Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Fri, 6 Jul 1990 02:11:26 -0400 (EDT) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Fri, 6 Jul 1990 02:10:56 -0400 (EDT) Subject: SPACE Digest V12 #18 SPACE Digest Volume 12 : Issue 18 Today's Topics: HST / WF-PC: Update from those who know. Re: SPACE Digest V11 #592 Re: grim tidings for the future yspace pics Galileo Update - 07/05/90 Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription notices, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 4 Jul 90 16:05:47 GMT From: unmvax!ariel.unm.edu!hydra.unm.edu!jade@ucbvax.Berkeley.EDU (Eric Jaderlund) Subject: HST / WF-PC: Update from those who know. Here is the poop, straight from the inside, geared mainly towards the Wide Field / Planetary Camera. ***************************************************************************** ***************************************************************************** WIFFPICKERS NEWS.703 ~16:00 3 JULY 90 PMA REPORT OF WFPC IDT June 27 - July 2, 1990 FROM AL BOGGESS: Dear Colleague: As you have no doubt heard from the press, the Hubble Space Telescope has serious optical problems. Since the media do not always communicate the technical details with full accuracy, I would like to inform the astronomical community about just what is wrong and what its consequences are likely to be. Tests in orbit have shown that the Optical Telescope Assembly has about half a wave (r.m.s.) of spherical aberration. If this error were entirely due to the shape of the primary (which is only an assumption) it would correspond to a mirror curvature that is too shallow, with a total center-to-edge error of about two microns. Consequently the images will not achieve their anticipated quality. At a compromise focus, star images have cores whose full width at half maximum is 65 to 70 milliarcsec. Although this core size is within specification, it contains only about 15 percent of the light. The remainder of the energy is in a faint halo that spreads over an arc second or more. The HST Science Working Group and the newly-formed HST Users Committee met on June 27/28 to consider the implications of this situation, which is obviously a major setback. The two groups concluded that HST never-the-less has capabilities that far exceed and complement those available on the ground and that its program should go forward vigorously, emphasizing the unique and valuable science that can be done with the telescope in its present condition. The Working Group and Users Committee drafted a short report to NASA summarizing their position, and that report is attached for your information. The cause and exact nature of the spherical aberration is still being analyzed. At present we do not know whether the error is in the primary mirror or the secondary or distributed in some way between them. Although there are force actuators on the back of the primary, they were designed to remove small amounts of coma and astigmatism. The correction needed now is a relatively large motion in a direction in which the mirror blank is quite stiff, and the actuators are not strong enough to do that job. Consequently, the aberration does not appear to be curable in orbit and the existing instruments will suffer degraded performance - more or less, depending on the particular instrument. A quick assessment of these performances is contained in the accompanying report. On the other hand, we now believe that the Advanced Scientific Instruments which are already planned and scheduled for in-orbit installation can be fully compensated for the aberration, so that two and a half or three years from now we can expect the WF/PC-II to provide the sharp imaging that we had intended to achieve in the present WF/PC. It is too early to state just what changes may be required in the HST observing program. The Project must thoroughly quantify the present performance of the observatory , and NASA and the Space Telescope Science Institute must reexamine their plans for observatory usage. In the meantime, I wanted you to read the facts as I know them. I encourage you to continue monitoring Ron Polidan's HST news reports on email and the ST Science Institute's reports for new information as it becomes available. Albert Boggess Project Scientist for HST ************************************** POSITION PAPER OF THE HST SCIENCE WORKING GROUP AND THE HST USERS COMMITTEE JUNE 29, 1990 SUMMARY Our groups met jointly on June 27 and 28, 1990, at the GSFC and received reports from key Project personnel about the status of the Hubble Space Telescope, with particular emphasis on the imaging performance. Although the program has clearly suffered a major setback due to telescope optics that are well below specification, we are convinced that the long-term prospects for completion of the science program are highly encouraging. Furthermore, a valuable subset of the scientific program can be executed with the telescope even in its present state, with the result that HST still has the potential to produce many key discoveries in the near future. HST right now has capabilities that vastly exceed ground-based observatories. Most important are spectroscopy, photometry and imaging at ultraviolet wavelengths, none of which are possible at all from the ground. High resolution visible-light imaging on bright objects will also be possible, achieving to some degree the original fine details expected in HST pictures. For the longer term, it appears highly probable that the full imaging capabilities of HST can be restored by straightforward modifications to