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At least 433 records · Page 24

Implementation Recommendations and Usage Boundaries for the Two-Dimensional Probability of Collision Calculation

The two-dimensional (2D) probability of collision (𝑃𝑐) estimation method relies on several assumptions that must be satisfied for accurate results. Monte Carlo analysis of ~44,000 conjunctions indicates that 2D-𝑃(sub 𝑐) pro-vides accurate estimates for most typical conjunctions, but occasionally underestimates 𝑃(sub 𝑐) significantly, indicating an assumption violation. A test to detect large-amplitude underestimation inaccuracies can be based on how much “offset-from-TCA” 2D-𝑃(sub 𝑐) values vary during a well-defined time interval bracketing closest approach. The test successfully detects all large-amplitude 2D-𝑃(sub 𝑐) underestimations found to date, but with a high false-alarm rate. The analysis also provides implementation recommendations and usage boundaries for the 2D-𝑃(sub 𝑐) method.

Hall, Doyle T.↗

An Operational Algorithm for Evaluating Satellite Collision Consequence

Risk is properly considered as the combination of likelihood and consequence; but conjunction assessment has usually limited itself to the consideration of only collision likelihood. When considered from an orbital regime protection perspective, the focus shifts to the question of the amount of debris that a collision might produce (the “consequence”). The present paper presents an operational algorithm for determining the expected amount of debris production should a conjunction result in a collision, and an assessment of the algorithm’s fidelity against a database of characterized objects.

Lechtenberg, Travis↗

An Operational Algorithm for Evaluating Satellite Collision Consequence

Risk is properly considered as the combination of likelihood and consequence; but conjunction assessment has usually limited itself to the consideration of only collision likelihood. When considered from an orbital regime protection perspective, the focus shifts to the question of the amount of debris that a collision might produce (the “consequence”). The present paper presents an operational algorithm for determining the expected amount of debris production should a conjunction result in a collision, and an assessment of the algorithm’s fidelity against a database of characterized objects.

Lechtenberg, Travis↗

Oceanic and Radiative Forcing of Medieval Megadroughts in the American Southwest

Multidecadal "megadroughts" were a notable feature of the climate of the American Southwest over the Common era, yet we still lack a comprehensive theory for what caused these megadroughts and why they curiously only occurred before about 1600 CE. Here, we use the Paleo Hydrodynamics Data Assimilation product, in conjunction with radiative forcing estimates, to demonstrate that megadroughts in the American Southwest were driven by unusually frequent and cold central tropical Pacific sea surface temperature (SST) excursions in conjunction with anomalously warm Atlantic SSTs and a locally positive radiative forcing. This assessment of past megadroughts provides the first comprehensive theory for the causes of megadroughts and their clustering particularly during the Medieval era. This work also provides the first paleoclimatic support for the prediction that the risk of American Southwest megadroughts will markedly increase with global warming.

Steiger, Nathan J.↗

Overview of NASA's Solar Electric Propulsion Project

NASA is continuing to develop and qualify a state of the art 13 kW-class Advanced Electric Propulsion System (AEPS) for NASA exploration missions through a contract with Aerojet Rocketdyne. An objective of the AEPS project is to empower the US space industry to accelerate the adoption of high power electric propulsion technologies by reducing the risk and uncertainty of integrating Solar Electric Propulsion (SEP) technologies into space flight systems. NASA and AEPS contract has recently initiated engineering hardware testing of the Hall Current Thruster (HCT), Power Processing Unit (PPU), and Xenon Flow Controller (XFC) at both the component and system levels. The successful completion of these tests will provide the required information to advance the AEPS system towards Critical Design Review. In support of the AEPS contract, NASA and JPL have been performing risk reduction activities to address specific concerns of the state of the art higher power Hall thruster propulsion system. These risk reduction activities have included long duration wear testing of the Technology Demonstration Unit (TDU) Hall thruster and cathode hardware, thermal cycling testing of TDU cathode heaters and coils, plasma plume measurements, and investigating PPU design. In addition to NASA propulsion development, the SEP project is developing the Plasma Diagnostic Package (PDP) and the SEP Testbed. The PDP is designed for use in conjunction with a high powered EP system to characterize in-space operation. The SEP Testbed system is developed for demonstration of Abstract: NASA is continuing to develop and qualify a state of the art 13 kW-class Advanced Electric Propulsion System (AEPS) for NASA exploration missions through a contract with Aerojet Rocketdyne. An objective of the AEPS project is to empower the US space industry to accelerate the adoption of high power electric propulsion technologies by reducing the risk and uncertainty of integrating Solar Electric Propulsion (SEP) technologies into space flight systems. NASA and AEPS contract has recently initiated engineering hardware testing of the Hall Current Thruster (HCT), Power Processing Unit (PPU), and Xenon Flow Controller (XFC) at both the component and system levels. The successful completion of these tests will provide the required information to advance the AEPS system towards Critical Design Review. In support of the AEPS contract, NASA and JPL have been performing risk reduction activities to address specific concerns of the state of the art higher power Hall thruster propulsion system. These risk reduction activities have included long duration wear testing of the Technology Demonstration Unit (TDU) Hall thruster and cathode hardware, thermal cycling testing of TDU cathode heaters and coils, plasma plume measurements, and investigating PPU design. In addition to NASA propulsion development, the SEP project is developing the Plasma Diagnostic Package (PDP) and the SEP Testbed. The PDP is designed for use in conjunction with a high powered EP system to characterize in-space operation. The SEP Testbed system is developed for demonstration of an integrated SEP end-to-end system performance. The paper will present an overview of the NASA and the AEPS contract activities and a summary of the associated NASA in-house activities.

