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NASA NTRS2004

In-flight propulsion system characterization for both Mars Exploration Rover Spacecraft

Two Mars Exploration Rover spacecraft were dispensed to red planet in 2003, culminating in a phenomenally successful prime science mission. Twin cruise stage propulsion systems were developed in record time, largely through heritage with Mars Pathfinder. As expected, consumable usage was minimal during the short seven-month cruise for both spacecraft. Propellant usage models based on pressure and temperature agreed with throughput models with in a few percent. Trajectory correction maneuver performance was nominal, allowing the cancellation of near-Mars maneuvers. Spin thruster delivered impulse was 10-12% high vs. ground based models for the intial spin-down maneuvers, while turn performance was XX-XX% high/low vs. expectations. No clear indications for pressure transducer drift were noted during the brief MER missions.

maneuvers↗

NASA NTRS2006

Selection Algorithm for the CALIPSO Lidar Aerosol Extinction-to-Backscatter Ratio

The extinction-to-backscatter ratio (S(sub a)) is an important parameter used in the determination of the aerosol extinction and subsequently the optical depth from lidar backscatter measurements. We outline the algorithm used to determine Sa for the Cloud and Aerosol Lidar and Infrared Pathfinder Spaceborne Observations (CALIPSO) lidar. S(sub a) for the CALIPSO lidar will either be selected from a look-up table or calculated using the lidar measurements depending on the characteristics of aerosol layer. Whenever suitable lofted layers are encountered, S(sub a) is computed directly from the integrated backscatter and transmittance. In all other cases, the CALIPSO observables: the depolarization ratio, delta, the layer integrated attenuated backscatter, beta, and the mean layer total attenuated color ratio, gamma, together with the surface type, are used to aid in aerosol typing. Once the type is identified, a look-up-table developed primarily from worldwide observations, is used to determine the S(sub a) value. The CALIPSO aerosol models include desert dust, biomass burning, background, polluted continental, polluted dust, and marine aerosols.

Omar, Ali H.↗

NASA NTRS2006

Microthruster Propulsion for the Space Technology 7 (ST7) Technology Demonstration Mission

For future applications to precision formation flying missions, NASA's New Millennium Program is scheduled to test colloid micro-Newton thrusters (CMNTs) on the ST7 technology demonstration mission. These CMNTs are part of a disturbance reduction system (DRS) on the ESA SMART-2 Spacecraft or LISA Pathfinder. The goal of the ST7 DRS is to demonstrate technologies necessary to meet the nanometer precision positioning control requirements of the LISA mission. In order to achieve these goals, the CMNTs are required to demonstrate a thrust resolution of less than 0.1 micro-N and a thrust noise of less than 0.1 micro-N/[square root]Hz for thrust levels between 5 and 30 micro-N. Developed by Busek Co. with support from JPL in testing an design, the CMNT has been developed over the last four years into a flight-ready microthrust system. The development, validation testing, and flight unit production of the CMNTs are described. Development tests and analysis include preliminary wear tests, propellant loading process verification, flow testing, and performance verification. Validation and flight unit verification includes thermal and structural analysis, life testing, thermal and dynamic load testing, and performance verification. Final delivery of the units is planned in 2007 with and planned launch and flight demonstration 2009.

microthruster↗

NASA NTRS2006

Wireless Command-and-Control of UAV-Based Imaging LANs

Dual airborne imaging system networks were operated using a wireless line-of-sight telemetry system developed as part of a 2002 unmanned aerial vehicle (UAV) imaging mission over the USA s largest coffee plantation on the Hawaiian island of Kauai. A primary mission objective was the evaluation of commercial-off-the-shelf (COTS) 802.11b wireless technology for reduction of payload telemetry costs associated with UAV remote sensing missions. Predeployment tests with a conventional aircraft demonstrated successful wireless broadband connectivity between a rapidly moving airborne imaging local area network (LAN) and a fixed ground station LAN. Subsequently, two separate LANs with imaging payloads, packaged in exterior-mounted pressure pods attached to the underwing of NASA's Pathfinder-Plus UAV, were operated wirelessly by ground-based LANs over independent Ethernet bridges. Digital images were downlinked from the solar-powered aircraft at data rates of 2-6 megabits per second (Mbps) over a range of 6.5 9.5 km. An integrated wide area network enabled payload monitoring and control through the Internet from a range of ca. 4000 km during parts of the mission. The recent advent of 802.11g technology is expected to boost the system data rate by about a factor of five.