the Second-Generation Scientific Instruments. These are already under development as Orbital Replacement Instruments (ORIs), to be installed in the observatory over the next several years. We recommend that the development of these ORIs be accelerated as much as possible. With determined effort, the WFPC-II camera could be installed in as little as 2 1/2 years, producing images that meet the original design goals. THE OPTICAL CAPABILITY We understand that there is approximately one-half wave rms spherical aberration error (2 micron center-to-edge surface error) in the OTA wavefront, leading to images that fail to meet the Level I 70% enclosed light specification by roughly a factor of 7. The observed image radius is 0.7", versus a specified radius of 0.1". For certain focal positions, the images possess sharp cores (~0.07" FWHM), so that at some level the high spatial resolving power of HST is preserved. However, these cores contain only ~15% of the light, the remaining light being dispersed over a wide halo comparable in size to ground-based images. A summary of what capabilities for science are allowed by these image properties and what can be done to recover the full Level I performance of the observatory is given below. THE SCIENTIFIC CAPABILITIES HST is an extremely versatile observatory with many modes of observation. Loss of image quality has damaged some of these, modes, but many remain wholly or largely intact. Temporarily being able to use only certain of these modes will not alter the fact that we will still be able to do forefront science 100% of the time, but the initial scientific emphasis will have to be different. The number of programs that can be done with the HST has always greatly exceeded the time available for their execution, and this remains true even with the telescope in its current state. The near-term observing plan will now have to give greater emphasis to ultraviolet imaging (FOC), ultraviolet spectroscopy (FOS and GHRS), and ultraviolet photometry (HSP), plus the use of bright core images in visible light (WF/PC and FOC). These, plus the ongoing astrometry program (FGS), will easily occupy all the time available and will return scientific results of great interest and utility. The fulfillment of the original imaging programs will still be possible, but will largely have to be scheduled later. These near-term programs are possible because HST, even in its present state, has unique capabilities that cannot be matched anywhere, either in space or on the ground. The core of the sharply focused image can yield sharp pictures for bright, high-contrast objects such as stars and galactic nuclei. The ultraviolet spectroscopic capability is still largely intact, although some trade-offs are now involved. Obtaining spectra at the planned spectral resolution and desired signal-to-noise will be possible, but the targets will have to be brighter, or the exposure times longer. Spectra of faint targets should also be possible, although with some loss of spectral purity. Fortunately, many programs of the HSP will not be impacted, and the astrometry capability of the FGS will apparently not be compromised at all. Realizing these capabilities will require some new effort; for example, it will be necessary to revise target acquisition methods for the small-aperture instruments and to develop image deconvolution algorithms far the cameras. However, these are not major tasks. Most encouraging of all, it should be possible ultimately to realize the full capability of the HST through the use of the Second-Generation Scientific Instruments (SIs). The WF/PC-II instrument that is currently planned for flight some 3 years after launch has an optical design that will permit complete correction of the errors in the OTA. The other two new Scientific Instruments, both already in development, will also be able to correct simply for the limitations of the telescope optics. The NICMOS instrument will extend the wavelength range of the HST and open up a new window to infra-red observations. The STIS instrument will expand the spectroscopic power of the HST by at least an order of magnitude beyond the goals for the first generation of spectrographs. Completion of all three of the Second-Generation Instruments is now clearly more urgent than ever. CONCLUSIONS AND RECOMMENDATIONS While some of the important scientific goals of the Hubble Space Telescope are currently not achievable because of the spherical aberration in the telescope optics, other unique scientific goals do remain viable, and HST therefore still has the potential to produce many important discoveries during its first years of operation. The original goals for the 15-year mission of the HST continue to be achievable. We therefore recommend that all necessary actions be taken to insure that HST will operate as productively as possible in the short-term, and that activities directed at restoring full capability over the long-term be pursued vigorously. In the short term, this means that on-going HST operations must be fully supported and that the telescope and instrument performance evaluations and analyses must be continued. We also need to adjust to the larger images by developing new target acquisition techniques and by modifying various other capabilities as indicated by the results of ongoing studies. For the longer term, it is clear that the full imaging capabilities of HST can be restored by suitable modifications to the Second-Generation Scientific Instruments, which are planned as Orbital Replacement Instruments (ORIs), to be installed