Date: Sat, 12 Dec 92 05:07:08 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #534 To: Space Digest Readers Precedence: bulk Space Digest Sat, 12 Dec 92 Volume 15 : Issue 534 Today's Topics: absolutely, positively overnight DC info dialog between D. Goldin and C. Sagan Electronic Journal of the ASA (EJASA) - December 1992 Terminal Velocity of DCX? (was Re: Shuttle ...) Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: 11 Dec 92 00:45:47 GMT From: Anthony J Stieber Subject: absolutely, positively overnight Newsgroups: sci.space In article <1992Dec10.225826.12281@eng.umd.edu> sysmgr@king.eng.umd.edu writes: >In article <1g89m0INN578@uwm.edu>, anthony@csd4.csd.uwm.edu (Anthony J Stieber) writes: >But they didn't call the SR-71 the Recon-STRIKE-71 before LBJ's mangling for >nothing. Yep. And I also heard about the drone launch accident that downed both the drone and the host SR-71. Are the speeds SR-71 craft fly at considered hypersonic? In any case release of anything in an atmosphere at high speeds is problematic. I suppose that a DC could be used like an ICBM bus and release ordnance while suborbital above the atmosphere. Physics packages, etc. would reenter on their own. The DC would put some distance between itself and the payload and either reenter as well or burn some fuel and take an orbit or two, perhaps for another bombing run. Bomb deorbit burn motors would make it easier for a bomber to loiter for days and not burn fuel to put bombs in a reentry trajectory. Price is certainly less than a B-2. Hmmm, I can see why the Air Force is interested... -- <-:(= Anthony Stieber anthony@csd4.csd.uwm.edu uwm!uwmcsd4!anthony ------------------------------ Date: Thu, 10 Dec 1992 23:27:48 GMT From: Brad Whitehurst Subject: DC info Newsgroups: sci.space In article <1992Dec10.152231.8279@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes: > >Question about the RL-10: what intake pressure do its pumps require >to avoid cavitation? Hudson emphasizes that reducing this pressure >is important in designing an SSTO, as lower pressure tanks can be >lighter. > > Paul F. Dietz As a data point, I was flipping through the new Aerospace America, which gave the rated thrust for the newest RL-10 at a combustion chamber pressure of 1000 psi. I suppose one could hazard some guesses on fuel pressures from that, although not knowing the pump's pressure ratio, the inlet pressure is still unknown. Just FYI. The same issue also notes that composite test tanks have been built for the NASP effort. Liquid H2 inside, 250 degrees F on the outside! -- Brad Whitehurst | Aerospace Research Lab rbw3q@Virginia.EDU | We like it hot...and fast. ------------------------------ Date: Thu, 10 Dec 1992 23:10:13 GMT From: "Loren I. Petrich" Subject: dialog between D. Goldin and C. Sagan Newsgroups: sci.space In article <1992Dec8.204847.11925@unocal.com> stgprao@st.unocal.COM (Richard Ottolini) writes: >Scattered throughout the evening were references to national politics. >Sagan joked about Republican party follies. I'd like to see some examples. -- /Loren Petrich, the Master Blaster /lip@s1.gov ------------------------------ Date: Thu, 10 Dec 1992 22:24:17 GMT From: Larry Klaes Subject: Electronic Journal of the ASA (EJASA) - December 1992 Newsgroups: sci.astro,sci.space,sci.space.shuttle,sci.misc,alt.sci.planetary THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC Volume 4, Number 5 - December 1992 ########################### TABLE OF CONTENTS ########################### * ASA Membership and Article Submission Information * Further Analysis of EVA Self-Rescue Data - Adam R. Brody * Transparency Films for Astrophotography - Brian G. Segal ########################### ASA MEMBERSHIP INFORMATION The Electronic Journal of the Astronomical Society of the Atlantic (EJASA) is published monthly by the Astronomical Society of the Atlantic, Incorporated. The ASA is a non-profit organization dedicated to the advancement of amateur and professional astronomy and space exploration, as well as the social and educational needs of its members. ASA membership application is open to all with an interest in astronomy and space exploration. Members receive the Journal of the ASA (hardcopy sent through United States Mail - Not a duplicate of this Electronic Journal) and the Astronomical League's REFLECTOR magazine. Members may also purchase discount subscriptions to ASTRONOMY and SKY & TELESCOPE magazines. For information on membership, you may contact the Society at any