PoS(SKADS 2009)006 toward Mars later in this decade ff ciency of deep space expeditions. ffi A broad variety of engineering considerations dictate use Although the prospective planetary missions are designed Communication with deep space missions usually employs C) allow communication to be maintained up to the edges / of the SKA will makedio it signals possible to from eavesdrop planetary onThis the probes kind weak with of ra- acceptable supportmission-critical data is operations particularly rates. and valuable can for beany serious short accommodated impact in without on SKA time operations. Thetrue latter in is view particularly of the plannedthe multi-view SKA. multi-user capability of of lower frequencies for science dataetary delivery from probes small to plan- Cassini-Huygens, larger the and radio powerfulto orbiters. link the In from orbiter the theUHF case were bands descending (400 of conducted probe MHz)Ganymede are at being and the considered Europa for micropenetrators frequencycraft up-link to from of of the the 2 orbiter joint space- (EJSM) GHz. ESA-NASA Europa design Jupiter study. Systemthrough Such Mission a low-power the transmitter up-linkting and low-directivity is antenna. transmit- to Similarly,which be is the expected conducted to international blastwill ExoMars o use mission theabove UHF missions radio and many communicationbeginning others from equipment. will 2020 be All a in perfect the operational match to phase the SKAto timetable. deliver the bulkthe of high-capacity science Ka-band and radio channels housekeepingfrequency (32 data GHz), band, through the such lower (800 as and X- 400 (8 MHz)space will GHz), communications. remain S These active lower (2 inperfectly frequency the consistent GHz) operations with arsenal are and the of operational UHF deep range of the SKA. dedicated Earth-based facilities equipped(such with as large the antennas NASA’scommonly Deep used Space scheme is Network, that of DSN).gain duplex The communication. antennas High most and(S powerful transmitters onboardof spacecraft the Solar System. However, the radio link system imposes er acquisition of data streams with the rate of tens bps through low-power ff cult if possi- ffi ect) makes sub- ff SKA P.A. Fridman, L.I. Gurvits, S.V. Pogrebenko for Deep Space Science Missions    T 2009 The Square Kilometre Array is conceived as a next generation radio astronomy facility superior to any existing   The SKA as a Direct-to-Earth Data Acquisition Facility S  telescope primarily in sensitivity terms. Theof science space drivers missions. of However, as the a SKA uniquelyhave project an sensitive do important receiving not role radio as include facility an data on ad-hoc acquisitionthis the addition planet contribution from to we in and the the assess tracking network foreseeable the of Earth-based future, potentialdeep assets the of of space SKA the space might missions. SKA science as This and a exploration assessmentEuropa programmes. receiving assumes In Jupiter facility DtE for System Direct-to-Earth support Mission (DtE) (EJSM). to delivery Wehard- a of show or prospective that science outer software data as task-specific from planet a piggy-back additions, mission,omni-directional on SKA such transmission nominal can as from science spacecraft o the operations at joint a with distance ESA-NASA operations, practically up no might to special be 10 AU. extremely Such valuable the means support, of especially during enhancing short science mission-critical return and e JIVE, Oudehoogeveensedijk 4, Dwingeloo, 7991PD, The Netherlands Abstract.  