View Video Presentation: https://doi.org/10.2514/6.2022-1771.vid Many guidance algorithms are built on a predictor-corrector algorithm for adjust- ing guidance parameters to meet terminal trajectory constraints. However these methods classically ignore the fact that the system is actually stochastic as they solve for the guidance solution. In this paper, we discuss recent developments in a robust predictor-corrector methodology for addressing the stochastic nature of guidance problems. This uncertainty is due to the imperfect navigation solution, as well as the presence of uncertainty in the dynamic models and vehicle performance parameters. We demonstrate the guidance algorithms on entry, descent and landing problems as well as for orbital guidance around small bodies.

This paper presents a novel fuel-efficient continuous-thrust maneuver targeting (CTMT) algorithm that is capable of planning finite, continuous maneuvers in a larger autonomous spacecraft guidance architecture. This is accomplished using a constant-thrust bilinear tangent guidance law in conjunction with an optimal Lambert algorithm and a Newton-Raphson predictor-corrector targeting scheme. This simple approach is capable of planning a plethora of different free-time and fixed-time single-burn, burn-coast intercept, or burn-coast-burn bilinear tangent maneuvers from an initial state/orbit to a desired state/orbit. For the study case of asteroid Bennu, when used with thrust levels that are greater than 5% of the surface acceleration of asteroid Bennu, the CTMT algorithm is able to converge on 99% of orbital transfers initiated from a circular, 1.5 km, terminator orbit. Furthermore, many of the continuous-thrust maneuvers calculated by the CTMT algorithm are the optimal constant-thrust trajectories between two states in the small-body dynamical environment, and they are able to be calculated hundreds of times faster with the CTMT algorithm than with state-of-the-art nonlinear optimization algorithms. Ultimately, the CTMT algorithm shows promise as a candidate for future autonomous guidance applications.

Exoplanet discoveries since the mid-1990's have revealed an astounding diversity of planetary systems. Studying these systems is essential to understanding planetary formation processes, as well as the development of life in the universe. Unfortunately, humanity can only observe limited aspects of exoplanetary systems by telescope, and the significant distances between stars presents a barrier to in situ exploration. In this study, we propose an alternative path to gain insight into exoplanetary systems: Bridge, a mission concept design to fly by an interstellar object as it passes through our solar system. Designed as a New Frontiers-class mission during the National Aeronautics and Space Administration (NASA) Planetary Science Summer Seminar, Bridge would provide a unique opportunity to gain insight into potential physical, chemical, and biological differences between solar systems as well as the possible exchange of planetary materials between them. Bridge employs ultraviolet/visible, near-infrared, and mid-infrared point spectrometers, a visible camera, and a guided impactor. We also provide a quantitative Monte Carlo analysis that estimates wait times for a suitable target, and examines key trades between ground storage and a parking orbit, power sources, inner versus outer solar system encounters, and launch criteria. Due to the fleeting nature of interstellar objects, reaching an interstellar object may require an extended ground storage phase for the spacecraft until a suitable target is discovered, followed by a rapid response launch strategy. To enable rapid response missions designed to intercept such unique targets, language would need to be added to future NASA announcements of opportunity such that ground storage and rapid response would be allowable components of a proposed mission.

This paper examines the ability of a bilinear tangent guidance law to perform continuous-thrust, single-burn orbital maneuvers in the small-body orbital environment (solar radiation pressure, etc.) and the capability of a Newton-Raphson predictor-corrector algorithm to perform free-time, state-to-state spacecraft guidance on initial state perturbations. This paper shows that low-thrust bilinear tangent is able to perform a wide variety of maneuvers with a wide variety of thrust levels around asteroid Bennu. Additionally, this paper shows that even with a high control authority, the size of initial state perturbations that can be corrected depends on the size of the target state's complex backward-reachable subspace and the location of the initial state of the maneuver in that subspace. For example, a 5 mN thruster on a 1000 kg spacecraft performed an aggressive shape and plane change maneuver for less than 3.5 g of fuel. The derived guidance algorithm then corrected 100% of initial state perturbations drawn from delta r similar to N(33,17.5) m and delta v similar to N(3,1.7) mm/s distributions. Ultimately, this paper shows that Newton-Raphson predictor-corrector bilinear tangent guidance is a capable guidance scheme when used on perturbations that lie within the reachable subspace of the target state.

