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NASA NTRS2007

Validation of ISS Floating Potential Measurement Unit Electron Densities and Temperatures

Validation of the Floating Potential Measurement Unit (FPMU) electron density and temperature measurements is an important step in the process of evaluating International Space Station spacecraft charging issues .including vehicle arcing and hazards to crew during extravehicular activities. The highest potentials observed on Space Station are due to the combined VxB effects on a large spacecraft and the collection of ionospheric electron and ion currents by the 160 V US solar array modules. Ionospheric electron environments are needed for input to the ISS spacecraft charging models used to predict the severity and frequency of occurrence of ISS charging hazards. Validation of these charging models requires comparing their predictions with measured FPMU values. Of course, the FPMU measurements themselves must also be validated independently for use in manned flight safety work. This presentation compares electron density and temperatures derived from the FPMU Langmuir probes and Plasma Impedance Probe against the independent density and temperature measurements from ultraviolet imagers, ground based incoherent scatter radar, and ionosonde sites.

Coffey, Victoria N.↗

NASA NTRS2001

An Experimental Investigation of the Effects of Charging on the International Space Station

An experimental investigation has been undertaken to determine the effects associated with operating the International Space Station (ISS) without a Plasma Contactor Unit (PCU). The role of the PCU is to maintain the potential of the ISS to within 40 volts of the ambient plasma potential. In the event of a PCU failure, ISS structure may charge to - 160 volts with respect to the Low Earth Orbit (LEO) plasma, due to the use of high voltage photovoltaic solar arrays. Operation without a PCU will result in the charging of the oxide layers on anodized aluminum components facing into the RAM direction. In this investigation, arcs were observed as a result of anodized materials charging in a plasma environment. Actual ISS materials were used in the investigation. The materials included meteoroid and debris shield samples, as well as components from the Extravehicular Mobility Unit (EMU). Results show that the occurrence of arcs was dependent on several factors including material composition and applied voltage. The breakdown thresholds for the materials tested will be shown, as well as the voltage and current waveforms during an arc event. The damage resulting from an arc will also be described. In addition, a description of associated operational hazards resulting from arcing on the spacecraft will be provided.

Schneider, Todd↗

NASA NTRS2011

SA13B-1900 Auroral Charging of the International Space Station

Electrostatic potential variations of the International Space Station (ISS) relative to the space plasma environment are dominated by interaction of the negatively grounded 160 volt US photovoltaic power system with the plasma environment in sunlight and inductive potential variations across the ISS structure generated by motion of the vehicle across the Earth's magnetic field. Auroral charging is also a source of potential variations because the 51.6? orbital inclination of ISS takes the vehicle to sufficiently high magnetic latitudes to encounter precipitating electrons during geomagnetic storms. Analysis of auroral charging for small spacecraft or isolated insulating regions on ISS predict rapid charging to high potentials of hundreds of volts but it has been thought that the large capacitance of the entire ISS structure on the order of 0.01 F will limit frame potentials to less than a volt when exposed to auroral conditions. We present three candidate auroral charging events characterized by transient ISS structure potentials varying from approximately 2 to 17 volts. The events occur primarily at night when the solar arrays are unbiased and cannot therefore be due to solar array current collection. ISS potential decreases to more negative values during the events indicating electron current collection and the events are always observed at the highest latitudes along the ISS trajectory. Comparison of the events with integral >30 keV electron flux measurements from NOAA TIROS spacecraft demonstrate they occur within regions of precipitating electron flux at levels consistent with the energetic electron thresholds reported for onset of auroral charging of the DMSP and Freja satellites. In contrast to the DMSP and Freja events, one of the ISS charging events occur in sunlight.

Minow, Joseph I.↗

NASA NTRS2002

Charging of the International Space Station Due to Its High Voltage Solar Arrays

The International Space Station (ISS) has the highest voltage solar arrays ever flown in Low Earth Orbit (LEO). The ISS power system (and structure) ground is at the negative end of the 160 V solar arrays. Due to plasma current collection balance that must be maintained in LEO, it is possible for a spacecraft to charge negative of the ambient plasma by up to its entire solar array voltage (-160 V for ISS).

