Space Nuclear Propulsion for Human Mars Exploration (2021) / Chapter Skim
Currently Skimming:
2 Nuclear Thermal Propulsion
2 Nuclear Thermal Propulsion
Pages 11-29
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 11... ...
The hydrogen turbopumps are used to control the mass flow rate and pressure of the hydrogen propellant. Figure 2.2 shows a reactor core cross section and fuel segment cluster of the NTP nuclear reactor of a type developed by the Rover and Nuclear Engine for Rocket Vehicle Applications (NERVA)
|
From page 12... ...
Reactor Reflector Control Drum Reactor Core Pressure Shell Propellant Bleed Propellant Feed Line to Turbopump Nozzle Nozzle Extension NERVA Nuclear Thermal Rocket Prototype 2 FIGURE 2.1 Photo of a nuclear thermal propulsion (NTP) system from the Rover/Nuclear Engine for Rocket Vehicle Ap plications programs (left)
|
From page 13... ...
The purpose of the tie tubes for the Rover/NERVA type cores is to regulate the temperature of the outer edge of the fuel elements and to provide some structural support to the fuel elements in the core. HISTORICAL OVERVIEW The Rover/NERVA reactor and NTP engine development program included a ground testing campaign that built and tested 22 reactors, using highly enriched uranium (HEU)
|
From page 14... ...
Although the fuel forms listed in Table 2.2 have not been demonstrated under the integrated effects of an NTP engine operation, for the most part, they were able to withstand the maximum operating temperatures shown without exhibiting significant degradation. While most of the Rover/NERVA research reactors did not use flight-configured engine hardware, there were a few reactors tested with NTP engine hardware components, with the XE-Prime being the system closest to 5 B.L.
|
From page 15... ...
to 2450 2250 820 to 850 4000 200,000 Pewee 1 2750 2550 875 500 25,000 NRX A series (A2, 2250 to 2100 A3, A5, A6) 2550 to 2400 810 to 870 1100 55,000 NRX/EST >2400 2300 >840 1100 XE-Prime >2400 2250 >710 1100 55,000 NOTE: In these tests, reactor fuels were exposed to the integrated effects of startup, operation, and shutdown through ground testing of a complete nuclear thermal propulsion engine configuration.
|
From page 16... ...
Thermal Propulsion NERVA/Rover Program Fuel Forms (General Electric (Particle Bed Former Soviet Fuel Forms and ANL) Reactor)
|
From page 17... ...
Current M&S capabilities can generate steady-state neutronic designs of NTP reactors to simulate the nuclear core sustaining a chain reaction.17,18 Reactor core models can be coupled with thermal-hydraulic, fluid models for simplified one-dimensional core-wide approximations and higher fidelity simulations for subscale analyses (i.e., using computational fluid dynamics simulations) .19,20 Numerous M&S design studies derive new concepts based on prior NERVA-type experiments.
|
From page 18... ...
Upcoming nonnuclear prototypic testing will include flowing hot-hydrogen furnace testing at temperatures greater than or equal to 2850 K of the following: tungsten-coated UN particles, ZrC-coated UN particles, tungsten/ molybdenum alloy-UN cermet composite fuel, and ZrC-UN cercer composite fuel, as well as full length cermet and cercer fuel elements. NASA has also indicated an interest in solid-solution carbide fuel technology with coated carbide particles.30 Although the United States has not successfully demonstrated NTP solid-solution quaternary carbide fuel forms, there is some limited documentation on the Russian RD-410 NTP fuel technology.31 Because the melting temperatures of UC2 and uranium carbide (UC)
|
From page 19... ...
Some of these models40,41 are also applicable to NTP engine subsystems and have been used to model both HEU and HALEU-type engines. Propellant Storage and Management Subsystem Long-term storage and active cryogenic technologies for LH2 have similarly evolved independently of NTP, but significant challenges must still be overcome to meet a storage time of perhaps 4 years for the baseline mission (2 years in an assembly plus 2 years for the round trip to Mars)
|
From page 20... ...
