Polar Mission Research Articles

Artificial Three-Body Equilibria for Hybrid Low-Thrust Propulsion

This paper proposes a new concept of creating artificial equilibrium points in the circular restricted three body problem, where the third body uses a hybrid of solar sail and solar electric propulsion. The work aims to investigate the use of a hybrid sail for artificial equilibrium points that are technologically di±cult with either of these propulsion systems alone. The hybrid sail has freedom in specifying the sail lightness number, then minimizing the required thrust acceleration from the solar electric propulsion thruster while satisfying the equilibrium condition. The stability analysis of such artificial equilibrium points by a linear method results in a linear time varying (mass) system. The freezing time method then provides unstable and marginally stable regions for hybrid solar sail artificial equilibria. We compare these propulsion systems with a given payload mass and mission life for a polar observation mission. For a near term sail assembly loading we find for the hybrid sail a substantially lower propellant mass compared to solar electric propulsion and lower sail length with respect to a solar sail, and a lower initial spacecraft mass.

Self-organized maps in scientific data analysis

The Thermal Ion Dynamics Experiment (TIDE) investigates low energy (0 - 500 eV) plasma in the Earth's magnetosphere, especially in the polar regions. It is part of NASA's larger POLAR mission. Shortly after the POLAR spacecraft was in orbit, TIDE's mass spectrometer functionality failed. However, data from other instruments can be used to create energy vs. time spectrograms. The number of peaks in these spectrograms relates to the composition of the plasma, so determining the number of peaks in the spectrogram effectively regains the mass spectrometer functionality. Kohonen self-organized maps (SOMs,) a type of neural network, are particularly suited to this problem due to the amount of data that needs to be analyzed and the algorithm's ability to find patterns within data. The algorithm leads to clustering of similar data points on the map. Ultimately, the location of the input data point on the map allows for determination of how many peaks the data point contains, and thus the composition of the plasma at that time. The SOM correctly classified 99% of the input data, making it a viable solution to the problem. Further research is planned, namely the possibility of extending this concept to investigate energetic neural atom (ENA) images in order to determine the source of these atoms.

Parametric Study of Spherical Rovers Crossing a Valley

T HE evidence ofwater onMars and the idea of using themoon as a staging ground for future planetary missions has increased interest in Martian and lunar exploration. Future missions will require the exploration of large areas on these surfaces because areas of scientific interest may be far away from the landing sites. Because of the inherent dangers with manned missions, rovers provide a viable option for future investigations of these regions. NASA currently employs wheeled rovers, including the Mars exploration rovers, to examine the Martian surface. These rovers are intricate and expensive, with limited ability to navigate rough terrain. This complicates gathering scientific data on Martian climate and geology and renders answering questions on the existence of water and life difficult. A vehicle capable of exploring large areas of terrain is the tumbleweed rover. A tumbleweed is a spherical (wind driven or selfpropelled) rover designed to provide superior mobility and greater accessibility on the surface of Mars and the moon. Compared with conventional wheeled rovers, a tumbleweed can cover vast distances faster and reach previously inaccessible areas of scientific interest, such as canyons and valleys. Because a tumbleweed is significantly less expensive than traditional rovers, multiple tumbleweeds can be deployed across the Martian or lunar surface for scientific surveys. The tumbleweed’s design is also well suited for polar missions because the rover can seek out water sources beneath a surface desert or an ice sheet, a task that cannot be done accurately from orbit. For these reasons, parametric studies describing and predicting a tumbleweed’s motion across the Martian or lunar terrain is valuable. The tumbleweed rover is based on concepts going back to the 1970s, where Jacques Blamont of the National Center for Space Studies developed the notion for wind-driven rovers. The concept has been pursued by several investigators at the NASA Langley Research Center (LaRC) and at the Jet Propulsion Laboratory (JPL). LaRC is focusing on concepts based on lightweight deployable structures, while JPL is focusing on inflatable concepts based on airbag landing technology. Other organizations, including Texas Technical University (TTU), North Carolina State University (NCSU), and the Swiss Federal Institute of Technology, are also examining wind-driven rover concepts. Research into the tumbleweed rover’s dynamics, however, is in its early stages. Feasibility studies on wind-driven mobility on the surface of Mars have been examined [1–8] and other studies have presented dynamic models for particular tumbleweed concepts [9– 14]. Several areas have been identified where the existing research can be expanded. Particularly, a numerical simulation model predicting a tumbleweed’s motion for arbitrary terrains is needed. Also required are parametric studies describing the tumbleweed’s behaviors on these terrains, which include flat planes, hills, ravines, and valleys. This paper presents parametric studies of a tumbleweed (or spherical) rover as it moves across a valley. The model used covers the rover’s bouncing, sliding, and rolling behaviors and its transitions between different terrain types. We present studies of the rover’s motion for various sets of parameters and initial conditions. Theses parametric studies will provide an understanding of the range of tumbleweed design parameters essential for mobility over shallow and deep valleys on Mars.

