Dennis G. Pelaccio

A safety and reliability analysis for space nuclear thermal propulsion systems

Abstract An initial exploration of the safety and reliability of a Nuclear Thermal Propulsion (NTP) system for a representative manned Mars mission is presented. The hypothetical mission goal, 0.95 probability of success, is apportioned among 15 mission phases using optimistic and pessimistic assumptions yielding an apportioned reliability goal for an NTP phase between 0.987 and 0.996. The reliability model for each phase utilizing NTP systems depends on five major systems including propulsion, which is composed of eight major subsystems. Preliminary analysis suggests that reliability of the reactor and the LH 2 turbopump subsystems are critical elements. The reliability of these subsystems is estimated using a variety of field data. Based on the analysis, it is credible that the NTP system can meet its goal during active thrusting. Furthermore, reliability during 3 cumulative hours of active thrusting is probably less important than the 9120 hours of standby (dormancy) between thrust phases. The dormancy period will require extensive study before initial design is attempted for such a mission.

Considerations and Lessons Learned in Implementing Effective, Low‐Cost, Unmanned Space Exploration Missions

Since the early 1990s, NASA has implemented a number of low‐cost, unmanned space exploration missions including the recent missions associated with the Mars Exploration Program, and also missions in the Discovery and Explorer Programs. This paper addresses a number of the system design and implementation considerations and lessons learned that must be addressed for these missions to be successful, and stresses that effective systems engineering practices must be adopted and applied consistently throughout all mission project phases. Emphasis is placed on highlighting effective approaches that have been successfully used in past programs. These considerations and lessons learned should be considered in formulating effective future technology demonstration and science exploration mission efforts for NASA’s Nuclear Systems Initiative (NSI) and New Frontiers Program.

An examination of emerging in-space propulsion concepts for one-year crewed mars missions

A study was completed that provides a meaningful, even-handed, comparison assessment of promising candidate, in-space, exploration propulsion concepts to support emerging “near-term” crewed Mars mission applications. In particular, the study examined the mission performance feasibility and risk of a number of near-, mid-, and far-term in-space propulsion concepts to support crewed Mars missions starting in 2018 that can have the crewed portion of the mission performed in one year or less. This study used exploration propulsion system team technology specialist advocates to identify seven meaningful, representative mission architecture scenarios to “best” demonstrate the capability of such in-space propulsion technology options to support the near-term crewed Mars mission requirement. Additionally, a common set of top-level mission/system requirements was established for the study, which was incorporated in the assessment of all the mission options considered. Mission performance for abundant chemical (Ab-...

Updated solid-core nuclear thermal propulsion engine trades

This study examined the application of state-of-the-art propulsion and reactor technologies to a near-term solid-core NERVA-based nuclear thermal propulsion system. Updated reactor performance and weight scaling laws were initially derived and input into a nuclear rocket engine system cycle design analysis code. Nuclear Thermal Propulsion (NTP) engine system weight, size, and performance are presented here for a large range of chamber pressures, nozzle area ratios, and thrust levels for three reactor fuel types operating at their corresponding temperatures. Operational characteristics and design features of representative NTP engine concepts are also presented.

Near-term lunar nuclear thermal rocket engine options

The Nuclear Thermal Rocket (NTR) is an attractive candidate propulsion system option for manned planetary missions. Its high performance capability for such missions translates into a substantial reduction in low-earth-orbit (LEO) required mass and trip times with increased operational flexibility. This study examined NTR engine options that could support near-term lunar mission operations. Expander and gas generator cycle, solid-core NERVA derivative reactor-based NTR engines were investigated. Weight, size, operational characteristics, and design features for representative NTR engine concepts are presented. The impact of using these NTR engines for a typical lunar mission scenario is also examined.

Nuclear thermal propulsion engine system design analysis code development

A Nuclear Thermal Propulsion (NTP) Engine System Design Analyis Code has recently been developed to characterize key NTP engine system design features. Such a versatile, standalone NTP system performance and engine design code is required to support ongoing and future engine system and vehicle design efforts associated with proposed Space Exploration Initiative (SEI) missions of interest. Key areas of interest in the engine system modeling effort were the reactor, shielding, and inclusion of an engine multi‐redundant propellant pump feed system design option. A solid‐core nuclear thermal reactor and internal shielding code model was developed to estimate the reactor’s thermal‐hydraulic and physical parameters based on a prescribed thermal output which was integrated into a state‐of‐the‐art engine system design model. The reactor code module has the capability to model graphite, composite, or carbide fuels. Key output from the model consists of reactor parameters such as thermal power, pressure drop, therm...

