A cube sat communication design for In-Space Assembly

A cube sat communication design for In-Space Assembly

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  A CubeSat CommunicationDesign for In-Space Assembly Ingeneral,the conventional designof asatelliteisbasedonthe modulararchitecturewhereeachsatellite subsystem has hardware and software autonomy. In the case of a CubeSatclass satellite,this kind of architecture did not prove its effectiveness since a significant number of CubeSats could not make a successof theirmissions.The goal of thischapterconsistsindevelopinganew designmethodologyof the CubeSat-class satellites. The CubeSat-class Spacecraft hardware has volume,mass, and power limitations more extreme than in othersatellites.Infact,the CubeSat-classspacecraftisaCube withdimensions10cmx 10cmx 10cm, mass one kilogrammaximumandthe availablepoweris about2Wattbymountingthesolarcellsonthe CubeSat structure. The CubeSat-class spacecrafts have the advantagesof being able to perform as a test bed for new core space technologiestobe appliedtospace programs,formuch lowercost,shorterschedule,andlessrisk. For this reason, the world leaders in space technology, including the US and Europe, are focusing their efforts on smaller satellites under the motto of “Faster, Cheaper, Better” that can perform missions traditionally assigned to large/medium satellites in the past. Keyword: LoRa, Communication solutions, lT service referral program, freeRTOS, SCADA solutions, embedded C++, embedded C, LTE modem. Satellite architecture overview The Data Handling Subsystem is considered as an interface between the control station and the other satellite subsystems. The Data Handling Subsystem modules include communication subsystem (antennas,modulator,demodulator)and on-boardcomputerwhichcontrolsthe satellitesubsystems.But how these subsystems are attached to the on-board computer, two principal architectures are distinguished. Star Architecture:The On-Boardcomputer(OBC) mustrun separate data linestoeachsubsystem.Inthis architecture,the OBCshouldhave manyperipheral interfacesequal tothe numberof satellite subsystems on board and perhaps there will be a problem of wiring. bus Architecture in this case, all satellite subsystemsare connectedtoabuswhichis like Local AreaNetwork(LAN)aboardthe satellite.Ingeneral,
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  we used aMaster slave protocol. The three simple Master-slave bus commonly used in the embedded system are: CAN (Controller Area Network), SPI (Serial Peripheral Interface) and I²C (Inter Integrated Circuit). CubeSat subsystems requirements The requirements of CubeSat-class spacecrafts are significantly different from their ancestors’ conventionalsatellites,andnewdesigntechniquesare neededtomeetthese evolvingrequirements.The unique requirementsof the Telecommunication CubeSatsatellite demonstrate thisevolution.The design needs to be relativelyinexpensive while at the same time computationally robust. It should consume limited power and must support the space environment by reducing susceptibility to radiation and thermal effects.Inaprevioustext,we supposedthatall the satellite subsystemsare intelligent.i.e.;each satellite subsystem has its own microcontroller. CubeSat satellite platform subsystems design Space environment An importantissue to consider,whichaffectsall electronicdevicesinspace environment,isradiation.It can lead to various types of problems. These problemsrange from operational malfunctions to physical damage of the devices. CMOS technology is preferred for space applications because of its high noise marginsandlowstaticpowerrequirements.Scalingandintegrationare otheradvancesCMOStechnology has overothersemiconductortechnologies.Onthe otherhand,CMOSissusceptivetotwotypesof space radiationeffectscausedbyelectronsandprotonstrapped bythe terrestrial magneticfield:Total Ionizing Dose (TID) and Single Event Effects (SEE). TID effects are the result of accumulated exposure to ionizing radiation. SEE are the result of a single high-energy particle that strikes the device. Data handling subsystem design In the satellite modular architecture (Wertz & Larson, 1999), each single subsystem has a dedicated hardware and software.The Cubesathas importantconstraintson cost, powerand mass,and especially on size. The approach that has been taken in this research consists of the integration of the maximum subsystems withinthe same unitconsideringthatsingle subsystemscanbe setupwithoutmodifyingthe operation of the remaining subsystems. As said before, the Data Handling Subsystem will integrate the Telecommunication Payload, the Telemetry/Telecommand functions as well as the active part of the thermal control subsystem.Inthissection,we willdescribeindetailthe mainconsiderationsandsolutions chosen during the design of the Data Handling Subsystem based on the fixed-point DSP processor. The design was split in two parts: The Hardware and Software Architectures. Data handling subsystem hardware architecture The Data Handling Subsystem hardware architecture is composed of three main parts: an on-board computer, Sensors and Control signals, and a VHF transceiver with associated antenna.
