The time limit for. shipping a POV is the same as for travel and HHG transportation limits (JTR Para 5366, POV. Transportation Time Limitation), 1 year from the date of retirement/separation with severance. pay or 180 days from the date of separation.
The envelope is the large bag that holds the helium gas. The envelope is generally cigar-shaped, for aerodynamic purposes, and made of a durable, airtight, lightweight fabric (polyester composites) that is much like the fabric of a space suit.
Helium Helium is a colorless unreactive gas that is less dense that air. It belongs to the Noble gases which is the last group on the far right of the Periodic table. All of the Noble gases are chemically unreactive because they contain a complete number of electrons in the outer shell. Helium gas if often used in party balloons as it is lighter than air. Helium is also found in the sun and the stars where it is formed through a series of nuclear fusion reactions involving hydrogen.