D/H ratio during the northern polar summer and what the Phoenix mission might measure

The Phoenix polar mission will land close to 68°N, 233°E in May 2008 at Ls ∼ 75 and operate 90 sols until Ls ∼ 125 with possible extension to Ls ∼ 142. Phoenix Meteorology (MET), Thermal and Evolved Gas Analyzer (TEGA) and Microscopy, Electrochemistry and Conductivity Analyzer (MECA) instrument packages will measure the air's temperature, water vapor concentration, ice crystal concentration and the water's stable isotope ratio D/H, and the D/H for the uppermost ground ice. This paper summarizes what is known about the seasonal cycle of atmospheric D/H and makes a theoretical connection between the atmospheric ratio and that expected from the ground ice that Phoenix will sample. A simple mixed cloud stable isotope model is used to show that the seasonal progress of D/H in the polar region cannot be used alone. It is argued that the seasonal cycle in D/H is explained by their being an interplay between multilatitudinal sources or reservoirs that have a range of reservoir D/H values. These reservoirs have different sizes and seasonal response times so that they release their water contributions at different times of the spring and summer and together explain most of the seasonal D/H observed by Mumma et al. (2003) and Novak et al. (2005). Phoenix observations from its high‐latitude vantage point during the summer and fall will add some atmospheric D/H values, temperature, water vapor concentration, and ice cloudiness data points that will constrain the various theoretical possibilities. The D/H of the ice recovered by Phoenix from the surface of the ground ice combined with the atmospheric D/H will suggest, whether the ground ice presently is a net receiver or supplier of water to the northern ice cap.

Survey of TES high albedo events in Mars' northern polar craters

Following the work exploring Korolev Crater (Armstrong et al., 2005) for evidence of crater interior ice deposits, we have conducted a survey of Thermal Emission Spectroscopy (TES) temperature and albedo measurements for Mars' northern polar craters larger than 10 km. Specifically, we identify a class of craters that exhibits brightening in their interiors during a solar longitude, Ls, of 60 to 120 degrees, roughly depending on latitude. These craters vary in size, latitude, and morphology, but appear to have a specific regional association on the surface that correlates with the distribution of subsurface hydrogen (interpreted as water ice) previously observed on Mars. We suggest that these craters, like Korolev, exhibit seasonal high albedo frost events that indicate subsurface water ice within the craters. A detailed study of these craters may provide insight in the geographical distribution of the ice and context for future polar missions.

Solar Polar Orbiter: A Solar Sail Technology Reference Study

An assessment is presented of a Solar Polar Orbiter mission as a Technology Reference Study. The goal is to focus the development of strategically important technologies of potential relevance to future science missions. The technology is solar sailing, and so the use of solar sail propulsion is, thus, defined a priori. The primary mission architecture utilizes maximum Soyuz Fregat 2-1b launch energy, deploying the sail shortly after Fregat separation. The 153 × 153 m square sail then spirals into a circular 0.48-astronomical-unit orbit, where the orbit inclination is raised to 90 deg with respect to the solar equator in just over 5 years. Both the solar sail and spacecraft technology requirements have been addressed. The sail requires advanced boom and new thin-film technology. The spacecraft requirements were found to be minimal because the spacecraft environment is relatively benign in comparison with other currently envisaged missions, such as the Solar Orbiter mission and BepiColombo.

