HERSCHEL/UVCI ALIGNMENT PLAN

DIPARTIMENTO DI ASTRONOMIA E SCIENZA DELLO SPAZIO HERSCHEL/UVCI ALIGNMENT PLAN M. Romoli (a), G. Corti (a), F. Landini (a) (a) Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze (Italy) Technical Report TR2-2004 Date: March 2004 Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, L.go E. Fermi 2, 50125 Firenze (Italy) Ph.+39 (055) 23.07.51

CONTENTS 1 APPLICABLE DOCUMENTS...3 2 INTRODUCTION...3 3 UVCI SPECIFICATIONS...4 3.1 REFERENCE SYSTEMS...6 4 TOLERANCE MATRIX...7 5 ALIGNMENT SCHEME... 10 6 UVCI ALIGNMENT PLAN... 10 6.1 Cor A integration, alignment, and verification... 10 6.1.1 Assembly of optical components on mechanical holders... 10 6.1.2 Polarimeter section integration and alignment... 11 6.1.3 Telescope component integration, alignment and verification on the optical bench (except IO)... 11 6.1.4 Boom assembly component integration... 13 6.1.5 Boom assembly integration and alignment on the optical bench... 13 6.1.6 Internal occulter integration and alignment... 14 6.1.7 Cor A alignment verification... 14 6.1.8 Cor A vibration test and alignment verification... 14 6.2 Cor B INTEGRATION, ALIGNMENT, AND VERIFICATION... 14 6.3 Cor A + Cor B INTEGRATION AND ALIGNMENT VERIFICATION... 15 6.4 UVCI VIBRATION TEST AND ALIGNMENT VERIFICATION... 15 6.5 UVCI INTEGRATION ON THE ROCKET MODULE... 15 6.6 UVCI ALIGNMENT VERIFICATION WITH SUN SENSORS... 15 7 LIST OF ACRONYMS... 16 Ref.: AlignPlan_TR.doc 2

1 APPLICABLE DOCUMENTS UVCI_030415_OWG Ultraviolet and Visible-light Coronagraph for HERSCHEL SR, UVCI OWG, April 15, 2003 UVCI_020115_NAL UVCI for HERSCHEL: AIV Plan, G. Naletto, January 15, 2002 UVCI_020221_OWG Concept design of the visible-light path for UVCI/Herschel, UVCI OWG, February 21, 2002 UVCI_020306_OWG UVCI for HERSCHEL Sounding Rocket (UVCI-0.3), UVCI OWG, March 6, 2002 UVCI_020717_PDR00 UVCI Design Specification, UVCI-SY-CGS-001, Carlo Gavazzi Space, July 17, 2002 UVCI_020717_PDR01 UVCI Design Report, UVCI-RP-CGS-001, Carlo Gavazzi Space, July 17, 2002 UVCI_020717_PDR02 UVCI Structural Analysis Report, UVCI-RP-CGS-002, Carlo Gavazzi Space, July 17, 2002 2 INTRODUCTION The Ultraviolet and Visible-light Coronal Imager (UVCI) of the HERSCHEL sounding rocket (SR) consists of two almost identical coronagraphs, Cor A and Cor B, mounted as shown in Figure 2.1 inside the rocket payload (Figure 2.2), each one consisting of a visible-light (VL) channel and a UV channel. Figure 2.1 - HERSCHEL/UVCI payload. The coronagraphs are coaligned with their optical axis directed toward the center of the Sun. The basic configuration of HERSCHEL/UVCI consists of 2 sandwich Optical Benches (OB) upon which are mounted the booms, the optical components and the data acquisition instruments. The optical components that will be subject to alignment are of two types: those who perform the imaging, and those who contribute to the solar disk light rejection. The imaging components are the two telescope mirrors: primary mirror (M1), and secondary mirror (M2); the bandpass filter (FM); the visible-light polarimeter assembly (PS); the visible-light detector (VLD); and the UV detector (UVD). The solar disk light rejection components are the boom, that includes the external occulter (EO), 5 baffles (BF), and the solar disk rejection mirror (M0); the internal occulter (IO); and the Lyot stop (LS) placed behind M2. Ref.: AlignPlan_TR.doc 3

