810-005, Rev. E DSMS Telecommunications Link Design Handbook 205, Rev. A 34-m and 70-m Command December 15, 2002 Document Owner: Approved by:^M ^M ----------------------- -----------------------^M R.W. Sniffin Date M.E. Levesque Date^M Command System Engineer Uplink Tracking and Command Service System Development Engineer ^M Released by:^M [Signature on file in TMOD Library]^M ------------------------^M DSMS Document Release Date Change Log^M Rev Issue Date Affected Paragraphs Change Summary^M Initial 1/15/2001 All Initial Release A 12/15/2002 All Provides description and capabilities of new DSN command equipment Note to Readers There are two sets of document histories in the 810-005 document, and these histories are reflected in the header at the top of the page. First, the entire document is periodically released as a revision when major changes affect a majority of the modules. For example, this module is part of 810-005, Revision E. Second, the individual modules also change, starting as an initial issue that has no revision letter. When a module is changed, a change letter is appended to the module number on the second line of the header and a summary of the changes is entered in the module's change log. Contents Paragraph Page^M 1 Introduction.......................................................................................... 4 1.1 Purpose............................................................................................. 4 1.2 Scope............................................................................................... 5 2 General Information .................................................................................. 5 3 Command Parameters ................................................................................... 9 3.1 RF Power ........................................................................................... 9 3.2 Carrier Frequency.................................................................................. 12 3.3 Subcarriers ....................................................................................... 13 3.4 Modulation Index .................................................................................. 13 3.5 Modulation Losses.................................................................................. 14 3.6 PCM Data Formats .................................................................................. 14 3.7 Data Rates ........................................................................................ 14 3.8 Idle Patterns...................................................................................... 15 3.9 Command Timing..................................................................................... 16 3.10 Command Verification ............................................................................. 16 3.11 Availability and Reliability...................................................................... 16 3.12 Emergency Support ................................................................................ 17 4 Proposed Capabilities................................................................................ 17 4.1 Direct Carrier Modulation.......................................................................... 17 Appendix A, References ................................................................................ 18 Illustrations Figure Page 1. Maximum Command Range for a Reference Spacecraft with an Omni-directional Antenna and a 0.5 Radian Command Modulation Index...................................................................... 7 2. Maximum Command Range for a Reference Spacecraft with a High-gain Antenna and a 1.2 Radian Command Modulation Index............................................................................. 8 3. Command Dataflow and Interfaces..................................................................... 10 4. Command Data Formats................................................................................ 15 Tables Table Page 1. Capabilities of DSN 70-m and 34-m Antennas .......................................................... 6 2. Reference Spacecraft Characteristics for Figures 1 and 2............................................. 7 3. Command Parameters ................................................................................. 