Person:

Lightsey, E. Glenn

Permanent Link

https://hdl.handle.net/1853/71462

Associated Organization(s)

Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

Organizational Unit

Space Systems Design Laboratory (SSDL)

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Publication Search Results

Now showing 1 - 10 of 13

Systems Architecture and Conceptual Design of a CubeSat Formation Serving as a Distributed Telescope

(Georgia Institute of Technology, 2020-11) Thatavarthi, Rohan ; Gundamraj, Athreya R. ; Carter, Christopher A. ; Lightsey, E. Glenn

The Virtual Super-Resolution Optics with Reconfigurable Swarms (VISORS) mission is a multi-CubeSat distributed telescope which will image the solar corona to investigate the existence of underlying energy release mechanisms. Such a task requires angular resolutions of less than 0.2 arc-seconds in extreme ultraviolet, which cannot be economically done with a conventional space telescope. Performing such a mission requires unprecedented relative navigation tolerances, a need for active collision avoidance, a development of intersatellite communication, and a propulsion system that enables the relative navigation maneuvers. The mission was initially conceived as a three 3U satellite formation in the NSF CubeSat Innovations Ideas Lab to address NSF science goals with innovative technologies. Once beginning conceptual subsystem design, it was evident that significant constraints linked to the three 3U satellite formation configuration limit the likelihood of mission success and increase mission risk. A trade study was conducted to determine potential resolutions to the problems associated with the initial three 3U satellite formation configuration. The completion of the trade study resulted in a major design change to a two 6U satellite configuration that resolved the issues associated with the initial configuration, improved mission success while reducing risk, and intends to incorporate novel CubeSat technologies, all of which enable the mission to move forward. This paper discusses the path that led the team to conduct the trade study, the design alternatives considered, and the innovative subsystem technologies that were conceived as a result of updating the satellite formation configuration.
Vertical Entry Robot for Navigating Europa (VERNE): Mission Concept System Design

(Georgia Institute of Technology, 2020-11) Bryson, Frances ; Nassif, Mohamed ; Szot, Phillip A. ; Chivers, Chase J. ; Daniel, Nathan L. ; Wiley, Bridget E. ; Plattner, Taylor ; Hanna, Ashley ; Tomar, Yashvardhan ; Rapoport, Samuel ; Spiers, Elizabeth M. ; Pierson, Sara ; Hodges, Amoree ; Lawrence, Justin ; Mullen, Andrew D. ; Dichek, Daniel ; Hughson, Kynan ; Meister, Matthew R. ; Lightsey, E. Glenn ; Schmidt, Britney E.

Several moons in our solar system, including Europa, are believed to host large bodies of liquid water beneath ice shells. These water bodies are compelling locations in the search for life beyond Earth, but present significant challenges to access in future planetary missions. The Vertical Entry Robot for Navigating Europa (VERNE) is a robotic mission concept to penetrate and operate within Europa’s ice shell and ocean funded through the Scientific Exploration Subsurface Access Mechanism for Europa (SESAME) program. SESAME requires a vehicle capable of penetrating a hypothetical 15 km Europan ice shell within three years. VERNE will utilize a thermo-mechanical drill to descend into the ice while a suite of onboard sensors constrains ice properties and look for life by analyzing the meltwater. Data will be relayed to a surface lander via a redundant communication system comprised of a primary optical fiber cable and secondary wireless acoustic repeaters. Upon nearing the base of the ice shell, VERNE will release an anchor and then breakthrough into the ocean to profile the upper 100 m of the ocean and ice interface, a region with high potential for evidence of life. Here we present the mission success criteria, concept of operation, and vehicle architecture. We identify key technologies that are currently available as well as those that require maturation to support future subsurface access of ocean worlds. Throughout this activity, the design team sought to leverage experience with analog environments on Earth to generate a concept which demonstrates that such a mission is feasible within the coming decades.
Design of a Green Monopropellant Propulsion System from the Lunar Flashlight CubeSat Mission

(Georgia Institute of Technology, 2020-08) Andrews, Dawn ; Huggins, Grayson ; Lightsey, E. Glenn ; Cheek, Nathan ; Lee, Nathan D. ; Talaksi, Ali ; Peet, Sterling ; Littleton, Lacey M. ; Patel, Sahaj ; Skidmore, Logan ; Glaser, Mackenzie J. ; Cavender, Daniel P. ; Williams, Hunter ; McQueen, Donald ; Baker, John ; Kowalkowski, Matthew

