DOMAIN OF THE INVENTION

[0001 ] This invention is relative to a manufacturing process for a type of telescope whose innovation is to have simultaneously the following characteristics:

- athermal

- lightweight

- optical quality for visible and IR applications

- low cost

- fast production cycle

- potential for compact system with low F number at no extra cost, the F-number being the ratio of the system’s focal length to the diameter of the entrance pupil

[0002] While telescopes with some but not all of the mentioned characteristics exist and can be designed to meet specific requirement, the proposed telescope fulfills all these aspects all together, making the design and the technology associated to this type of telescopes innovative.

[0003] While referring to a design of a specific prototype telescope already produced, the invention covers any possible optical and mechanical design based on the proposed method of production of the optical surface and design of athermal, or non athermal, telescopes based on the specific coupling between the optical surface and the mechanical structure of the telescope.

STATE OF THE ARTS AND ITS SHORTCOMINGS

[0004] A large range of telescopes exist for many applications: terrestrial telescopes, space telescopes, airborne telescopes, for scientific and military and civilian applications. Their functions are for imaging, detection, LIDAR, data transmission and reception, etc. Each application has specific requirements for which the telescope is designed, mainly driven by optical quality, mass, interface, stability to environmental conditions such as temperature and vibrations. The more stringent the requirement are, generally, the more difficult it becomes to design and build the telescopes, requiring longer manufacturing times and increased costs. No telescopes exist that comprise at the same time all of the following characteristics:

- athermal

- lightweight

- optical quality for visible and IR applications

- low cost

- fast production cycle

- potential for compact system with low F number at no extra cost.

State of the art telescopes can achieve some of the mentioned performances but not all together. A major shortcoming of telescopes with replicated Fresnel lenses is that they do not have good optical quality for visible and IR applications. Furthermore, high quality space telescopes with great stability as far as temperature and vibration concur cost a lot and require very long time and elaborate manufacturing processes. Commercial off the shelf telescopes are not athermal. And aluminum mirrors produced by diamond turning have not enough good optical quality and roughness for application in the visible and near IR wavelengths.

[0005] Telescopes with low F number are largely required but often not produced because of their high cost associated with the difficulty in the manufacturing of their high aspherical optical surfaces that requires special polishing machines and a dedicated metrology. OBJECT OF THE INVENTION AND TECHNICAL TASKS TO BE SOLVED

[0006] It is therefore an object of this invention to produce cheap, and even disposable telescopes. Thus, it is the main object of the invention, regardless of the application area, to provide a telescope of low cost for the resulting performance simultaneously:

- athermal

- lightweight

- optical quality for visible and IR applications

- low cost

- fast production cycle

- potential for compact system with low F number at no extra cost.

THE SOLUTION ACCORDING TO THE INDEPENDENT CLAIMS

[0007] The technical tasks are solved by a manufacturing process for a telescope according to claim 1 . The use of a specific material both for the mirrors and for the mechanical structure make the telescope athermal. The use of metal with low density (i.e. aluminium), that can be further easily machined, makes the telescope lightweight. The use of a precise replication technology to shorten the manufacturing time of the optics makes the telescope low cost and allows the possibility of high volume production due to the short time production process.

[0008] The telescope according to the manufacturing process of this invention does not have any of the mentioned shortcomings while it comprises all the mentioned characteristics all together making it a good solution for many optical applications. And the proposed mirror manufacturing technology based on replication overcomes the cost problem by decreases greatly the costs and the production time when many identical telescopes are required.

[0009] The invention will be disclosed and explained referring to the figures which show examples of executions. They show:

Figure 1 A backing structure that provides structural stability to the mirror;

Figure 2 A telescope, in this case a Ritchey-Chretien reflector with a diameter of

200 mm and a focal length of 500 mm that comprises a primary mirror and a secondary mirror, both produced with the proposed technology, and with an athermal design;

Figure 3 An optical master for a primary mirror of a telescope used to form the thin layer of Nickel with the mirror on top of it during its manufacturing through replication;

Figure 4 An optical master for a secondary mirror of a telescope used to form the thin layer of Nickel with the mirror on top of it during its manufacturing through replication;

Figure 5 A primary mirror;

Figure 6 A secondary mirror.

[0010] This telescope is based on optical surfaces that are produced by replication technology from precise optical masters whose shape is opposite in curvature with regard to the desired mirror. The concept is to have as many as required or as few as just one optical master, where maximum effort and resources can be allocated to reach a very good optical quality, from which many mirrors can be replicated. The masters can be produced in glass, ceramic, plastic, metal or any other material and can be as thick and heavy as required to facilitate the fabrication process. The replication technology, that in this case is a deposition of a thin layer of metal but could be any layer deposited by a coating process is being transferred directly to the telescope structural component thereby producing an essentially finished telescope.

[001 1 ] The structure can be made in any suitable lightweight material including aluminium alloy to perfectly match the coefficient of thermal expansion of the metallic layer so that any change of temperature will not deform the mirror. As an alternative, the material can be e.g. Carbon Fibre Reinforced Polymers (CFRP), Silicon-Carbide (SiC) or Carbon-fiber reinforced Silicon Carbide (CeSiC®) which consists of a matrix of Silicon Carbide (SiC) reinforced with microscopic carbon fibers of various compositions and lengths. The material is characterized by exceptional hardness and stiffness, high thermal conductivity, a low coefficient of thermal expansion down to cryogenic temperatures, and a relatively high fracture toughness (due to the C-fibers). Furthermore, the manufacture of CeSiC components is quick and cost-competitive, and can be adapted to designs of virtually any complexity. Additionally, the backing structure can be made lightweight by machining it in a conventional machine shop and relatively cheap because there are no demanding requirements for the precision of the backing structure since the imperfections of manufacturing of the backing structure are compensated by the bonding layer that fills the gap between it and the optical surface layer. This backing structure can also be made of materials with different coefficient of thermal expansion (CTE) with respect to the electroformed layer. The bonding material, then generally softer, can absorb the differentials.

