Foamcore Flight Experience

The EOSS ATV module, Fig. 1, was built entirely from 0.21” foamcore in one weekend.  The U-shaped package form was designed to protect the mirror from landing impact while housing the camera, servo, title board and ATV transmitter with minimal wasted space.  The mirror, its drive and servo are integrated into a single module which slides into a mating slot in the package wall.  Extra space was designed in to accommodate a filter wheel and servo for future video experiments.

Figure 1: EOSS ATV Module This 5-oz. housing has survived the rigors of six launches and recoveries.  The only repair required was strengthening the camera hold down strut after its first flight.  Since then, preflight preparation consists of no more than cleaning the mirror and fitting dry desiccant. webnote: This module is shown attached to the Shuttle II here.

The loran-C receiver preamp is supported 8 feet below the main payload package to reduce QRN from the payload computer.  It’s packaged in a 2” diameter heptagonal approximation to a cylinder with conical ends to minimize drag.  It’s survived five trips and a number of field disassemblies to troubleshoot loran reception problems.

webnote: We've upgraded to a GPS module also built of foam core by Mike.

FOAMCORE PROPERTIES

Foamcore, also known as mattboard, is a composite sheet material comprising a core of closed-cell, high-density Styrofoam sandwiched between two sheets of thin poster board.  It’s sold in hobby and art supply stores in thicknesses ranging from 0.2 to 0.4 inches.  Although used primarily for matting pictures for framing, it is occasionally used in architectural models and packaging mockups of proposed electronic products.  A 2 x 4 ft sheet of white ¼” foamcore, enough for several large payload packages, retails for about $5.00. 

The 0.21” thick material used for the ATV package weighs 2.12 oz.  per square foot.  Despite its light weight, foamcore is surprisingly strong and rigid.  The optical alignment between the camera and mirror has remained unchanged through six landings. 

The Styrofoam core material provides an moderate thermal R-value.  The 175 cubic inch interior of the ATV module held above -30 F during a 2.5-hour flight to 93,000 feet and back with less than 5 watts interior heat dissipation.  Thicker foamcore provides more insulation, but an ordinary low-density insulation grade sheet foam liner inside a thinner foamcore shell is more weight-effective.

SURFACE AND MOISTURE TREATMENTS

The poster board surface tolerates moderate amounts of water without damage.  Moisture resistance can be improved with a light coat of acrylic spray paint, however.   Loud orange provides a highly visible target for the recovery team.  Clear Scotch brand packaging tape is nice for attaching “Return to Sender” labels and has served well for package closures in lieu of Kapton tape.  

Interior condensation during descent through a cloud may be averted by including a desiccant-filled breather.  We used a plastic pill bottle with each end perforated by about ten 1/16” holes.  The bottle cap is glued with RTV into a matching hole in the package wall, and the bottle is filled with 1 oz of dry silica gel desiccant before the flight.  This 2 oz of prevention may be dispensed with if your weather forecast is clear.  Desiccant packs found in the packaging for consumer products may provide some lighter-weight protection.

A brightly-colored plastic newspaper sack can provide both moisture and abrasion protection for packages shaped like rolled-up newspapers.

EMI shielding is easily applied by gluing ordinary aluminum foil to the foamcore surface using Elmer’s glue.  Good electrical contact to the foil is achieved by taping down ½” wide strips of copper foil.  The copper is roughened to form gastight contact into the aluminum foil with sharp dimples made with a center punch.  Similar strips with points on both sides of the foil are used to bond cover seams. Conductive adhesive metal EMI tape is ideal, but rather expensive.