L.A.R.S. - Mobile Ground Station For CubeSat Operations .

2y ago
8 Views
2 Downloads
617.63 KB
7 Pages
Last View : 2d ago
Last Download : 2m ago
Upload by : Kairi Hasson
Transcription

70th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019.Copyright 2019 by the International Astronautical Federation (IAF). All rights reserved.IAC-19.B4.3.9x50773L.A.R.S. - Mobile ground station for CubeSat operationsSebastian Fexer*, Lars-Christian HauerInstitute of Space Systems, German Aerospace Center (DLR), Robert-Hooke-Str. 7, 28359 Bremen, Germany,E-Mail: sebastian.fexer@dlr.de; lars-christian.hauer@dlr.de* Corresponding AuthorAbstractMany of the CubeSat and SmallSat operators in the academic field suffer from the fact that the ground stationoperations for Telemetry, Tracking and Control of their satellites is often quite challenging to maintain for theduration of a mission.The DLR Institute of Space Systems in Bremen, Germany, presents a remote controllable mobile ground stationfor CubeSat/SmallSat operations which completely fits inside a 20 ft shipping container. It operates in theVHF/UHF amateur radio frequency bands (144-146 MHz and 430-440 MHz) and is prepared for S band (2400-2450MHz) using fully redundant state-of-the-art software-defined-radio transceivers. With the ground station presented inthis paper, automated satellite operations with different satellites can be achieved.Tests with different SmallSats and CubeSats have demonstrated promising results of great performance with highsensitivity in reception, even at low elevations. Currently, the ground station is located for testing purposes at theJade Weser Airport in Wilhelmshaven, Germany. In the near future it is planned to move the station to a northernlocation to achieve optimal contact opportunities to connect and remain in contact for longer durations in polarsatellite orbits.Keywords: (maximum 6 keywords) CubeSat; SmallSat; ground stationAcronyms/AbbreviationsAutomatic Dependent Surveillance - Broadcast(ADS-B)Automatic Identification System (AIS)Direct Down Conversion (DDC)Inter frequency (IF)Low earth orbit (LEO)Low-frequency Arctic Radio Station (L.A.R.S.)Power amplifier (PA)Power Supply Unit (PSU)Radio Frequency (RF)Receiver (RX)Software defined radio (SDR)Telemetry, Tracking & Control (TT&C)Transceiver (TRX)Two-line element (TLE)IAC-19-B4.3.9x50773Ultra High Frequency (UHF)Uninterruptable Power Supply (UPS)Universal Time, Coordinated (UTC)Very High Frequency (VHF)Weak Signal Propagation Reporter (WSPR)Page 1 of 7