HF fades caused by multiple wave fronts detected by a dipole antenna in the ionosphere

An experiment on transionospheric HF propagation was carried out in 1978 using a dedicated ground transmitter at Ottawa and the sounder receivers of the ISIS 1 and ISIS 2 spacecraft. This paper deals with resulting data from ISIS 2 at 1400 km altitude. Fade frequencies of one to a few hertz on 9.303‐MHz fixed‐frequency carrier signals were measured and were found to be confined to satellite locations between about 3° and 20° equatorward of the transmitter. The majority of the fades were of the Faraday type, involving ordinary (O) and extraordinary (X) wave components. There was also a smaller number of single‐mode fades interpreted as a beat interference between two O‐mode or two X‐mode rays that take different routes to the spacecraft. Rays traced through model ionospheric density distributions based on tomographic data show that rays launched toward the equator are more susceptible to focusing by latitudinal periodicity than rays launched toward the pole. Such refractive effects can produce two same‐mode rays with equal intensities and different propagation directions. Swept‐frequency ionograms interleaved with fixed‐frequency measurements have also been used to model density distributions in altitude and latitude. These distributions were used iteratively with three‐dimensional ray tracing to find rays that connected the transmitter with the position of the satellite at times of interest along its path. Faraday fade rates thus predicted agree with those observed equatorward of the transmitter. Geometric optics cannot account for observed X‐mode to O‐mode signal ratios of at least 10 dB in other parts of the passes, ruling out deep Faraday fades. This research supports planning for coordinated ground‐space radio experiments in the upcoming Enhanced Polar Outflow Probe satellite mission.

Cylindrical lower‐hybrid electron holes at the Earth's dayside magnetopause

The analytic model of lower‐hybrid electron holes (Jovanović and Shukla, 2004) is applied to analyze the strong coherent unipolar electric field signals perpendicular to the ambient magnetic field with a characteristic frequency in the lower‐hybrid frequency range, recorded at the dayside magnetopause by the Polar mission (Mozer et al., 2004). On the basis of a good agreement with theoretical predictions, these structures are identified as the oblique cylindrical electron holes. Their localization results from the balance of nonlinearity associated with the electrons that are trapped along the magnetic field direction and undergo the × drift in the perpendicular direction and the dispersion provided by the electron polarization drift. It is suggested that electron holes can be related to the nonlinear evolution of the Buneman instability of lower‐hybrid waves, driven by the parallel electric field that develops in the course of collisionless reconnection.

Evidence for subsurface water ice in Korolev crater, Mars

Following the work of Kieffer and Titus (2001, Icarus 154, 162–180), we present results of thermal IR observations of Korolev crater, located at ∼ 73 ° latitude in the martian northern polar region. Similar to techniques employed by Titus et al. (2003, Science 299, 1048–1050), we use infrared images from the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey to identify several regions within the crater basin with distinct thermal properties that correlate with topography. The THEMIS results show these regions exhibit temperature variations, spatially within the crater and throughout the martian year. In addition to the variations identified in the THEMIS observations, Mars Global Surveyor Thermal Emission Spectrometer (TES) observations show differences in albedo and temperature of these regions on both daily and seasonal cycles. Modeling annual temperature variations of the surface, we use TES observations to examine the thermal properties of these regions. This analysis reveals the crater interior deposits are likely thick layers (several meters) of high thermal inertia material (water ice, or extremely ice-rich regolith). Spatial variations of the physical properties of these regions are likely due to topography and possibly variations in the subsurface material itself. The nature of these deposits may help constrain polar processes, as well as provide context for the polar lander mission, Phoenix.

An overview of the scientific objectives and technical configuration of the NeUtral Atom Detector Unit (NUADU) for the Chinese Double Star Mission

The scientific objectives of an advanced NeUtral Atom Detector Unit (NUADU) designed for the Chinese Double Star Polar Mission, which is scheduled for launch in July 2004, are described. The potential during this mission to realize, hitherto unprecedented, integrated studies of global dynamic magnetospheric processes through combining with NUADU data contemporaneous measurements made aboard the CLUSTER II, IMAGE and TWINS spacecraft is also discussed and a short technical account of NUADU provided.