11 1 Introduction 1.1 Purpose This module provides performance parameters for the elements of the Deep Space Mission System (DSMS) that are exclusively used for sending commands to spacecraft. It is intended to assist the telecommunications engineer in designing an uplink (or forward space link) that is compatible with currently installed DSMS equipment. It also contains brief descriptions of future enhancements that have been proposed for this equipment and capabilities that are being maintained for legacy customers using the previous generation of command equipment. 1.2 Scope The discussion in this module is limited to command equipment used with the Deep Space Network (DSN) 70-m antennas and the 34-m antennas with the exception of the 34m High-speed Beam Waveguide (HSB) antenna. Performance parameters of command equipment used with the DSN 26-m and 34-m HSB antennas may be found in module 213, 26-m Subnet Command. Detailed performance of equipment used for purposes in addition to command is covered elsewhere in 810-005. Information on antennas, exciters, and transmitters have been included as a convenience and should be verified against their primary source. In particular, the following modules should be considered 101 70-m Subnet Telecommunications Interfaces, 103 34-m HEF Subnet Telecommunications Interfaces, 104 34-m BWG Stations Telecommunications Interfaces, and 301 Coverage and Geometry. 2 General Information Each antenna in the DSN is capable of sending commands to one spacecraft at a time. Each Deep Space Communications Complex (DSCC) contains one 70-m and from two to four 34-m antennas. There are two types of 34-m antennas. The first is the so-called high-efficiency (HEF) antennas that have their feed, low-noise amplifiers, and transmitter located on the tilting structure of the antenna. These antennas were named when a less-efficient 34-m antenna was in use by the DSN and the name has survived. The efficiency of all DSN 34-m antennas is now approximately the same. The second type of 34-m antenna is the beam waveguide (BWG) antenna where the feeds, low noise amplifiers and transmitters are located in a room below the antenna structure and the radio frequency energy is transferred to and from the antenna surface by a series of mirrors encased in a protective tube. The capabilities of each antenna type and, in the case of the BWG antennas, of the individual antennas are different and must be considered in designing a command link. Often, the selection of antenna for uplink will depend on the downlink frequencies it supports. Table 1 lists the uplink and downlink frequency ranges for each antenna type and provides approximate ranges for uplink Effective Isotropic Radiated Power (EIRP). The modules referred to above should be consulted for exact values and other parameters. The telecommunications link designer is cautioned against making designs dependent on the 70-m antenna as there is only one per complex and it subject to severe scheduling constraints. Table 1. Capabilities of DSN 70-m and 34-m Antennas Antenna Downlink Uplink Power EIRP Range Remarks Frequency Frequency Type Ranges (Mhz) Ranges (MHz) (kW) (dBm) 70-m 2270 - 2300 2110 - 2120 0.2 - 20.0 20 - 115.1 - 134.1 1 per complex * 8400 - 8500 2110 - 2120* 400* 134.1 - 147.2* Power above 20 kW and 7145 - 7190 0.2 - 20.0 124.8 - 143.8 EIRP above 134.1 dBm is intended for spacecraft emergency support 34-m 2200 - 2300 7145 - 7190 0.2 - 20.0 119.4 - 138.4 1 per complex HEF 8200 - 8600 34-m 2200 - 2300 2025 - 2070 0.2 - 20.0 0.2 107.6 - 126.6 1 per complex S/X/K 8400 - 8500 2070 - 2090 - 5.0 0.2 - 107.8 - 121.8 Provides both Deep BWG 32100 - 32600 2090 - 2120 20.0 0.2 - 20.0 107.9 - 126.9 Space and Earth 7145 - 7190 119.3 - 138.7 orbiter support. 7190 - 7235 0.2 - 5.0 119.3 - 133.3 34-m 8400 - 8500 7145 - 7190 0.2 - 20.0 119.3 - 138.7 2 at Goldstone DSCC X/K BWG 32100 - 32600 7190 - 7235 0.2 - 5.0 119.3 - 133.3 1 at Madrid DSCC Figures 1 and 2 illustrate the DSN command capabilities assuming a reference spacecraft employing a residual carrier uplink and having the characteristics specified in Table 2. These figures show that command range at low bit rates is limited by the spacecraft carrier tracking performance. At higher bit rates, the range is limited by available Eb/No. Figure 1 is intended to show performance during a spacecraft emergency that forces the use of an omnidirectional antenna. The uplink modulation index has been intentionally lowered to 0.5 radians to direct more power to the carrier. Figure 2 assumes a more typical spacecraft configuration using a high-gain antenna and an uplink modulation index of 1.2 radians. Command data are delivered to the DSN Stations in one of two formats. The first is referred to as the Throughput Command format and is described in DSN Document 820-013, module