There are two main advantages of a human being located at the sight of exploration. The first is that humans are currently able to deal with a much higher flow of sensory data. From this data they are able to pick out the interesting features which they should explore. More importantly, when a person is able to directly manipulate and move around his or her environment, that person is able to build up a model of the world from which hypothesis can be constructed and tested.
The second advantage is the incredible strength of human dexterity and planning abilities. Once an astronaut has noticed an object that interests him, he is able to quickly walk over to it and do a quick examination. For example, when a geologist encounters an interesting outcrop of rock, he will probably smash off a sample, grab a chuck, and examine it up close. It would take a robot a long time to do these same tasks whether guided from Earth or running autonomously.
McGreevy and Stoker (1991) give a summary of what a geologist does in the field: "Geologic field work consists of highly integrated perceptual, cognitive, manipulative, and locomotion behaviors organized around a hierarchy of scientific goals and methods, and it is unlikely that automation and robotics will be able to replace this human capability any time soon. Thus, for missions beyond the mere rote gathering of rocks, that is, for planetary surface field work, human presence is required." The geologists they interviewed said, "`we smash a lot of rocks' to find a good sample." As a geologist explores, they "move through an environment and manipulate it at will, so as to come to understand it."
Another proponent of human exploration, Paul Spudis (1992), gives us some insight into what tasks humans are especially suited to over machines. He says that, "exploring a planet brings out the best in people and the worst in machines." He names three areas at which humans excel: "installing complex instruments, replacing equipment, and doing field work." One example Spudis sites is particularly enlightening: Soviet Luna 15, 16, 20, 24 missions to the Moon show that coring is very difficult for robots to accomplish. No complete cores were returned from any of these missions. However, with the Apollo missions, three attempts to obtain cores were made. Despite many difficulties, all three return the full 8 ft core.
The ability to improvise and improve the current situation is an important human strength that is often seen in Antarctic exploration. One recent example is with NASA Ames' Telepresence Demonstration Project. While the group was in Antarctica this year, they discovered they had an opportunity to try a telepresence link from near McMurdo base to Ames Research Center; something they had not planned to do until a year later. While they were on the ice, their field engineer was able to reprogram part of the system to allow for this new capability. The flexibility of these people allowed them to pull off something that they were not capable of when they left for the ice.
Now that we have gone through the strengths of people doing exploration, let us take a quick look at what are weaknesses of humans. The first problem is with the psychology of astronauts. These people are under a number of pressures: stress, danger, homesickness, and loneliness. These pressures can degrade the performance of a field scientist.
Secondly, there are some serious physical limitations of the human body. Every astronaut requires sleep and life support in order to stay alive. These requirements drive the development of any exploration system as can be seen with the SIMM habitat, SEV, and Mars suit which consume a major portion of the mass budget of the system.
Perhaps the greatest negative of a human presence on any expedition is the potential for loss of life. The US, in particular, is extremely upset at any loss of its astronauts, as evidenced by the explosion of the Shuttle Challenger. The loss of one of twenty micro rovers on a missions would undoubtedly be noted by the country, but would not cause a great public outcry.
Another set of advantages of robotics is that they can be made to be hardier that humans. It is possible to integrate radiation shielding and error correction to electronic components and structures can be constructed of materials not susceptible to break down from radiation. A feature of machines not currently available in humans is the ability to switch off components and hibernate. A lander could be programmed to sleep during the winter when solar power does not provide enough power to run the scientific instruments.
The last main set of benefits of machines is extremely useful to augment human capabilities while exploring. These are primarily things that humans can do, but machines can easily do better. An extremely simple example is a powered drill. It would take forever for an astronaut to hand crank a core into the surface, where as a powered drill can get a core in a comparatively very short time. On the computational side, machines are much better at crunching numbers and keeping records. An astronaut could write on a map and field notes any observations and measurements made, but a computer in the form of a geographical information system (GIS) could record this information and provide virtually instant access of any stored information to astronaut on an EVA. This would provide a much better system that frees up the astronaut from clutter and lets him focus on field work rather than note taking. Machines can also augment the sensory capabilities of humans by, for example, providing imaging in parts of the spectrum not seen by human eyes.
