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.
The U.S. alone produces 75 percent of the world's helium. Today, the U.S. alone produces 75 percent of the world's helium. Nearly half of that total, or roughly 30 percent of the world's helium supply, comes from the U.S. Federal Helium Reserve. That reserve is held in a huge natural underground reservoir near Amarillo called the Bush Dome.