Lowell Observatory

1
HOPI FAA Safety PDR

• 6 November, 1998
• Lowell Observatory

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

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

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.

5
Overview
Stellar Occultation
Geometry
Toward
Occulted Star
Motion of Occulting object
Occulting
object
Shadow of
Occulting object
Earth
.
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.
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

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.
9
Overview
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.

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.

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 its worth.

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.
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.

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 gt 10.

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.

17
Overview
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.

19
Schedule

• Schedule Chart Placeholder

20
FHA

• Overview
• Cryogen Boiloff
• Pressure Vessel issues
• Aircraft Pressure Boundary
• Mass Budget
• G Loading
• Lasers Gases
• Electrical Hazards

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.

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.

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.

24
FHA

• 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
• Addl contingency 45 lb
• TOTAL 700 lb

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).

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
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).

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
  8.7925300/13206-1 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.

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.

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
  1.2316700/13206 -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.

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.

32
FHA

• Flange bearing failure, continued
• The margin of safety, MS, is MS AFbru/Mg-1
  1.1840700/13206-1 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.

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.

34
FHA

• Flange pin shear, continued
• The margin of safety isMS AFsu/Mg-1
  0.7916700/13206-1 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.

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 instruments 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.

36
FHA

• Flange bolt hole shear tear-out, continued
• 9g forward load, continued
• The margin of safety is given byMS AFsu/Mg-1
  34.916700/13209-1 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.

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 3.4916700/2030-1
  28

CG, 10 from flange
dcg
Downward 6g load
dbc
Tear-out component of load
Bolt circle, 39 in diameter
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

39
FHA

• Containment and Penetration Analysis
• Not done in the FAA SI handbook, so not done here
  either.

40
FHA

• Lasers and Gases
• NONE

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.

42
FHA
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.

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?

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.

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 Fsu pdbht / M g - 1
• Bearing failure MS Fbru prbt / M g - 1

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.

48
Stress Analysis

• Major Optical Components, continued
• The results are summarized in the table
  belowLoad Case Margin of
  SafetyShear Tear-out 5.2Pin (screw)
  shear 3.8Bolt head tear-out 5.7Bearing
  Failure 4.5

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
  1x1/8 angle brackets made of 6061-T6 aluminum
  and fastened to the main work surface and braces
  with 10-32 screws.

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.

51
Stress Analysis

• Electronics Enclosures, continued
• The results are summarized in the table
  belowLoad Case Margin of
  SafetyShear Tear-out 9Pin (screw)
  shear 3.4Bolt head tear-out 8Bearing
  Failure 5.7

52
Stress Analysis

• Dewar Overpressure
• For a cylinder, tensile stress due to pressure
  is Fs P r / twhere P is the pressure
  difference, r is the cylinder radius and t is the
  cylinders wall thickness.
• The margin of safety is MS Ftu/Fs - 1where
  Ftu is the ultimate tensile strength of the
  material, 25.3 ksi for 6061-T6 aluminum.

53
Stress Analysis

• Dewar Overpressure, continued
• For the dewar, r4.16, t0.148, and P 90
  psi(a factor of three more than the burst disk
  pressure).The tensile stress is 904.16/0.148
  2500 psi.
• For the nitrogen can, r3.5, t0.125, and P
  90 psi. The tensile stress is 903.5/0.125
  2500 psi.
• The margin of safety is 25300/2500 - 1 9.1

54
Stress Analysis

• Dewar Overpressure, continued
• The safety factor for a flat circular plate (I
  think of it as a dewar window) isMS (4Ftu/kP)
  (t/D)2 - 1
• Ftu is the ultimate tensile strength of the
  materialk is 1.125 for a simply supported
  circular plateP is the pressure differentialt
  is the plate thicknessD is the plate diameter

55
Stress Analysis

• Dewar Overpressure, continued
• For the nitrogen can ends, t0.5, D7.25 MS
  (425,300/1.12590) (0.5/7.25)2 - 1 3.8
• For the dewar ends, t0.5, D8.625MS
  (425,300/1.12590) (0.5/8.625)2 - 1 2.4
• For the dewar window, t 3mm, D 38mm, and the
  tensile strength for fused silica is 7100 psi.
  (4700 psi with a safety factor of 1.5). ThenMS
  (44700/1.12590) (3/38)2 - 1 0.16
• If the dewars burst disk fails to rupture, the
  dewar window will fail before the dewar end
  plates fail.

