The optical slit sensor as a standard sensor for spacecraft attitude determination

The basic concept of an optical slit sensor as a standard altitude sensor is considered for any missions using a spinning spacecraft or where rotating sensors or mirrors could be used. Information available from a single sensor or from two sensors is analyzed. A standard slit sensor package is compared with the altitude package flown on the first synchronous meteorological satellite

Predicted multiply-imaged X-ray AGNs in the XXL survey

We estimate the incidence of multiply-imaged AGNs among the optical counterparts of X-ray selected point-like sources in the XXL field. We also derive the expected statistical properties of this sample, such as the redshift distribution of the lensed sources and of the deflectors that lead to the formation of multiple images, modelling the deflectors using both spherical (SIS) and ellipsoidal (SIE) singular isothermal mass distributions. We further assume that the XXL survey sample has the same overall properties as the smaller XMM-COSMOS sample restricted to the same flux limits and taking into account the detection probability of the XXL survey. Among the X-ray sources with a flux in the [0.5-2] keV band larger than 3.0x10$^{-15}$ erg cm$^{-2}$ s$^{-1}$ and with optical counterparts brighter than an r-band magnitude of 25, we expect ~20 multiply-imaged sources. Out of these, ~16 should be detected if the search is made among the seeing-limited images of the X-ray AGN optical counterparts and only one of them should be composed of more than two lensed images. Finally, we study the impact of the cosmological model on the expected fraction of lensed sources.Comment: 15 pages, 7 figures, 1 table, accepted for publication in MNRA

Analytical, circle-to-circle low-thrust transfer trajectories with plane change

Orbit averaging techniques are used to develop analytical approximations of circle-to-circle low-thrust trajectory transfers with plane-change about the Sun. Separate expressions are developed for constant acceleration, or thrust, electric propulsion, solar sail propulsion and combined, or hybrid electric (constant acceleration or thrust) / solar sail propulsion. The analytical expressions uniquely allow the structure of circle-to-circle low-thrust trajectory transfers with plane-change about the Sun to be understood, and the optimal trajectory structure is analytically derived for each propulsion system considered. It is found that the optimal fixed thrust electric propulsion transfer reduces the orbit radius with no plane change and then performs the plane-change, while the optimal solar sail and hybrid transfers combine the reduction of orbit radius with some plane change, before then completing the plane change. The optimal level of plane change during the reduction of orbit radius is derived and it is found the analytically-derived minimum time solar sail transfer is within 1% of the numerically-derived optimal transfer. It is also found that, under the conditions considered, a sail characteristic acceleration of less than 0.5 mm/s2 can, in 5-years, attain a solar orbit that maintains the observer-to-solar pole zenith angle below 40 degrees for 25 days; the approximate sidereal rotation period of the Sun. However, a sail characteristic acceleration of more than 0.5 mm/s2 is required to attain an observer-to-solar pole zenith angle below 30 degrees for 25 days within 5-years of launch. Finally, it was found that the hybridization of electric propulsion and solar sail propulsion was, typically, of more benefit when the system was thrust constrained than when it was mass constrained

An earth pole-sitter using hybrid propulsion

In this paper we investigate optimal pole-sitter orbits using hybrid solar sail and solar electric propulsion (SEP). A pole-sitter is a spacecraft that is constantly above one of the Earth's poles, by means of a continuous thrust. Optimal orbits, that minimize propellant mass consumption, are found both through a shape-based approach, and solving an optimal control problem, using a direct method based on pseudo-spectral techniques. Both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows consistent savings on propellant mass fraction. Finally, is it shown that for sufficiently long missions (more than 8 years), a hybrid spacecraft, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft

Making the move from C to Python with mechanical engineering students

Work is underway in the Mechanical Engineering Department at San Jose State University to transition the first course in computer programming (ME 30 Computer Applications) and a follow-on course, ME 106 Fundamentals of Mechatronics, from C to Python. Both courses make extensive use of a microcontroller to teach the fundamentals in both subjects, and heretofore have used the C language and the Arduino platform, but now both courses have moved to Python and to the Adafruit Feather M4 Express board, which can run Python natively on its associated microcontroller. Prior to the transition to Python, ME 30 had a relatively high failure rate between about 10 - 35%. Since transitioning to Python, the failure rate dropped dramatically to about 3% in the fall of 2019. The paper will outline the previous structure of the courses, explain the motivation for transitioning from C to Python, and discuss the pros and cons of the transition observed to date

Recruiting VR Troopers: Bringing Introductory Programming Projects to Life in Virtual Reality

Classes in introductory programming often focus on solving small, succinct problems that can typically be completed in few lines of source code. While useful for learning the basics of algorithm implementation and language syntax, this method suggests to learners that all programming problems exist in isolation and are self-contained. In contrast, most programming assignments faced by fresh graduates are large in scope and require use of many pre-built libraries and extensions. As a result, students are not entirely prepared to write code that will function within a larger system. To address this problem, an introductory C programming course at Valparaiso University has explored the use of virtual reality as a means to motivate students to have fun while practicing coding skills and showcase the power of working within constraints of a complex system. Students are provided a brief introduction to the OpenGL 3D graphics framework and then asked to design a small, optionally animated, scene using their current knowledge of the C programming language. Later in the semester, these same students are brought into a VisCube Virtual Reality system to experience their scenes in a fully immersive environment. The VisCube uses eight rendering paths and stereo displays to generate a 3D scene in a 10’x8’x6’ cube. This exercise serves to show students that even a simple scene can then easily expanded to display in a virtual reality environment. We discuss the project assignment and student impacts using assessment and provide a brief discussion of how this can be adapted to facilities with other viualization capabilities

Generation of optimal trajectories for Earth hybrid pole sitters

A pole-sitter orbit is a closed path that is constantly above one of the Earth's poles, by means of continuous low thrust. This work proposes to hybridize solar sail propulsion and solar electric propulsion (SEP) on the same spacecraft, to enable such a pole-sitter orbit. Locally-optimal control laws are found with a semi-analytical inverse method, starting from a trajectory that satisfies the pole-sitter condition in the Sun-Earth circular restricted three-body problem. These solutions are subsequently used as first guess to find optimal orbits, using a direct method based on pseudospectral transcription. The orbital dynamics of both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows savings on propellant mass fraction. Finally, it is shown that for sufficiently long missions, a hybrid pole-sitter, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft