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NASA NTRS1992

Planetary mission opportunities with nuclear electric propulsion

An assessment is made of the applicability, benefits, and requirements of nuclear-electric propulsion (NEP) for solar system-exploration missions, within the framework of SP-100 reactor-based power technologies and 30-cm ring-cusp thruster technology. An initial launch date of 2005 is projected from a program-inception date of 2000. The missions in question encompass orbitings and flybys of Pluto, accomplishing in 10-13 years which would ballistically require a transfer time of 40 years; a Neptune orbiting; a Jupiter grand tour which will orbit each of the moons in turn; a Uranus orbiting; and a multiple mainbelt asteroid rendezvous orbiting six selected asteroids.

Kelley, James H.↗

NASA NTRS1971

Uranus and Neptune orbiter missions via solar electric propulsion

The characteristics and capabilities of solar electric propulsion for performing orbiter missions at the planets Uranus and Neptune are described. An assessment of the scientific objectives and instrumentation requirements, their relation to orbit size selection, and parametric analysis of solar electric propulsion trajectory/payload performance are included. Utilizing the Titan 3D/Centaur launch vehicle, minimum flight times of about 3400 days to Uranus and 5300 days to Neptune are required to place the TOPS spacecraft into the nominal orbits. It has been shown that solar electric propulsion can be used effectively to accomplish elliptical orbiter missions at Uranus and Neptune. However, because of the very long flight time required, these mission profiles are not too attractive. Previous studies have shown that nuclear electric propulsion, if developed, would allow much faster trips; 5 years to Uranus and 8 years to Neptune.

Friedlander, A. L.↗

NASA NTRSDate not supplied

Imaging Science Requirements for a Uranus Flagship Mission

Introduction: Our presentation will summarize the requirements for UV/Visible/Near-IR remote-sensing imaging science instruments (including mapping spectrometers) envisioned for the Uranus Orbiter and Probe (UOP) mission recommended by the recent planetary decadal survey. The Uranus system offers many targets for imaging investigations. Imaging science investigations are crucial to answering fundamental questions about various physical processes that shape the Uranian system and drive its evolution. Each science objective addressed through imaging has requirements for observation and illumination geometries as well as coverage and resolution in the spatial, spectral and temporal dimensions. By combining the requirements for the diverse science targets in the Uranian system, we present a set of overarching imaging science requirements for UOP. Atmospheric Science: The study of Uranus’ atmosphere is crucial in understanding the planet's energy balance and interior heat flux. Imaging observations map how the atmosphere scatters incident solar radiation. Imaging is key to characterizing planetary-scale energy/material transport though global atmospheric dynamics and local meteorology. Hyperspectral mapping combined with radiative transfer analysis reveals the vertical distribution of clouds and hazes. Chronicling temporal variabilities of atmospheric features is key to understanding the various processes that operate within the dynamic Uranian atmosphere. A comprehensive understanding of Uranus' atmosphere is essential in deciphering the planet's origins and evolution as well as providing insight into the broader field of planetary and exoplanetary science. Magnetospheric Interactions: Imaging science is critical to understand the elusive Uranian aurorae. Mapping the aurorae and their temporal dynamics will reveal the interaction of Uranus’ complex magnetosphere with the solar wind. The apparent decades-long cooling of Uranus’ upper atmosphere is thought to be due to changes in energy input from the overlying magnetosphere, and so mapping and quantifying the auroral evidence for this energy flux is particularly relevant for upper atmospheric science In addition, Uranus’ large moons may generate auroral footprints, which can be used to constrain the planet’s unusual magnetic field structure. Satellite Interiors: Imaging science can address the potential habitability of the larger moons of Uranus by measuring their shapes and rotational states (including librations), which combined with gravity data are crucial to understanding their internal density structure. Satellite Origins: Origin markers such as organics and volatiles may be preserved on the satellite surfaces, which may be sensed by UV/IR mapping. Imaging combined with the moons’ densities may reveal whether the moons formed in Uranus’ circumplanetary disk, rings, or from ejecta of a giant impact on Uranus. Satellite Geology: Imaging investigations, including stereo imaging to obtain topography, will enable constraining each satellite’s geologic history by investigating the distributions and morphologies of impact craters, tectonic and potential cryovolcanic features, and regolith and mass wasting deposits. These records will help unravel the past complex history of orbital resonances that occurred between Uranian satellites, which may have driven geologic activity. Analyses of these features will also point to resurfacing styles and modification processes important for understanding each moon’s thermal evolution, and any present-day geological activity, including potential subsurface deep oceans or possible current activity. Additionally, hyperspectral imaging will enable mapping the surface composition and identifying the potential presence of material that may point to a subsurface ocean, such as ammonia-bearing species. Rings and Small Moons: Imaging observations elucidate the physical processes that contribute to the complex ring-moon system’s inferred unstable state. Imaging surveys will seek smaller moons and other debris that could provide evidence of past collisions, while precise astrometric data of moons will determine the current dynamical state of the system. Many of Uranus' rings are exceptionally narrow, and images of the rings covering a broad range of longitudes, and high-resolution images of features within the rings will reveal how these rings are confined and maintained, as well as illustrating the rings' internal structure and dynamics. Images of the rings and moons obtained at a variety of wavelengths and lighting conditions are also needed to quantify the composition and the size distribution of the small satellites and ring particles.