of the following addresses: Astronomical Society of the Atlantic (ASA) c/o Center for High Angular Resolution Astronomy (CHARA) Georgia State University (GSU) Atlanta, Georgia 30303 U.S.A. asa@chara.gsu.edu ASA BBS: (404) 564-9623, 300/1200/2400 Baud. or telephone the Society Recording at (404) 264-0451 to leave your address and/or receive the latest Society news. ASA Officers and Council - President - Don Barry Vice President - Nils Turner Secretary - Ingrid Siegert-Tanghe Treasurer - Mike Burkhead Directors - Bill Bagnuolo, Eric Greene, Tano Scigliano Council - Bill Bagnuolo, Bill Black, Mike Burkhead, Frank Guyton, Larry Klaes, Ken Poshedly, Jim Rouse, Tano Scigliano, John Stauter, Wess Stuckey, Harry Taylor, Gary Thompson, Cindy Weaver, Bob Vickers ARTICLE SUBMISSIONS Article submissions to the EJASA on astronomy and space exploration are most welcome. Please send your on-line articles in ASCII format to Larry Klaes, EJASA Editor, at the following net addresses or the above Society addresses: klaes@verga.enet.dec.com or - ...!decwrl!verga.enet.dec.com!klaes or - klaes%verga.dec@decwrl.enet.dec.com or - klaes%verga.enet.dec.com@uunet.uu.net You may also use the above addresses for EJASA back issue requests, letters to the editor, and ASA membership information. When sending your article submissions, please be certain to include either a network or regular mail address where you can be reached, a telephone number, and a brief biographical sketch. Back issues of the EJASA are also available from anonymous FTP at chara.gsu.edu (131.96.5.29) DISCLAIMER Submissions are welcome for consideration. Articles submitted, unless otherwise stated, become the property of the Astronomical Society of the Atlantic, Incorporated. Though the articles will not be used for profit, they are subject to editing, abridgment, and other changes. Copying or reprinting of the EJASA, in part or in whole, is encouraged, provided clear attribution is made to the Astronomical Society of the Atlantic, the Electronic Journal, and the author(s). Opinions expressed in the EJASA are those of the authors' and not necessarily those of the ASA. This Journal is Copyright (c) 1992 by the Astronomical Society of the Atlantic, Incorporated. FURTHER ANALYSIS OF EVA SELF-RESCUE DATA IAA-92-0385 Adam R. Brody Senior Aerospace Engineer/Experimental Psychologist Sterling Software NASA Ames Research Center Moffett Field, California, U.S.A. Copyright (c) 1992 by Sterling Software. Published by the International Astronautical Federation (IAF), with permission. Abstract A means for rescuing a stranded Extra-Vehicular Activity (EVA) astronaut is necessary to ensure future safe space station operations. One promising device is a hand-held thruster similar to the Hand-Held Maneuvering Unit (HHMU) from the GEMINI and SKYLAB programs of the 1960s and 1970s. A study was performed in the Virtual Interactive Environment Workstation (VIEW) at NASA Ames Research Center. Three Initial (Separation) Velocities (0.5, 1.0, and 1.5 m/s) were crossed with five Initial Spin Velocities (0, #177#0.1, #177#0.3) to yield 15 different trials. An Attitude Hold system was also modeled, which, when combined with the 15 combinations of separation and spin velocity, provided 30 distinct trials. Recent examinations of the data reveal that Initial (Separation) Velocity and Initial Spin Velocity each produced main effects and combined to produce an interaction effect on Solution Time. Solution Time increased with Initial Velocity and absolute Initial Spin Velocity. Final Roll Angle also increased Initial Spin Velocity. Attitude Hold Fuel increased with absolute Initial Spin Velocity. Interaction effects revealed that main effects were less pronounced at the lowest Initial Velocity level. Introduction There are a number of organizations in the United States developing devices to be used to return a stranded EVA astronaut to a space station after an accidental separation. Some of the devices merely extend the reach of the stranded crewperson with a pole or other apparatus. These will only work when the separation velocity is so small that the crew can unstow and operate the rescue tool before s/he drifts further than the instrument's maximum operational range. Once this maximum range is exceeded, propulsive techniques must be used. One possible propulsive device is the Hand-Held Maneuvering Unit (HHMU) initially used in the United States' GEMINI program. Three different models (varying by propellant type, total