Expensive USA Gandhi stamp Cover. T547 Space X-15 Rocket Plane Cover White Signed 4-21-61

Hello Gandhi Collectors,

One of the expensive cover with Gandhi Stamps was sold on ebay. Check it out.

Buyer: SRM2382

Price : $67

Seller: 3curls1wave

The North American X-15 rocket-powered aircraft/spaceplane was part of the X-series of experimental aircraft, initiated with the Bell X-1, that were made for the USAAF/USAF, NACA/NASA, and the USN. 

The X-15 set speed and altitude records in the early 1960s, reaching the edge of outer space and returning with valuable data used in aircraft and spacecraft design. As of 2011, it holds the official world record for the fastest speed ever reached by a manned rocket-powered aircraft.

During the X-15 program, 13 of the flights (by eight pilots) met the USAF spaceflight criteria by exceeding the altitude of 50 miles (80 km) thus qualifying the pilots for astronaut status. The USAF pilots qualified for USAF astronaut wings, while the civilian pilots were later awarded NASA astronaut wings.

Of all the X-15 missions, two flights (by the same pilot) qualified as space flights per the international (Fédération Aéronautique Internationale) definition of a spaceflight by exceeding 100 kilometres (62.1 mi, 328,084 ft) in altitude.

According to me this is unique cover for space philatelist because of signature of some space person.

Thanks

KP.