Lunar Flashlight is a 6U CubeSat mission from NASA's Jet Propulsion Laboratory that will search for water-ice deposits near the lunar south pole. Lunar Flashlight aims to add to the flight experience of deep-space CubeSats by demonstrating an orbit insertion using a green monopropellant propulsion system designed uniquely for this mission. Developed by NASA Marshall Spaceflight Center (MSFC) and Georgia Tech's Space Systems Design Laboratory (SSDL), the Lunar Flashlight Propulsion System (LFPS) delivers over 2500 N-s of total impulse for the orbit insertion and necessary attitude maneuvers. The custom propulsion system fits within a 2.5U volume and has a total wet mass of less than six kilograms. It will be fueled by AF-M315E, which is a green monopropellant developed by the Air Force Research Laboratory (AFRL) as a safer alternative to hydrazine. Additive manufacturing is utilized to fabricate several components of its primary structure. Upon completion, Lunar Flashlight may become the first CubeSat to achieve orbit around a celestial body besides Earth. The LFPS aims to be a pathfinder device for CubeSat missions by demonstrating how monopropellant systems, green monopropellant fuel, and additive manufacturing can be utilized to expand the reach of small satellite space exploration.
Relating Collision Probability Miss Distance Indicators in Spacecraft Formation Collision Risk Analysis

(Georgia Institute of Technology, 2020-08) Núñez Garzón, Ulises E. ; Lightsey, E. Glenn

Active spacecraft formation flying collision avoidance schemes monitor collision risk through indicators such as miss distance and collision probability. This paper compares collision probability measures based on planar projections to their three-dimensional counterparts. In this analysis, it is found that the former overestimate the latter. Additionally, this work compares the consistency of risk assessments based on miss distance and collision probability. Certain statistics of relative position are well suited for collision risk assessments because their local minima and collision probability local maxima are anticorrelated, and vice versa. These results help connecting both types of indicators into a cohesive framework.
Autonomous Navigation for Crewed Lunar Missions with DBAN

(Georgia Institute of Technology, 2020-03) Jun, William W. ; Cheung, Kar-Ming ; Milton, Julia ; Lightsey, E. Glenn ; Lee, Charles

With the recent push for a crewed Lunar mission to descend, land, and ascend from the Moon, there is a need for real-time position, velocity, and orientation knowledge of a Lunar spacecraft. Proposed approaches to achieve this include the use of weak-signals received from GPS and Deep Space Network (DSN)-aided measurements, but these all require significant hardware development and active tracking from multiple ground stations. Additionally, these solutions may be unavailable during close approach and landing. This paper extends the previously published relative Doppler-based positioning scheme (Law of Cosines – LOC) and an absolute Doppler-based scheme (Conic Doppler Localization – CDL) with the aid of range measurements and an inertial measurement unit (IMU) to create the Doppler Based Autonomous Navigation (DBAN) architecture. DBAN allows for real-time, autonomous positioning with as few as one Lunar orbiter and a reference station on the surface of the Moon. The LOC scheme is a relative navigation architecture that converts Doppler measurements into Doppler-based range measurements with the aid of a reference station and at least one satellite. In addition, the CDL scheme is an absolute navigation architecture that converts Doppler measurements into conic sections for angle-based positioning. These schemes allow for localization with solely Doppler measurements that can be made using existing hardware, with significant performance improvements when including range measurements. However, the existing drawback with these schemes is that they require a static user; they can be biased through the Doppler shift produced by a dynamic user. However, with the aid of range measurements, an IMU, and a non-linear Kalman filter, DBAN can correct these biases and provide continuous Doppler-based navigation. In this analysis, the Lunar Gateway and the Lunar Relay Satellite (LRS) were used with a pre-existing reference station located on the south pole of the Moon to localize a user during orbit, descent, and landing. A surface constraint assumption was optionally implemented using the knowledge of the altitude of the user as a constraint. Satellite ephemeris, velocity, and external and internal measurement errors were modeled as Gaussian variables and embedded in Monte Carlo simulations to increase fidelity. An Extended Kalman Filter (EKF) was used to ensure quick convergence without effects from linearization during intervals of high user dynamics. Ultimately, the DBAN architecture may provide real-time positioning, velocity, and orientation knowledge with a minimal navigation infrastructure that relaxes hardware requirements and utilizes as few as one orbiter.
Localizing in Urban Canyons using Joint Doppler and Ranging and the Law of Cosines Method