Plasma Diagnostics Package↗

CRMS Special Case Event Identification & Course of Action Concept of Operations

This package presents the CRMS identification of special Conjunction cases and the documented process for handling these special cases. The presentation is beneficial to anyone considering performing Conjunction Assessment by identifying and understanding the types of special cases that requires attention.

Duncan, Matthew G.↗

Mars Opposition Piloted Nuclear Electric Propulsion (NEP)-Chem Vehicle

Many previous studies have examined sending crews to and from Mars. The most economical involved a ‘conjunction’ class whereby the crew spends around 500 days on Mars surface waiting for a ‘cheap’ return. The total mission time results in a mission duration around 3 years. Given the current demonstrated crew maximum of a 1 year stint on ISS, it is interesting to look at reducing that time to only two years, thus reducing risk and minimizing time in the Martian System. In order to meet such a short mission an ‘opposition’ class Mars mission (which includes a Venus flyby) was chosen. The energy required to perform such a mission in only two years (for the 2036 opportunity at least) is about three times that of the 3 year conjunction mission. The rocket equation clearly shows that this mission would then require several times the propellant of the three-year mission unless the Isp of the propulsion system can be increased. Electric propulsion can provide the 3-10x improvement in Isp but even with a nuclear reactor power levels could approach 10 MWe. As an alternative, a smaller reactor (1.5 MWe class) joined together with a chemical stage was found to allow for using each propulsion system to its best advantage: low thrust in interplanetary space and chemical in the gravity wells of Earth and Mars. Indeed, the use of high Isp, low thrust during the interplanetary leg of the journey’s reduced the required capture/departure ∆Vs by 5-10X. Lowering the NEP power also allowed fitting the power system into a single SLS launch – which limited the radiator area to ~ 2500m^2. For the first look a reactor using fuels created by the SP-100 program with a limit of ~1200K was assumed. Starting in the ‘Lunar Gateway’ also allowed for use of commercial tankers to fuel the vehicle in a relative benign place. A top level summary of the mission design, concept of operations, as well as a conceptual point design of the vehicle is described.

Nuclear Electric Propulsion↗

Orbit determination of Stardust from the Annefrank asteroid fly-by through the Wild 2 Comet encounter

Stardust is a 3-axis stabilized spacecraft that maintains its attitude by firing a pair of its one sided- thrusters. this thruster arrangement causes Stardust to produce unbalanced torques at each thruster firing, which yields an undesired perturbing force and makes navigation a challenge. In addition to this perturbing force, Stardust Navigation contended with the problems caused by the contamination of the Navigation Camera and the experience of flying through 2 solar conjunctions during Stardust's inbound leg to the Wild 2 encounter. Both the contamination and the solar conjunctions were major challenges Navigation had to overcome.