Herwitz, Stanley↗

NASA NTRS2006

Using SCIAMACHY and Ground-based FTS Measurements to Test the OCO X(sub CO2) Retrieval and Validation Approach

Global, space-based observations of atmospheric CO2 with precision, resolution, and coverage needed to monitor sources and sinks: a) Spectra of reflected/scattered sunlight in NIR CO2 and O2 bands used to estimate X(sub CO2) with large sensitivity to surface; b) A-train orbit (1:15 PM polar sun sync); c) 16 day repeat cycle samples seasonal cycle on semi-monthly intervals; and d) NASA ESSP (Earth Space System Pathfinder) scheduled for Sept 2008 launch; 2 yrs lifetime. Initial comparison of SCIAMACHY and FTS retrievals for Park Falls: a) Positive bias in X(sub CO2) of approx. 10 ppm; and b) Negative bias in surface pressure After correction of spectral artifacts in O2A band: a) Largely improved agreement between SCIAMACHY and FTS X(sub CO2) (without clear bias) and in surface pressure; and b) Standard deviation of SCIAMACHY X(sub CO2 approx. 6 ppm. Good qualitative agreement with GEOS-CHEM, with GEOS-CHEM underestimating seasonal cycle. OCO is a dedicated CO2 instrument and will achieve much higher accuracy and precision: a) much higher spectral resolution (by factor of 20); and b) smaller ground pixels (by factor of 600).

CO2 measurements↗

NASA NTRS2006

Maximum von Mises Stress in the Loading Environment of Mass Acceleration Curve

Method for calculating stress due to acceleration loading: 1) Part has been designed by FEA and hand calculation in one critical loading direction judged by the analyst; 2) Maximum stress can be due to loading in another direction; 3) Analysis procedure to be presented determines: a) The maximum Mises stress at any point; and b) The direction of maximum loading associated with the "stress". Concept of Mass Acceleration Curves (MAC): 1) Developed by JPL to perform preliminary structural sizing (i.e. Mariners, Voyager, Galileo, Pathfinder, MER,...MSL); 2) Acceleration of physical masses are bounded by a curve; 3) G-levels of vibro-acoustic and transient environments; 4) Convergent process before the couple loads cycle; and 5) Semi-empirical method to effectively bound the loads, not a simulation of the actual response.

von Mises stress↗

NASA NTRS2005

2nd International Planetary Probe Workshop

Included are presentations from the 2nd International Planetary Probe Workshop. The purpose of the second workshop was to continue to unite the community of planetary scientists, spacecraft engineers and mission designers and planners; whose expertise, experience and interests are in the areas of entry probe trajectory and attitude determination, and the aerodynamics/aerothermodynamics of planetary entry vehicles. Mars lander missions and the first probe mission to Titan made 2004 an exciting year for planetary exploration. The Workshop addressed entry probe science, engineering challenges, mission design and instruments, along with the challenges of reconstruction of the entry, descent and landing or the aerocapture phases. Topics addressed included methods, technologies, and algorithms currently employed; techniques and results from the rich history of entry probe science such as PAET, Venera/Vega, Pioneer Venus, Viking, Galileo, Mars Pathfinder and Mars MER; upcoming missions such as the imminent entry of Huygens and future Mars entry probes; and new and novel instrumentation and methodologies.

Venkatapathy, Ethiraj↗

NASA NTRS2005

Deep Space Network Capabilities for Receiving Weak Probe Signals

Planetary probes can encounter mission scenarios where communication is not favorable during critical maneuvers or emergencies. Launch, initial acquisition, landing, trajectory corrections, safing. Communication challenges due to sub-optimum antenna pointing or transmitted power, amplitude/frequency dynamics, etc. Prevent lock-up on signal and extraction of telemetry. Examples: loss of Mars Observer, nutation of Ulysses, Galileo antenna, Mars Pathfinder and Mars Exploration Rovers Entry, Descent, and Landing, and the Cassini Saturn Orbit Insertion. A Deep Space Network capability to handle such cases has been used successfully to receive signals to characterize the scenario. This paper will describe the capability and highlight the cases of the critical communications for the Mars rovers and Saturn Orbit Insertion and preparation radio tracking of the Huygens probe at (non-DSN) radio telescopes.

