1、 Recommendation ITU-R SA.1014-3 (07/2017) Radiocommunication requirements for manned and unmanned deep space research SA Series Space applications and meteorology ii Rec. ITU-R SA.1014-3 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical
2、 use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World
3、 and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for
4、 the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series o
5、f ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodeterminat
6、ion, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellit
7、e news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2017 ITU 2017 All rights reserved. No part of this publicati
8、on may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R SA.1014-3 1 RECOMMENDATION ITU-R SA.1014-3 Radiocommunication requirements for manned and unmanned deep space research (1994-2006-2011-2017) Scope This Recommendation briefly describes some essential charact
9、eristics of space research service (deep space) radiocommunications. These characteristics influence or determine the requirements for selection of candidate bands, coordination, band sharing and protection from interference. Keywords Deep space, radiocommunication, telemetry, telecommand, data rate
10、, earth stations, space stations, ranging, radio science Related Recommendations and Reports Recommendation ITU-R SA.1015, Report ITU-R SA.2167, Report ITU-R SA.2177. The ITU Radiocommunication Assembly, considering a) that radiocommunications between the Earth and stations in deep space have unique
11、 requirements; b) that these requirements affect the selection of candidate band, band sharing, coordination, protection from interference and other regulatory and frequency management matters, recommends that the requirements and characteristics described in the Annex for deep space radiocommunicat
12、ions should be taken into account concerning space research service (deep space) and its interaction with other services. Annex Radiocommunication requirements for manned and unmanned deep space research 1 Introduction This Annex presents some characteristics of deep space research missions, the fun
13、ctional and performance requirements for radiocommunications needed to conduct deep space research by means of spacecraft, and the technical methods and parameters of systems used in connection with such missions. 2 Rec. ITU-R SA.1014-3 Considerations regarding bandwidth characteristics and requirem
14、ents are found in Report ITU-R SA.2177. 2 Radiocommunication requirements Deep space missions require highly reliable radiocommunications over long periods of time and great distances. For example, a spacecraft mission to gather scientific information at the planet Neptune takes eight years and requ
15、ires radiocommunication over a distance of 4.65 109 km. The need for high e.i.r.p. and very sensitive receivers at earth stations is a result of the large radiocommunication distances involved in deep space research. Continuous usage of space research service (deep space) radiocommunication bands is
16、 a consequence of the several missions now in existence and others being planned. Because many deep space missions continue for periods of several years, and because there are usually several missions in progress at the same time, there is a corresponding need for radiocommunication with several spa
17、cecraft at any given time. In addition, each mission may include more than one spacecraft, so that simultaneous radiocommunication with several space stations will be necessary. Simultaneous coordinated radiocommunication between a space station and more than one earth station may also be required.
18、2.1 Telemetering requirements Telemetering is used to transmit both maintenance and scientific information from deep space. Maintenance telemetering information about the condition of the spacecraft must be received whenever needed to ensure the safety of the spacecraft and success of the mission. T
19、his requires a weather independent radiocommunications link of sufficient capacity. This requirement is a partial determinant of the frequency bands that are preferred for deep space research (see Report ITU-R SA.2177). Science telemetering involves the sending of data that is collected by the on-bo
20、ard scientific instruments. The required data rate and acceptable error rate may be quite different as a function of the particular instrument and measurement. Table 1 includes maximum required data transmission rates for scientific and maintenance telemetering. TABLE 1 Maximum required bit rates fo
21、r deep space research Direction and function Link characteristic Weather independent Normal High data rate Earth-to-space Telecommand (bit/s) Computer programming (kbit/s) Audio (kbit/s) Video (Mbit/s) 1 000 50 45 4 1 000 100 45 12 2 000 200 45 30 Space-to-Earth Maintenance telemetering (bit/s) Scie
22、ntific data (kbit/s) Audio (kbit/s) Video (Mbit/s) 500 115 45 0.8 500 500 45 8 2 105 3 105 45 30 Rec. ITU-R SA.1014-3 3 Telemetering link capacity has steadily increased with the development of new equipment and techniques. This increase can be used in two ways: to gather larger amounts of scientifi
23、c data at a given planet or distance; and to permit useful missions to more distant planets. For a particular telemetering system, the maximum possible data rate is proportional to the inverse square of the radiocommunication distance. The same link capacity that provides for a data rate of 134 kbit
24、/s from the vicinity of the planet Jupiter (9.3 108 km) would also provide for a data rate of 1.74 Mbit/s from the vicinity of the planet Venus (2.58 108 km). Because higher data rates require wider transmission bandwidths, the ability to effectively utilize the maximum telemetering capability depen
25、ds on the width of allocated bands, and the number of simultaneous mission spacecraft that are within the earth station beamwidth and are operating in the same band. An important contribution to telemetering has been the development of coding methods that permit operation with a lower signal-to-nois
26、e ratio. The coded signal requires a wider transmission bandwidth. The use of coded telemetering at very high data rates may be limited by allocation width. 2.2 Telecommand requirements Reliability is the principal requirement of a telecommand link. Commands must be received accurately and when need
27、ed. The telecommand link is typically required to have a bit error rate not greater than 1 106. Commands must be received successfully, without regard to spacecraft orientation, even when the primary high gain antenna may not be pointed towards the Earth. For such circumstances, reception using a ne