K M Sayanagi↗

NASA NTRS2016

Science Instrument Sensitivities to Radioisotope Power System Environment

Radioisotope Power Systems (RPS) have been and will be enabling or significantly enhancing for many missions, including several concepts identified in the 2011 Planetary Science Decadal Survey. Some mission planners and science investigators might have concerns about possible impacts from RPS-induced conditions upon the scientific capabilities of their mission concepts. To alleviate these concerns, this paper looks at existing and potential future RPS designs, and examines their potential radiation, thermal, vibration, electromagnetic interference (EMI), and magnetic fields impacts on representative science instruments and science measurements. Radiation impacts from RPS on science instruments are of potential concern for instruments with optical detectors and instruments with high-voltage electronics. The two main areas of concern are noise effects on the instrument measurements, and long-term effects of instrument damage. While RPS by their nature will contribute to total radiation dose, their addition for most missions should be relatively small. For example, the gamma dose rate from one Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) would be an order of magnitude lower than the environmental dose rate at Mars, and would have a correspondingly lower contribution to instrument noise and to any permanent damage to payload sensors. Increasing the number of General Purpose Heat Source (GPHS) modules used in an RPS would be expected to increase the generated radiation proportionally; however, the effect of more GPHS modules is mitigated from a strictly linear relationship by self-shielding effects. The radiation field of an RPS is anisotropic due to the deviation of the modules from a point-source-geometry. For particularly sensitive instruments the total radiation dose could be mitigated with separation or application of spot shielding. Though a new, higher-power RPS could generate more heat per unit than current designs, thermal impact to the flight system could be mitigated with shading and pointing if required by the mission. Alternatively, excess heat could prove beneficial in providing needed heat to spacecraft components and instruments in some thermal environments. Vibration for a new higher-power Stirling Radioisotope Generator (SRG) would be expected to be similar to the recent Advanced Stirling Radioisotope Generator (ASRG) design. While vibration should be low, it must be considered and addressed during spacecraft and instrument design. EMI and magnetic fields for new RPS concepts are expected to be low as for the current RPS, but must be considered and addressed if the mission includes sensitive instruments such as magnetometers. The assessment conducted for this paper focused on orbiter instrument payloads for two representative mission concepts- a Titan Saturn System Mission (TSSM) and a Uranus Orbiter and Probe (UOP)-since both of these Decadal Survey concepts would include many diverse instruments on board. Quick-look design studies using notional new RPS concepts were carried out for these two mission concepts, and their specific instrument packages were analyzed for their interactions with new RPS designs. The original Decadal Survey TSSM and UOP concepts did not have complete instrument performance requirements so typical measurement requirements were used where needed. Then, the general RPS environments were evaluated for impacts to various types of instruments. This paper describes how the potential impacts of the RPS on science instruments and measurements were assessed, which impacts were addressed, proposed mitigation strategies against those impacts, and provides an overview of future work.