CMD-4-9. The second is referred to as the Space Link Extension (SLE) format, an implementation of the Consultative Committed for Space Data Systems (CCSDS) recommendation 912.1, Space Link Extension Forward CLTU Service, and is described in DSN Document 820-013, module 0163- Telecomm. Both of these formats include command symbols to be transferred to the spacecraft and ancillary information for such things as routing, ensuring the integrity of the Earth segment of the communications link, and providing the customer limited control of the command process as described in the aforementioned documents. Figure 1. Maximum Command Range for a Reference Spacecraft with an Omni- directional Antenna and a 0.5 Radian Command Modulation Index. (Figure omitted in text-only document) Table 2. Reference Spacecraft Characteristics for Figures 1 and 2. Parameter Value Antenna Gain less pointing loss Omnidirectional 0 dB S-band Hi-gain 30 dB X-band Hi-gain 39.7 dB Other RF losses -1.8 dB System Temperature 500 K Carrier Loop Bandwidh 100 Hz Required Carrier Margin 12 dB Command Detection Losses -1.5 dB Required E_b/N_o 9.6 dB Figure 2. Maximum Command Range for a Reference Spacecraft with a High-gain Antenna and a 1.2 Radian Command Modulation Index. (Figure omitted in text-only document) The only function performed at the stations is the mechanism whereby command data are extracted from the delivery format and converted to an RF signal suitable for reception by a spacecraft. This means that all commands including prefix symbols, and command data symbols must be generated at the appropriate Mission Operations Center (MOC) or Project Operations Control Center (POCC). If coding such as Bose-Chaudhuri-Hocquenghem (BCH) is required, it must be accomplished before the commands are delivered to the DSN. The DSN may perform checks for format compliance, but it will not interpret nor modify the contents of any command. Neither does it guarantees error free command delivery to the spacecraft. It is up to the project to provide its own error detection and correction schemes. The DSN has the capability to operate its command equipment without radiating commands while simultaneously recording the data stream that has been accepted from a project. A limited number of these command recordings for each project may be stored at the DSCCs for use in an emergency (such as loss of communication from an operations center during a critical mission event) to place a spacecraft in a safe condition. The procedure for the use of these recordings is beyond the scope of this document. The DSMS includes the Advanced Multi-mission Operations System (AMMOS) at the Jet Propulsion Laboratory (JPL) to provide the user interface for JPL projects. It also contains an implementation of the CCSDS Recommendation 727.0, CCSDS File Delivery Protocol (CFDP) service that is available for use with spacecraft that have incorporated this protocol within their flight software. This service takes data files prepared at, or delivered to AMMOS, converts them to SLE protocol, and delivers them to the station for transmission to a file store onboard the customer’s spacecraft. Error-free delivery to a spacecraft supporting this protocol can be ensured when the fully acknowledged transmission mode is specified. Although the process of file delivery to AMMOS is beyond the scope of this document, it might include such methods as delivery from a CFDP service at an MOC or POCC, file transfer protocol (ftp), or media delivery. Figure 3 illustrates the command data flow and the interfaces by which command services are provided. All interfaces to the DSN secure network are made at the Central Communications Terminal at JPL. All missions are strongly encouraged to utilize the SLE Forward CLTU Service because it is an implementation of an international standard. The Throughput Command Service is intended for legacy missions but is expected to be in operation for many years and may be selected for missions with a strong heritage to one or more legacy missions. In addition to the interfaces by which command data are delivered to the DSN, a management interface is required for selecting the particular set of parameter appropriate for the spacecraft being supported. A discussion of this interface is contained in DSN Document 810-007, DSMS Mission Interface Design Handbook. 3 Command Parameters The following paragraphs provide a discussion of the principal command parameters. Parameters that are a function of antenna type were summarized in Table 1. Parameters that are independent of antenna type are summarized in Table 3. 