Click the arrow to watch the Cygnus post-launch media briefing. Video source: NASA.
One day after their scheduled launch was postponed due to increased radiation caused by a solar flare, Orbital Sciences launched the Cygnus cargo module today
This time, the launch was threatened by a “DFO.” Not many casual observers (including me) knew what that was, but the explanation finally surfaced on Twitter. DFO is an acronym for Distinct Focusing Overpressure. To quote a NASA document:
Distant focusing is defined as an atmospheric phenomenon that can produce greatly enhanced overpressure due to sonic velocity gradients with respect to altitude. These enhanced overpressures can break windows in distant communities, which may result in personal injury. Distant focusing overpressure, sometimes referred to as far field blast overpressure, is of concern in the event of a large explosion on or around the launch pad and occurs only under certain meteorological conditions.
The DFO violation cleared before launch, as did the discovery of duck hunters within the potential blast radius.
Cygnus is scheduled to arrive at the International Space Station on Sunday January 12. It's the first of eight cargo deliveries under a Commercial Resupply Services contract between Orbital and NASA.