1. Introduction Radio astronomythroughout the and entire history of space spacea flights, for century. more One exploration than might half recallthe are the rocket detection of placed intertwined the inby upper orbit the stage venerable the of Lovell first telescopeOctober at artificial 1957 Jodrell satellite, as Bank an Sputnik, in example theexploration of UK of radio in astronomy Space. support Twelve to yearsa the later, high in day July forturned the 1969, Parkes it to Radio was be Telescope the inhistorical only Australia TV which Earth-based translation facility ofsteps able the on to the Apollo-11 receive Moon. crew the allow The us making to format first provide ofeficial a this comprehensive interactions contribution review between of does radio mutuallyof not ben- space. astronomy But and without exploration tinue any in doubts, these the interactions future,here will during aims con- the at SKA assessinging era. the facility The potential for study of Direct-to-Earth presented deep space the delivery missions. Usually, SKA of these missions as science areeither equipped a data high-gain with receiv- from antennas forence broad-band data transmission to of Earth sci- fly-by or spacecraft. In operate both withprospective cases, data missions the measured relay data in viaand rate tens higher. orbiters However, of as of or a modern kilobits back-upschemes to and per and the second recovery nominal operations data during delivery andbehaviour after of non-nominal a spacecraft (e.g.streams in of safe-mode), merely a bits receiptdemonstrated of per in data second the are Huygens extremely missiondetection valuable. on of As the Titan in Probes 2005, carrierbiting Cassini just tone spacecraft a transmitted (eavesdropping, toward in thestantial e or- impact onregime the of overall eavesdropping outcomethrough of of a usually low-directivity the antenna is weak mission. extremelyble di signal This at all transmitted even for themunication most facilities. sensitive dedicated The deep overwhelmingly space superior com- sensitivity SKADS C S.A. Torchinsky, A. van Ardenne, T. van4-6 den November Brink-Havinga, 2009, A.J.J. Chˆateaude Limelette, van Belgium Es, A.J. Faulkner (eds.) W C PoS(SKADS 2009)006 / 6 20 1.84 1,84 SEFD, J 3 20 0.92 1.23 SEFD, J 84 11 1.6 2.15 SEFD, J UHF-band S - band X-band ). dB ective area of the Square Kilometre Array ff 0 AU: elsberg C tracking facility is discussed by Jones (2004). . / Name SKA - SKA - ff Arecibo 1 or 0 10 E = aperture array − parabolic dishes tr 0 . G 5 The two primary communication resources are the trans- The huge e will be multiplied on 0.75. = tr P 4. The probe’sgain antenna is omnidirectional (i.e., the antenna 5. The system equivalentTable 1. flux densities (SEFD) are given in Table 1: System noise temperature and SEFD of three radio telescopes mitted power and thecation channel systems, bandwidth. one In many ofthe communi- these other. Therefore, resources the is communicationas systems more either are power-limited precious classified or than bandwidth-limited. Insystems, power-limited coding schemes are used toof save bandwidth, power at whereas the in expense ficient band-limited modulation systems techniques spectrally canat ef- be the used expense of to power.nication save We systems bandwidth think it that is indesign the deep and available space operational power commu- restrictions. which Hence,be defines classified these main as systems power-limited. may which radio telescopes are muchDSN facilities. more In sensitive all than the standard casesat above, relatively the low probes frequencies, will broadcast certainlymaking not them higher suitable than targets 8well for GHz, established radio in telescopes radio operating astronomy at practice GHz bands. located practically anywhere in theSKA Solar System. as The a case S for Below we present estimates of SKAconsiderations DtE for options the under probe’s various signal strength and modulation. 2. Radio link power budget We analyse the SKAfollowing assumptions: DtE communication scheme under the 1. TheR distance from Earth to a transmitting probe is (SKA) would enable DtE communication from a distant S 2. The communication ison conducted at the UHF-, standard S- frequenciestively. and of X-bands 400, 2.3 and3. 