AU603025B2 - Main mirror for a reflecting telescope - Google Patents

Description

(IMPORTANT- Cross out inapplicable words in above Form,) (Juli 1986)

PCT

OPI DATE 14/06/89 AOJP DATE 20/07/89 APPLN. I D 27872 89 PCT NUMBER PCI/DE88/00726 INTERNATIONALE ANrV INTERNATIONALE ZUSAV11V1h~NAKJh11 AU1- L)EM UEBIET 'DES PATENTWESENS (PCT) (51) Internationale Patcntklassifikation 4: (11) Internationale Veroffentlichungsnummer: WO 89/ 04980 G02B 5/10, 23/00 At(43) Internationales Veroffentlichungsdatum: 1. Juni 1989 (01,06.89) (21) Internationales Aktenzeichen: PCT/DE88/00726 Verdffentlicht Mit internationalem Recherchenberich t.

(22) Internationales Anmeldedatum: 17. November 1988 (17.11.88) (31) Prioritiitsaktenzeichen: P 37 39 841.5 (32) Priorit~tsdatum: 20. November 1987 1.87) 6 (33) Prioritiitsland: DE (71)(72) Anmelder und Erfinder: HODGENELL, Hermann isedmet coa s unde [DE/DE]; Maxdorfer Str. 47, D-6715 Lambsheimn S~Io 49 aI~ ns cadec u or Be-!in 33 (DE).

(81) Bestimniungsstaaten: AU, JP, KR, SU, US.

(54) Title: MAIN MIRROR FOR A REFLECTING TELESCOPE (54) Bezeich,-,ung: PRIMXRSPIEGEL FOR EIN SPIEGELTELESKOP (57) Abstract A main mirror for a reflecting telescope comprises a plurality of individual polygonal reflecting elements (1 to 11) and positioning and adjusting elements (12) Connected thereto. Prior art main mirrors of this type have a poor capacity for transmitting point images and for modulation and are unsuitable for use in the infrared region, because the positioning and adjustment elements, in particular the measuremont sensors arranged in the region of the separating lignes between the individual polygonal reflecting 6lcments (I to 11) emit interfering thermal radiation. Further,more, the polygonal reflecting elements (I to 11) of prior art main mirrors (20) are expensive to manufacture. In order to remedy these drawbacks, the reflecting surface forms a complete circle by means of connecting reflecting elements (I to 8) connected radially to the outer edges of the polygonal reflecting elements the reflecting elements (I to 11) are made from a lightweight preformed material, and the positioning and adjustment elenments (12) are arranged below the reflecting elements (I to 11).

(57) Zusaanmenfassung, Die Erfindung bezieht sich auf einen Primlirspiegel fdr emn Spiegelteleskop, aus einer Vielzahl 6irizeli-er, vieleckiger Spiogelk6rper (I bis 11) und aus diesen zugeordneten Lagerungs- und Justierelementen Es hat sich gezeigt, da emn voibekannter Primtlrspiegel dieser Art einerseits emn schlechtes Plunktbild- und Modulations-Obertragupgverhalten aufweist und andererseits nicht infrarottaugli ch ist, da din im Bereich der Trennilinien zwischen den einizel'ien vieleckigen Spiegelk6rpern (I bis 11) angeordneten Lagerungs- und Justierlemente, insbe ,ondere deren Mei~sensoren, einc stbrfnde Wilrmestrahlung a geben. Schliealich sind dic vieleckigen Spiegelkrpet bi I des vorbekaninten Primiirspiegels aufwendig in der Flerstellung. Zur Vermeidung dieser Nachteile sieht die Erfindon:. vor, dA~ die Spiegelflutche durch radial an die Auaenrilnder der vieleckig ,en Spieget16rper anschliellende AnschluS-Spiegelkutrper (I bis 8) eine Vollkreisflllche bildet, dag die Spiegelkutrper (I bis 11) aus massereduziertemn vorgeformten Werkstoff gebildet sind und daa die Lagerungsund Justierelemente (12) unterhalb der Spielvelk6rper (I bis 11) angeordnet sind.

:s I i 1 PRIMARY REFLECTOR FOR A REFLECTOR TELESCOPE S SI

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h 4 se aS 31r The invention relates to a primary reflector for a reflector telescope. It has particular but not exclusive application to reflector telescopes which comprise a plurality of polygonal reflector bodies, and positioning and adjusting elements assigned to said reflector bodies.