3.1 RF Power RF power is produced by variable beam klystron amplifiers that permit saturated operation over a relatively wide power range by adjustment of the drive power and beam voltage. The 20 kW transmitters can be saturated at power levels as low as 1 kW and unsaturated operation is possible down to 200 W, The 400 kW S-band transmitter operates saturated from 200 kW to 400 kW and unsaturated operation is possible at power levels as low as 20 kW. The efficiency of the transmitters falls off rapidly as power level decreases so there is little, if any, energy savings by operating at a lower power level. On the other hand, the life of the klystrons is a function of power level so operating at reduced power should be considered wherever possible. Figure 3. Command Dataflow and Interfaces. (Figure omitted in text-only document) Table 3. Command Parameters Parameter Value Remarks RF Power Output See Table 1 Also see modules 101, 103, and 104 Effective Isotropic See Table 1 Also see modules 101, Radiated 103, and 104 Power (EIRP) Carrier Frequency See Table 1 Also see modules 101, 103, and 104 Subcarrier Frequencies Sinewave 999 Hz - 250075 Hz Squarewave 100 Hz - 1000 Hz Subcarrier 0.1 Hz Sinewave and Squarewave Frequency Resolution Harmonic and >45 dB Below subcarrier Spurious Signals amplitude (dB-V) (Sinewave Subcarrier) Harmonic Response < 6 dB Attenuation of 7th (Squarewave harmonic (dB-V) Subcarrier) Subcarrier >1 x 10^-9 For all measurement Stability times from 100 s through 12 h (derived from station frequency standard) PCM Data Formats NRZ-L, M, S See Figure 4 Bi-f-L, M, S Modulation Index Range Sinewave Subcarrier 0.1 - 1.52 6 - 87 degrees radians Squarewave 0.1 - 1.40 6 - 80 degrees Subcarrier radians Modulation Index +/-10% Of carrier suppression Accuracy in dBs Modulation Index +/-3% Of carrier suppression Stability in dBs over a 12-h period Data Rates Subcarrier Frequency/2n, 1 = n = 11 Sinewave Subcarrier 1 bps - 125037.5 bps Squarewave 1 bps - 500 Subcarrier bps Coherency to +/-6deg Offset between Subcarrier bit/symbol transitions and subcarrier zero crossings. Data Rate Stability >1 x 10^-9 For all measurement times from 100 s through 12 h (derived from subcarrier stability) Parameter Value Remarks Inter-command None (Carrier modulation only), carrier and command subcarrier, carrier, command subcarrier and idle pattern Idle Pattern 8-bit repetitive Command Timing 0.1 s 0.1 s plus 1 - 8 bit times if idle pattern is present Pre-track 20 m With Transmitter warm-up Calibration or band change 5 m Transmitter already warmed-up Availability 98.9% Mean-time between 2200 h Command Aborts The calibration process for setting RF power starts at approximately one tenth of the desired power and gradually increases over a few minutes until the desired power is reached. Therefore, changing power during a tracking pass may have unexpected results. For example, a decision to raise the power from 5kW to 20kW will result in a momentary reduction to approximately 2kW followed by a gradual increase to 20kW. A decision to lower the power from 20kW to 5kW will result in a momentary reduction to approximately 500W followed by a gradual increase to 5kW. 3.2 Carrier Frequency The DSN considers establishment of carrier frequency to be a tracking function as opposed to a command function. Small frequency changes such as might be required for Doppler compensation will have little effect on the transmitter output. Larger frequency changes such as might be required to command two spacecraft within the same beamwidth may cause the transmitter output to vary by as much as 1-dB due to ripple across the klystron passband. Should this happen, the operator at the station will be warned that the transmitter should be re- calibrated. This warning may be ignored to no detriment other than the power output being as much as 1-dB from the requested value. The S/X/K BWG subnet has two klystron amplifiers that share a common power supply and cooling system. Therefore, a change of band will require a minimum of 20-minutes to cool-down the klystron that is no longer needed and warm-up and calibrate the other klystron. The S-band klystron at these stations is step-tunable to provide coverage over the entire uplink band. Changing from one band segment to another requires turning off the transmitter, changing the band segment, and re-calibrating at the new frequency. 