Nasa Grant Ngr33-011-009 Final Technical Report
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NASA GRANT NGR33-011-009 FINAL TECHNICAL REPORT FEASIBILITY STUDY FOR THE USE OF A YF-12 AIRCRAFT AS A SCIENTIFIC INSTRUMENT PLATFORM FOR OBSERVING THE 1970 SOLAR ECLIPSE Prepared for Headquarters National Aeronautics and Space Administration Washington, D. C. 20546 Robert D. Mercer Principal Investigator September 18, 1973 The Dudley Observatory 100 Fuller Road Albany, New York 12205 Abstract This is the Final Technical Report on NASA Grant NGR33-011-009 entitled, "Feasibility Study for the Use of a YF-12 Aircraft as a Scientific Instrument Platform for Observing the 1970 Solar Eclipse". The study was successfully completed in the fall of 1968 with a presentation to the Office of Solar Physics at NASA Headquarters and with the submittal of supporting scientific and technical reports. That information indicated that a YF-12 or SR-71 type aircraft could be instrumented with several cameras and a ten-inch, f/43.2 telescope feeding spectrographic and photometric systems for measurements of the solar corona and chromosphere. Spatial resolution radially across these regions as low as twenty-five kilometers might be achievable. Total time for observations could be as long as ninety minutes with most of that time spent above ninety percent or more of the atmosphere. A recommended schedule for aircraft instrumentation and flight check-out was given at the presentation in 1968. Representatives in the office of the Assistant Secretary of the Air Force for Research and Engineer- ing, who controls operations for these aircraft, tentatively approved these plans. No official costs were made available to the Principal Investigator (PI), but such an undertaking was acknowledged to be expensive with estimated costs in the one-to-six million dollar range. As a result of funding constraints on NASA at that time and lack of success by the PI in his efforts to elicit additional financial support from other interested agencies, the results of this feasibility study could not be utilized. However, the study also included a short assessment of feasibility for all solar eclipses through 1981. The solar eclipse of 1977 in the northeastern Pacific Ocean was shown to be equally as useful for YF-12 or.SR-71 aircraft observations as the eclipse of 1970. This Final Technical Report together with its references will review the scientific and engineering findings of the study as presented in late 1968. Background In the winter of 1967 Mr. Robert D. Mercer, then an officer in the U.S. Air Force, made an approximate check on the velocity of the lunar umbra as it would travel over the earth during the solar eclipse of 1970., He found the minimum velocity to be about 1300 knots with the shape of the velocity curve approximating the function for the derivative of the arcsin. For almost a two hour period, using the minimum velocity as a midpoint, the speeds would be below 2000 knots and deceleration/acceleration would not exceed 1.0 ft./sec. This velocity/acceleration profile was well within the capability of several new military aircraft then flying. It not only seemed possible to follow an eclipse for a considerably longer time than would otherwise be possible using scientifically outfitted aircraft, such as the NASA Convair 990, but it also appeared feasible for the first time to move within the umbra, particularly along its boundary. This latter capability could permit study of the chromosphere for tens of minutes instead of only ten to twenty seconds. Furthermore, the high altitude capabilities of these fast military vehicles would open up telluric passbands where data had been excluded to previous observers, expecially in the infrared which is badly attenuated by atmospheric water vapor over large spectral regions. The first aircraft considered for this work was the XB-70A, the test version of a supersonic bomber completing its schedule of flights for the Air Force. However, discussions with Col. J. Cotton, the chief test pilot, revealed significant operational and maintenance constraints that would severely compromise its scientific utility. Col. Cotton suggested that serious consideration be given to using the YF-12A, an aircraft with a very unique altitude and airspeed flight envelope and three of which were then available. The sum of these ideas was presented verbally to Drs. H. Glaser, J. Gill and Mr. M. Dubin at NASA Headquarters in April of 1967 and followed up with a proposal in writing. NASA and Dr. C. L. Hemenway mutually arranged for Mr. Mercer to pursue the feasibility of this idea at the Dudley Observatory. Prior to formal implementation of this study Mr. Mercer prevailed on NASA Headquarters to transfer funds to the Flight Mechanics Branch of the Computing and Analysis Division at the Manned Spacecraft Center for the development of a computer program to calculate eclipse locations, their velocities, accelerations, and boundaries versus time and flight altitude, Mr. Mercer derived the required vector equations, defined inputs and outputs, and flow-charted the problem. Mr. R. Piersall performed programing, computer checkout, and documentation. Attachment 1 to this report entitled, "Eclipse Determination, Program D074, Project 1191," is a copy of that documentation. 