A known reflector telescope of this kind is the Mauna Kea reflector telescope which has a 10m diameter reflector which is still in the planning stage (Sterne und Weltraum, 1984/8-9, p.412, Appl. Optics, No. 14, 2631-2641). In this reflector telescope, the primary reflector is formed from 36 hexagonal reflector bodies which combine in a honey-comb structure, to form the reflector surface. In the centre of the reflector surface, at the Cassegrain focus, a segment of the reflector surface is omitted to facilitate observation. Manufacture of the individual hexagonal reflector bodies themselves is very problematic. The reflector bodies are segments of a paraboloid which must each be cut into a hexagonca shape (Appl. Optics, Vol.19 (1980), No. 14, 2332-2340).

Each reflector is manufactured from a circular blank by first accurately deforming the blank by applying specific shearing and bending forces to the borders of the blank.

Once the blank is so deformed, a spherical shape is ground into the blank. Then the forces are removed. Insofar as the applied forces have been accurately selected, each reflector body conforms to a desired shape of a paraboloid segment of the primary reflector once the forces have been unloaded. However, it is found that faults occur when cutting these segments to hexagonal shape.

-2- Furthermore, the positions of the individual thin-walled hexagonal reflector bodies have to be readjusted, depending on the position of the primary reflector of the reflector telescope, on thrusts due to wind and on temperature variations. For this purpose, the support points of each reflector body are connected with three position controllers to refocus the reflector body and to adjust it in two inclination directions. At the edges of the reflector bodies, displacement sensors are provided which measure the displacements of adjacent reflector bodies with respect to each other. Together with three inclination sensors which measure the total curvature of the reflector body, the displacement sensors provide information which is processed in a computer system controlling the total of 108 position controllers. Since there are a total of 168 different sensors, many of whose function may be duplicated i by other sensors, failure of a few individual sensors can Sbe tolerated. This arrangement allows the front sides of the reflector bodies to be left free from disturbing monitoring systems. Sensors and position controllers must op operate with an accuracy of at least 50 nm.

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Theoretical investigations were undertaken for the primary reflector of the reflector telescope described in German patent DE 35 38 208. The reflector bodies of this invention are circular-disk shaped, such that free spaces for the support of the reflector bodies and for the supporting bars structure or its shadow artas are formed between the individual circular reflector bodies. It has been found that these free spaces jeopardize the suitability of the primary reflector to detect infrared radiation because the metal components in the viscinity of the free spaces of the support structure of the primary reflector transmit their own local thermal radiation to the detector positioned at the focus of the primary reflector.

This local radiation interferes with signals received from space. The ability of the primary reflector Af L -o 0 i -3to detect infrared radiation from outer vpace is necessary for detecting dark bodies in outer space, ;eing present as mass, but not visible for the human eye .ky means of the primary reflector. Theoretically, the phenomenon of local infrared thermal radiation of the free spaces can be minimised by technical counter-measures but these countermeasures are extremely expensive.

Similar theoretical investigations were undertaken for the primary reflector of the Mauna Kea reflector telescope which has a 10m reflector diameter. Here, too, disturbing local infrared radiations were discovered, in spite of the basically closed reflector surface, infrared radiation ocould still be guided back to the sensors positioned at the area of the contact lines of the adjacent hexagonal reflector bodies (the sensors being provided for measuring the displacement of adjacent reflector bodies with respect to each other). The primary reflector of the Mauna Kea reflector telescope has a total of 168 displacement sensors and a total of 36 hexagonal reflector bodies. These too o. radiate an appreciable amount of local radiation which ge again results in a disturbing amount of local infrared i radiation. Thus, the primary reflector according to the o a state of the art not only has the problem that the individual reflector bodies, which during manufacture are ground under load, are only ground in the form of an s.o 00 aspherical off-axis section, but also has the problem of having impaired ability to detect infrared from space due to the absolute necessity of having displacement sensors.

Finally, the non-uniform outer edge margin contour of the known primary reflector which is composed of hexagonal reflector bodies, has resulted in poor point image and poor modulation transmission behaviour.

r: A i7 S ii 4 Hence it has been found that a known primary reflector of this species has a poor point image and modulation transmission behaviour and is not adequately capable of detecting infrared from space because the positioning and adjusting elements arranged in the area of the border lines between the individual polygonal reflector bodies, in particular the measuring sensors thereof, emit disturbing local heat radiation. Finally, the polygonal reflector bodies of the known primary reflector are expensive to manufacture.

According to the present invention there is provided a primary reflector for a reflector telescope, said reflector comprising a plurality of polygonal reflector bodies manufactured from blanks, a reflector surface, and positioning and adjusting elements assigned to and positioned below said reflector !od.kes wherein the reflector surface is a generally circalar surface with one or more curved edge margins, said surface being formed substantially by said reflector bodies, a number of said reflector bodies being radially positioned at and/or adjacent to said curved edge margins, eaich of said reflector bodies is provided with a support structure having hollow spaces for reducing the weight of each of said reflector bodies, the blanks of said reflector bodies, prior to grinding and polishing, have a surface shape approximately corresponding to the aspherical shape of a segment of the reflector surface, and during manufacture, the blanks are ground and polished fcr the final processing of surface and shape of the reflector surface.

