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HOPI FAA Safety PDR

HOPI FAA Safety PDR. 6 November, 1998 Lowell Observatory. Overview. Staff Introductions Ted Dunham - PI, Overall responsibility Jim Elliot - Co-I Brian Taylor - Software Ralph Nye - Mechanical Design Jim Darwin - Machinist Rich Oliver - Electronics Technician. Overview.

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HOPI FAA Safety PDR

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  1. HOPI FAA Safety PDR 6 November, 1998 Lowell Observatory HOPI FAA Safety PDR

  2. Overview • Staff Introductions • Ted Dunham - PI, Overall responsibility • Jim Elliot - Co-I • Brian Taylor - Software • Ralph Nye - Mechanical Design • Jim Darwin - Machinist • Rich Oliver - Electronics Technician HOPI FAA Safety PDR

  3. Overview • Character of the Instrument • Special Purpose Science Instrument for SOFIA • Occultation Observing • What are occultations? • Deployment operation will be common • Guest Investigator use • SOFIA Testing - most stringent requirements • OPERATIONAL FLEXIBILITY IS CRITICAL HOPI FAA Safety PDR

  4. Overview • HOPI is a high-speed imaging system • Two CCD detectors capable of fast readout • Reimaging optics, one set optimized for 0.3-0.6 microns, the other for 0.4-1.0 microns • Unbinned image scale 0.33 arcsec/pixel • Selectable filters, Hartmann and Focault tests. • Goal - Allow simultaneous mount on SOFIA with FLITECAM to extend coverage to 5 mm. HOPI FAA Safety PDR

  5. Overview Stellar Occultation Geometry Toward Occulted Star Motion of Occulting object Occulting object Shadow of Occulting object Earth HOPI FAA Safety PDR .

  6. Overview An occultation occurs when an object in the solar system passes between an observer and a star. The figure above shows how the object's shadow is cast on the Earth by the starlight. The object's motion causes the shadow to move across the Earth. The path of the shadow across the Earth's surface is called the occultation track. The cartoon on the left shows how the occultation appears as seen by an observer. The occulting object moves across the sky, approaching a star. If the observer is in the correct position on the Earth, the star disappears behind the object. HOPI FAA Safety PDR

  7. Overview • Operation with FLITECAM is important • Simultaneous IR imaging capability needed for: • Certain occultation opportunities • SOFIA testing • FLITECAM is just beginning to be defined • This is the biggest certification issue we face • We are trying to allow for FLITECAM mount HOPI FAA Safety PDR

  8. Overview View of HOPI with red and blue channels in place. Electronics are located under the instrument. The figures on the next sheet show views from the left and top. Note the small dewar sizes. HOPI FAA Safety PDR

  9. Overview HOPI FAA Safety PDR

  10. Overview • This view shows HOPI as seen looking toward the telescope. The large circular plate is the 41” mounting flange. The red optics are on the left, the blue on the right. The mounting location for the bare CCD or FLITECAM is at top center. HOPI FAA Safety PDR

  11. Overview The Hartmann test mode requires a modification to the red side of HOPI. Some additional optics are installed and the camera lens is removed. These are small and fully contained inside the instrument case. HOPI FAA Safety PDR

  12. Overview A high-throughput mode is possible by moving either dewar (the red one is shown here) to the top center location. No reimaging optics are in the path. The other CCD can image the outer part of the field for what it’s worth. HOPI FAA Safety PDR

  13. Overview The preferred location for FLITECAM is at top center. Here its dewar is assumed to be 12 inches in diameter and 24 inches long. HOPI FAA Safety PDR

  14. Overview • Instrument Envelope • A cone with 41” base at the flange and 12 3/8” radius 2 meters from the flange representsthe instrument envelope. Two electronics boxes protrude. • Could rotate about theoptical axis to fix this. HOPI FAA Safety PDR

  15. Overview • The HOPI dewars will be made by Precision Cryogenics Inc. (PCI) like the EXES and FORCAST dewars. • This drawing is for a similar PCI dewar for another Lowell project. • The fused silica windows will have a safety factor > 10. HOPI FAA Safety PDR