8.4 The MHz, probe respec- transmitter power isW. considered in the range 1-25% 10 of this power islated spent on carrier the frequency transmission signal, of so the in unmodu- the following calculations 5 W). < C. Usually, / C. Even if the role of the / ering the probe’s data onboard ff culties). C in the Cassini-Huygens mission), the relay / ffi C. The Cassini–Huygens mission is an example of / cult due to a considerable attenuation of the signal in ` ere et al. 2008), ExoMars. Another class of missions C and not necessarily toward the Earth. The probe’s C is performed by an indispensable probe’s carrier (e.g. / ffi / 10 bar. Communication from such the probe is particu- An alternative to the traditional relay scheme is a Direct-to- Recently major space agencies began to assess design op- In the traditional relay scheme, a planetary probe is ∼ include deep-diving probesplanets, into e.g. dense the atmospheresCosmic of mission Vision giant Kronos programme (Marty proposedaims et to under study al. the the Saturn 2008). atmosphereof This in-situ ESA’s at mission the pressure level larly di Such a low power linkvide makes a it down-link practically to impossible Earthisting from to DSN-style the pro- facilities probe or usingscopes presently any (beyond operational of detecting the radio ex- a tele- considerable carrier di signal, and even this with Earth (DtE) communication method.advantages, It especially brings in the in case aplanetary of number communicating probes of data from – landers,face vehicles, penetrators, etc. atmosphere DtE makes andcomponent unnecessary sur- an of extremely a costly mission,relay S a relay S as the Cassini S scheme imposes severe ballistictional restrictions limitations, and in other particular,broadcast on opera- from timing and the duration probe.sponsible of for All a the in very considerable all,of fraction scientific of the the data relay cost delivered of from schemethe one the is bit relay probe re- to scheme Earth. enables Ofto considerably course, be higher delivered amount from ofby the data DtE. probe But to DtE Earthscheme, than can especially can be during be considered criticalprogramme. provided as events a of a backup probe’s to science the relay tions for the next generationare planetary expected probes. to These missions reacherations their around destinations and 2020Cosmic begin or in-situ Vision later. op- programme, Inmulti-spacecraft a missions, with Europe, probes number going under to ofand Titan (TandEM TSSM the proposals study, Coustenis et ESA’s call al. 2008),(Laplace for Europa and and Ganymede EJSMChassefi study, Blanc et al. 2008), Venus (EVE, dense atmosphere. Since attenuation grows withprobe frequency, the broadcasts at frequencies below 1 GHz – the range, at such the scheme requiresthe relay bu S such the communication scheme: thenicated data Huygens from Probe the commu- descentthe phase of Cassini the spacecraft. mission As tomission, Titan was via an demonstrated ad-hoc by direct thenal receipt Huygens by of Earth-based the radioable Huygens asset telescopes and carrier turned contributed sig- to out(Lebreton the et to overall al. success be 2005). of the a mission valu- equipped with a low-gain antennarelay roughly S oriented toward the transmitter power is limited to several watts (typically 44serious restrictions on the missiongrow rapidly operations. with The the restrictions increase ofThese the restrictions distance are to the particularly spacecraft. severeetary for probes. short-living In plan- most cases,housekeeping planetary telemetry probes data relay via science orbiters and or flyby S P.A. Fridman et al.: SKA as a Direct-to-Earth Data Acquisition Facility , , . . . = 2 5 PoS(SKADS 2009)006 f 4) − -th M (8) m ∆ = 2 sec) AU m / ) 10 W M 5 α , / log ( = = = M RW = cos orthogonal are variable W · : , .... k k 5 2 processing of as a function 2 α , , BER gives the trans- 1 1 and BPSK. it is possible to 10 . Fig. 5 demon- T = 5 5 / − = and = − = k M power 10 M tr tr m = 10 = , frequency shift keying G e f f G coherent T = A BER , SNR erent orthogonal signals, ≤ is the signal-to-noise ratio bit RW t ff 0 AU, ≤ . BER power , : 5 for uncoded BPSK the nec- is the zenith angle of the target ] SNR RW t T / is transmitted on one of the ) = 5 α (for aperture array, S-band) and SNR f bandwidth expansion − k R ∆ K = 10 , antenna gain power m is the duration of a symbol. For ex- tr must be equal to 9.6 dB (or 9.099). bit 40 P + − = T 5 c ) where − f T SNR = × 1. α ( , 10 for the value ( is called π = T = 5, there are 32 di 2 sys corresponds to one of the / tr cos as a parameter. BER W e f f power T BER 1 , / = (for parabolic dishes, X-band), distance k , A G as parameter. α is the transmission rate. cos[2 5 , , . Theoretically, by increasing bit is the duration of signal transmission per 1 bit and − k tr = K R ective area of SKA as of the plane phase array is A W RW bit M , SNR G ff / bit 10 T f tr = ) orthogonal signals can be calculated using the follow- / 60 T 75 = ective transmission rate is SNR . ∆ ) G 1 k M t = ff 3 , ( 2 2 = bit tr = m To obtain In the following example, the M-ary Table 2 contains the values of transmission rate (bit Quadriphase shift keying (M-ary phase modulation, M Fig. 2 shows bit error probabilities as function of the trans- In reality, the transmission antenna gain may significantly The e The probability of bit error for the = s = P log tr sys M BER P Therefore, the ratio for uncoded BPSK and the SKA core, per bit, RW , denoted byBPSK, QPSK, but has the equivalent the bitBPSK . same rate is bit-error two performance times higher as than for mission rate at S-bandfrom calculated Tables 1, for the several distance radio telescopes SNR vary. Fig. 3 shows BERSKA as and a function of transmission rate for proportional to source. Fig. 4 shows BER asfor a SKA function and of the transmission rate essary mission rate achievableof for a given strates how the transmissionAU) rate for depends the of the radio distance telescopes (in in Tables, and signals which modulate carrier signals. (MFSK) is used: each symbolnary corresponding sequence to of a particular the bi- length where ample, for The transmitter power parameters. 3.2. MFSK Another option for increasing thethe transmission rate use is based of on M-aryof the orthogonal length signals. Every binary sequence each at its own frequency.The The e total bandwidth is T frequencies during an interval The ratio (2 reach the Shannon’s limit. (6) (2) (1) (7) (3) and a F Shannon . ∆ K is the dura- / J b , T 0 and the cor- 23 − , . ) (4) ) ) is the transmission → power 10 F bit , we get 693 or, in decibels , C ) . 1) (5) RW ∆ × is called the C 0 F dt RW − power F bit 2 = SNR ∆ t bit 2 23 SNR F − . ∆ / = ∆ 1 e = / × C C SNR e RW b ∞ = SNR 2 x SNR 2 Z 6 dB (uncoded binary modu- T 1 (2 . k p + + P.A. Fridman et al.: SKA as a Direct-to-Earth Data Acquisition Facility 45 9 , log π , the binary phase-shift-keying ( F is used: 5 2 C ff 1 (1 (1 Q ∆ − = e sys power 2 2 √ = A 75 W and the radio telescopes from = . = kT bit tr 0 log = log power 2 as: · G bit bit ) R SNR F F tr 5 x π ( BPSK P = , 4 SNR = SNR Q power = ∆ = ∆ SNR SNR bit tr = BER P C C P decreases the ratio ( SNR is the signal-to-noise ratio per bit, 6 dB. This value of SNR power . bit bit 1 1 and − = SNR = SNR SNR tr bit G . This formula sets the limit on transmission rate but not on where tion of signal transmission per 1rate. bit Using and this newrate notation equal and to making the the channel transmission capacity, bit and SNR given channel where When limit In practice, it isa not bit possible error to probability reach of the 10 Shannon limit. For modulation requires lation). Therefore, for this case, theexistence Shannon of limit a promises the theoretical improvementuse of of 11.2 special dB coding through (see the section 4). 3.1. BPSK and QPSK A digital modulationis scheme widely with used phase-shift in1990). keying space It (PSK) communication provides systems bothmum (Yuen a bandwidth. et For low the al. bit-error-rate case(BPSK), (BER) of BER the can and binary be mini- estimated phase-shift as keying follows: Fig. 1 shows the potential channelAU, capacity for the distance 5.0 Tables 1. the error probability. In digitalof communication, merit rather another than figure 3. Bit error probability and transmission rate The signal-to-noise ratio (SNR)bandwidth for equal the to 1 received Hz signal is in the The potential transmission bitShannon’s rate formula can for be the estimated capacityadditive using of white the a Gaussian channel noise perturbed with by the bandwidth responding value PoS(SKADS 2009)006 = < B sec) bit / P in AU will be R , antenna bit SNR erent M is tr ff P at zenith angle, 5 2 dB (instead SNR , and the SKA . − − 5 is achieved with 0 α − 5 10 , − 2 = 10 < m 10 = ) B bit = α 2 code. Thus the error- P MFSK for di ( / for uncoded BPSK). BER SNR cos 59 dB), turbo code (thresh- BER · . dB 9 5 6 . 