Morphology of the ring current derived from magnetic field observations

Abstract. Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ~3 RE and a main westward ring current at ~4–7 RE for all levels of geomagnetic disturbances. In general, the in-situ observations show that the ring current varies as the Dst index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (~0.5MA) and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ~3MA, whereas the total symmetric ring current is ~1MA. Thus, the partial ring current contributes dominantly to the decrease in the Dst index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in the sense of region-2 field-aligned currents, downward into the ionosphere near the dusk and upward out of the ionosphere near the dawn. Key words. Magnetospheric physics (current systems; storms and substorms; magnetospheric configuration and dynamics)

Tomorrow's energy today with Axane

Axane Fuel Cell Systems is a young, French-based company that is taking full advantage of its parent group, the industrial gases giant Air Liquide, to develop integrated alternative power generation solutions using its own PEM fuel cell technology combined with the supply of hydrogen. A prototype fuel cell was even operated successfully on a polar mission at extremely low ambient temperatures. Now the company is gearing up to commercialize the technology in products for early-adopter niche markets.

Telemachus: a mission for a polar view of solar activity

Telemachus is a polar solar-heliospheric mission described in the current NASA Sun–Earth Connections Roadmap (2003–2028). To continue the quest begun by Ulysses, Telemachus will be injected into a 0.2 AU × 2.5 AU solar polar orbit after gravitational encounters with Venus, Earth (twice) and Jupiter, followed by a maneuver at first perihelion. With an orbital period of 1.5 years, it will pass over the solar poles at a radial distance of 0.37 AU. The behavior of solar polar flows (heretofore unobservable) will provide critical boundary conditions on the transport of solar magnetic fields. Manifestations of the global flows and fields are the solar dynamo, formation of active regions, emission of the solar wind and the heliospheric magnetic field, launching of coronal mass ejections, eruption of solar flares, acceleration of solar energetic particles, and ultimately the dynamics of the entire heliosphere.

Identification of substorms within storms

The storm–substorm relationship is one of the central issues in magnetospheric physics. Whether there is a unique relationship between substorms and storms is still being debated. During geomagnetic storm periods, magnetic disturbances take place globally, and auroras become very active over the entire oval. These often make identification of a substorm, which has smaller magnetic and optical effects, difficult, if not impossible. This study is based on 23 storms and 167 concurrent substorms that occurred from May 1996 to October 1998 with simultaneous global ultraviolet auroral observations from NASA's Polar mission. It is found that the auroral breakups occurred more frequently in the main phase than in the recovery phase within the storms; ∼45% of the studied events occurring within 10 h before the end (start) of the storm main (recovery) phase; the storm intensity ( D st) does not affect the occurrence of auroral breakup; and D st changes (Δ D st) have no effect on the occurrence frequency of auroral breakup.

High-frequency direction finding in space

Transionospheric propagation experiments at high frequency (HF) are planned in the Enhanced Polar Outflow Probe small-satellite mission. Crossed dipoles connected to a HF receiver in the spacecraft will be used to measure parameters of incident waves originating from coordinated ground transmitters. This article is concerned with the measurement of one important wave parameter: its direction of arrival (DOA). Two important issues about the receiving antenna signals are addressed here: the effective length of the dipoles, and the computational method of determining the DOA from the amplitudes and relative phase of signals. The electric field radiated by the monopole elements composing the dipoles has been calculated using the NEC4 code. With recourse to the reciprocity principle that the effective length of the active dipole equals that of the same dipole as a receiving antenna, the dependence of the effective length on DOA has been computed, for various antenna-spacecraft configurations. For 3 m monopoles combined as dipoles, and for frequencies between 5 and 18 MHz, effective lengths can be well approximated using a simple expression for a short dipole, with modest adjustment to include asymmetries of the transmitting members. The radiation-reception patterns of isolated monopoles are quite symmetric, implying that the experiment does not depend critically on dipole signals. The antenna models provide a basis for the numerical technique for inverting the amplitude and phase of voltages induced by an plane wave incident on crossed dipoles to the DOA of the wave. The procedure assumes a cw elliptically polarized wave, taking account of plasma effects. The mathematics leads to expressions for the induced dipole voltages as functions of the wave vector azimuthal and polar angles. The inverse determination of the DOA angles is underspecified for only two dipoles, and requires selecting the true solution from two or more possible azimuth-polar pairs throughout the 4π sr solid-angle space surrounding the spacecraft. The selection of the solution will be guided by values expected for the known ground-transmitter and satellite positions, and by other wave parameter measurements.

