Stamp Museum >> World Space Stamps >> US Space Stamps >> Viking to Mars Commemorative Stamp, 1978
The U.S. Viking Mars Orbiter Commemorative Stamp: 1991
Viking Mars Orbiter, 29 cents, Scott Catalog No. 2572, Issued in 1991
This mult-color stamp was first issued in 1991.
For further reading, see NASA's Viking: Mission to Mars.