28、arly omnidirectional spacecraft antenna is required. Very high e.i.r.p. is needed at earth stations because of low spacecraft antenna gain, and to provide high reliability. With computers on the spacecraft, automatic sequencing and operation of spacecraft systems is largely predetermined and stored
29、on-board for later execution. For some complicated sequences, automatic operation is a requirement. Telecommand capability is required for in-flight alteration of stored instructions, which may be needed to correct for observed variations or malfunctions of spacecraft behaviour. This is particularly
30、 true for missions of long duration, and for those circumstances where sequencing is dependent on the results of earlier spacecraft events. For example, the commands for spacecraft trajectory correction are based on tracking measurements and cannot be predetermined. The range of required command dat
31、a rates is given in Table 1. Reliable telecommand includes the need for reliable maintenance telemetering that is used to verify that commands are correctly received and loaded into command memory. 2.3 Tracking requirements Tracking provides information used for spacecraft navigation and for radio s
32、cience studies. 2.3.1 Navigation The tracking measurements for navigation include radio-frequency Doppler shift, the round-trip propagation time of a ranging signal, and the reception of signals suitable for long baseline interferometry. The measurements must be made with a degree of precision that
33、satisfies navigation requirements. Measurement accuracy is affected by variations in velocity of propagation, knowledge of station location, timing precision, and electronic circuit delay in earth and space station equipment. Table 2 lists a current example of the requirements for navigation accurac
34、y and the associated measurements. 4 Rec. ITU-R SA.1014-3 TABLE 2 Navigation and tracking requirements Parameter Value Navigation accuracy (m) 300 (at Jupiter) Doppler measurement accuracy (Hz) 0.0005 Range measurement accuracy (m) 0.15 Accuracy of earth station location (m) 1 Ranging (Earth-to-spac
35、e for telecommand the sub-carrier is often sinusoidal. The modulation index is adjusted to provide a desired ratio of residual carrier power to data sideband power. This ratio is selected to provide optimum carrier tracking and data detection in the receiver. RF carrier and data sub-carrier demodula
36、tion is accomplished by phase-locked loops (PLLs). Data detection generally uses correlation and matched filter techniques. Video and audio links for manned missions may use other modulation and demodulation techniques. Typically, bandwidth-efficient (offset) QPSK and GMSK modulation and demodulatio
37、n are used in these cases with carrier tracking accomplished via Costas loops instead of PLLs. 4.3 Coding In a digital telecommunication link, error probability can be reduced if the information bandwidth is increased. Coding accomplishes this increase by translating each data bit into a larger numb
38、er of code symbols in a particular way. Some examples of coding types are block and convolutional codes. After transmission, the original data are recovered by a decoding process that is matched to the code type. The performance advantage of coded transmission is related to the wider bandwidth, and
39、can vary from to 3.8 dB (convolutional coding, bit error ratio of 1 103) to more than 9 dB (rate 1/6 turbo coding). 4.4 Multiplexing Science and maintenance telemetering may be combined into a single digital data stream by time division multiplexing; or may be on separate sub-carriers that are added
40、 to provide a composite modulating signal. A ranging signal may also be added in combination with telemetering or telecommand. The amplitude of the different data signals is adjusted to properly divide the transmitter power between the carrier and the information sidebands. 4.5 Ranging Ranging is pe
41、rformed from an earth station using the space station transponder in the two-way mode. Ranging modulation on the Earth-to-space signal is recovered in the transponder and used to modulate the space-to-Earth carrier. At the earth station, comparison of the transmitted and received ranging codes yield
42、s a transmission delay measurement proportional to distance. A fundamental limitation to ranging precision is the ability to measure time correlation between the transmitted and received codes. The system currently in use employs a highest code frequency of 2.062 MHz. The code period is 0.485 s and
43、resolution to 1 ns is readily achieved, assuming sufficient signal-to-noise ratio. This resolution is equivalent to 30 cm in a two-way path length, 15 cm in range. This meets the current navigation accuracy requirements of Table 2. For the 1 cm accuracy needed for radio science experiments (see 2.3.
44、2) a code frequency of at least 30 MHz is required. Current SRS deep space pseudo-noise (PN) ranging systems use a maximum chip rate of 24 MChip/s. 4.6 Antenna gain and pointing For the parabolic antennas typically used in space research, the maximum gain is limited by the accuracy with which the su
45、rface approaches a true parabola. This latter limitation places a bound on the maximum frequency that may be effectively used with a particular antenna. Rec. ITU-R SA.1014-3 9 One factor in surface accuracy, common to both earth and space station antennas, is manufacturing precision. For earth stati
46、on antennas, additional surface deformation is caused by wind and thermal effects. As elevation angle is varied, gravity introduces distortion of the surface, depending on the stiffness of the supporting structure. For space station antennas, size is limited by permissible mass, by the space availab
47、le in the launch vehicle, and by the state of the art in the construction of unfurlable antennas. Thermal effects cause distortion in space station antennas surfaces. The maximum usable gain of antennas is limited by the ability to point them accurately. The beamwidth must be adequate to allow for t
48、he angular uncertainty in pointing. All the factors that cause distortion of the reflector surface also affect pointing accuracy. The accuracy of the spacecraft attitude control system (often governed by the amount of propellant which can be carried) is a factor in space station antenna pointing. Th
49、e precision with which the location of the earth and space stations are known with respect to each other affects the minimum usable beamwidth and the maximum usable gain. Table 6 shows typical limits on antenna performance. TABLE 6 Current limitations on accuracy and maximum antenna gain Space station antennas Earth station antennas Limiting parameter Typical maximum value of parameter Maximum gain Typical maximum value of parameter Maximum gain Accuracy of dish surface 0.24 mm r.m.s., 3.7 m dish 61 dBi(1) at 34 GHz 0.53 mm r.m.s., 70 m dish 84 dBi(1) at 34 GHz