  16. Overview • The HOPI dewars will be made from 6061-T6 aluminum tubing and pipe to reduce welding. • Outside dimensions will be approximately 8.5” diameter by 9” long with a 2” long fill stem. The vacuum vessel walls will be 0.148” thick. • The nitrogen can will be 7” ID by 5” long. Its walls will be 0.125” thick. • The end plates on both the dewar and the nitrogen can will be 0.5” thick. HOPI FAA Safety PDR

  17. Overview HOPI FAA Safety PDR

  18. Overview • Certification Philosophy • Goal - Preserve as much optical flexibility as possible within the original certification. • Large margins to allow for FLITECAM mount • Certify main structure, electronics mounts, and optical mounting method, but not exact locations of optical elements. Include sufficient margin to allow for different configurations. • New elements would need new certification. HOPI FAA Safety PDR

  19. Schedule • Schedule Chart Placeholder HOPI FAA Safety PDR

  20. FHA • Overview • Cryogen Boiloff • Pressure Vessel issues • Aircraft Pressure Boundary • Mass Budget • G Loading • Lasers & Gases • Electrical Hazards HOPI FAA Safety PDR

  21. FHA • Cryogen Boiloff • Liquid nitrogen only, no helium • Normal boiloff rate is 1.5 cu ft/hour per dewar • Maximum boiloff rate for a dewar at ambient internal pressure is ~2 cu ft/min at STP. • Total liquid capacity is 3 liters per dewar, corresponding to 70 cu ft of gas at STP. • Worst case - both dewars boil dry in ~35 minutes and displace 0.2% of the cabin volume. HOPI FAA Safety PDR

  22. FHA • Pressure Vessel Issues • Dewars will be made by Precision Cryogenics, like FORCAST and EXES. • If the dewar neck tube is blocked, rising pressure could rupture the dewar • Burst disks with an operating pressure of 30 psi will be used, a cryogenic one on the nitrogen can, a room temperaure one on the dewar case. • There is no oxygen displacement hazard. HOPI FAA Safety PDR

  23. FHA • Aircraft Pressure Boundary • Formed by windows in the vacuum pipe. The instrument case is not a pressure vessel. • 6.5” diameter windows will be either CaF2 (20 mm thick) or sapphire (6 mm thick) depending on cost. • Window thicknesses are appropriate for a 1 atmosphere pressure differential with a safety factor of at least 20. • DC-8 windows have safety factors ranging from 7-14. HOPI FAA Safety PDR

  24. Mass Budget CCD Electronics 20 lb x 2 CCD Pwr. Supply 15 lb x 2 “Hair” box 25 lb Dewars 25 lb x 2 Vacuum pipe 20 lb Blue dichroic/field lens 6 lb Blue collimator assy 15 lb Blue fold mirror 6 lb Blue camera lens 4 lb Blue filter/focus assy 15 lb Red collimator assy 40 lbs Red fold mirror 6 lb Red camera lens 4 lb Red filter/focus assy 15 lb Hartmann optics 10 lb Mounting plate 100 lb Base plate 150 lb Side walls 66 lb Top and back plates 20 lb Additional bracing 33 lb Add’l contingency 45 lb TOTAL 700 lb FHA HOPI FAA Safety PDR

  25. FHA • G Loading • Failure of 3/4” thick flange in: • Tension failure, one pin location only • Shear tear-out, one pin location only • bearing failure, one pin location only • pin shear, one pin only • bolt hole shear tear-out • Estimated CG is on-axis (side-side), 4” below the optical axis (top-bottom), and 10” forward of the mounting flange (fore-aft). HOPI FAA Safety PDR

  26. FHA • Flange failure in tension • Here the “cap” on the flange above the center of the top pin tears off. Flange diameter = 41” Bolt/pin circle diameter = 990 mm = 38.976” D = 6.361” HOPI FAA Safety PDR

  27. FHA • Flange failure in tension, continued • The distance along the bottom of the “cap” from the pin to the edge of the plate isD = sqrt(20.52 - 19.4882) = 6.361 inches • The area under tension is A = (2D - dpin) * tp = 8.79 sq. in. • Here dpin is the pin diameter (1”) and tp is the plate thickness (3/4”). HOPI FAA Safety PDR