The reflector bodies which are not at or adjacent said edge margins may be of identical shape and may be ground and polished in composite action during manufacture.

I 4 1 1- L The plurality of polygonal reflector bodies may comprise regularly and irregularly shaped polygonal reflector bodies, said irregulary shaped bodies being radially positioned at and/or adjacent said curved edge margins, said regularly shaped bodies being positioned away from said edge margins.

Said plurality of reflector bodies may be made of quartz or K quartz ceramics. Said support structure may be provided with a honey-comb structure provided with said hollow I spaces.

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Displacement sensors for measuring the relative positions .of the individual reflector tndies may be mounted in said hollow spaces and that, by means of a computer-aided t..

system, the displacement sensors may be used to control o actuating elements and the adjusting elements which are necessary for accurate adjustment and control of the reflector bodies and which allow for permanent monitoring.

T!e reflector bodies may take the shape of an aspherical off-axis section. Preferably, the primary reflector is of parabolic shape. However, it is to be appreciated that a o different shape may also be provided, e.g. for a Ritchey-Chretien reflector telescope. If the overall diameter or the large total aperture of the primary S.i reflector is large, its individual reflector bodies may be off-axis sections of the primary reflector.

In the following an embodiment of the invention is described in more detail by way of example only with reference to the accompanying drawings in which: Fig 1. shows a top view of an embodiment of the primary reflector according to the present invention having a central apertt're, PU0

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c~ 6- Fig 2. shows an enlarged perspective representation of an individual hexagonal reflector body of the primary reflector of Fig i, Fig 3. shows the support elements of a reflector body in the area of a support element, and Fig 4. shows a cross-section through the reflector body in the area of a support element.

The primary reflector 20 for a reflector telescope is shown in Fig 1. It consists of a plurality of polygonal reflector bodies 1 to 11 and of positioning and adjusting 0 elements 12 assigned thereto. The outer edge margin of the e primary reflector 20 is formed from irregularly shaped t polygonal reflector bodies 1 to 6 having different shapes, whose outer edges each conform to a segment of curvature of the edge of the primary reflector 20. Adjacent to these outer edge margin reflector bodies 1-6, towards the interior, are further irregularly shaped polygonal edge margin reflector bodies 7, 8. Thereafter the surface of the primary reflector 1 is formed by a plurality of regular hexagonal reflector bodies 9. A circular aperture 19 is located towards the centre of the primary reflector around which are positioned a number of irregularly shaped SI. inner edge margin polygonal reflector bodies 10, 11 which each have a curved outer edge which conforms to a segment of the curvature of the central aperture 19. In this way, i the reflector surface of tha primary reflector 20 is achieved by the plurality of regular hexagonal reflector bodies 9 and by each of the edge margin reflector bodies 1 to 8 being generally joined radially to outer borders of the outermost regular hexagonal reflector bodies 9 to form a full-circle surface. In the centre of the primary reflector 20, around its central aperture 19, further edge margin reflector bodies 10, 11 are provided at the outer borders of the regular hexagonal reflector bodies 9.

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Each reflector body 10, 11 and in particular each regular hexagonEl reflector body 9 is manufactured from a blank which consists of a preformed, low-weight material having a honey-comb structure. Preferred materials are quartz, quartz glass or quartz ceramics which allow for a low-weight construction of the primary reflector. Due to the large total aperture width of the primary reflector the individual reflector bodies 1 to 11 consist of low-weight materials and form off-axis sections of a primary reflector. Since the blanks are preformed, they need only be finished with grinding and polishing. This means that the blank of each reflector body 1 to 11 is generally already in its final shape prior to the grinding process, and is only processed with respect to surface and shape by means of the grinding process. The blanls can either be ground individually or ground in group., that is, in composite action. The underside of each reflector body 1 to 11 is provided with boreholes 21 into which individual positioning and adjusting elements 12 engage.

A substantially closed, full-circle surface reflector surface of the primary reflector, being itself formed of a plurality of polygonal reflector bodies, allows outstanding point image achievement as well as excellent modulation transmission function. Furthermore, the arrangement of all support and adjustments elements below the reflector bodies means that in the area of the effectively closed reflector surface, little disturbing local infrared sources are present, and thus, little disturbing local infrared radiation will be generated such that the primary reflector is able to proficiently detect infrared from outer space.

The individual reflector bodies of the primary reflector are made of preformed light-weight structures. The nonedge margin reflector bodies are substantially hexagonal in shape whilst the edge margin reflector bodies are polygonal shape, some of which have a curved border.

