"The Space Telescope will be launched in 1985 and will improve considerably our observational possibilities, but not the visibility of outer planetary systems. The solar system as seen from Alpha Centauri is presented, as well as the nearest stars and the main cameras of the Space Telescope. As a possible improvement the action of a distant and star-shaped screen is described; that screen is 100 to 800 meters and placed 1 million kilometer in front of the telescope; it allows one to avoid the dazzling effect of the stars and to look for planets such as Jupiter and Saturn up to 20 to 40 light-years. Such planets as Earth and Venus are a little less visible. The visibility of satellites such as the Moon is discussed; it remains at the limit of our technical possibilities. This conceptual paper does not consider in detail the technical difficulties involved.
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"From the time of the initial design work on space telescopes, various researchers were intrigued by the possibility of using these new instruments as extrasolar planet detectors. Soon however astronomers Roman and Spitzer realised that unaided, a 3-metre telescope of the Hubble variety would be incapable of observing an extrasolar planet because of the greater visible energy radiated by the primary star. The visual magnitude difference between a Sun-like star and a Jupiter-like planet, for example, is about 23.
A possible solution to this problem is to place a suitably designed occulter larger than the telescope's resolution element in the line of sight between the telescope and the primary star. With most of the light from the primary removed an LST-sized telescope will see a Jupiter-sized planet with an S/N « 1.00, for an occulter-telescope separation of 104 km, and a "semi-infinite plane" occulting disc.
With a longer occulter-telescope separation and a more complicated occulter, observation of Earth-like planets becomes possible. By a "more complicated occulter" astronomers mean an occulter which throws a blacker shadow by reducing reflectivity smoothly towards zero rather than abruptly. An occulting disc edged with sharp spikes (think of a sunflower) might be suitable According to Spitzer the use of this occulter was pointed out by R. Danielson at Princeton. As Roman and Spitzer discussed the difficulties of occulter design and maintaining occulter-Hubble separation, it occurred to Roman that the Moon itself could be employed as an occulter !
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The Large Space Telescope is scheduled to be launched in the early 1980's. Later in that decade, when the space tug becomes available, it should be possible to shuttle Hubble to any desired station between the Earth and Moon, opening up many opportunities for lunar-occultation-aided extrasolar planet.
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Early in the next decade, we might desire to increase the number of nearby stars that can be studied in an LST planet detection search by launching balloon occulters on cislunar trajectories. If 1975 Apollo-Soyuz linkup is a harbinger of the future and not a mere aberration, we can anticipate possible excting ventures. A Hubble could be launched by an European rocket and possibly operated by Americans on Liberty at the same time that a Soviet Soyuz is towing a balloon occulter on a Zond circumlunar trajectory !
If budgetary constraints intensify severely, the occulter could be unmanned or eliminated altogether if we are willing to settle for a survey of only those stars in the Moon's orbital plane.
One approach that should be investigated and has not, to our knowledge, yet been considered would be to mount a variant of Hubble - on a balloon and loft it to about 30 km. Then, the balloon-mounted telescope could be used in conjunction with an orbiting occulter in the manner considered for the orbiting Hubble.
This draw inspiration from the abandonned Stratoscope series, as described in a 1971 brochure of the NASA Marshall.
Stratoscope I was a 12 inch diameter telescope that flew in 1957. It is unique in the sense that it was carried to 80 000 feet by a balloon.
Stratoscope II was more ambitious – housed with a four-tons nacelle it had three times the diameter, carrying a 36 inch aperture telescope. It flew in 1963 but it had severe technical issues. Only eight flights were made between 1963 and 1971, half of them plagued by technical glitches.
