FIGURE 12. LH2 NTR takes the Mars Mission
Payload and its Rocket System from LEO to HEEO.

• mass for radiation shields
• mass for building structures & vehicles
  
  Sequence of Events for NEO Resource Utilization

Figure 13 A Steam NTR takes the Mars mission
payload from HEEO to Mars. At the gas station it
takes on fuel from space.

TABLE3. Propellant or Mass Needed from Space to refuel
Tankers returning to the Comet for another Load. Note: a
Cryo Fueled return uses about 29 Mg to return 500Mg

To use these resources we would first send prospecting vehicles, to find other object like it and to assay what we
found. Then we would send contact probes to determine how much material there is, where it is, its composition,
and to determine other parameters needed for extracting it. Figure 4 shows this.

This first mission would extract water and store it in a tank. Figure 5 shows this. Then a tanker would return some
of the water for use as propellant to "fuel"the next trips to the comet. Figure 6 shows this. To speed up the
availability of propellants available in Earth orbits we could send more tankers directly from Earth. These would tap
the storage tank and return water to Earth orbits. Figure 7 shows this.

Figure 8 shows that the tankers would return propellant to Earth orbits. These tankers would return relatively
small amounts of water, but the amount is large compared to what we launch to orbit today, and could be enough to
use as propulsion for the manned missions to Mars. Figure 9 shows this. A "gas station" in space would result.

The steps envisioned are:
* prospecting
* first tanker mission:extract, store in tank
* subsequent missions:multiply payback
* gas station store & dispense
* initiate manned Mars mission

The analysis that follows shows how the launch of a ~10 Mgtanker would return about 500 Mg to High Elliptic
Earth Orbit (HEEO) once every 4.2 years, the period of the comet.

A "refinery" in Earth orbit cold use electric generators to power electrolysis and liquefaction systems to provide
rocket fuels, as well as rocket propellants. The fuels would support chemical propulsion rockets for use in the space
near Earth. The refinery would supply the "gas station." For reference, an ISU(1990) study showed that a 1