Satellite telemetry, tracking, and command (TT&C) is a crucial activity needed to maintainthe health of a spacecraft or sometimes to facilitate payload data download. TT&Cground operations are facilitated by a communication device known in the TT&C communityas a baseband. State-of-the-art baseband systems currently in the market haveseveral financial and technical limitations. Financial drawbacks include high capital expenditure,operational expenditure, maintenance costs, and high upgrade costs, whiletechnical limitations include both upgradability and scalability.This thesis presents the feasibility study of a software-defined baseband (SDB) as aviable alternative to existing basebands. The SDB considered here is implemented on aradio architecture that consists of a general-purpose processor for performing radio functionsand low-cost commercial-off-the-shelf, software-defined radio frontends for signalsampling. The research questions focus on the feasibility and design aspects of this SDB.This thesis approaches the design of the SDB with a software development cyclethat involves functional analysis (design), verification, and validation of the radio functionsconstituting the SDB system. The radio functions are the telemetry receiver andthe telecommand transmitter. Functional analysis is performed through functional flowblock diagrams. The verification process is performed through simulations that take intoaccount realistic channel impairments for missions operating in the S-band and characterizedby the Consultative Committee for Space Data Systems (CCSDS) as category Amissions (less than 2 million km). Validation is performed on a laboratory testbed andseveral orbiting satellites.Through the above software development cycle, the telemetry receiver and telecommandtransmitter are developed using the open-source GNU radio development kit. Modulationschemes, line codes, and filters along with CCSDS forward error correction codescommonly employed in TT&C communications are successfully designed, verified in simulations,and validated in a hardware testbed. The performance results from the validationtests demonstrate that it is feasible to implement the SDB TT&C radio functions on theadopted radio architecture.Finally, this thesis investigates in detail the novel concept of multiple spacecraft peraperture (MSPA) that enables communication with several spacecraft from a single antenna.It focuses on in-band interference and out-of-band emissions arising from radiatingmultiple telecommand links from a low-cost SDR frontend. An MSPA transceiver is successfullydeveloped and integrated into the SDB system. Validation tests show that itis feasible for the integrated MSPA transceiver to radiate two telecommand links whileconforming to spectral regulations.

The miniaturization of spacecraft has brough the possibility of conducting space missions to a vast portion of private enterprises and scientific institutions. The inaccessibility of modest developers to the resources that governmental agencies and primary contractors utilize to develop conventional satellites has not been an obstacle for them to apply different, more agile and risk-seeking approaches. However, the failure rate of Small Satellite missions has increased to a higher degree than the total number of missions, particularly if only CubeSats are considered.

The research conducted in this thesis proposes an improvement to the development of space systems by focusing on the verification and validation processes. For that, the thesis revolves around two main areas. First, the thesis deals with the engineering methodology. The notions of concurrent engineering are generalized and combined with the test-driven development and behavior-driven development methodologies to perform the parallel, yet integrated, development of the various spacecraft subsystems that can be at different maturity levels. For example, these processes have been applied in-house to the development of onboard computers and telecommunication systems. The proposed methodology allows for the automation of the engineering workflow and the early detection and correction of defects in the system by frequently testing it along the process.

Secondly, the research also deals with the development and utilization of a simulation environment that fits the proposed methodology. The thesis provides advancements on hardware-in-the-loop simulation techniques with a particular focus on frictionless platforms. Such a platform can perform, but is not limited to, dynamic simulations. Additionally, the thesis also provides the characterization of the platform to use it as a reference for comparison with other similar ones.

All in all, the simulation environment has demonstrated to provide the versatility needed by the methodology. Such environment has served as a platform to develop different subsystems from the simulation of physical models to the testing of actual hardware prototypes. Two studies are provided as examples of such accomplishments, i.e., a study with the remote simulation of cooperative maneuvers and a different one with the development of flexible appendages for a spacecraft.