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    Development Of An Integrated Spacecraft Guidance, Navigation, and Control Subsystem For Automated Proximity Operations
    (Georgia Institute of Technology, 2014-09) Shulte, Peter Z. ; Spencer, David A.
    This paper describes the development and validation process of a highly automated Guidance, Navigation, & Control (GN&C) subsystem for a small satellite on-orbit inspection application. The resulting GN&C subsystem performs proximity operations (ProxOps) without human-in-the-loop interaction. The paper focuses on the integration and testing of GN&C software and the development of decision logic to address the question of how such a system can be effectively implemented for full automation. This process is unique because a multitude of operational scenarios must be considered and a set of complex interactions between various GN&C components must be defined to achieve the automation goal. The GN&C subsystem for the Prox-1 satellite is currently under development within the Space Systems Design Laboratory at the Georgia Institute of Technology. The Prox-1 mission involves deploying the LightSail 3U CubeSat, entering into a leading or trailing orbit of LightSail using ground-in-the-loop commands, and then performing automated ProxOps through formation flight and natural motion circumnavigation maneuvers. Operations such as these may be utilized for many scenarios including on-orbit inspection, refueling, repair, construction, reconnaissance, docking, and debris mitigation activities. Prox-1 uses onboard sensors and imaging instruments to perform its GN&C operations during on-orbit inspection of LightSail. Navigation filters perform relative orbit determination based on images of the target spacecraft, and guidance algorithms conduct automated maneuver planning. A slew and tracking controller sends attitude actuation commands to a set of control moment gyroscopes, and other controllers manage desaturation, detumble, thruster firing, and target acquisition/recovery. All Prox-1 GN&C components are developed in a MATLAB/Simulink six degree-of-freedom simulation environment and are integrated using decision logic to autonomously determine when certain actions should be performed. The complexity of this decision logic is the main challenge of this process, and the Stateflow tool in Simulink is used to establish logical relationships and manage data flow between each of the individual GN&C hardware and software components. Once the integrated GN&C simulation is fully developed in MATLAB/Simulink, the algorithms are autocoded to C/C++ and integrated into flight software. The subsystem is tested using hardware-in-the-loop on the flight computers and other hardware.
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    Deployable Drag Device for Launch Vehicle Upper Stage De-orbit
    (Georgia Institute of Technology, 2014-09) Long, Alexandra C. ; Spencer, David A.
    Orbital debris is a growing problem in low Earth orbit; it has crossed a threshold of critical density where the number of debris objects will grow exponentially unless mitigated. Spent launch vehicle upper stages represent a problematic category of orbital debris in highly utilized orbits. They can stay in orbit for well over 100 years if left to deorbit naturally, and they represent a significant fraction of large space debris in low-Earth orbit. It is estimated that removing a few large objects per year will mitigate the exponential growth of debris. To address the debris problem, a trade study was conducted to determine a deployable drag device to accelerate the orbit degradation of upper stages. Following the operation of the upper stage, the drag device will be deployed to decrease the orbit lifetime of the system. The design is targeted toward upper stages launched into orbital altitudes ranging from 650-850 km. Three categories of deployable drag devices are being investigated: drag sails, inflatable aerodynamic decelerators, and electrodynamic tethers. These are compared to the option of using residual propellant in the upper stage to perform a burn to initiate a deorbit trajectory. The device will be mounted to the upper stage using a standardized secondary payload launch interface, such as a CubeSat deployer device or the EELV Secondary Payload Adapter (ESPA). The trade study compared the drag device configurations based on cost, risk, and deorbit time. A maximum deorbit period of 25 years is a performance design requirement. The propulsive option was shown to be the lowest cost option, however the drag device is more mass efficient and has less of an impact to the payload capability of the launch vehicle. An aerostable drag sail design is proposed as a baseline design for the device.
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    Regression Analysis of Launch Vehicle Payload Capability for Interplanetary Missions
    (Georgia Institute of Technology, 2010-09) Wise, Marcie A. ; Lafleur, Jarret M. ; Saleh, Joseph H.
    During the conceptual design of interplanetary space missions, it is common for engineers and mission planners to perform launch system trades. This paper provides an analytical means for facilitating these trades rapidly and efficiently using polynomial equations derived from payload planner’s guides. These equations model expendable launch vehicles’ maximum payload capability as a function of vis-viva energy (C3). This paper first presents the motivation and method for deriving these polynomial equations. Next, 34 polynomials are derived for vehicles among nine launch vehicle series: Atlas V, Delta IV, Falcon 9, and Taurus, as well as H-IIA, Long March, Proton, Soyuz, and Zenit. The quality of fit of these polynomials are assessed, and it is found that the maximum 95th percentile model fit error for all 34 vehicles analyzed is 4.43% with a mean of 1.44%, and the minimum coefficient of determination (R²) is 0.99967. As a result, the equations are suitable for launch vehicle trade studies in conceptual design and beyond. A realistic example of such a trade for the Mars Reconnaissance Orbiter mission is provided.
