Date: Fri Aug 27 1993 13:51:02
From: Anson Kennedy
Subj: Mars Observer PI #1 1/
The following is the first of three articles posted to USENET's
sci.space 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
From: email@example.com (Mike Malin)
Subject: MOC PI Comments: Face on Mars (Long)
Sender: firstname.lastname@example.org (USENET News System)
Organization: Mars Observer TES Project, ASU, Tempe AZ
Date: Sat, 21 Aug 1993 19:19:09 GMT
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.
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
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
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.
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).