generator in an orbit that is outside the debris zone (greater than 1.2 Earth radii), and spending most of the time
beyond the Moon. In this scenario, the water is converted into cryogenic rocket fuel. The entire 3500 to 5500 Mg
would be available. An LH2 NTR would take the crew cab, ECCV and lander to HEEO, as previously shown.

TABLE 5 shows that 5500 Mg of cryofuel at HEEO would support some 120 day missions. And 2400 Mg of fuel
would support any form of 150 day mission.

SUMMARY--CONCLUSIONS & OBSERVATIONS

The scenario of utilizing rocket fuel from NEOs for manned Mars missions appears to provide substantial
benefits over using terrestrial propellants launched to Earth orbit.

* Mars Missions with small or no HLLV
* possibly with existing, e.g. Titan IV upgraded, vehicles
* small NTRs

These benefits may actually enable manned Mars missions due to the possible reduction of HLLV flights and
Earth orbit assembly requirements associated with large propulsion vehicles launched from Earth. Perhaps the need
for heavy lift vehicles may be eliminated altogether, thus further reducing the development and schedule risks
associated with a Mars mission. Existing launch vehicles are found to be adequate in the scenario put forward.
Additionally,NTR size and operational temperature are reduced, thus reducing safety hazards and development cost
and schedule risks.

* affordable space ventures
* simplest possible use of existing space resource

The resource water could be used directly, without splitting, as rocket propellant. A Space Transportation System
would result. The simplicity is most attractive.

Cheap spacetransportation could make commercialization of space ventures feasible and eliminate decisions
between space activities and immediate human needs on Earth. Materials from space, in addition to propellant,
combined with inexpensive transportation in space could enable a truly sustainable and expanding space program in
our solar system and beyond.

* construction materials &natural resources
* without mining Earth in any way

Other major benefits in addition to spacefaring may be enabled by space resources. The opportunities
associated with inexpensive transportation and materials available in space could perhaps eliminate the compromise
between standard of living and the environment. Preserving the Earth's environment by eliminating power
production on the Earth's surface may be possible, for instance. Structural materials obtained from non-terrestrial
sources could perhaps be retrieved to Earth orbit and fashioned into large solar arrays for supplying Earth's energy
needs. Therefore, decoupling solar power satellites (SPS) from large launch mass requirements (and hence cost)
could perhaps make SPS feasible. This scenario would reduce or eliminate nuclear power plants and nuclear waste,
and global warming from coal, oil, and gas. Also reduced or eliminated would be the coal mining, oil drilling,
uranium mining,and gas extraction corresponding to electrical power production on Earth. In this way, space
resources may allow mankind to maintain (or perhaps improve with cheaper kilowatt-hours) the standard of living
and preserve the environment.

*find "trivially close" water bearing NEO

Study of LEO to Mars option reveals great value to find objects 3 km/s closer than rather typical NEO. This would
permit propulsive delivery to LEO of massive palyoads.

The same effect can be obtained with a significant percent of the known periodic comets and with NEOs by using
Earth gravity assist. The returning tanker would be put into an orbit where its V[!]changes from about 9 km/s to one
with period exactly 2 years. Then the V[!]drops to about 4.6 km/s, and the mission is about 2 km/s closer. But a
gravity assist maneuver involves a 2 year delay. Objects with very small [!]V from Earth orbit capture typically
require less than 1 year for payload delivery.

Such closer NEOs exist and tend to be devolatized, smaller (.1 to .5 km) and are 2 to 3 km/s closer than comet
NEOs. These very close NEOs (VNEO) are so close that direct propulsive delivery of massive quantities of fuel to
LEO from them is feasible and economically attractive.