70th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019.Copyright 2019 by the International Astronautical Federation (IAF). All rights reserved.1. Introduction and backgroundThe mobile ground station L.A.R.S. (Low-frequencyArctic Radio Station) has been initially designed toassist in TT&C of the AISat Mission of the DLRInstitute of Space Systems in Bremen [1]. The groundstation is able to operate in the VHF and UHF amateurradio bands and is prepared for S Band.Besides the rooftop mounted VHF/UHF groundstation at the Institute of Space Systems, there was thewish for an additional automated ground station.Moreover, in the exchange with other CubeSat operatorssuch as universities, it seemed often to be a challenge tomaintain operations for the duration of a mission.Especially if an (academic) organisation or university isdeveloping and launching its first CubeSat, knowledgeand experience in radio equipment and ground stationantennas has to be gained, e.g. by the help of a localradio amateur group. Also the availability of thenecessary facilities to implement a ground station (withan exposed and quiet place for antennas, space for cablerouting, with radio room) has to be first established.Further challenges can evolve due to staff related issueslike student fluctuation or unusual working times.Additionally, the site locations are mostly fixed andclose to the satellite operators’ premises (e.g. auniversity). This might not be always the optimum sitefor the used satellite orbit (e.g. close to the equator forISS deployed CubeSats or near the polar regions forsuch orbits).Below, a closer look is taken at the available passes ofthe Danish polar orbiting 1U CubeSat AAUSAT4 [2] atdifferent locations.Table 1 shows as an example ideal passes onSeptember 16th, 2019 with the maximum elevation for aground station located in Bremen, Germany. Onlypasses with an elevation of α 15 deg. are shown.In contrast, Table 2 depicts the available passes of thissatellite at the same day in Thule, Greenland.It can be seen that three times more passes are availablewhich leads to significantly higher available downlinkamount per day. Especially, if the remotely locatedground station is used in addition to the fixed one.Table 2. Available passes of AAUSAT4 on 16.09.19 inThule, Greenland with the maximum 516:1322.417:4949.419:2378.420.5847.222:3240.32. Description of the L.A.R.S. systemIn the subsequent paragraphs, the different parts ofthe system will be described in more detail. The focuswill especially be placed on details regarding a robustconcept, which can outstand harsh environment andoperate with reduced available service, sincemaintenance personnel frequently visiting the facilitywill not be always available at a remote arctic location.E.g. a suitable antenna concept without moving partshad to be chosen to minimize maintenance effort.2.1 The container – facility and utilitiesA standard 20 ft long shipping container is used tohouse the ground station (as shown in Fig. 1). Itsinterior is split into two areas: a storage and workingroom, and the utilities room containing the servers andRF hardware (displayed in Fig. 2). The latter ones areeach mounted inside a vibration-damped rack assembly.Table 1. Available passes of AAUSAT4 on 16.09.19 atthe Bremen ground station with the maximum elevationUTCα/deg.11:3348.213:0719.122:2377Fig 1. Exterior view of the L.A.R.S.ground stationIAC-19-B4.3.9x50773Page 2 of 7

70th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019.Copyright 2019 by the International Astronautical Federation (IAF). All rights reserved.Fig 2. View from the working area into the utilityroomThe electric power system of the containerguarantees a 230 V/50 Hz line voltage. All criticalcomponents are connected to a fully-redundant UPSsystem. A 10 kW transformer (115 V/230 V) at theelectric main line can be joint up in circuit, if thecontainer is placed in a country with a predominant linevoltage of 115 V.To ensure moderate room temperatures inside, aclimate concept has been implemented to includeinsulation, two-zone-ventilation and a convectionheating. The temperatures in the critical areas arecontinuously monitored, logged and the data can beaccessed via web interface. Furthermore, the electriccurrent drawn by the heater unit is logged to have theopportunity to detect anomalies.The roof of the container is equipped with anantenna mounting and support rack to hold the fourmain antennas as well as secondary antennas like shortwave wires in place. It also offers space for futureextensions. For container transport and relocation it canbe detached and stowed inside the container.Fig 3. Remote controlled user terminal with applicationsoftwareTo provide convenient access to all functions, aremote controlled user terminal has been designed.Utilizing three touch-sensitive screens, all functions andstatuses can be accessed. The graphical user interface isinspired by industrial control panels and henceoptimized for operation via touch screen. A moredetailed insight into the software is given in section 1.5.2.3 Antenna system for TT&CA trade-off has shown that an “eggbeater” antenna[3] (displayed in Fig. 1, mounted on top of the masts)can be a good choice for satellites in LEO orbit in thegiven frequency bands of VHF and UHF. This type ofantenna has a cardioid shaped radiation pattern (see Fig.4). It features a low wind loading and furthermore hasno moving parts (e.g. a rotator) which can be critical touse and maintain under arctic environment. Moreover, itoffers circular polarization.2.2 Computer hardware and remote controlThe ground station is equipped with a fullyredundant server system for data storage, controlling theRF hardware and the coding/decoding of the satellitesignals. Housekeeping such as temperature data- andheater status logging or CCTV camera control isrealized with a Raspberry Pi based system.The communication to the outside world ismaintained by a permanent VPN tunnel to the institute’spremises in Bremen, Germany.Fig 4. Cardioid shaped antenna radiation pattern of aneggbeater antenna (normalized)IAC-19-B4.3.9x50773Page 3 of 7