This paper will provide an introduction and overview of Area-of-Effect Softbots (AoES), which are currently in development under a Phase 2 NASA Innovative Advanced Concepts (NIAC) project. AoES are designed to operate in proximity to, and on the surface of, small asteroids to support mining and planetary defense missions. Their unique design and capabilities are dependent on the incorporation of soft, compliant, and lightweight materials. AoES have a large area-to-mass ratio which allows them to take advantage of the peculiarities of the dynamical environment around small asteroids. Specifically, AoES will use solar radiation pressure to sail to the surface of the target asteroid after being deployed at a safe altitude from a mothership around the asteroid. This capability and the associated control laws will be demonstrated, removing the need for propulsion systems. Furthermore, the large, flexible surface area allows for robustness with respect to uncertainty about the asteroid surface structure - it can provide flotation to prevent sinking into a very loose, dusty regolith, and also provide anchoring to the surface through natural and electroadhesion forces. The enabling technology that will allow the AoES design loop to close is a new class of soft actuators known as HASEL actuators. These actuators harness an electrohydraulic mechanism, whereby electrostatic forces generate hydraulic pressure to drive shape change in a soft fluid-filled structure. HASELs provide an extremely power- and mass-efficient mechanism for actuating the large flexible surface areas that are the essential components defining AoES. Current system design, requirements, and key tradeoffs will be discussed - with a particular focus on the actuation, mobility, anchoring, materials, and power systems/components. The nominal mission profile and concept of operations for using AoES in an asteroid mining mission will be outlined.

Author: Donald H. Kuettel III Active orthotic devices for joint articulation have a vast number of applications that could benefit many people. Examples include joint articulation for people suffering from disabilities, increased load carrying capacity and walking distance for humans, and

The environmental degradation of intermediate heat exchanger (IHX) materials in impure helium has been identified as an area with major ramifications on the design of very high-temperature reactors (VHTR). It has been reported that in some helium environments, non-ductile failure is a significant failure mode for Alloy 617 with long-term elevated-temperature service. Non-ductile failure of intermediate exchangers can result in catastrophic consequences; unfortunately, the knowledge of creep crack initiation and creep crack growth (CCG) in candidate alloys is limited. Current codes and code cases for the candidate alloys do not provide specific guidelines for effects of impure helium on the high-temperature behavior. The work reported here explores creep crack growth characterization of Alloy 617 and Alloy 800H at elevated temperatures in air and in impure helium environments, providing information on the reliability of these alloys in VHTR for long-term service. Alloy 617 was found to exhibit superior CCG resistance compared to Alloy 800H. For Alloy 617 tested at 973 K (700 °C), a notable increase in the resistance to crack growth was measured in air compared to that measured in the helium environment; CCG results for Alloy 800H suggest that air and helium environments produce similar behavior. Testing of grain boundary-engineered (GBE) Alloy 617 samples revealed that, although the technique produces superior mechanical properties in many respects, the GBE samples exhibited inferior resistance to creep crack growth compared to the other Alloy 617 samples tested under similar conditions. Grain size is noted as a confounding factor in creep crack growth resistance.

Investigating creep crack growth under extreme environmental conditions is a challenging yet essential undertaking for the assessment of structural lifetimes of critical components subjected to extreme working conditions for long periods of time. For example, there is currently a need to evaluate structural materials for Next Generation Nuclear Plants (NGNPs) which will operate very high temperature helium-cooled reactors (VHTRs) for generating electricity and co-generating hydrogen using the process heat from the reactor. The primary helium coolant is expected to operate at temperatures at or above 750 °C. In order to evaluate candidate materials for the intermediate heat exchangers, such as Inconel 617 and Alloy 800H, we have developed a creep crack growth (CCG) test apparatus which was designed to test compact tension specimens at temperatures up to 850 °C in controlled environments, including impure helium environments, following ASTM standard E 1457–07. Details of the design of the CCG apparatus will be discussed.

Next Generation Nuclear Plant (NGNP) designs for very-high-temperature reactors (VHTR) employ intermediate heat exchanger (IHX) for which the material demands are extreme. Currently, Alloy 617 and Alloy 800H are considered to be among the candidate materials for the high-temperature, helium-cooled environments that are planned for these systems. The primary helium coolant is expected to operate at temperatures at or above 750 °C, and creep crack growth (CCG) of these candidate alloys is of particular concern for their reliability in VHTRs for long-term service. Using an apparatus that was designed and constructed in-house, CCG testing was conducted on compact tension specimens at temperatures up to 850 °C in controlled environments, including air and impure helium, following ASTM standard E 1457-07. Overall, our CCG testing revealed that Alloy 617 exhibits superior resistance to creep crack growth compared to Alloy 800H. Trends observed in the mechanical behavior and microstructure of the candidate alloys as a function of environment will be discussed.