10 as a function of distance = 2) and multiple iterations (Sklar / 5 1 = . The transmitter power − thr = , noncoherent : a combination of parallel concatena- ). The coding gain obtained with this 10 AU e f f bit 5 A = = 7 dB), pragmatic Shannon limit (threshold Shannon limit . SNR 0 and BPSK (9 . This means that BER 6 dB). . 2 dB) and theoretical Shannon limit (threshold are the parameters. = 2 code rate). For binary modulation and . 1 / dB dB turbo codes 0 α − 6 7 thr . , distance , = = 2 ≈ K bit and pragmatic = thr thr , , 40 tr a bit bit bit G = SNR Today, the largest part of the promised coding gain can be An analytical expression of BER for a particular scheme of Fig. 10 demonstrates four curves: the dependance of trans- Table 3 contains the values of transmission rate (bit Application of channel coding (especially with turbo 5 − 7 dB (for 1 sys . SNR SNR shown in Fig. 8. codes) makes this advantagebe of also MFSK mentioned lessful that obvious. for the It VLBI wide where must astrometric spectrum the measurements. probe’s of signal MFSK may be is used use- for radio- 4. Coding gain A considerable gain in BERing performance special can be coding achievedConsultative of us- Commmittee the for bithas Space recommended stream Data the before error System controlcessfully modulator. (CCSDS) standards applied The which in many were space suc- missions.of Serial Read-Solomon concatenation outer code (255,223)ing and convolutional (inner cod- code) wasVoyager, used Giotto, by Galileo both NASAcoding and is ESA (missions 7 whereas the bitmission error rate for probability uncoded as a function of the trans- SNR reached with tion of binary convolutional coders withtive interleaving decoding and itera- (Divsalar &Habinc Pollara et 1995, Dolinar al.ing et. 1998, provides al Heegard bit 1998, dB error & of performance Wicker the within 1999). Shannonby a Turbo limit. CCSDS few cod- The show tenths documents that(Habinc of 1998). recently future a published missions will use turbo coding turbo code is not known. Manymade numeric to simulations obtain have such been estimates.ities Fig. 9 for shows bit-error turbo probabil- code (rate 2001). The Shannoncapacity limit of is the approachedShannon’s but channel limit). the tends normalized toThe zero following threshold (as value of in turboused the code further: for case the bit-error of0 probability the 10 of -1.6 dB) isperformance often of used turbo for codeShannon a is limit rate (Sklar within 2001). 1 0.5 dB of the pragmatic mission rate for for the SKA core,BPSK S-band. The (threshold curves correspond to uncoded old T in S-band for turbo-codedcore BPSK, (aperture array), gain ) k = ≥ α (9) , ( η × (10) dy M ] cos 1 75 and 2] . · − / 0 5 M 2 · and ) ) , additional processing 10 tr 5 K dt · − P 2 FSK 2 t , 5 . 70 − 10 1 e = = y = symbol Z −∞ sys T π e f f . 2 1 A × noncoherent SNR √ , each signal transmits ) 1)] · erent M is shown in Fig. ( sec) for uncoded BPSK and 1 T / 2 ◦ ◦ ff − + ◦ ◦ − × 0 0 M ; X-band (parabolic dishes), n q n 60 30 ( ( K [1 1 = = / , transmitter power = = − + ∞ α α n α α y 40 −∞ power ( FSK AU 1) , Z = − − 5 [ π ( = S-band, aperture array sys 1 2 1 SNR 1 1.0 3.0 5.0 10.0 X-band, parabolic dishes − 1.274.03 3.82 12.09 6.37 20.15 12.74 40.30 T UHF-band, aperture array − symbol 12.74 38.23 63.72 127.43 √ MFSK for di exp , n X 1.0 3.0 5.01.0 10.0 3.0 5.0 10.0 1.0 3.0 5.0 10.0 1.0 3.0 5.0 10.0 M = 0.73 2.197.28 3.64 21.85 36.41 7.28 72.82 2.216.98 6.62 20.94 11.04 34.90 22.07 1.27 69.80 4.03 3.82 12.09 6.37 20.15 12.74 40.30 2.30 6.91 11.51 23.03 2.558.06 7.65 24.18 12.74 40.30 25.49 80.59 8 22.07 66.22 110.36 220.72 12.74 38.23 63.72 127.43 25.49 76.46 127.43 254.86 × · . 