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    Comparative Reliability of GEO, LEO, and MEO Satellites
    (Georgia Institute of Technology, 2009-10) Hiriart, Thomas ; Castet, Jean-Francois ; Lafleur, Jarret M. ; Saleh, Joseph H.
    Reliability has long been a major consideration in the design of space systems, and in recent years it has become an essential metric in spacecraft design trade-space exploration and optimization. The purpose of this paper is to statistically derive and compare reliability results of Earth-orbiting satellites as a function of orbit type, namely geosynchronous orbits (GEO), low Earth orbits (LEO) and medium Earth orbits (MEO). Using an extensive database of satellite launches and failures/anomalies, life data analyses are conducted over three samples of satellites within each orbit type and successfully launched between 1990 and 2008. Because the dataset is censored, the Kaplan-Meier estimator is used to estimate the reliability functions. Plots of satellite reliability as a function of orbit altitude are provided for each orbit type, as well as confidence bounds on these estimates. Using analytical techniques such as maximum likelihood estimation (MLE), parametric fits are conducted on the previous nonparametric reliability results using single Weibull and mixture distributions. Based on these parametric fits, a comparative reliability analysis is provided identifying similarities and differences in the reliability behaviors of satellites in these three types of orbits. Finally, beyond the statistical analysis, this work concludes with several hypotheses for structural/causal explanations of these trends and difference in on-orbit failure behavior.
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    Statistical Reliability Analysis of Satellites by Mass Category: Does Spacecraft Size Matter?
    (Georgia Institute of Technology, 2009-10) Dubos, Gregory F. ; Castet, Jean-Francois ; Saleh, Joseph H.
    Reliability has long been recognized as a critical attribute for space systems, and potential causes of on-orbit failures are carefully sought for identification and elimination through various types of testing prior to launch. From a statistical or actuarial perspective, several parameters of the spacecraft, such as mission type, orbit, or spacecraft complexity, can potentially affect the probability of failure of satellites. In this paper, we explore the correlation between satellite mass, considered here as a proxy for size, and satellite reliability, and we investigate whether different classes of satellite, defined in terms of mass, exhibit different reliability profiles. To this end, we first conduct nonparametric analysis of satellite reliability based on a sample of 1,444 satellites. The satellites are organized in three main categories defined by satellite mass (Small – Medium – Large). Three nonparametric reliability curves are thus derived. We then provide parametric fits of the reliability curves to facilitate the identification of failure trends. We proceed to the comparative analysis of failure profiles over time and clearly identify different reliability behaviors for the various satellite mass categories. Finally, we discuss possible structural and causal reasons for these trends and failure differences, in particular with respect to design, testing and procurement.
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    Survey of Flexibility in Space Exploration Systems
    (Georgia Institute of Technology, 2008-09) Lafleur, Jarret M. ; Saleh, Joseph H.
    An increasingly common objective in the design of new space systems is the property of flexibility, or the capability to easily modify a system after it has been fielded in response to a changing environment or changing requirements. The body of research on this topic has been growing, but substantial work remains in developing metrics for characterizing system flexibility and trading it against other metrics of interest. This paper samples from the history of space exploration to glean heuristic insight into characteristics of flexibility in space exploration systems and their potential application to future systems. Divided into categories of intra- and inter-mission modification, examples include the Hubble Space Telescope, Mir space station, International Space Station, Apollo, Space Shuttle, and robotic Venera program. In several cases, metrics are identified which show clear performance gains due to changes after a system is fielded, and in all cases, environment or requirement changes that prompted system change are identified. Also discussed are examples where flexibility proved critical to mission success. Modular design and separation of functionality are recognized as likely flexibility-enabling characteristics. Also, briefly discussed are examples of non-configurational (e.g. software and trajectory) flexibility in space exploration applications.
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    A Concept for the Entry, Descent, and Landing of High-Mass Payloads at Mars
    (Georgia Institute of Technology, 2008-09) Korzun, Ashley M. ; Stahl, Benjamin A. ; Dubos, Gregory F. ; Quicksall, John J. ; Iwata, Curtis K.
    The architecture concepts and aggressive science objectives for the next phases of Mars exploration will require landed masses an order of magnitude or greater than any Mars mission previously planned or flown. Additional studies have shown the requirements for missions more ambitious than the 2009 Mars Science Laboratory (~ 900 kg payload mass) to extend beyond the capabilities of Viking-heritage entry, descent, and landing (EDL) technologies, namely blunt-body aeroshells, supersonic disk-gap-band parachutes, and existing TPS materials. This study details a concept for Mars entry, descent, and landing capable of delivering a 20 t payload within 1 km of a target landing site at 0 km MOLA. The concept presented here explores potentially enabling EDL technologies for the continued robotic and eventual human exploration of Mars, moving beyond the Viking-heritage systems relied upon for the past 30 years of Mars exploration. These technologies address the challenges of hypersonic guidance, supersonic deceleration, precision landing, and surface hazard avoidance. Without support for the development of these enabling technologies in the near term, the timeline for the successful advanced exploration of Mars will likely extend indefinitely.
