Weather on the launch pad

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  • Nasa's Orion 'Mars Ship' set for its maiden test flight on Thursday 4th December 2014. This test flight was postponed for several reasons, including gusty winds. Picture by Nasa.

    Wind speed forecasts for Florida (average wind speed in mph) for Thursday and Friday. The winds are from an easterly direction, but should be lighter around Cape Canaveral (on the east coast) on Friday, at 15mph, rather than nearer 21mph today. Picture by MeteoGroup.

    Lightning strikes a conductor rod on a space shuttle launch pad. A sophisticated lightning detection network gives Nasa guidance as to when it may be dangerous to commence a launch. Picture by Nasa.

  • Weather on the launch pad
    04.12.2014 16:27

    Between 12:05 and 14:44 GMT on Thursday 4th December, the US space agency (Nasa) had a launch ‘window’ for a test flight of its Orion Mars capsule. The rocket was due to lift off from the Kennedy Space Centre, Cape Canaveral, on the eastern coast of Florida.

    This particular launch is unmanned, and aims to test key technologies in a capsule that could eventually help get humans to Mars. However, the countdown was held several times, due to a combination of a boat travelling too close to the launch area, gusty winds, and also a small technical fault. Eventually the launch on Thursday was postponed. While two of these factors were potentially avoidable, the impact of weather on a rocket launch is more difficult to manage. 

    The weather elements which cause most difficulty to launching a rocket are lightning strikes and wind speed. Strong winds can be disruptive, especially when there is wind shear present. Large changes in wind speed over small vertical distances can create difficulties for a rocket’s control systems. In strong wind shear, enormous aerodynamic loads and stresses can quickly develop, which can result in the rocket completely losing control and crashing. Wind shear tends to be greatest in the lowest few kilometres of the atmosphere, so immediately after launch.

    Lightning is dangerous to a space mission for different reasons. The physical size, shape and metallic structure of a rocket make it very vulnerable to a lightning strike just after take off, once away from the relative safety of the lightning conductor rods on the launch pad. The large payload of fuel and millions of pounds worth of sensitive electronic equipment make the concept of a lightning strike potentially very dangerous, as well as devastating to the mission. Due to the hazards posed by thunderstorms, a sophisticated lightning detection network is installed at the Kennedy Space Centre to warn of approaching or developing thunderstorms. This, combined with high resolution weather radar, can provide advanced warning of lightning strikes.

    So why was Cape Canaveral selected as a suitable launch site for US space missions? Florida has the highest rate of lightning strikes per year in any US state, with summer thunderstorms creating gusty winds. There is also the threat of hurricanes between June and November. There are two main reasons. Due to the laws of physics, the closer a launch site is to the Earth’s equator, the less fuel and energy required to get a rocket into space (thus, reducing costs). The second reason is that the Earth is rotating from west to east. Thus, launching a rocket in an eastwards direction means that some extra momentum can be gained from using the Earth’s rotation. Southern California would be less storm prone than Florida, but any departing rocket would then pass over the USA immediately after take off. If the craft suffered difficulties, this would threaten a possible impact on a populated area, rather than into the Atlantic.

    On Thursday 4th December, there was a 15-20mph north-easterly wind with some stronger gusts, which was enough to prevent a safe launch. Another attempt will be made to launch on Friday 5th December, when wind speeds are expected to be slightly lower.

    By: Matthew Dobson