Monday, August 13, 2007

Update on SDG-6's overnight stay...

After looking more closely at the area where Soli Deo Gloria 6 came down early on Sunday morning (~3:30am EDT), I think it is likely that the payload did, indeed, come to rest on the ground.

What brought it down? Probably frost - a problem which also plagued Vin Lally's low altitude superpressure balloons back in the '60s and for which no solution was ever found.

The frost would have melted into dew by mid-morning and then, as it evaporated, the balloon would have been able to rise again. The much faster - and earlier - descent on Sunday evening was undoubtedly due to actual loss of gas through pinholes in the envelope. The flight was over by this point, frost or no frost.


Mark Caviezel said...

was it cold enough for frost? Is a alt v time chart available for the flight?

- Mark

Robert Rochte said...

I haven't made such a chart yet - when I do, I'll post it here.

Ambient was, IIRC, around 50F during the daytime - have to check the soundings for nighttime temps and humidity.

Given the opaqueness of the polyester film in the IR, the top of the balloon could have experienced significant radiative cooling. I haven't run the numbers yet, but dew is a definite possibility and I think that frost is not out of the question.

Even if we're dealing with dew, the hygroscopic coating on the outside of the balloon (a mistake this time - more on this later) could have easily absorbed enough moisture to give the system negative bouyancy. If my experience during the initial coating procedure on this balloon is any indication, then it would have taken several hours for the coating to dry out again.