ARTEMIS Mission Overview: From Concept to Operations

ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun) repurposed two spacecraft to extend their useful science (Angelopoulos, 2010) by moving them via lunar gravity assists from elliptical Earth orbits to L1 and L2 Earth-Moon libration orbits and then to lunar orbits by exploiting the Earth-Moon-Sun dynamical environment. This paper describes the complete design from conceptual plans using weak stability transfer options and lunar gravity assist to the implementation and operational support of the Earth-Moon libration and lunar orbits. The two spacecraft of the ARTEMIS mission will have just entered lunar orbit at this paper's presentation

A Report of an Epidemic With Certain Cases Presenting the Picture of Meningo-Encephalitis:

n/

Short- and Long-Term Propagation of Spacecraft Orbits

The Planetary Observer Planning Software (POPS) comprises four computer programs for use in designing orbits of spacecraft about planets. These programs are the Planetary Observer High Precision Orbit Propagator (POHOP), the Planetary Observer Long-Term Orbit Predictor (POLOP), the Planetary Observer Post Processor (POPP), and the Planetary Observer Plotting (POPLOT) program. POHOP and POLOP integrate the equations of motion to propagate an initial set of classical orbit elements to a future epoch. POHOP models shortterm (one revolution) orbital motion; POLOP averages out the short-term behavior but requires far less processing time than do older programs that perform long-term orbit propagations. POPP postprocesses the spacecraft ephemeris created by POHOP or POLOP (or optionally can use a less accurate internal ephemeris) to search for trajectory-related geometric events including, for example, rising or setting of a spacecraft as observed from a ground site. For each such event, POPP puts out such user-specified data as the time, elevation, and azimuth. POPLOT is a graphics program that plots data generated by POPP. POPLOT can plot orbit ground tracks on a world map and can produce a variety of summaries and generic ordinate-vs.-abscissa plots of any POPP data

Placebo-controlled phase 3 study of oral BG-12 or glatiramer in multiple sclerosis.

BACKGROUND: BG-12 (dimethyl fumarate) is in development as an oral treatment for relapsing-remitting multiple sclerosis, which is commonly treated with parenteral agents (interferon or glatiramer acetate). METHODS: In this phase 3, randomized study, we investigated the efficacy and safety of oral BG-12, at a dose of 240 mg two or three times daily, as compared with placebo in patients with relapsing-remitting multiple sclerosis. An active agent, glatiramer acetate, was also included as a reference comparator. The primary end point was the annualized relapse rate over a period of 2 years. The study was not designed to test the superiority or noninferiority of BG-12 versus glatiramer acetate. RESULTS: At 2 years, the annualized relapse rate was significantly lower with twice-daily BG-12 (0.22), thrice-daily BG-12 (0.20), and glatiramer acetate (0.29) than with placebo (0.40) (relative reductions: twice-daily BG-12, 44%, P<0.001; thrice-daily BG-12, 51%, P<0.001; glatiramer acetate, 29%, P=0.01). Reductions in disability progression with twice-daily BG-12, thrice-daily BG-12, and glatiramer acetate versus placebo (21%, 24%, and 7%, respectively) were not significant. As compared with placebo, twice-daily BG-12, thrice-daily BG-12, and glatiramer acetate significantly reduced the numbers of new or enlarging T(2)-weighted hyperintense lesions (all P<0.001) and new T(1)-weighted hypointense lesions (P<0.001, P<0.001, and P=0.002, respectively). In post hoc comparisons of BG-12 versus glatiramer acetate, differences were not significant except for the annualized relapse rate (thrice-daily BG-12), new or enlarging T(2)-weighted hyperintense lesions (both BG-12 doses), and new T(1)-weighted hypointense lesions (thrice-daily BG-12) (nominal P<0.05 for each comparison). Adverse events occurring at a higher incidence with an active treatment than with placebo included flushing and gastrointestinal events (with BG-12) and injection-related events (with glatiramer acetate). There were no malignant neoplasms or opportunistic infections reported with BG-12. Lymphocyte counts decreased with BG-12. CONCLUSIONS: In patients with relapsing-remitting multiple sclerosis, BG-12 (at both doses) and glatiramer acetate significantly reduced relapse rates and improved neuroradiologic outcomes relative to placebo. (Funded by Biogen Idec; CONFIRM ClinicalTrials.gov number, NCT00451451.).clinical trial, phase iiicomparative studyjournal articlemulticenter studyrandomized controlled trialresearch support, non-u.s. gov't2012 Sep 20importedErratum in : N Engl J Med. 2012 Oct 25;367(17):1673