RPS↗

NASA NTRSDate not supplied

Uranus Flagship-class Orbiter and Probe Using Aerocapture

Exploration of the Ice Giants, especially Uranus, via orbiter and atmospheric probes, is required to answer pressing science questions that have been raised in the latest National Academies of Sciences Planetary Decadal Survey. Since the Ice Giants are the farthest planets from Earth, traditional fully-propulsive orbit insertion missions have transit times to the planetary bodies bordering 13-15 years and require a large amount of propellant (wet mass percentages of around 60-70%) for the orbit insertion maneuver, leaving less mass for the scientific payload and a planetary probe. Aerocapture uses aerodynamic forces generated by flight within a planetary atmosphere to decelerate and achieve orbit insertion. Aerocapture has been considered for several past missions but it has not been demonstrated. However, recent developments in thermal protection systems (TPS), guidance and control (G&C), and interplanetary navigation capabilities show the potential for using rigid, heritage entry vehicle configurations already flown at other planetary bodies for Ice Giants aerocapture. Aerocapture can robustly deliver spacecraft to Ice Giant orbits, while substantially increasing on-orbit payload mass (more than 40%) that can be used for a robust atmospheric entry probe. Additionally, the aerocapture maneuver would reduce the interplanetary transit time by 2-5 years (15-30%) relative to fully-propulsive orbit insertion. Recent work has shown that a flagship-class mission can be conducted in a shorter time than fully-propulsive missions if using aerocapture. This paper will consider the merits of including aerocapture as the orbit-insertion mechanism for a Uranus mission. Specifically, the implications of aerocapture orbit insertion for in-situ atmospheric probes will be discussed. The Uranus Orbiter and Probe concept mission study [3] is considered as the potential payload. Results from a recent NASA Space Technology Mission Directorate (STMD)-funded activity that is designing an aerocapture mission for a Uranus orbiter will be presented.

Soumyo Dutta↗

NASA NTRSDate not supplied

Uranus Flagship-class Orbiter and Probe Using Aerocapture

Soumyo Dutta↗

NASA NTRSDate not supplied

Heatshield for Extreme Entry Environment Technology (Heeet) and 3D Woven TPS Readiness for Outer Planet Probe Missions

Recent mission studies have shown entry at Uranus or at Neptune will require 3-D Woven TPS, either the two-layer HEEET or the single layer 3MDCP, with 3MDCP being more mass efficient. The 3MDCP capability being developed to support MSR EES is sufficient for the Ice Giants if the probe size is 1.25 m or less. [The Uranus Orbiter Probe (UOP) Flagship study for the Decadal used a 1.26m diameter probe.] For larger diameters, dual layer HEEET is easily scalable and is already at TRL 6. It is possible to develop a seam approach that would allow the use of 3MDCP; the resultant mass savings could warrant such a development. Ames is already working on a concept towards this. If aerocapture becomes part of the mission design for Uranus, delivery of the probe from orbit will be easier. Whether or not the probe is delivered from orbit, 3-D Woven (HEEET or 3MDCP) is the only TPS qualified to enable Ice Giant in situ probes. In addition to UOP, Saturn probe mission concepts will be enabled by 3-D Woven, either HEEET or 3MDCP. Launch periods for the UOP flagship or a Saturn probe mission in the early to mid 2030s requires the community to ensure that the 3D woven capability does not atrophy. Currently other than MSR EES, no other mission requires 3-D wovens, and the manufacturing for MSR will be completed by 2023. A gap in production of 5 or more years requires careful monitoring of the industrial base. In addition, manufacturing of 3-D woven TPS, from procurement and weaving to molding and infusion, is a minimum 2-year activity. In response to the threat of atrophy and the time critical and intensive nature of restarting weaving, advocacy from OPAG to NASA SMD for a sustainability effort would ensure in situ exploration of the outer planets in the decades to come.