The two coronagraphs, Cor A and Cor B, differ in the UV path: Cor A will measure the HI Lyα 121.6 nm line intensity and Cor B will measure the HeII Lyα 30.4 nm line intensity. Therefore, they differ in the coatings of the telescope mirrors, the bandpass filter (Cor B has a filter mechanism to switch from the VL channel to the UV channel, because, as opposed to Cor A, they do not work in parallel), the detector, but the geometry and the optical design are identical, and both coronagraphs require the same alignment procedure. Figure 2.2 - Rocket's payload volume with HERSCHEL/UVCI. 3 UVCI SPECIFICATIONS Table 3.1 summarizes all the UVCI optical specifications. The reference axis is the telescope axis to which all off-axes (y-axis direction) refer to. All distances are along the z-axis. Table 3.1 - UVCI optical specifications. Effective focal length Field of View 470 mm 1.5 3.2 R @ 1 AU Shape: annular sector External occulter (EO) Inner radius: 31.0 mm ± TBD mm Outer radius: 53.5 mm ± TBD mm Off-axis: -75.0 mm ± 0.5 mm Distance EO-M0 2300 mm ± TBD mm Ref.: AlignPlan_TR.doc 4

Surface shape: spherical Sun-light Rejection mirror (M0) Curvature radius: 4600 mm ± 1 mm Inner radius: 18 mm ± TBD mm Outer radius: 65 mm ± 1 mm Off-axis: -75.0 mm ± 0.5 mm (Main axis: -0.517º) Distance M0-M1 400 mm Surface shape: off axis ellipsoidal Primary mirror (M1) Radius: 26.0 mm ± 0.1 mm Curvature radius: 500.0 mm ± 1 mm Conic constant: -0.6377 ± 0.008 Off-axis: -75.0 mm ± 0.5 mm (Main axis: 0.0º) Distance M1-Primary focal plane (PFP) Distance PFP-IO 248.24 mm 24.9 mm Shape: annular sector Internal occulter (IO) Inner radius: 3.45 mm ± 0.01 mm Outer radius: 5.30 mm ± 0.01 mm Off-axis: 7.5 (Main axis: 18.0º) Distance IO-M2 Distance M1-M2 406.86 mm 680.0 mm Surface shape: off axis ellipsoidal Secondary mirror (M2) Radius: 29.5 mm ± TBD mm Curvature radius: 561.4 mm ± 0.75 mm Conic constant: -0.1518 ± 0.0013 Off-axis: 128 mm ± 0.5 mm (Main axis: 0.0º) Distance M2-Filter Filter (FM) 408.69 mm Shape: circular Radius: 19.05 mm (Diameter 1.5") Off-axis: 63.9 mm ± 0.4 mm (Main axis: 4.0º) Filter Helium (HeF) Shape: circular Radius: 15.0 mm Off-axis: 32.3 mm ± 0.5 mm (Main axis: 0.0º) Distance M2-FP (UV path) Distance HeF-FP (UV path) Distance Filter-VL polarimeter (Front lens) VL Polarimeter 808.55 mm 200 mm 493.0 mm Total length: 274.2 mm Diameter: 50 mm Off-axis: 57.8 mm ± 0.5 mm (Main axis: 0.0º) Distance VL polarimeter VL FP (Back lens) 94.9 mm Scale factor: 0.44 arcsec/µm; ~6 arcsec/pixel UV and VL Focal Plane (FP) Image size: 13.8 mm (1024x1024 with 13.5 µm pix size) Spot size (paraxial): < 10 µm over whole field Off-axis: UV: 0.0 mm ± 0.5 mm (Main axis: 0.0º) VL: 59.3 mm ± 0.5 mm (Main axis: -6.1º) Ref.: AlignPlan_TR.doc 5

