Date: Fri Aug 27 1993 13:51:02 Subj: Mars Observer PI #1 1/ SKEPTIC - The following is the

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Date: Fri Aug 27 1993 13:51:02 From: Anson Kennedy Subj: Mars Observer PI #1 1/ SKEPTIC ------------------------------- The following is the first of three articles posted to USENET's newsgroup by the Mars Observer Principle Investigator. In them, he addresses the criticisms Richard "Mars Face" Hoagland has been raising in the media recently. These should provide good ammunition for anyone who is debating Hoagland groupies. --- Anson Newsgroups: Path:!netcomsv!decwrl!uunet!!asuvax!ennews! From: (Mike Malin) Subject: MOC PI Comments: Face on Mars (Long) Message-ID: Sender: (USENET News System) Organization: Mars Observer TES Project, ASU, Tempe AZ Date: Sat, 21 Aug 1993 19:19:09 GMT Lines: 194 This posting is from Mike Malin, Principal Investigator of the Mars Observer Camera, in response to the net discussions that have been going on during the past two weeks. Please do not respond to the e-mail address above. My only link to the network is through this third party and I don't want them deluged with replies. I do read the net occassionally and will try to respond when time and interest permit. Topic: Observations of the "Face on Mars" and other such "Things" by the Mars Observer Camera There have been a lot of questions about whether or not the Mars Observer Camera (MOC) will observe the "Face on Mars" or other features in the Cydonia region on Mars. This note will (try) to describe what we are going to do and why. BACKGROUND For those of you not familiar with the topic, several Viking images show features on the surface of Mars that, in the eyes of some people, resemble "faces," "pyramids," and other such "artifacts." The most famous of these is the "Face on Mars" and associated features "The City," "The Fortress," "The Cliff," "The Tholus," and "The D&M Pyramid." A fairly substantial "cottage" industry has sprung up around these features, with several books having been written about them, newsletters published, public presentations, press conferences, and, of course, National Enquirer and other "tabloid" published reports. The basic premise of these people is that the features are artificial, and are messages to us from alien beings. Their tack is to say, "These should be rephotographed by Mars Observer, since with high resolution we should be able to PROVE that these are artificial. If these are in fact artificial, this would rank as one of the greatest discoveries in history and thus every effort should be made to acquire images." Evidence cited as presently "proving" these are unnatural landforms include measurements of angles and distances that define "precise" mathematical relationships. One of the most popular is that "The D&M Pyramid" is located at 40.868 degrees North Latitude, relative to the control network established by Merton Davies (the RAND scientist who has been more or less singularly responsible for establishing the longitude/latitude grids on the planets) to an accuracy (actually, a precision) of order 0.017 degrees. They point out that 40.868 equals arctan (e / pi); alternatively, one of the advocates notes that the ratio of the surface area of a tetrahedron to its circuscribing sphere is 2.72069 (e = 2.71828), which, if substituted for e in the above arctan equation gives 40.893 degrees, which is both within the physical perimeter of the "Pyramid" and within the above stated precision. Other mathematical relationships abound. The advocates of this view argue that "no scientific study of these features has been conducted under NASA auspices" and that NASA and the conservative science community are conspiring to keep the "real" story from the American public. The conventional view is that this is all nonsense. The Cydonia region lies on the boundary between ancient upland topography and low-lying plains, with the isolated hills representing remnants of the uplands that once covered the low-lying area. The features seen in these mesas and buttes (to bring terrestrial terminology from the desert southwest to bear on the problem) result from differential weathering and erosion of layers within the rock materials. The area is of considerable importance to geologists because it does provide insight into the sub-surface of Mars, and to its surface processes. The measurement of angles and distances seems so much numerology, especially when one understands the actual limitations in the control network (of order 5-10 km, or 0.1-0.2 degrees) and the imprecision of our corrections of the images (neglecting, for example, topography when reprojecting data for maps) on which people are trying to measure precise angles and distances. Even given accurate data, however, most science does not depend solely on planimetric measurements, even when using photographs. There are many other attributes used to examine features that don't work for these things. No one in the planetary science community (at least to my knowledge) would waste their time doing "a scientific study" of the nature advocated by the proponents of the "Face on Mars is Artifical" perspective. To provide you with an idea of the magnitude of this issue, consider that I spend roughly a quarter of my time these days trying to prepare thoughtful answers to (often abusive) letters from people who analyse every word in every sentence in every paragraph in every letter I have written on the subject (they send copies of my letters to each other and exerpt them in their newsletters). They see innuendo and hidden meaning everywhere. I also have it on first-hand authority that at least 2 NASA Headquarters managers spend similar amounts of time responding to letters sent over from Congressmen whose constituents write about "The Face" and to which NASA is obligated to respond. THINGS LIMITING MARS OBSERVER CAMERA OBSERVATIONS Before I discuss the observations MOC will make of "The Face on Mars," some facts about the camera and its ability to look at specific locations are needed. 