Propellant-free propulsion technology has taken a critical step toward
reality, completing a series of systems tests at NASA’s Marshall Space
Flight Center in Huntsville, Ala.
The Propulsive Small Expendable Deployer system – called ProSEDS –
is a tether-based propulsion experiment that draws power from the space
environment around Earth, allowing the transfer of energy from the Earth
to the spacecraft.
Inexpensive and reusable, ProSEDS technology has the potential to
turn orbiting, in-space tethers into “space tugboats” — replacing heavy,
costly, traditional chemical propulsion and enabling a variety of space-based
missions, such as the fuel-free raising and lowering of satellite orbits.
The initial flight of ProSEDS, scheduled for early summer, will mark
the first time a tether system is used for propulsion. To be launched
from Kennedy Space Center, Fla., ProSEDS will fly aboard an Air Force
Delta II rocket and demonstrate an electrodynamic tether’s ability to
generate significant thrust.
“We achieved an important milestone with our tests in November,” said
ProSEDS project manager Leslie Curtis of the Marshall Center’s Space
Transportation Directorate. “Using a vacuum chamber to represent the
space environment, we successfully simulated the first 16 hours of the
experiment’s initial flight.”
In orbit, ProSEDS will deploy from a Delta-II second stage a 3.1-mile-long
(5 kilometers), ultra-thin bare-wire tether connected with a 6.2-mile-long
(10 kilometers) non-conducting tether. The interaction of the bare-wire
tether with the Earth’s ionosphere will produce thrust, thus lowering
the altitude of the stage.
Although the mission could last as long as three weeks, the first day
is the most critical, because the primary objective of demonstrating
thrust with the tether should be achieved during the experiment’s first
24 hours.
During the mission profile tests last November, engineers from the
Marshall Center, along with their partners in academia and industry,
tested the experiment’s multiple systems as if the flight were actually
taking place.
“We took ProSEDS through every step of the mission’s first 16 hours,”
Curtis said. “We operated its hardware, batteries, cables and software,
activated and deactivated systems, and collected and transmitted data
as we would during an actual flight.”
During the tests, all subsystems functioned as designed, including
the hollow cathode plasma contactor, a critical component that enables
the tether system to complete its electrical circuit.
During the flight, the process of collecting energy will begin when
the electromagnetic portion of the tether collects electrical current
along the tether’s length as it moves through the Earth’s magnetic field.
To keep the current flowing, the plasma contactor reconnects the electrons
with the invisible, electrically charged plasma that surrounds the Earth,
emitting the electrons back into space so it can complete its circuit.
“We were pleased to see the plasma contactor perform well throughout
the test, even under conditions outside its expected operating range,”
said Curtis. “It demonstrated the robustness of its design and the performance
range of the ProSEDS operating system.” The contactor was designed and
built by the Electric Propulsion Laboratory in Monument, Colo.
Additional testing of ProSEDS hardware leading to its launch will include
thermal testing, tether deployment and final system verification with
flight software.
NASA’s industry team for the ProSEDS experiment includes the University
of Michigan in Ann Arbor, Alpha Technologies of Huntsville, Ala., Electric
Propulsion Laboratory of Monument Colo., the Smithsonian Astrophysical
Observatory in Cambridge, Mass., Tether Applications Inc. of Chula Vista,
Calif., and Triton Systems Inc. in Chelmsford, Mass.
The ProSEDS experiment is managed by the Space Transportation Directorate
at the Marshall Center.