Asmar, Sami↗

NASA NTRS2005

Study of Some Planetary Atmospheres Features by Probe Entry and Descent Simulations

Characterization of planetary atmospheres is analyzed by its effects in the entry and descent trajectories of probes. Emphasis is on the most important variables that characterize atmospheres e.g. density profile with altitude. Probe trajectories are numerically determined with ENTRAP, a developing multi-purpose computational tool for entry and descent trajectory simulations capable of taking into account many features and perturbations. Real data from Mars Pathfinder mission is used. The goal is to be able to determine more accurately the atmosphere structure by observing real trajectories and what changes are to expect in probe descent trajectories if atmospheres have different properties than the ones assumed initially.

Gil, P. J. S.↗

NASA NTRS2005

Should We Believe Atmospheric Temperatures Measured by Entry Accelerometers Traveling at "Slow" Near-Sonic Speeds?

Mars Pathfinder's Accelerometer instrument measured an unexpected and large temperature inversion between 10 and 20 kilometer altitude. Other instruments have failed to detect similar temperature inversions. I test whether this inversion is real or not by examining what changes have to be made to the assumptions in the accelerometer data processing to obtain a more "expected" temperature profile. Changes in derived temperature of up to 30K, or 15%, are necessary, which correspond to changes in derived density of up to 25% and changes in derived pressure of up to 10%. If the drag coefficient is changed to satisfy this, then instead of decreasing from 1.6 to 1.4 from 20 kilometers to 10 kilometers, the drag coefficient must increase from 1.6 to 1.8 instead. If winds are invoked, then speeds of 60 meters per second are necessary, four times greater than those predicted. Refinements to the equation of hydrostatic equilibrium modify the temperature profile by an order of magnitude less than the desired amount. Unrealistically large instrument drifts of 0.5-1.0 meters per square second are needed to adjust the temperature profile as desired. However, rotational contributions to the accelerations may have the necessary magnitude and direction to make this correction. Determining whether this hypothesis is true will require further study of the rigid body equations of motion, with detailed knowledge of the positions of all six accelerometers. The paradox concerning this inversion is not yet resolved. It is important to resolve it because the paradox has some startling implications. At one extreme, are temperature profiles derived from accelerometers inherently inaccurate by 20K or more? At the other extreme, are RS temperature profiles inaccurate by this same amount?

Withers, Paul↗

NASA NTRS2006

NASA's Future X-ray Missions: From Constellation-X to Generation-X

Among the most important topics in modern astrophysics are the formation and evolution of supermassive black holes in concert with galaxy bulges, the nature of the dark energy equation of state, and the self-regulating symmetry imposed by both stellar and AGN feedback. All of these topics are readily addressed with observations at X-ray wavelengths. NASA's next major X-ray observatory is Constellation-X, which is being developed to perform spatially resolved high-resolution X-ray spectroscopy. Con-X will directly measure the physical properties of material near black holes' last stable orbits and the absolute element abundances and velocities of hot gas in clusters of galaxies. The Con-X mission will be described, as well as its successor, Generation-X (anticipated to fly approx.1 decade after Con-X). After describing these missions and their driving science areas, the talk will focus on areas in which Chandra observing programs may enable science with future X-ray observatories. These areas include a possible ultra-deep Chandra imaging survey as an early Universe pathfinder, a large program to spatially resolve the hot intracluster medium of massive clusters to aid dark energy measurements, and possible deep spectroscopic observations to aid in preparatory theoretical atomic physics work needed for interpreting Con-X spectra.

Hornschemeier, A.↗

NASA NTRS2006

The Aquarius Ocean Salinity Mission High Stability L-band Radiometer

The NASA Earth Science System Pathfinder (ESSP) mission Aquarius, will measure global ocean surface salinity with approx.120 km spatial resolution every 7-days with an average monthly salinity accuracy of 0.2 psu (parts per thousand). This requires an L-band low-noise radiometer with the long-term calibration stability of less than or equal to 0.15 K over 7 days. The instrument utilizes a push-broom configuration which makes it impractical to use a traditional warm load and cold plate in front of the feedhorns. Therefore, to achieve the necessary performance Aquarius utilizes a Dicke radiometer with noise injection to perform a warm - hot calibration. The radiometer sequence between antenna, Dicke load, and noise diode has been optimized to maximize antenna observations and therefore minimize NEDT. This is possible due the ability to thermally control the radiometer electronics and front-end components to 0.1 Crms over 7 days.

