Mar 19, 2011 09:14 GMT  ·  By

Only two days after the first spacecraft entered orbit around Mercury, the US Postal Service (USPS) has produced a batch of 30 million postage stamps marking the momentous event. They will be released in pairs, with another unique stamp celebrating Alan Shepard, the first US astronaut in space.

The USPS began printing the new stamps even before the NASA MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) probe achieved orbital insertion.

It has been traveling through space for about 6 and a half years, and had already carried out one flyby of Earth, two flybys of Venus, and three flybys of Mercury before its main thruster was fired to achieve deceleration on Thursday evening, March 17.

Even though mission controllers at the Johns Hopkins University (JHU) Applied Physics Laboratory (JPL) put on a brave face now, after success was achieved, the maneuver MESSENGER had to undergo was not risk-free.

Its main thruster had to burn steadily for 15 minutes at exactly the right time in order for the prove to slow down sufficiently to allow for itself to be captured by Mercury's gravitational pull.

“Despite its proximity to Earth, the planet Mercury has for decades been comparatively unexplored. For the first time in history, a scientific observatory is in orbit about our solar system's innermost planet,” says Sean Solomon.

The expert is the principal investigator of the MESSENGER mission, which is managed by the APL. “Mercury's secrets, and the implications they hold for the formation and evolution of Earth-like planets, are about to be revealed,” he said.

But apparently the USPS never doubted the success of the mission, as evidenced by the fact that they printed the new stamps even before the probe reached its target. The new postage stamps read “First Spacecraft to Orbit Mercury.”

They will be released on May 4, alongside stamps celebrating NASA astronaut Alan Shepard as the first US citizen to fly to outer space. He was the second-ever person to achieve this feat on May 5, 1961, just after Russian cosmonaut Yuri Gagarin reached orbit on April 12, 1961.

Shepard went on to lead the NASA Apollo 14 mission to the Moon, and then became the fifth person ever to walk the surface of Earth's natural satellite, Space reports.

“These two historic missions […] frame a remarkable 50-year period in which America has advanced space exploration through more than 1,500 manned and unmanned flights,” the USPS announces in a press release.