Recent experimental measurements of space platform charging at LEO altitudes

The estimation of the extent of electrical charging of space platforms at low earth orbit (LEO) altitudes has been a subject of interest for a number of years. Early estimates based on theoretical current-voltage relationships of Langmuir and Blodgett and Parker and Murphy predicted a wide range of possible electrical potentials for a platform being actively charged at LEO altitudes. The experimental success of early electron beam experiments suggested that the early theories were incomplete. This has led to the development of space experiments specifically designed to study the degree of electrical charging resulting from electron beam emission, and also supplementary experiments to determine the current voltage relationship of large structures biassed to high voltages in the LEO environment. The paper will discuss some of the results of vehicle electrical potential from recent sounding rocket experiments involving charging of a space platform by both electron beam emission, and by the application of differential bias between elements of the platform.     

Temporal analysis of suspended solid in Tokyo Bay by Landsat data

The amount of suspended solid (S.S.) discharged from Tokyo metropolitan area is estimated by use of multi-temporal Landsat data from 1979 to 1980. The method to estimate S.S. was verified with sea truth data which was observed with Landsat passes covering Tokyo Bay. The radiometric information is normalized against seasonal change of sun illuminations and atmospheric conditions. Path radiance estimation methods were discussed, because its effects are very sensitive to the estimation of S.S. concentration by Landsat MSS data. Temporal changes of S.S. distribution was also interpreted.     

Observation of the lunar topography by the laser altimeter LALT on board Japanese lunar explorer SELENE

The SELENE Laser Altimeter (LALT) is designed to map the Moon’s topography and will be launched in summer 2007. LALT incorporates Q-switched Cr doped Nd:YAG laser (1064 nm) with an output energy of 100 mJ and 1 Hz repetition frequency for about one year mission period. The laser pulse travels to the Moon’s surface and reflections from the surface are detected by a silicon avalanche photo-diode. The ranging distance is 50–150 km with about 5 m accuracy. Several corrections for accurate ranging data are investigated. The flight hardware has been qualified and passed all the integration tests. A principal goal of the LALT instrument is to obtain a much more detailed lunar topographic map which is superior in global coverage, measurement accuracy and number of data points to previous observations and models. The overall science objectives of LALT are (1) determination of lunar global figure, (2) internal structure and surface processes, (3) exploration of the lunar pole regions, and (4) reduction of lunar occultation data.     

Paths not taken – The Gossamer roadmap’s other options

Highly efficient low-thrust propulsion is increasingly applied beyond commercial use, also in mainstream and flagship science missions, in combination with gravity assist propulsion. Another recent development is the growth of small spacecraft solutions, not in size but in numbers and individual capabilities.Just over ten years ago, the DLR-ESTEC Gossamer Roadmap to Solar Sailing was set up to guide technology developments towards a propellant-less and highly efficient class of spacecraft for solar system exploration and applications missions: small spacecraft solar sails designed for carefree handling and equipped with carried application modules.Soon, in three dedicated Gossamer Roadmap Science Working Groups it initiated studies of missions uniquely feasible with solar sails such as Displaced L₁ (DL1) space weather advance warning and monitoring, Solar Polar Orbiter (SPO) delivery to very high inclination heliocentric orbit, and multiple Near-Earth Asteroid (NEA) rendezvous (MNR). Together, they demonstrate the capability of near-term solar sails to achieve at least in the inner solar system almost any kind of heliocentric orbit within 10 years, from the Earth-co-orbital to the extremely inclined, eccentric and even retrograde. Noted as part of the MNR study, sail-propelled head-on retrograde kinetic impactors (RKI) go to this extreme to achieve the highest possible specific kinetic energy for the deflection of hazardous asteroids.At DLR, the experience gained in the development of deployable membrane structures leading up to the successful ground deployment test of a (20 m)², i.e., 20 m by 20 m square solar sail at DLR Cologne in 1999 was revitalized and directed towards a 3-step small spacecraft development line from as-soon-as-possible sail deployment demonstration (Gossamer-1) via in-flight evaluation of sail attitude control actuators (Gossamer-2) to an envisaged proving-the-principle flight in the Earth-Moon system (Gossamer-3). First, it turned the concept of solar sail deployment on its head by introducing four separable Boom Sail Deployment Units (BSDU) to be discarded after deployment, enabling lightweight 3-axis stabilized sailcraft. By 2015, this effort culminated in the ground-qualified technology of the DLR Gossamer-1 deployment demonstrator Engineering Qualification Model (EQM). For mission types using separable payloads, such as SPO, MNR and RKI, design concepts can be derived from the BSDU characteristic of DLR Gossamer solar sail technology which share elements with the separation systems of asteroid nanolanders like MASCOT. These nano-spacecraft are an ideal match for solar sails in micro-spacecraft format whose launch configurations are compatible with ESPA and ASAP secondary payload platforms.Like any roadmap, this one contained much more than the planned route from departure to destination and the much shorter distance actually travelled. It is full of lanes, narrow and wide, detours and shortcuts, options and decision branches. Some became the path taken on which we previously reported. More were explored along the originally planned path or as new sidings in search of better options when circumstance changed and the project had to take another turn. But none were dead ends, they just faced the inevitable changes when roadmaps face realities and they were no longer part of the road ahead. To us, they were valuable lessons learned or options up our sleeves. But for future sailors they may be on their road ahead.     

