The electrodynamic tether sling, a spinning tether with electrodynamic thrust, is described and has the ability to catapult spacecraft onto a variety of trajectories without the need for propellant. The electrodynamic force is used to recover the transferred momentum, change the orbit of the tether, and, because of its asymmetric design, alter the spin rate of the tether. A simple bang-bang current control scheme is developed for the spin-up maneuver, and an elliptical spiral current control scheme is developed to increase the energy of the orbit of the tether while maintaining the perigee close to the high-magnetic-field region near Earth. The equations of motion governing the system are derived and used to demonstrate the effectiveness of the two control schemes. An integral motion of the planar attitude dynamics within magnetic equatorial orbits is obtained, which aids in comprehending the dynamic structure of the attitude motion of the electrodynamic tether sling under the influence of gravitational and electrodynamic torques.

Enumeration of the problem space for the multiple-outage missed-thrust problem is a significant factor for determining what types of analysis is feasible to conduct. An exhaustive examination of the multiple-outage problem is one method for conducting missed-thrust analysis. In this paper, we explore the combinatorics of the problem, providing methods of calculating and estimating the number of possible missed-thrust cases when discretizing a trajectory to consider the effects of multiple missed-thrust events. We examine the difficulties of enumerating all possible cases, and examine when it may be desirable to conduct an exhaustive enumeration rather than a stochastic Monte-Carlo-type analysis. For missions which cover large time scales or feature high resolutions for their analysis, the combinatorics of the problem quickly grow excessively large, but the exhaustive formulation can still provide useful insight for smaller problems or with the right assumptions. We also explore various sub-problems, and their enumeration, such as the partial-thrust problem and the consideration of only critical regions of the trajectory, their potential applicability to the field of missed-thrust analysis, and connections to mathematical topics.

Small satellite constellations in multiple-inclination, low-circular orbits around Mars and Venus have the potential to perform a range of high-value science investigations within cost-constrained missions. A major challenge for small satellites is that they require large ΔV to enter low-circular orbits, which can drive up both spacecraft mass and cost. Compared to chemical propulsion, which requires large amounts of propellant, and electric propulsion, which requires large solar arrays and comes with long flight times, aerocapture enables direct access to low-circular orbits at Mars and Venus with minimal ΔV. The study shows how drag-modulation aerocapture, when combined with small B-plane targeting maneuvers, allows the delivery of multiple small satellites to various-inclination, low-circular orbits to establish a constellation. Preliminary cost estimates indicate that by reducing the required ΔV for orbit insertion, aerocapture can potentially reduce the cost of a small satellite going to a low-circular Mars orbit compared to propulsive insertion. The ability of low-cost spacecraft to enter planetary orbits will enable a new paradigm of interplanetary missions using small dedicated launch vehicles and planetary constellations at Mars and Venus.

ABS T R A C T Ocean Worlds such as Europa and Enceladus are known to harbor subsurface liquid water oceans under their icy crust and are high-priority targets for in situ exploration. Compared to the Moon and Mars, Ocean Worlds likely present a significantly more challenging environment for surface mobility systems due to the extremely cold temperature, high radiation dosage, and poorly constrained material properties under these conditions. Small-diameter wheels such as those used by Mars rovers are prone to slip-sinkage in loose soil and damage from sharp rock and ice formations. A 4-wheel rover with a simple drive system and large deployable compliant tires is proposed as a solution for extreme terrain mobility on Ocean World surfaces. The present work describes the design and construction of a single wheel test rig and a prototype large-diameter deployable wheel for Ocean World rovers and initial test results. The test rig allows independent control of the vertical load, slip ratio, slip angle, and camber angle, and accommodates large-diameter deployable wheels. The test rig features a modular test bed that can simulate varied surface features such as fine-grained ice, smooth hard ice, sharp ice formations, and large ice boulder fields. & COPY; 2023 ISTVS. Published by Elsevier Ltd. All rights reserved.

