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Electric Propulsion:
GRC is leading the Prometheus 1 Electric Propulsion Segment
(EPS) development during the Prometheus Project’s Phase A and B activities.
The proposed Prometheus missions require electric propulsion systems
with high specific impulse (ISP), high power/thrust, and most of all,
long life. A trade of state-of-the-art (SOTA) and electric propulsion
systems currently in laboratory form or under development was made to
select the most promising type of electric propulsion system to pursue
for the proposed Prometheus applications.
The Prometheus 1 EPS is composed of an Ion Thruster Subsystem for main
propulsion, a Power Processing and Control Subsystem, a Propellant Feed
Subsystem, and the Structures and Mechanisms and Thermal Control Subsystems.
A Hall Thruster Subsystem has also been proposed to provide attitude
control and additional acceleration at critical points during a mission.
The Ion Thruster Subsystem is composed of eight 30 kW Herakles ion thrusters
providing primary propulsion. The operating performance of 7000 seconds
ISP is critical to enabling the proposed Jupiter Icy Moons Obiter (JIMO)
mission with a reasonable dry weight for spaceship and mission hardware.
Top-level propulsion system requirements also include long-life (operating
at full power for more than 8 years) and radiation tolerance to survive
Jupiter’s environment. To aid in the ion thruster design for Prometheus
1, a pre-cursor Herakles ion thruster is undergoing long duration wear
testing (up to 2000 hours) in Vacuum Facility 6 at GRC (March to July
2005). This test, while short compared to the required lifetime expected
for the JIMO mission, will demonstrate the ability of the thruster design
to operate for long periods, uncover any unexpected problems, and begin
to assess the long-life features of the thruster components. A similar
long duration test is being run in the same timeframe on a different
pre-cursor Herakles thruster at NASA’s Jet Propulsion Laboratory. GRC is leading the Herakles
Ion Thruster design, development, and test activities through the preliminary
design phase. For more information on ion thrusters and their development,
visit http://www.grc.nasa.gov/WWW/ion/. For more information on electric
propulsion and space test facilities and capabilities at GRC, visit
http://facilities.grc.nasa.gov/epl/ or http://facilities.grc.nasa.gov/facilities/space.html.
The Hall Thruster Subsystem includes six large Hall thrusters, for possible
operation at Europa (one of Jupiter’s icy moons) with 2000 seconds ISP,
but provides over twice the thrust (per kW) as the ion thrusters. The
Hall Thruster Subsystem also includes 12 small Hall thrusters used for
attitude control.
The EPS Power Processing & Control Subsystem is made up of the three different PPU types needed to power
the ion thrusters and two types of Hall thrusters.
The Propellant Feed Subsystem includes a xenon tank, high pressure feed assembly,
and low pressure feed assemblies.
The EPS Structures & Mechanisms subsystem is made up of two Thruster Pod Assemblies and two Thruster
Boom Assemblies. The EPS Thermal Control Subsystem consists of multi-layer insulation,
micrometeoroid shields, thermal control elements, and temperature sensors.
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