Stratoscope III is a 48-inch aperture telescope launched by balloon, but the study is to include recommendations to make it shuttle-compatible. We won't wait for the shuttle in developing Stratoscope III, but it will be a prime candidate for sortie use. By shuttle-compatible we only mean that where possible we shall choose systems that are compatible between balloons and sortie. A major problem is in thermal design — i.e. , the shuttle must operate in sunlight, a balloon does not. Stratoscope III has less support than LST, but could do a very valuable preliminary work in preparation for LST. A decision about whether to go ahead with Stratoscope III is due Sept. Oct. 1972. The Stratoscope III will provide a broad range of scientific instruments for stellar observations. It will be a successor to the balloon borne SIII and a predecessor to the Large Space Telescope. The S-III baselined for this study is a scaled-down version of Itek's 3-m concept proposed for LST. instrument that will fly on shuttle sortie missions.
Whether the seeing in the lower stratosphere is stable enough for such an approach to be feasible remains to be seen. Other significant problem areas in such a stratospheric approach are determination of whether the ~0.005 arc sec. target-locking accuracy of Hubble could be approached by a balloon-mounted telescope, and whether the line of sight between the telescope and occulter could be maintained to an accuracy of ~ 1 resolution element during the duration of the observation.
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A more likely austerity measure is possible reduction in size of the first space telescope. If the primary mirror of the LST is reduced to 2 metres, detection of Jovian planets with an S/N ^0.2 would be possible. If we are limited by S/N « 0.02- 0.03 for planet detection, then Earth-like planets would probably be invisible to this miniature LST. A final application of Hubble technology is to construct a multimirror telescope. Any two Cassegrain-focus telescopes can be combined optically to synthesise a larger-resolution instrument.
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The possibility that a coronograph on the Space Telescope when it is launched into a 500 km orbit in 1986 could aid in locating planets in other star systems is examined. Attention is given to the view of the solar system from Alpha Centauri; it is shown that even Jupiter would be a 21.9 magnitude object at that distance. However, the optics of the Space Telescope will only permit objects down to 17th magnitude to be viewed near a bright object such as a star. Consideration is given to the efficiency of a coronograph, which increases with the distance from the image. The analyses are used to study methods for selectively viewing different wavelengths emitted from a star system through a star-shaped screen in order to discern outer planets. The technique is valid only if the Space Telescope is placed in an orbit of several millions of miles around the sun. The first and second Sun-Earth libration points are very attractive locations for such a space-based observatory.
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After reviewing these approaches, we must conclude that the first optical observations of extrasolar planets will probably be made by Hubble, used in conjunction with a (possibly lunar) occulter. However, detection using an orbital occulter and an LST mounted on a stratospheric balloon seems feasible and may well be less expensive than the space telescope approach. Other terrestrial approaches seem capable of statistically demonstrating the existence of extrasolar planets but may not be capable of moving beyond the existence theorem for these worlds. To obtain reasonably accurate photometric signatures of extrasolar planets circling Solar-type stars, orbital multi-mirror approaches used in conjunction with occulters seems superior. Optical observations of Jupiter-like planets circling Barnard's Star and other nearby red dwarfs probably requires a lunar observatory. The situation regarding extrasolar planet optical observation is not atypical in science or other human endeavours. We can probably detect some nearby planetary systems reasonably easily and inexpensively, once the LST is developed.
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Three approaches have been identified. A ground-based telescope could benefit from a suborbital occulter carried by a sounding rocket or the X-15, if it had not been retired; a balloon-borne Hubble would have its occulter in orbit around Earth; and an orbital Hubble could use the Moon itself (!) as an occulter. Ideas Jules Verne would have appreciated, particularly the balloon carried telescope or using the Moon as an occulter.
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Flower-shaped space occulters to shut a star light and disclose the little planets orbiting them: it is a rather poetic concept French aviator and poet Antoine de Saint Exupéry would have loved !
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"In the decades ahead, one of the most exciting adventures in astronomy, particularly from space, will be the search for planets around stars. If planets are found to be as abundant in the Universe as some of us suspect, the impact on human philosophy may be greater than that of any other astronomical discovery of our time, and the challenge to send spacecraft to visit these newly discovered "Other Worlds" could well become the driving force of space science if prospective advances in propulsion systems materialize.
Several methods for the detection of extra-solar planets have been discussed. Among these methods, the quest for radial velocity variation can be pursued fairly well from observatories on the ground, while a serious effort at direct imaging detection through apodization may have to wait further advances in the figuring and control of large optics. Therefore, I want to focus attention on astrometry, which can particularly benefit from a telescope in space, and for which the likelihood of detection is not dependent on the spatial orientation of a planetary system.