Venus is known for its extreme surface temperature and its sulfuric acid clouds. But the cloud layers on Venus have similar temperature and pressure conditions to those on the surface of Earth and are conjectured to be a possible habitat for microscopic life forms. We propose a mission concept to explore the clouds of Venus for up to 30 days to evaluate habitability and search for signs of life. The baseline mission targets a 2026 launch opportunity. A super-pressure variable float altitude balloon aerobot cycles between the altitudes of 48 and 60 km, i.e., primarily traversing the lower, middle, and part of the upper cloud layers. The instrument suite is carried by a gondola design derived from the Pioneer Venus Large Probe pressure vessel. The aerobot transmits data via an orbiter relay combined with a direct-to-Earth link. The orbiter is captured into a 6-h retrograde orbit with a low, roughly 170-degree, inclination. The total mass of the orbiter and entry probe is estimated to be 640 kg. An alternate concept for a constant float altitude balloon is also discussed as a lower complexity option compared to the variable float altitude version. The proposed mission would complement other planned missions and could help elucidate the limits of habitability and the role of unknown chemistry or possibly life itself in the Venus atmosphere.

A quantitative and comparative assessment of the feasibility and mass benefit of using aerocapture at all atmosphere-bearing solar system destinations is presented, considering both lift and drag modulation control techniques. Aerocapture is shown to be feasible at Mars, Titan, and Venus with existing entry vehicles and flight-proven thermal protection system (TPS) materials, and requires no significant technology developments before use on a science mission. Aerocapture at Uranus and Neptune is viable with blunt-body aeroshells (L/D of 0.30-0.40) and Heatshield for Extreme Entry Environment Technology TPS for certain high arrival V & INFIN; interplanetary trajectories. The mass benefit offered by aerocapture is compared to alternative orbit insertion techniques such as purely propulsive insertion and aerobraking. Aerobraking outperforms aerocapture for missions to Mars and Venus with arrival V & INFIN; less than 6 km/s. For outer planet missions, aerocapture offers substantial mass benefit depending on the arrival V & INFIN;, Titan (300-1700% more mass), Uranus (100-600%), and Neptune (80-400%), in addition to significant reduction in flight time. The study recommends a low-cost drag modulation aerocapture demonstration mission at Earth to establish flight heritage for aerocapture and lower the risk for future science missions.

Mounting evidence of chemical disequilibria in the Venusian atmosphere has heightened interest in the search for life within the planet's cloud decks. Balloon systems are currently considered to be the superior class of aerial platform for extended atmospheric sampling within the clouds, providing the highest ratio of science return to risk. Balloon-based aerial platform designs depend heavily on payload mass and target altitudes. We present options for constant- and variable-altitude balloon systems designed to carry out science operations inside the Venusian cloud decks. The Venus Life Finder (VLF) mission study proposes a series of missions that require extended in situ analysis of Venus cloud material. We provide an overview of a representative mission architecture, as well as gondola designs to accommodate a VLF instrument suite. Current architecture asserts a launch date of 30 July 2026, which would place an orbiter and entry vehicle at Venus as early as November 29 of that same year.

Let us start by considering a system consisting of only two particles: P 1 and P 2 as shown in Fig. 1.1. Later we generalize to a system of n particles.

We now consider the problem of using an orbit model to predict the motion of a satellite in the real world. Suppose we have assembled a credible analytical orbit model by combining the effects of the second zonal harmonic developed in Chap. 8 with the effects of atmospheric drag developed in Chap. 11 . Further, let us assume we have obtained some tracking data on a satellite of interest, and we have an initial estimate of that satellite's orbit.

We consider the gravitational potential due to a planet that is not a uniform sphere. We let P be the location of a unit mass at a distance r from C (the center of mass) of a bounded distribution of matter having a total mass M. Let dm be a differential element of the mass distribution, located at point Q, a distance ρ from C.

Modern perturbation theory is attributed to Poincaré. Early attempts by astronomers were plagued by the appearance of terms increasing with time. Such terms are referred to as secular terms and may affect the convergence of the solution. A large variety of perturbation methods suppressing the secular terms have been developed, including a method by Poincaré and Lindstedt.

A performance analysis for aerocapture at Uranus and Neptune is presented and considers entry corridor width, peak deceleration, peak heat rate, total heat load, and the effect of postcapture orbit on the design parameters. Aerocapture mass benefit vs chemical capture is also quantified. Design relationships are found that can be used in flight system sizing for future studies involving aerocapture. Results are obtained for interplanetary trajectories for launch years from 2025 to 2036, including both chemical capture and high arrival V-infinity. The results show that based on the current assumption for errors and uncertainties aerocapture at Uranus and Neptune requires a mid-lift-to-drag ratio between 0.6 and 0.8. Technology recommendations are made for aerocapture missions to Uranus and Neptune.