Person:

Christian, John A.

Permanent Link

https://hdl.handle.net/1853/71157

Associated Organization(s)

Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

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Publication Search Results

Now showing 1 - 10 of 16

Lunar Crater Identification using Triangle Reprojection

(Georgia Institute of Technology, 2023-08) Thrasher, Ava C. ; Christian, John A. ; Molina, Giovanni ; Hansen, Michael ; Pelgrift, John Y. ; Nelson, Derek S.

Image-based terrain relative navigation is a critical capability for future lunar exploration missions. Images of the lunar surface containing craters can be compared to on-board maps to identify craters and estimate the spacecraft position. While there are many ways to accomplish the crater identification task, this work explores a method using triangulation and crater triangle pattern projections. Specifically, potential matching crater patterns from the catalog and image are used to triangulate the spacecraft position, allowing for construction of line-of-sight directions to the potential matching catalog craters. The projection of these directions in the image can be compared to the observed craters to accept or reject the match hypothesis. In this paper, we demonstrate the algorithm's capability in handling various types of input errors and what tolerances can be tuned to achieve a desired performance. Additionally, an initial look at flight software implementation is included.
Lunar Reflectance Modeling for Terrain Relative Navigation

(Georgia Institute of Technology, 2023-08) DeVries, Carl ; Christian, John A.

Feature matching techniques often encode a brightness pattern from an image without knowledge of the underlying scene. This makes feature matching difficult when illumination conditions change significantly between images or are not consistent with onboard maps. The brightness patterns in images of the lunar surface can be partially described by a surface reflectance model which can often be parameterized by quantities known onboard from a sun sensor and calibrated camera. Unfortunately, these models can be intractable due to their complexity. This work develops a reduced-order lunar reflectance model for future illumination-informed feature descriptor development.
Initial Orbit Determination Using Relative Position Measurements

(Georgia Institute of Technology, 2023-08) Henry, Sébastien ; Christian, John A.

This work explores the problem of initial orbit determination (IOD) using relative position measurements between a pair of spacecraft in Keplerian orbits. We first show that the solution to this problem is not unique, even under certain classes of perturbations. We propose an algorithm to retrieve the inertial state of both orbiting spacecraft using the relative acceleration and Lambert's problem. Various options are compared to estimate the relative acceleration from a set of relative position measurements. Simulation results suggest that the proposed IOD algorithm is suitable for onboard navigation filter (re)initialization, and can thus improve constellation and formation-flying mission autonomy.
Analytical Methods in Crater Rim Fitting and Pattern Recognition

(Georgia Institute of Technology, 2023-08) Krause, Michael ; Price, Jonathan ; Christian, John A.

Upcoming lunar missions are expected to utilize optical measurements for navigation. View invariants enable "lost-in-space" terrain relative navigation about cratered celestial bodies. Lunar crater rims form ellipses when imaged. Noisy measurements of points lying along this rim will be obtained, and may be fit to an ellipse to calculate the invariants. Hyper least squares (HLS) provides an attractive performance benefit compared to traditional (or total) least squares for this task. An analytical derivation of the covariance of these invariants in the presence of noise is presented, and is used to analyze performance of the invariants in realistic situations.
LOST in Space: Optimal Triangulation for Celestial Localization

(Georgia Institute of Technology, 2022-10) Henry, Sébastien ; Christian, John A.

Optical measurements are a key part of modern interplanetary navigation. The statistically optimal Linear Optimal Sine Triangulation (LOST) algorithm is applied to the context of celestial navigation. In addition to optimal triangulation methods, celestial navigation requires the consideration or target ephemeris errors, light aberration, and light time-of-flight. In most cases, only light aberration and light time-of-flight change the expected direction of the measured line-of-sight (LOS). These effects are found to be non-negligible at typical observer velocities (for light aberration) and planet velocities (for light time-of-flight). The effects of the position uncertainty of planets are only important when the observer is close to them. The LOST framework provides a mechanism to conveniently consider all of these effects.
Crater Projection in Linear Pushbroom Camera Images

(Georgia Institute of Technology, 2022-10) Mancini, Michela ; DeVries, Carl ; Thrasher, Ava C. ; Christian, John A.

Science images of the Moon and Mars are often captured with pushbroom cameras. Craters with elliptical rims are common objects of interest within the the images produced by such sensors. This work provides a framework to analyze the appearance of crater rims in pushbroom images. With knowledge of only common ellipse parameters describing the crater rim, explicit formulations are developed and shown to be convenient for drawing the apparent crater in pushbroom images. Implicit forms are also developed and indicate the orbital conditions under which craters form conics in images. Several numerical examples are provided which demonstrate how different ellipse formulations can be interpreted and used in practice.
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.
Geometric Initial Orbit Determination From Bearing Measurements

(Georgia Institute of Technology, 2022-08) Duff, Timothy ; Mancini, Michela ; Leykin, Anton ; Christian, John A.

Initial orbit determination (IOD) from only bearing measurements is a classical problem in astrodynamics. The classical solutions of Gauss, Laplace, and others can solve this problem with three bearing measurements collected at known times. In this work, we apply concepts from algebraic geometry to investigate purely geometric solutions to this same problem. It is shown that five optical sightings at unknown times may be used to determine the orbit of an unknown spacecraft. The solution only requires knowledge that the spacecraft is following a conic orbit, with no need for any orbit propagation as part of the IOD process.
Lidar Odometry for Lunar Terrain Relative Navigation

(Georgia Institute of Technology, 2022-08) DeVries, Carl ; Christian, John A. ; Hansen, Michael ; Crain, Tim

Future missions to the lunar surface are expected to make use of LIDAR sensors for navigation during landing. This is especially true when the lunar landing must be accomplished under lighting conditions that are undesirable for camera based navigation. Moreover, when local maps of the lunar terrain are also poor or unavailable to the lander in real-time, concepts from LIDAR odometry (LO) are highly relevant. This work develops an algorithmic framework for LO suitable for supporting future lunar exploration missions.
System Design and Analysis for Cislunar Space Domain Awareness Through Distributed Sensors

(Georgia Institute of Technology, 2022-08) Badura, Gregory ; Shimane, Yuri ; Gregoire, Alaric ; Patel, Rohan ; Gilmartin, Matthew ; Gangolli, Kunal ; Visonneau, Lois ; Tysor, Joshua ; Manojkumar, Saikrishna ; Humphrey, Francis ; Valenta, Christopher ; Blair, Reilly ; Lourenco, Nelson ; Hodkin, Jason ; Sudol, Alicia ; Borowitz, Mariel ; Gunter, Brian C. ; Christian, John A. ; Ho, Koki

This paper summarizes an ongoing Georgia Tech effort to provide a cislunar space domain awareness (SDA) solution based on distributed space-based sensors that complement existing Earth-based assets. Distributed space-based SDA architectures complement one another via a diverse constellation geometry to overcome the sensing limitations of any single architecture. Our unique technical approach to this solution focuses on analyzing the links to a "Cislunar Custody Chain" via a diverse team of sensor, policy, and orbital dynamics experts. Our analysis will provide solutions towards creating the best actionable policy knowledge given the challenges of tracking and detecting objects within the Cislunar volume.