(Georgia Institute of Technology, 2019-09) Jun, William W. ; Cheung, Kar-Ming ; Lightsey, E. Glenn ; Lee, Charles

The performance of Global Navigation Satellite System (GNSS) based navigation can be limited in urban canyons and other regions with narrow satellite visibility. These regions may only allow for less than the minimum of four satellites to be visible, leading to a decay of positional knowledge. A scheme with Joint Doppler and Ranging (JDR) and relative positioning, known as the Law of Cosines (LOC) method, is introduced in this paper that utilizes Doppler and pseudorange measurements from a minimum of two GNSS satellites to obtain a position fix. The user’s GNSS receiver was assumed to output both corrected pseudorange and Doppler shift measurements for each tracked satellite. The velocity vector of each satellite was calculated using broadcast satellite ephemerides. Additionally, the location of the reference station was known and Doppler measurements from the GNSS receiver at the reference station were transmitted to the user. Ephemerides from eight GNSS satellites were simulated with the user and reference station approximately 12 km apart in San Francisco. Gaussian error sources were modelled and randomized in Monte Carlo simulations, adding error to the receiver’s known satellite ephemeris, satellite velocity, Doppler, and pseudorange measurements. Each unique pair of 2 satellites was employed for the positioning of the user using the LOC method for over 10,000 Monte Carlo simulations. With reasonable assumptions on measurement error, the average 2D topocentric Root-Mean-Square-Error (RMSE) performance of all pairs of satellites was 23 meters, reducing to 10 meters by removing specific pairs with poor geometry. However, with a new technique called Terrain Assisted – JDR (TA-JDR), which uses accurate topographic information of the user’s region as a faux pseudorange measurement, the average RSME of the satellite pairs was reduced to approximately 7 meters. The use of the JDR-LOC scheme and its variants may not only be useful in urban canyons, but also in other GPS-denied unfriendly environments. Ultimately, the JDR-LOC scheme was capable of achieving navigational solutions with an RMSE as low as 7 meters for users with limited GNSS satellite visibility, with only the use of a GNSS receiver and a reference station.
Exploration of Safing Event Models for Interplanetary Spacecraft

(Georgia Institute of Technology, 2019-03) Pujari, S. ; Lightsey, E. Glenn ; Imken, Travis

Unexpected spacecraft failures and anomalies may prompt on-board systems to change a spacecraft’s state to a safe mode in order to isolate and resolve the problem. The motivation for this paper is to investigate methods to tailor the impact of safing events for spacecraft of different classes, destination, duration, and other categories of interest. Modeling spacecraft inoperability due to a spacecraft entering safe mode could enable mission planners to more effectively manage spacecraft margins and shape design and operations requirements during the conceptual design phase. This paper contributes to the area of safing event modeling by using available datasets to develop various distributions of frequency and recovery durations of safing events for interplanetary spacecraft missions. A safing event dataset compiled by JPL is first split into multiple subsets based on various mission classifiers. Using a previously developed mission simulation framework, a distribution of the likelihood of inoperability rates is computed through a Monte Carlo simulation. Three main safing event model types are formulated, implemented, and compared in this paper: a single Weibull distribution, a mixture of two Weibull distributions, and a Gaussian Process model. For each model type, two distributions are incorporated into the mission simulation framework: time-between-events and the recovery duration of a safing event. By specifying appropriate parameters in the mission simulation framework and Gaussian Process model, a Monte Carlo simulation is conducted for a solar-electric Mars orbiter similar to the proposed Next Mars Orbiter. Mission implications from simulated outage times and safing events by each model could motivate greater operability, faster fault resolution by operations teams, and greater system margins. By incorporating Gaussian Process models into a mission simulation framework, a process is established by which historical mission data may be incorporated and used to model future safing events for interplanetary mission concepts. This enables mission planners to make more informed decisions during spacecraft development.
Single-Satellite Doppler Localization with Law of Cosines (LOC)

(Georgia Institute of Technology, 2019-03) Cheung, Kar-Ming ; Jun, William W. ; Lee, Charles ; Lightsey, E. Glenn

