CRAFTI: A Canadian Asteroid Mission

Historically, planetary exploration has been performed using large, complex, and costly spacecraft that have attempted to bring a laboratory of instruments with them. Only in the early days of the American and Russian space programs were the missions less complex and more focused. The Canadian Robotic Asteroid Flyby and Tentatively Impact (CRAFTI) mission proposes to return to some of the philosophies of that era, and to bring modern microsatellite design philosophies into planetary exploration. The CRAFTI mission is a concept study being undertaken by the University of Toronto Institute of Aerospace Studies Space Flight Laboratory (UTIAS-SFL) and the Canadian Space Society, with funding from the Canadian Space Agency and technical support from Dynacon Enterprises Limited. The study is aimed at proving that microsatellite technology can, and should, be applied to planetary exploration. The principal investigator is Dr. Kimmo Innanen of York University, and the lead engineer is Henry Spencer of UTIAS-SFL. The target of this project is a Near Earth Asteroid suitable for a relatively slow flyby, tentatively chosen to be Toutatis during its 2008 closest approach with the Earth. Asteroids present the best target for such a mission, as they offer the greatest possible science return for relatively simple instruments and relatively low mission cost. In addition, a flyby during closest approach turns out to be a surprisingly easy mission. The CRAFTI mission presents an opportunity to prove that microsatellite technology has come of age, not only in Earth orbiting spacecraft, but also in the realm of planetary exploration. The key to success is a careful tradeoff between available spacecraft resources and mission design, and having on board only what is absolutely necessary for the mission to succeed. This paper will highlight the tradeoffs, and examine the proposed spacecraft design and overall mission plan

Fiber Optic Gyro-Based Attitude Determination for High-Performance Target Tracking

Small satellite-enabled terrestrial target tracking applications from low-Earth orbit are demanding stringent pointing performance, prompting the need for developing high-precision attitude estimation and control systems that adhere to cost and mass constraints. The attitude determination and control system onboard the Space Flight Laboratory’s NEMO-class satellite platforms uses an extended Kalman filter and low-cadence (1Hz) star-tracker measurements to constrain the attitude and rate estimation errors to within 0.05° and 0.04°/s (2-σ), respectively. In addition, the pointing error of this satellite platform is constrained to below 0.3° (2-σ) for ground target tracking applications. However, in order to meet the stability requirements of future missions that require precise target-tracking capabilities, a combination of star tracker and high frequency gyro-measurements is preferred. Leveraging high-grade miniaturized and commercially-accessible fiber optic gyroscopes (FOGs) with sampling frequencies of ≥ 2Hz, a high-performance attitude determination and control system suitable for target tracking micro- and nano-satellites is under development at the Space Flight Laboratory of Toronto, Canada. This paper discusses the design of an attitude estimation filter tailored to constrain the ground target pointing error of NEMO-class satellites to well below 0.3° (3-σ). To evaluate the performance of this filter, precision target tracking simulations were conducted, and the results demonstrated significant improvement in some state estimates when a combination of three-orthogonally mounted FOGs operating at high cadence (5Hz) and a single star tracker operating at 1Hz were implemented

On-Orbit Results from the CanX-7 Drag Sail Deorbit Mission

As a proactive solution to the orbital debris problem, the Space Flight Laboratory (SFL) has developed a passive drag sail deorbit device to remove small satellites from low-Earth orbit (LEO). Upon end-of-mission, the drag sail can be deployed to decrease the ballistic coefficient of the host spacecraft. Without any further operator intervention, the drag sail will interact with Earth’s upper atmosphere to decrease the spacecraft’s orbital energy causing it to eventually deorbit. In order to demonstrate the drag sail technology on-orbit, it has been included as the primary payload on-board the CanX-7 mission, which was launched in September 2016. After successfully completing a seven-month aircraft tracking campaign using the CanX-7 ADS-B payload, the drag sails were deployed in May 2017. This paper provides a first look at the on-orbit results from the CanX-7 mission, focusing on the performance of SFL’s drag sail device

Guidance, Navigation, and Control for Agile Small Spacecraft with Articulating Solar Arrays

Payload operations for small satellites are often impacted by the need to allocate time for modifying the attitude to perform power generation or orbit maneuvering. A typical small satellite design would consist of a single rigid body with body-mounted solar cells, making the power generation subject to the spacecraft’s attitude. Often to achieve the high power generation that is required to enable the payload function, the attitude must be specifically set to maximize the solar cell area facing the Sun, which typically means diverting it from an attitude that is useful for payload operations for some period of time. At the scale of modern global constellations, these downtimes in the payload operation schedule can greatly reduce the overall capability of the system. By including deployable, articulating solar arrays in the design of small spacecraft, array pointing can be decoupled from the mainpayload pointing operations. With these pieces decoupled, payload operations can proceed uninterrupted while the articulating arrays ensure sufficient power generation. In this paper, the dynamic equations of the multibody system are derived, and guidance, navigation, and control (GNC) considerations are presented for achieving decoupled attitude and articulation objectives. Results from simulation of a sample mission show that agile target tracking attitude maneuvers can be performed together with array solar tracking with negligible impact on overall payload pointing performance