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  On board computer Theon-Board Computer board as illustrated is a hardware board in which is implemented the flight software. The flight software controls the whole operations of the satellite and is built around a 16 bits DSP TMS320C5416 from Texas Instrument (Texas Instrument, 2002). The hardware board includes, moreover,one analogue interface connectedtothe RadioFrequencymodule(Transceiverandantenna), two analogue to digital converters for the acquisition of the Telemetry housekeeping data, a EEPROM memory containing the flight software, a JTAG port for the flight software programming and finallythe control signals,byusingsomeDSPInput/outputsignals,inparticular,toactivate ordeactivatethe heater. illustrates the hardware architecture of the on-board computer. All the components on the on-board computerlogicboardare chosenwithSMD(Surface MountedDevice) packagesforspace savingandhigh density mounting in order to minimize the weight and dimensions of the logic board. Transceiver A COTS amateurradiotransceiverwasadoptedtobe the mainflightradiodue topower,weight,andtime constraints(Horan, 2002; Lu, 1996). The transceiver,integratedinside the payload,operatesinamateur VHF bandand consistsof the “guts” of a low cost Yaesu VX1R(Hunyadi et al.,2002), arguablyone of the smallest and lightest handheldson the market. The radio is two stackable double sided PCBs measuring approximately5× 5 cm2. The small size of CubeSatslimitsthe amountof energyprovidedbysolararrays; therefore power availability is a constraint on both the spacecraft processor and the communications systems.Powerissuppliedfrom5V bustoradiate only1Watt RF powerwhichachievesapositivebudget link (see Table 1). Current consumption for the receiver and transmitter is 150 mA and 400 mA, respectively. Only slight modifications will be required to make this component space worthy. We use onlythe RFpartsof the VX-1R.The transceiverisinterfacedwiththe DSPprocessorbymeansof AF (Audio Frequency) andPTT (PushTo Talk) commandsignals.AFsignalsconsistof transmitand receive signalsof the AFSK and GMSK modems which carry data packet, whereas PTT command signal allows the DSP to choose the transmittingandreceivingfrequencies of theradio.Thetransmittingandreceivingfrequencies will be fixed on the 145.825 satellite frequency. The FMsignal output from the transceiver is fed to an omnidirectional antenna.
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  Conclusion As the satellitecommunity transitions towards inexpensive distributed small satellites, new methodologiesneedtobe employedtoreplace traditional designtechniques.The ongoingresearchwill contribute to the developmentof these costsavingmethodologies.The goal of the integrationof all the intelligences of the various satellite subsystems in only one intelligent subsystem is to minimize componentexpenditureswhilestillprovidingthereliabilitynecessaryformissionsuccess.Associatinglow cost ground terminalswithalow-costTelecommunicationCubeSat-classsatellitewill allowuniversitiesto access space communicationswithavery economical system.The presentwork,dealingwiththe design of the Low-cost Telecommunication CubeSat-classspacecraft, shows hardware and software solutions adopted to cut down the system cost. The hardware utilizes commercial low-cost components and the software isoptimizedusingassemblerlanguage.The on-BoardComputerunitissmall device thatcanbe mounted on any small satellite platform to serve telecommunications applications such as mobile localization and data collection. By using a single CubeSat satellite and low-cost communications equipment, Telecommunications systems can be kept at the extreme low end of the satellite communications cost spectrum.