Modern day localization requires multiple satellites in orbits, and relies on ranging capability which may not be available in most proximity flight radios that are used to explore other planetary bodies such as Mars or Moon. The key results of this paper are: 1. A novel relative positioning scheme that uses Doppler measurements and the principle of the Law of Cosines (LOC) to localize a user with as few as one orbiter. 2. The concept of “pseudo-pseudorange” that embeds the satellite’s velocity vector error into the pseudorange expressions of the user and the reference station, thereby allowing the LOC scheme to cancel out or to greatly attenuate the velocity error in the localization calculations. In this analysis, the Lunar Relay Satellite (LRS) was used as the orbiter, with the reference station and the user located near the Lunar South Pole. Multiple Doppler measurements by the stationary user and the reference station at different time points from one satellite can be made over the satellite’s pass, with the measurements in each time point processed and denoted as from a separate, faux satellite. The use of the surface constraint assumption was implemented with this scheme; using the knowledge of the altitude of the user as a constraint. Satellite’s ephemeris and velocity, and user’s and reference station’s Doppler measurement errors were modeled as Gaussian variables, and embedded in Monte Carlo simulations of the scheme to investigate its sensitivity with respective to different kinds of errors. With only two Doppler measurements, LOC exhibited root mean square (RMS) 3D positional errors of about 22 meters in Monte Carlo simulations. With an optimal measurement window size and a larger number of measurements, the RMS error improved to under 10 meters. The algorithm was also found to be fairly resilient to satellite velocity error due to the error mitigating effects in the LOC processing of the pseudo-pseudorange data type. A sensitivity analysis was performed to understand the effects of errors in the surface constraint, showing that overall position error increased linearly with surface constraint error. An analysis was also performed to reveal the relationship between the distance between the user and the reference station; a distance of up to 100 km only lead to an increase of 10 meters in RMS 3D position error. Ultimately, the LOC scheme provides localization with a minimal navigation infrastructure that relaxes hardware requirements and uses a small number of navigation nodes (as small as one).
Development and Testing of a 3-D-Printed Cold Gas Thruster for an Interplanetary CubeSat

(Georgia Institute of Technology, 2018-03) Lightsey, E. Glenn ; Stevenson, Terry ; Sorgenfrei, Matthew

This paper describes the development and testing of a cold gas attitude control thruster produced for the BioSentinel spacecraft, a CubeSat that will operate beyond Earth orbit. The thruster will reduce the spacecraft rotational velocity after deployment, and for the remainder of the mission it will periodically unload momentum from the reaction wheels. The majority of the thruster is a single piece of 3-D-printed additive material which incorporates the propellant tanks, feed pipes, and nozzles. Combining these elements allows for more efficient use of the available volume and reduces the potential for leaks. The system uses a high-density commercial refrigerant as the propellant, due to its high volumetric impulse efficiency, as well as low toxicity and low storage pressure. Two engineering development units and one flight unit have been produced for the BioSentinel mission. The design, development, and test campaign for the thruster system is presented.
Accuracy/Computation Performance of a New Trilateration Scheme for GPS-Style Localization

(Georgia Institute of Technology, 2018-03) Cheung, Kar-Ming ; Lightsey, E. Glenn ; Lee, Charles H.

We recently introduced a new geometric trilateration (GT) method for GPS-style positioning. Preliminary single-point analysis using simplistic error assumptions indicates that the new scheme delivers almost indistinguishable localization accuracy as the traditional Newton-Raphson (NR) approach. Also, the same computation procedure can be used to perform high-accuracy relative positioning between a reference vehicle and an arbitrary number of target vehicles. This scheme has the potential to enable a) new mission concepts in collaborative science, b) in-situ navigation services for human Mars missions, and c) lower cost and faster acquisition of GPS signals for consumer-grade GPS products. The new GT scheme differs from the NR scheme in the following ways: 1. The new scheme is derived from Pythagoras Theorem, whereas the NR method is based on the principle of linear regression. 2. The NR method uses the absolute locations (xi, yi, zi)’s of the GPS satellites as input to each step of the localization computation. The GT method uses the Directional Cosines Ui’s from Earth’s center to the GPS satellite Si. 3. Both the NR method and the GT method iterate to converge to a localized solution. In each iteration step, multiple matrix operations are performed. The NR method constructs a different matrix in each iterative step, thus requires performing a new set of matrix operations in each step. The GT scheme uses the same matrix in each iteration, thus requiring computing the matrix operations only once for all subsequent iterations. In this paper, we perform an in-depth comparison between the GT scheme and the NR method in terms of a) GPS localization accuracy in the GPS operation environment, b) its sensitivity with respect to systematic errors and random errors, and c) computation load required to converge to a localization solution.