Williams, Kenneth↗

(abstract) SIR-C/X-SAR: A Multifaceted Radar

The Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SAR-C/X-SAR) was a joint US/German/Italian project, with flights aboard the shuttle Endeavor in April and October 1994. SIR-C/X-SAR is the first spaceborne multifrequency, multipolarization radar. The SIR-C and the X-SAR were designed to operate in conjunction with each other, collecting data over common sites. Scientists around the world are using the data in conjunction with ground measurements to conduct experiments relating to Earth's ecology, geology, hydrology, and oceanography. In addition, the data are the most comprehensive set yet available for engineering characterization of spaceborne SAR capabilities relative to various radar phenomenology and methodology. Preliminary results show changes between missions in vegetation, ice, snow, flooding, and volcano activity.

imaging↗

Compass Final Report: Nuclear Electric Propulsion (NEP)-Chemical Vehicle 1.2

Many previous studies have examined sending crews to and from Mars. The most economical involved a ‘conjunction’ class whereby the crew spends around 500 days on Mars waiting for a ‘cheap’ return. The total mission time results in over a 1000-day mission duration (about 3 years). Given the current experience level of only one year on the International Space Station (ISS), it of interest to reduce that time to only two years, thus reducing risk and minimizing required Mars surface infrastructure. The Phase 1.1 Study goal was stated as follows, “Determine the feasibility of a two-year roundtrip class Mars mission concept of operation that enables boots on Mars no later than 2036.” While the Phase1 study did show feasibility for the NEP-Chemical option, the 2036 Opposition opportunity was found to stress the schedule due to proposed technology development schedules. A 2039 Opposition (which requires even more energy than the 2036 case) was chosen as representative for Phase 1.2. Phase 1.2 also sought to further refine the concept, building on the feasibility, but addressing several challenges brought by the red team and habitat team. Given the date of 2039, nearer term technologies, primarily nuclear thermal and nuclear electric were deemed as the most viable for these missions. As will be shown, the energy required to perform such a mission in only two years (for the 2039 opportunity at least) is about three times that of the three-year conjunction mission. The rocket equation shows that this mission would then require several times the propellant of the three-year mission unless the specific impulse (ISP) of the propulsion system can be increased. Based on lunar needs, a limit of five Space Launch System (SLS) launchers with 8.4m fairings was imposed for the piloted transportation portion of the mission, limiting the size of the system. When using nuclear electric propulsion, the main limiting factor was packaging the required radiator area. The higher Isp nuclear electric propulsion (NEP) system option is described herein but with a twist: in order to keep the size of radiators packageable in one SLS and use proven reactor power system technology (~1200K reactor outlet temperature and superalloy-class Brayton) the NEP system had to be combined with a chemical propulsion system. This combination of electric propulsion and high thrust chemical was found to be useful in previous design studies combining solar electric propulsion (SEP) and chemical propulsion. Such a combination allowed the low-thrust system to provide significant change in velocity (∆V) during the interplanetary portions of the mission, thereby notably reducing the ∆V required by the high thrust system to capture and depart from the Mars gravity well. Here the high thrust ‘impulsive’ system is more efficient due to the Oberth Effect. A plethora of trades, both at the mission and system level, as well as the subsystem level were performed to develop these vehicle concepts. An entire family of NEP-Chemical transportation vehicles is described herein. The main driver and the primary focus was the piloted vehicle but additional concepts for cargo were performed using the same ‘building blocks’ in order to reduce costs and provide commonality.

Nuclear Power↗

Lessons learned from replicating services for flood prediction and monitoring in Asia to the assessment of hurricane impacts in Central America

In October and November 2020, two dangerous back-to-back hurricanes, Eta and Iota, made landfall in Central America. The SERVIR program - a joint effort of NASA and the U.S. Agency for International Development, and whose motto is “connecting space to village” was able to leverage two tools originally developed for use in other regions for predicting and assessing the flood impacts of the hurricanes. The GEOGLoWS Streamflow Prediction tool - originally implemented in the Hindu Kush Himalayan region - was used for predicting potential flooding ahead of landfall by Eta and Iota. In conjunction, the Hydrologic Remote Sensing Analysis for Floods (HYDRAFloods) framework - originally developed along with SERVIR-Mekong - was used for post-event flood mapping, leveraging its ability to map floods in cloud-covered areas using synthetic aperture radar (SAR) imagery from the Copernicus program. Both tools were used in support of disaster coordination efforts being led by the Central American Regional Disaster Prevention Center (CEPREDENAC), in conjunction with its sister agency, the Regional Water Resources Committee (CRRH). The support provided to regional entities - and to their stakeholder national governments - served as an example of rapid generation of Earth observation products for disaster response. Feedback on those products was also provided, especially in terms of the implications of (i) calibration of predicted river volumes, and (ii) the latency of the input Earth observation imagery and attempts to map the floods’ maximum extents. An upcoming NASA DEVELOP project will also seek to strengthen the capability of CEPREDENAC and CRRH to apply HYDRAFloods for future extreme events. The application of the tools also provides a useful case study on capacity building, in terms of how Earth observation data and models can be replicated across regions.

