Contamination Effects on Fixed-Bias Langmuir Probes

Langmuir probes are standard instruments for plasma density measurements on many sounding rockets. These probes can be operated in swept-bias as well as in fixed-bias modes. In swept-bias Langmuir probes, contamination effects are frequently visible as a hysteresis between consecutive up and down voltage ramps. This hysteresis, if not corrected, leads to poorly determined plasma densities and temperatures. With a properly chosen sweep function, the contamination parameters can be determinedfromthemeasurementsandcorrectplasmaparameterscanthenbedetermined.Inthispaper, we study the contamination effects on fixed-bias Langmuir probes, where no hysteresis type effect is seen in the data. Even though the contamination is not evident from the measurements, it does affect the plasma density fluctuation spectrum as measured by the fixed-bias Langmuir probe. We model thecontaminationasasimpleresistor-capacitorcircuitbetweentheprobesurfaceandtheplasma.We find that measurements of small scale plasma fluctuations (meter to sub-meter scale) along a rocket trajectoryarenotaffected,butthemeasuredamplitudeoflargescaleplasmadensityvariation(tensof meters or larger) is attenuated. From the model calculations, we determine amplitude and cross-over frequency of the contamination effect on fixed-bias probes for different contamination parameters. The model results also show that a fixed bias probe operating in the ion-saturation region is affected less by contamination as compared to a fixed bias probe operating in the electron saturation region

Error Analysis of Multi-Needle Langmuir Probe Measurement Technique

Multi-needle Langmuir probe is a fairly new instrument technique that has been flown on several recent sounding rockets and is slated to fly on a subset of QB50 CubeSat constellation. This paper takes a fundamental look into the data analysis procedures used for this instrument to derive absolute electron density. Our calculations suggest that while the technique remains promising, the current data analysis procedures could easily result in errors of 50% or more. We present a simple data analysis adjustment that can reduce errors by at least a factor of five in typical operation

Langmuir Probe Measurements in the Ionosphere

Electric probes have been the primary instruments for the in situ investigation of plasma parameters in the Earth’s ionosphere. This dissertation is a compendium of three papers, each dealing with a separate spacecraft that carried one or more instruments based on the electric probe technique. The first paper presents data from the Sudden Atom Layer sounding rocket that carried an RF Impedance Probe, a DC fixed-bias Langmuir Probe (DCP), and an Electric Field Probe. The combined dataset indicates a case of payload surface charging, the causes of which are investigated within the paper. A generic circuit model is developed to analyze payload charging and behavior of Langmuir-type instruments. Our analysis indicates that the anomalous charging event was an outcome of triboelectrification of the payload surface from neutral dust particles present in the Earth’s mesosphere. These results suggest caution in interpreting observations from the Langmuir class of instrumentation within dusty environments. The second paper presents data from the Floating Potential Measurement Unit (FPMU) that is deployed on the International Space Station. The FPMU instrument suite consists of three different Langmuir-type probes and a Plasma Impedance Probe (PIP). We first give a brief overview of the instrumentation, and then describe the algorithm used to reduce Langmuir probe I-V curves to plasma parameters. It is shown that the derived temperatures agree well with International Reference Ionosphere (IRI) model, while the derived density matches better with the USU-Global Assimilation of Ionospheric Measurement model. The third paper presents the dataset from the EQUIS II sounding rocket campaign. The rocket payloads carried a PIP, a DCP, and an internally heated Sweeping Langmuir Probe. The ratio of the payload surface area to the cumulative area of the instrument and its guard was about 250. We show that on small sounding rocket payloads the DCP technique of relative electron density measurement is not very accurate. We further show that the ion saturation region analysis of the I-V curve produces absolute ion density that matches very well with the absolute electron density derived from the PIP, and the derived temperatures agree reasonably well with the IRI model

Miniature Planar Ion Probe for CubeSat Missions

One of the crucial measurements for characterizing any space weather event is absolute plasma density and plasma density fluctuations, both spatially and temporally. Among the various methods to perform in-situ plasma density measurements is a simple Langmuir probe. This poster discusses the various implementations of a Langmuir probe and why a Planar Ion Probe (PIP) is the easiest and best method to measure high cadence absolute ion density. The researchers then present the design and performance of a PIP for the NASA LLITED dual CubeSat mission which is expected to be manifested for flight in late 2019. Performance data for the constructed PIP instruments is also presented. This includes noise analysis and calibration data, as well as refined instrument requirements. Due to its intended CubeSat platform, the designed instrument has extremely low size, weight, and power requirements. Thus, if needed, it can be deployed as a patch on multiple faces of a CubeSat, thereby reducing attitude control requirements as well as enabling the study of the wake structure around the spacecraft

Observations of Triboelectric Charging Effects on Langmuir-Type Probes in Dusty Plasma

