SPOT Trace – Altitude Reports Way Beyond Spec

The SPOT Trace with Annotated Dimensions

SPOT LLC, the maker of the SPOT Gen 3, the SPOT GPS Messenger, as well as the SPOT Trace, specifies it products have an upper altitude limit of 21,325 feet.  The implication is that these devices are not designed to report latitude or longitude data once a flight passes through this limit.  

Nonetheless, the SPOT Trace has been flown successful beyond this maximum.  In one instance the flight location was reported successful all the way up (and back) from 65,000 feet.  In a more recent test, the Trace properly reported location coordinates at 33,000 feet.  To be clear, the SPOT itself was not reporting altitude as it just gives latitude and longitude data; a separate method was used to capture altitude and link it to the SPOT location data.


High altitude flight hobbyist should understand that the SPOT products are very sensitive to their orientation to the sky.  Simply put, they must face “up” to reliably send location data to the overhead satellite receiver network. A separate blog post discusses a customized gimbal designed to keep the Trace always facing up during balloon flight.

On Minimizing Payload Weight - Can the A1100 Be Flown Without Its Covering?

One of the cameras used on Mayberry Galactic flights is the Canon A1100 – an inexpensive point-and-shoot camera typically found on eBay for less than $40.  With the aim of reducing unnecessary weight on flights, the plastic shell covering of A1100 became a target. The thought being is the camera’s housing has low functional value once the “core” of the camera is placed inside the payload box.  The payload box provides the protection.  The A1100’s covering was estimated to weigh 20 grams.  Each gram of mass – at least by one altitude prediction tool’s estimate -- reduces flight altitude by roughly 10 feet therefore, eliminating the housing could get us 200 feet higher.

To test the viability of the idea, a sacrifical A1100 was purchased on eBay –for about $14.  Although functional, it had some mechanical issues and so was perfect for experimenting on.

After carefully removing nine (9) #000 screws (these are very tiny), the front and back covers separated away from the camera.  In examining the exposed camera body, it became clear that the cover is more than a shell.  The “buttons” built into the housing provided contacts between two or more conductively points on the camera’s core.  When the cover is removed, there is no longer a way to effectively make these contacts.  In other words, without a cover, the control functions no longer work – with the exception of the simple on/off button.

The conclusion is that the outer camera shell cannot  practically be removed to save mass – it is integral to the camera's operation.  This is too bad as the actual of the housing's mass was not 20 grams as estimated, but rather 30.8 grams.  Eliminating the cover for flight would have been a nice weight reduction. The quest for reducing weight while maximizing function continues!

Payload Container Material Testing and Recommendation

Launching a balloon normally means sending up a container -- often referred to as the "payload box" or "balloon sat" -- housing cameras, trackers, and perhaps other devices or items to be taken to near space.  For novices, payload containers often start as a store-bought product: a Styrofoam ice chest, a soft-sided lunch box, or even a fishing tackle box.  But if you are serious about wanting to climb as high as possible,  you will want to make a custom payload container. It is one of the best ways to eliminate excess weight on your flight train as you can build a box that is just the right size for your equipment. And in turn, it minimizes the amount of lifting gas (e.g., helium) needed, providing for more room for gas expansion in the balloon envelope. The result: a better likelihood of reaching maximum altitude.

Making your own custom payload box can be a very enjoyable project.  To begin such a project, you likely will first want to know the answer to very basic question.  “What is the 'best' material for payload container construction?”  'Best' is defined by materials having:

(1) the lowest weight per area

(2) the highest insulating property

(3) the greatest cushioning for a hard landing, and 

(4) the sturdiest overall construction

1 1/2" Styrofoam, 1/2" Pink Foam Construction Panel, 1/4" Foam Core Board

Four different materials were considered, measured and tested: 

1 ½” medium density “white” Styrofoam 

1" medium density "white" Styrofoam

½” high density “pink” construction grade foam panel

¼” foam core art board

The following table summaries the testing results:

                                        Grams / sq. in.      R-Value      Cush         Constr. Strength     Overall Score

           

1 ½” Styrofoam         .351                5.8        High            High                  8

1” Styrofoam             .234                4.0        Med             High                  9   

½” Pink Panel            .274               3.0        Med             High                  6

¼” Foam Core           .225               1.0         Low             Med                  5

Foam Core: Offers low mass for a given area – coming in at .225 grams per square inch – 36% lighter than 1 ½” “White” Styrofoam.  However, it has little insulting capability against the cold, has doubtful cushioning for a violent crash, and has limited construction strength.  Overall rating: 5 / 10

½” Pink High Density Foam: The high-density construction-grade panel foam is 22% lighter than 1 ½” Styrofoam.  It offers good insulting value for its density – listed as R-3.   But its thickness may not be the best protection in a hard crash.  Its ½” width does makes it a somewhat challenging material for box construction.  Overall rating: 6 /10

1” White Styrofoam: Styrofoam has very low mass per area of the materials considered coming in at .234 grams per square inch.  The 1" thickness offer very good insulating value at R 4.  And the 1" thickness provides good protection for hard landings and offers a nice width for building.  Its major downfall is that it is difficult to find as an off-the-self product, often requiring special order from a retailer.  If you can find it, it is the ideal material-- of the four listed here-- for payload construction.  Overall rating: 9/10

1 ½” White Styrofoam: This material has the heaviest mass per area of those tested, coming in at .351 grams per square inch.  Its thickness benefits the payload in two signifiant ways: It has an insulating R value of 6 and it provides excellent protection of equipment in case of a hard crash. Overall rating is 8/10.