FIGURE 10: Simple Tanker Vehicle uses Water for
Propulsion and delivers Water as Payload. The Keys to
Low Mass Tankers and Structures are 1. Micro Gravity
Objects 2. Low Vapor Pressure Propellants, such as
Water and 3. Low Decelerations resulting from
comparatively Long Duration Propulsive Captures at
HEEO.

FIGURE 11, Propellant used ("wasted") decreases to a
Limiting Value as the Reactor Power increases. As the
Propellant Exit Temperature becomes Colder the Rocket
Performance decreases, increasing Propellant Usage.

bringing periodic comet materials back to Earth orbits. The orbit of comet Wilson Harrington is far more accessible
than any of theother periodic comets.

Utility of Comet Resource

The comets contain about 50% water ice. Rockets can use the water directly, without splitting into gasses, as
propellant for propulsion. Electrolysis and liquefaction of the water produces one of the most convenient rocket
fuels, liquid Oxygen and liquid hydrogen, referred to as LOX and LH2.

Sensors passing through the comet tail and other direct, satellite measurement of the Comet Halley indicated that
the comet interiors contain permafrost or frozen mud at -50 C. (See Huebner 1990). In addition, they contain ~5%
CO, ~5% CO2, and ~1/2% bound nitrogen, e.g. ammonia, urea or other Carbon-Hydrogen Oxygen Nitrogen
(CHON) compounds (Huebner 1990).

Calculations indicate that simple propulsion systems can use this rocket propellant to bring back to Earth orbits
massive quantities of fuel and construction materials. The availability of such materials in Earth orbits enables a
change in the way people access space. It reduces the amount of material that must be launched from Earth by at
least two orders of magnitude. This enables:

* launch of ships with empty fuel tanks

TABLE 1. Propellant Used versus Reactor Power and
Mixed Mean Outlet Temperature. Note: 800 MW Re-^{TABLE 2. Various Options for sending Vehicle to Comet}
actor uses 2675 Mg Water Propellant to deliver 500^{for the First Time require Launched Mass, IMLEO, shown}
Mg to HEEO, and 200 MW Reactor uses 4384 Mg. ^{here. SplitLaunches would Rendezvous the Propellant with}
the Payloads.