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CHAPTER 23 PROSPECTS FOR MANNED MARS MISSIONS ELLIOTT C. LEVINTHAL Studies called "EMPIRE" (standing for Early Manned Planetary-/nter- planetary .Roundtrip Expeditions) were initiated early in 1962 by the Future Projects Office for the Marshall Space Flight Center. These and related studies by other NASA centers were intended to bring to light the technical problems associated with such missions. The emphasis of these studies was on single and multiple planetary fly-bys, with some considera- tion given to planetary orbital and landing missions. The time period con- sidered was the early 1970's. The contractors were Aeronutronic Division (Philco-Ford Motor Company), Lockheed Missiles and Space Company and General Dynamics/Astronautics. Studies relating to the time period 1975-85 were initiated in early 1963, by contracts with General Dynamics/ Fort Worth and Douglas Aircraft Company. Follow-on EMPIRE studies were carried out by Lockheed and General Dynamics/Astronautics. In addition, studies were made of a Mars Excursion Module by Aeronutronic, a Mars Mission Module (MMM) by North American Aviation's Space and Information Division, and an Earth Return Module (ERM) by Lock- heed under the direction of the Manned Spacecraft Center. Complementary to these efforts were studies initiated by the Ames Research Center early in 1963 for a Manned Mars Landing and Return Mission. These studies were conducted by North American Aviation and by the TRW Space Technology Laboratories. 436

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Prospects for Manned Mars Missions 437 The complete reports or summary volumes of all the above except the General Dynamics/Fort Worth and Douglas Aircraft Company studies were reviewed. This review was not penetrating or critical but was intended to survey the types of missions considered, the time period during which they might occur, a rough estimate of their costs, and their realtionship to other NASA programs. Three classes of manned planetary missions have been considered: manned round-trip planetary fly-bys; orbiters; and landers. All of these would have the capability of including small and medium-sized unmanned orbiting, hard or soft landed probes as part of the mission. Unmanned, survivable landers containing instrument payloads on the order of 2500 kg could not, however, be included as part of the "minimum" manned fly-by mission described below. All the systems considered consisted of surface launch vehicles and orbital launch vehicles. The surface launch vehicle places the spacecraft and orbital launch vehicle in Earth orbit. From this orbit, the orbital launch vehicle provides the excess velocity for the particular transfer tra- jectory chosen. Many trajectory studies have been carried out. The trajec- tories fall into two main classes: high energy trajectories, which can provide either light side or dark side Martian fly-bys; and low energy trajectories, which provide light side Martian fly-bys. The high energy trajectories, besides being characterized by the requirement for higher energies from Earth orbit and shorter trip times for fly-bys, dip within the Earth's orbit. (Because of their increased exposure to solar flares, compared to the low energy trajectories that are never within the Earth's orbit, the high energy trajectories are known as "hot" and the low as "cool".) The trajectory studies show that on the basis of energy requirements, a dual planet fly-by (Venus and Mars) is not much harder to accomplish than a Martian fly-by. The use of trajectories that pass near Venus, either in- bound or out-bound, increases the number of possible departure dates for flights between Earth and Mars. Trip times range from 400 days for high energy fly-bys to 630 days for low energy fly-bys and depend upon the year of launch, distance of nearest approach to Mars and the escape propulsion system. All of the Martian missions studied required either the use of several Saturn V's as Earth launch vehicles or the development of a post- Saturn launch vehicle. These studies considered several orbiting launch vehicles, including those using either chemical or nuclear propulsion stages. The fly-by mission described below requires a two-stage nuclear booster for the orbital launch vehicle.