M Gasch↗

NASA NTRS1989

Small satellites of Uranus - Disk-integrated photometry and estimated radii

Voyager imaging data is used to study the evolution of the Uranian system, focusing on the disk-integrated properties and radii of the 10 small satellites orbiting Uranus interior to Miranda (Smith et al., 1986). Reflectances are derived for the two objects that are spatially resolved by the Voyager observations. The relative sizes of the satellites are estimated on the basis of relative apparent brightness (disk-integrated flux). The results are discussed in the context of the origin of these satellites and their relationship to the material forming the rings of Uranus.

Thomas, Peter↗

NASA NTRS1971

Mission operations for unmanned nuclear electric propulsion outer planet exploration with a thermionic reactor spacecraft.

Mission operations are presented for comet rendezvous and outer planet exploration NEP spacecraft employing in-core thermionic reactors for electric power generation. The selected reference missions are the Comet Halley rendezvous and a Jupiter orbiter at 5.9 planet radii, the orbit of the moon Io. The characteristics of the baseline multi-mission NEP spacecraft are presented and its performance in other outer planet missions, such as Saturn and Uranus orbiters and a Neptune flyby, are discussed. Candidate mission operations are defined from spacecraft assembly to mission completion. Pre-launch operations are identified. Shuttle launch and subsequent injection to earth escape by the Centaur D-1T are discussed, as well as power plant startup and the heliocentric mission phases. The sequence and type of operations are basically identical for all missions investigated.

Spera, R. J.↗

NASA NTRSDate not supplied

6-DoF Uranus Aerocapture Trajectory Analysis

The Uranus Orbiter and Probe mission has been identified as the highest priority flagship mission for this decade. Delays in launch opportunities may make existing fully-propulsive orbit insertion mission types unfeasible. Aerocapture can potentially alleviate these challenges while providing a solution flexible to different launch opportunities. While the space technology that aerocapture leverages have been flight-proven, aerocapture as-a-whole has not been formally demonstrated. This paper presents a novel 6-DoF aerocapture trajectory analysis applied to Uranus. The paper presents the 6-DoF simulation framework, inspired from Mars Science Laboratory. Trajectory comparisons, including Monte Carlo simulations, to existing 3-DoF solutions are presented to understand the information learned from increasing the modeling level-of-fidelity.

Rohan G Deshmukh↗

NASA NTRSDate not supplied

6-DoF Uranus Aerocapture Trajectory Analysis

Aerocapture↗

NASA NTRS1975

Improved planetary orbit mission capabilities in the Shuttle era by use of space-storable propulsion systems

Planetary-orbit mission capabilities will be greatly improved by the advent of space-storable retropropulsion systems with liquid fluorine and hydrazine as bipropellants even when the Shuttle/Tug is used as launch vehicle. Having a specific impulse as large as 375 sec, a multimission propulsion module using space-storable propellants with Pioneer or Mariner spacecraft as payload can perform Mercury, Saturn, and Uranus orbiter missions, and even some comet rendezvous missions, more cost effectively and flexibly than one using earth-storable propellants. It also can reduce trip time to the outer planets significantly. This paper presents mission requirements, technology status, system design and performance, development schedules, and costs based on data derived in a recent design and feasibility study.

Meissinger, H. F.↗

NASA NTRS1975

Advanced bipropellant systems for use on planetary orbiters

Planetary orbit mission capabilities will be greatly improved by the advent of space-storable retro-propulsion systems with liquid fluorine/hydrazine as bipropellants, even when the Space Shuttle/Space Tug is used as launch vehicle. With a specific impulse as high as 375 sec, a multimission propulsion module designed for Pioneer or Mariner class spacecraft as payload and using space-storable propellants, can perform Mercury, Saturn and Uranus orbiter missions, and even some comet rendezvous missions. It also can reduce trip times to the outer planets significantly. The paper presents mission requirements, propulsion technology status, system design, performance, development schedules and cost data, based on results of a recent design and feasibility study.