3.1 REFERENCE SYSTEMS The Global Reference System (GRS) used in this tolerance analysis is shown in Fig. 3.1. UVCI is an off-axis telescope, where the optical axis of the beam path, from EO to FP, lays on a plane which will be called optical axis plane. Fig. 3.1 - Global Reference System (GRS) for one coronagraph. The origin of the axes is the center of the front face of EO; the z-axis is directed along the optical axis of the boom assembly from EO towards M0; the y-axis is directed along the optical axis plane. The G.R.S. will be operatively defined by an alignment cube glued on the optical bench and by the position of a test reticle mechanically placed on the primary mirror focal plane. In order to define the stability requirements and the mechanical positioning tolerances a Local Reference System (LRS) is defined for each component, such that the origin of the reference is centered in the GRS coordinates of the component as defined in Tab. 3.2. The LRS of some components can also be tilted with respect to the GRS as specified by the M x, M y, M z, tilts in Tab. 3.2. Note that for M1 and M2 the origin of their LRS is placed in the center of the mirror, but it is not tilted, as the real optical axis of these two off-axis mirrors is parallel to the GRS z-axis. Ref.: AlignPlan_TR.doc 6

Tab. 3.2 - GRS component coordinates. LRS origin position and reference tilt relative to GRS. Assembly Name Boom-Assy Bench-Assy X [mm] Effective nominal position (G.R.S.) Y Z Mx My [mm] [mm] [deg] [deg] Mz [deg] ITEM External occulter (EO) 0 0 0 0 0 0 Disk rejection mirror (M0) 0 0 2300-0.517 0 0 Baffle 1 (B1) 0 0 375 0 0 0 Baffle 2 (B2) 0 0 770 0 0 0 Baffle 3 (B3) 0 0 1100 0 0 0 Baffle 4 (B4) 0 0 1390 0 0 0 Baffle 5 (B5) 0 0 1640 0 0 0 Primary mirror (M1) 0 0 2694.36 0 0 0 Primary focal plane (PFP) 0 75.0 2451.8 12 0 0 Internal occulter (IO) 0 82.54 2426.9 18 0 0 Secondary mirror (M2) 0 203.0 2034.76 0 0 0 Filter mechanism (FM) 0 139.6 2428.69 4 0 0 He Filter (HeF) 0 107.3 2628.55 0 0 0 UV detector (UVD) 0 75 2828.55 0 0 0 Polarimeter (PL) (Front lens) 0 133.54 1935.67 0 0 0 VL detector (VLD) 0 134.89 1566.60-6.1 0 0 4 TOLERANCE MATRIX The tolerance matrix for the optical components mechanical positioning is given in Tab. 4.1 together with the tuning range and resolution of the alignment tool. Tab. 4.2 gives the tolerance matrix for each assembly mechanical positioning with relative compensator range and resolution. Ref.: AlignPlan_TR.doc 7

Tab. 4.1 - Tolerance matrix for optical components mechanical positioning. Assembly name Boom-assembly Bench-assembly Item EO M0 B1 B2 B3 B4 B5 M1 IO M2 FM UVD PL VLD Mechanical Mounting Tolerances (L.R.S.) x(mm) 0.05 0.05 0.5 0.5 0.5 0.5 0.5 0.05 0.05 0.05 1 0.1 0.1 0.1 y(mm) 0.05 0.05 0.5 0.5 0.5 0.5 0.5 0.05 0.05 0.05 1 0.1 0.1 0.1 z(mm) 1.0 0.05 0.5 0.5 0.5 0.5 0.5 0.5 0.05 0.5 0.5 0.1 0.5 0.1 M x (deg) 1.0 0.02 1.0 1.0 1.0 1.0 1.0 0.05 1.0 0.05 0.1 0.1 0.1 0.1 M y (deg) 1.0 0.02 1.0 1.0 1.0 1.0 1.0 0.05 1.0 0.05 0.1 0.1 0.1 0.1 M z (deg) 1.0 1.0 N/A N/A N/A N/A N/A 0.1 0.1 0.1 N/A 1.0 N/A 1.0 Tuning Range (L.R.S.) x(mm) - - - - - - - ±3.0 ±3.0 ±3.0 - - ±3.0 - y(mm) - - - - - - - ±3.0 ±3.0 ±3.0 - - ±3.0 - z(mm) - - - - - - - ±3.0 ±3.0 ±3.0 ±3.0 ±3.0 ±3.0 ±3.0 M x (deg) - ±1.0 - - - - - ±10 - ±10 ±10 - ±10 - M y (deg) - ±1.0 - - - - - ±10 - ±10 ±10 - ±10 - M z (deg) - - - - - - - ±5 ±5.0 ±5 - - - - Tuning Resolution (L.R.S.) x(mm) - - - - - - - 0.05 0.05 0.05 - - 0.05 - y(mm) - - - - - - - 0.01 0.01 0.01 - - 0.05 - z(mm) - - - - - - - 0.01 0.01 0.01 0.05 0.01 0.05 0.01 M x (deg) - 0.005 - - - - - 0.05-0.05 0.05-0.05 - M y (deg) - 0.005 - - - - - 0.05-0.05 0.05-0.05 - M z (deg) - - - - - - - 0.08 0.03 0.08 - - - - Positioning tolerances and tuning range and resolution are derived using the following limits: mechanical inserts in the optical bench: 0.01 mm; micrometer resolution: 0.01 mm; rotation tool resolution: 5 arcminute; peelable shim thickness: 0.05 mm. Ref.: AlignPlan_TR.doc 8

