By Klaus Schmidt Oct 30, 2012 spacefellowship.com

On a calm clear high-desert October evening, Interorbital Systems’ NEPTUNE rocket series’ main engine roared to life in its first hot-firing test. The engine, the IOS GPRE 7.5KNTA (General Purpose Rocket Engine; 7,500lb-thrust; Nitric Acid; Turpentine; Ablative cooling), blasted a 22-foot (6.71-meter) plume of fire across Interorbital’s Mojave Spaceport test area, scorching the sand an additional 50 feet (15.24 meters) beyond the plume end.