0. The MOC is body fixed to the spacecraft. It has no independent pointing capability. It makes pictures the same way a fax machine does (i.e., the scene is moved past the single line detector). 1. Cross-track Field of View - The MOC has a very small field of view (0.44 degrees), which is about 3 km from the 400 km orbital altitude. It typically takes very small images at very high resolution (lots of data). Anything wider than 3 km cannot be imaged in its entirety. 2. Along-track Field of View - The MOC's downtrack field of view is limited by the amount of data that will fit in its buffer (about 10 MB). If one uses the entire buffer (which is not likely to be completely empty unless its planned to be) and 2:1 realtime predictive compression, this translates to a downtrack image length of about 15 km. We've designed the camera to be able to average pixels together to synthesize poorer resolution, which frees up data. Under the best case buffer availability, an 8X summed image would be 3 km wide (but only 256 pixels across) by 40960 pixels long which, at 12 m/pxl (8 X 1.5) would be almost 500 km long. 3. Pointing Control Instability - The spacecraft uses IR horizon sensors for in-orbit pointing control. Owing to variations in the IR flux of the horizon with latitude, season, surface topography, atmospheric dust content, cloudiness, and other meteorological and climatological conditions, the control capability is about 10 mrad (0.6 degrees = 4 km), which is larger than the MOC field of view. 4. Spacecraft Position Uncertainty - The position of the spacecraft is determined by radio tracking for 8 hours (roughly 4.5 hours of actually seeing the spacecraft) a day, and by computing the position of the Earth, Mars, and the spacecraft in an inertial coordinate system. It takes a few days to do this, and to use it to determine where the spacecraft will be a few days later. By that time, gravity perturbations, atmospheric drag, and autonomous momentum unloadings will have changed the orbit. Error studies suggest that the uncertainty seven days after the end of a given orbit can be represented as a 40 second uncertainty in the time the spacecraft will be at a specific point in its orbit. This translates (at the orbital rate of the spacecraft projected on the ground of 3 km/s) to 120 km downtrack and (because Mars rotates at 0.24 km/s at the equator) 9.6 km crosstrack. At 40 degrees latitude, the crosstrack uncertainty is 7.4 km. 5. Non-inertial Position Uncertainty - The position of the spacecraft is determined inertially. As noted above, the position of the longitude/latitude grid is also uncertain to about 5-10 km. 6. Orbit Spacing - If, in spite of the preceding, orbits were equally spaced, then the average spacing of orbits at the equator for the 687 day mission would be about 2.5 km, which means that each spot on the equator will fall within the MOC field of view in (possibly) two images. In fact, the repeat distance is just over 3.1 km, again assuming equal spacing, and it is more than likely that each spot on the equator will only be seen once. At 40 degrees latitude, the spacing is roughly 2.4 km, and any location will be seen, at most, twice. Given Items 1-5, it is most likely that some places will be overflown twice, and others not at all, and that our ability to predict this is very limited. We are attempting to address some of these issues with, for example, optical navigation. This could reduce the spacecraft position uncertainty by perhaps a factor of five or more. We will try to create a new control grid with higher precision (perhaps as good as 1 km). But we cannot do anything about the orbit spacing or the pointing control or the width of the MOC field of view. Thus, hitting anything as small as a specific 3 km piece of the planet is going to be very difficult. And what about the fact that Mars has a very dynamic atmosphere? The one orbit we fly over something of interest, it may be cloudy, or dusty. SO, WHAT ARE WE GOING TO DO Despite providing a number of people involved with the "private" studies of the "Face of Mars" with exactly the same information I've just noted, they continue to think I am purposefully avoiding taking the picture they want. They are very concerned that the MOC is being run by a company and that I will try to ransom or profit from the "important" data (as if they are not). And talk of conspiracy is everywhere. But it isn't the case: if we get a picture of "The Face," we will most definitely release it. "The Face on Mars," "The City," "The Fortress," "The Cliff," "The Tholus," "The D&M Pyramid," etc. are in our target database (now they want detailed copies of that binary data base!). We will try to get pictures (its almost impossible not to try to take the pictures, since the data base and initial targeting effort is fully automatic). Of course, given the factors noted above, I'd be stupid to tell people we were definitely, without doubt, and postively without uncertainty going to get a picture of any of these things. For one thing, they would then cry that I was hiding the picture if in fact we never got one. So my approach has been not to promise anything, which of course gets me in trouble, too. BOTTOM LINE: We will try. We more than likely will not succeed. There is no conspiracy. We are not ignoring the problem (just the people, who are making a real nuisance of themselves).


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