Bruce P. Block

The Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatile Evolution Mission

The Neutral Gas and Ion Mass Spectrometer (NGIMS) of the Mars Atmosphere and Volatile Evolution Mission (MAVEN) is designed to measure the composition, structure, and variability of the upper atmosphere of Mars. The NGIMS complements two other instrument packages on the MAVEN spacecraft designed to characterize the neutral upper atmosphere and ionosphere of Mars and the solar wind input to this region of the atmosphere. The combined measurement set is designed to quantify atmosphere escape rates and provide input to models of the evolution of the martian atmosphere. The NGIMS is designed to measure both surface reactive and inert neutral species and ambient ions along the spacecraft track over the 125–500 km altitude region utilizing a dual ion source and a quadrupole analyzer.

The Gas Chromatograph Mass Spectrometer for the Huygens Probe

The Gas Chromatograph Mass Spectrometer (GCMS) on the Huygens Probe will measure the chemical composition of Titans atmosphere from 170 km altitude (∼1 hPa) to the surface (∼1500 hPa) and determine the isotope ratios of the major gaseous constituents. The GCMS will also analyze gas samples from the Aerosol Collector Pyrolyser (ACP) and may be able to investigate the composition (including isotope ratios) of several candidate surface materials.The GCMS is a quadrupole mass filter with a secondary electron multiplier detection system and a gas sampling system providing continuous direct atmospheric composition measurements and batch sampling through three gas chromatographic (GC) columns. The mass spectrometer employs five ion sources sequentially feeding the mass analyzer. Three ion sources serve as detectors for the GC columns and two are dedicated to direct atmosphere sampling and ACP gas sampling respectively. The instrument is also equipped with a chemical scrubber cell for noble gas analysis and a sample enrichment cell for selective measurement of high boiling point carbon containing constituents. The mass range is 2 to 141 Dalton and the nominal detection threshold is at a mixing ratio of 10− 8. The data rate available from the Probe system is 885 bit/s. The weight of the instrument is 17.3 kg and the energy required for warm up and 150 minutes of operation is 110 Watt-hours.

Microfabricated thermal modulator for comprehensive two-dimensional micro gas chromatography: design, thermal modeling, and preliminary testing

In comprehensive two-dimensional gas chromatography (GC x GC), a modulator is placed at the juncture between two separation columns to focus and re-inject eluting mixture components, thereby enhancing the resolution and the selectivity of analytes. As part of an effort to develop a microGC x microGC prototype, in this report we present the design, fabrication, thermal operation, and initial testing of a two-stage microscale thermal modulator (microTM). The microTM contains two sequential serpentine Pyrex-on-Si microchannels (stages) that cryogenically trap analytes eluting from the first-dimension column and thermally inject them into the second-dimension column in a rapid, programmable manner. For each modulation cycle (typically 5 s for cooling with refrigeration work of 200 J and 100 ms for heating at 10 W), the microTM is kept approximately at -50 degrees C by a solid-state thermoelectric cooling unit placed within a few tens of micrometres of the device, and heated to 250 degrees C at 2800 degrees C s(-1) by integrated resistive microheaters and then cooled back to -50 degrees C at 250 degrees C s(-1). Thermal crosstalk between the two stages is less than 9%. A lumped heat transfer model is used to analyze the device design with respect to the rates of heating and cooling, power dissipation, and inter-stage thermal crosstalk as a function of Pyrex-membrane thickness, air-gap depth, and stage separation distance. Experimental results are in agreement with trends predicted by the model. Preliminary tests using a conventional capillary column interfaced to the microTM demonstrate the capability for enhanced sensitivity and resolution as well as the modulation of a mixture of alkanes.

The Planet-B neutral gas mass spectrometer

The Planet-B neutral gas mass spectrometer is designed for in-situ measurements of the gas composition in the upper atmosphere of Mars. The sensor uses a dual frequency quadrupole mass analyzer with a mass range of 1–60 amu (atomic mass units) and two electron multipliers to cover the dynamic range required. The ion source, which is collinear with the analyzer, operates in two different modes: 1) a closed source mode measuring non-surface reactive neutral species that have thermally accommodated to the gas inlet walls; and 2) an open source mode measuring chemically surface active species by direct beaming with no surface collisions. The in-line Retarding Potential Analysis (RPA) system selects the mode of operation. An onboard Field Programmable Gate Array (FPGA) is used to control the instrument operating parameters in accordance with pre-programmed sequences and to package the telemetry data. The sensor is sealed and maintained in a vacuum prior to launch and will be opened to the environment of Mars after orbit insertion. Measurements of He, N, O, CO, N2, NO, O2, Ar, and CO2 will be done at periapsis and the data will be used to determine the variation of the neutral atmosphere density and temperature with altitude, local solar time and season. Measurements are possible from 130–140 km to 500 km depending on the gas species, chemical background, and instrument measurement mode. The data will contribute to the studies of thermosphere energetics, lower atmosphere meteorology (e.g. dust storms) and serve as a resource for studies of the interaction of the upper atmosphere with the solar wind.