delta-v, and other attributes) were developed and used. Experimentation continued in the SKYLAB program. The device simulated in the current series of experiments is analogous to the HHMU. However, neither the thruster configuration nor the propellant is specified. The amount of thrust is recorded as a thrusting duration. The thrust force multiplied by the duration yields the impulse, which when divided by the system mass, yields the change in velocity or delta-v. This value for delta-v may then be used to determine propellant mass for any combination of propellant specific impulse and thruster configuration. The current study was performed in the Virtual Interactive Environment Workstation (VIEW) laboratory at the NASA Ames Research Center. This simulator facility provided the user with a stereoscopic visual image of the space station from which s/he has become separated. The visual scene was altered not only by the equations of motion governing orbital flight, but also by the changes in orientation and position of the operator's head. In this way, an effective EVA simulation was realized. This study demonstrated the viability of using VIEW as an EVA simulation facility. It also revealed separation velocity to be the most important factor characterizing a separation scenario with fuel consumption, maximum range, and time to reach maximum range increasing linearly with separation velocity. In addition, no significant benefits from an attitude hold capability were uncovered (although a null effect cannot be proven). EVA trainers at the Johnson Space Center in Houston, Texas, were sufficiently impressed with the study that they considered using the facility for astronaut EVA rescue training. This collaboration was precluded by lack of funding. Many of the results of this study were presented elsewhere. [1, 2, 3] Space limitations prevented inclusion of all the results; additional results are described here. Also, the stated result that no statistically significant solution time effects were found was incorrect. These effects will also be discussed here. Method One highly-trained subject was used in this study. The subject, situated in the VIEW, experienced sudden separations from the virtual space station to which he was previously tethered. Using hand gestures, which commanded the fore and aft firings of a virtual hand-held thruster, he effected his returns to the station. The subject was trained until he was able to recover consistently from a variety of separation scenarios. The subject was presented with an assortment of failure scenarios with varying initial velocities, and rotation rates. The opportunity to use attitude hold was allowed on only half the trials. Since preliminary investigations revealed starting location to have less of an effect on rescue performance than other input parameters, all separations began at the center of mass of the space station. Motion began in the direction of the minus velocity vector. Three initial (separation) rates (0.5, 1.0, and 1.5 m/s) were used in the study. These values were selected as appropriate based upon separation dynamics tests performed on the KC-135 aircraft. In these tests, test subjects were assisted in achieving the maximum separation rates possible; a maximum separation rate of 1.5 m/s (4.5 ft/s) was achieved. The maximum rotation rates were found to be 4.5 RPM (0.47 rad/s) in roll, 10.1 RPM (1.06 rad/s) in pitch and 5.8 RPM (0.61 rad/s) in yaw. [4] The five rotation rates (-0.3, -0.1, 0, 0.1, 0.3 rad/s) in this study were crossed with the translation rates to yield a trial set of 15 different trials. Initial rates were the same about all axes. Both negative and positive values were used because preliminary testing suggested a handedness effect might be present. The capability to use attitude hold was added as another factor raising the number of distinct trials to 30. The subject was presented with 2 different random orders of these 30 trials in groups of 5. Dependent variables included: Mission duration, total velocity increment, impact velocity, and maximum range from the station along all three axes. The subject was allowed one attempt at a rescue per trial. The trial was aborted if he passed the station. These aborted missions were immediately reflown. The hand-held thruster fired an 8.9 N (2-pound) force along the direction of the hand in either the fore or aft direction. All thrusts that were not directed precisely through the center of mass of the