Leonard A. Dudzinski

Artificial Gravity Vehicle Design Option for NASA's Human Mars Mission Using "Bimodal" NTR Propulsion

Recent human Mars exploration studies at NASA have focused on a split mission approach involving predeployment of surface and orbital cargo elements followed by piloted missions with long surface stays (-500 days) and “l-way” transit times of -6 to 7 months. In the event an aborted landing or major surface system failure forces an early return to the crew transfer vehicle (CTV), astronauts could spend the entire mission duration (-900 days) in a weightless environment. An artificial gravity CTV design capable of countering the potentially debilitating physiological effects of “zero gravity” is described which uses “bimodal” nuclear thermal rocket (NTR) propulsion. With its high specific impulse (Isp -850-l 000 s), attractive engine thrust-to-weight ratio (-3-i 0) and demonstrated feasibility, the NTR is the most promising propulsion technology for future human exploration missions to the Moon, Mars and near Earth asteroids. Because only a minuscule amount of enriched uranium235 fuel is consumed in a NTR during the primary propulsion maneuvers of a typical Mars mission, engines configured for both propulsive thrust and modest power generation (referred to as “bimodal” operation) provide the basis for a robust, “power-rich” stage enabling a propulsive Mars capture capability for the CTV. A common “bimodal” NTR (BNTR) “core” stage powered by three -15 thousand pounds force (klbf) BNTRs supplies 50 kWe of total electrical power for crew life support and an active refrigeration system enabling long term, “zero-boiloff” liquid hydrogen (LH2) storage. On the piloted CTV, the bimodal NTR core stage is connected to the inflatable -----------------------------------------------------------------------*Ph.D./Nuclear Engineering, Senior Member AIAA ‘*Aerospace Engineer, Member AIAA “TransHab” crew module via an innovative, spinelike “saddle truss” (approximately 22 meters in length) which is open underneath to allow easy jettisoning of the “in-line” LH2 propellant tank following the trans-Mars injection (TMI) burn. The CTV then initiates vehicle rotation at o 4 revolutions per minute (rpm) to provide the TransHab crew with a Mars gravity field (-0.38 g E) during the outbound transit. A higher rotation rate (w 6 rpm) can provide -0.8 gE on the return leg to help reacclimate the crew to Earth’s gravity after their -500 day stay at Mars. In addition to supplying artificial gravity and abundant power for the crew, a Mars architecture using BNTR transfer vehicles also has a lower total launch mass, fewer transportation system elements and simpler mission operations than competing “non-nuclear” chemical and solar electric propulsion (SEP) options. INTRODUCTION AND BACKGROUND Over the last 3 years, NASA’s intercenter Mars Exploration Study Team has been evaluating a split cargo / piloted mission approach for sending humans to Mars in the 2014 timeframe. Payload masses have continued to be refined and updatedl, and a variety of space transportation technology options have been examined*,s. In the FY98 reference mission profile, the crew traveled to Mars under “zero gravity” conditions and landed on its surface in a common transit / habitat module integrated into an aerobraked lander configuration. Two cargo flights preceded the piloted mission and were used to predeploy surface assets and a separate transfer stage for returning the crew to Copyright

2001: A Space Odyssey Revisited—The Feasibility of 24 Hour Commuter Flights to the Moon Using NTR Propulsion with LUNOX Afterburners

