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3.4 Mgreactor/engine mass 5.5 Mgstructure and reaction control system 9.0 Mgradiation shadow shield With the above payload and non-tank dry weights, the required piloted vehicle size requires that over 800 Mg be launched from Earth into LEO. This includes approximately 315 to 375 Mg of trans-Mars insertion (TMI) H2 propellant and about 160 to 180 Mg for Mars Orbit Capture (MOC) and trans-Earth insertion (TEI). The current plans allow for no rendezvous in Mars orbit for the crew to meet a previously delivered MEV; therefore, the piloted vehicle must take the piloted lander (MEV) along in a "full-up" configuration. The cargo vehicle mass in LEO is on the order of 200 Mg for delivering 45 Mg to the surface of Mars. The cargo flights use from about 90 to 100 Mg of propellant for TMI and MOC. The recommended number of 45 Mg packages to be delivered to the surface of Mars for a manned exploration mission are three or four. For both the piloted vehicle and the cargo vehicles, the payloads are intended to be launched into Earth orbit with a 250 Mgclass HLLV. This results in at least a seven-HLLV launch scenario with substantial on-orbit assembly required. These circumstances may be prohibitive to Mars exploration. Options for NEO Resource Utilization--IMLEO and Propellant from NEO's We have analyzed a few options for supplying the propellants for a manned mission. These are only examples, to be used as "existence theorems" suggesting that propellants and fuels from space can be used for manned missions. The objective is to seek ways to perform themissions without the use of aheavy lift launch vehicle (HLLV). The cases we examined include 1. using steam propulsion starting from HEEO, 2. using cryofuel propulsion from an orbit next to the Space Station Freedom, and 3. using cryofuel propulsion from HEEO. All missions begin with sending an initial set of vehicles to the comet. The first time we go to the comet we send just a single extractor, purifier, storage tank and a tanker. The second time we go we send as many tankers as we can. The first vehicles consist of an extractor, a purifier, a storage tank and a tanker. The first three items may consist of a single, 10 Mgpayload. The water purification method could be a vortex tank as suggested by Stone (1976). The important question to be answered is: How much launch capacity would be needed to send the first vehicles from LEO to the comet? The options range from using steam propulsion to using Ion Nuclear Electric propulsion. TABLE 2 shows that if we use LH2 NTR'sor Ion NEP systems then the the initial mass at LEO (IMLEO) and the resulting launch systems are moderate. An Ion NEP system would require only two Titan IV launches or a single, Shuttle payload launch. An LH2 NTR would require 3 such launches, two of which launch only propellant. We could send all the tankers using Ion NEP propulsion. In this case we would be delivering not only a tanker but a fresh electric generator and a fresh, ice melting heat source. Note that the payback is ~500 Mg at HEEO for each 22 Mg launched from Earth. Another way to send the remaining tankers to the comet would first send them to HEEO and then fuel them from space to send them the rest of the way. Sending a tanker from LEO to HEEO requires an additional Titan IV launch. All the options may use tankers fueled from space for subsequent missions to bring back propellant or rocket fuel ore from space. What kind of launch systems would it take to send all the remaining vehicles to the comet? The question to be answered here is: What is the propellant or fuel mass needed to send a tanker back to the comet when it is fueled from space? We would only launch tankers, not rocket fuel. The optionsto do this include steam or LH2 NTR and cryo propulsion. TABLE 3 shows the propellant from space needed to fuel such vehicle return trips to the comet. TABLE 3 shows that cryo-fueling them could require as little as 29 Mg per tanker. A cryofuel booster sending them to the comet requires 19 Mg of fuel(derived from water) from space. The LH2 NTR requiring 25 Mg of LH2 would require 9 times that much water starting material, which is not competitive. A steam rocket would require a little less than 63 Mg of water. If 500 Mg are returned during the first trip, then this is sufficientto send 8 tankers from HEEO to the comet. If we use steam propulsion, then we increase our fuel at HEEO by a factor of 8 each trip. If we use cryo we increase our fuel by 25. But in all cases, no more launches are required. Note that since the tankers weigh about 15 Mg and they return about 500 Mg s, the payback per tanker is about 33 to 1, per trip.