Pronounced cracking was observed in ZrC coatings on graphite composite fuel coolant channel surfaces even at temperatures as low as about 1500 K in the NERVA program, although more recent research has made advances in this area.43 NASA and DOE will need to determine if current or planned HEU or HALEU fuel feedstock production capabilities will be sufficient to meet the needs of the NTP baseline mission. Key issues include identification of a suitable fuel architecture.
|
From page 21... ...
If NASA plans to apply nuclear thermal propulsion (NTP) technology to a 2039 launch of the baseline mission, NASA should expeditiously select and validate a fuel architecture for an NTP system that is capable of achieving a propellant reactor exit temperature of approximately 2700 K or higher (which is the temperature that corresponds to the required specific
|
From page 22... ...
If NASA plans to apply nuclear thermal propulsion (NTP) technology to the baseline mission, NASA should develop high-capacity tank systems capable of storing liquid hydrogen (LH2)
|
From page 23... ...
Ground tests of integrated NTP reactor and engine subsystems would reduce technical risk. Such testing has been used for all previous liquid rocket engines for flight.46 While it may be possible to characterize integrated system performance using a nonnuclear, electrically heated environment, the accuracy of such testing may be a challenge for NTP systems, which have tightly coupled neutronic-thermal-hydraulic response characteristics.
|
From page 24... ...
and identification of potential failure mechanisms, may also be performed to further develop an understanding of system-level performance parameters. Following the separate effects, component, and subassembly ground testing, system-level nuclear ground testing phases would take place.
|
From page 25... ...
These flight tests could incorporate the cargo missions planned before first flight of crew. These missions would need to be carefully defined and instrumented to fully characterize system performance, including engine operation for the total throughput of LH2 required for the baseline mission (i.e., a round-trip crewed mission)
|
From page 26... ...
Subscale in-space flight testing of NTP systems cannot address many of the risks and potential failure modes associated with the baseline mission NTP system and therefore cannot replace full-scale ground testing. With sufficient M&S and ground testing of fully integrated systems, including tests at full scale and thrust, flight qualification requirements can be met by the cargo missions that will precede the first crewed mission to Mars.
|
From page 27... ...
Multiple cargo precursor missions are planned to deliver supplies to Mars prior to the first crewed mission, and these cargo missions could satisfy flight qualification requirements of the integrated NTP engine system. The first of these missions will need to be launched no later than 2033 to provide enough time to address any emergent issues before the 2039 crewed mission.
|
From page 28... ...
28 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 STMD Flight Demonstration Missions on Cryogenic Fluid Storage and Transfer Cargo Mission Development and Launch Cargo Mission Flight Vehicle Development, Integration, and Launch Cargo Mission Prototype Propulsion System Prototype Fabrication, Safety Assessments and Integration Nuclear Systems and Mission Prototype Preliminary Prototype Critical Launch Approval Design (Final) Design PDR CDR PDR CDR Reactor Fuel, Moderator, and Control Reactor Design Systems Manufacture Human Mission Development and Launch Trade Mars Human study Human Mission Flight Vehicle Exploration HEU Development, Integration, and Launch Mission #1 vs Fuel Technology HALEU Development Safety Assessments and Nuclear Nonnuclear Systems and Mission Launch Approval Separate Integrated Effects Tests Engine Technology Testing Development Ground Nuclear Tests PDR CDR Ground-based Test Facilities Safety Analyses FIGURE 2.4 Nuclear thermal propulsion development roadmap for the baseline mission, with a 2039 launch of the first human mission.
|
From page 29... ...
Subscale NTP flight testing cannot replace full-scale ground testing. Flight qualification requirements could be satisfied by leveraging the sequence of cargo missions occurring before the first crewed mission, with the first cargo mission in the 2033 timeframe.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.