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    Design Space Pruning Heuristics and Global Optimization Method for Conceptual Design of Low-Thrust Asteroid Tour Missions
    (Georgia Institute of Technology, 2008-09) Alemany, Kristina ; Braun, Robert D.
    Electric propulsion has recently become a viable technology for spacecraft, enabling shorter flight times, fewer required planetary gravity assists, larger payload masses, and/or smaller launch vehicles. With the maturation of this technology, however, comes a new set of challenges in the area of trajectory design. In 2006, the 2nd Global Trajectory Optimization Competition (GTOC2) posed a difficult mission design problem: to design the best possible low-thrust trajectory, in terms of final mass and total mission time, that would rendezvous with one asteroid in each of four pre-defined groups. Even with recent advances in low-thrust trajectory optimization, a full enumeration of this problem was not possible. This work presents a two-step methodology for determining the optimum solution to a low-thrust, combinatorial asteroid rendezvous problem. First is a pruning step that uses a heuristic sequence to quickly reduce the size of the design space. Second, a multi-level genetic algorithm is combined with a low-thrust trajectory optimization method to locate the best solutions of the reduced design space. The proposed methodology is then validated by applying it to a problem with a known solution.
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    Methods for Navigation in the Nearby Interstellar Medium
    (Georgia Institute of Technology, 2022-09) Christian, John A.
    Recent years have seen an increased interest in sending dedicated spacecraft to explore the nearby interstellar medium (NISM). Such a mission would be instrumented to study the so-called heliosphere on the outskirts of our Solar System, where the solar wind and helopspheric magnetic field interact with interstellar environment (e.g., cosmic radiation). While the scientific value of such a mission is clear, the design and operation of a spacecraft to accomplish this mission is difficult. Indeed, due to the immense distances involved, navigation is expected to be amongst the most challenging tasks. This work explores a variety of navigation observables and frameworks that one might use to navigate a mission within the NISM. Detailed models are presented for all of the major sources of navigation information, including Earth-based radiometric tracking, visible-spectrum star sightings, X-ray pulsar navigation (XNAV), StarNAV, and others. The utility of these observables is then studied within an orbit determination framework, along with consideration of the quality of state knowledge most likely required to operate in the NISM. Issues related to time-keeping are also discussed. Numerical results are presented as a way to illustrate the efficacy of various approaches.
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    UniSpace+50: Shared Vision Common Action
    (Georgia Institute of Technology, 2017-09) Pellegrino, Passimo ; Gibson, Alexander ; Mariscal, Juan Carlos ; Schulte, Peter Z.
    UNISPACE+50 marks the fiftieth anniversary of the first UNISPACE conference, held in 1968. In June 2018, the international space community will be together in Vienna to articulate a new long-term vision for space around four pillars (space economy, space society, space accessibility, and space diplomacy), which will serve as a guide in shaping the future of space and in driving space investments. As a product of UNISPACE III, the Space Generation Advisory Council (SGAC) attaches great importance to this conference series and aims to contribute to the wider strategic reflection promoted by UNOOSA in the lead-up to UNISPACE+50, by bringing into the process the views of the future generation of space leaders. Building on both the conclusions of a working group on UNISPACE+50 by SGAC and the Dubai Declaration, the objective of this paper is three-fold. First, it proposes a new long-term vision for space, as envisioned by UNISPACE+50. Second, it offers concrete ideas for action in support of such a vision. Third, it identifies the role that the young professionals space community can play in the UNISPACE+50 process and ensuing debates, including through the action of SGAC. The paper argues that the pursuit of the proposed vision statement requires work along six areas of action. These include strengthening the outer space regime and global space governance, by elaborating ethical principles and norms of responsible behaviour in outer space and ensuring compliance with international agreements; making international cooperation the norm for future space activities, recognizing it as a long-term investment for all parties involved; conducting space activities to generate tangible societal and economic benefits for all humankind; building capacity across space markets and value chains; placing outer space topics on as many national political agendas as possible; making the space sector a leading force in major technology development. The paper concludes that the young professionals space community is well placed to inform these actions and the means with which to accomplish them, as well as to engage and liaise more closely with both the wider space and non-space communities to ensure future buy-in and active collaboration. Not only could these actions contribute to nurturing the strategic reflection promoted by UNOOSA in the framework of the UNISPACE+50 process, but they could also offer organizations, such as SGAC, potential avenues for the future and ideas about how to evolve and move forward in partnership with their own stakeholders.