Thermal protection systems for space vehicles: A review on technology development, current challenges and future prospects

Enceladus’s long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around Saturn or Enceladus) and from the moon’s surface. In preparation for the National Academies of Sciences, Engineering and Medicine 2023–2032 Planetary Science and Astrobiology Decadal Survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at Enceladus: Is the subsurface ocean inhabited? Why, or why not? Trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. The team found that Orbilander, a mission concept that would first orbit and then land on Enceladus, represented the best balance. Orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. The Orbilander mission concept demonstrates that scientifically compelling but resource-conscious Flagship-class missions can be executed in the next decade to search for life at Enceladus.

/pdf/the-enceladus-orbilander-mission-concept-balancing-return-4ah077nl4a.pdf

The Enceladus Orbilander Mission Concept: Balancing Return and Resources in the Search for Life

An effect of shielding of an intense solar radiation towards a solar probe with the use of micron-sized SiC particles generated during ablation of a composite thermal protection material is estimated on a basis of numerical solution to a combined radiative and heat transfer problem. The radiative properties of particles are calculated using the Mie theory, and the spectral two-flux model is employed in radiative transfer calculations for non-uniform particle clouds. A computational model for generation and evolution of the cloud is based on a conjugated heat transfer problem taking into account heating and thermal destruction of the matrix of thermal protection material and sublimation of SiC particles in the generated cloud. The effect of light pressure, which is especially important for small particles, is also taken into account. The computational data for mass loss due to the particle cloud sublimation showed the low value about 1 kg/m2 per hour at the distance between the vehicle and the Sun surface of about four radii of the Sun. This indicates that embedding of silicon carbide or other particles into a thermal protection layer and the resulting generation of a particle cloud can be considered as a promising way to improve the possibilities of space missions due to a significant decrease in the vehicle working distance from the solar photosphere.

Self-generated clouds of micron-sized particles as a promising way of a Solar Probe shielding from intense thermal radiation of the Sun

Interstellar probe – Destination: Universe!

Although no known asteroid poses a threat to Earth for at least the next century, the catalogue of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1-3. A test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation1. NASA's Double Asteroid Redirection Test (DART) mission is a full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by the impact of the DART spacecraft4. Although past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in the orbit of Dimorphos7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary. 

https://doi.org/10.1038/s41586-023-05810-5

Successful kinetic impact into an asteroid for planetary defence

The NASA Double Asteroid Redirection Test (DART) is a technology demonstration mission that will test the kinetic impactor technique on a binary near-Earth asteroid system, Didymos. Didymos is an ideal target, since the 780 m primary, Didymos A, is well characterized, and the 163 m secondary, Didymos B, is sufficiently small to allow measurement of the kinetic deflection. Didymos also represents the population of Near Earth Objects that are the asteroids most likely to pose a near-term threat to Earth. Scheduled to launch in June 2021, the DART spacecraft will autonomously intercept Didymos B in October 2022, altering the orbit period of Didymos B with respect to Didymos A. The impact will occur when the Earth-Didymos range is close enough to allow observation by Earth-based optical and radio telescopes. The spacecraft will be guided to the impact by its on-board autonomous real-time system Small-body Maneuvering Autonomous Real-Time Navigation (SMART Nav). In addition, DART is carrying a 6U CubeSat provided by Agenzia Spaziale Italiana (ASI). The CubeSat will provide imagery documentation of the impact, as well as in situ observation of the impact site and resultant ejecta plume. The development is currently in Phase C, with mission Critical Design Review (CDR) planned for summer 2019. It is a substantial challenge to navigate the DART spacecraft to a hypervelocity impact with the Didymos secondary. The DART spacecraft will carry an ion propulsion system with the NASA Evolutionary Xenon Thruster Commercial (NEXT-C)engine, which provides flexibility in trajectory design to achieve the desired Didymos arrival conditions. The trajectory maximizes the asteroid deflection with an arrival velocity of 6 km/s relative to Didymos-B, while maintaining a proximity to Earth that allows both observation of the impact, and sufficient communication gain to recover imagery of the target upon the approach. Additionally, NEXT-C allows the mission an opportunity to fly by another asteroid and characterize SMART Nav performance seven months prior to its use for the Didymos impact. The DART spacecraft carries 22 m2 solar arrays to generate the ~3.5 kW needed to power the NEXT-C engine. These long arrays introduce substantial flexible body motion to the spacecraft. This motion must be managed carefully to maintain the DART narrow angle camera on the target asteroid, even while performing the necessary autonomous ΔV maneuvers required to intercept the target. Guidance to Didymos B is further complicated by having to switch targets late in the approach, as SMART Nav must target the primary asteroid initially, as the secondary is too small to be resolved by the narrow angle camera until ~1 hour prior to impact. Shadowing of both primary and secondary set by arrival lighting makes it challenging to impact at the center of Didymos B. The spacecraft streams images back to Earth in real time, up until impact.

