Major Areas of Opportunity - Implications of Emerging Micro-and Nanotechnologies - page 107

FIGURE 3-17 Spacecraft power for INTELSAT satellites. Data from Martin, D.H. 2000.
Communications Satellites, 4th ed. Reston, Va.: American Institute of Aeronautics and
Astronautics, Inc.
and are expected to more closely match their commercial counterparts as mission
needs, e.g., radar and direct broadcast of video data, converge.
Micro- and nanofabrication enables a radically new form of high-specific-
impulse electric propulsion that uses field ionization or field evaporation to ion-
ize propellant atoms or molecules, which are subsequently accelerated by an
applied electric field to generate thrust. Field ionization and emission are electron
tunneling phenomena that require electric fields of 10 7 to 10 8 watts per centime-
ter, which can be generated using 100 to 1,000 volts across a 0.1-micron gap. If
the emitting surface has a radius of curvature of ~30 nanometers or less, local
electric field enhancement occurs, dropping the required voltages to the 10- to
100-volt range. Micro- and nanofabrication enables field emission and ionization
using tens of volts instead of kilovolts. Conventional ion engine design requires
magnetic plasma confinement, multiple power supplies, and roughly a hundred
piece parts such as accelerator grids and capacitors, while a field-ionization-
based ion engine would require no magnetic field, only two power supplies, and
fewer than 10 piece parts. This approach creates an essentially two-dimensional
ion engine that is scalable in area and thrust, thus commoditizing high-specific-
impulse thrust for spacecraft.
Field emission sources are currently under development as an enabling tech-
nology for flat panel displays, simplified microwave tubes, and vacuum micro-
electronics. 190,191,192 Examples of field emission sources include Spindt cathodes,
diamond like carbon coatings, and carbon nanotubes. 193,194,195 Field emission