Engineering topics
Novak, Keith
Publications and source records attributed to Novak, Keith.
Thermal design and validation of Mars 202 gas Dust Removal Tool (gDRT)
As part of the science goals for the planned Mars 2020 mission, two instruments, PIXL and SHERLOC, intend to study the Mars surface at a close scale. These two instruments are planned to be used on smooth rock surfaces that are free of dust and other particles. Such surfaces are prepared by using a drill with an abrading drill bit; residual dust and particles are then blown away using a compressed gas system—the Gas Dust Removal Tool (gDRT). Early in the design process a risk of valve leakage below the vendor’s -20C rating was identified. To mitigate this risk a parallel path was implemented: 1) qualify the valves to operate at -135C, and 2) develop thermal control capability to elevated temperatures in case qualification efforts are unsuccessful. While qualification efforts are ongoing, it is expected that the valves will be qualified to an operating temperature of -135C. In the event that qualification is not successful, thermal control has been realized via a thermally isolated valve configuration and thermostatically controlled heaters. Thermal testing of gDRT has validated this design and enabled thermal model correlation in order to provide more accurate survival energy predictions. The resulting energy consumption for heating the valves at the Jezero landing site represents a minimal impact to the Rover energy budget.
Thermal Modeling of Mars Ground for Surface Missions
Thermal analysis packages are capable of including ground temperature effects for orbital and surface thermal analyses. In particular, Thermal Desktop® offers the option of specifying ground temperatures as a function of time for planetary surface modeling. While suitable for many cases, this approach is not sufficient if an object has local interactions with the ground that could significantly affect the ground temperature. Ground modeling is necessary for the Mars 2020 rover thermal design and analysis since shadowing and heat dissipation from the rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) can result in significant temperature deviations of the local ground. The Mars 2020 thermal team is explicitly modeling the Martian ground so that these local temperature effects can be captured. The upper portion of the ground is modeled, and material and optical properties of the ground are varied in order to match data collected from orbiting science instruments. Atmospheric surface temperature, sky temperatures, and solar loads from a Mars General Circulation Model (GCM) are used as boundary conditions, resulting in a ground surface temperature profile consistent with the GCM predictions. The rover model is then placed on this modeled ground so that the effects of shadowing and MMRTG dissipation on the ground temperature can be captured.
Thermal Design, Analysis, and Sensitivity of a Sample Tube on the Martian Surface
NASA will launch a rover to Mars in 2020 to collect and cache samples of Martian rocks and regolith for potential return to Earth on a future mission. The collected samples will be placed in tubes, hermetically sealed, and deposited on the surface of Mars for a period of up to 10 years. Preventing the deposited samples from overheating is an important consideration in order to ensure their scientific integrity. The samples are required to remain below 60 °C, however there is a goal to keep them below 40 °C. This temperature requirement is challenging, considering that the maximum surface temperature of Mars is 38 °C and the tube must be thermally controlled through only passive means. As a result, a significant effort has been made to design a tube to contain the samples and investigate innovative tube surface treatments that maintain proper sample temperatures without significant adverse effects of sample contamination. The tube uses a specialized aluminum oxide coating to prevent overheating on the Martian surface. The maximum predicted tube temperature is relatively insensitive to local thermal inertia, ground contact, and ground slope, but is very sensitive to landing site latitude and dust deposition. The maximum predicted sample temperature in the +/- 30° landing latitude range with worst case assumptions is 54 °C, but many of the potential landing sites have significantly cooler maximum predicted sample temperatures. This paper describes the thermal design, analysis, and sensitivity studies performed on the sample tubes and also discusses operational considerations.
Mars 2020 Mobility Actuator Thermal Testing and Model Correlation
This paper describes the thermal testing and model correlation of a mobility actuator planned for use on the Mars 2020 Rover. The mobility actuator is identical to those which have been successfully flown and operated on the Mars Science Laboratory (MSL) Curiosity rover since its successful landing on Mars in August of 2012. The actuator consists of a motor, brake, and encoder paired with a four stage planetary gear box. In this thermal test, the actuator was instrumented with a number of thermocouples on both the interior and exterior of the gearbox. Heaters and a cold plate were used to generate thermal gradients across the actuator in vacuum, low pressure GN2, and low pressure CO2 environments in an effort to correlate a thermal model and develop a better understanding of how heat flows through the mechanism. This testing resulted in the successful model correlation of a simplified thermal model, and yielded important insights regarding the conductance of ball bearings and gear-to-gear contact. Ball bearing thermal conductance in a low pressure environment can be estimated by using correlations for vacuum thermal conductance along with a multiplier to account for increased gas conduction, and gear-to-gear conductance can be estimated by accounting for gas and grease conduction between two gears.
Summary and Status of 5 Mechanical Pumped Fluid Loop (MPFL) Projects Currently in Process at the Jet Propulsion Laboratory (JPL) for the Planned Europa Mission, Mars 2020, Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), Orbiting Carbon Observatory (OCO-3), and Cold Atom Lab (CAL)
No abstract available
MLI Blanket Effective Emittance Variance and Its Effect on Spacecraft Propellant Line Thermal Control
Multi-Layer Insulation (MLI) blankets commonly employed for temperature control of spacecraft propellant lines consistently show large variances in their effective emittances. These variances are primarily due to workmanship, hence are hard to control or predict. Unfortunately, the variances are also the primary drivers of propellant line temperatures, thus leading to large predicted temperature uncertainties and increased risks to the success of space missions. JPL has gained significant knowledge of these variances from Mars spacecraft designs over more than two decades. This knowledge has led to improved analytical approaches to bound existing designs, emphasis on increased temperature visibility for design verification and model correlation, as well as methods for improving the robustness of propellant line thermal designs.
Thermal Response of the Mars Science Laboratory Spacecraft During Entry, Descent and Landing
No abstract available
MLI Blanket Effective Emittance Variance and its Effect on Spacecraft Propellant Line Thermal Control
No abstract available
A Curious Year on Mars - Long-Term Thermal Trends for Mars Science Laboratory Rover's First Martian Year
By the time of this writing, Curiosity, the Mars Science Laboratory (MSL) Rover, has weathered four seasons in Gale Crater, just south of and approaching the foothills of the 5-km high Aeolis Mons, known as "Mount Sharp," at 4.59 deg south latitude. The mission design included a much broader latitude range of 30 deg north to 30 deg south constraining some of the Rover environmental requirements and operations. To date, Curiosity has relayed over 150 MB of thermal telemetry. Curiosity has relayed over 150 MB of thermal telemetry through four seasons. The trends and idiosyncrasies revealed through four seasons of telemetry from Mars are discussed. The better-characterized thermal environment allows for less conservatism in operational models and increases the amount of science data collection. Examples include: the elimination of overheating concerns for some cameras and the use of the previous sol's temperature telemetry along with the conservative soak temperature curve from the winter thermal model, to produce a custom heating prescription for the upcoming weeks thus increasing operation time and reducing heating times. This paper discusses the lessons learned for Rover operation as well as general idiosyncrasies discovered about the local environment-such as the effect of orientation on subsystem temperature variation, a regular morning and afternoon wind, ground and air microclimates with distinct temperature differences from other terrain, and how the Rover affects the local environment. This paper further documents and explains some of the interesting highs and lows of the temperature telemetry data as well as offers explanations for sudden temperature changes on board the Rover.