Characteristics of piezoelectric lead zirconate titanate multilayered detector bombarded with hypervelocity iron particles

A cosmic dust detector is currently being developed using a piezoelectric lead zirconate titanate (PZT) element. The characteristics of the multilayered detector (MD), which was composed of one hundred PZT disks, were investigated by bombarding it with hypervelocity iron particles supplied by a Van de Graaff accelerator. It was confirmed that there was a linear relationship between the signal amplitude observed from MD and the momentum of the particles. As compared with the single-layered detector (SD) that was composed of one PZT disk, it was found that the sensitivity of MD was ∼3 times higher than that of SD within the limits of the experimental conditions.     

Laboratory experiments on spacecraft charging and its neutralization

Simulation experiments on spacecraft charging in space plasma and its neutralization are performed in relation to the electron beam experiment (SEPAC) on Space Shuttle Spacelab 1. A spacecraft simulator or a spherical probe is immersed in a magnetized plasma and a positive high voltage with respect to the plasma is externally applied to it. The current-voltage characteristics follow quite well with the theoretical model of Parker and Murphy [1] in the low voltage, low pressure region. When the voltage rises to more than the ionization potential of the surrounding neutral gas, it departs from the model and the effect of plasma production by the electron current becomes very important. The same kind of ionization effect as this has also been observed in our rocket experiments with an electron beam. The enhancement of the ionization effect by an additional neutral gas injection causes a considerable suppression of the potential rise of a spacecraft emitting an electron beam. This is demonstrated with the SEPAC accelerators in a large space chamber experiment.     

Electron beam experiments in Japanese satellites and rockets

Electron beam experiments in space that have been done and planned in Japan are reviewed. 200eV, 1mA electron beam is emitted from a satellite and several types of wave excitation such as UHF and ω_ce have been observed. The satellite potential and the energy spectrum of returning electrons are measured by Langmuir probes and electrostatic energy analyser. In rocket experiments of K-10-11, K-10-12, K-9M-57, K-9M-58, K-9M-61 and K-9M-66, several types of electron guns were used whose power ranges from 1mW to 1KW. The rocket potential was measured by Langmuir probes and floating probes and optical line emission measurement and wave measurements were also done. The rocket potential was not so high as expected from the balance with ionospheric plasma but strongly affected by the plasma production by the emitted electron beam and return electrons.     

The Genesis Discovery Mission: Return of Solar Matter to Earth

The Genesis Discovery mission will return samples of solar matter for analysis of isotopic and elemental compositions in terrestrial laboratories. This is accomplished by exposing ultra-pure materials to the solar wind at the L1 Lagrangian point and returning the materials to Earth. Solar wind collection will continue until April 2004 with Earth return in Sept. 2004. The general science objectives of Genesis are to (1) to obtain solar isotopic abundances to the level of precision required for the interpretation of planetary science data, (2) to significantly improve knowledge of solar elemental abundances, (3) to measure the composition of the different solar wind regimes, and (4) to provide a reservoir of solar matter to serve the needs of planetary science in the 21st century. The Genesis flight system is a sun-pointed spinner, consisting of a spacecraft deck and a sample return capsule (SRC). The SRC houses a canister which contains the collector materials. The lid of the SRC and a cover to the canister were opened to begin solar wind collection on November 30, 2001. To obtain samples of O and N ions of higher fluence relative to background levels in the target materials, an electrostatic mirror (‘concentrator’) is used which focuses the incoming ions over a diameter of about 20 cm onto a 6 cm diameter set of target materials. Solar wind electron and ion monitors (electrostatic analyzers) determine the solar wind regime present at the spacecraft and control the deployment of separate arrays of collector materials to provide the independent regime samples. This revised version was published online in August 2006 with corrections to the Cover Date.     

Search for primordial antiparticles with BESS

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) has been carried out to search for primordial antiparticles in cosmic rays. In ten flights from 1993 to 2004, it measured the cosmic-ray antiproton spectrum in the energy range 0.1–4.2 GeV at various solar activity conditions. It also searched for antideuterons and antihelium nuclei, and it made precise measurement of cosmic-ray particle spectra. The BESS program has been extended to long duration balloon (LDB) flights in Antarctica (BESS-Polar) with the goal of achieving unprecedented sensitivity in the search for primordial antiparticles. This report describes recent results from BESS and progress of the BESS-Polar program.     

Search for antihelium: Progress with BESS

In this paper, we report searches for antihelium in cosmic rays using two recently flown magnetic rigidity spectrometers. BESS-TeV had extended rigidity with an MDR of 1.4 TV and had a flight duration of one day. BESS-Polar was optimized for collecting power. It was flown for 8.5 days and had an MDR of 240 GV. The former flight allows us to explore a previously unexplored rigidity band and the latter flight yields a factor of three improvement in the overall BESS limit. No antihelium candidate was found in the rigidity ranges of 1–500 GV, and 0.6–20 GV, among 7 × 10⁴ events taken with BESS-TeV, and 8 × 10⁶ events taken with BESS-Polar, respectively.