Per ardua ad astra ("Through adversity to the stars" or "Through struggle to the stars") is the motto of the Royal Air Force and other Commonwealth air forces such as the RAAF, RNZAF, the SAAF, as well as the Royal Indian Air Force until 1947. The RCAF used it until 1968 after which it used the motto "sic Itur ad Astra." It dates from 1912, when it was adopted by the newly formed Royal Flying Corps.
The first Commanding Officer of the Royal Flying Corps (Military Wing) was Colonel Frederick Sykes. He asked his officers to come up with a motto for the new service; one which would produce a strong esprit de corps.
Not long after this, two junior officers were walking from the Officers' Mess at Farnborough to Cody's Shed on Laffan Plain. As they walked they discussed the problem of the motto and one of them, Lieutenant J. S. Yule, mentioned the phrase Sic itur ad Astra, from Virgil. He then expanded on this with the phrase Per Ardua ad Astra, which he translated as, "Through Struggles to the Stars". Colonel Sykes approved of this as the motto and forwarded it to the War Office. It was then submitted to the King, who approved its adoption.
Yule is believed to have borrowed the phrase from Sir Henry Rider Haggard's fantasy novel The People of the Mist (1894). The first chapter includes the sentence: "To his right were two stately gates of iron fantastically wrought, supported by stone pillars on whose summit stood griffins of black marble embracing coats of arms and banners inscribed with the device 'Per Ardua ad Astra'". It is possible that Rider Haggard had taken it from the Irish family of Mulvany, who had used it as their family motto for centuries, translating it as "Through Struggles to the Stars".
There is no single definitive translation, as both "ardua" and "astra" can carry a range of associations. The Royal Air Force and other Commonwealth air forces most often translate it as "Through Adversity to the Stars".
The motto of the Royal Air Force Regiment omits the ad astra part, becoming simply per ardua. Conversely, the name of the building that originally housed the Air Ministry, became Adastral House, based only on 'ad astra. The Royal Canadian Air Force and many other entities use the similar motto per aspera ad astra.