70th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019.Copyright 2019 by the International Astronautical Federation (IAF). All rights reserved.Fig 5. UHF antenna attached to test boom during ice test.The ice layer has an approximately height of 13 cm (r.)The eggbeater antenna consists of two loops, eachone wavelength in circumference, shifted by 90 degreeto each other. The required circular polarization isachieved by a phase difference (e.g. via phasing lines)between the feed of the two loops.The added ground plane can be either made of metalwires or from a solid sheet and provides the desiredunidirectional antenna pattern. The distance between theantenna and the ground plane is responsible for theshape of the radiation pattern and the maximum gain,which can be around approximately 4 to 6 dBi [4].The eggbeater antennas used in this project have a peakgain of approximately 5.5 dBi.For redundancy reasons, two antennas for each of theamateur frequency bands are used.Extensive tests were conducted in low temperaturesand the resulting side effects were studied, such as snowand ice affecting the antenna’s performance. Theantennas have been prepared with different layers ofsnow and ice of different height and extent and weresubsequently measured using a network analyser. Fig. 5shows an UHF antenna during a test with ice coverageof 13 cm. The measurement results are illustrated inFig. 6.Fig. 7. RF rack. From top to bottom: redundant transceivers, switching matrix, VHF/UHF/S Band frontends,PSUThe tests have shown that light to medium snowcoverage has almost no influence on the performance ofthe input reflection coefficient/S-Parameter S11. Underconditions with heavy icing, a right shift towards higherfrequencies could be observed. A satisfying inputreflection coefficient (S11 -10 dB) at the desiredfrequencies could not be achieved any longer. As aconsequence, the antennas with a solid metal sheetground plane have been replaced by a version withmetal wires, which prevents excessive accumulation ofsnow and ice.2.4 The hardware of the RF systemThe complete RF section of the container is installedin a dedicated 19 inch rack. In Fig. 7 the partresponsible for the satellite section is shown.Fig 6. Measured input reflection coefficient S11 of UHFeggbeater antennas for different snow/ice conditionsIAC-19-B4.3.9x50773Page 4 of 7

70th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019.Copyright 2019 by the International Astronautical Federation (IAF). All rights reserved.Fig 8. Simplified block structure of the VHF segment of the RF unit of the L.A.R.S. ground station2.4.1RF frontendThe RF frontend is divided into three independentpaths with almost identical block structure for eachfrequency band (VHF/UHF/S Band).In Fig. 8, a (simplified) block structure of the VHFbranch is shown. Each branch is connected to aswitching matrix which is responsible for the correctdistribution of the RX/TX IF signals to one of the twotransceivers.In the following, the signal path will be explainedfor the illustrated VHF branch as an example.Looking at the receiving signal path as seen fromthe antenna side, a bank of surge protectors is installedto guard the following section from possibleovervoltage. A switching unit allows to choose betweenthe two redundant antennas, followed by a RF switchfor RX/TX, a bandpass filter for preselection and a lownoise amplifier.The subsequent two-way transverter block isresponsible for the down conversion of the signaltowards the IF, which is located in the short wave band.Finally, the switching matrix (not included in the figure)routes the signal to the RX input of one of thetransceivers. These will be described further in section2.4.2.In transmitting mode, the IF signal, modulated by thetransceiver and routed through the switching matrix,enters the VHF branch at the transverter input. Therethe signal is being upconverted and enters the poweramplifier stage. To suppress harmonics, a low pass filteris integrated in the PA section. This is especiallyimportant, since the third harmonic falls into the UHFamateur band.To avoid mismatching at the PA output which could forexample occur in the case of an antenna failure andpossibly lead to damage, an isolator is connectedIAC-19-B4.3.9x50773downstream. Behind the RX/TX switch, the antennaselector, and the surge protectors, the antennas areconnected.The maximum PA output power of the VHF and UHFbranch is 100 W each, S band offers 10 W.2.4.2Transceiver system and IT interfaceAs the last stage in the RF chain, two redundanttransceivers are connected to the switching matrix withtheir respective IF outputs. These commercial all-digitalshortwave radios are based on the direct downconversion technology and inhibit some specialmodifications for their application in the ground station.Instead of using hardware modems with limitedflexibility and problematic interchangeability (due toremote operations), the approach of softwaremodulation/demodulation was preferred.The transmission of the baseband signals between thetransceiver and the server system is realized via simpleaudio connection. In each server system, one highquality sound card is installed for this purpose.This method emerged as a quasi-standard in the amateurradio community and a lot of free and open-sourcesoftware is available for signal reception. For differentprotocols or uplink transmission for a mission, theappropriate software has to be provided by the satelliteoperator.2.5 Software and reception systemThe whole system is managed by a proprietarysoftware, consisting of a driver on the server side, andthe user interface on the remote user terminal side. Itacts as an interface between the user and the hardware,which is controlled by different bus systems. Thetransceivers are each controlled via USB, the RFhardware such as the switching matrices and amplifiers,as well as the diagnostic system via CAN bus.Page 5 of 7