Double Asteroid Redirection Test: The Earth Strikes Back

Since the beginning of space exploration, one of the most ambitious goals has been to explore beyond the boundaries of our solar system. Ground and Earth-orbit based systems have given a deep understanding of the overall characteristics of the heliosphere in the local interstellar medium and how the characteristics of our solar system are similar to and different from other systems. Viewing the heliosphere from outside will allow, for the first time, a more complete understanding of how a star system evolves and interacts with the Universe. Interstellar missions have been studied for decades. The primary reasons we have not yet explored this region are critical limitations in technology. These include a lack of propulsion that can achieve the high speeds needed to get to the heliospheric boundary in reasonable time, reliable systems that can function for the long lifetime needed, reasonable communications capabilities at interstellar range, and constraints on mission resources such as power when more than 100 AU from the Earth. Recent developments in launch systems, execution of long-lived missions such as New Horizons, new radioisotope power systems, and advanced communications systems have for the first time allowed for a practical, feasible near-term mission that can achieve the goal of exploring outside the solar system. We present recent results of a concept study that examined possible missions that could be launched as early as 2030 using existing, or near-existing, technology. These possible missions support significant payloads for heliospheric science, with the potential for additions to the payload for planetary investigations or astrophysics. The concept study includes a detailed look at possible trajectories in launch years from 2030 to 2040 with flyout speeds at least twice that of Voyager 1 and 2, and significant opportunities for tuning the flyout direction to maximize the heliophysics return as well as allow encounters with outer planets or Kuiper Belt Objects. We present a summary of trade studies performed to investigate the constraints and design space for an interstellar probe. These trades include a comparison of trajectories that include gravity assists at Jupiter and at the Sun to increase speed, optimization of the telecommunications architecture to balance data downlink rate with power usage, and spacecraft control methods to allow precise pointing for telecommnications while minimizing propellant usage for an extremely long-lived mission. We present a spacecraft design that can support the potential payloads designed to operate reliably for 50 years, while allowing for communications from 1000 AU.

Interstellar Probe: A Practical Mission to Escape the Heliosphere

NASA’s Solar Probe Plus (SPP) is approaching within 9.5 solar radii from the center of the sun. The SPP thermal protection system (TPS) is a 2.7 meter heat shield. The heat shield reaches temperatures of 1400uC on its front surface, its worst thermal case, and is subjected to launch loads, its worst mechanical case. The front surface of the thermal protection system is coated with an optically white coating in order to reduce the front surface temperature of the TPS and reduce the resulting heat flow into the spacecraft. At the temperatures experienced by the TPS, the optical properties are influenced by temperature more than in standard thermal control surfaces. Being able to accurate predict the optical performance of the coating at the temperature extremes of the mission is critical to understanding the thermal capabilities of the spacecraft and thermal protection system. A coating has been developed that can meet the requirements of the SPP TPS and it has been engineered to improve its optical properties at high temperature.

Development of a High-Temperature Optical Coating for Thermal Management on Solar Probe Plus

Development of a Thermal Simulator to Thermally Test the Solar Probe Plus Spacecraft

Solar Probe Plus (SPP) is a NASA mission that will go within ten Solar Radii of the sun. One of the crucial technologies in this system is the Thermal Protection System (TPS), which shields the spacecraft from the sun. The TPS is made up of carbon-foam sandwiched between two carbon-carbon panels, and is approximately eight feet in diameter and 4.5 inches thick. At its closest approach, the front surface of the TPS is expected to reach 1200°C, but the foam will dissipate the heat so the back surface will only be about 300°C. Solar Probe Plus is scheduled to launch in 2018, and the program is in the beginning stages of integration and testing. As part of the testing process, SPP's cooling system and the full spacecraft will undergo thermal tests. Radiation from the back of the TPS plays a large part in both of these systems thermal environment. To get the back surface of the TPS to 300°C, large amounts of energy needs to be put into the top of the TPS. However, there are not many thermal chambers that can accommodate the amount of energy required at the vacuum environment required to simulate space. It is also extremely risky to expose the flight hardware to that much energy. Instead, a Thermal Simulator will be used that mimics the thermal and geometric footprint of the bottom of the TPS. The Thermal Simulator is designed as an oven box, similar in size and shape to the flight TPS, which uses tubular heaters to heat a 32 mil thick aluminum bottom sheet. The heaters and bottom sheet are supported by a large stainless steel structure. The sides and top of the structure are blanketed using stainless steel sheets. To verify the concept, a miniature simulator was built and tested. Despite a successful trial simulator, there were difficulties extrapolating the design into a larger size. This paper will focus on the construction and testing of the full-sized simulator. After extensive structural and thermal analysis, the full simulator was fabricated and assembled. A thermal vacuum test was done at NASA Goddard Space Flight Center in chamber 238. At high vacuum, the bottom sheet was successfully brought to 250°C, 300°C, and 350°C with gradients of +/−30°C. Each temperature point was held for at least three hours after steady state was achieved. This simulator will be used in winter 2017 for the Integrated Thermal Vacuum Test, and again in the future for the full spacecraft test. By successfully executing the thermal system testing using GSE, we will prove that a full system can be validated using piecemeal testing.

Elizabeth Congdon

Papers

Double Asteroid Redirection Test: The Earth Strikes Back

Interstellar Probe: A Practical Mission to Escape the Heliosphere

Development of a High-Temperature Optical Coating for Thermal Management on Solar Probe Plus

Development of a Thermal Simulator to Thermally Test the Solar Probe Plus Spacecraft

Full scale thermal simulator development for the solar probe plus thermal protection system