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438 MARTIAN LANDINGS: MANNED MANNED FLY-BY "The Saturn V appears incapable of launching a single nuclear stage into orbit with sufficient propellant to accomplish the Mars low energy fly- by" [Lockheed, 1964]. The total trip time for this flight is 650-680 days. Assuming the development of a two-stage nuclear booster, a multi-Earth launch mode utilizing three Saturn V launches reasonably assures Mars fly- by capability. At the level of fiscal 1965 funds, it was estimated a "mini- mum" fly-by mission could be accomplished by 1975. The estimates of Lockheed of the cost were, in their Follow-On Study, $3.5 to 3.8 billion plus $2.3 billion for nuclear engine development for one flight in 1975. General Dynamics/Astronautics [1963], by subtraction from a much more elaborate mission, estimates the cost of a fly-by which might be launched in 1975 at about $12 billion. Aeronutronic [1962] estimates a dual planet fly-by at $12.6 billion. These cost estimates are given solely to indicate range. In many of these studies they are presented simply as extrapolations from general cost surveys appearing in McGraw-Hill's Handbook of Astro- nautical Engineering [1961], with no pretensions to precision. Photographic observations could be made during the course of a manned fly-by mission. In one such case, it was estimated that about a hundred overlapping photographs could be taken during a period of about an hour and a half, when the spacecraft would be relatively close to the planet. The reconnaissance and scientific instrumentation carried on board would include, in addition to a 120-inch focal length camera, an infrared camera, a small radar set of moderate resolution, and scientific instruments repre- senting an extension of Mariner/Centaur experiments, weighing 204 kg. In addition, there is the possibility that a 105 kg probe could be launched from the manned fly-by vehicle. One report characterizes the mission as follows: "The flyby is a limited, one-shot, narrow-swath reconnaissance tool, subject to continuous scale and angular-rate variation detrimental to optimum sensor design and to data interpretation. Its best use may be for operational test of future-mission equipment and possible for accurate insertion of a reliable unmanned reconnaissance orbiter and/or lander" [Lockheed, 1964]. MANNED ORBITER MISSION Missions that remain in orbit about Mars for 30 to 50 days and last for a total of 400 to 450 days require orbital departure weights of the

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Prospects for Manned Mars Missions 439 order of 106 kg. Based on a 90 per cent probability of the success of a single Saturn V launch—with the capability of 150,000 kg in Earth orbit, refueling requirements, and the number of different modules to be as- sembled in orbit—one would need to be prepared for twenty or more Saturn V launches to assure an 80 per cent probability of mission success (assuming operational nuclear engines). This has led to the conclusion that a launch vehicle much more powerful than the Saturn V is required for these missions—one with a capability of placing about 500,000 kg in Earth orbit. The following estimates are pertinent to reconnaissance missions. To map the planet with a resolution of 10 meters, a 4-bit grey level scale, and a factor of * for overlapping, requires 1.44 X 1013 bits [General Dynamics, 1963]. Assuming a storage capacity of 1000 lines/mm of film, the storage weight for data would be 8,000 kg (compared to total estimated weights of 50,000 kg for a Mars orbiter module and 25,000 kg for a Mars manned lander module). For complete transmission within 100 days at 2 cycles/bit, it would require a bandwidth of 3.22 X 106 cycles. This suggests the use of the crew for on-board data evaluation and selection. The following quotation from a Lockheed report enumerates some of the engineering difficulties that this, in turn, presents: "Feasibility studies on the system requirements for implementing onboard crew evaluation must include sophisticated estimates of re- quirements for rapid data-processing; storage and retrieval of refer- ence-frames (both prermission and post-orbit); automatic aids to the comparison of past and current reconnaissance shots and the cor- relation of many-source data; display/control techniques to integrate the crew into the man-machine loop; computer size to perform the access and retrieval function, as well as more complex calculations. Feasibility studies of the rapid reconnaissance-evaluation function— still problematic for giant ground systems—are still in the embryonic stage for onboard space-vehicle application" [Lockheed, 1964]. MANNED MARS LANDERS While some of the first studies indicated that manned landings would be feasible from the engineering point of view in the 1970's, the follow-on studies predicted a time period in the 1980's. These predictions require a post-Saturn launch vehicle with a capability of placing about 500,000 kg in Earth orbit, nuclear vehicles, and the development of improved multi- start rocket techniques. The cost estimates range from an $18.5 billion