3.3 Subcarriers Both sinewave and squarewave subcarriers are available. Subcarrier frequencies are initialized from an entry in the activity service table but may be changed during a support activity providing no command waveform is being radiated. This technique can be used to provide a limited amount of subcarrier Doppler compensation recognizing that command modulation (including the subcarrier) must be removed when the subcarrier frequency is changed. Changing the subcarrier frequency will cause a corresponding change in data rate because these two items are coherent. See the discussion on data rate for details. 3.4 Modulation Index The modulation index is established by applying a variable-amplitude voltage to the phase modulator in the exciter. The amplitude of this voltage can be adjusted in 255 steps of approximately 0.0065 radians. The range of 0.1 radians through 1.52 radians occupies approximately 220 of these steps. The modulating voltage is calibrated periodically at the 3-dB carrier suppression point for both sinewave and squarewave subcarriers. The calibration interval is selected to assure a carrier suppression within 10% of the specified value in dBs at any time between calibrations. For example, a sinewave modulation index of 0.67 radians (38.5deg) will produce a carrier suppression of 1.0 dB +/- 0.1 dB. A sinewave modulation index of 1.13 radians (64.5deg) will produce a carrier suppression of 3.0 dB +/-0.3 dB. The modulation index is initialized from an entry in the activity service table but may be changed during a support activity providing no command waveform is being radiated. Carrier power suppression and data power suppression as functions of modulation index angle are: Sine-wave subcarrier: P_C/P_T(dB) = 10log[2J_0^2(theta_D)], dB (1) P_D/P_T(dB) = 10log[2J_1^2(theta_D)], dB {first upper and lower sidebands} (2) Square-wave subcarrier: P_C/P_T(dB) = 10log[cos^2(theta_D)], dB (3) P_D/P_T(dB) = 10log[sin^2(theta_D)], dB {all sidebands} (4) where theta_D = data modulation index, radians, peak P_T = total power P_C = carrier power P_D = data power J_0 = zero-order Bessel function J_1 = first-order Bessel Function 3.5 Modulation Losses The bandpass of all elements in the command path with the exception of the S-band power amplifier at the 34-m S/X/K BWG stations is adequate to make modulation losses negligible over the frequency and power ranges specified in Table 1. The modulation losses at the 34-m S/X/K BWG stations are negligible provided the klystron frequency step is properly selected. 3.6 PCM Data Formats The DSN Command System produces a pulse code modulated (PCM) waveform that is binary phase-shift keyed (BPSK) onto a subcarrier. That is, phase-shift keyed with a signaling level of +/-90deg and resulting in a fully suppressed subcarrier. The six supported PCM data formats are illustrated in Figure 4. The data format is established at the start of a support activity by an entry in the activity service table. 3.7 Data Rates Bit rates for NRZ modulation and symbol rates for bi-phase modulation are available over the range of 1 to 125,037.5 bps or sps. They are derived from the subcarrier frequency generator using a binary divider of 2^n where n can be from 1 to 11. Thus, a 1 bps data stream would require a minimum sinewave subcarrier of 1024 Hz and the lowest bit rate available for a 1000 Hz subcarrier would be 1.953125 bps. For a 16000 Hz subcarrier, the bit or symbol rate can be between 7.8125 and 8000 bps. For a 250075 Hz subcarrier, the bit or symbol rate can be between 122.1069 and 125037.5 bps. A 1 bps data stream would require a minimum squarewave subcarrier of 128 Hz and the lowest bit rate available for a 100 Hz subcarrier would be 1.5625 bps. For a 1000 Hz subcarrier, the bit or symbol rate can be between 1.953125 and 500. Figure 4. Command Data Formats (Figure omitted in text-only document) The data rate entry in the activity service table is rounded to the nearest acceptable value depending on the subcarrier frequency selected. The data rate may be changed during a support activity providing no command waveform is being radiated. However, a data rate change will have no effect unless it is large enough to cause a different binary divisor to be calculated. Small changes in subcarrier frequency will result in an equivalent change in data rate. A specification of a data rate midway between two valid data rates may result in a change in the binary divisor when the subcarrier frequency is changed. 