Ferguson, Dale C.↗

NASA NTRS2006

Impact of Solar Array Position on ISS Vehicle Charging

The International Space Station (ISS), because of its large structure and high voltage solar arrays, has a complex plasma interaction with the ionosphere in low Earth orbit (LEO). This interaction of the ISS US Segment photovoltaic (PV) power system with the LEO ionospheric plasma produces floating potentials on conducting elements of the ISS structure relative to the local plasma environment. To control the ISS floating potentials, two Plasma Contactor Units (PCUs) are installed on the Z1 truss. Each PCU discharges accumulated electrons from the Space Station structure, thus reducing the potential difference between the ISS structure and the surrounding charged plasma environment. Operations of the PCUs were intended to keep the ISS floating potential to 40 Volts (Reference 1). Exposed dielectric surfaces overlying conducting structure on the Space Station will collect an opposite charge from the ionosphere as the ISS charges. In theory, when an Extravehicular Activity (EVA) crewmember is tethered to structure via the crew safety tether or when metallic surfaces of the Extravehicular Mobility Unit (EMU) come in contact with conducting metallic surfaces of the ISS, the EMU conducting components, including the perspiration-soaked crewmember inside, can become charged to the Space Station floating potential. The concern is the potential dielectric breakdown of anodized aluminum surfaces on the EMU producing an arc from the EMU to the ambient plasma, or nearby ISS structure. If the EMU arcs, an electrical current of an unknown magnitude and duration may conduct through the EVA crewmember, producing an unacceptable condition. This electrical current may be sufficient to startle or fatally shock the EVA crewmember (Reference 2). Hence, as currently defined by the EVA community, the ISS floating potential for all nominal and contingency EVA worksites and translation paths must have a magnitude less than 40 volts relative to the local ionosphere at all times during EVA. Arcing from the EMU is classified as a catastrophic hazard, which requires two-failure tolerant controls, i.e., three hazard controls. Each PCU is capable of maintaining the ISS floating potential below the requirement during EVA. The two PCUs provide a single failure tolerant control of ISS floating potential. In the event of the failure of one or two PCUs, a combination of solar array shunting and turning the solar arrays into their own wakes will be used to supply control of the plasma hazard (Reference 3). The purpose of this paper is to present on-orbit information that shows that ISS solar array placement with respect to the ISS velocity vector can control solar array plasma charging, and hence, provide an operational control for the plasma hazard. Also, this paper will present on-orbit information that shows that shunting of the ISS solar arrays can control solar array plasma charging, and hence, provide an additional operational control for the plasma hazard.

Alred, John↗

NASA NTRS1983

Space station: Cost and benefits

Costs for developing, producing, operating, and supporting the initial space station, a 4 to 8 man space station, and a 4 to 24 man space station are estimated and compared. These costs include contractor hardware; space station assembly and logistics flight costs; and payload support elements. Transportation system options examined include orbiter modules; standard and extended duration STS fights; reusable spacebased perigee kick motor OTV; and upper stages. Space station service charges assessed include crew hours; energy requirements; payload support module storage; pressurized port usage; and OTV service facility. Graphs show costs for science missions, space processing research, small communication satellites; large GEO transportation; OVT launch costs; DOD payload costs, and user costs.

Source record↗

NASA NTRS2022

Cosmic Radiation Effect on Silicon Photonic Mach-Zehnder Modulator

We evaluated the radiation effects of cosmic rays on silicon Mach-Zehnder Modulator loaded on International Space Station. Permanent changes of refractive index (10 -3 ) and carrier lifetime reduction have been observed after 6 months’ radiation.

Mach-Zehnder interferometers↗

NASA NTRS2005

Mission Analysis for LEO Microwave Power-Beaming Station in Orbital Launch of Microwave Lightcraft