Tab. 4.2 - Tolerance matrix for assemblies mechanical positioning. Mechanical Mounting Tolerances (L.R.S.) Assembly name Telescope tube Bench Assy 1 + Bench Assy 2 UVCI Sun Sensors x(mm) 0.05 N/A TBD y(mm) 0.05 N/A TBD z(mm) 0.1 N/A TBD M x (deg) 0.002 0.002 TBD M y (deg) 0.002 0.002 TBD M z (deg) 1.0 N/A TBD x(mm) - - - Tuning Range (L.R.S.) y(mm) - - - z(mm) - - - M x (deg) ±0.1 ±0.1 TBD M y (deg) ±0.2 - TBD M z (deg) - - TBD Tuning Resolution (L.R.S.) x(mm) - - - y(mm) - - - z(mm) - - - M x (deg) 0.001 0.0005 TBD M y (deg) 0.005 - TBD M z (deg) - - TBD Ref.: AlignPlan_TR.doc 9

5 ALIGNMENT SCHEME The integration, alignment and verification will be performed according to the following scheme: Cor A integration, alignment, and verification o Assembly of optical components on mechanical holders o Polarimeter section integration and internal alignment o Telescope component integration, alignment and verification on the optical bench (except IO) o Boom assembly component integration o Boom assembly integration and alignment on the optical bench o Lyot trap alignment verification o Internal occulter integration and alignment o Cor A alignment verification o Cor A vibration test and alignment verification Cor B integration, alignment, and verification (same as Cor A) Cor A + Cor B integration and alignment verification UVCI vibration test and alignment verification UVCI integration on the rocket module UVCI alignment verification with Sun sensors 6 UVCI ALIGNMENT PLAN 6.1 Cor A integration, alignment, and verification 6.1.1 Assembly of optical components on mechanical holders The telescope mirrors M1 and M2, the IO and the detectors are to be mounted and glued onto the corresponding mechanical holder before being mounted on the OB. The specifications of the manufactured optics must be provided by the manufacturer or checked. The interface between optics and holder is described in a TBD document. The accuracy with which the optics are mounted on the holder with respect to the nominal interface position determines the adjustment ranges of the alignment tools for the component alignment on the OB. Tab. 6.1 describes the tolerance matrix for the mechanical assembly of the optics on the holders. A z-rotation tools must be foreseen on the M1 holder in order to be able to pre-align M1. The tuning range and resolution are respectively ±5 0 and 0.08 0. Ref.: AlignPlan_TR.doc 10