Meissinger, H. F.↗

NASA NTRS2013

Characterizing Uranus with an Ice giant Planetary Origins Probe (Ice-POP)

We now know from studies of planetary transits and microlensing that Neptune-mass planets are ubitquitous and may be the most common class of planets in the Galaxy. As such it is crucial that we understand the formation and evolution of the ice giant planets in our own solar system so that we can better understand planet formation throughout the galaxy. An entry probe mission to Uranus would help accomplish this goal. In fact the Planetary Decadal Survey recommended a Uranus orbiter with entry probe but did not explore in detail the specifications for the entry probe. NASA Ames is currently studying thermal protection system requirements for such a mission and this has led to questions regarding the minimum interesting science payload of such an entry probe. The single most important in-situ measurement for an ice giant entry probe is a measurement of atmospheric composition. For Uranus this would specifically include the methane and noble gas abundances. An in situ measurement of the methane abundance, from below the methane cloud, would constrain the atmospheric carbon abundance, which is believed to be roughly 30 to 50 times solar. There are hints from the transiting planets that extrasolar ice giants show comparable or even greater enhancements of heavy elements compared to their primary stars. However the origin of this carbon enhancement is controversial. Is Uranus a "failed core" of a larger gas giant or was the atmosphere enhanced by accretion of icy planetesimals' Constraining atmospheric abundances of C and perhaps S or even N from below 5 bars would provide badly needed data to address such issues. A measurement of the N abundance would provide clues on the origin of the planetesimals that formed Uranus. Low N-abundance indicates planetesimals from 'warmer' regions where N was mainly in form of NH3, whereas a strong enrichment could indicate planetesimals / cometary material from the colder outer regions of the nebula. Furthermore CO and HCN have been detected in Neptune but not in Uranus. A measurement of the abundance of either would constrain the source mechanisms for these molecules (exogenic or internal). A major surprise from the Galileo Entry Probe was that the heavier noble gases Ar, Kr, and Xe are enhanced in Jupiter's atmosphere at a level comparable to what was seen for the chemically active volatiles N, C, and S. It had been generally expected that Ar, Kr, and Xe would be present in solar abundances, as all were expected to accrete with hydrogen during the gravitational capture of nebular gases. Enhanced abundances of Ar, Kr, and Xe is equivalent to saying that these noble gases have been separated from hydrogen. There are several mechanisms that could accomplish this but these hypotheses require further testing. Measurement of noble gas abundances in an ice giant would constrain the planetary formation and nebular mechanisms responsible for this enhancement. Standard three-layer models of Uranus find that the outer, predominantly H/He layer of Uranus does not reach pressures high enough (approximately 1 Mbar) for H2 to transition to liquid metallic hydrogen. However, valid models can also be constructed with a smaller intermediate water-rich layer, with hydrogen then reaching the metallic hydrogen phase. If this occurs, He should phase separate from the hydrogen and ``rain out," taking along a substantial abundance of Ne, as suggested for Jupiter (and likely also for Saturn). Hence He and Ne depletions could be probes of the planet's structure in the much deeper interior. A determination of Uranus' atmospheric abundances, particularly of the noble gasses, is thus critical to understanding the formation of Uranus, and giant planets in general. These measurements can only be performed with an entry probe. The second key measurement would be a temperature-pressure sounding to provide ground truth for remote measurements of atmospheric temperature and composition and to constrain the internal heat flow. This would also establish that the methane abundance measurements have indeed been made below any possible methane cloud. Finally an ultra stable oscillator would measure wind speeds and constrain atmospheric dynamics. In our presentation we will discuss the importance of all of these measurements and argue that an entry probe is a crucial component of any ice giant mission.

Marley, Mark S.↗

NASA NTRS1987

Surface waves on Uranus' magnetopause

Uranus' magnetosphere has a well-developed, thick magnetopause that was fully traversed twice by Voyager 2, once inbound to the planet and once outbound. This boundary appears to resemble earth's magnetopause in approximate shape and even to the extent of supporting surface waves which were observed on the inbound pass at a distance of 18.3 Uranus radii. There were apparently eight partial transitions from the magnetosheath into the current sheet of the magnetopause at this time, followed by a final complete transition to the magnetosphere. Six of the estimated normal vectors to the local boundary show clear evidence of oscillations in the slope with typical angular excursions, from one partial transition to the next, of about 90 deg. The vectors oscillated approximately in a plane that was severely tilted by about 49 deg with respect to Uranus' orbital plane.

Lepping, R. P.↗

NASA NTRS2021

The Science Case for Spacecraft Exploration of the Uranian Satellites: Candidate Ocean Worlds in an Ice Giant System

The 27 satellites of Uranus are enigmatic, with dark surfaces coated by material that could be rich in organics. Voyager 2 imaged the southern hemispheres of Uranus’s five largest “classical” moons—Miranda, Ariel, Umbriel, Titania, and Oberon, as well as the largest ring moon, Puck—but their northern hemispheres were largely unobservable at the time of the flyby and were not imaged. Additionally, no spatially resolved data sets exist for the other 21 known moons, and their surface properties are essentially unknown. Because Voyager 2 was not equipped with a near-infrared mapping spectrometer, our knowledge of the Uranian moons’ surface compositions, and the processes that modify them, is limited to disk-integrated data sets collected by ground- and space-based telescopes. Nevertheless, images collected by the Imaging Science System on Voyager 2 and reflectance spectra collected by telescope facilities indicate that the five classical moons are candidate ocean worlds that might currently have, or had, liquid subsurface layers beneath their icy surfaces. To determine whether these moons are ocean worlds, and to investigate Uranus’s ring moons and irregular satellites, close-up observations and measurements made by instruments on board a Uranus orbiter are needed.

Richard J. Cartwright↗

NASA NTRSDate not supplied

State of the Art Thermal Protection Systems at NASA for Outer Planet Probes and TPS Developments in Support of Mars Sample Return Mission

In the recent NASA Planetary Science Decadal Survey (2023-2032) the committee recommended that the highest scientific priority of NASA’s robotic exploration efforts this decade should be completion of Mars Sample Return (MSR) and recommended to prioritize the Uranus Orbiter and Probe as the highest-priority new flagship missions for the next decade while Saturn Probe is one of the themes still under consideration for New Frontiers. This short course presentation will discuss relevant environments for outer planet missions and TPS materials under development at NASA and their readiness to meet mission needs. In addition the presentation will discuss the status of thermal protection system for the MSR Earth Entry System that brings the Martian samples safely through the Earth’s atmosphere.

Thermal Protection Systems↗

NASA NTRSDate not supplied

Onboard Navigation Error Analysis for Aerocapture at Uranus

Capturing into an orbit around Uranus using aerocapture allows one to design a mission with faster interplanetary trajectories and less propellant requirements. Such an aerocapture mission would rely on the onboard Guidance, Navigation, and Control (GNC) subsystems to successfully capture into an orbit around Uranus. Uncertainty in the state information and the noise in the sensor measurements induce navigation errors in the guidance and control subsystems, which can affect the overall performance of the aerocapture mission at Uranus. Understanding the effect of these navigation errors on mission performance is essential. To this end, this work considers different sensors with varying quality to understand their impact on the overall mission performance. In addition, this paper studies the impact of the uncertainty in the initial states used to initialize the onboard navigation filter and understands their effect on mission performance. This paper also shows the onboard navigation errors obtained from the Linear Covariance (LinCov) analysis and uses them for verification and validation (V&V) of the results from Program to Optimize and Simulate Trajectories-II (POST2).

Pardha Sai Chadalavada↗