High Power Electric Propulsion
Encyclopedia
High Power Electric Propulsion (HiPEP) is a variation of ion thruster
. It was ground-tested in 2003 by NASA
and was intended for use on the Jupiter Icy Moons Orbiter
, which was canceled in 2005.
ions are produced using a combination of microwave
and magnetic fields. The ionization is achieved through a process called Electron Cyclotron Resonance
(ECR). In ECR, the small number of free electrons present in the neutral gas gyrate around the static magnetic field lines. The injected microwaves' frequency is set to match this gyrofrequency and a resonance is established. Energy is transferred from the right-hand polarized portion of the microwave
to the electrons. This energy is then transferred to the bulk gas/plasma
via the rare - yet important - collisions between electrons and neutrals. During these collisions, electrons can be knocked free from the neutrals, forming ion-electron pairs. The process is a highly efficient means of creating a plasma in low density gases. Previously the electrons required were provided by a hollow cathode
.
of 6,000-9,000 seconds, and a propellant throughput capability exceeding 100 kg/kW. The goal of the project, as of June 2003, was to achieve a Technology readiness level
of 4-5 within 2 years.
On page 8 of the September 2004 HiPEP report NASA/TM—2004-213194 says the pre-prototype HiPEP produced 670 mN of thrust at a power level of 39.3 kW using 7.0 mg/s of fuel giving a specific impulse of 9620. Downrated to 24.4 kW, the HiPEP used 5.6 mg/s of fuel giving a specific impulse of 8270 s and 460 mN of thrust.
Ion thruster
An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and...
. It was ground-tested in 2003 by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
and was intended for use on the Jupiter Icy Moons Orbiter
Jupiter Icy Moons Orbiter
The Jupiter Icy Moons Orbiter was a proposed spacecraft designed to explore the icy moons of Jupiter. The main target was Europa, the suspected ocean of which is one of the places where simple alien life is a possibility in our solar system...
, which was canceled in 2005.
Theory
The HiPEP thruster differs from earlier ion thrusters because the xenonXenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
ions are produced using a combination of microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
and magnetic fields. The ionization is achieved through a process called Electron Cyclotron Resonance
Electron cyclotron resonance
Electron cyclotron resonance is a phenomenon observed both in plasma physics and condensed matter physics. An electron in a static and uniform magnetic field will move in a circle due to the Lorentz force...
(ECR). In ECR, the small number of free electrons present in the neutral gas gyrate around the static magnetic field lines. The injected microwaves' frequency is set to match this gyrofrequency and a resonance is established. Energy is transferred from the right-hand polarized portion of the microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
to the electrons. This energy is then transferred to the bulk gas/plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
via the rare - yet important - collisions between electrons and neutrals. During these collisions, electrons can be knocked free from the neutrals, forming ion-electron pairs. The process is a highly efficient means of creating a plasma in low density gases. Previously the electrons required were provided by a hollow cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
.
Specifications
The thruster itself is in the 20-50 kW class, with a specific impulseSpecific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
of 6,000-9,000 seconds, and a propellant throughput capability exceeding 100 kg/kW. The goal of the project, as of June 2003, was to achieve a Technology readiness level
Technology Readiness Level
Technology Readiness Level is a measure used by some United States government agencies and many of the world's major companies to assess the maturity of evolving technologies prior to incorporating that technology into a system or subsystem...
of 4-5 within 2 years.
On page 8 of the September 2004 HiPEP report NASA/TM—2004-213194 says the pre-prototype HiPEP produced 670 mN of thrust at a power level of 39.3 kW using 7.0 mg/s of fuel giving a specific impulse of 9620. Downrated to 24.4 kW, the HiPEP used 5.6 mg/s of fuel giving a specific impulse of 8270 s and 460 mN of thrust.