Access Doors on Foamcore Balloon Payload Boxes

Payloads at Launch

Payloads at Launch

I have used foam core sheets to construct high altitude balloon payload boxes for many years. They are inexpensive, lightweight, and very durable. It is easy to cut ports and holes for cameras, instruments, antennas, and wires. And it is no great loss if they are damaged during recovery.

An excellent description of foamcore construction techniques by Mike Manes (W5VSI) is available from EOSS. This is where I learned from.

Here, I would like to describe some ‘features’ included in our/my construction. Recently, I’ve begun including a back door to aid in manipulating and connecting wires and hardware in the box..

When I began flying HiBals, I selected black foamcore, with hopes of heating the payload somewhat during the flight. Heating during the flight is negligible. The foam probably reduces heat transfer into the box. In addition the lowering air pressure reduces heat conduction within the box, so even heaters don’t help a lot. Fortunately, the worst cooling occurs only for a relatively short time during decent as cold stratospheric air is sucked back into the box. The black color may be a little more visible (at low altitudes) against the light blue sky. I haven’t incorporated this yet, but after seeing how reflective materials aid in seeing model rockets, I will start adding reflective tape to the boxes, in hopes that glints of sunlight will aid in seeing the box.

After working with too many wires on a video transmission payload (ATV), where I had too many wires I couldn’t get at, I figured an access port would be valuable. While we use a shelving system that should slide in and out of the box, trying to manipulate rear wires can be frustrating.

Rear Door

Rear Door

Another “innovation”is to use plastic wall anchors as grommets. The wall side gets clipped off using wire cutters. These are used to confine tie wraps used to close doors, and strings for tring thepayload to the payload train. These don’t eliminate cutting and ripping of the boxes, especially during tree recoveries, but they do reduce it. We run four strings though the corners of the box. These are tied off with swivels at both ends to tie through the train.

grommet example

wall anchor grommet example

The group I work with has had some discussion about whether this type of door reduces the structural strength of the box. An alternative is to cut a smaller door in the basic box, along one of the folded edges. However I will continue to use this design for now.

Foamcore box layouts

Fly High!