A REVISION TO THE ROADMAP FOR THE ROBOTIC AND HUMAN EXPLORATION OF MARS:
A NECESSARY AERIAL SCOUT MISSION
A REVISION TO THE ROADMAP FOR THE ROBOTIC AND HUMAN EXPLORATION OF MARS:
A NECESSARY AERIAL SCOUT MISSION
Most Mars mission timelines propose to answer many science questions, including their stated highest-priority questions, did life ever exist on Mars, and does it exist now.
Is the currently proposed Mars exploration architecture the best suited to answer the first question? The answer is no, it is not. In the Phase 1 timeline as proposed, there is a deficiency that would most likely preclude the successful accomplishment of one of these major tasks. That task is, determining if life has existed on Mars in the past.
Some have argued that the main question should be whether potential life on Mars resulted from a second genesis. (McKay, 2001) While this may be true for academics and scientists in this field, it is not true for the general public. The general public, which will ultimately decide whether to fund decades-long projects on Mars, will for the most part be uninterested in the arcane findings of same or different structures of amino acids. Their main interest world wide is, did life on Mars exist, and does it exist now.
A case can be made that finding fossil life may be an even greater priority than finding present life. First, if life existed for a billion years, fossils would locally be quite abundant, in contrast to likely small remnants of existing life. This means an exponentially greater chance of success, and perceived successes by the general public are an absolute necessity in the decades ahead. Secondly, fossil remnants would provide a selection of different life forms as they evolved through time, providing a fascinating long-term study of the evolutionary process off-planet, in contrast to the simple yes/no answer to the second genesis question among potentially few survivors.
It is not a question of doing either/or. It is a question of what the priorities should logically be.
The current set of Mars missions is not optimized to discover Mars fossils in any reasonable time period. The task of finding past and present life have been lumped together as being quite similar, and requiring similar approaches. They are actually quite different tasks.
There is a fundamental misassumption being made that the best place to look for evidence of past life is where there is the highest probability of finding present life. This is an error. Current areas of aqueously deposited sediments containing underground water, thought to be areas with the best chance for finding existing life, are not the best place to look for evidence of past life.
Most researchers feel that we would find actual fossil evidence of past life on Mars in the form of stromatolites, fossilized remains of mats of single celled organisms. (McKay et al., 1992 ; Farmer, 1997 ; Des Marais, 1998) These, if they existed, would be present during the period several billion years ago when Mars was wet and warmer. They would have been deposited in layers in the then-current water sediments as the colonies built up, and became buried by geological processes.
Let us look at the places today on the Earth where we find fossil stromatolites. Most of the stromatolite finds in North America are known. Where do we find them? Most stromatolites are associated with Precambrian outcrops, one of the oldest rock formations known, which would be consistent with their being the oldest known organisms that have left a fossil record.
We find these Precambrian stromatolite-bearing outcrops in only a few places. They are almost inevitably in the very high mountains or in other areas where Precambrian rock is exposed. The most extensive stromatolite area in the U. S. is in the high mountain areas of Glacier National Park. (Fenton and Fenton, 1936 ; Rezak, 1957) Another significant area is the Snowy Range peaks of the Medicine Bow Mountains of Wyoming. (Knight and Keefer, 1966) Other finds are in the Northern Wind River Range, (Middleton, 2001) and in the Canadian Rockies and shield area (Hofmann, 1998).
Since stromatolites are the oldest fossils, they were laid down first, and are thus buried the deepest in the rock layers. Major mountain ranges upthrusted by plate tectonics fold these deep layers upward, where erosion wears off the overlaying rock, exposing sections of the deep Precambrian layers, and thus the stromatolites.
On Mars, major plate tectonics do not appear to have occurred. Thus the stromatolites lie where they were deposited, deep underground. The major place where they would be exposed would be in any deep penetration of Mars, such as the sidewalls of Valles Marineris, and the sidewalls of the deepest impact craters. Looking for ancient Mars stromatolites in the surface layers of water-deposited sediments would not be a good use of scarce resources.
Many places in the roadmap call for discovery driven science and missions. However, scientific investigation is somewhat different than discovery. And it is discovery that needs to take precedence at this time.
Let us look at how an Earth field paleontologist goes about discovering new findings. What they would do is go out into the field and cover the maximum amount of territory possible. During that time they would be actively looking visually for the forms of any fossils to be found. It is the form, the morphology, the shape, the topology of a fossil that defines it as a life form in the field, and it is by visual identification that one discovers it. In the discovery phase, the primary mode of operation is by visual identification.