Over the last decade French astronomer Lacroute slowly refined his space astrometry project. After ten years, Lacroute felt the technology was mature enough. In November 1973, he proposed to ESRO two possible options of a space astrometry satellite, further presented to the agency advisory structure by Jean Kovalevsky. These two options were different in their scientific objectives and, as a consequence, in their principles.
The TD option proposed to use a TD-1 type satellite, systematically scanning the sky and observing all 150 000 stars brighter than a given magnitude. The Agena / space station option would on the contrary observe a pre-determined programme of up to 40 000 selected stars prepared in advance. This option permitted to include objects of special interest but required long and complex pointing. Such a system could use more powerful optics and could reach fainter stars, but won't yield as many measurements as a scanning satellite. The European Space Agency ultimately picked up the TD-1, scanning option. It is now known as Hipparcos.
Although primarily build for star astrometry, Hipparcos spun a fascinating concept: to bring Van De Kamp controversial astrometric search for extrasolar planets into space, far above the deceptive atmospheric turbulence.
In this search for extra-solar planetary systems, the European Astrometry Satellite (Hipparcos) can play a leading role if its lifetime is not too short or if its successor is not too late in materializing. It may be able to answer a scientifically and philosophically exciting question: Does the Universe abound with planets? The ability of Hipparcos to search effectively for extra- solar planetary systems is assessed in terms of its astrometric accuracy, magnitude, threshold, and lifetime. Given the performance (0.0015 arc-second at 11th magnitude) estimated in the Phase A study, Hipparcos should detect any "Jupiters" associated with at least 80 stars, provided its lifetime can be extended. A better detector aboard Hipparcos, perhaps a Charged Coupled Device (CCD), would increase the number of candidates that can be investigated.
And that bring us back to the abandonned Agena / space station option. Unlike Hipparcos, it would observe a pre-determined programme of up to 40 000 selected stars prepared in advance. This option permits to include objects of special interest but requires long and complex pointing. Such a system could use more powerful optics and could reach fainter stars. It would also have a very long useful life and may benefit from regular upgrades by astronauts emplacing better and better CCDs as technology improve.
Other instruments potentially able to participate in this search include the Space Telescope camera systems (which account for my interest in the search) and the Space Telescope fine guidance system (discussed at this Colloquium by W. H. Jefferys). Perhaps Hipparcos can observe the bright-star candidates for planetary systems, while the Space Telescope observes some faint candidates.
In developing plans for the Hipparcos mission, particularly with regard to choosing its lifetime, I urge ESA to consider participating in this exciting search for "Other Worlds".
William A. Baum
(William Alvin “Bill” Baum is a versatile astronomer, the a co-author on about 20 papers from HST on stellar populations in galaxies and the cosmological distance scale, the amount of missing matter, and dark energy. In 1965 he was appointed Director of the NASA-funded Planetary Research Center in Flagstaff, Arizona. Since 1977 William Baum is a prominent member of the science team that proposed, designed, and tested the Wide-Field and Planetary Camera revolutionary Charge-Coupled Devices (CCDs) to be flown on the Hubble Space Telescope.)
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ARIZONA NEW SPACE TELESCOPE.
Aden B. Meinel of the Yerkes Observatory at the University of Chicago was selected in 1955 to lead a survey of 150 mountain ranges and pick the best site for a new national observatory. The search quickly narrowed to sites in the desert Southwest — four in Arizona and one in California. Kitt Peak had the edge with its clear weather, steady atmosphere and proximity to the UA's astronomy program. The Kitt Peak National Observatory was founded on a sacred Tohono O'odham mountaintop in 1958.
Meinel, Kitt Peak's founding director, joined the University of Arizona in 1961 as an astronomy professor, and his breakthroughs in optics not only led to a new generation of telescopes, but formed the core of another world-class UA program.