  28. FHA • Flange failure in tension, continued • The ultimate tensile strength of 6061-T6 aluminum (Ftu), from the FAA SI handbook, accounting for a safety factor of 1.5, is 25.3 ksi. • The margin of safety, MS, is MS = AFtu/Mg - 1 = 8.79*25300/1320*6-1= 27 • Here M is the instrument mass, taken to be the maximum SOFIA SI weight to allow for FLITECAM, and g is the 6g downward load. HOPI FAA Safety PDR

  29. FHA • Flange shear tear-out • Here a triangular piece of the flange tears out. • The two lengths that fail areD = d/cos(40) - rpin = 0.82” • The shear area isA = 2D tp = 1.23 sq in. HOPI FAA Safety PDR

  30. FHA • Flange shear tear-out, continued • The ultimate shear strength of 6061-T6 aluminum (Fsu), from the FAA SI handbook, accounting for a safety factor of 1.5, is 16.7 ksi. • The margin of safety, MS, is MS = AFsu/Mg-1 = 1.23*16700/1320*6 -1= 1.6 • Here M is the instrument mass, taken to be the maximum SOFIA SI weight to allow for FLITECAM, and g is the 6g downward load. HOPI FAA Safety PDR

  31. FHA • Flange bearing failure • Here the pin causes an inelastic deformation of the mounting plate and the hole deforms. • The bearing area A = p rpin tp = 1.18 sq in • The allowable yield stress fromthe FAA SI Handbook, Fbru, accounting for the safety factorof 1.5, is 40.7 ksi. HOPI FAA Safety PDR

  32. FHA • Flange bearing failure, continued • The margin of safety, MS, is MS = AFbru/Mg-1 = 1.18*40700/1320*6-1 = 5 • Here M is the instrument mass, taken to be the maximum SOFIA SI weight to allow for FLITECAM, and g is the 6g downward load. HOPI FAA Safety PDR

  33. FHA • Flange pin shear • Here the pin shears off. • Shear area is the cross-sectional area of the 1” diameter pin, A = prpin2 = 0.79 sq in. • The pin material is stainless steel with a shear strength exceeding that of 6061-T6 aluminum. The ultimate shear strength for the aluminum material, (Fsu), from the FAA SI handbook, accounting for a safety factor of 1.5, is 16.7 ksi. HOPI FAA Safety PDR

  34. FHA • Flange pin shear, continued • The margin of safety isMS = AFsu/Mg-1 = 0.79*16700/1320*6-1 = 0.7 • Here M is the instrument mass, taken to be the maximum SOFIA SI weight to allow for FLITECAM, and g is the 6g downward load. • The actual margin of safety will be larger by the ratio of the shear strength of the pin material to that of 6061-T6 aluminum. HOPI FAA Safety PDR

  35. FHA • Flange bolt hole shear tear-out • Here the bolt heads tear through the flange either because of the 9g forward load or the moment applied to the top of the flange by the 6g downward load acting on the instrument’s moment. • 9g forward load: • The total shear area is given by A = p dbh tp nbolts = p * 0.74” * 0.75” * 20 = 34.9 sq in.Here dbh is the bolt head diameter (washers would help), tp is the plate thickness, and nbolts is the number of bolts. HOPI FAA Safety PDR

  36. FHA • Flange bolt hole shear tear-out, continued • 9g forward load, continued • The margin of safety is given byMS = AFsu/Mg-1 = 34.9*16700/1320*9-1 = 48 • 6g downward load coupled through instrument CG • Assume the full load is taken on the two top bolts so the shear area is given by A = p dbh tp nbolts = p * 0.74” * 0.75” * 2 = 3.49 sq in.Here dbh is the bolt head diameter (washers would help), tp is the plate thickness, and nbolts is the number of bolts. HOPI FAA Safety PDR

  37. FHA • Flange bolt hole shear tear-out, continued • The tear-out load is smallerthan the downward loadby the ratio dcg/dbc. • The tear-out load is thenLt = dcg/dbc M g = 10/39 * 1320 * 6 = 2030 lbs • The margin of safety is given by MS = A Fsu / Lt - 1 = 3.49*16700/2030-1 = 28 CG, 10” from flange dcg Downward 6g load dbc Tear-out component of load Bolt circle, 39” in diameter HOPI FAA Safety PDR