in the observatory over the next several years. We recommend that the development of these ORIs be accelerated. Finally, we recommend that the first Maintenance and Refurbishment Mission, which will install the WF/PC-II in place of the original WF/PC, be directed to proceed as expeditiously as possible, with the goal of being completed in less than 2 1/2 years rather than the planned 3-year schedule. By way of conclusion, we would like to emphasize that an enormous number of technically difficult challenges involved in the design of HST have been successfully met. These include the basic smoothness of the optics, the high degree of accuracy required from the Pointing Control System, and the proper functioning of a suite of complex scientific instruments, to name only a few. In comparison to the huge investment already made in HST, the effort involved in correcting the optical aberrations is fairly small. In comparison to the planned 15-year lifetime of HST, the few-year delay until delivery of WFPC-II is also small. With this perspective in mind, we feel it is important to keep our eyes on the long-term future and work diligently to realize the full potential of the observatory, which is still a fully viable goal. For the HST Science Working Group For the HST Users Committe Albert Boggess Arthur Davidsen ****************************************************************************************************************************************************************Posted by: Eric Jaderlund University of New Mexico Dept. of Physics and Astronomy jade@hydra.unm.edu ******************************************************************************** ------------------------------ Date: 5 Jul 90 14:40:56 GMT From: thorin!homer!leech@mcnc.org (Jonathan Leech) Subject: Re: SPACE Digest V11 #592 In article <9007051334.AA29826@alw.nih.gov> AZM@cu.nih.gov writes: >Does anyone on this list KNOW anything at all about just what the h**l >IS going on with the Hubble? I have seen it firmly stated here that >... >To my nose, the whole thing is beginning to stink like some kind of >coverup, but if so, just what the h**l are they trying to cover up? The fact that the majority of people who've posted about Hubble are speaking from no knowledge and a lot of preconceptions. Take everything you read on the net with a large grain of salt, and it will go down better. -- Jon Leech (leech@cs.unc.edu) __@/ "Why do you suppose we only feel compelled to chase the ones who run away?" "Immaturity." _Dangerous Liasons_ ------------------------------ Date: 5 Jul 90 23:21:05 GMT From: uoft02.utoledo.edu!fax0112@tut.cis.ohio-state.edu Subject: Re: grim tidings for the future In article <00939390.89FB7C00@KING.ENG.UMD.EDU>, sysmgr@KING.ENG.UMD.EDU (Doug Mohney) writes: > In article <14997@thorin.cs.unc.edu>, leech@homer.cs.unc.edu (Jonathan Leech) writes: >>>Funny how all those projects were successful on economy budgets rather than >>>deluxe class "big science" tickets. >> >> You think Galileo is on an economy budget? Try again. > > Compared to what? Hubble? Galileo is a $902 million project compared to HST's $1.5billion (+ expenses down the road). Magellan is $463 million and the gamma ray obs is $500 million. Those aren't small potatoes! Robert Dempsey Ritter Observatory ------------------------------ Date: 4 Jul 90 23:35:04 GMT From: beguine!Eric.Lybeck@mcnc.org (BBS Account) Subject: yspace pics Try the following: ames.arc.nasa.gov pub/SPACE/ plains.nodak.edu gif funic.funet.fi They all have about 25 rather large files... Eru :wq ------------------------------ Date: 5 Jul 90 18:04:24 GMT From: swrinde!zaphod.mps.ohio-state.edu!usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov!baalke@ucsd.edu (Ron Baalke) Subject: Galileo Update - 07/05/90 GALILEO MISSION STATUS July 5, 1990 The Galileo spacecraft is 90.4 million miles from Earth, which means the round-trip communication time is 16 minutes, 12 seconds. Speed in orbit is 53,000 mph; the speed will reach a minimum of 49,467 mph in August, when Galileo's present orbit takes it farthest from the Sun; it will then move back, approaching Earth from the nightside this December. Preliminary reports on Galileo's Venus observations last February, just presented at a conference in the Netherlands, show tantalizing glimpses of cloud structure in the lower atmosphere, quite different from the cloud-top patterns seen previously. Galileo's imaging system, which obtained day-side pictures through both violet and near-infrared filters, showed previously undetected markings at lower levels; the near-infrared mapping spectrometer, viewing both night and day sides, found structure and brightness variations at various IR wavelengths. These analyses are based on a small sample of data read out by the spacecraft last spring, and they offer great promise for the full Venus playback in late November, as well as for the comprehensive study of Jupiter's atmosphere scheduled to begin in 1995. Meanwhile on the spacecraft, things are generally quiet. Scheduled calibrations and engineering maintenance tasks continue to be performed, and the "cruise science" instruments continue to collect their data. Telemetry readings are as expected and spacecraft performance is excellent. ___ _____ ___ /_ /| /____/ \ /_ /| | | | | __ \ /| | | | Ron Baalke | baalke@mars.jpl.nasa.gov ___| | | | |__) |/ | | |___ Jet Propulsion Lab | baalke@jems.jpl.nasa.gov /___| | | | ___/ | |/__ /| M/S 301-355 | |_____|/ |_|/ |_____|/ Pasadena, CA 91109 | ------------------------------ End of SPACE Digest V12 #18 *******************