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I I *1 -8- The reflector bodies are ground and polished such that the degrees of freedom of the grinding and polishing tools enable an off-axis segment of a primary reflector surface to be prepared. The guidance of the polishing tools is actively computer-controlled by means of polar coordinates.

Thus, a primary reflector of large diameter can be prepared, the reflector bodies of which being immediately off-axis are ground and end-polished, being joined together in a substantially free of gaps manner.

Fig 3. shows the perspective arrangement of an individual hexagonal reflector support platform 12 having a total of six positioning and adjusting elements 12 on a support plate 16. As shown in Fig 4, the individual positioning and adjusting elements 12 penetrate the boreholes 21 on the undersides of the individual reflector bodies 9, without protruding out of their reflector surface. The double-walled support plate 16 is provided with pressure-medium supplies 14, 15 which are connected to actuating elements, embodied as positioning and adjusting cylinders 18, in which positioning and adjusting pistons 17 are guided, being connected in an integral manner with the positioning and adjusting elements 12. In this way, the reflector bodies 1 to 11 of the primary reflector 20 can be adjusted.

The positioning and adjusting elements of each reflector body 1 to 11 are arranged and adjusted such that each corresponding reflector body 1 to 11 can be held in any position required by the primary reflector, by means of hydraulically controllable supports, in order to accurately focus the primary reflector. The positioning and adjustment elements may be constantly readjusted by means of computer-controlled fine-adjustment elements. This means that for the different irregularly shaped reflector bodies of the outer edge margins, arrangement of positioning and adjusting elements is selected differently with regard to consideration of stability and weight of the respective reflector body.

9 Thus the positioning support and adjustment elements, and the inclination sen,sors are disposed on the undersides of the reflector bodies. Thus, each reflector body can be controlled separately for adjustment to a common focus.

This is computer-controlled since extremely fine, tolerances have to be met. The optically ineffective separation lines between the individual reflector bodies are, thus, substantially free from any disturbing thermal radiation and do not affect image quality. Thus, the primary reflector is absolutely infrared-suitable and is extremely infrared sensitive. The diameter is extendable, theoretically, without limits.

In a manner not shown in detail, displacement sensors are located in the hollow spaces of the reflector bodies wherein the displacement sensors do not hinder the ability of the primary reflector to detect infrared from outer space.

A large low-weight reflector (not illustrated), being ground to produce a surface which is symmetric with respect to the axis of rotation, can be positioned in the centre of the primary reflector to create a full circular ixurface.

The embodiment has been advanced by way of example only and modifications are possible within the scope of the invention.

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Claims (7)

1. A primary reflector for a reflector telescope, said reflector comprising a plurality of polygonal reflector bodies manufactured from blanks, a reflector surface, and positioning and adjusting elements assigned to and positioned below said reflector bodies wherein the reflector surface is a generally circular surface with one or more curved edge margins, said surface being formed substantially by said reflector bodies, a number of said reflector bodies being radially positioned at and/or adjacent to said curved edge margins, each of said reflector bodies is provided with E support structure having hollow spaces for reducing the weight of said reflector bodies, the blanks of said reflector bodies prior to grinding and polishing, have a surface shape approximately corresponding to the aspherical shape of a segment of the reflector surfaice, and during manufacture the blanks are ground and polished for the final processing of surface and shape of the reflector surface.

2. A primary reflector according to claim 1 wherein the reflector bodies, which are not at or adjacent said edge margins, are of identical shape and are g.it ,nd and polished in composite action during manufacture.

3. A primary reflector according to claim 1 or 2 wherein said plurality of polygonal reflector bodies comprise regularly and irregularly shaped polygonal reflector bodies, said irregularly shaped bodies being radially positioned at and/or adjacent said curved edge margins, said regularly shaped bodies being positioned away from said edge margins. i i Cnrr~ '1 11

4. A primary reflector according to any one of claims 1 to 3 wherein said plurality of reflector bodies are made of quartz or quartz ceramics.

A primary reflector according to any one of claims 1 to 4 wherein said support structure is provided with a honey-comb structure provided with said hollow spaces.

6. primary reflector according to any one of claims 1 and 5 wherein displacement sensors for measuring the relative positions of the individual reflector bodies are S. mounted in said hollow spaces and that,. by means of a computer-aided system, the displacemenG sensors are used to control actuating elements and the adjusting elements which are necessary for accurate adjustment and control of the Sreflector bodies and which allow for permanert monitoring.

7. A primary reflector substantially as hereinbefore described and illustrated with reference to the Saccompanying drawings. oee t i DATED THIS 2ND DAY OF AUGUST, 1990. HERMANN HUGENELL i By Its Patent Attorneys GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. Wi