70th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019.Copyright 2019 by the International Astronautical Federation (IAF). All rights reserved.The two redundant servers are acting as a “main”and “spare” device, both running the host drivers. Innominal operation, only the “main” server controls theground station system. If the host drivers, which containa watchdog functionality, detects some anomaly in formof unresponsivity of the “main” system, all functionalitywill be automatically handed over to the “spare” system.In the user interface, six “quick access” buttonsallow access to user-defined satellite scenarios. But allrelevant parameters like frequency offset, bandwidth,modulation etc. can be also changed “on-the-fly”. Thebuilt-in Doppler correction provides the correctfrequency for up- and downlink. The used method forthe Doppler correction can be selected. For instance, viaorbital parameters (TLE file) or maximum signalstrength. With the use of a dedicated program, availablepasses can be visualized and scheduled.2.5.1Monitoring systemAll critical voltages, currents, temperatures (e.g. forthe PA) or the transmitter output- vs. reflected powerare monitored and transmitted to the main system viaCAN bus. From here, the data is distributed to theservers and finally provided to the operator.2.6 Additional reception systemsIn addition to the ground station’s main purpose ofsatellite operations, there was still space for otherrelated RF systems, which are partially experimental.These are described briefly in the following paragraphs.2.6.1Automatic Identification System (AIS)The AIS system is a worldwide system for maritimevessel tracking. Ships above a certain tonnage as well asall passenger ships are required to be equipped with anAIS transmitter. These transmitters broadcast thecurrent position as well as additional information likespeed, heading etc. on 162 MHz.Since the DLR - Institute of Space Systems has avariety of activities in the AIS sector – including theAISat, which carried several receivers and antennatechnology on board, AIS ground reference stations hadto be available for comparison of the data. TheL.A.R.S. ground station is equipped with a commercialAIS receiver, which data whose data is stored andmakes it available in the network.2.6.2position, start and destination or ground speed on 1090MHz. ADS-B, also satellite based, has been a researchtopic at the Institute of Space Systems for a long time.Aboard the ESA satellite PROBA-V, an ADS-Breceiver from DLR has been tested successfully [5].Like for the AIS system, having access to groundreference data is desired to compare it with the recordeddata from space.A small redundant dual-receiver unit is used for thispurpose. The received data can be directly streamed tothe local network. For reception, a 1090 MHz groundplane antenna is mounted atop the container.2.6.3WSPR multiband receiverThe WSPR protocol, initiated by the US Americanradio amateur Joe Taylor (K1JT), is used to establishconnections between radio stations and transmit theresults to an internet database. A distinctive feature ofthe protocol is, that only a very low signal-to-noise ratiodown to approximately -28 dB (on average) is requiredfor proper reception.WSPR is mainly used in low-power (QRP)transmissions, typically below 1 W, to draw conclusionsabout the atmospheric propagation of radio waves.Usually, WSPR is mostly being used on short wavefrequencies, since their propagation behaviour is mostprone to atmospheric conditions. The stations with thecorresponding call signs and successful connections canbe seen at a map of the project’s web site [6].The L.A.R.S. container inhibits a multibandmedium-/short wave WSPR receiver which can listen toeight bands from 160 m up to 10 m simultaneously.Received and decoded spots are uploaded to theproject’s website. A similar decoder is installed on theGerman Antarctic research station Neumayer III (callsign DP0GVN). Currently, the receiver is also linked tothe recently established WSPRlive database, whichcollects, analyses and illustrates the received data of allreceivers participating in the network [7].Antennas used for the WSPR receiver are twowindom wire antennas in diversity configuration.3. Results and discussionSince the establishment of the L.A.R.S. groundstation at the institute’s premises, a multitude ofsatellites were successfully received. Even satelliteswhich do not have a (nearly) polar orbit, e.g. theAustralian UNSW-EC0 [8] which has been deployedfrom ISS, could be received with acceptable signalstrength.ADS-B aircraft monitoringADS-B is an aircraft surveillance system, whereeach aircraft broadcasts information like the currentIAC-19-B4.3.9x50773Page 6 of 7