Stromatolites are similar to other fossil forms in that they are very recognizable, especially with some experience. One discovers stromatolites by their gross physical features, which are very characteristic. Many specialists of course then do microscopic studies to characterize different species.
METHODS TO DISCOVER MARS STROMATOLITES
Slow Mars ground rovers will not be the most efficient ways to discover potential Mars stromatolite outcrops, especially given the probable location in vertical formations.
Below is given a potential Scout mission that would focus on the very important task of finding outcrops of Mars stromatolites. This should be a high priority mission as early as possible in the Phase 1 cycle. Putting high-value analytic and sample-return assets down on Mars prior to extensive high-speed surveys capable of detecting stromatolites would seem to be a very high-risk gamble with multi-billion dollar assets.
Orbiting imagers will not be able to detect the structure of such fossils. The current best asset we have, the MRO, has a resolution of 11 in. per pixel. We will probably never achieve the resolution needed for this task from orbit.
ARCHITECTURE FOR RAPID EXO-PALEONTOLOGICAL SURVEY OF MARS
This proposal is for a rapid robotic aerial survey of the Martian landscape with streaming of the data back to Earth and massive public participation in its analysis.
One would start with a high-resolution radar data base of the Martian topography. The data base would then be loaded into a flying platform capable of long duration Mars flight. This would be pre-programmed to systematically fly remotely over all areas of geological interest, such as up and down all canyon walls and around all crater walls, etc. This flying platform should be capable of sustained flight for up to one year, which obviously goes beyond our current or proposed capabilities in Mars flight.
This flying platform would take a series of overlapping very-high resolution pictures with the best state-of-the-art camera available. These would be streamed back to Earth in near real time. This would likely require an upgrade of our Mars satellite communications up-link capabilities which could be provided on the delivery vehicle.
The radar data from the Mars Global Surveyor's MOLA-2 (Mars Orbital Laser Altimeter) may be adequate. It has a vertical accuracy of <10 m., a surface spot size of 130 m., and an along-track shot spacing of 330 m. (NASA, 1996) If this is not adequate, perhaps it could be re-programmed for higher resolutions. If not, then a new surveyor would have to be put up.
A number of Mars airplanes are in development. Ames Research Center is developing the Matador, (Dino, 2006) which would fly for 45 min. before crashing. The Mars ARES flight vehicle being developed by Langley has a mass of 149 kg, a payload of 9kg, and an anticipated flight life of 1-2 hours until it crashes (Guynn et al., 2003).
This proposal would envision a plane with a somewhat larger payload, but with the capabilities for very long term sustained flight. One way to approach this problem is to mount a nuclear thermal rocket to an airplane. The propellant would be atmospheric CO2, which could be continuously replenished in flight. While CO2 is less efficient than hydrogen, it has the advantage of being free and available on Mars.
Dr. Robert Zubrin has demonstrated flight in a test plane using CO2 as a propellant and hot mass as a heat source. (Zubrin et al., 2000) This was simply a box of heated dense material. CO2 was fed through this hot mass and emerged through a rocket nozzle. The wing span of the test plane was a few meters wide. Film of actual test flight of this plane was shown at the 2005 Mars Society convention. In its most fundamental sense, this current proposal simply replaces Zubrin's test plane's box of hot mass, which of course has to be periodically reheated, with a box of nuclear material which will remain hot for a very long time.
The Peewee and others in the KIWI and NERVA series of nuclear rockets demonstrate the feasibility of using solid core nuclear heat sources to accelerate gas to obtain good flight characteristics. Particle Bed reactors have overcome some of the original problems with fuel rod erosion. (Pike, 2005) Dr. Stanley Borowski from the Glenn Research Center has been developing designs for a bimodal nuclear rocket for Mars space missions (Borowski, 2001). Currently the Pratt & Whitney Co. is developing the Triton, a trimodal nuclear rocket with a thrust of about 15,000lb or 66.7 kNewtons (Joyner, 2004). The proposed nuclear rocket for the Mars airplane would be 0.5% of this output. There was also a design called the Escort, which was a design based on the military requirements for a long-life, high-Isp propulsion system that could maneuver in orbit and defend and attack satellites. Its power was to be in the 500-1000 ft.-lb. range, so this design would be in roughly the size range needed.
The nuclear heat source for a Mars rocket-powered airplane could be a very simple straight-through design. There should be no requirements for complex electric power production, and controls could be very simple or even some eliminated, as this plane would fly continuously at a set speed for its mission lifetime. The wings would provide ample area to mount enough solar cells to power the compressor, pump, and electronics, thus obviating the need for complex hybrid designs.