Tab. 6.1 - Tolerance matrix for optics mounting on holder. Optics name Mechanical Mounting Tolerances (L.R.S.) M1 M2 PFP IO VLD & UVD x(mm) 0.2 0.2 0.1 0.2 0.1 y(mm) 0.2 0.2 0.1 0.2 0.1 z(mm) 0.2 0.2 0.1 0.2 0.1 M x (deg) 1.0 1.0 1.0 1.0 0.5 M y (deg) 1.0 1.0 1.0 1.0 0.5 M z (deg) 1.0 1.0 1.0 1.0 1.0 6.1.2 Polarimeter section integration and alignment TBD 6.1.3 Telescope component integration, alignment and verification on the optical bench (except IO) All telescope components, with the exception of the internal occulter (IO), are mounted and aligned on the optical bench (OB). The OB is described in section 5.1.1 of UVCI-RP-CGS-001, whereas the optical components holders are described in section 5.1.4 of the same document. The OB is provided with inserts for the optical components holders and through holes for the interface with the Cor B OB. The reference system used to position the inserts within 0.01 mm tolerances is marked by a alignment cube C1 placed on the OB in a TBD position, near the M0 end of the telescope tube. The normal to a face of the cube should is parallel to the z-axis within a measured angle, provided with the OB. C1 defines the experiment input optical axis. The OB can be mounted on an alignment bench in two ways: (option 1) clamped to the empty Cor B OB and placed horizontally on pillars; (option 2) on a flat alignment bench with planarity better than 0.1 mm. The optical components holders are designed to be mounted on the OB in a nominal position mechanically defined within 0.01 mm tolerances; additional alignment adjustments, when required, are to be performed with displacement and rotation tuning features described in section 5.1.4 (UVCI-RP-CGS-001) for each holder by means of custom fine tuning tools described in section 5.1.5 (z-y displacements tool) (see Fig.6.1) and 5.1.6 (z rotation tool) (see Fig.6.2) of the same document. A z- displacement tool for the detectors and a alignment tool for the polarimeter must be envisioned (TBD). Ref.: AlignPlan_TR.doc 11

Fig. 6.1 - z-y dispalcement tool. Fig. 6.2 - z rotation tool. For the telescope alignment on the OB a M0 stop aperture simulator a primary focal plane reticle (PFP) and a alignment visible detector (AVD) are required. Their characteristics are TBD. a) A collimated beam in the visible is aligned with the OB using the alignment cube C1. The collimated beam is optically translated to coincide with the input beam optical axis by means of a mirror flat or glass flat. The collimated beam is mounted on a fixture that can rotate the beam around the x and y axes in order to simulate all field angles of the experiment field-of-view. The range of the collimated beam tuning is ±1 o with 0.1 o resolution. b) A M0 stop aperture simulator is mounted on the OB in the nominal mechanical position. The stop aperture simulator will serve as a reference for the Lyot trap positioning. c) A PFP reticle (TBD) is mounted in its nominal position using the internal occulter inserts. d) M1 is mounted on the OB and aligned using the z-y displacements tool and the z rotation tool. e) M2 (+ Lyot trap (LT)) and the AVD are mounted in their nominal mechanical position. The alignment visible detector replaces the UV detector (UVD). M2 require the z-y displacements tool and the z rotation tool (mounting this tool on M2+LT holder is TBD). AVD holder and alignment tool are TBD. f) M2 and AVD are adjusted using proper alignment tools, that can be removed, until the correct alignment is reached. The optical alignment is reached when the optical performances listed in Tab 6.2 are met. g) The M0 simulator image on the M2 plane allows to verify the correct alignment of the Lyot trap behind M2. h) The filter mechanism (FM) is metrologically integrated on the OB. The reflection off the filter surface determines the polarimeter (PL) optical axis. The accuracy Ref.: AlignPlan_TR.doc 12

on the PL optical axis inclination is TBD (This could require a more accurate alignment of the filter mechanism). i) Alignment of the polarimeter : TBD. The alignment tool for the PL is TBD. j) The alignment of the VLD follows the same procedure of alignment of the AVD. k) The AVD is replaced by the UVD. Tab 6.2 - Telescope alignment requirements on the focal plane. Field 90% ensquared energy X (in Y (in in µm in pixel deg) deg) 0 0 17 1 (TBC) 0.4 0 17 1 (TBC) 0.6 0 17 1 (TBC) 0.8 0 17 1 (TBC) 1.0 0 17 1 (TBC) 0-0.4 17 1 (TBC) 0-0.6 17 1 (TBC) 0-0.8 17 1 (TBC) 0-1.0 17 1 (TBC) 0 0.4 17 1 (TBC) 0 0.6 17 1 (TBC) 0 0.8 17 1 (TBC) 0 1.0 17 1 (TBC) 6.1.4 Boom assembly component integration The telescope tube assembly (TT) consists of: 1 boom 1 external occulter (EO) 1 Sun disk rejection mirror (M0) assembly 5 baffles 1 removable M0 tuning mechanism The TT is described in section 5.1.2 of UVCI-RP-CGS-001. The TT is mechanically assembled and no optical internal alignment is needed. At the two ends of the boom on the outer skin two alignment cubes (C2, C3) are glued in order to verify the deformation of the boom with and without the 1g deformation (1g deformation: 0.8mm). 6.1.5 Boom assembly integration and alignment on the optical bench The TT is integrated on the OB using two supports like those described in section 5.1.3 of UVCI-RP-CGS-001 (see also Fig.6.3). Support B is the one closer to M0 and has a pivot system to allow TT to rotate around the y-axis and the x-axis (see ). y- axis and x-axis translation are obtained respectively by shifting and shimming the pivot. Support A is provided with one micrometer that tilts TT around the y-axis. Tilting around the x-axis is achieved by shifting the TT to OB interface. Ref.: AlignPlan_TR.doc 13