A detailed mission analysis study has been performed for a 1 km diameter, rechargeable satellite solar power station (SPS) designed to boost 20m diameter, 2400 kg Micr,oWave Lightcraft (MWLC) into low earth orbit (LEO) Positioned in a 476 km daily-repeating oi.bit, the 35 GHz microwave power station is configured like a spinning, thin-film bicycle wheel covered by 30% efficient sola cells on one side and billions of solid state microwave transmitter elements on the other, At the rim of this wheel are two superconducting magnets that can stor,e 2000 G.J of energy from the 320 MW, solar array over a period of several orbits. In preparation for launch, the entire station rotates to coarsely point at the Lightcraft, and then phases up using fine-pointing information sent from a beacon on-board the Lightcraft. Upon demand, the station transmits a 10 gigawatt microwave beam to lift the MWLC from the earth surface into LEO in a flight of several minutes duration. The mission analysis study was comprised of two parts: a) Power station assessment; and b) Analysis of MWLC dynamics during the ascent to orbit including the power-beaming relationships. The power station portion addressed eight critical issues: 1) Drag force vs. station orbital altitude; 2) Solar pressure force on the station; 3) Station orbital lifetime; 4) Feasibility of geo-magnetic re-boost; 5) Beta angle (i..e., sola1 alignment) and power station effective area relationship; 6) Power station percent time in sun vs, mission elapsed time; 7) Station beta angle vs.. charge time; 8) Stresses in station structures.. The launch dynamics portion examined four issues: 1) Ascent mission/trajecto1y profile; 2) MWLC/power-station mission geometry; 3) MWLC thrust angle vs. time; 4) Power station pitch rate during power beaming. Results indicate that approximately 0 58 N of drag force acts upon the station when rotated edge-on to project the minimum frontal area of 5000 sq m. An ion engine or perhaps an electrodynamic thruster (i.e., geomagnetic re-boost) station-keeping system can maintain the orbit altitude. The rate at which the power station s superconducting magnetic energy storage system (SMES) is 'charged' directly relates to the beta angle since the station is operating in the edge-on attitude. The maximum charge rate occurs when the beta angle is at its maximum because time in the sun and projected area of the station are, too, at their maximums For the maximum charge of 2000 G.J with a maximum beta angle of 52 degrees, approximately 3 hours (2 orbital revolutions) are required to reach the full charge, while about 16 hours (10.3 revolutions) are required when the beta angle is 10 degrees. Overall, the LEO station concept appears to be a viable candidate fo1 the formidable power-beaming infrastructure needed to boost MWLC into low earth orbit.

Myrabo, L. N.↗

NASA NTRS2004

Assessment and Control of Spacecraft Charging Risks on the International Space Station

The International Space Station (ISS) operates in the F2 region of Earth's ionosphere, orbiting at altitudes ranging from 350 to 450 km at an inclination of 51.6 degrees. The relatively dense, cool F2 ionospheric plasma suppresses surface charging processes much of the time, and the flux of relativistic electrons is low enough to preclude deep dielectric charging processes. The most important spacecraft charging processes in the ISS orbital environment are: 1) ISS electrical power system interactions with the F2 plasma, 2) magnetic induction processes resulting from flight through the geomagnetic field and, 3) charging processes that result from interaction with auroral electrons at high latitude. Recently, the continuing review and evaluation of putative ISS charging hazards required by the ISS Program Office revealed that ISS charging could produce an electrical shock hazard to the ISS crew during extravehicular activity (EVA). ISS charging risks are being evaluated in an ongoing measurement and analysis campaign. The results of ISS charging measurements are combined with a recently developed model of ISS charging (the Plasma Interaction Model) and an exhaustive analysis of historical ionospheric variability data (ISS Ionospheric Specification) to evaluate ISS charging risks using Probabilistic Risk Assessment (PRA) methods. The PRA combines estimates of the frequency of occurrence and severity of the charging hazards with estimates of the reliability of various hazard controls systems, as required by NASA s safety and risk management programs, to enable design and selection of a hazard control approach that minimizes overall programmatic and personnel risk. The PRA provides a quantitative methodology for incorporating the results of the ISS charging measurement and analysis campaigns into the necessary hazard reports, EVA procedures, and ISS flight rules required for operating ISS in a safe and productive manner.