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440 MARTIAN LANDINGS: MANNED calculation of General Dynamics [1963], which allows about $1 billion for a Mars excursion vehicle, to an Aeronutronic [1964] estimate of $40 billion. This last represented an extrapolation from a detailed study of a Manned Excursion Module with a 10 to 46 day capability for surface exploration and a two-man, 1000 kg scientific payload. The excursion module was estimated at a total cost of $6.16 billion for development and production and was projected as 10 to 15 per cent of the cost of total mission—giving $40 billion as the total mission cost. RELATIONSHIP OF MANNED MARS MISSION TO OTHER MISSIONS Disregarding any other issues, it is generally agreed that the engineering success of the Mars Manned Lander Mission demands extensive recon- naissance. In most reports this task is presumed to be carried out by un- manned spacecraft. Aeronutronic [1962] states: ". . . // is essential that probes be flown into the Mars atmosphere, that experiments be landed on the Mars surface, and that pictures of Mars be obtained with higher resolutions than currently available from the Earth. These efforts should use unmanned spacecraft and be conducted at the earliest opportunity. The availability of more precise data on Mars and the near Mars environment was presumed in the planning for MEM, but was not included in the estimated funds to accomplish the over-all MEM program." We have also the following statement from the TRW Space Technology Laboratories [ 19 64] : "A vital precursor for manned Mars stopover missions is the un- manned probe mission, which will obtain crucial data about the Mars environment, particularly the properties of the atmosphere. This information is urgently needed in establishing design criteria and functional requirements for the follow-on manned missions. In view of the rapidly expanding program of manned Mars planning studies, which is indicative of the increasing interest in interplanetary ex- ploration, steps should be taken to accelerate the precursor probe missions." The General Dynamics report, while emphasizing the need for recon- naissance, also points to the technological objective of "demonstrating the feasibility of manned flight from the activity sphere of our planet into that of the other" as another prerequisite for planetary surface exploration (Mars is considered the only planet for which this can now be seriously

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Prospects for Manned Mars Missions 441 planned). These two objectives can be combined, which ties the manned capture (non-landing) missions to Mars. This has the disadvantage of post- poning until the 1980's any extensive reconnaissance for any purposes— technological or scientific. As General Dynamics [1963] notes, by not combining them, "one is free to consider demonstration of the feasibility of a planetary capture mission by a flight to Venus. If this flight is success- ful, a repetition in the form of a fast capture mission to Mars appears not warranted." This has the advantage that the manned feasibility mission to Venus requires considerably less mass in Earth orbit and would be possible to implement at an earlier date than a Mars mission. It also frees early reconnaissance from the restrictions man imposes on these missions (for example, long stays in orbit or on the surface over several Martian seasons). An extensive general consideration of the Manned Missions and their utilization is included in Lockheed's Follow-On Study: "Deeper considerations . . . will raise additional serious doubts as to the usefulness of contributions expected from the manned nonstop trips. In fact, the fly-bys viewed in relation to other schemes of plane- tary exploration are seemingly characterized by their transient usefulness, and hence appear to be of sufficiently low import that their alleged contributions may be easily provided by the automatic probes" [Lockheed, 1964]. Nevertheless, they find need for a fly-by mission as a realistic "training" flight to serve as a bridge reaching from unmanned probes and manned near-Earth missions to the first manned planetary stopovers. They feel the fly-by should be considered in the mid-1970 time period to prepare for manned stopovers in the mid-1980's. In conclusion, unmanned automated orbiters and landers should be planned that can carry out the scientific exploration of Mars. Any desire for manned missions makes this more, rather than less, urgent. The reconnaissance requirements for manned missions are not likely to be in- compatible with the scientific objectives of unmanned missions and they impose similar requirements for sophistication. REFERENCES Aeronutronic Division, Philco, Ford Motor Company, EMPIRE Final Report, Dec. 21, 1962. Aeronutronic Division, Philco, Ford Motor Company, Summary Report: Study of a Manned Mars Excursion Module (U). Publ. No. U-2530, May 13, 1964.

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442 MARTIAN LANDINGS: MANNED General Dynamics/Astronautics, A Study of Early Manned Interplanetary Mis- sions. Final Summary Report No. AOK 63 0001, Jan. 31, 1963. Lockheed Missiles and Space Company, Summary Report: Early Manned Inter- planetary Mission Study, Volume 1. No. 8-32-63-1, March 1963. Lockheed Missiles and Space Company, Manned Interplanetary Missions; Follow-On Study, Final Report; Volume 1—Summary No. 8-32-64-1, Jan. 28, 1964. McGraw-Hill Book Co. Handbook of Astronautical Engineering, H. H. Koelle (Ed.), 1961. TRW Space Technology Laboratories, Manned Mars Landing and Return Mis- sion, Volume 1 (Summary). No. 8572-6011-RU-OOO, March 28, 1964.