subject, which was located in the center of the subject's back, added rotational motion along one or more axes. An 8.9 N (2-pound) thruster requires 31 seconds to accelerate the simulated crew mass of 274 kilograms to 1 m/s. This thrust must be through the center of mass to avoid adding rotational motion. This is virtually impossible, so achieving a velocity of 1 m/s typically requires more than 31 seconds. [3] The simulated space station was located in a 270 nautical mile circular orbit around the planet Earth. Since it was impractical to keep up with the rapidly changing design of space station FREEDOM, the station was represented by two intersecting 5-meter trusses. The horizontal dimension was 50 meters and the vertical dimension was 100 meters. [5] Results A data entry error prevented the discovery of several solution time effects that were indeed present. Initial (separation) velocity and initial spin velocity each produced statistically significant main effects on solution time. They also combined for an interaction effect. These effects were statistically significant at the five-percent level and are discussed here. Solution time increased monotonically with initial velocity as described in Figure 1. This effect is intuitive and fits with similar effects on fuel consumption, final axial velocity, and maximum range. [1, 2, 3] This effect was non-linear, however. Tripling the separation rate from 0.5 to 1.5 m/s quadrupled the solution time, for example. This was because the ratio of thrusting time to solution time was lower at the two highest separation rates than at 0.5 m/s. Since proportionately less time was spent thrusting at the higher rates, those missions took longer than a simple multiple of the fastest response would predict. There was more of a "thrust and wait" strategy with the longer missions than with the shortest one. Proportionately more time was spent verifying progress at the higher velocity separations than at the lower velocity separations. Figure Descriptions Figure 1: Initial velocity effect on solution time. A solution time effect was also observed with Initial Spin Velocity as the independent variable. The plot appears as Figure 2. Fuel consumption also increased with initial spin velocity as did maximum range. [1, 2, 3] Trials with higher initial spin velocities were more difficult from which to recover. Figure 2: Initial spin velocity effect on solution time. Separation velocity and spin velocity combined to produce an interaction effect on solution time as described in Figure 3. Separations at a rate of 0.5 m/s were not affected by spin velocity as much as separations at the two higher rates. Rapid response times precluded greater impact of initial spin rate. The asymmetries in the plots are due to a handedness effect. The thruster commands were sent with the right hand only. Figure 3: Separation and spin velocity interaction. Initial spin velocity also produced a main effect on final roll angle. Interaction effects with attitude hold, and separation velocity x initial spin velocity, and separation velocity x initial spin velocity x attitude hold interactions were also present. Final roll angle increased with initial spin velocity as described in Figure 4. Since final roll velocity (V spin Xf) remained close to initial spin velocity [1, 2, 3] and solution times were greater for higher initial spin rates than for lower rates, final roll angle was proportional to initial spin velocity. The more time the subject spun at a given rate, the greater the final angle was. Figure 4: Final Roll Angle verses Initial Spin Velocity Two interaction effects were observed in the final roll angle data. Attitude hold and separation velocity were the disturbing factors leading to inconsistent main effects. When the subject had the capability of using attitude hold, the final roll angle was much closer to zero than when attitude hold was unavailable. This effect is described in Figure 5. Figure 5: Attitude Hold x Initial Spin Velocity Interaction. A two-way interaction between separation velocity and initial spin velocity was also discovered. This effect appears in Figure 6. Again, the curve for the 0.5 m/s separation velocity data is more shallow and less pronounced than the other curves. At higher separation velocities, the effect of initial spin velocity is more prominent. Figure 6: Initial Spin Velocity x Separation Velocity Interaction. A second-order interaction of Separation Velocity x Initial Spin Velocity x