[0012] The direct producing of an essentially conventional design telescope mirror with the mentioned characteristics is but one possibility when the mirrors subsequently can be integrated in the telescope. The telescope structure will be designed so that all the mechanical parts are made with the same metal, e.g. aluminium-alloy, used for the backing structure. The alternative is to carry out this process on a completed telescope structure eliminating the assembly and integration process, further reducing costs.

[0013] In case of optical systems, it is usually very expensive to produce the optical surface of the mirrors because of the elaborate efforts for obtaining a good quality of the mirror. The here proposed technology allows to greatly reduce these costs since the efforts are only necessary for the master which is then used to produce many mirrors, even in numbers greater than one hundred. Further, the use of the backing structure, in particular of a lightweight backing structure, allows to produce a mirror more lightweight than a conventional mirror since less structural requirements are given for the backing structure in respect to a mirror that is ground and polished directly. As a consequence and benefit, very complex optical systems to form very compact lightweight, athermal telescopes can be designed and produced at low cost.

[0014] The telescope as shown in figure 1 is designed so that all the mechanical parts are made with the same metal, e.g. aluminium-alloy, comprising:

- the primary mirror 1

- the secondary mirror 2

- the optical tube 3 - the supports of the secondary mirror 4

- the alignment system for the secondary mirror 5

- the interface for their installation 6

- the supports for the focal plane instrumentation 7.

A telescope so made is insensitive to change of temperature. The use of low density alloy allows to design a very lightweight telescope. The use of all metal parts allows to machine any component as desired without restrictions being a metal easily machinable so to minimise the mass in respect to the mechanical stability. Finally, the proposed manufacturing process for the optical parts allows to have mirrors of the same metal used for the other components of the telescope which is usually impossible when low cost direct polishing of aluminium mirrors is considered or when the mirrors are made in standard glass or ceramic. The alternative is to carry out this process on a completed telescope structure eliminating the assembly and integration process, at a very high cost.

[0015] Figure 2 shows a telescope, in this case a Ritchey-Chretien reflector, with a diameter of 200 mm and a focal length of 500 mm that comprises a primary mirror and a secondary mirror, both produced with the proposed technology, and with an athermal design. The use of such a backing structure 8 as shown in figure 2 enables to make it lightweight. And consequently it allows to produce a mirror more lightweight than a conventional mirror since less structural requirements are needed for the backing structure 8 in respect to a mirror that is ground and polished directly. In this case therefore, very complex optical systems to form very compact lightweight telescopes as shown in figure 1 can be designed and produced at low cost, being then also possible to design optical system with high aspherical mirrors.

[0016] The production of the optical mirrors is explained in more detail in view of figures 3 and 4. An optical component with a curvature opposite to the mirror required but with the same required optical quality in term of surface shape and roughness is put into an electrolytic bath where the applied current transfers metal ions and deposit them on the master, the cathode. The thin layer of metal deposited on the cathode, e.g. a nickel layer 1 1 whose thickness may range from a few microns to a few millimetres, becomes the optical surface of the mirror 1 . Before removing it from the master or mandrel 9, the thin layer is bonded by an adhesive or glue 10, solder or any other attachment process to a mechanical reinforcing structure 8. Such adhesive material 10 can e.g. be Indium or any other low melting alloy. After the hardening of the bond, the thin layer 1 1 is finally released from the master or mandrel 9. It has maintained the optical quality of the master 9. The master 9 can be then cleaned and re-used to produce another mirror.

[0017] The same principle does apply for manufacturing a secondary mirror as shown in figure 4. The thin layer 1 1 on the mandrel 9 is glued to the backing structure 12 for said secondary mirror 2.

[0018] Given the short time to deposit the thin layer 1 1 and to bond it to the backing structure 8, 12, this process is fast, and it allows the production of quality large optical mirrors as shown in figures 5 and 6, making it therefore also cost effective. Additionally, mirrors characterised by low F number and great asphericity, usually very expensive, can be replicated in a very short time and a very low cost since the cost is mainly the one of the master and therefore diluted when a great number of mirrors are produced by the same master.

[0019] As said the backing structure 8, 12 for the mirrors can be made in any suitable material including aluminium alloy to perfectly match the coefficient of thermal expansion of the metallic layer 1 1 so that any change of temperature will not deform the mirror. Additionally, the backing structure 8 as shown in figure 2 in an example can be made lightweight by machining it in a conventional machine shop and relatively cheap because there are no demanding requirements for the precision of the backing structure since the imperfections of manufacturing of the backing structure are compensated by the bonding layer that fills the gap between it and the optical surface layer.

List of Numerals

1 primary mirror

2 secondary mirror

3 optical tube

4 supports of the secondary mirror

5 alignment system for the secondary mirror

6 interface for their installation

7 supports for the focal plane instrumentation

8 backing structure of primary mirror 1 master, mandrel

glue

nickel layer

backing structure of secondary m irror 2 mandrel to backing structure 12 backing structure of primary mirror 1