In the mid-1960s Meinel become Department Head of the Optical Science Center at the University of Arizona, and a colleague of Gerard Kuiper, the director of the University’s Lunar and Planetary Laboratory until his death in 1973. At some point Meinel came up with the idea of a synthetic aperture telescope whereby multiple mirrors could combine their images to create the equivalent of a larger diameter mirror. It was a major breakthrough.
Astronomers had been somewhat stymied since the late 1940s, when conventional glass mirror telescopes reached their practical limit. Starting in the late 1960s, the idea of making larger telescopes using a series of smaller mirrors started gaining traction among younger astronomers, but it was such a paradigm shift that most veterans in the field dismissed it. At the UA, Meinel was a leading proponent of this new telescope design.
Nearly everything about Meinel telescope broke from convention, from its mirrors and optical system to its alignment and mounts.
"There were two or three dozen innovative ideas that were put into that telescope," says Robert Shannon, a retired UA optical sciences professor who was responsible for building the optics on the Multiple Mirror Telescope and went on to become director of the Optical Sciences Center from 1982 to 1992. "Virtually all of them, including the idea of multiple mirrors, are used in the large telescopes being built nowadays."
Meinel telescope, however, was groundbreaking in another, incredible way.
The story goes that when the Defense Department canceled the manned orbital laboratory project (MOL) in 1969 Meinel slyly talked the Air Force into giving him the seven leftover 72-inch mirror blanks, and he began work on what would become the Multiple Mirror Telescope.
Meinel, who initially used the name "Project Colt" for the telescope's six-mirror design, published a paper describing the telescope in 1970. His paper led to a collaboration between the UA and Fred Whipple at the Smithsonian Astrophysical Observatory, which offered a location near the top of Mount Hopkins, south of Tucson.
The MMT should have been constructed jointly by the Smithsonian Institution and the University of Arizona on the basis of a Memorandum of Understanding signed on December 23, 1971. But in 1972 Meinel faced a major crisis. He was bluntly told by the military that the mirrors were needed elsewhere. Ultimately, and unfortunately, the MMT had to settle for a classic mirror with an equivalent aperture of 186 inches (4.7 meters). After a lengthy development and construction period, the telescope saw first light on May 9, 1979.
Meinel was greatly frustrated by the military decision that sunk his multi-mirror idea. Procuring those space, military mirrors had been an extraordinary adventure, but he was expressedly forbidden to talk about it to anybody.
It all had started in 1969, the year men walked on the Moon. Unbestknown to the populace, another very advanced space program had been run in parallel. Just like Apollo and its Kennedy harrowing deadline (before this decade is out) spy satellites were a great tribute to mankind technological prowess.
(OTL MMT with its six mirrors "borrowed" from the canceled MOL manned spy satellite. ITTL it will be different)
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OFFICE OF THE ADMINISTRATOR
September 12, 1969
To: the honorable Robert C. Seamans, Jr. Secretary of the Air Force
Washington, D. C. 20330
Dear Bob:
As you know, NASA's long range plans in space astronomy point toward the eventual development and operation of very large diffraction limited orbital telescopes. One step along the way that we are considering is a large stellar telescope (ATM-B) for operation with the second "dry workshop", planned for flight in 1974. We have, with the assistance of the MOL team, taken steps to have Dr.
Aden Meinel of the University of Arizona and Mrs. Olivier and Waite from the Marshall Space Flight Center examine the existing MOL hardware at Eastman Kodak.
Their purpose is to make a preliminary evaluation as to the suitability of this equipment for stellar astronomy, the steps that might be required to so modify it, and the probable compatibility of the system with the Apollo Telescope Mount and dry workshop. We expect to have their preliminary findings within several weeks.
In the event their report is positive, NASA would see the next step as a detailed technical feasibility study. Under the circumstances, this study would be classified and probably best contracted' for by the DOD with reimbursement from NASA. We feel we can progress this far without any commitment being sought or implied as to the'actual use of DORIAN systems or technology by NASA.
If the feasibility study were to show significant advantages of such utilization, we could then come to grips with the security and program policy issues that this might raise.