Capacity building↗

Effect of Cross-Correlation of Orbital Error on Probability of Collision Determination

This paper discusses the effect of global model error on probability of collision (Pc) determination. Modifications to the Pc formulation for cross-correlation of orbital error in prediction are developed and assessed for recent conjunctions. While specific geometries can be identified or constructed to produce significant change in Pc for the modified formulation, it is of operational interest to quantify the relative occurrence of such cases for satellite conjunction risk assessment. Such analysis is feasible per data collections in place over the past year.

Cross-correlation↗

Effect of Cross-Correlation of Orbital Error on Probability of Collision Determination

This paper discusses the effect of global model error on probability of collision (Pc) determination. Modifications to the Pc formulation for cross-correlation of orbital error in prediction are developed and assessed for recent conjunctions. While specific geometries can be identified or constructed to produce significant change in Pc for the modified formulation, it is of operational interest to quanti- fy the relative occurrence of such cases for satellite conjunction risk assessment. Large-scale analysis is feasible per data collections in place over the past year.

Steve Casali↗

Configuration and Projected Capabilities of the Common Habitat Medical Care Facility

The Common Habitat is a large, long-duration habitat being explored as part of a conceptual study (not an active NASA program) that uses an SLS core stage Liquid Oxygen (LOX) tank as its primary structure. It is intended for use on the Moon as part of a permanently occupied outpost, on Mars as part of an outpost that will be occupied for hundreds of days at a time, and in deep space as part of the Deep Space Exploration Vehicle where it will support crewed missions up to 1200 days in duration. A study of internal orientation and crew size resulted in a Common Habitat configuration sized for a crew of eight with a three-deck horizontal orientation. Additional work outside the scope of this paper is developing a vertical translation system, a crew mobility aids system based on wearable gecko-derived grippers, and a crew seating/restraint system. These systems are all assumed for use in conjunction with the Medical Care Facility, which is needed to maintain crew well-being during these missions, where distance from Earth precludes the possibility of evacuation to Earth. This paper describes recent improvements in the Common Habitat Medical Care Facility and associated benefits for crew survivability in long duration missions beyond Earth orbit. These improvements were made with the assistance of a NASA Pathways intern whose experience includes a tour of duty in Afghanistan as an Army combat medic with the 691st GHOST-T, attached to the 1st and 7th US Special Forces Groups as part of Operation Freedom’s Sentinel, where he helped provide far-forward surgical capabilities in austere combat environments. The initial baseline Medical Care Facility was developed working in conjunction with University of Houston Space Architecture graduate students. The facility was placed on the upper deck of the Common Habitat in a location that provided privacy, operational volume, and was close to the vertical translation pathway. The notional outfitting repurposed component CAD models from unrelated studies and notionally indicated a level of care roughly equivalent to that aboard the International Space Station. The CAD modeling provided notional stowage volumes, a deployable surface, some fixed equipment, an ultrasound, and a potentially reconfigurable treatment table. While this facility is clearly a competent arrangement, it was desired to leverage available expertise and upgrade the station given the vast distances from Earth to be experienced by the Common Habitat. Key driving requirements applied to the upgrade included to provide Medical Level of Care V, offer enhanced telemedicine capabilities, provide patient physical accommodation, provide caregiver access to the patient from all sides, include sliding pocket doors for access to hygiene and to the Vertical Translation System, and to add any additional capability possible for the best achievable medical care. The first step in the facility upgrade was to quantify the current medical inventory on the International Space Station and ensure that sufficient stowage volume was present for this purpose. To that end, the ISS medical kits were reviewed, and eight full size mid deck lockers were placed in the facility. A number of additional devices were also added, based on the intern’s combat medic experience. Also, two fixed shelves and one horizontal work surface were added to the Medical Care Facility, with the shelves providing storage space for the additional devices and the work surface providing a location for the caregiver to work or stage equipment. Four display monitors were added to the wall above the horizontal work surface, supporting data display, telemedicine, conferencing, or other needs. The existing treatment table was replaced with a mobile surgical stretcher-chair. Two additional doors were added to the Medical Care Facility. One leads directly to the hygiene compartment, allowing it to support medical operations in addition to providing galley/wardroom support. The other door leads directly into the Vertical Translation System. The wall adjacent to the subsystems bay was moved, adding additional volume to the Medical Care Facility. This improved caregiver access to the patient and allowed for a larger number of caregivers to be present. It also provided options for relocation of support equipment relative to the patient as needed. In the upgraded Medical Care Facility, the Surgical Stretcher-Chair and the Vertical Translation System can work together to provide incapacitated crew member transport from a site of injury on any deck of the Common Habitat to the Medical Care Facility. It can also support patient treatment in a variety of positions including a variety of sitting postures and a supine posture at a variety of pitch angles. The facility can also support caregiver office work for review of examination results, private consultation, inventory and maintenance, and a variety of other purposes. A forward activity will be to conduct evaluations of the Medical Care Facility with different medical scenarios. Additionally, ambient and task lighting selections remain as forward work. The eight mid deck lockers can be augmented to use as portable equipment carts, similar to a manner in which maintenance facility stowage was used as portable carts during the NASA Desert Research and Technology Studies in the Constellation Program. Trash accommodation will also need forward work to assess, including provision for wet trash, dry trash, and biological waste. It will be important to assess a redesign of the surgical stretcher-chair. The commercial version used in the upgrade can only enable vertical translation in the seated configuration, requiring the patient to bend both hips and knees. A possible redesign of the chair will allow for vertical translation without requiring any bending at the hip or knees. Also, the commercial version is wheeled, making it mobile in gravity but unanchored in microgravity. Work will be needed to adapt the chair for gravity-independent performance. The hygiene compartment can be redesigned for dual-use medical scrub and galley handwash facility. Pending sufficient volume, it may also be possible to place sanitation equipment in this location to clean medical tools. Finally, most space architectures have never allowed for more than one incapacitated crew member, but several scenarios could potentially injure two or more crew in the same incident. This facility could be assessed to determine its present ability to address two or more injured crew in parallel and determine the potential upper limit for number of treatable crew in a multi-crew injury scenario, or to treat polytrauma of a single patient.

