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Nuclear Propulsion

•  Create a hot, high pressure gas and expand through a nozzle. Nuclear reactors are heat sources:

–  Fission – lowest energy yield •  Absorption of neutrons in fuel material such as uranium

–  Fusion – higher energy yield

•  Join two nuclei to produce a single nucleus and energy

–  Antimatter – highest energy yield •  Collide matter and antimatter particles resulting in complete

conversion of mass into energy

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International Atomic Energy Agency

Report titled: The Role of Nuclear Power and Nuclear Propulsion in the Peaceful Use of Space, published in 2005

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Nuclear Propulsion Performance

From Sutton and Biblarz

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Fission

•  Splitting atom into many smaller fragments •  Usually induced by bombarding uranium-235 with

neutrons –  Fissionable atom catches neutron and splits –  Usual isotopes:

•  Iodine 131 •  Caesium-137 •  Strontium-90

•  Combined weight of fission products is less than the original weight (~0.1%)

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Fission Reactors

•  Solid Core (T/W~1) –  Propellant is simply heated by a solid fuel core –  Isp ~ 800 sec

•  Particle Bed –  Propellant is pumped through a bed of nuclear material

(T/W~1) –  Isp ~ 1000 sec

•  Liquid Core (T/W>1) –  Uses liquid fissionable material, not solid –  Isp ~ 1500 sec

•  Gas Core (T/W>1) –  Propellant passes through a fissioning plasma –  Isp ~ 7000 sec

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Fission Fragment Propulsion

•  Fission produces very highly energetic fragments

•  Uses these fragments as the actual propellant by allowing them to escape the reactor –  Fragments are ionized, so directional

control can be achieved –  Fragments move at very high speed –  Isp is estimated to be over 1,000,000

sec •  Reactor would need to be either very big,

or use reprocessed nuclear fuel

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Fission Reactor Propulsion

Gas Core

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ROVER Program

•  1955-1973, Los Alamos •  First nuclear thermal rocket

built and tested, called KIWI

•  Uncoated Solid Uranium Oxide Plates Stacked with Hydrogen dumped onto it

•  Produced 70MW with an exhaust temp of 2700K KIWI Engine Destructibility Test

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Nuclear Engine for Rocket Vehicle Applications (NERVA)

•  Developed by the Office for Space Nuclear Propulsion (SNPO) 1960-1972 with: –  Multi-mission capabilities –  Man rating –  Minimum chamber temperature and pressure of 2400 K and 450 psi –  Endurance of 600 minutes –  Transportable by land, air and sea

•  Integrated KIWI B into flight package

•  NRX-Engine System Test

–  Reactors developed to withstand launch loads

–  Demonstrate restart capabilities and controllability

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Fusion

•  The joining of two nuclei to produce a single nucleus and energy

•  The difference in mass between the products and reactant is the energy produced

•  Cleaner than fission •  Difficult to actually get the nuclei to fuse, due to the

electric repulsion caused from both nuclei having positive charges

•  Possible fuels: deuterium and tritium

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Fusion Propulsion

•  Magnetic Confinement Fusion (MCF) –  Recreate the sun’s method –  Heat fuel to millions of

degrees with a plasma to increase the chance that nuclei will collide and fuse

–  Problem is controlling and containing the plasma

–  Very massive magnets required to contain plasma

Tokamak Reactor at Princeton

can get to 108 Kelvin

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Nuclear Electric Propulsion

•  Created through heat from a nuclear reactor converted to electrical energy through thermoelectric or thermionic conversion •  No need for solar energy •  Operates in deep space •  Advantages are high Isp, high power, and high thrust •  Problems:

Developing high power electric thrusters Developing low specific mass power Need to shield crews from nuclear radiation

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Nuclear Electric Xenon Ion System (NEXIS)

•  Use high efficiency, thrust, power

•  Large scale nuclear electric propulsion

•  Powered with commercial electric power

•  JIMO –  Jupiter Icy Moon

Orbiter –  NEXIS

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Matter-Antimatter Annihilation

•  Collision of matter and antimatter particles results in complete conversion of mass into energy

•  Highest energy density known to exist •  Only 100 milligrams of antimatter would be needed to

match the propulsive power of the space shuttle

Type of reaction Energy density (J/kg)

Chemical 1x107

Fission 8x1013

Fusion 3x1014

Annihilation of matter 9x1016

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Antimatter Production Capabilities

•  About 1-10 nanograms of antiprotons are produced each year at Fermilab in Chicago and CERN in Switzerland (not nearly enough)

•  Proposed antimatter factories could produce enough for some simpler propulsion concepts

•  Current portable storage capabilities are limited to 1010

antiprotons for 1 week using a Penning Trap •  1020 antiprotons are thought to be needed for complete

antimatter propulsion

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Antimatter Propulsion Concepts

Type Specific Impulse Maximum Antimatter Used

Proposed Range

Solid Core 1,000 sec Depends on mission Within solar system

Gas Core 2,500 sec Depends on mission Within solar system

Antimatter Catalyzed Micro Fission/Fusion (ACMF)

13,500 sec 1 microgram Within solar system

Antimatter Initiated Micro Fusion (AIM)

61,000 sec 10 milligrams 10,000 AU in 50 years

Plasma Core 5,000 to 100,000 sec 10 kilograms 10,000 AU in less time

Beam Core >10,000,000 sec 1,000 megagrams Interstellar

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Antimatter Catalyzed Micro Fission/Fusion •  Antimatter-matter annihilation is used to induce a fission reaction which is in

turn used to induce a fusion reaction which minimizes the problems associated with each type of reaction, yikes

•  ICAN–II is a Penn State proposed spacecraft that would use this engine

–  Requires 140 nanograms of antiprotons for 30-day manned mission to Mars –  Total mass of 625 metric tons with 82 metric tons for payload –  Could be built within the next two decades

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Antimatter Initiated Micro Fusion (AIM)

•  Antimatter is used to initiate a fusion reaction •  AIM Star is a Penn State proposed spacecraft

that would use this type of engine for an unmanned mission to the Oort cloud in 50 years –  Fire continuously for 22 years –  Reach 0.003 times the speed of light –  Coast through the Oort cloud taking

measurements