Since this would be designed to run continuously without stopping once started, and with no throttling, the heat unit could perhaps be designed to give off just enough power to accelerate the gas thruster, and no more, obviating the need for radiators to radiate excess heat.
The development of a thermal nuclear rocket running continuously for a year would be several orders of magnitude longer than test runs of any past nuclear rockets, which have only been run for periods of under 1 hour. The main problem is with the erosion of the nuclear fuel assemblies by the hot gasses. However, Russell Joyner, Discipline Chief, Propulsion Systems Analysis of Pratt & Whitney said in an interview "..running at low temperatures where the reactor surface temperatures are running at 1600oK or lower versus with the propulsion mode running at 2600oK-to-2700oK there is significant (engine) 'life', we're talking years" (Behrhorst, 2004).
Thus, if these lower temperatures can be used for continuous aircraft propulsion in the Martian atmosphere, then engine life should be adequate. Another potential problem is nozzle embrittlement at these time lengths. However, embrittlement is normally thought of as a problem with H2 entrapment at grain boundaries. If CO2 does not exhibit this property, then this may not be a problem.
Shielding requirements could be kept extraordinarily low, as there would be no human contact with the robotic plane. A temporary shield could be fitted for launch, and jettisoned in orbit.
POWER DENSITY OF NUCLEAR FUEL
As the fuel expelled is continuously available, the real Isp to be considered is how many pounds of thrust are produced per pound of fissionable material. A common rule of thumb is that nuclear fissionable fuel contains a million times as much energy per unit mass as chemical fuel. In theory the Isp of a thermal nuclear rocket with continuously available gaseous fuel would be one million times the 450 sec. Isp of the best chemical rocket ( assuming 100% efficiency). Thus one lb. of fissionable material equals 5,208 days of 1 ft./lb's. of thrust.
The Ares Mars Airplane has a thrust/weight ratio of 1 to 24.6 . Thus for a 2000 lb Mars Airplane, this might require 81.3 lbs, or 361.6 Newtons of thrust. For this 2000 lb Mars airplane, one pound of fissionable material would equal 64 days of flight. For one year of flight this would equal approximately 5.7 lb. of fissionable material, assuming 100% efficiency.
Flying at night would require that enough CO2 fuel be gathered in the day to propel the craft through the dark hours. Alternatively, the craft could circle the planet every day, always keeping in the sunlight to power the compressor. At the Mars equator, the diameter is 21,360 Km. With a Mars day of approximately 24.5 Earth hours, it would have to fly at a speed of 872 Km/Hr in order to circle Mars in one Mars day. In the higher latitudes this would of course be reduced.
However, there is another potentially even simpler nuclear technology on the horizon. The U. S. Air Force is developing a nuclear propulsion system for drone aircraft that it is hoping will allow them to fly for months at a time. It is focusing on what they are calling a quantum nucleonic reactor. This obtains energy by using X-rays to cause particles in the nuclei of radioactive hafnium-178 to jump down several energy levels, liberating energy in the form of gamma rays, which could be used to produce a jet of heated air. (Graham-Rowe, 2003)
The original research was conducted by Carl Collins (Collins, 1999) and has been challenged by others in the scientific community (Schwarzschild, 2004; Weinberger, 2004). The Air Force seems willing to continue to investigate it, and if proven, would be a much lighter and simpler nuclear power source for a Mars airplane.
ANALYSIS AND OUTREACH
The main advantage of this program is that it would involve many thousands of people in a direct and personal way. All of the images produced could be put on the web. The public would then be encouraged to survey them, as there would not be enough scientists to adequately analyze all the millions of images. This would bring tremendous interest, enthusiasm, and ownership of the space program to millions of people all around the world. People could sign up for their own square km. of terrain to search. Anyone could literally be the first person to discover fossil evidence of life on Mars. A prize of a million dollars to the first person to spot a Mars fossil would of course add interest.
There could be stromatolite identification training sites and other support provided. Mars stromatolite identification training sites do exist (Thieltges, 2006)
Complexity Analysis has been show to be able to detect stromatolites through automatic searches, but it does require a high resolution image such as provided by this proposal ( Storrie-Lombardi, 2004a). Short wave infrared spectroscopy can identify potential stromatolite rock types, but not stromatolites themselves ( Brown, 2004 ; Storrie-Lombardi, 2004b)
This proposal could make very long-term flights on Mars feasible using nuclear heat sources. Once areas of high interest are discovered on Mars, then rovers and sample collectors can be dispatched to them, maximizing the effectiveness of the most precious resource, scientists' time on Mars.
This proposal maximizes the efficiency of data returned per time and money spent, as well as the very necessary factor of energizing public interest, enthusiasm and participation in future Mars and space exploration.
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