A solo robot working out in the field has a completely different perspective while doing field work. A teleoperated vehicle, in the simplest form, may not retain any information of the area it traverses. On the other end of the spectrum, the most complex autonomous vehicle will have detailed terrain models and a variety of other information on board, but the robot has little or no understanding of that information. All of the scientific work is done by humans located elsewhere. The autonomous vehicle has to either rely on simple reactive controls or it has to have a large computation capability since planning and decision making are such tough computational tasks.
Another draw back of robotic exploration is the limited dexterity of automated actuators (grippers, tools, and such) as compared to the human hand. This greatly reduces the flexibility of these systems. For example, a human is able to do simple repairs such as replacing fuses without much trouble as seen with the repair of the Solar MAX satellite by replacing three blown fuses. However, a robotic system must rely on redundancy and the cleverness of Earth based operators to remain operational. An example of this is the Galileo high gain antenna which is stuck partially closed. Operators have tried all sorts of tactics and maneuvers to dislodge the stuck ribs to no avail. The robotic spacecraft is able to continue its mission due to the redundant design of including a second, low gain, antenna which is currently working. On a human mission, an astronaut would be sent on an EVA to open the ribs by hand.
It is important that the cores are labeled and oriented properly for numerous reasons. For example, if the cores' orientations are not carefully marked then any paleo-magnetism or paleocurrent readings on the cores will be almost entirely useless. However, it is assumed that not all cores will be returned to either the base and/or to Earth. Some cores may be photographed, sampled, and then simply discarded.
On each mission the deployed stations will be left in the field. When a SEV returns from each mission, it will be reloaded with new deployable stations. Since there are a larger number of stations that can be carried on an expedition, they may be initially deployed in area near the main base. This will allow for detailed initial characterization of the seismic noise and weather patterns in the area of the base. Once the stations are needed, they can be picked up and taken on expeditions.
The basic weight has not been carefully studied, but the stations should weigh less than fifteen kilograms each. Additionally, their weight will depend on what instruments are added to each unit on top of the basic design. They should be designed for a long duration life span so they can be used in conjunction with a number of different experiments and extend the global Mars network survey.
One possible setup, that has not as of yet been considered for use on Mars, would be to add the capability to date rock grains. This technique uses a laser to vaporize a series of individual grains. The Argon released is measured in a mass spectrometer for K/Ar dating. The biggest limiting factor is the power output of the laser required - to do effective dating, at least 5-7 watts, non-pulse is needed. Currently such technology is available in a size that is suitable for use in one of the SEVs or the SEV trailer, but it needs to be space qualified for use on Mars. Also, if as in several other proposed Mars missions, there is a nuclear reactor present, then it may be possible to do Ar40/Ar39 dating.
Mapping Analysis Acquisition Mapping Board Handlens Rock Hammer Laser Rangefinder Hardness Tester Tongs Clinometer Color Chart Scoop Magnet Sample Bags Element Analyzer Sample Containers Temperature Probe Still Camera Video Camera GnomonFIELD PORTABLE TOOLS TABLE 2.3.2.4.6-1
Mapping (subsurface) Analysis Acquisition Ground Penetrating Radar X-ray Fluorescence Coring Drill Seismic Multispectral Imaging Core Drive Tubes Penetrometer Shovel and Pick Sample Scale SawFIELD TRANSPORTABLE TOOLS TABLE 2.3.4.4.6.2
The SEV makes a strong base of operation for a GPR system. When the vehicle is stationary or moving very slow, the system is able to "stack" multiple soundings to remove random noise from the data. This is a very effective technique and is used extensively. While the vehicle is moving, the system will not be able to stack as many echoes but it will still be able to provide a good view of the subsurface. This has been proven with radars mounted on helicopters that are flown over glaciers and one van has been outfitted to survey roads.