Nuclear engine system simulation (NESS) program update

The second phase of development of a Nuclear Thermal Propulsion (NTP) engine system design analysis code has been completed. The standalone, versatile Nuclear Engine System Simulation (NESS) code provides an accurate, detailed assessment of engine system operating performance, weight, and sizes. The critical information is required to support ongoing and future engine system and stage design study efforts. This recent development effort included incorporation of an updated solid‐core nuclear thermal reactor model that yields a reduced core weight and higher fuel power density when compared to a NERVA type reactor. NESS can now analyze expander, gas generator, and bleed cycles, along with multi‐redundant propellant pump feed systems. Performance and weight of efficient multi‐stage axial turbopump can now be determined, in addition to the traditional centrifugal pump.Key code outputs include reactor operating charactertistics and weights and well as engine system parameters such as performance, weights, dimensions, pressures, temperatures, mass flows and turbopump operating characteristics for both design and off‐design operating conditions. Representative NTP engine system designs are also shown. An overview of NESS methodology and capabilities is presented in this paper, with special emphasis being placed on recent code developments.The second phase of development of a Nuclear Thermal Propulsion (NTP) engine system design analysis code has been completed. The standalone, versatile Nuclear Engine System Simulation (NESS) code provides an accurate, detailed assessment of engine system operating performance, weight, and sizes. The critical information is required to support ongoing and future engine system and stage design study efforts. This recent development effort included incorporation of an updated solid‐core nuclear thermal reactor model that yields a reduced core weight and higher fuel power density when compared to a NERVA type reactor. NESS can now analyze expander, gas generator, and bleed cycles, along with multi‐redundant propellant pump feed systems. Performance and weight of efficient multi‐stage axial turbopump can now be determined, in addition to the traditional centrifugal pump.Key code outputs include reactor operating charactertistics and weights and well as engine system parameters such as performance, weights, dim...

Nuclear electric propulsion operational reliability and crew safety study

The objective of this study was to establish the initial quantitative reliability bounds for nuclear electric propulsion systems in a manned Mars mission required to ensure crew safety and mission success. Finding the reliability bounds involves balancing top-down (mission driven) requirements and bottom-up (technology driven) capabilities. In seeking this balance we hope to accomplish the following: (1) provide design insights into the achievability of the baseline design in terms of reliability requirements, given the existing technology base; (2) suggest alternative design approaches which might enhance reliability and crew safety; and (3) indicate what technology areas require significant research and development to achieve the reliability objectives.

Development of a robust space power system decision model

NASA continues to evaluate power systems to support human exploration of the Moon and Mars. The system(s) would address all power needs of surface bases and on-board power for space transfer vehicles. Prior studies have examined both solar and nuclear-based alternatives with respect to individual issues such as sizing or cost. What has not been addressed is a comprehensive look at the risks and benefits of the options that could serve as the analytical framework to support a system choice that best serves the needs of the exploration program. This paper describes the SAIC developed Space Power System Decision Model, which uses a formal Two-step Analytical Hierarchy Process (TAHP) methodology that is used in the decision-making process to clearly distinguish candidate power systems in terms of benefits, safety, and risk. TAHP is a decision making process based on the Analytical Hierarchy Process, which employs a hierarchic approach of structuring decision factors by weights, and relatively ranks system des...

Engine cycle design considerations for nuclear thermal propulsion systems

A top‐level study was performed which addresses nuclear thermal propulsion system engine cycle options and their applicability to support future Space Exploration Initiative manned lunar and Mars missions. Technical and development issues associated with expander, gas generator, and bleed cycle near‐term, solid core nuclear thermal propulsion engines are identified and examined. In addition to performance and weight the influence of the engine cycle type on key design selection parameters such as design complexity, reliability, development time, and cost are discussed. Representative engine designs are presented and compared. Their applicability and performance impact on typical near‐term lunar and Mars missions are shown.