ARISSat-1 Critical Design Review Orlando, Feb 15, 2010 Mechanical Bob Davis, [email protected]@amsat.org

ARISSat-1Critical Design Review

Orlando, Feb 15, 2010

Mechanical

Bob Davis, [email protected]

mailto:[email protected]

Feb 15, 2010 ARISSat-1 CDR 2

Introduction• Mechanical subsystem includes structure

and electronics boxes.• Scope

– Requirements– Design– Safety Considerations– Verification– Operations– Status


Requirements• Simple structure that can be implemented quickly• Provide attachment for:

– SMEX solar panels– electronics boxes (IHU, Rx/Tx, MPPT, Control Panel)– Orlan-M battery (integration on ISS)– Kursk experiment (integration in Russia)– Spare experiment box– 4 cameras– 2 whip antennas– Handles

• Survive Progress loads (“CargoTransReqP103.doc”)• Low outgassing• Venting of volumes


Path to Structure

• Prior to July 2009, SuitSat-2 used a Russian spacesuit


Foamboard Mockups

August 2009 September 2009


Exploded View

Russian battery

IHU

MPPT

Rx/Tx

September 2009


Solar Panel ViewsOctober 2009


Interior and Cover Views


Design Methodology• For conservative structure, we want low stresses, small deflections,

and high frequencies (or at least >>50 Hz)• All “masses” are attached to the Top & Bottom Plates, which are ¼”

thick aluminum– Thick enough for helical thread inserts– Much faster to process than honeycomb sandwich panels– Easy to over-design (which also lessens analysis burden)– Given schedule, the above advantages outweigh the mass penalty

• The Plates are separated by custom machined angles in the four corners, also ½” thick

• Side Panels (with SMEX Solar Panels) act only as shear planes• Small angle extrusion joins edges of Side Panels to Top & Bottom

Plates• Added flanges to die cast aluminum electronics boxes


Sample: Top Plate


Sample: IHU Box


Sample: Cover Ass’y(Back when it was Aluminum not Lexan)


Camera Mirror• Unsuccessful search to find first-

surface VDA mirror on any Lexan (by name brand)

• Several options for first-surface VDA mirror on unknown polycarbonate (no paperwork)

• Starting search for VDA mirror on aluminum– “grainy” finish will result in degraded

image quality• Can we find contact for the astronaut

spacesuit “sleeve-mounted mirrors”?• Considering simpler triangular

brackets with pockets for bonding opposite edges of the mirror– Mirror is then positively captured– Bracket dims independent of mirror

thickness (because we shim pocket)

Monolithic mirror bracket concept


Side Camera Angle• Dimensions of mirror are very sensitive to angles (FoV & mirror)

• Image requires mirror at least 1.5” wide x 1.75” long (57° from horizontal)

• Verified screw heads and mirror bracket are not in FoV


Safety Considerations

• All external edges/corners are rounded

• All materials are low outgassing

• Handles sized for gloves


Analysis Methods• No Finite Element Model (FEM) or Analysis (FEA); just hand calcs• Plate natural frequency per, Vibration Analysis for Electronics Equipment 3rd

Edition by Steinberg 2000, and per Dynamic Analysis and Failure Modes of Simple Structures by Schiff, 1990

• Honeycomb per above and Spacecraft Structures and Mechanisms edited by Sarafin And Larson, 1995

• Vertical Angle combined loading per Spacecraft Structures and Mechanisms by Sarafin & Larson, 1995

• Fastener combined loading per Analysis and Design of Flight Vehicle Structures by Bruhn 1973 and per NASA Technical Memorandum 106943 Preloaded Joint Analysis Methodology for Space Flight Systems

• Vented volumes in depressurization per AIAA-87-1598 Payload Venting in Worst Case Shuttle Environments

• General References– MIL-HDBK-5J Metallic Materials and Elements for Aerospace Vehicle Structures– Roark’s Formulas for Stress and Strain 7th Edition by Young & Budynas, 2002– Space Mission Analysis and Design, 3rd Edition by Wertz & Larson, 1999– FEMCI Book, http://femci.gsfc.nasa.gov/femcibook.html


Margins Summary• Simultaneous 10g vertical and 6g horizontal• Material Factors of Safety

– Yield, FSy = 1.2– Ultimate, FSu = 1.5

• Threaded fastener Factor of Safety– FS = 2.0

• All margins are large• Partial summary table below


Sample: Top Plate Frequency


Sample: Top Plate Screws


Sample: IHU Box


Vented Volumes• Structure and all electronics boxes have vent holes• Gap between Solar Panels & Covers can vent via small

harness holes in SMEX, and “through” perimeter Velcro• Used at least twice the vent hole cross-sectional area

suggested by AIAA-87-1598 Payload Venting in Worst Case Shuttle Environments– Rule of thumb: 0.050” in2 unrounded hole for each 1.0 ft3

generates 0.5 psi pressure (box bloating) during ascent

• Always sought redundant holes in the event paint, tape, or potting caused a plugging event


Verification• Structure was prototyped

– Changed Camera mount, some longer free-running Helicoils

• Observatory level vibration testing– Expected @ GSFC

• Kursk experiment mass mockup• No Orlan-M battery (not installed for launch either)

– Levels TBD from “CargoTransReqP103.doc”, Requirements for International Partner Cargo Transported on Russian Progress and Soyuz Vehicles, П32928-103 (discussed later)


Drawing Status• Structure - 15• Solar Panels & Covers - 6• Electronics Boxes - 18• Cameras - 3• Tabletop Stand - 0• Shipping Container - 0• Vibration Adapter - 0• Thermal Vacuum Adapter - 0


Fabrication Status• Structure – in plating• Solar Panels & Covers – bonding & Lexan change• Electronics Boxes – painted & taped• Cameras – waiting for brackets drawing• Tabletop Stand - sketch• Shipping Container – purchased; mod?• Vibration Adapter – pending facilities• Thermal Vacuum Adapter – pending facilities

Documents

ARISSat-1 Critical Design Review Orlando, Feb 15, 2010 Mechanical Bob Davis, [email protected]@amsat.org