Pellerano, Fernando A.↗

NASA NTRS2006

The Development Of Enabling Technologies For Submillimeter-Wave Remote Sensing of Ice Clouds From Space

This paper presents the chronological development of technologies and techniques that have led to a satellite mission concept aimed at quantifying the temporal and spatial distributions of upper tropospheric ice clouds. The Submillimeter-wave and Infrared Ice Cloud Experiment (SIRICE) is an Earth System Science Pathfinder mission concept designed to improve our understanding of the upper tropospheric water cycle and its coupling to the Earth s radiation budget. Ice outflow from convective storm systems is known to play an important role in regional energy budgets; however, ice generation and subsequent precipitation and sublimation are poorly quantified. SIRICE will provide measurements of ice cloud distributions and microphysical properties which are needed for understanding the crucial link between the hydrologic and energy cycles. The SIRICE measurement platform is comprised of two integrated instruments, the Submillimeter/millimeter-wave radiometer (SM4) and the Infrared Cloud Ice Radiometer (IRCIR). The primary instrument is the SM4, a conical scanner that provides a 1600 km swath of the Earth's surface at 53 degree incidence. The SM4 has 6 linearly polarized receivers measuring 12 spectral bands centered at 183 GHz, 325 GHz, 448 GHz, 643 GHz and 874 GHz; two receivers at 643 GHz measure horizontal and vertical polarizations. Submillimeter-wavelengths are well suited to the remote sensing of ice clouds due to the relative size of the wavelengths to particle sizes. Upwelling emission from lower tropospheric water vapor is scattered by the ice clouds thus causing a brightness temperature depression at submillimeter wavelengths. The IRCIR is a push broom imager with approximately 1500 km swath and spectral channels at 11 and 12 micrometers. This combination of coincident infrared and submillimeter-wavelength measurements were chosen because of its ability to provide retrieval of ice water path and median particle size for a wide range of ice clouds from thin cirrus to thick anvil structures. Over the past decade there has been a parallel development of submillimeter-wave technologies, demonstration instruments, and remote sensing techniques that have led to the present SIRICE mission concept. Mapping of these developmental paths reveals the origins, rational and maturity of features of the SIRICE payload such as its channel selection, compact design, and multipoint calibration. This presentation traces the evolution of the SIRICE mission concept from the early 1990's to its present status.

Racette, Paul↗

NASA NTRS2006

The Fourier-Kelvin Stellar Interferometer (FKSI) Nulling Testbed II: Closed-loop Path Length Metrology And Control Subsystem

The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for an imaging and nulling interferometer in the near to mid-infrared spectral region (3-8 microns), and will be a scientific and technological pathfinder for upcoming missions including TPF-I/DARWIN, SPECS, and SPIRIT. At NASA's Goddard Space Flight Center, we have constructed a symmetric Mach-Zehnder nulling testbed to demonstrate techniques and algorithms that can be used to establish and maintain the 10(exp 4) null depth that will be required for such a mission. Among the challenges inherent in such a system is the ability to acquire and track the null fringe to the desired depth for timescales on the order of hours in a laboratory environment. In addition, it is desirable to achieve this stability without using conventional dithering techniques. We describe recent testbed metrology and control system developments necessary to achieve these goals and present our preliminary results.

Frey, B. J.↗

NASA NTRS2007

The Calipso Thermal Control Subsystem

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is a joint NASA-CNES mission to study the Earth s cloud and aerosol layers. The satellite is composed of a primary payload (built by Ball Aerospace) and a spacecraft platform bus (PROTEUS, built by Alcatel Alenia Space). The thermal control subsystem (TCS) for the CALIPSO satellite is a passive design utilizing radiators, multi-layer insulation (MLI) blankets, and both operational and survival surface heaters. The most temperature sensitive component within the satellite is the laser system. During thermal vacuum testing of the integrated satellite, the laser system s operational heaters were found to be inadequate in maintaining the lasers required set point. In response, a solution utilizing the laser system s survival heaters to augment the operational heaters was developed with collaboration between NASA, CNES, Ball Aerospace, and Alcatel-Alenia. The CALIPSO satellite launched from Vandenberg Air Force Base in California on April 26th, 2006. Evaluation of both the platform and payload thermal control systems show they are performing as expected and maintaining the critical elements of the satellite within acceptable limits.