Before construction of the base, the astronauts will have to survey the area for the best site on which to located the habitat structure. A subsurface void that went unnoticed could pose a major hazard to the crew. Collapse of a ground void under the habitat would probably compromise the integrity of the many seals. The people in Florida who build their homes over limestone caves that collapsed to form sink holes would probably concur that this is a major concern! A second problem, which is less dramatic, but still just as important is soil compaction. GPR can be used to make a three-dimensional survey of soil porosity so we can predict how the regeolith will react to loading from structures. Therefore it is imperative that the SEV is used to make a detailed survey using GPR and its coring device to ensure the stability of the habitat.
The search for voids may possibly be extended to the moving SEV. If the SEV had its GPR antenna mounted on a boom out in front of the vehicle, the crew could monitor the GPR data real-time on a digital strip chart as they traverse unknown dangerous territory. It is not know how stable the martian surface is and this could be a major hazard for the crew. A system like this has not been tried but it is a strong possible application.
The most advanced GPR system in general use is the pulseEKKO III system made by a Canadian firm. It was developed under funding of the Canadian Geologic Survey. The pulseEKKO III has a total system weight of 22.25 kg and is carried around in a wheel barrow. (Ref. Annan and Davis, 1992) This weight includes three antennas that cover 50, 100, and 200 MHz. This system does not use the latest in technology and is not an integrated system so a GPR system for martian exploration will most likely be in the in the 5 to 10 kg range for a much improved system. From the experience of field use of this system, it has been concluded that "GPR data provide ... excellent sedimentological information, which has been used to evaluate raw materials potential of different types of land forms." (Ref. Sutinen, 1992) Even using this system, it is possible to rapidly survey an area. For example, using this system carried by hand, a 8 km line was surveyed in about 6 hours (Ref. Dallimire and Davis, 1992).
GPR systems have already begun to show their value. From space shuttle based radar soundings, scientists were able to discover an underground river, roads, and a lost trading city. In the northern Canadian territories, GPR has been used to help understand massive ground ice and how it interacts with other rock units (Ref. Pilon, Allard, Seguin, 1992). And finally taking GPR up to high frequencies and ranges of several meters, it has been possible to detect fractures up a few millimeters thick within rock (Ref. Davis and Annan, 1992).
The camera should be mounted up high on a roof top mast to give the best view of the SEV and surrounding areas. Together with a strong telescoping lens system, the astronauts will be able to gain a large amount of useful information about areas that they were only able to travel near, thereby greatly increasing the value of the SEV expeditions. The mast will allow the people inside the SEV to get a bird's eye view of any work they are doing with the robotic manipulators that are mounted on the front of the vehicle.
There are two choices for the imaging. The first is a binocular system, which allows for the SEV to be easily used in a telepresence mode when desired. Range information can be calculated by comparing the location of an object in both images, which can be done automatically by the on-board computer. The monocular system main advantage is that it provides a savings in weight and complexity. A monocular system is still usable for telepresence but may be more fatiguing to the human operator.
A laser range finder running in parallel with the video camera(s) is extremely important. This will allow the SEV crew to quickly build up a high resolution geologic map containing the location of the data or observations taken. The laser range finder will also allow distances to be overlaid on images of the terrain to assist the SEV crew in planning their route over the martian surface and help them to keep in their size perspective straight in this foreign world.
There is one major concern with doing searches for organic molecules from the SEV that needs to be considered. The presence of humans inherently contaminates almost every surface of the SEV with organic contaminants: from single molecules, cells, and bacteria and small critters. This is a major concern which must be addressed but it does not preclude trying to do these kinds of experiments, just that caution should be used in interpreting these results.