3.8 Idle Patterns The DSN command equipment can be configured to operate in three modes during a command support activity. The command mode is initialized from an entry in the activity service table but may be changed during a support activity providing no command waveform (subcarrier or subcarrier and data) is being radiated. The first of these is carrier only as might be used during a support activity not involving commands. In this mode, all command modulation is removed whenever command data are not being radiated. The second mode is subcarrier only in which a continuous, unmodulated subcarrier is transmitted to the spacecraft at the specified frequency and modulation index. The third mode is subcarrier with a customer defined 8- bit idle pattern. Samples of idle patterns are: all zeros, all ones, or alternating zeros and ones. If a sequence cannot be specified as an 8-bit pattern, it must be originated at the MOC or POCC as command bits. The transition between an idle pattern and command bits can only occur at 8-bit boundaries. 3.9 Command Timing The customer may specify a first bit radiation time within the command data stream to an accuracy of 0.1 s. If an idle pattern has been specified, the actual first bit radiation time will be from 1 to 8 bit times later than the specified radiation time. Commands will be radiated upon receipt if no first bit radiation time is specified. If contiguous radiation of commands is desired, it is the customer's responsibility to ensure that the commands are delivered at a rate sufficient to satisfy the radiation requirements while not overflowing the buffering capability of the command equipment. Further details can be found in 820-013 modules CMD-4-9 (Throughput Command) and 0163-Telecomm (SLE Command). 3.10 Command Verification The command equipment constantly monitors the output of the exciter to verify that the requested modulation index is within acceptable limits. No test on data content is performed because there is no independent source of data available for comparison. In addition, the transmitter power level, waveguide configuration, presence of frequency and timing references, and software health are monitored. Failure of a monitored parameter will cause a command abort. Exciter, transmitter, and microwave monitoring may be disabled upon customer request. 3.11 Availability and Reliability The DSN Command System availability is 98.9 percent. The mean time between command aborts is 2200 hours of command time. This number was obtained from analysis of several years of operational data at the Goldstone DSCC involving the previous generation of command equipment. The number is considered valid because most aborts were caused by factors external to the command equipment. There is no history available from which an undetected command bit error rate can be determined but it is believed to be significantly less than 3 in 108 transmitted bits and may be as low as 1 in 10^13 which is the error rate of the communications channel between the customer and the stations. 3.12 Emergency Support The DSN Command System provides a means for replay of command files that have been recorded earlier and stored at the station for emergency use during periods when communications between the MOC or POCC and the station cannot be established. The procedure for using these command recordings is covered in document 810-007, DSMS Mission Interface Design Handbook. 4 Proposed Capabilities The following capability has not yet been implemented by the DSN but has adequate maturity to be considered for spacecraft mission and equipment design. Telecommunications engineers are advised that any capabilities discussed in this section cannot be committed to except by negotiation with the Interplanetary Network Directorate (IND) Plans and Commitments Program Office. 4.1 Direct Carrier Modulation A partial implementation of the CCSDS Medium Rate Command Recommendation (CCSDS Recommendation 401.0B, paragraph 2.2.7) will be implemented. NRZ bit rates and bi-phase symbol rates of 8000, 16000, 32000, and 64000 will be available. Bit or symbol rates in excess of 64000 bps/sps will not be available due to exciter bandwidth restrictions. Carrier and data suppression for direct carrier modulation is calculated using the equations for squarewave modulation (3) and (4). Appendix A References 1 CCSDS 727.0-R-2, CCSDS file Delivery Protocol, Red Book, February 2000. 2 CCSDS 401.0-B, Recommendations for Radio Frequency and Modulation Systems, May 2000. 3 CCSDS 912.1-R-2, Space Link Extension - Forward CLTU Service Specification, Red Book, February 2000. 4 810-007, Deep Space Mission System Mission Interface Design Handbook, to be published 5 820-013 module CMD-9, Command Radiation Service, July 15, 2000 6 820-013 module 0163-Telecomm, Space Link Extension Forward Link Service, September 30, 2001