Attitude Hold was also revealed by the data. The effects appear as Figures 7a and 7b for the disabled and enabled Attitude Hold conditions respectively. The use of attitude hold greatly reduced the final roll angle. Again, the curve for the 0.5 m/s data was shallower than those for the other two. Figure 7a: Second order interaction with Attitude Hold Disabled. Figure 7b: Second order interaction with Attitude Hold Enabled. The data from trials in which Attitude Hold was available were looked at separately to determine if there were any effects regarding number of attitude hold commands or attitude hold fuel used along any particular axis. The Pitch Attitude Hold data appear as a U-shaped plot in Figure 8. More pitch attitude hold fuel was used at greater initial spin rates. Physically, more fuel is needed to eliminate higher initial spin rates than lower rates. The moment of inertia for the pitch axis was 108 kg-m2. An 8.9 N thruster at the end of a 1-meter moment arm produces a torque of 8.9 N-m. These values yield an angular acceleration of 0.08 rad/s2. At this rate, 1.25 s of thrust are required to produce a spin rate of 0.1 rad/s. Similarly, 3.75 s are needed to produce a rate of #177#0.3 rad/s. The data in Figure 8 reveal actual (simulator) values to be fairly close to theoretical values. In some cases, the subject reduced some of the pitching himself, thus reducing the amount of time the pitch attitude hold was needed. In other cases, the subject contributed to the rotational motion and the attitude hold system had to work harder to make up for this addition. Figure 8: Pitch Attitude Hold Fuel. An interaction effect with Separation Velocity and Initial Spin Velocity was also uncovered with these data. Again, the 0.5 m/s data produced the shallowest curve. Pitch Attitude Hold fuel increased with separation velocity. Figure 9: Initial Spin Velocity x Separation Velocity Interaction for Pitch Attitude Hold Fuel. Discussion In every interaction effect involving Initial Velocity discussed here, and all cases (except final out-of-plane velocity) listed elsewhere, [1, 2, 3] the curve for the lowest Initial Velocity was the shallowest of the three. The lower solution times associated with the lowest separation velocity (average = 51 s) prevented the curves from taking a shape similar to those representing the higher velocity data. The solution times were too short to let some of the effects come through. Shorter solution times precluded the development of certain effects in other studies also. [6, 7] There is a qualitative distinction between self-rescue from a separation velocity of 0.5 m/s and rescue from higher rates. More research is needed to better quantify these effects. Preliminary simulation results indicate that a hand-held thruster is capable of serving as an EVA self-rescue device. Its utility is greater than any physical extension of the crewmember's body since it has a greater range of operation. Further study, including a flight experiment on Space Shuttle Mission STS-49 (May of 1992), will reveal more about the capabilities and deficiencies of such a system. Other parameters to be examined include thruster magnitude and system geometry. Motion-base carriage and air bearing floor facilities can also contribute as described elsewhere. [1, 2, 3] This is a field of study in its infancy and more attention and funding is encouraged. References 1. Brody, Adam R., R. Jacoby, and S. R. Ellis, "Simulation of Extra-Vehicular Activity (EVA) Self-Rescue", SAE Technical Paper 911574, Warrendale, Pennsylvania, July 1991. 2. Brody, Adam R., R. Jacoby, and S. R. Ellis, "EVA Self-Rescue Simulation in the Virtual Interactive Environment Workstation (VIEW)", Space Safety and Rescue 1990-1991, Science and Technology Series, American Astronautical Society, San Diego, California, in press. 3. Brody, Adam R., R. Jacoby, and S. R. Ellis, "EVA Self-Rescue Using a Hand-Held Thruster", JOURNAL OF SPACECRAFT AND ROCKETS, in press. 4. Porter, S., "Separation Dynamics Tests," 1989. 5. Brody, Adam R., R. Jacoby, and S. R. Ellis, "Man Overboard! What Next?", International Academy of Astronautics IAA-91-584, Paris, France, October 1991. 6. Brody, Adam R., S. R. Ellis, A. J. Grunwald, and R. F. Haines, "Interactive Displays for Trajectory Planning and Proximity Operations", JOURNAL OF SPACECRAFT AND ROCKETS, in press. 