Parallel-in-space-time, adaptive finite element framework for non-linear parabolic equations

We present an adaptive methodology for the solution of (linear and) non-linear time dependent problems that is especially tailored for massively parallel computations. The basic concept is to solve for large blocks of space-time unknowns instead of marching sequentially in time. The methodology is a combination of a computationally efficient implementation of a parallel-in-space time finite element solver coupled with a posteriori space-time error estimates and a parallel mesh generator. While we focus on spatial adaptivity in this work, the methodology enables simultaneous adaptivity in both space and time domains. We explore this basic concept in the context of a variety of time-steppers including Θ-schemes and Backward Difference Formulas. We specifically illustrate this framework with applications involving time dependent linear, quasi-linear and semi-linear diffusion equations. We focus on investigating how the coupled space-time refinement indicators for this class of problems aspect spatial adaptivity. Finally, we show good scaling behavior up to 150,000 processors on the NCSA Blue Waters machine. This conceptually simple methodology enables scaling on next generation multi-core machines by simultaneously solving for large number of time-steps, and reduces computational overhead by locally refining spatial blocks that can track localized features. This methodology also opens up the possibility of efficiently incorporating adjoint equations for error estimators and invers

Adaptable, Multi-Mission Design of CanX Nanosatellites

Through the development of a low-cost, 5 kg multi-mission nanosatellite bus at the University of Toronto Institute for Aerospace Studies’ Space Flight Laboratory, a number of new and interesting applications are now possible on a nanosatellite platform. Two ventures currently underway that adopt the multi-mission nanosatellite bus are an astronomy mission, CanX-3 (also known as the BRight Target Explorer - BRITE), and a dual-satellite formation flight mission, CanX-4/5. CanX-3 is a space telescope that will monitor long-term light fluctuations from the brightest stars in our galaxy to study stellar structure and galactic evolution. CanX-4/5 will demonstrate precise formation flight by controlling position to the 1 m level, and by providing determination with an order of magnitude better accuracy, all via a commercial GPS receiver and a custom propulsion system. The driving force behind the multi-mission concept is the objective of reducing non-recurring engineering design costs. While this approach violates microspace philosophy by not tailoring to each specific mission, this paper argues that consideration and combination of the mission requirement sets allow a limited generic approach that holds to the basic tenets of the philosophy, allowing substantial cost savings to be realized, over and above the case of tailoring to specific mission interests

Flow into a well by electric and membrane analogy

CER55DFP11.Includes bibliographical references.October, 1955.Proceedings - American Society of Civil Engineers, Engineering Mechanics Division, 1955

Chemical Abundances of Seven Irregular and Three Tidal Dwarf Galaxies in the M81 Group

We have derived nebular abundances for 10 dwarf galaxies belonging to the M81 Group, including several galaxies which do not have abundances previously reported in the literature. For each galaxy, multiple H \ii regions were observed with GMOS-N at the Gemini Observatory in order to determine abundances of several elements (oxygen, nitrogen, sulfur, neon, and argon). For seven galaxies, at least one H \ii region had a detection of the temperature sensitive [OIII] $\lambda$4363 line, allowing a "direct" determination of the oxygen abundance. No abundance gradients were detected in the targeted galaxies and the observed oxygen abundances are typically in agreement with the well known metallicity-luminosity relation. However, three candidate "tidal dwarf" galaxies lie well off this relation, UGC 5336, Garland, and KDG 61. The nature of these systems suggests that UGC 5336 and Garland are indeed recently formed systems, whereas KDG 61 is most likely a dwarf spheroidal galaxy which lies along the same line of sight as the M81 tidal debris field. We propose that these H \ii regions formed from previously enriched gas which was stripped from nearby massive galaxies (e.g., NGC 3077 and M81) during a recent tidal interaction.Comment: 37 pages, 10 figures, accepted for publication in ApJ. Slit positions in Table 2 have been update

Restructuring the Tridiagonal and Bidiagonal QR Algorithms for Performance

We show how both the tridiagonal and bidiagonal QR algorithms can be restructured so that they be- come rich in operations that can achieve near-peak performance on a modern processor. The key is a novel, cache-friendly algorithm for applying multiple sets of Givens rotations to the eigenvector/singular vector matrix. This algorithm is then implemented with optimizations that (1) leverage vector instruction units to increase floating-point throughput, and (2) fuse multiple rotations to decrease the total number of memory operations. We demonstrate the merits of these new QR algorithms for computing the Hermitian eigenvalue decomposition (EVD) and singular value decomposition (SVD) of dense matrices when all eigen- vectors/singular vectors are computed. The approach yields vastly improved performance relative to the traditional QR algorithms for these problems and is competitive with two commonly used alternatives— Cuppen’s Divide and Conquer algorithm and the Method of Multiple Relatively Robust Representations— while inheriting the more modest O(n) workspace requirements of the original QR algorithms. Since the computations performed by the restructured algorithms remain essentially identical to those performed by the original methods, robust numerical properties are preserved