Koontz, Steve↗

NASA NTRS2003

Assessment and Control of Spacecraft Charging Risks on the International Space Station

Electrical interactions between the F2 region ionospheric plasma and the 160V photovoltaic (PV) electrical power system on the International Space Station (ISS) can produce floating potentials (FP) on the ISS conducting structure of greater magnitude than are usually observed on spacecraft in low-Earth orbit. Flight through the geomagnetic field also causes magnetic induction charging of ISS conducting structure. Charging processes resulting from interaction of ISS with auroral electrons may also contribute to charging albeit rarely. The magnitude and frequency of occurrence of possibly hazardous charging events depends on the ISS assembly stage (six more 160V PV arrays will be added to ISS), ISS flight configuration, ISS position (latitude and longitude), and the natural variability in the ionospheric flight environment. At present, ISS is equipped with two plasma contactors designed to control ISS FP to within 40 volts of the ambient F2 plasma. The negative-polarity grounding scheme utilized in the ISS 160V power system leads, naturally, to negative values of ISS FP. A negative ISS structural FP leads to application of electrostatic fields across the dielectrics that separate conducting structure from the ambient F2 plasma, thereby enabling dielectric breakdown and arcing. Degradation of some thermal control coatings and noise in electrical systems can result. Continued review and evaluation of the putative charging hazards, as required by the ISS Program Office, revealed that ISS charging could produce a risk of electric shock to the ISS crew during extra vehicular activity. ISS charging risks are being evaluated in ongoing ISS charging measurements and analysis campaigns. The results of ISS charging measurements are combined with a recently developed detailed model of the ISS charging process and an extensive analysis of historical ionospheric variability data, to assess ISS charging risks using Probabilistic Risk Assessment (PRA) methods. The PRA analysis (estimated frequency of occurrence and severity of the charging hazards) are then used to select the hazard control strategy that provides the best overall safety and mission success environment for ISS and the ISS crew. This paper presents: 1) a summary of ISS spacecraft charging analysis, measurements, observations made to date, 2) plans for future ISS spacecraft charging measurement campaigns, and 3) a detailed discussion of the PRA strategy used to assess ISS spacecraft charging risks and select charging hazard control strategies

Koontz, Steve↗

NASA NTRS1987

Accommodating life sciences on the Space Station

The NASA Ames Research Center Biological Research Project (BRP) is responsible for identifying and accommodating high priority life science activities, utilizing nonhuman specimens, on the Space Station and is charged to bridge the gap between the science community and the Space Station Program. This paper discusses the approaches taken by the BRP in accomodating these research objectives to constraints imposed by the Space Station System, while maintaining a user-friendly environment. Consideration is given to the particular research disciplines which are given priority, the science objectives in each of these disciplines, the functions and activities required by these objectives, the research equipment, and the equipment suits. Life sciences programs planned by the Space Station participating partners (USA, Europe, Japan, and Canada) are compared.

Arno, Roger D.↗

NASA NTRS1984

Concept for a commercial space station laboratory

The concept of a privately owned and operated fee-for-service laboratory as an element of a civil manned space station, envisioned as the venture of a group of private investors and an experienced laboratory operator to be undertaken with the cooperation of NASA is discussed. This group would acquire, outfit, activate, and operate the labortory on a fee-for-service basis, providing laboratory services to commercial firms, universities, and government agencies, including NASA. This concept was developed to identify, stimulate, and assist potential commercial users of a manned space station. A number of the issues which would be related to the concept, including the terms under which NASA might consider permitting private ownership and operation of a major space station component, the policies with respect to international participation in the construction and use of the space station, the basis for charging users for services received from the space station, and the types of support that NASA might be willing to provide to assist private industry in carrying out such a venture are discussed.

Wood, P. W.↗

NASA NTRS2010

Experimental Charging Behavior of Orion UltraFlex Array Designs

The present ground based investigations give the first definitive look describing the charging behavior of Orion UltraFlex arrays in both the Low Earth Orbital (LEO) and geosynchronous (GEO) environments. Note the LEO charging environment also applies to the International Space Station (ISS). The GEO charging environment includes the bounding case for all lunar mission environments. The UltraFlex photovoltaic array technology is targeted to become the sole power system for life support and on-orbit power for the manned Orion Crew Exploration Vehicle (CEV). The purpose of the experimental tests is to gain an understanding of the complex charging behavior to answer some of the basic performance and survivability issues to ascertain if a single UltraFlex array design will be able to cope with the projected worst case LEO and GEO charging environments. Stage 1 LEO plasma testing revealed that all four arrays successfully passed arc threshold bias tests down to -240 V. Stage 2 GEO electron gun charging tests revealed that only the front side area of indium tin oxide coated array designs successfully passed the arc frequency tests