7. Brody, Adam R. and S. R. Ellis, "Effect of an Anomalous Thruster Input During a Simulated Docking Maneuver", JOURNAL OF SPACECRAFT AND ROCKETS, Volume 27, Number 6, 1990, pages 630-633. About the Author - Adam R. Brody received S.B. and S.M. degrees in Aeronautics and Astronautics from the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, and a diploma as a member of the founding conference of the International Space University (ISU). Adam also received his M.A. degree in Psychology from San Jose State University in California. Adam is a senior aerospace engineer/experimental psychologist for Sterling Software, Palo Alto, California. Among the NASA Ames Research Center organizations with which he has worked are the Centrifuge Facility Project Office, Human Interface Research Branch, EVA Systems Branch, and the Aerospace Human Factors Research Division. Adam is the author of over thirty-five research papers on various topics relating to performance aspects of humans in space. Adam pioneered a comprehensive study of the human factors and manual control aspects of orbital flight and he developed the Space Station Proximity Operations Simulator at Ames for his studies. He also initiated a research program to quantify EVA rescue requirements, and created of an orbital trajectory planning tool for the Macintosh computer system. Adam's research interests include the human factors and manual control requirements of space station proximity operations and other manned space flight operations. Recent work includes development and simulation of an EVA self-rescue technique using the Virtual Interactive Environmental Workstation (VIEW). Currently, he serves as the human factors expert on the systems engineering staff of the Centrifuge Facility Project Office at Ames, where he developed the Payload Resource In Space Monitor (PRISM) for tracking resources on the FREEDOM space station. He is currently using object-oriented rapid prototyping to develop software requirements for the space station facility. Adam is a member of the Space Operations and Support Technical Committee of the American Institute of Aeronautics and Astronautics, where he is chairman of the Human Factors, Automation and Robotics Sub-committee. He is also a member of the National Air and Space Museum, the Union of Concerned Scientists, a founding sponsor of the CHALLENGER Center, and a charter member of the Technology Center of Silicon Valley. His biography is listed in Personalities of America, the Dictionary of International Biography, Who's Who of Emerging Leaders in America, Who's Who Among Young American Professionals, and Who's Who in the West. Adam is the author of "Soviet Spacecraft Docking Experience", published in the October 1992 issue of the EJASA. Adam may be reached through the Internet at either: adam_brody@qmgate.arc.nasa.gov or brody@eos.arc.nasa.gov TRANSPARENCY FILMS FOR ASTROPHOTOGRAPHY by Brian G. Segal Reprinted with permission from the March-April 1991 issue of NOVA NOTES, the Newsletter of the Halifax Centre of The Royal Astronomical Society of Canada (RASC). The thought of tools for astrophotography usually brings to mind images of huge apertures, fluorite elements, exotic guiders, freezing cold cameras bathed in dry ice (usually redundant in Canada), dead accurate drive systems, the soft red glow of reticules and tired eyes - not to mention those supportive, understanding spouses condemned to yet another night of just sitting there in the dark! However, given a decent array of hardware, the most important consideration facing the aspiring cosmic snapshooter is the choice of "weapons", otherwise known as film. There is a kind of decision tree that one must work through: Black and white or color; print or transparency; fine and slow or grainy and fast; Kodak, Fuji, Konica, Illford, etc.. Not surprisingly, many astro-shooters tend to specialize. Given the time it takes to make astronomical images (other than the Moon or Sun) and the number of opportunities for total, partial, or incidental SNAFUs, simplification is a good strategy. Consequently, my astrophotographic odyssey has been mostly confined to the use of various transparency (slide) films. They are my medium of choice. Different ones are suitable for different applications. I have done considerable work with EKTACHROME 400, KODACHROME 64, and FUJICHROME 50, 100, 400, and 1600. I have also shot FUJICHROME 400 at an effective exposure value of ISO 800 and had it push processed. The slower films have been used exclusively for solar photography and some lunar when the Moon is at least at first quarter phase. The