1 0 1 1 − 1 − = FSK k dB , − dB dB − nS NR k , distance 2 k dB η 0 5 dB dB dB dB dB 5 2 k 10 − 2 dB dB dB dB dB dB , ; UHF-band (aperture array), ,W − 5 0 2 5 0 5 0 10 5 0 tr = = tr ,W 10 10 10 K coherent = ,W ,W ,W = = = tr 10 P symbol G tr tr ======tr tr tr = tr = = = orthogonal signals is calculated using the following P exp[ tr tr P P P 60 G G tr tr tr tr tr tr tr = k G NC C tr tr tr G G 1 2 G G G G G G G = G G G SNR 1 + = FSK FSK sys , , n BER T The probability of bit error for the M , , 6 2 BER BER . P P 3-dB loss in the Earthatmosphere ionosphere, are interplanetary taken medium into and account. Jupiter 0 The bit error probability asfor a uncoded function of the transmission rate where 8. MFSK requires aresource larger is bandwidth less important than than an the BPSK transmitter power. and this ing expression (Proakis 2001, p. 259): bit simultaneously. As shownary in frequency shift Fig. keying (MFSK) 6, givesrate that a higher than the transmission an uncoded uncoded M- BPSK for a fixed BER of expression (Proakis 2001, p. 310): the SKA core, form S-band (aperture array) 46Table 2: The DtE transmission rate (bit antenna gain P.A. Fridman et al.: SKA as a Direct-to-Earth Data Acquisition Facility ,

= PoS(SKADS 2009)006 K , η 70 0 = = sys α T and antenna gain W ; X-band (parabolic 5 London − / 75 . 10 0 · , zenith angle 0 = . 2 sec) at S-band for the SKA 1 / m = 5 http://track.sfo.jaxa. BER tr Dordrecht 10 / P · S-band X-band 5 . UHF-band 1 ; UHF-band (aperture array), = K 1.0 3.0 5.0 10.0 1.0 3.0 5.0 10.0 4.93 14.80 24.67 49.345 2.47 7.40 12.34 24.68 e f f 19.7410.07 59.21 30.21 98.69 50.35 197.38 100.70 9.8695.035 29.61 15.11 49.35 25.18 98.69 50.35 60 1.0 3.0 5.0 10.0 A 5.642.88 16.921.41 28.20 8.63 4.23 14.39 56.40 7.05 28.77 14.1 = sys AU AU AU AU AU AU T , transmitter power , AU AU 0 0 AU 0 0 ,W . . ,W . . 6 K 10 . 10 0 0 tr 5 7 tr 7 5 . . ,W 0 P 10 P 5 7 , turbo-coded BPSK and = tr = = = 40 = = = P = ` ere E., Korablev O., Imamura T., et al. 2009, European = = R R R R = R R dB η R R R 0 sys T = , sion to EuropaVision and Programme, Exp. the Astronomy, Jupiter 23, 849 System for ESA’s Cosmic Venus Explorer (EVE): anAstronomy, 23, in-situ 741 mission to Venus, Exp. Titan and Enceladus mission, Exp. Astronomy, 23, 893 Space Communications, TDA ProgressPropulsion Report Laboratory, Pasadena, 42-120, California, Jet Feb.pp. 15, 29-39. 1995, and Space Communications, jp/spaceops98/paper98/track5/5e011.pdf Core andTelemetry Devices Channel Coding Standard, Implementingftp://ftp.estec.esa.nl/pub/vhdl/doc/Turbo.pdf the Updated CCSDS Academic Publishers, Boston with theS. Square Rawlings, Elsevier, p. Kilometre 1537 Array, eds.ing C. of the Huygens Carilli probe on Titan, and Nature 438, 758 ploring the depths of Saturnthrough with an probes international and mission, remote Exp. sensing Astronomy, 23, 947 McGraw-Hill 8 tr . dishes), additional 3-dB loss in EarthJupiter atmosphere ionosphere, are interplanetary taken medium into and account. 0 References Blanc M., Alibert Y., Atreya S.K. et al., 2009, Laplace: a mis- Chassefi Coustenis A., Atreya S.K., Balint T.Divsalar et S. al., 2009, and TandEM: Pollara F. 1995, Turbo Codes forDolinar Deep- S., Divsalar D. and Pollara F. 1998Habinc S. Turbo et Codes al. 1998, Development Plan for Turbo Encoder Heegard, C. and Wicker, S. B., 1999, Turbo coding, Kluwer Table 4: The DtE transmission rate (bit core (aperture array), Jones D. 2004, Spacecraft tracking with the SKA, in Science Lebreton J.-P. et al., 2005, An overview of the descent and land- Marty B., Guillot T., Coustenis A. et al., 2009, Kronos:Proakis, ex- J. G, 2001, Digital communications. 4th ed. Boston G , = AU 100 5 e f f = ∼ A studies of , distance K in situ 40 . C with a transmitter tr / = G sys T , ◦ ◦ 8 sec) in S-band for turbo-coded ◦ 1 GHz (see e.g. Marty et al. . / 0 0 60 30 ∼ = P.A. Fridman et al.: SKA as a Direct-to-Earth Data Acquisition Facility 47 = = = η α α α 0 dB. = 75 and antenna gain 1.0 3.0 5.01.0 10.0 3.0 5.0 10.0 1.0 3.0 5.0 10.0 . 