70th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019.Copyright 2019 by the International Astronautical Federation (IAF). All rights reserved.As a next step, the relocation to a final site in thearctic regions is planned to serve polar orbitingsatellites. Furthermore, upgrade options regarding alow-maintenance S Band antenna have to be evaluated.AcknowledgementsFig 9. Comparison of received of AAUSAT4 datareception between ground stations, pass on 19.09.19starting at 11:17 UTCIn Fig. 9, a pass of AAUSAT4 is shown, which hasbeen received with the institute’s fixed ground station aswell as with the L.A.R.S. container. The fixed one usesa rotatable cross-yagi array antenna with a gain of 17dBi and mast mounted pre-amplifier. As a decodingsoftware, the freeware “Soundmodem 0.18b” in 2k4baud mode has been used. Each properly decoded signalduring the pass is marked with a dot in the graph, thecolor depicts the corresponding reception site. Despitethe much weaker link budget of the L.A.R.S. container(due to the antenna design), still most of the messagescould be decoded properly. Currently, some parametersin hard- and software are still analysed and optimized toachieve even better results and avoid mid-pass messagelosses.In addition to the containers’ main task as a satelliteground station, it has been continuously upgraded withadditional RF equipment.To achieve a better and more realistic testingenvironment, the ground station has been temporarilyrelocated from the Institute of Space Systems in Bremento a remote location at the Jade Weser Airport nearWilhelmshaven, approximately 70 km northwest ofBremen. After the transfer of the ground station fromthe densely populated technology park of Bremen to themore rural area, a significant reduction of the noise floorcould be achieved. Especially the reception of shortwave signals for the WSPR receiver has beendramatically improved. Also the AIS and ADS-Breceivers profit from the proximity to the sea, respectivethe airport. Due to its versatility, the ground station hadbeen also assisted in tracking a high-altitude balloonduring a mission, just by remotely reconfiguring thesoftware.IAC-19-B4.3.9x50773We thank all colleagues and partners being involvedin the project, especially Alexander Smolko, PascalSolmaz and Tom Thienel for the excellent technicalassistance during the different phases of the project.References[1] B. Suhr et.al., AISat-1: Analysis Results, DeutscherLuft- und Raumfahrtkongress (DLRK) der DGLR,Rostock, Germany, 2015, 22 – 24 Sept.[2] AAUSAT4 Homepage of the University of accessed 13.09.19).[3] Dick Janson, Antennas for Space Communication,in: H. Ward Silver, Steven R. Ford, Mark J. Wilson(Eds.), The ARRL Antenna Book for RadioCommunications, ARRL, 22nd Edition, Newington,CT, USA, 2013, pp. 17-2/3; 17-8.[4] Alois Krischke, Rothammels Antennenbuch, 13thEdition, DARC Verlag, Baunatal, 2013.[5] T. Delovski, K. Werner et.al., ADS-B over SatelliteThe world’s first ADS-B receiver in Space, SmallSatellites Systems and Services Symposium,Mallorca, Spain, 2014, 26 – 30 May.[6] The Weak Signal Propagation Reporter Network,http://wsprnet.org, (accessed 16.09.19).[7] WSPRLive Website, https://wsprlive.net, (accessed16.09.19).[8] J.W. Cheong et.al., Design and Development of theUNSW QB50 Cubesat - EC0, InternationalAstronautical Congress, Guadalajara, Mexico, 2016,26 – 30 Sept.Page 7 of 7

