The stretched lens array (SLA) [spacecraft solar power]

At IECEC 2001, this team presented a paper on the new stretched lens array (SLA), including its evolution from the successful SCARLET array on the NASA/JPL Deep Space 1 spacecraft. Since that conference, the SLA team has made significant advances in SLA technology, including component-level improvements, array-level optimization, space environment exposure testing, and prototype hardware fabrication and evaluation. This paper describes the evolved version of the SLA, highlighting recent improvements in the lens, solar cell, photovoltaic receiver, rigid panel structure, and complete solar array wing. In addition to excellent durability in the space environment, the near-term SLA will provide outstanding wing-level performance parameters: 180 W/kg specific power; 300 W/m/sup 2/ power density; 300 V operational voltage; 85% savings in cell area (cm/sup 2//W) and cell-related cost ($/W) compared to planar arrays; 9 kW/m/sup 3/ stowed power at launch.     

Walker Model for Radar Sensing of Rigid Target Fields

The objective of this primarily tutorial item is to describe a general model for the observable data and the appropriate data processing involved in sensing rigid target fields with coherent radars. Any number of radars may be involved, and the scene and each radar may be in any kind of motion-with no restrictions on motion through resolution cells during the coherent processing time of the radars. The motions are assumed to be known. To some extent motion parameters can be estimated from the radar data, e.g., by adaptive parameter adjustments in the data processing; however, this subject is beyond the scope of this discussion. In large measure, the analysis in this item highlights the central conceptual result obtained by J.L. Walker as described in [1] -a major work in radar theory.     

On Uniform Sampling of Amplitude Modulated Signals

For a bandpass waveform produced by the amplitude modulation of a low-pass signal, it is shown that the corresponding bandpass signal may be recovered from its samples taken at a uniform rate which is equal to or less than half the sampling rate called for in applying the classical bandpass sampling theorem.     

Policy for robust space-based earth science,technology and applications

Satellite remote sensing technology has contributed to the transformation of multiple earth science domains, putting space observations at the forefront of innovation in earth science. With new satellite missions being launched every year, new types of earth science data are being incorporated into science models and decision-making systems in a broad array of organizations. Policy guidance can influence the degree to which user needs influence mission design and when, and ensure that satellite missions serve both the scientific and user communities without becoming unfocused and overly expensive. By considering the needs of the user community early on in the mission-design process, agencies can ensure that satellites meet the needs of multiple constituencies. This paper describes the mission development process in NASA and ESA and compares and contrasts the successes and challenges faced by these agencies as they try to balance science and applications within their missions.     

Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission

The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE _FWHM/E≈15 %. The dominant ion species (H⁺, He⁺, and O⁺) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance.     

Gravity modeling in aerospace applications

The science of inertial navigation has evolved to the point that the traditional gravity model is a principal error source in advanced, precise systems. Specifically, the unmodeled vertical deflections of the earth's gravitational field are a major contributor to CEP (circular error probable) divergence in precise terrestrial inertial navigation systems (INS). Over the years, several studies have been undertaken to the development of advanced techniques for accurate, real-time compensation of gravity disturbance vectors. More complex on-board gravity models which compute vertical deflection components will reduce the CEP divergence rate, but imperfect modeling due to on-board processing limitations will still cause residual vertical deflection errors. In order to eliminate or reduce gravity-induced errors in the INS requires measurement of gravity disturbance values and in-flight compensation to the inertial navigator. It is assumed in this paper that gravity disturbance values have been measured prior to the airborne mission and various techniques for compensation are to be considered. As part of a screening process in this study, several gravity compensation techniques (both deterministic and stochastic models) were investigated. The screening process involved identification of gravity models and algorithms, and developments of selection criteria for subsequent screening of the candidates.     

Planetary protection issues of private endeavours in research,exploration, and human access to space: An environmental economics approach to forward contamination

In light of the rapidly growing New Space Economy, the landscape of space exploration and development activities will certainly become much more complicated year by year. Relevant commercial space actors have already emerged, pushing the boundaries of entrepreneurial space ventures beyond the Earth-oriented upstream and downstream market segments and opening up the path towards the novel segments of space exploration, space resources utilization, and space research. Planetary protection is usually defined as a set of guidelines concerning the avoidance of bidirectional biological material exchange between the Earth and other celestial bodies. Recent success stories of established and new-entrant NewSpace actors, although posing no realistic planetary protection threat at present, clearly indicate that serious work needs to be done in order for the relevant guidelines to keep up with the rapid advances of the technology development cycles that occur within NewSpace companies. This need may become even more urgent, as space entrepreneurs acquire and develop the resources and competencies to target the currently underserved market segments of space research, exploration, and utilization. As of now, these capabilities were maintained solely by public space agencies; thus, all planetary protection priorities, strategies, and responsibilities were discussed, agreed-upon, and delegated for implementation among national and international working groups of public stakeholders. Although top-down regulations can be effective in controlling the quality and conformity of the deliverables of private subcontractors to public contractors, international planetary protection frameworks might need to evolve even beyond such unmet public-private interaction and partnership models. For this reason, this study did not focus on the legal and political issues of mandating NewSpace actors to adhere to planetary protection guidelines; rather, drawing from the field of sustainable development on Earth, an environmental economics approach was followed, with the goal of viewing the relationship between planetary protection and private space exploration and development as another “tragedy of the commons” problem that must be settled accordingly. After the problem’s framing, i.e. the conceptual presentation and synthesis of four extraterrestrial non-excludable goods, the initial approach of their total economic value, and the negative externalities of their exploitation, a discussion of the forward contamination mitigation costs was conducted. Drawing from the literature and using examples from both the terrestrial and aerospace sectors, a pre-emptive move was suggested: the establishment of a global industry consortium for the pre-competitive collaboration in forward contamination mitigation technologies, centered on an international planetary protection analogue program and its respective testbed facility.     

Space and Copenhagen: The role of satellites

A half-day meeting on the role of satellites in combating climate change was added on to the eleventh annual European Interparliamentary Space Committee meeting in London, October 2009. Organized by the UK Parliamentary Space Committee and the European Space Policy Institute, the meeting's four speakers covered a range of issues, before engaging in discussion with questions from the floor. The main points raised are presented below.     

SAR resolution in the presence of phase errors

The author analyzes the effects of phase errors on synthetic aperture radar (SAR). The theory is applied to the following question: how does the achievable resolution vary with the carrier frequency when optimum quadratic focus and/or optimum processing interval (synthetic aperture length) are used? Numerous related results are given, so that much of the material is tutorial. For phase errors corresponding to uncompensated motion, the best achievable RMS resolution with any phase error spectrum satisfies the derived equation. For motion-induced phase errors it is seen that resolution improves with increasing carrier frequency when the first term in the expression applies (e.g. for phase errors concentrated at low frequencies) and resolution is independent of carrier frequency when R δ/v/v is the smaller term (e.g. with broad band or high frequency phase errors)