Support A Support B Fig 6.3 - Telescope tube supports. a) M0 stop aperture is positioned and aligned in such a way that M1 form its image inside the Lyot trap. The fine tuning along the x-axis and y-axis translation is performed with the above described support B tunings. The correct alignment is performed by illuminating M0 with a bright light source. b) A collimated beam aligned with the system optical axis defined by the alignment cube C1 is shined through the EO aperture and the correct alignment of EO with M0 is found using the fine tuning adjustments of support A. Important: 1g deformations need to be taken into account after the amount of deformation has been assessed using the alignment cubes C2 and C3. 1g deformations are compensated using a micrometrically adjustable support for the EO end of TT. 6.1.6 Internal occulter integration and alignment The internal occulter (IO) is integrated on the optical bench in its nominal position. The fine alignment is performed using the z-y displacement tool and the z rotation tool using the alignment configuration described in section 6.1.5 step b). 6.1.7 Cor A alignment verification The Cor A alignment verification is perfomed using the alignment configuration described in section 6.1.3 step a), with the exception of the IO alignment that has to be verified following the procedure described in section 6.1.5 step a). 6.1.8 Cor A vibration test and alignment verification After TBD vibration tests the alignment is verified by using the procedure described in section 6.1.7 6.2 Cor B INTEGRATION, ALIGNMENT, AND VERIFICATION See section 6.1. Ref.: AlignPlan_TR.doc 14

6.3 Cor A + Cor B INTEGRATION AND ALIGNMENT VERIFICATION Cor A and Cor B are integrated using the interface described in section 5.1.1 of UVCI- RP-CGS-001. Fine tuning is provided for z-y displacements and for x-axis rotation using a M z pin. The integration is performed according to the following procedure: a) Cor A is mounted on bulkhead simulator with the y-z plane horizontal and the x- axis directed downwards. b) Cor B is placed on top of the bottom of Cor A and interfaced through the M z pin and at least one loose interface bolt. c) The alignment is obtained using the collimated beam described in section 6.1.3 step a) and a TBD optical system (for example a beam splitter and a folding mirror properly aligned) to send two parallel collimated beams to both coronagraphs. The fine tuning is performed for displacements along the z-axis and y-axis and for rotations around the x-axis. d) Once the alignment is verified, the interface bolts are tightened. 6.4 UVCI VIBRATION TEST AND ALIGNMENT VERIFICATION After TBD vibration tests the alignment is verified by using the procedure described in section 6.3 6.5 UVCI INTEGRATION ON THE ROCKET MODULE TBD 6.6 UVCI ALIGNMENT VERIFICATION WITH SUN SENSORS TBD Ref.: AlignPlan_TR.doc 15

7 LIST OF ACRONYMS AVD Alignment visible detector BF Baffle BH Bulkhead EB Electronic box EO External occulter FM Filter mechanism (Cor B) or mount (Cor A) FP Focal plane GRS Global Reference System IO Internal occulter LRS Local Reference System LT Lyot trap M0 Sun disk rejection mirror M1 Primary mirror M2 Secondary mirror OB Optical bench PL Polarimeter section TBC To be confirmed TBD To be defined TT Telescope tube UVD UV detector VLD Visible-light detector Ref.: AlignPlan_TR.doc 16