The motor should burn for a full two minutes
The test firing of a new first-stage rocket motor which could one day launch US astronauts was called off just seconds before ignition on Thursday.
The stoppage was put down to a power failure in a hydraulics unit controlling the rocket's nozzle.
The US space agency was not immediately able to state a new date for the test at manufacturer ATK's Utah facility.
The five-segment booster is intended to power the early flight phase of Nasa's proposed Ares 1 launch vehicle.
The tall rocket would lift the new Orion crew capsule into orbit.
The two-minute horizontal test-burn of the solid-fuel booster should give ATK and Nasa engineers valuable performance data.
Further engineering data will come from the October flight of a demonstrator version of the Ares 1 known as Ares 1-X.
The US space agency is scheduled to retire its space shuttles next year, and has begun the development of a new human space launch "architecture" called Constellation.
The architecture calls for two new rockets: the Ares 1 to launch crew, and a new heavy-lift rocket known as Ares 5 that could put into orbit the equipment needed by an Orion capsule to travel to the Moon and beyond.
However, all the systems are under review by a top-level panel led by former Lockheed Martin chairman and chief executive Norm Augustine. President Barack Obama has asked the panel to assess different options for getting US astronauts into space.
Some commentators expect the Ares development plans to be modified or even cancelled.