Habitat↗

Configuration and Projected Capabilities of the Common Habitat Medical Care Facility

The Common Habitat is a large, long-duration habitat being explored as part of a conceptual study (not an active NASA program) that uses an SLS core stage Liquid Oxygen (LOX) tank as its primary structure. It is intended for use on the Moon as part of a permanently occupied outpost, on Mars as part of an outpost that will be occupied for hundreds of days at a time, and in deep space as part of the Deep Space Exploration Vehicle where it will support crewed missions up to 1200 days in duration. A study of internal orientation and crew size resulted in a Common Habitat configuration sized for a crew of eight with a three-deck horizontal orientation. Additional work outside the scope of this paper is developing a vertical translation system, a crew mobility aids system based on wearable gecko-derived grippers, and a crew seating/restraint system. These systems are all assumed for use in conjunction with the Medical Care Facility, which is needed to maintain crew well-being during these missions, where distance from Earth precludes the possibility of evacuation to Earth. This paper describes recent improvements in the Common Habitat Medical Care Facility and associated benefits for crew survivability in long duration missions beyond Earth orbit. These improvements were made with the assistance of a NASA Pathways intern whose experience includes a tour of duty in Afghanistan as an Army combat medic with the 691st GHOST-T, attached to the 1st and 7th US Special Forces Groups as part of Operation Freedom’s Sentinel, where he helped provide far-forward surgical capabilities in austere combat environments. The initial baseline Medical Care Facility was developed working in conjunction with University of Houston Space Architecture graduate students. The facility was placed on the upper deck of the Common Habitat in a location that provided privacy, operational volume, and was close to the vertical translation pathway. The notional outfitting repurposed component CAD models from unrelated studies and notionally indicated a level of care roughly equivalent to that aboard the International Space Station. The CAD modeling provided notional stowage volumes, a deployable surface, some fixed equipment, an ultrasound, and a potentially reconfigurable treatment table. While this facility is clearly a competent arrangement, it was desired to leverage available expertise and upgrade the station given the vast distances from Earth to be experienced by the Common Habitat. Key driving requirements applied to the upgrade included to provide NASA’s Medical Level of Care V, offer enhanced telemedicine capabilities, provide patient physical accommodation, provide caregiver access to the patient from all sides, include sliding pocket doors for access to hygiene and to the Vertical Translation System, and to add any additional capability possible for the best achievable medical care. The first step in the facility upgrade was to quantify the current medical inventory on the International Space Station and ensure that sufficient stowage volume was present for this purpose. To that end, the ISS medical kits were reviewed, and eight full size mid deck lockers were placed in the facility. A number of additional devices were also added, based on the co-author’s combat medic experience. Also, two fixed shelves and one horizontal work surface were added to the Medical Care Facility, with the shelves providing storage space for the additional devices and the work surface providing a location for the caregiver to work or stage equipment. Four display monitors were added to the wall above the horizontal work surface, supporting data display, telemedicine, conferencing, or other needs. The existing treatment table was replaced with a mobile surgical stretcher-chair. Two additional doors were added to the Medical Care Facility. One leads directly to the hygiene compartment, allowing it to support medical operations in addition to providing galley/wardroom support. The other door leads directly into the Vertical Translation System. The wall adjacent to the subsystems bay was moved, adding additional volume to the Medical Care Facility. This improved caregiver access to the patient and allowed for a larger number of caregivers to be present. It also provided options for relocation of support equipment relative to the patient as needed. In the upgraded Medical Care Facility, the Surgical Stretcher-Chair and the Vertical Translation System can work together to provide incapacitated crew member transport from a site of injury on any deck of the Common Habitat to the Medical Care Facility. It can also support patient