Epicycles and oscillations: The dynamics of the LISA orbits

This paper presents a modern treatment of epicycle theory, which is an exact series representation of Keplerian motion, and uses that theory to develop the first analytic method for analyzing the higher order dynamics of the LISA orbits. LISA, the Laser Interferometer Space Antenna mission, uses a constellation of three spacecraft in heliocentric space and takes advantage of particular solutions of the Clohessy-Wiltshire equations, a first-order approximation of gravitational dynamics, to keep the constellation an equilateral triangle. The higher-order analysis presented here suggests a modification of the basic LISA orbit architecture which may improve the stability of the constellation

How to Maneuver Around in Eccentricity Vector Space

The GRAIL mission to the Moon will be the first time that two separate robotic orbiters will be placed into formation in orbit around a body other than Earth. The need to design an efficient series of maneuvers to shape the orbits and phasing of the two orbiters after arrival presents a significant challenge to mission designers. This paper presents a simple geometric method for relating in-plane impulsive maneuvers to changes in the eccentricity vector, which determines the shape and orientation of an orbit in the orbit plane. Examples then show how such maneuvers can accommodate desired changes to other orbital elements such as period, incination, and longitude of the ascending node

Earth Orbit Raise Design for the ARTEMIS Mission

ARTEMIS is a mission to send two spacecraft from Earth orbit to libration orbits around the Moon Lagrange points and then into lunar orbit. Lunar flybys were used early in the mission to send the spacecraft into low-energy lunar transfers which were designed libration orbits for minimal deltaV. ARTEMIS began by raising the Earth orbits of each spacecraft to achieve the planned lunar flybys. Spacecraft conguration and operation constraints made the Earth orbit raise phase of the mission a signicant mission design challenge by itself. This paper describes the process used to and trajectories that achieved mission goals and the resulting series of Earth orbits that culminated in successful lunar flybys

Flight Dynamics Challenges for the GRACE Follow-On Mission

The GRACE Follow-On (GRACE-FO) mission is a partnership between NASA and the German Research Centre for Geosciences (GFZ) and will be operated by the German Space Operations Centre (GSOC) / DLR. The baseline launch date is in August, 2017. It is a follow on mission for the successful GRACE (Gravity Recovery and Climate Experiment) mission. Two twin satellites are flying approximately 220 kilometers apart in a polar, nearly circular orbit starting at an altitude of 500 kilometers, which slowly decreases during the mission. For a nominal mission lifetime of 5 years detailed measurements of Earth’s gravity field and atmosphere are collected and provided to the science community to support an understanding of the distribution and flow of mass on and within the Earth. Key tasks are getting into and maintaining the formation of the two satellites and operation of the experimental Laser Ranging Interferometer (LRI) payload allowing highly accurate inter-satellite range rate determination. This paper gives an overview of the GRACE-FO mission and its main Flight Dynamics challenges. A deeper look into the formation acquisition strategy and the operations support of the LRI instrument is provide

The Eccentric Behavior of Nearly Frozen Orbits

Frozen orbits are orbits which have only short-period changes in their mean eccentricity and argument of periapse, so that they basically keep a fixed orientation within their plane of motion. Nearly frozen orbits are those whose eccentricity and argument of periapse have values close to those of a frozen orbit. We call them "nearly" frozen because their eccentricity vector (a vector whose polar coordinates are eccentricity and argument of periapse) will stay within a bounded distance from the frozen orbit eccentricity vector, circulating around it over time. For highly inclined orbits around the Earth, this distance is effectively constant over time. Furthermore, frozen orbit eccentricity values are low enough that these orbits are essentially eccentric (i.e., off center) circles, so that nearly frozen orbits around Earth are bounded above and below by frozen orbits

Low Lunar Orbit Design via Graphical Manipulation of Eccentricity Vector Evolution

Low lunar orbits, such as those used by GRAIL and LRO, experience predictable variations in the evolution of their eccentricity vectors. These variations are nearly invariant with respect to the initial eccentricity and argument of periapse and change only in the details with respect to the initial semi-major axis. These properties suggest that manipulating the eccentricity vector evolution directly can give insight into orbit maintenance designs and can reduce the number of propagations required. A trio of techniques for determining the desired maneuvers is presented in the context of the GRAIL extended mission