The prospects for 24 hour commuter flights to the Moon, similar to that portrayed in 2001: A Space Odyssey but on a more Spartan scale, are examined using two near term, high leverage technologies: liquid oxygen (LOX)-augmented nuclear thermal rocket (NTR) propulsion and lunar-derived oxygen (LUNOX) production. Iron-rich volcanic glass, or orange soil, discovered during the Apollo 17 mission to Taurus-Littrow, has produced a 4 percent oxygen yield in recent NASA experiments using hydrogen reduction. LUNOX development and utilization would eliminate the need to transport oxygen supplies from Earth and is expected to dramatically reduce the size, cost and complexity of space transportation systems. The LOX-augmented NTR concept (LANTR) exploits the high performance capability of the conventional liquid hydrogen (LH2)-cooled NTR and the mission leverage provided by LUNOX in a unique way. LANTR utilizes the large divergent section of its nozzle as an afterburner into which oxygen is injected and supersonically combusted with nuclear preheated hydrogen emerging from the engines choked sonic throat, essentially scramjet propulsion in reverse. By varying the oxygen-to-hydrogen mixture ratio, the LANTR engine can operate over a wide range of thrust and specific impulse (Isp) values while the reactor core power level remains relatively constant. The thrust augmentation feature of LANTR means that big engine performance can be obtained using smaller, more affordable, easier to test NTR engines. The use of high-density LOX in place of low density LH2 also reduces hydrogen mass and tank volume resulting in smaller space vehicles. An implementation strategy and evolutionary lunar mission architecture is outlined which requires only Shuttle C or in-line Shuttle-derived launch vehicles, and utilizes conventional NTR-powered lunar transfer vehicles (LTVs), operating in an expendable mode initially, to maximize delivered surface payload on each mission. The increased payload is dedicated to installing modular LUNOX production units with the intent of supplying LUNOX to lunar landing vehicles (LLVs) and then LTVs at the earliest possible opportunity. Once LUNOX becomes available in low lunar orbit (LLO), monopropellant NTRs would be outfitted with an oxygen propellant module, feed system and afterburner nozzle for bipropellant operation. Transition to a reusable mission architecture now occurs with smaller, LANTR-powered LTVs delivering ~400% more payload on each piloted round trip mission than earlier expendable all LH2 NTR systems. As initial lunar outposts grow to eventual lunar settlements and LUNOX production capacity increases, the LANTR concept can enable a rapid commuter shuttle capable of 24 hour one way trips to and from the Moon. A vast deposit of iron-rich volcanic glass beads identified at just one candidate site located at the southeastern edge of Mare Serenitatis could supply sufficient LUNOX to support daily commuter flights to the Moon for the next 9000 years!

Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion

A conceptual vehicle design enabling fast, piloted outer solar system travel was created predicated on a small aspect ratio spherical torus nuclear fusion reactor. The initial requirements were satisfied by the vehicle concept, which could deliver a 172 mt crew payload from Earth to Jupiter rendezvous in 118 days, with an initial mass in low Earth orbit of 1,690 mt. Engineering conceptual design, analysis, and assessment was performed on all major systems including artificial gravity payload, central truss, nuclear fusion reactor, power conversion, magnetic nozzle, fast wave plasma heating, tankage, fuel pellet injector, startup/re-start fission reactor and battery bank, refrigeration, reaction control, communications, mission design, and space operations. Detailed fusion reactor design included analysis of plasma characteristics, power balance/utilization, first wall, toroidal field coils, heat transfer, and neutron/x-ray radiation. Technical comparisons are made between the vehicle concept and the interplanetary spacecraft depicted in the motion picture 2001: A Space Odyssey.

A spherical torus nuclear fusion reactor space propulsion vehicle concept for fast interplanetary travel

A conceptual vehicle design enabling fast outer solar system travel was produced predicated on a small aspect ratio spherical torus nuclear fusion reactor. Initial requirements were for a human mission to Saturn with a>5% payload mass fraction and a one way trip time of less than one year. Analysis revealed that the vehicle could deliver a 108 mt crew habitat payload to Saturn rendezvous in 235 days, with an initial mass in low Earth orbit of 2,941 mt. Engineering conceptual design, analysis, and assessment was performed on all major systems including payload, central truss, nuclear reactor (including diverter and fuel injector), power conversion (including turbine, compressor, alternator, radiator, recuperator, and conditioning), magnetic nozzle, neutral beam injector, tankage, start/re-start reactor and battery, refrigeration, communications, reaction control, and in-space operations. Detailed assessment was done on reactor operations, including plasma characteristics, power balance, and component design.A conceptual vehicle design enabling fast outer solar system travel was produced predicated on a small aspect ratio spherical torus nuclear fusion reactor. Initial requirements were for a human mission to Saturn with a>5% payload mass fraction and a one way trip time of less than one year. Analysis revealed that the vehicle could deliver a 108 mt crew habitat payload to Saturn rendezvous in 235 days, with an initial mass in low Earth orbit of 2,941 mt. Engineering conceptual design, analysis, and assessment was performed on all major systems including payload, central truss, nuclear reactor (including diverter and fuel injector), power conversion (including turbine, compressor, alternator, radiator, recuperator, and conditioning), magnetic nozzle, neutral beam injector, tankage, start/re-start reactor and battery, refrigeration, communications, reaction control, and in-space operations. Detailed assessment was done on reactor operations, including plasma characteristics, power balance, and component design.