treatment in a variety of positions including a variety of sitting postures and a supine posture at a variety of pitch angles. The facility can also support caregiver office work for review of examination results, private consultation, inventory and maintenance, and a variety of other purposes. A forward activity will be to conduct evaluations of the Medical Care Facility with different medical scenarios. Additionally, ambient and task lighting selections remain as forward work. The eight middeck lockers can be augmented to use as portable equipment carts, similar to a manner in which maintenance facility stowage was used as portable carts during the NASA Desert Research and Technology Studies in the Constellation Program. Trash accommodation will also need forward work to assess, including provision for wet trash, dry trash, and biological waste. It will be important to assess a redesign of the surgical stretcher-chair. The commercial version used in the upgrade can only enable vertical translation in the seated configuration, requiring the patient to bend both hips and knees. A possible redesign of the chair will allow for vertical translation without requiring any bending at the hip or knees. Also, the commercial version is wheeled, making it mobile in gravity but unanchored in microgravity. Work will be needed to adapt the chair for gravity-independent performance. The hygiene compartment can be redesigned to serve both as a medical scrub facility and for galley hand washing. Pending sufficient volume, it may also be possible to place sanitation equipment in this location to clean medical tools. Finally, most space architectures have never allowed for more than one incapacitated crew member, but several scenarios could potentially injure two or more crew in the same incident. This facility could be assessed to determine its present ability to address two or more injured crew in parallel and determine the potential upper limit for number of treatable crew in a multi-crew injury scenario, or to treat polytrauma of a single patient.

Common Habitat↗

Characterization of in-Space Propulsion Trade Space to Support Initial Human Mars Segment

The National Aeronautics and Space Administration’s Exploration Systems Development Mission Directorate has been developing architecture concepts for human missions to Mars in alignment with the agency’s Moon to Mars blueprint objectives. The focus of the Architecture Development Office has been to decompose the blueprint objectives into the characteristics and needs for both lunar and Mars missions and develop functional needs to enable an integrated end-to-end mission architecture. One of the key components of a human Mars mission is the in-space transportation system that delivers crew and cargo to Mars vicinity and return crew safely back to Earth. The Mars Architecture Team has been evaluating four in-space transportation options to satisfy this functional need: 1) Hybrid Nuclear Electric/ Chemical Propulsion, 2) Nuclear Thermal Propulsion, 3) Hybrid Solar Electric/ Chemical Propulsion, and 4) All-Chemical propulsion. To answer the question “which transportation option is best?” decision makers will need to understand the performance characteristics—and limitations—for each architecture in the context of their preferred metric. Each option could be considered “better” than the others, depending on whether the primary selection criteria is fast, cheap, maximum cross-government applicability, maximizes commercial capabilities, and/or any other desired metrics. The Mars Architecture Team has completed considerable analysis on the Hybrid Nuclear Electric/Chemical Propulsion concept over the past three years. The Space Nuclear Propulsion program has also conducted significant work on the Nuclear Thermal Propulsion concept. The Hybrid Solar Electric/Chemical Propulsion concept, derived from technology planned for the Gateway program, was originally configurated for minimum vehicle stack mass (and, hence, minimum Earth-launched mass/cost), leveraging a highly efficient propulsion system on a minimum energy Conjunction Class trajectory. Historically, All-Chemical concepts were considered impractical due to the enormous propellant mass required, even for minimum energy Conjunction Class/long stay mission opportunities. However, considering the emerging commercial heavy-lift capabilities, the concept must be reevaluated across a range of concepts that leverage reusable launch vehicle capabilities to reduce the cost of launching large quantities of transportation elements needed for missions of various duration. This paper aims to provide an overview of the in-space transportation assessment work that is on-going within NASA.