Higher order parametric excitation modes for spaceborne quadrupole mass spectrometers

This paper describes a technique to significantly improve upon the mass peak shape and mass resolution of spaceborne quadrupole mass spectrometers (QMSs) through higher order auxiliary excitation of the quadrupole field. Using a novel multiresonant tank circuit, additional frequency components can be used to drive modulating voltages on the quadrupole rods in a practical manner, suitable for both improved commercial applications and spaceflight instruments. Auxiliary excitation at frequencies near twice that of the fundamental quadrupole RF frequency provides the advantages of previously studied parametric excitation techniques, but with the added benefit of increased sensed excitation amplitude dynamic range and the ability to operate voltage scan lines through the center of upper stability islands. Using a field programmable gate array, the amplitudes and frequencies of all QMS signals are digitally generated and managed, providing a robust and stable voltage control system. These techniques are experimentally verified through an interface with a commercial Pfeiffer QMG422 quadrupole rod system. When operating through the center of a stability island formed from higher order auxiliary excitation, approximately 50% and 400% improvements in 1% mass resolution and peak stability were measured, respectively, when compared with traditional QMS operation. Although tested with a circular rod system, the presented techniques have the potential to improve the performance of both circular and hyperbolic rod geometry QMS sensors.

A low power, high-speed miniaturized thermal modulator for comprehensive 2D gas chromatography

In comprehensive two-dimensional gas chromatography (GC×GC), a modulator is placed at the juncture between two separation columns to focus and re-inject eluting mixture components, and thereby enhance the selectivity, sensitivity, and analyte capacity. Here, we present the design, fabrication, and testing of a two-stage microscale thermal modulator (µTM). The °™ cryogenically trap analytes eluting from the first column and thermally inject them into the second column. For this operation, each stage is periodically heated to 200 °C for 100 ms and then cooled to −50 °C for a few second. Preliminary results using a conventional capillary column interfaced to the µTM demonstrate successful modulation of a mixture of alkanes with a sensitivity enhancement as high as 24 folds

GeoSTAR-II: A prototype water vapor imager/sounder for the PATH mission

We describe the development and progress of the GeoSTAR-II risk reduction activity for the NASA Earth Science Decadal Survey PATH Mission. The activity directly addresses areas of technical risk including the system design, low noise receiver production, sub-array development, signal distribution and digital signal processing.

The Mars analytical chemistry experiment

Future missions to Mars will offer the opportunity to continue the search for organic molecules accessible from the surface, and to better quantify the cycling of volatile elements through geochemical pathways. This presentation describes an analytical instrument suite that is designed to measure elemental, isotopic, and potential organic signatures contained in the atmosphere and near surface reservoirs on Mars. The Mars analytical chemistry experiment (MACE) combines two unique mass-spectrometer-based instruments to accomplish these measurements. The first instrument combines a sample handling system with a reusable pyrolysis oven for processing solid materials. Evolved volatile gases from the pyrolyzer are either oxidized for elemental analysis, or sent through a preconcentrator into a 2D gas chromatograph for separation of organics. The processed gas stream is then sent to a high resolution dynamic time-of-flight mass spectrometer for detection. The second instrument is designed primarily for direct atmospheric measurements, using a combination of catalyst beds, getters, and cryogenic traps to separate and concentrate species of interest, such as noble gases. Concentrated gases are subsequently detected with a second, dedicated static mass spectrometer to avoid possible contamination from the pyrolysis of organics in the first process. A breadboard version of each of these instruments has been demonstrated in the laboratory. In this presentation, we discuss the design, applicability, and capabilities of the MACE suite in more detail

Enabling the Next Generation of Spaceborne Quadrupole Mass Spectrometers

The quadrupole mass spectrometer (QMS) has over 30 years of spaceflight heritage in making important neutral gas and low energy ion observations. Given their geometrical constraints, these instruments are currently operated at the extreme limit of their capabilities. However, a technique called higher order auxiliary excitation provides a set of novel, robust, electronics-based solutions for improving the performance of these sensors. By driving the quadrupole rods with an additional frequency nearly twice that of the normal RF operating frequency, substantially increased abundance sensitivity, maximum attainable mass resolution, and peak stability can be achieved through operation of voltage scan lines through the center of formed upper stability islands. Such improvements are modeled using numerical simulations of ion trajectories in a quadrupole field with and without applied higher order auxiliary excitation. When compared to a traditional QMS with a mass range up to 500Da, sensors can be designed with the same precision electronics to have expected mass ranges beyond 1500Da with a power increase of less than twice that of its heritage implementations.

Development of GPS constellation power monitor system for high accuracy calibration/validation of the cygnss L1B data

The Cyclone Global Navigation Satellite System (CYGNSS) uses the Global Positioning System (GPS) constellation (32 satellites) as the active source in a bi-static radar configuration, with CYGNSS acting as the passive radar receiver. A knowledge of Equivalent Isotropically Radiated Power (EIRP), based on transmit power and antenna pattern of GPS satellites, is of great importance in the accurate calibration of L1B data (bistatic radar cross section, BRCS) of the CYGNSS mission. However, the current knowledge of the EIRP of GPS satellites is limited. There exists an uncertainty of transmit power, and only 20 laboratory-measured antenna patterns have been published. Due to the azimuthal asymmetry of the patterns, the yaw attitude of GPS satellites may affect the EIRP. Therefore, a ground-based GPS constellation power monitor system has been built to accurately and precisely measure GPS signals in watts and, from that, estimate the transmit powers and antenna patterns of all GPS satellites. Measurement data without absolute calibration demonstrates that the GPS yaw attitude does affect the received power. A low noise amplifier (LNA) and calibration subsystem implemented on a PID controlled thermal plate is calibrated with a liquid nitrogen source, showing stable and reasonable results. With the absolute calibration of GPS signals. the retrieved GPS parameters will serve as inputs to the CYGNSS L1B calibration algorithm to improve the data accuracy.