“Bimodal” NTR and LANTR propulsion for human missions to Mars/Phobos

The nuclear thermal rocket (NTR) is one of the leading propulsion options for future human missions to Mars due to its high specific impulse (Isp ∼850–1000 s) and attractive engine thrust-to-weight ratio (∼3–10). Because only a miniscule amount of enriched uranium-235 fuel is consumed in a NTR during the primary propulsion maneuvers of a typical Mars mission, engines configured for both propulsive thrust and modest power generation (referred to as “bimodal” operation) provide the basis for a robust, “power-rich” stage enabling propulsive Mars capture and reuse capability. A family of modular “bimodal” NTR (BNTR) vehicles are described which utilize a common “core” stage powered by three 66.7 kN (∼15 klbf) BNTRs that produce 50 kWe of total electrical power for crew life support, an active refrigeration/reliquification system for long term, “zero-boiloff” liquid hydrogen (LH2) storage, and high data rate communications. Compared to other propulsion options, a Mars mission architecture using BNTR transfer v...

Space Propulsion via Spherical Torus Fusion Reactor

A conceptual vehicle design enabling fast outer solar system travel was produced predicated on a small aspect ratio spherical torus nuclear fusion reactor. Analysis revealed that the vehicle could deliver a 108 mt crew habitat payload to Saturn rendezvous in 204 days, with an initial mass in low Earth orbit of 1630 mt. Engineering conceptual design, analysis, and assessment were performed on all major systems including nuclear fusion reactor, magnetic nozzle, power conversion, fast wave plasma heating, fuel pellet injector, startup/re-start fission reactor and battery, and other systems. Detailed fusion reactor design included analysis of plasma characteristics, power balance and utilization, first wall, toroidal field coils, heat transfer, and neutron/X-ray radiation.

Application of a small nuclear thermal/nuclear electric bimodal vehicle for planetary exploration

Results of a study of a small NTR/bitnodal propulsion system study are presented. Orbiter missions to Pluto, Neptune, and Jupiter are presented for a reactor and power conversion system that generates 1000 Ibf thrust and 20 to 40 kWe of electricity. Xenon ion electric propulsion is assumed to use the electrical output of the reactor. Results indicate that these outer planet missions are feasible and the masses delivered are quite in keeping with the current trends within NASA to develop new spacecraft that are much smaller, much lighter, and more autonomous.

FAST INTERPLANETARY PROPULSION USING A SPHERICAL TORUS NUCLEAR FUSION REACTOR PROPULSION SYSTEM

LWlkg respect&ely2s4., Although contestable, it is the A conceptual. vehicle de&n enabling fast outer solar system travel was produced predicated on a. small aspect ratio sphekical torus nuclear fusion reactor. .Analysis revealed that the vehicle could deliver a 108 mt crew habitat payload to Saturn rendezvous "in 214 days, with an initial mass in low Earth orbit of 2,640 mt. Engineering conceptual design, analysis, and assessment was performed on all major systems including payload, central truss, nuclear fusion reactor, power, magnetic nozzle, fast wave plasma" heating, tankage, startup/re-start fission reactor and battery, refrigeration, communicationS, reaction control, mission design, and space operations. Detailed fusion reactor design analysis included plasma characteristics, power balance/utilization, first wall, toroidal field coils, and heat transfer. judgment of the a&hors and m&y in the field that only a single space propulsion t&hnology exists at this time. that can reasonably be expected to offer this capability: nuclear fusion, &her magnetic or inertial cotimement. Based in part on the results of previous s&lies2,5 of the ,attributes and shortcomings of various classes of reactor "towards space propulsion, a closed magnetic syskm was chosen for this design concept. The high power density achievable in closed systems, improved confinement, spin polarization of the fuel, density and temperature profile peaking provided a distinct advantage @ their application towards space propulsion. The small aspect ratio spherical torus was chosen to serve as the basis for the vehicle concept.