2.3 Antenna system for TT&C A trade-off has shown that an “eggbeater” antenna [3] (displayed in Fig. 1, mounted on top of the masts) can be a good choice for satellites in LEO orbit in the given frequency bands of VHF and UHF. This type of a cardioid shaped radiation pattern (see Fi

Related Documents:

Strategy 6: Mobile Workload Mobile devices are increasingly driving mainframe workloads April 2014: Mobile Workload Pricing – 60% reduction in mobile workload CPU to R4HA peak MUST be from mobile device MUST show connection to mobile device – Mobile Safari good – Desktop Safari not good Mobile to mainframe is .

Independent Personal Pronouns Personal Pronouns in Hebrew Person, Gender, Number Singular Person, Gender, Number Plural 3ms (he, it) א ִוה 3mp (they) Sֵה ,הַָּ֫ ֵה 3fs (she, it) א O ה 3fp (they) Uֵה , הַָּ֫ ֵה 2ms (you) הָּ תַא2mp (you all) Sֶּ תַא 2fs (you) ְ תַא 2fp (you

Mobile Communication Services . Offerings Detail Samsung SDS America Public Sector Capabilities Mobile ERP Health IT Mobile Groupware SAP Mobile BI Dashboard Oracle/Siebel Mobile CRM for Pharmaceutical Sales Mobile Device Management Mobile Applications (Android OS) . Android Mobile App & UI. 10 Offerings Detail Conceptual .

Mobile 3G/4G, pushing wireless boundaries to enable the best mobile experiences 2 Mobile connectivity is an amazing technical achievement, 4 critical to the mobile experience Wireless fundamentals are the foundation to mobile powered by Mobile 3G/4G technologies Appreciating the magic of mobile requires un

Mobile advertising helps developers of mobile apps obtain revenue without directly charging users. Therefore, advertising is a key component of the mobile app ecosys-tem. Mobile advertising is typically integrated into mobile apps via an advertising library or SDK (AdSDK), which fetches and displays mobile ads while the app is running.

SAP Mobile SDK or SAP Mobile Server installed, you must provide a license. See Obtaining a License on page 1. If you are installing SAP Mobile SDK on a system where a version of SAP Mobile Platform Runtime is already installed, the SAP Mobile SDK installer installs using the SAP Mobile Server license. See Chapter 2, Installing SAP Mobile SDK on .

Mobile Marketing with Channel Mobile It's time to harness the power of mobile!! The Power of Mobile The Power of Mobile Operator revenues - 5.4 trillion cumulative 2013 - 2017 Analysts predict a SIM penetration of 97% in 2017 Mobile data traffic expected to grow by 79% annually from 2012 - 2017

Mobile App Banking With Mobile Check Deposit/ Remote Deposit Capture (RDC) INTRODUCTION Using Mobile App members can use their It's Me 247 logon to gain access to mobile check deposit, mobile banking, transfer money, and much more. Interested in getting started with Mobile App and Mobile Check Deposit? Read this helpful booklet to learn more .