRS H,I,J or a direct link toKa-band ground stations for science data transfer. LEO spacecraft communications forcommanding and housekeeping telemetry would utilize existing S-band capabilities. A keytechnology that enables this dual use concept is a spacecraft Ka-band phased array antenna. Asingle phased array antenna, properly placed on a LEO spacecraft, has the potential to support thedual use concept in addition to reducing spacecraft mass and volume, while eliminating torquedisturbances associated with gimbaled antennas.The TDRS H,I,J Ka-band space-to-space links will operate in bands allocated on a co-primarybasis to inter-satellite service. The return link from the user spacecraft to TDRS H,I,J will betunable across the 25.25 to 27.5 GHz band with a channel bandwidth up to 650 MHz [1]. TheTDRS space-to-ground links will continue to operate at Ku-band. An allocation exists from 25.5to 27 GHz for space-to-ground links that overlaps with the TDRS H,I,J return space-to-space link

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allocation enabling the potential for the dual use concept. This space-to-earth allocation wouldallow users the flexibility of transferring science data in real-time at moderate data rates viaTDRSS, or transferring data once per orbit at high data rates to a ground station.

TDRS H,I,J

User LEO Spacecraft

Ku-Band SGL

Cmd and Tlm

S & Ka-Band

S-Band

• Ka-band direct downlink for high rate science data (> 300 Mbps) • S-band cmd (Š 2 kbps) and tlm (Š 512 kbps)

S-Band

•TDRSS Ka-band return service for science data • S-band service cmd (Š 2 kbps) and tlm (Š 32 kbps)

S & Ka-Band

S/Ka-Band Ground Terminal

Mission Operations

Center

TDRSS White Sands

Complex

Potential use of single Ka-band phased array antenna for both TDRSS and ground contacts

Cmd and Tlm

Figure 2 - Architecture for Dual TDRSS/Direct-to-Ground Ka-Band Communications

3.2 ENABLING KA-BAND TECHNOLOGIES

Key technologies to enable the dual TDRSS/direct-to-ground communications concept include Ka-band phased arrays, solid state power amplifiers, and high data rate ground terminal receivers.Space qualified Ka-band technology developments in the commercial sector are being drivenprimarily by the future providers of mobile satellite services. These include systems such asIridium, Odyssey, Teledesic, and Spaceway.Within NASA/GSFC, a number of Ka-band related technology development programs are ongoingand aimed at potential use by NASA’s future science missions. These include a Ka-bandspacecraft phased array antenna, digital high rate receivers for ground stations, and the TDRSSFourth Generation User Transponder. A potential dual use design for the NASA developed phasedarray antenna would require an array of several hundred elements resulting in a gain ofapproximately 27 dB at a maximum scan angle of ±60 degrees. A total array RF power ofapproximately 5 watts would allow the transfer of science data at a few Mbps via TDRS H,I,J orhundreds of Mbps directly to a ground station. This phased array, used in conjunction with aNASA developed S-band Fourth Generation TDRSS User Transponder, will result in significantreductions in size, weight, power consumption, and cost for LEO science missions compared toexisting TDRSS transponders. The Fourth Generation Transponder design has an option for a Ku-band exciter and “scars” for future Ka-band upgrades.

3.3 MINIMUM EIRP REQUIREMENTS AND ACHIEVABLE RETURN LINK DATARATES

The achievable return link data rate via TDRS H, I, J is determined by the received power at theTDRS antenna from the LEO spacecraft. TDRSS specifies received power requirements (Prec) for

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signal acquisition and the achievable data rate [2]. The required LEO spacecraft EIRP can becalculated from the TDRS Prec requirements by considering free space and other transmissionlosses. The achievable data rate for direct-to-ground transmission is determined by LEOspacecraft EIRP, ground antenna G/T and link losses. A center frequency of 26.375 GHz isassumed for both TDRSS and direct-to-ground data transfers.Figure 3 illustrates achievable data rates as a function of spacecraft EIRP TDRS H,I,Jcommunications and direct-to-ground communications. Multiple curves are provided for thedirect-to-ground case representing various ground antenna sizes. The 1.5 GHz bandwidthallocation for direct-to-ground services limits the bit rate for BPSK modulation with rate 1/2coding to 500 Mb/sec. A for 10-5 bit error rate is assumed for all curves.