Investigation of Earth’s mesosphere using sounding rockets equipped with a myriad of instruments has been a highly active field in the last 2 decades. This paper presents data from three separate instruments: an RF impedance probe, a DC fixed bias Langmuir probe, and an electric field probe, that were flown on a mesospheric sounding rocket flight investigating the presence of charged dust within and/or around a sporadic metal layer. The combined data set indicates a case of payload surface charging, the causes of which are investigated within this paper. A generic circuit model is developed to analyze payload charging and behavior of Langmuir-type instruments. The application of this model to the rocket payload indicates that the anomalous charging event was an outcome of triboelectrification of the payload surface from neutral dust particles present in the Earth’s mesosphere. These results suggest caution in interpreting observations from the Langmuir class of instrumentation within dusty environment

Plasma Density Analysis of CubeSat Wakes in the Earth’s Ionosphere

Spinning or tumbling CubeSats with Langmuir probes deployed on booms will render spin-modulated plasma densities as the probes move in and out of the spacecraft wake. It is traditionally assumed that the lower-density measurements from the spin cycle are made in the spacecraft wake, and the higher-density measurements are outside the wake. Although this assumption is valid for larger spacecraft in the Earth’s ionosphere, this paper scrutinizes its validity for CubeSats in similar conditions. Spacecraft–plasma interactions (surface charging, plasma sheaths, and wakes) are less understood for CubeSats, and the small CubeSat dimensions must be considered with respect to characteristic length scales of the space plasma environment, namely, the Debye length. Spacecraft Plasma Interaction Software, a spacecraft charging analysis tool, is used to investigate CubeSat interactions with the mesothermal plasma environment. For low-density and cold-plasma ionospheric conditions, the CubeSat dimension of 10 cm is comparable to the sheath thickness. The simulations show that, under such circumstances, a negatively charged CubeSat in mesothermal ionospheric conditions creates an ion focus region in the far wake. An independently written, first-principles code in MATLAB demonstrates that this feature is a direct result of the CubeSat behaving like a Langmuir probe in the thick-sheath model. The work performed in this paper cautions the community toward assuming CubeSats to have density depletion in their wake and stresses the necessity of having an accurate attitude solution and proper boom length design to derive ambient plasma densities from spin-modulated Langmuir probe measurements on CubeSats

Multi-Site Simultaneous Time-Resolved Photometry with a Low Cost Electro-Optics System

Sunlight reflected off of resident space objects can be used as an optical signal for astrometric orbit determination and for deducing geometric information about the object. With the increasing population of small satellites and debris in low Earth orbit, photometry is a powerful tool in operational support of space missions, whether for anomaly resolution or object identification. To accurately determine size, shape, spin rate, status of deployables, or attitude information of an unresolved resident space object, multi-hertz sample rate photometry is required to capture the relatively rapid changes in brightness that these objects can exhibit. OSCOM, which stands for Optical tracking and Spectral characterization of CubeSats for Operational Missions, is a low cost and portable telescope system capable of time-resolved small satellite photometry, and is field deployable on short notice for simultaneous observation from multiple sites. We present the electro-optical design principles behind OSCOM and light curves of the 1.5 U DICE-2 CubeSat and simultaneous observations of the main body of the ASTRO-H satellite after its fragmentation event

A Low Power Command and Control Module for Small Satellites

Utah State University/Space Dynamics Laboratory has developed a low power computer system for command and control, attitude determination, and telemetry for small spacecraft. The system has been developed for the 15-kilogram class Ionospheric Observation Nanosatellite Formation (ION-F) satellites. This constellation of three satellites is being built by Utah State University (USUSat), University of Washington/Cornell University (DawgStar), and Virginia Polytechnic Institute (HokieSat) and is part of the AFSOR/DARPA University Nanosatellite program with additional support from industry, NASA, the Air Force Research Labs, and the Air Force Space Test Program. The command and data handling (C&DH) system is based upon industrial-grade components, including a third generation Hitachi SuperH RISC processor and radiation tolerant ACTEL FPGAs. The memory subsystem is comprised of 256 Kbytes of EEPROM, 8 Mbytes of redundant flash memory, and 5 Mbytes of SRAM. The C&DH system also contains a 16 Mbyte telemetry buffer, digital and analog I/O interfaces, and a DMA-oriented CMOS camera system. The C&DH is radiation tolerant to approximately 5k Rad total dose. Single event upsets are dealt with at the hardware level by over current monitoring circuitry, redundant voting memory configurations, and multiple software watchdog timers. The entire computer system consumes less than 1.75 Watts peak, with an average of 1 Watt, and provides an 80-MIPS, 32-bit computation platform for a small spacecraft. An initial prototype satellite has successfully passed extensive environmental testing and demonstrated the advanced capabilities of the ION-F C&DH system