In the longer term, we are vitally interested in the question of how NASA should move in the development and testing of very large optics, and what role the classified capabilities — technology and facilities — should play therein. This topic can await further elaboration until the
more immediate questions of existing hardware have been resolved.
Sincerely,
Homer E. Newell • NASA Associate Administrator for space science
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September 15, 1969
OFFICE OF THE SECRETARY
SAMUEL H. HUBBARD
Technical Advisor
MOL Program
MEMORANDUM FOR NRO DIRECTOR DR. WILLIAM MC LUCAS
SUBJECT:
NASA Astronomy Program Considerations of KH-10 DORIAN "Manned Orbiting Laboratory" Technology for space astronomy missions
The NASA Orbiting Astronomy activities center principally on the OAO Program. This program which has been underway since 1965 is approaching completion of a highly successful and scientifically useful year of astronomical observations by OAO-II.
As to the NASA's future intentions relative to this field, a very strong case has been made to the Presidential Space Task Group for a vigorous orbital astronomy program even if faced with severe and unanticipated funding restrictions.
The Agency's plans call for an evolutionary continuation of the OAO series featuring instrument improvements in both performance and capability. By OAO-G, in the early 1980's, the plan calls for a man tended 120-inch diameter diffraction limited telescope in orbit for a much extended duration. To reach this goal, it has been estimated that a program expenditure level of $100 million annually will be necessary commencing no later than FY 1971. This would be about twice their current level.
A large but very uncertain fraction of this $100 million level is planned for the acquisition of manufacturing and test facilities capable of developing the 3 meter optic. Hence the sudden interest in the Eastman facilities.
As I see it, the problem has two distinct facets. One of these is the physical facilities required; and the second is the technology involved in designing, manufacturing and adequately testing the optic. At Colonel Allen's suggestion, I discussed this matter with
Dr. A. Meinel who along with others has just recently completed a review of the status of competence and capabilities of our major optical manufacturer for Dr. Land under his PSAC responsibilities. Based on this current information it is Mienel's view that the existing technological and facilities basis at both Perkin Elmer and Itek are, with some relatively minor upgrading, quite capable of doing the NASA job. Incidently, Meinel also calls attention to the existence of the imminently applicable but near idle 150 inch colimator at Wright Field.
The second factor, NASA's desire to avoid repeating the learning phase represented by Eastman's experience with DORIAN, could be far more severe. However, with suitable consulting services which appear readily available, Meinel believes this, too, could be largely avoided.
An uncertainty in this entire business is the schedule by which NASA would want the 3 meter mirror if it can be assumed that technology is not constraining. I am aware of some discussion of a two meter stellar telescope, a derivative of the Apollo Telescope Mount, as a primary element of the second Skylab in AAP. This mission is currently scheduled for mid calendar 1974. In order to meet such a schedule, the telescope work should be initiated at once--especially if it is to be done by a supplier other than Eastman. Perhaps if a sufficient transfer of technology could be arranged, NASA could begin a two meter program with either Itek or Perkin Elmer and a more lengthy three meter program with the other. Meinelfeels either could do either job. This would unquestionably be costly and program scheduling factors might not require a parallel development.
However, it would certainly be a welcome (in many quarters) shot in the arm for the country's optics community.
A second and potentially related step would be to follow a two meter telescope in AAP in mid 1970 with a two meter or larger telescope in the OAO series in late 1970. Such a program could entail by-passing OAO-E and F in favor of what is now planned as OAO-G.
A program of this scope is being discussed within NASA and is reported to be favorably received. NASA has expressed interest in studying the problem of integrating a KH-10size mirror into the ATM design and will, I understand, ask for permission to make such an analysis. It should involve briefing not more than two or three people on the Eastman operation. Attendant to the study would be an estimate by someone like Dr. Meinel as to the degree of difficulty involved in getting from the DORIAN primary mirror design to one suitable for stellar astronomy.
To summarize, it appears that an approach can be developed that will make possible an adequate "white" facility capable of fulfilling NASA requirements. There also appears to be a way in which excessive duplication of existing developments can be avoided.
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