3.4 CONTACT AND THROUGHPUT ANALYSIS

Eleven-day simulations were performed for a sun-synchronous LEO spacecraft with an orbitaltitude of 705 km and an inclination of 98.2°. Fifteen LEO spacecraft antenna orientations werestudied as shown in Figure 4, and the four orientations showing the best performance (left side, leftbottom edge, right bottom edge, and right side) are discussed in this paper in terms of daily contacttime and daily throughput. Constellations of two and three TDRS spacecraft were considered.Ground stations at Wallops Island, VA; Fairbanks, AK; McMurdo Station, Antarctica; andSpitsbergen, Norway were postulated. For TDRS contacts, 3° earth horizon clearance wasrequired in order to comply with ITU limits on power flux density at the earth’s surface. Themaximum scan angle of the LEO spacecraft phased-array antenna was set at 60° to avoidgeneration of grating lobes. It should be noted that communications blockage due to spacecraftappendages was not considered in the simulations.The duration of TDRS contact opportunities were trimodally distributed. Each TDRS had onedaily long opportunity and many short ones. About 75% of the long opportunities lasted 139 to148 minutes, and the other 25% lasted a total of 223 minutes. For side mounted antennas, mostshort opportunities lasted between 42 and 71 minutes, and a few were shorter. For bottom edgeantennas, most short opportunities lasted less than 10 minutes. Ground opportunities for sidemounted antennas lasted 7 minutes on average and 10 minutes maximum. For bottom edgeantennas, they averaged 7.5 minutes, with 12 minutes maximum. Side mounted antennas offeredsubstantially fewer ground contact opportunities than bottom edge antennas.

For transmissions via the TDRSS, side-facing antennas provide almost twice as much throughputas bottom left- or right-edge antennas. On the other hand, side-facing antennas perform less wellfor direct-to-ground transmissions than bottom-edge antennas. The best choice between left andright antenna locations depends on the particular orbit and ground terminal locations. The timeperiods of maximum latency for left and right locations differ by 12 hours. For a given LEOsatellite EIRP, the data rate via TDRSS is one eighth of the rate to a 1-m ground antenna, but thecontact windows via TDRSS last 10 to 30 times longer. Additional analyses would be required forspecific spacecraft configurations to take into account communications blockage due toappendages, which typically would result in decreased throughput from the analysis shown here.

References1. 405-TDRS-RP-SY-001, TDRS H,I,J Technical Requirements Specification.2. 530-SNUG, Space Network (SN) Users’ Guide, Revision 7, November 1995.

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0.1

1

10

100

1000

10000

25 30 35 40 45 50 55 60

TDRS H,I,J(Rate 1/2, Autotrack Mode)

NOTES:1. Direct-to-ground data rates calculated at maximum range and assumes 10E-5 BER, rate 1/2 coding, 7.7 dB rain loss, and 2 dB implementation loss.2. Direct-to-ground and TDRS H,I,J data rate calculations include 2 dB scan loss, and 0.5 dB polarization loss.3. Achievable data rates will be higher than indicated by curves for losses less than those specified in notes 1 and 2 above.4. Spacecraft EIRP = maximum EIRP - scan loss - polarization loss

Maximum BPSK Data Ratedue to 1.5 GHz Space-to-EarthBandwidth Limitation

Minimum Power for TDRS H,I,JAntenna Autotrack Acquisition

Spacecraft EIRP (dBWi, see note 4)

Figure 3 - Achievable Data Rates versus Spacecraft EIRP

Zenith Direction

Pitch Axis

Yaw Axis (Nadir)

Roll Axis (Velocity Direction)

1

2

34

5

6

7

89

10

1112

13

1415

Selected Antenna Locations for Coverage Analysis

Surfaces

1. Top (T)

2. Front (F) 3. Left (L)

4. Right (R)

5. Bottom (B)

Edges

6. Top-Right (TR) 7. Front-Top (FT)

8. Front-Left (FL) 9. Front-Right (FR)

10. Front-Bottom (FB)

11. Bottom-Left (BL)

12. Bottom-Right (BR)

Corners

13. Top-Front-Right (TFR)

14. Bottom-Front-Left (BFL)

15. Bottom-Front-Right (BFR)

Figure 4 - LEO Spacecraft Phased Array Antenna Locations for Coverage Analysis