Preventive protection against thunderstorms during spacecraft launches

Satellites are a necessity in modern life for a variety of purposes (weather forecasting, scientific exploration, long-range communications, etc.).

The vehicles that place satellites in orbit are sensitive to natural and rocket-induced lightning threats. That is why NASA developed the LLCC set of rules to assess whether the weather conditions permit the launches. Since its application, incidents such as those of Apollo 12 and Atlas-Centaur 67 have not occurred again. Within these criteria, the ambient electric field plays an essential role and is measured by a network of field mills (electrostatic field sensors) at the Kennedy Space Center.

Satellite launch activity and space exploration missions are continuously growing. Communication satellites are indispensable for modern life and represent a multi-billion dollar investment. Satellites are launched into orbit by specifically designed launch vehicles. These are usually rockets with control and guidance systems1.

On the other hand, space exploration is an area of increasing relevance for technological, scientific, and often also political reasons. As a result, the demand for launch facilities and programmes continues to grow, making it a lucrative business proposal1.

Inclement weather is the main cause of launch delays and cancellations. Launch vehicles, as well as space shuttles, are sensitive to the threat of lightning during the launch and transit through the lower atmosphere. Rockets contain oxidising agents, fuel, and also electro-explosives devices for self-destruction if necessary. A lightning strike could therefore have catastrophic consequences resulting in loss of lives, time and economic costs1.

The threat of a thunderstorm led to the development of meteorological criteria to mitigate the lightning risk during launch. They are known as Lightning Launch Commit criteria (LLCC). Since their implementation, about 5% of launches at Cape Canaveral/John F. Kennedy Space Center (KSC) have been cancelled and 35% have been postponed2.

In fact, the Artemis I orbital mission, scheduled for launch on 29 August 2022, had to delay the refuelling due to storms at sea. After completion of the refuelling operation, temperature problems were found in one of the rocket engines. The mission was delayed several times due to technical issues, but also due to the presence of tropical storms Ian and Nicole. The mission was successfully launched on 16 November 2022.

Below, we comment on NASA’s LLCC spacecraft launch rules and the importance of electrostatic field detectors for assessing the risk of lightning strikes in the area.

NASA’s Lightning Launch Commit Criteria (LLCC)

LLCCs are a set of rules, developed by NASA and other US federal organisations to mitigate the risk of impacts during spacecraft launches. They cover both natural and rocket-induced releases. The latest version of the LLCCs is published in the 2017 NASA-STD-4010 standard3. However, LLCCs and their associated definitions are continually revised based on new knowledge and experience accumulated over the years of the US space programme4.

While the thunderstorm threat was considered in the early days of the space age until the launch of Apollo 12 in 1969 vehicle-induced lightning produced by flying through highly electrified clouds that are not naturally discharging4 was not taken into account.

In the case of Apollo 12, two induced lightning strikes were observed during the first minute of the flight. These impacts caused permanent damage to non-critical sensors, as well as temporary failures of critical systems. The mission was completed, thanks to the crew’s problem resolution. Because of this incident, new rules were introduced prohibiting flying near thunderstorms or through certain types of non-thunderstorm clouds, but with a potential risk of electrification1.

In contrast, the 1987 Atlas-Centaur 67 (AC 67) rocket, which contained the Fleetsatcom satellite, suffered an impact induced by the rocket passing through an electrified cloud. This lightning-caused a failure of the vehicle’s guidance system. As a result of an unplanned rotation, stresses were generated and the rocket began to break apart and was ordered to self-destruct. Debris recovered from the Atlantic Ocean confirmed that a lightning strike had occurred1.

However, it was determined that, although the LLCCs in force in 1987 were deficient, the main responsibility for the disaster was the wrong assessment, because the correct one would have prevented the liftoff of AC 675.

A standard NASA-STD-4010 provides uniform engineering and technical requirements for procedures, practices and methods for NASA programmes and projects. Also, Technical Publication NASA/TP-2016-219439 of 20165 provides the scientific basis for the standard, although this document is based on the LLCCs of August 2014, and therefore does not include any subsequent amendments that may be in the 2017 standard.