The petrographic microscope is used to look at the light transmitted through a "thin section" of a rock. In order for this technique to work, the samples must ground down and finally polished to a 30 to 40 micron thickness. The first step in this process is to use a rock saw (basically a diamond saw or equivalent) to cut a sample down to about 1.5 x 3 x .5 cm block. This saw is also listed as one of the field tools. It will most likely require a cooling system if it is operated within the SEV lab area, but it should not be used inside the SEV due to the dust and general mess that it would create. If the SEV's atmosphere reacts with the samples, then most of the samples will have to remain within the sample boxes in a Mars atmosphere.
Noise is one of the major impediments to getting good seismic data. There are several sources of noise in the Earth. The worst problem is with people and traffic. Crews usually have do their work at night to reduce this problem. On Mars, the only human source of noise is from the operations of the base and the six astronauts so this is not a big concern on Mars. A global source of noise on Earth is the oscillations of the oceans. It is 7 to 14 Hz noise that is even detectable in the highlands of Tibet. Again, there are no oceans on Mars and the tidal effects of the Phobos and Demos are very tiny. A final big problem is with wind. It is especially prevalent if a detector is only laying on the surface and not on a spike or buried. Wind should be the only big problem for Mars. Even this problem is greatly reduced by the lower atmospheric pressure. Due to the lower pressure, the wind on Mars will exert a force equal to that experienced on Earth with a wind that is approximately 10% of the Martian wind speed. Therefore, on Mars the biggest limiting factors are the number and quality of the detectors and the strength and control of the seismic sources.
In addition to the network of seismic detectors that should be in place from a variety of Mars precursor missions, the SEV will lay its own set of detectors. The primary detectors will be a line of geophones that are deployed and retrieved from an SEV. Optimally, on Earth, a crew will lay a cable of 120 detectors over 6 km. The geophones weigh a few pounds each. The cable weighs about 60 lb. for 500 meters. (Ref. Klemperer, 1993). This is not a realistic system for use on Mars. Another option is to lay out boxes containing a geophone and a timer. The timer will turn on the device at a time just before the test and store the data. After the sounding is done, the devices are then be picked up and the data is downloaded to the SEV. In addition to the string of geophones, the seismic profiles will rely heavily on the stations deployed from the SEV on excursions which are equipped with high quality seismometers. In order to keep all of these instruments exactly sinked up, the MACS satellite needs to provide a timing signal to all of the seismic stations and the SEV.
There are a several choices for seismic source pulses. The simplest method is to hit a spike into the ground with a good sized sledge hammer. This is very cheap and easy, but is only able to sense about 100 meters below the surface. This is the system that will be used on the first SEV excursion. The next level up in imaging ability is a weight drop system. The SEV will drop a large mass of about 100 kilograms from a height of a meter or two. On Earth, the drop tube is pumped down to a low pressure. The atmospheric pressure on Mars is low enough that there should be very little drag on the falling mass. Unfortunately, the lower gravity will give the falling weight much less energy. This system can be augmented with an electromagnetic accelerator if there is enough power available on future SEVs.
There are two additional methods which are much harder to do on Mars but have much greater ability to image deep within the martian crust. These are "Vibroseis" ¨ and explosives. Vibroseis involves vibrating an entire vehicle on a pad at a variety of frequencies between 8 and 40 Hz. The problem with explosive charges is that the charges have to be placed at least 5 to 10 meters below the surface and the explosives are a heavy expendable. These two systems, are able to image to much greater depths: a 50 kg shot on Earth can image up to 70 km down into the Earth's crust. With much larger shots, it is possible to image up to about 200 km horizontally.
Finally, Mars itself provides a fantastic and free seismic source to image the internal structure of the planet: marsquakes. This should be a focus more for non-human missions.
The initial system will consist of about 10 to 20 geophones and the source which will be a sledge hammer struck on a stake. The sounding will only attempt to image the top 100 meters of the surface. As the human missions to Mars continue, more geophone units will be brought to strengthen the line. Additionally, a weight drop system will be added to one of the vehicles to provide an improved seismic source.