Advances in Launch Vehicle Electronics in India

Electronics forms an integral part of a launch vehicle. As vehicles advance in capacity and complexity so does electronics concurrently with other aerospace technologies. The paper first describes technological advances in Navigation, Guidance and Control (NGC) system, and Telemetry, Tracking and Command (TTC) system, the two basic functional blocks of launch vehicle electronics, in early 70s to meet the demands of India's first launch vehicle SLV-3. It, then, describes the advances that took place in onboard electronics in 80s, and 90s to meet the requirements of polar and geosynchronous missions, as well as from developmental to operational missions. The paper also indicates future technological trends in this area.

Ethological observations on a small group of wintering members at Dumont d'Urville station (Terre Adélie)

The goal of this study was to demonstrate the role of isolation on the social behaviour of individuals and to characterize its adaptation as a function of time. The ethological method used was a quantitative description of the spatial positioning of a sub-group of 13 wintering members during the morning, midday and evening meals at Dumont d'Urville station. The observation protocol required the completion of first daily and then weekly (every Thursday) observation maps at different stages of the 13 month long polar mission, from the information seminar in France, the trips outward and return aboard the Astrolabe, the two summer campaigns at the beginning and at the end of the mission and the overwintering period. Results, mainly expressed as human concentration and spatial dispersion indexes, have successively shown organization, disorganization and reorganization periods of the small group without any significant cycling. Socialisation rules promoting the group building in the early period, conflict factors and relay steps (external perturbations breaking the isolation, transitions during group displacement from one stage to another) promoting the maintenance of the social cohesion, are outlined in the discussion.

Statistics of the mid‐altitude cusp observed by Polar

The Polar GGS space mission has allowed the northern hemispheric polar cusp region to be probed in a variety of ways to further our understanding and knowledge of the processes that occur within this region. The discovery of pulsed, energy‐dispersed ion injections on newly‐opened field lines (Pulsed Particle Signatures, or PPSs), the magnetospheric plasma signatures of transient reconnection, is one such advancement in our knowledge. Utilising a ∼22 months subset of Polar's mission, we perform a statistical study of the dayside traversals of the cusp region by the spacecraft to determine the extent and location of PPSs as well as the prevailing Interplanetary Magnetic Field (IMF) conditions under which they occur. In this paper we report upon the broad extent of these signatures in latitude and local time regardless of IMF orientation, and show that PPSs occur under both southward and northward IMF conditions in high percentages, although favouring southward directed IMF. These results are discussed in terms of previous statistical studies of reconnection signatures, and in terms of lobe and low latitude reconnection.

Ral ground station for small missions

A 12.5 m S Band ground station was installed at Chilton in 1980. It was used as the prime ground station for the Infrared Astronomy Satellite (IRAS) and later for command and control of the UK Active Magnetospheric Particle Tracer Explorer mission (AMPTE). More recently, it has been brought back into use for the low cost and more autonomous operations with the Advanced Composition Explorer (ACE) satellite and is being prepared for the UK Space Technology Research Vehicle (STRV) and two polar orbiter missions. This paper reviews, after 18 months of operations, the performance achieved in supporting ACE with the autonomous systems put in place at Chilton as well as, the cost effectiveness. Maintenance of an ageing antenna has been a challenge and is discussed. More automatic systems are planned for STRV including prototyping work on the new CCSDS standards for Space Link Extension services which should allow interoperability between the STRV Control Centre and the two UK antennas at Chilton and West Freugh. The advent of polar orbiting operations will increase the need for multi-satellite operations (i.e. ACE, STRV, Moroccosat and Badr-B will be operating together) and the need for contention resolution and rapid switching between the missions. New equipment standards and web-based systems play a key role in the achievements reported.

The prospects for enhanced international polar-orbiting satellite cooperation

With robust polar satellite missions demonstrated and/or operational in the USA, Europe, Japan, China, Russia, India, and Brazil, and with other nations also likely to develop such capability, this paper examines the prospects for as well as the potential challenges to closer and perhaps more formal international polar satellite cooperation. In suggesting that now is the time to explore the development of a coordinated polar observing system, the present paper identifies potential contributors, assesses the relevance of existing space-based Earth observation international coordination mechanisms, and considers three potential models for a future system.