  38. FHA • G Loading Summary • Tension failure MS = 27. Unrealistic failure mode • Shear tear-out MS = 1.6 • Bearing failure MS = 5 • Pin shear failure MS = 0.7 (for aluminum pin) • Bolt hole shear tear-out • 9g forward load case MS = 48 • 6g down coupled load case MS = 28 HOPI FAA Safety PDR

  39. FHA • Containment and Penetration Analysis • Not done in the FAA SI handbook, so not done here either. HOPI FAA Safety PDR

  40. FHA • Lasers and Gases • NONE HOPI FAA Safety PDR

  41. FHA • Electrical Hazards • No high voltages (AC power is the highest) • No high currents • Most electronics is COTS • Sun, SDSU, industrial PC chassis & boards, Trak GPS, motor driver “bricks”, fiber modems • Some homemade electronics • Small timing circuit, fiber interfaces, and cables with Teflon or Tefzel insulation. HOPI FAA Safety PDR

  42. FHA HOPI FAA Safety PDR

  43. Stress Analysis • Main Work Surface • Top and bottom plates are 5mm 304 stainless. • Both plates will be attached to the mounting flange and side plates with angle and screws. • Additional braces will be attached to both plates with angle and screws also. • Optical components will be mounted to the top plate, electronics to the bottom. HOPI FAA Safety PDR

  44. Stress Analysis • Main Work Surface, continued • What kind of stress calculations are needed for the envisioned angle bracket mounting method? • Will we need to fasten the top and bottom plates together by means other than the attachments to the main structure? • The optical breadboard normally comes with 1/4-20 tapped holes. 1/4-28 is possible to get if necessary. Should we do this? HOPI FAA Safety PDR

  45. Stress Analysis • Major Optical Components • The optics will be mounted as clusters of connected lenses in modules. • The modules will be fastened to the work surface by either 1/4-20 or 1/4-28 screws. • The worst case component is the 40 lb red collimator lenses and fold mirror assembly. • Analyses will be done assuming a 9g load for simplicity although this load is often too high. HOPI FAA Safety PDR

  46. Stress Analysis • Major Optical Components, continued • Ignore the failure in tension case since shear tear-out is always more of a problem. • All analyses done for only one bolt. • The safety margins are as in the FHA section: • Shear tear-out: MS = Fsu 2(d/cos40-rb)t /Mg - 1 • Pin (screw) shear: MS = Lmax / M g - 1 • Bolt head tear-out: MS = Fsupdbht / M g - 1 • Bearing failure: MS = Fbruprbt / M g - 1 HOPI FAA Safety PDR

  47. Stress Analysis • Major Optical Components, continued • The variable definitions are: • Fsu = ultimate shear strength, 16.7 ksi for 6061-T6 • Fbru = max. bearing strength, 40.7 ksi for 6061-T6 • Lmax = max. screw shear load from MIL-HDBK-5G, 992 lbs for #10, 1718 lbs for 1/4”, assuming 35ksi material • d = distance of bolt hole center to edge of plate, 1/2” • t = thickness of plate, 1/8” • rb = radius of bolt hole, 0.095” for #10, 0.125” for 1/4 • dbh = diameter of bolt head, 0.30” for #10, 0.37” for 1/4 • Mg = mass of unit times g load. HOPI FAA Safety PDR

  48. Stress Analysis • Major Optical Components, continued • The results are summarized in the table below:Load Case Margin of SafetyShear Tear-out 5.2Pin (screw) shear 3.8Bolt head tear-out 5.7Bearing Failure 4.5 HOPI FAA Safety PDR

  49. Stress Analysis • Electronics Enclosures • The worst case enclosure is the industrial PC chassis for the “hair” box at 25 lbs. • Analyses will be done assuming a 9g load for simplicity although this load is often too high. • The enclosures will be held in place with 1”x1/8” angle brackets made of 6061-T6 aluminum and fastened to the main work surface and braces with 10-32 screws. HOPI FAA Safety PDR

  50. Stress Analysis • Electronics Enclosures, continued • Ignore the failure in tension case since shear tear-out is always more of a problem. • All analyses done for only one bolt. • Use the equations for margin of safety and the values for screw dimensions etc. from the Major Optical Components section. HOPI FAA Safety PDR

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