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Payload Construction Considerations Techniques

LSU 06/04/2007. Payload Construction. 2. Payload Constraints. Federal Aviation Authority (FAA) places constraints on what can be flown on a balloon without a flight waiverMaximum weight of ~5.4 kg (~12 lbs.)Density less than 13.2 g / cm2 (~3 oz / in2 )Weight of balloon vehicle is ~2.5 kgLeaves a

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Payload Construction Considerations Techniques

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    1. LSU 06/04/2007 Payload Construction 1 Payload Construction Considerations & Techniques Ballooning Unit, Lecture 2

    2. LSU 06/04/2007 Payload Construction 2 Payload Constraints Federal Aviation Authority (FAA) places constraints on what can be flown on a balloon without a flight waiver Maximum weight of ~5.4 kg (~12 lbs.) Density less than 13.2 g / cm2 (~3 oz / in2 ) Weight of balloon vehicle is ~2.5 kg Leaves about 2.5 kg for student payloads We will fly about 5 payloads, so each payload will be constrained to ~500 grams Size is limited to a cube volume with 15 to 20 cm sides

    3. LSU 06/04/2007 Payload Construction 3 Vehicle Interface Only a mechanical interface between payload & flight vehicle Two flight string cords are separated by ~17 cm Both strings must pass through payload with a break

    4. LSU 06/04/2007 Payload Construction 4 Rough Payload Dimensions

    5. LSU 06/04/2007 Payload Construction 5 Construction Materials - Metal Advantages of using metal like Aluminium Strong and relatively light weight Comes in many different forms & sizes Easily machined and bolted together Relatively inexpensive Disadvantages of using metal Heavy (15 cm cube with 1 mm sheet Al would weigh ~360 grams) Excellent thermal conductor

    6. LSU 06/04/2007 Payload Construction 6 Construction Materials - Composites Composites include materials such as G-10, Fiberglass, Carbon fiber extrusions, NOMEX honeycomb sandwich Advantages of using composites Extremely strong and light weight Comes in sheets and extruded shapes Relatively easy to cut Excellent thermal insulator

    7. LSU 06/04/2007 Payload Construction 7 Construction Materials - Foamcore Foamcore (or mattboard) is a composite material Core of closed-cell, high-density polystyrene foam Cladding is thin poster board Advantages of foamcore Inexpensive and readily available Strong and rigid Lightweight (15 cm cube with ź” thick walls weighs ~116 g) Thermal insulator Easy to cut and glue Disadvantages of foamcore Available as sheet stock only Not as strong as other composite materials or metals

    8. LSU 06/04/2007 Payload Construction 8 Foamcore Properties Trade name is Fome-CorŽ and GatorfoamŽ Fome-Cor website site http://www.gatorfoam.com/ Fome-Cor thickness from 1/8” to 3/8” and sheet size from 20” x 30” to 48” x 120” Gatorfoam thickness from 3/16” to 2” and sheet size of 4’ x 8’ or 5’ x 10’ Gatorfoam uses a resin impregnated wood-fiber veneer as the cladding and is more durable than Fome-Cor Similar product sold in hobby and art supply stores and sometimes referred to as mattboard 2’ x 4’ sheet of white ź” mattboard cost ~$5 ź” thick material weighs ~0.065 g / cm2

    9. LSU 06/04/2007 Payload Construction 9 Foamcore Handling Recommended document from “Edge of Space Sciences (EOSS)” “Foamcore Payload Construction” by Mike Manes Document contents include: Surface and moisture treatments Adhesives Foamcore joinery Cutting – Holes – Bends – “Curved” Shapes – Cones Hardware attachment Summarize contents over next slides

    10. LSU 06/04/2007 Payload Construction 10 Surface Treatments Mattboard will tolerate moderate amounts of water without damage Light coat of acrylic spray paint to improve resistance Loud orange color for visibility Use desiccant packs to reduce condensation Packs from pharmacy bulk drug shipments or consumer products EMI shielding by gluing Al foil to outside surface White (Elmer’s) glue appears to work fine Electrical contact with taped down, roughened copper foil strips Al foil surface also good for thermal properties

    11. LSU 06/04/2007 Payload Construction 11 Adhesives Silicone RTV sealant is adhesive of choice for critical joints High adhesion and resilience even at low temperatures Long curing time and out gassing of acetic acid vapor Epoxy is very strong but can become brittle in extreme cold

    12. LSU 06/04/2007 Payload Construction 12 Cutting Foamcore Materials needed for construction Modeling knife and a good supply of new, sharp blades Machinist’s square, metal straightedge (12”, 36”), spring clamps Cutting surface (large cardboard or hardboard) and flat work table Hot-melt, low temperature glue gun and glue Keep knife blade sharp Replace blade after 3 – 5 feet of cutting Clearing mark using square and straightedge where to cut Cut in three passes Hold knife blade against straightedge and cut upper surface on 1st pass Don’t move straightedge and on 2nd pass cut through foam layer On 3rd pass cut through bottom surface

    13. LSU 06/04/2007 Payload Construction 13 Holes and Bends Mark center and diameter of hole on both sides of foamcore Use a straight pin pushed perpendicular to the board to transfer the hole center Use knife to cut perpendicular to board through cladding on both sides, then finish up by cutting through foam For a mitered bend cut a groove of width W through the top clad and the foam to depth D Put hot-glue in groove and bend For a bend of angle ? the groove width is W = 2(T-P)tan(?/2)

    14. LSU 06/04/2007 Payload Construction 14 Steps for Mitered Corner

    15. LSU 06/04/2007 Payload Construction 15 Other Construction Tips Can also make curved and conical shapes using same groove and folding technique (See document for formulae) Minimize number of glue joints Put glue joints where stress is minimized Reinforce glued joints with tape, glued strips or triangular webs Joints to box floor should be folded or reinforced Heavy components (e.g. batteries) should be distributed near floor of box and supports reinforced Might use a double box where interior box houses temperature sensitive components and is separated from the other box by loose, high R insulation Access to interior is probably best through top where stress are less

    16. LSU 06/04/2007 Payload Construction 16 Interior Attachments Electronic card guides can be formed from strips of mattboard glued to the interior walls T-nuts or ordinary nuts taped or glued to the mattboard can be used for machine screw mounting Sheet metal or deck screws can be used for low-stress, openable joint if screw passes through a double layer of cladding Connectors / electrical feedthroughs / switches need to be hot-glued to snug-fitting holes in the wall Flight vehicle string interface tubes should penetrate box top and bottom and be securely glued to joint corners

    17. LSU 06/04/2007 Payload Construction 17 References http://www.eoss.org/onlinepubs/construction/foamcore/foamcore.htm - “Foamcore Payload Construction” by Mike Manes, available on EOSS website, 2nd Edition, 3/28/01 http://www.gatorfoam.com/ - Website of Fomecor and Gator board products

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