VICE PRESIDENT’S COLUMN The next few months include a number of opportunities for SSI members to get together and learn more about the work that we share. As you know, in May of this year SSI and Princeton University will hold the eighth of our series of conferences on Space Resources and Space Manufacturing. As a supporter of SSI’s research, you are invited to participate in this event. These conferences are “where the action is” in the field of Nonterrestrial Materials Research. The people who are shaping the future of space development present their work here and there is a resulting excitement that’s hard to describe. Because we are limited to about 200 participants it’s a good idea to make your plans early. Drop us a note if you would like a registration packet. It has been three years since the SSI Expedition to Cape Canaveral and the Epcot Center. One of the highlights of the trip was a seminar on the basic principles of spaceflight. On March 27, 1987 Captain Edward Daley and I will present a more detailed one-day seminar on basic spaceflight as a part of the Sixth Space Development Conference in Pittsburgh. SSI is a co-sponsor of this conference which is an annual production of the L5 Society (soon to merge with the National Space Institute). Dr. O’Neill is scheduled to give the keynote address at this event. The theme of the conference is Return to the Vision. If you would like further information on this conference or spaceflight course, please contact us. SSI Bulletin Board Experiment The Institute now has an experimental computer bulletin board set up at our Princeton offices. The board contains information about SSI research and other activities. The phone number of the board, which operates evenings, nights and weekends, is 609-921-7079. The System Operator is Mr. Derek Fields of Princeton. This board supports several “conferences” or special message areas such as External Tanks Research, Lunar Development and Support Teams. We look forward to your experimenting with this new communications tool! Gregg Maryniak GUEST COLUMN Dr. James French, former Senior Technical Manager at the Jet Propulsion Laboratory, is currently Vice President of Engineering for the American Rocket Company of Menlo Park, California. PART n Continued from Jan/Feb issue of UPDATE LOW-COST LUNAR POLAR MISSIONS by J. R. French In searching for deeper subsurface volatiles, as discussed in the previous issue, a radar sounder would be required. A relatively low frequency (e.g. L-band/VHF or HF) is required to penetrate rock or regolith. A radar operating in L-band, carried by the Space Shuttle, was able to distinguish ancient river beds and other geological features buried beneath the sands of the Sahara desert. The radar flown on the Apollo mission operated in three frequencies in the VHF and HF bands (Ref. 6). A radar for probing beneath the Lunar surface would be much less sophisticated than the Shuttle-borne system, lacking imaging capability. A system more like the Apollo system would be able to provide depth profiles of reflective layers which might represent liquid water. The preferred survey orbit for missions of this type is polar (90 degrees inclination to the equator). While an orbit of this inclination is mandatory for a survey of the poles in any case, it has the additional advantage of providing a complete survey of the Moon since the orbit plane is essentially fixed in space while the Moon rotates beneath it as it proceeds in its orbit about Earth. Thus at the end of one lunar period (approximately 28 days) the orbit will be passing over the same features as it was at the beginning of the period having moved over the entire Moon (as viewed from the Moon) during the intervening period. Since the gamma-ray spectrometer accepts radiation from whatever is in its line of sight, its resolution of areas on the Moon is a function of orbital altitude. The lower the orbit, the better the resolution. This is limited however by practical considerations. Even though the Moon has no atmosphere to cause orbital decay, low orbits tend to be unstable because of the Moon’s slightly irregular shape. This deviation from a perfect sphere will perturb the orbit significantly and will eventually lead to impact unless propulsion maneuvers are conducted to trim the orbit. How low an orbit is used depends upon how frequently the project management is willing to interrupt data taking for maneuvers, how much propellant is carried, and the accuracy with which the orbit can be monitored. All this is a suitable subject for study and tradeoff once a project is underway. As a strawman value however, an altitude of 50 km might be reasonable. This altitude yields a field of view of about 800 km in diameter which is essentially the horizon to horizon distance on the Moon from that altitude. Gamma-ray spectrometers have been flown in Lunar orbit on the Apollo missions. Those missions however were confined to low orbital inclinations and thus no high latitude or polar data was obtained. A polar orbiting mission was considered as part of an extended Apollo program but was not funded. An interesting possibility is the addition of an X-ray detector to the instrument. The two detectors can share much of the same electronics and are complementary in detection capability. For the mission, the instrument requires an accumulated observation time over a given point on the surface of about 10 hours in order to collect enough data to begin to resolve (continued on page 2) THE HIGH FRONTIER® NEWSLETTER VOLUME XIII ISSUE 2 MARCH/APRIL 1987 SPACE STUDIES INSTITUTE RO. BOX 82 PRINCETON, NEW JERSEY 08540 Low cost Lunar Polar Probe searching for frozen volatiles. Copyright 1987 Space Studies Institute
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