Gasbarre, Joseph F.↗

NASA NTRS2007

Airborne Validation of Spatial Properties Measured by the CALIPSO Lidar

The primary payload onboard the Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite is a dual-wavelength backscatter lidar designed to provide vertical profiling of clouds and aerosols. Launched in April 2006, the first data from this new satellite was obtained in June 2006. As with any new satellite measurement capability, an immediate post-launch requirement is to verify that the data being acquired is correct lest scientific conclusions begin to be drawn based on flawed data. A standard approach to verifying satellite data is to take a similar, or validation, instrument and fly it onboard a research aircraft. Using an aircraft allows the validation instrument to get directly under the satellite so that both the satellite instrument and the aircraft instrument are sensing the same region of the atmosphere. Although there are almost always some differences in the sampling capabilities of the two instruments, it is nevertheless possible to directly compare the measurements. To validate the measurements from the CALIPSO lidar, a similar instrument, the Cloud Physics Lidar, was flown onboard the NASA high-altitude ER-2 aircraft during July- August 2006. This paper presents results to demonstrate that the CALIPSO lidar is properly calibrated and the CALIPSO Level 1 data products are correct. The importance of the results is to demonstrate to the research community that CALIPSO Level 1 data can be confidently used for scientific research.

McGill, Matthew J.↗

NASA NTRS2004

Small-RPS Enabled Mars Rover Concept

Both the MER and the Mars Pathfinder rovers operated on Mars in an energy-limited mode, since the solar panels generated power during daylight hours only. At other times the rovers relied on power stored in batteries. In comparison, Radioisotope Power Systems (RPS) offer a power-enabled paradigm, where power can be generated for long mission durations (measured in years), independently from the Sun, and on a continuous basis. A study was performed at PL to assess the feasibility of a small-RPS enabled MER-class rover concept and any associated advantages of its mission on Mars. The rover concept relied on design heritage from MER with two significant changes. First, the solar panels were replaced with two single GPHS module based small-RPSs. Second, the Mossbauer spectroscope was substituted with a laser Raman spectroscope, in order to move towards MEPAG defined astrobiology driven science goals. The highest power requirements were contributed to mobility and telecommunication type operating modes, hence influencing power system sizing. The resulting hybrid power system included two small-RPSs and two batteries. Each small-RPS was assumed to generate 50We of power or 62OWh/sol of energy (BOL), comparable to that of MER. The two 8Ah batteries were considered available during peak power usage. Mission architecture, power trades, science instruments, data, communication, thermal and radiation environments, mobility, mass issues were also addressed. The study demonstrated that a new set of RPS-enabled rover missions could be envisioned for Mars exploration within the next decade, targeting astrobiology oriented science objectives, while powered by 2 to 4 GPHS modules.

Mars exploration↗

NASA NTRS2006

Testing Fundamental Properties of Ionic Liquids for Colloid Microthruster Applications

NASA's New Millennium Program is scheduled to test a Disturbance Reduction System (DRS) on Space Technology 7 (ST7) as part of the European Space Agency's (ESA's) LISA Pathfinder Mission in late 2009. Colloid Micronewton Thrusters (CMNTs) will be used to counteract forces, mainly solar photon pressure, that could disturb gravitational reference sensors as part of the DRS. The micronewton thrusters use an ionic liquid, a room temperature molten salt, as propellant. The ionic liquid has a number of unusual properties that have a direct impact on thruster design. One of the most important issues is bubble formation before and during operation, especially during rapid pressure transitions from atmospheric to vacuum conditions. Bubbles have been observed in the feed system causing variations in propellant flow rate that can adversely affect thruster control. Bubbles in the feed system can also increase the likelihood that propellant will spray onto surfaces that can eventually lead to shorting high voltage electrodes. Two approaches, reducing the probability of bubble formation and removing bubbles with a new bubble eliminator device in the flow system, were investigated at Busek Co., Inc. and the Jet Propulsion Laboratory (JPL) to determine the effectiveness of both approaches. Results show that bubble formation is mainly caused by operation at low pressure and volatile contaminants in the propellant coming out of solution. A specification for the maximum tolerable level of contamination has been developed, and procedures for providing system cleanliness have been tested and implemented. The bubble eliminator device has also been tested successfully and has been implemented in recent thruster designs at Busek. This paper focuses on the propellant testing work at JPL, including testing of a breadboard level bubble eliminator device.

bubble formation↗