2 Technical Progress under the Grant Formal award of Research Grant NGR 33-011-009 to the Dudley Observatory with Mr. Mercer as Principal Investigator (PI) was effected in August 1967. This work was performed under the technical monitorship of Drs. H. Glaser and G. Oertel in the Solar Physics Office, Code SG, under the Office for Space Science and Applications at NASA Headquarters. The initial collection of information on the YF-12A and its sister ship, the SR-71A, was slowed while the appropriate administrative and security arrangements were worked out by the PI, NASA Headquarters, the U.S. Air Force and their prime contractor on these aircraft, the Advanced Develop- ment Projects Group of the Lockheed-California Company. Once the data on the eclipse track for March 1970 was available, planning began to determine the most useful flight profile for observing the chromosphere, which is more difficult to study than the corona. From these profiles it was possible to compute accurate solar pointing and the range of angles over which a heliostat would have to move to feed a fixed- position, long focal length telescope. Consideration of other, non-eclipse investigations was carried out as a parallel effort under this study so that proposed aircraft modifications could be justified in terms of their fullest scientific utility. Although aircraft structural features were not exactly known at first, some information was available on the contours of the outer skin mold line.. This was compared to the required observing angles versus aircraft headings to determine the useable portion of the velocity profile. When detailed specifications on the aircraft did become available, particularly operational capabilities, it was quickly apparent that the total time in the umbra would increase from sixty to about ninety minutes. In either case, this would require the use of tanker aircraft for aerial refueling. The group assisting the Assistant Secretary of the Air Force for Research and Engineering indicated that such support could be arranged without difficulty. Also, at the suggestion of that office, consideration for using the SR-71A, a strategic reconnaissance version of the aircraft, was added to the study. Data on the aircraft's instrumentation bays and on-board systems showed that a ten-inch, f/43.2, Schiefspiegel telescope could be accommodated and coupled with spectrographic, photometric and photographic systems. A closed circuit television for remote monitoring and control of these systems could also be included so that an Experiment Systems Operator (ESO) could appropriately position and rotate a slit spectograph on the image of the chromosphere or corona during flight. The ESO could also make use of the autopilot and on-board computer to vary flight path headings in order to vary the position of the vehicle with respect to the umbral-penumbral 3 Technical Progress under the Grant - Continued boundary for analysis of the chromosphere in radial slices as narrow as twenty-five kilometers at the sun. This feat would represent not only a five-fold improvement over ground-based resolutions, but also, it would, provide an increase in observation time by more than a factor of one hundred. Finally, the success of the computer program for computation of eclipse tracks and their related data permitted the study to.be enlarged in scope to include all solar eclipses over the expected operational life- time of these aircraft. This effort indicated that the eclipses of March 1970 and October 1977 were the most ideally suited for these aircraft, because the angle of the viewing port in the right-hand chine instrumenta- tion bay would allow the heliostat to feed the full ten-inch aperture of the telescope. While the eclipse of June 1973 would be the best of the twentieth century, it would be too far overhead for good viewing by the long focal length system. However, instruments mounted in the nose compartment would have much greater flexibility in pointing, and, in general, their viewing opportunities would only be a function of the minimum in umbral speeds over the one-and-a-half decades investigated. Eclipses in March 1970, July 1972, October 1977 and February 1979 would be the simplest and least expensive to support in terms of aircraft operations and maintenance. All matters considered, the eclipse in 1977 would be the very best for utilization of this aircraft. The eclipse of 1970 provided an ideal opportunity to begin this work, since it would have been the initial check-out of this new capability, where all modifications to the vehicle could be used again without change. A resume, showing specific details for all of this work is presented as Attachment 2 to this report.