Mars↗

A 1 MW Solar Electric and Chemical Propulsion Vehicle for Piloted Mars Opposition Class Missions

Previous investigations have extensively explored crew missions to and from Mars, with a prevailing approach termed the 'conjunction' class, necessitating an approximately 500-day stay at Mars for a cost-effective return. However, this configuration results in a mission duration exceeding 1000 days (roughly 3 years). In order to reduce crew health and surface operations risks, a shortened mission duration of 850 days is being explored by using a short ~30 day Mars surface stay and a ‘opposition’ class approach. A non-nuclear approach is possible by combining solar electric propulsion and a chemical stage. While past mission concepts for the conjunction missions also used solar electric propulsion they limited the SEP power to <700 kW. In order to achieve the 850 day round trip more SEP power is needed. A 1MW class SEP-Chem vehicle was found sufficient to perform the 850 day mission. The biggest challenge for the design will be the large, high power solar arrays, mainly from their deployment and stability. This work describes the design of the SEP-Chem vehicle, assembled in a Near Rectilinear Halo Orbit (NRHO) and employing super-heavy class and the Space Launch System (SLS) launchers.

SEP-Chem↗

Characterization of in-Space Propulsion Trade Space to Support Initial Human Mars Segment

The National Aeronautics and Space Administration’s Exploration Systems Development Mission Directorate has been developing architecture concepts for human missions to Mars in alignment with the agency’s Moon to Mars blueprint objectives. The focus of the Architecture Development Office has been to decompose the blueprint objectives into the characteristics and needs for both lunar and Mars missions and develop functional needs to enable an integrated end-to-end mission architecture. One of the key components of a human Mars mission is the in-space transportation system that delivers crew and cargo to Mars vicinity and return crew safely back to Earth. The Mars Architecture Team has been evaluating four in-space transportation options to satisfy this functional need: 1) Hybrid Nuclear Electric/ Chemical Propulsion, 2) Nuclear Thermal Propulsion, 3) Hybrid Solar Electric/ Chemical Propulsion, and 4) All-Chemical propulsion. To answer the question “which transportation option is best?” decision makers will need to understand the performance characteristics—and limitations—for each architecture in the context of their preferred metric. Each option could be considered “better” than the others, depending on whether the primary selection criteria is fast, cheap, maximum cross-government applicability, maximizes commercial capabilities, and/or any other desired metrics. The Mars Architecture Team has completed considerable analysis on the Hybrid Nuclear Electric/Chemical Propulsion concept over the past three years. The Space Nuclear Propulsion program has also conducted significant work on the Nuclear Thermal Propulsion concept. The Hybrid Solar Electric/Chemical Propulsion concept, derived from technology planned for the Gateway program, was originally configurated for minimum vehicle stack mass (and, hence, minimum Earth-launched mass/cost), leveraging a highly efficient propulsion system on a minimum energy Conjunction Class trajectory. Historically, All-Chemical concepts were considered impractical due to the enormous propellant mass required, even for minimum energy Conjunction Class/long stay mission opportunities. However, considering the emerging commercial heavy-lift capabilities, the concept must be reevaluated across a range of concepts that leverage reusable launch vehicle capabilities to reduce the cost of launching large quantities of transportation elements needed for missions of various duration. This paper aims to provide an overview of the in-space transportation assessment work that is on-going within NASA.

Mars↗