9.87 29.61 49.35 98.69 and the SKA core (aperture array), 31.2198.69 93.63 296.07 156.04 493.45 312.09 986.90 17.0954.06 51.28 162.16 85.47 270.27 170.94 540.55 19.74 59.21 98.69 197.38 0 170.94 512.81 854.68 1709.00 62.417197.38 187.251 312.09 592.14 624.17 986.90 1974.00 ers instantaneous frequency coverage from 10 GHz, unlike traditional DSN-style fa- · 5 ff − zenith angle, tr ∼ P − 10 α dB dB dB dB dB dB dB dB dB , ) can provide for the transmission rate of C at the distance of 5 AU, transmitter power equal = 2 / 5 0 5 0 0 5 2 10 10 10 ,W ,W ,W m tr tr tr m ======) = = = P P P α tr tr tr tr tr tr 5 tr tr tr ( BER G G G G G G G G G 10 · cos We note that MFSK is also convenient for VLBI tracking Our main conclusion is as follows: The SKA core will be able to receive digital information In addition to the high sensitivity, illustrated by our calcu- · 100 MHz to 5 5 . power of 5 W from asion distance of rate up of to 10 several AUgain, with tens the see of transmis- Table bps 4. using BFSK and turbo-coding 2008). In this non-standardalso communication might become regime, an the indispensable asset. SKA since it is bettermono-chromatic suited carrier. for group delay measurements than a from a planetary probe or interplanetary S bps from a S lations, the SKA o ∼ atmospheres of giant planets (e.g. Jupiter,munication Saturn) at require frequencies com- below 5 W and antenna gain Gt 10 5. Conclusions The analysis describedpotential in of this the memovalue, SKA indicates we a as note significant GHz a that (considered DtE at to facility. the betivity As close communication of to the SKA), frequency the the benchmark of(1 band turbo-coded 2.3 of DtE maximum link sensi- with the SKA core cilities able to operatequency within bands. relatively Such narrow the dedicatedtant frequency fre- asset agility for supporting might communication be fromas an planetary a probes impor- mission back-up,Huygens e.g. up-link similar communication to tothe “eavesdropping” the non-standard on Cassini the down-link spacecraft(Lebreton at at et the al. 2005). frequency Planetary of probes 2040 for MHz transmitter power Table 3: The DtE transmission rateBPSK, (bit PoS(SKADS= 2009)006 tr G , W 75 . 3 = , transmitter an- tr W P , 75 . AU 3 0 . = 5 tr = P , R AU 0 . 5 = R Fig. 2: The bit errorfor probability radio telescopes as in a Table 1, function BPSK, of the transmission rate Fig. 3: The bit errorfor probability the as SKA-core, a BPSK, functiontenna of gain the is transmission the rate parameter. 1. Specifications.pdf http://www.skatelescope. SKA the Square Kilometre Array, org/PDF/Preliminary NJ, p.497 and Space Communications, Proc. IEEE,1990, vol. p. 78, 1250 n. 7., July Fig. 1: The channelradio capacity telescopes from as Table a 1. function of bandwidth for several Schilizzi R.T. et al., 2007, Preliminary Specifications for Sklar, B., 2001, Digital communications, Prentice-Hall, Inc., Yuen, J. H. et al., 1990, Modulation and Coding for Satellite 48 P.A. Fridman et al.: SKA as a Direct-to-Earth Data Acquisition Facility PoS(SKADS 2009)006 for uncoded bit SNR MFSK with the symbol set size as the parameter. coherent Fig. 6: The bitMFSK error probability (multiple as FSK) aBPSK function with curve of is the also plotted symbol for set comparison. size is the parameter; Fig. 7: The bit errorfor probability uncoded as a function of the transmission rate = tr P , for 5 − , zenith angle is 10 W = 75 . 3 BER = tr P , P.A. Fridman et al.: SKA as a Direct-to-Earth Data Acquisition Facility 49 AU 0 . 5 = R 1. = tr G , W 75 . 3 Fig. 5: Theradio transmission telescopes rate in as Table a 1 function and of constant distance in AU for Fig. 4: The bit errorfor probability the as SKA-core, a BPSK, functionthe of parameter. the transmission rate PoS(SKADS 2009)006 . 5 − 10 = BER , 1 = tr G , W 75 . 3 = tr P Fig. 10: The transmissionBPSK, rate turbo as a code, function pragmaticcore, of and distance theoretical for Shannon uncoded limits: SKA for turbo bit SNR MFSK with the symbol set size as the pa- noncoherent 2) and multiple iterations. The Shannon limit of -1.6 dB / code (rate 1 is approached. Fig. 9: The bit-error-performance as a function of Fig. 8: The bit errorfor probability uncoded as a functionrameter. of the transmission rate 50 P.A. Fridman et al.: SKA as a Direct-to-Earth Data Acquisition Facility