only limiting factor in this situation is the mechanical stability of your system. The exposures have to be made on the long side, compared with the focal length of the lens. A prime focus shot of the Sun taken on an unstable 2000 mm scope will blur at the slightest vibration unless you can shoot at 1/2000th of a second, which is unlikely. If you are looking at shutter speeds of from one second to 1/500th of a second, you had better have a real solid mount and lock up your camera's mirror if it is an SLR system. I have had good results with KODACHROME 64 and both FUJICHROME 50 and 100 when shooting the Sun with a Thousand Oaks full aperture solar filter. Effective focal lengths of up to 25,000 mm through eyepiece projection have yielded surprisingly good results on calm days. Naturally at the higher magnifications various factors come into play, including the amount of glass in the system, the seeing, and the care taken by the photographer. I have also used both EKTACHROME 400 and FUJICHROME 400 for this type of photography. The trade off is a cooler color cast and a lot more grain, especially during the longer exposures. Generally, we are told, slow films have better reciprocity characteristics than faster ones: There seems to be some substance to that claim. However, you do achieve between a two to three-stop advantage, which translates to faster shutter speeds and less camera shakes - in theory, anyway! I have also used pushed FUJICHROME 400 for lunar shots using a 1000 mm f/11 Maksutov. The results were surprisingly good and allowed me to photograph an almost full Moon without a drive. Deep sky work is a very different challenge. All but the brightest objects require relatively long exposures (to a daytime photographer, anything longer than a few seconds is very long). Even with the very fast print films (ISO 3200), ten minutes would be a minimum exposure for the majority of diffuse and faint objects. As film speed decreases, exposure length grows exponentially. Each stop represents a doubling of exposure time as the ISO value is reduced. Each doubling of exposure time increases the risk of any number of problems, from the gradual accumulation of dew or frost to unfortunate happenstance - like sneezing your head into the eyepiece, resulting in possible eye damage and shaking the optics. As any slide presentation will demonstrate, various emulsions have very different characteristics. There are some factors which will influence the choice of films. While EKTACHROME 400 tends to bring out certain red nebular emissions very effectively, it suffers from a lower contrast than its FUJICHROME 400 cousin. In fact, the sky background tends to a kind of purplish cast while the FUJI retains very black skies over fairly long exposures. Naturally the seeing and general sky conditions have to be comparable, but certainly my experience over a range of targets and nights has confirmed this situation. I do find, however, that the FUJI requires more exposure for certain objects, particularly planetaries. FUJICHROME RSP 1600 is the fastest transparency film in the FUJI line. Its optimum rated value is ISO 1600, although it can be pulled to ISO 800 or pushed to ISO 3200. Although KODAK makes EKTACHROME P800/1600, a film that makes similar claims, in fact its optimum rating is ISO 800 with a one or two-stop push possible. The fact that the FUJI product is "comfortable" at 1600 means that the one-stop push to 3200 is asking less of the film. As push processing does have both color shift and granular effects on the final image, the less push, the better. I have used the RSP 1600 in daylight as well as night time photography and can attest to its quality. It has surprisingly fine grain characteristics and although rather high in contrast compared to a slower chrome film, its color response is quite good. The higher contrast level is a plus in astrophotography. The skies in exposures of up to forty minutes stay quite blue-black with very good color range in the stars and gasses. You will have to be careful of several things, though: GUIDING: Very sensitive emulsions gather light at an alarming speed. Any deviations in guiding are preserved obviously and mercilessly for all time within seconds. With ISO 400 films a bit of wander due to periodic drive error or distractions of one sort or another can be recovered from with little or no evidence. However, a quick glimpse at a meteor at the wrong moment with ultra-fast film can leave a lasting memory