Many requirements, one solution
The Kennedy Space Center’s Florida launch location is ideal because Kennedy Space Center is close to the equator. This means that the earth’s rotation effectively gives an extra push during the launch so that less fuel is needed to reach space. Unfortunately, Florida can often be a challenging launch site because it has the highest rate of lightning discharges per kilometer in the USA making it the lightning capital of the country. To combat the dangers, the Kennedy Space Center required a lightning monitoring system that could work in parallel with a lightning protection system. Both systems had to be effective at every critical point during a spacecraft’s launch program. Spacecraft are initially assembled inside a huge building called the Vehicle Assembly Building. They are then transported to the pad on special heavy duty transporters called Mobile Launcher Platforms where final preparations and mission checks are performed prior to launch.
A spacecraft is vulnerable to lightning strikes from the moment it emerges from the Vehicle Assembly Building until it is finally launched into space. During this time it is important to continuously monitor numerous points both inside and outside the spacecraft to help determine any possible problems that may have occurred due to induced electrical transients from lightning in the area.
To achieve this, HBM developed a system that the Kennedy Space Center utilizes to measure induced currents and voltages at some 120 measurement points. By monitoring multiple points it is possible to identify places where high induced currents occur and hence determine where possible damage might have happened. A number of factors had to be taken into account when developing the lightning monitoring system. Kennedy Space Center has a high
average ambient temperature that can often reach in excess of 90 ° (32 °C) while humidity is also very high, meaning that any system had to be very resistant to corrosion and dampness. Another factor was the high risk of damage from shock and vibration that are present during a spacecraft’s launch making it necessary for the system to meet specific standard military specifications. It was also considered very important that the transmitter’s input power be DC only. This would allow for battery operation, providing
complete isolation, when lightning was nearby. However, it was just
as equally important to switch in a DC charging circuit via a remotely controlled output switch on the transmitter once the storm had passed to keep the batteries charged to monitor operations continuously. The solution selected that satisfied all of the Kennedy Space Center’s requirements was HBM’s Genesis HighSpeed with Perception software as this is a high-resolution DAQ system available out of the box that can monitor up to 64 channels in a single mainframe with a 25 MHz bandwidth and is capable of recording at up to 100 MS/s. It is also capable of window triggering from any channel.
Equipment at the test point included a 7600 fiber-optic transmitter rated at 100 MS/s with 14-bit resolution and 25 MHz bandwidth. The transmitters are housed with stainless steel304; the same material used to protect the Gateway Arch in St. Louis, Missouri, as it does not stain or corrode as easily as ordinary stainless steel. Fiber optic cable was selected because of the long lengths needed – up to 12 km – between the many measuring points. HBM’s equipment has a full scale accuracy of 0.1 % at lengths of over 800 m and benefits from automatic cable length correction while preventing cross channel skew.
