Unmanned Exploration of Venus and Mars with Voyager Spacecraft Systems
Dr. Robert Duncan-Enzmann, ca. 1960
The writers and their staff have just completed a program to guide the unmanned exploration of Venus and Mars and designed space vehicles to accomplish the variable missions of the Voyager Experiments. The program for unmanned exploration has taken full cognizance of the facts that new data concerning Venus and Mars will be available before any Voyager flights are undertaken, that booster capabilities are variable, that each experiment will influence the subsequent, that scheduling at the launch complexes narrows launch windows to approximately 30 days, and that instrumentation will be improved between initial design phases and design freeze. Strong emphasis was placed on mission planning at AVCO, and planning was integrated with spacecraft design. It is felt that the methods of planning (a priority matrix optimizing boosters available, launch windows, instrumentation, conditions on Mars & Venus, and information desired by the scientific community) will remain valid and helpful when the program is funded.
Vehicle design, scientific mission analysis, and cost planning at AVCO were guided by the three voiced priorities of NASA:
1) Environmental protection of Mars & Earth
2) Geological/geophysical studies
3) Preparation for manned landings (possibly the EMPIRE Missions).
These are given in the current order of importance. They have been subdivided into areas of study or disciplines and weighted as explained in the text.
Earth to planetfall trajectory, type of planetary capture, and landing site selection have been guided by three considerations which are:
1) The voiced priorities of NASA
2) Observational detail concerning Venus and Mars
3) Equipment available at a particular launch window.
The above indicates that the timing of the missions is important and that not only do the above considerations influence an exploration program, but also the times of launch and conditions on the target planet. When all these items, with conditions on the target planet, are considered in the priority matrix, an exploratory program is the result.
Voyager Program: AVCO is one of the contractors who was given a study contract. The company’s point of view is that the space vehicle is the means of accomplishing the end of unmanned exploration of Venus and Mars. In the case of Mars, efforts have been directed toward preparation for eventual manned landings. In the case of both Venus and Mars, both vehicles and exploration have been designed with the view of optimizing the end result with a minimum expenditure of time, equipment, and types of experiments. Voyager is envisioned as a post-Mariner effort, and the study is therefore designed to be modified by new information from Mariner and other means of observing Venus and Mars.
Voyager Spacecraft: The spacecraft for the Mars and Venus explorations are modifications of a single basic design, the only marked differences being in the construction of the landers. In the case of the Venus craft, the landers have been modified to serve as atmospheric probes for the initial expeditions and to survive under extreme environmental conditions during later expeditions.
Booster Equipment and Launch Windows: Spacecraft design has been limited by weights dictated by launch windows (times of optimum transfer), the current state-of-the-art instrumentation, battery and radioisotope power supplies, communications and command links, reentry heat shields, protection of the craft in space from thermal stresses and meteoroid impacts – in short, everything that places a weight penalty on the booster. It might be thought that greater propulsive force would broaden launch windows. However, this is not necessarily the case. A thirty-day window is dictated by scheduling needs at the launch pads as well as trajectory considerations.
Mission Profiles: The Venus mission is complicated by more difficult thermal problems: microwave mapping problems from the orbiter, the overwhelming atmosphere of the planet, and consequently, reentry problems with surface survival and communications difficulties. The Mars mission is complicated by sterilization problems. This has dictated the bus and lander trajectories, placing the orbiter on fly-by trajectory, which is computed to be stable for fifty years, making it possible to leave the orbiter unsterilized.
Orbiter-Lander/Probe-Configuration: The configuration is flexible and concurrently allows for use of much equipment for flights to both Venus and Mars. It is possible to use orbiters with probes or landers, orbiters with multiple landers, or a bus with multiple landers. The multiple configurations have been selected so that adaptation may be made as information from Mariner and early Voyager flights is returned.
Orbiter Bus: Unsterilized transport vehicle, first-line communications, planetary mapper & observer, space experiments.
Atmospheric Probes: To study atmosphere of Venus in particular, to prepare for later expeditions.
Landers: The design for Venus and Mars differs radically. Detailed information, works on principle of multi-measurements which support multi-disciplines assigned on theory of geomorphic provinces, and
cyclic changes that may be generated by organisms, provision for bio-pack with animals born by Cesarean section for study of possible pathogenic organisms as final step before manned landings.
Atmospheric Considerations: Schilling atmosphere designs (maximum), Kaplan atmosphere (minimum), planning is directed toward minimum atmosphere. Explain M/CDA vs VJ/CDA for reader.
Communications: DSIF-Loop, Lander to Orbiter Link (Venus & Mars), Lander directional antenna, Lander semi-omnidirectional antenna (in case of failure of erection)
Guidance & Orientation: Guidance to Mars, to the landing spot, into orbit, Orientation of the lander on the surface, and the orientation of TV photographs from the orbiter (Venus and Mars).
Reliabilities: Brief comment on reliabilities of fractions of the missions. This may be tabulated on a list that is similar to that outlining the missions in the introduction. The “total” will give the reliability of the entire mission.
Mission Objectives: This article is, in a sense, written in the reverse order in which Scientific Mission Analysis and Voyager Design were done. In planning, the broad priorities of NASA were tabulated and then subdivided into disciplines. Most-wanted questions were asked in each discipline. The questions were then reduced to measurements, with priorities assigned to each measurement by each discipline. The measurements desired, the ranges desired, and the priorities were placed in a matrix. This was then used to select instruments. It is thought that when the program is funded and plans are being made to launch Voyager Craft that, a similar matrix could be “fed” by the interested scientific community. The writers wonder, however, just how the scientists should be weighted. Perhaps they could judge each other! Perhaps views will coincide closely enough to make this unnecessary.
Some of the most wanted information for environmental protection, facilitation of later expeditions, and scientific purposes:
Environmental Protection: Is there life on Mars? What is its origin? What characteristics, and is it dangerous, useful, or functionally indifferent to mankind and Earthly life?
Later-Expeditions: Characteristics of the atmosphere of Mars and Venus. Surface environment of Venus and internal structure. Can H2O, H2, O2 be secured on the surface of Mars?
Scientific Interest: Has the surface of Mars been shaped by meteor impact with slight changes due to erosion? What is the internal structure and how much energy is produced inside the planet? Have ice ages been manifested on Mars? What characterizes its atmospheric circulation? What characterizes its exosphere, ionosphere, cosmic ray flux? What is the geological history of this planet? Of Venus?
A methodical program includes design of the spacecraft about the scientific questions that need to be answered. The questions answered will both provide an encyclopedic background concerning Mars and Venus and provide necessary information for later manned expeditions or permanent stations.