Golofaro, Joel T.↗

NASA NTRS2015

Electrostatic Model Applied to ISS Charged Water Droplet Experiment

The electrostatic force can be used to create novel relative motion between charged bodies if it can be isolated from the stronger gravitational and dissipative forces. Recently, Coulomb orbital motion was demonstrated on the International Space Station by releasing charged water droplets in the vicinity of a charged knitting needle. In this investigation, the Multi-Sphere Method, an electrostatic model developed to study active spacecraft position control by Coulomb charging, is used to simulate the complex orbital motion of the droplets. When atmospheric drag is introduced, the simulated motion closely mimics that seen in the video footage of the experiment. The electrostatic force's inverse dependency on separation distance near the center of the needle lends itself to analytic predictions of the radial motion.

Stevenson, Daan↗

NASA NTRS1994

Auroral interactions with ISSA

Due to its high inclination orbit, International Space Station Alpha (ISSA) will occasionally experience surface charging by the high energy electrons of the auroral environment. This study looks at the frequency of these occurrences and recapitulates a charging model. ISSA should expect about 80 auoral encounters annually. If the plasma contactor is not run continuously, the vehicle may charge several hundred volts. Charge storage on standard space station coatings should not be a problem, but care must be taken that materials are not introduced inadvertently that cannot bleed off accumulated charge in a reasonable time. A conductivity requirement may be used to ensure surface materials do not charge to high voltages, or store charge for long periods of time.

Purvis, Carolyn K.↗

NASA NTRS2023

Charge-Sign Dependent Cosmic-Ray Modulation Observed with the Calorimetric Electron Telescope on the International Space Station

We present the observation of a charge-sign dependent solar modulation of galactic cosmic rays (GCRs) with the Calorimetric Electron Telescope onboard the International Space Station over 6 yr, corresponding to the positive polarity of the solar magnetic field. The observed variation of proton count rate is consistent with the neutron monitor count rate, validating our methods for determining the proton count rate. It is observed by the Calorimetric Electron Telescope that both GCR electron and proton count rates at the same average rigidity vary in anticorrelation with the tilt angle of the heliospheric current sheet, while the amplitude of the variation is significantly larger in the electron count rate than in the proton count rate. We show that this observed charge-sign dependence is reproduced by a numerical “drift model” of the GCR transport in the heliosphere. This is a clear signature of the drift effect on the long-term solar modulation observed with a single detector.

O. Adriani↗

NASA NTRS1996

Photovoltaic Plasma Interaction Test 2

The International Space Station (ISS) program is developing a plasma contactor to mitigate the harmful effects of charge collection on the station's large photovoltaic arrays. The purpose of the present test was to examine the effects of charge collection on the solar array electrical circuit and to verify the effectiveness of the plasma contactor. The results showed that the plasma contactor was able to eliminate structure arcing for any array output voltage. However, the current requirements of the plasma contactor were higher than those for prior testing and predicted by analysis. Three possible causes for this excess current demand are discussed. The most likely appeared to be a high local pressure on or very near the surface of the array as a result of vacuum tank conditions. Therefore, in actual space conditions, the plasma contactor should work as predicted.

Kaufman, Bradford A.↗

NASA NTRS1990

The Navstar GPS master control station's Kalman filter experience

The Navstar Global Positioning System (GPS) is a highly accurate space based navigation system providing all weather, 24 hour a day service to both military and civilian users. The system provides a Gaussian position solution with four satellites, each providing its ephemeris and clock offset with respect to GPS time. The GPS Master Clock Station (MCS) is charged with tracking each Navstar spacecraft and precisely defining the ephemeris and clock parameters for upload into the vehicle's navigation message. Briefly described here are the Navstar system and the Kalman filter estimation process used by MCS to determine, predict, and ensure quality control for each of the satellite's ephemeris and clock states. Routine performance is shown. Kalman filter reaction and response is discussed for anomalous clock behavior and trajectory perturbations. Particular attention is given to MCS efforts to improve orbital adjust modeling. The satellite out of service time due to orbital maneuvering has been reduced in the past year from four days to under twelve hours. The planning, reference trajectory model, and Kalman filter management improvements are explained.

Scardera, Michael P.↗