on the emulsion. FOGGING: Ultra-high speed films are very susceptible to ambient light, whether from city lights, celestial background light, or that yard light your neighbor has installed across the valley just to make your observing that much more of a challenge! The message is to be in a dark place and wait *patiently* for astronomical twilight to surrender to real night! With any transparency processing it is a good idea to write those three important words "DO NOT CUT" on the envelope. Although I always take the precaution of exposing the first frame in daylight to give the processors a reference frame, I much prefer to cut and mount my own slides for two reasons: 1 - I use a mini-cassette recorder for note-taking during a session. All of the data is subsequently preserved frame by frame. Thus, when the film comes back, I simply turn on the tape and review the strip of film to my own commentary. As I cut and mount the slides, the information is recorded in indelible ink on the mount. You cannot count on the processor to sequentially mount your slides: They do screw up at times! 2 - There are, alas, always shots that do not make it. Why bother having them mounted? Another transparency material that is often overlooked is black and white negative film. A negative tonal "slide" can be quite dramatic and add another dimension to projectable images. Whatever the application you may have planned for your astrophotography, transparency films offer a variety of choices and possibilities. If you decide that you have an image that simply must be printed, you can always go the route of reversal printing and have a large internegative made. Thus, the versatility of transparency films makes them an attractive option for astrophotography. Related EJASA Articles - "Astrophotography the Easy Way", by Harry Taylor - October 1991 "Telescopes: A Novice's Guide", by Steven M. Willows - March 1992 About the Author - Brian G. Segal is a visual artist living in Antigonish, Nova Scotia, Canada, where he has operated a ceramic design studio with his wife, Julia, for the past sixteen years. In addition, Brian is a professional commercial photographer specializing in still life and product, architectural, and corporate/industrial photography. Brian's hobby is astrophotography, which he tackles with a twenty- centimeter (eight-inch) Meade SCT, a bunch of hardware, various slide films, and the clear, very dark skies of his rural location - whenever it decides to clear up, that is! Brian is also a member of the Executive Committee of the Halifax Centre of the Royal Astronomical Society of Canada (RASC). Brian's Internet address is: astro@esseX.stfx.ca THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC December 1992 - Vol. 4, No. 5 Copyright (c) 1992 - ASA ------------------------------ Date: 11 Dec 92 01:31:58 GMT From: Pat Subject: Terminal Velocity of DCX? (was Re: Shuttle ...) Newsgroups: sci.space In article jbh55289@uxa.cso.uiuc.edu (Josh 'K' Hopkins) writes: >gary@ke4zv.uucp (Gary Coffman) writes: > >>I support the DC-X tests. The data developed may be useful in later >>vehicles and the cost is not excessive. Like the X-15, however, I >>doubt it's design will scale to commercial products. How many airliners >>are derived from the X-15? The SR71 is the only manned vehicle that vaguely >>resembles the X-15 and it's flight systems are entirely different. And >>it's being retired as not cost effective for it's mission. > >Actually, I think shuttle derived a fair amount of value from the X-15 research >even if it doesn't look the same. In addition saying that the SR-71 is being I imagine that the X-15, set up a huge amount of data for the NASP as well as the STS. the X-15 also probably provided test data for the ICBM re-entry vehicle design. i think NASA programs such as SABER?, HL-20, ... pulled data from the X-15. the X -15 also procided a lot of data on RCS systems, redundant system design and thermal stress design. The only reason commercial products did not come out of the entire plane was that we decided to run away from space during the Nixon administration. Goldin was just on TV, talking abou;the X-15, and how 25 years ago we stepped away from the cutting edge. now if we had kept pushing forward, instead of deciding that attacking small asian countries was a more noble purpose for the US, we would have regular trips to mars by now. ------------------------------ End of Space Digest Volume 15 : Issue 534 ------------------------------