56
Stress Analysis

• Instrument Cart
• Floor loading is the issue here
• The cart has not been designed, but we assume it
  weighs less than 300 lbs, for a total weight of
  cart instrument, including FLITECAM, of 1600
  lbs, the maximum SI weight.
• The wheel contact area must be adequate to avoid
  floor damage when the weight is held by three
  wheels, at 530 lbs per wheel.
• The floor load limit in ICD SIC-TA-01 is TBD.

57
Operations

• Installation Timeline
• Arrive with equipment a week before installation
• Integrate instrument in the lab on its cart
• Transport to and mount on TAAS for checkout
• Transport to aircraft and install on the
  telescope
• Store cart in the lab

58
Operations

• Ground Operations
• Dewar fills will occur nominally twice a day.
• Over weekends, dewars can warm up.
• Cooldown should take lt 8 hours (TBD).
• Instrument tests and data transfer operations
  will occur during the days.
• Power will be required with the aircraft out of
  the hangar for two hours prior to takeoff.

59
Operations

• Instrument Interfaces
• Mechanical interface to telescope and rack
• Cart carrying instrument to the telescope
• GPS antenna required on the aircraft
• 120V/60Hz power required at rack and on telescope
• Vacuum line for the evacuated gate valve pipe

60
Operations

• Power Budget
• Telescope-mounted parts
• Blue electronics 120 W
• Red electronics 120 W
• Hair box 150 W
• Contingency 100 W
• TOTAL 490 W

• Power Budget
• Rack-mounted parts
• Computer 140 W
• Monitor 180 W
• Tape drive 90 W
• 2 disk drives 150 W
• GPS receiver 40 W
• Contingency 100 W
• TOTAL 700 W

61
Operations

• Motorized reconfiguration during flight
• Done during normal telescope operation
• Focus of red and blue channels
• Pupil stop positioning
• Filter wheel rotation
• During Hartmann operation, MLM and setup lens are
  in the filter wheel and can be changed.

62
Operations

• Manual reconfiguration during flight
• Cage the telescope before reconfiguration
• Insert/remove Hartmann collimator, folding
  mirrors, and beamsplitter/LED source
• Insert/remove pupil imaging optics and knife edge
  for Focault test
• Dummy weights provided to maintain balance
• Swap dewars or electronics in case of failure
• Simple repairs in case of in-flight failure

63
Operations

• Reconfiguration between flights
• Add or delete FLITECAM
• Bare CCD mode - one CCD dewar in upper posn.
• Change filter wheel contents, pupil stop size
• Change pressure seal. There are 4 configurations
• 2 windows, vacuum pipe evacuated
• 1 window in gate valve assy, no pipe at all
• 1 window at gate valve end of pipe, no vacuum in
  pipe
• 1 window at instrument, no pipe.

64
Operations

• Modifications and Upgrades
• Possibilities still under consideration
• Image motion compensation camera system
• Infrared system to take the place of FLITECAM?
• Unknown modifications for future observations
• These modifications would follow their own
  certification timeline.

65
Documentation

• Safety and Airworthiness Documents
• FAA Certification Notebook
• This will be kept live by recording major
  maintenance and instrument upgrades as they
  occur. It will include procedures and
  certification docs.
• Drawing Set.
• The numbering system will be based on the HAWC
  system in the FAA book, but simplified for our
  instrument and modified to fit the existing
  Lowell drawing system as follows.

66
Documentation

• Drawing numbers will be of the form EXP083-XNN
  nnS EXP083 is HOPIs Lowell project number.
• Here X is a letter designation
• M for mechanical (including cryo and vacuum)
  systems
• E is for electrical systems
• O is for optical systems

67
Documentation

• NN is a subsystem number. 00 is a table defining
  all the subsystems. The drawings under subsystem
  01 are assembly drawings of the full system.
• nn is a drawing number. 00 is a table of
  contents for all the drawings in this subsystem.
  Drawings may have more than one sheet.
• S is a drawing size, ranging from A to E.
• All drawings will have a title block similar to
  the one shown in the FAA certification manual.

68
ContinuedAirworthiness

• Little expected airworthiness-related maintenance
• Inspect pressure seal windows prior to each
  flight series.
• Inspect cabling insulation prior to each flight
  series.
• Check for loose fasteners prior to each flight
  series.
• Test burst disks at intervals TBD?
• Insure fasteners in good condition when changed.

69
Outstanding Issues

• FLITECAM development
• Burst disks
• Mounting large computer monitor on rack
• What modifications of COTS equipment will be
  required?
• Need strength information on NAS hardware