Although there are sometimes romantic and silk-scarf attitudes attributed to this type of business, in the final analysis we are professionals and will accept risks but, not undue risks...
- Colonel Frank Borman, testifying before the House of Representatives (April 10, 1967)
Perhaps lightning strikes thrice? Well, blog posting does, at any rate. Since I know NASA investigates the hell out of every anomaly, I tracked down their analysis of the Apollo 12 lightning strike.
It's just shy of 100 pages all told, and full of stupid math and stuff, but has a lot of interesting bits that even a lay person can get the gist. Here's the executive summary:
The Apollo 12 space vehicle was launched on November 14, 1969, at 11:22 a.m. e.s.t, from launch complex 39A at Kennedy Space Center, Florida. At 36.5 seconds and again at 52 seconds, a major electrical disturbance was caused by lightning. As a result, many temporary effects were noted in both the launch vehicle and spacecraft. Some permanent effects were noted in the spacecraft and involved the loss of nine non-essential instrumentation sensors. All noted effects were associated with solid-state circuits, which are the most susceptible to the effects of a discharge.
Analysis shows that lightning can be triggered by the presence of the long electrical length created by the space vehicle and its exhaust plume in an electric field which would not otherwise have produced natural lightning. Electric fields with sufficient charge for triggered lightning can be expected to contain weather conditions such as the clouds associated with the cold front through which the Apollo 12 vehicle was launched. The possibility that the Apollo vehicle might trigger lightning had not been considered previously.
The Apollo space vehicle design is such that a small risk of triggered lightning is acceptable. In accepting this minimal risk for future flights, launch rule restrictions have been imposed with respect to operations in weather conditions associated with potentially hazardous electric fields.
About those "nine non-essential instrumentation sensors":
The nine sensors which failed consisted of five thermocouples and four pressure/temperature transducers. These devices are all located in the same general plane of the service module. Four of the thermocouples which failed were mounted on the exterior skin of the service module and were to be used to determine the relative sun angle ; however, these are not required for mission success as alternate methods of determining sun angle are available...
The fifth failure was a thermal measurement located on the nuclear particle analyzer, which is of the same design as the four thermocouples discussed previously.
The remaining four sensors which failed were used to measure propellant quantities in the service module reaction control system. These sensors detect pressure and temperature through a semiconductor strain gage mounted on a pressure-sensing diaphragm on each of the four propellant tanks...Alternate means of determining propellant quantity were available; therefore, these failures had no effect on the mission.
The probability of inadvertent operation of the pyro initiating circuits is remote since all wiring is within the command module and is not in close proximity with the external skin. Even if the induced voltage was of sufficient magnitude, the duration of electrical discharge (microseconds) seconds).
So, also not a bit deal. And yeah, launching a giant lightning rod into big, angry clouds might cause some fireworks:
A space vehicle can initiate lightning from an electrified cloud because of its effect on the electric field lines in the atmosphere. The space vehicle is an excellent electrical conductor which may be effectively extended by the presence of the exhaust plume.
The launch of such a vehicle has the effect of suddenly introducing a long electrical conduction path into the atmosphere where no such path existed before. This, in turn, produces a distortion in the electric field equipotential lines such that the electric field or potential gradient is greatly increased at the top of the vehicle and below the exhaust plume.
At the top of the vehicle, the field may be increased by a factor of several hundred as illustrated in figure 10.
Some of the conclusions:
5. Analysis of the spacecraft design to withstand triggered lightning effects indicates the following:
a. The designs of the ordnance systems are reasonably safe.
b. The normal bonding practices followed provide the required first-order protection to all systems.
c. The automatic abort system is considered reasonably safe from improper operation.
d. Solid-state devices are most susceptible, and some effects may be expected which may jeopardize mission success should a discharge occur.
6. Analysis of the launch vehicle design to withstand triggered lightning effects indicates the following:
a. The probability of lightning damage to the vehicle hardware is deemed negligible.
b. The computer influence from a lightning strike may be subtle and varied in flight. The built-in programing checks and the computer system redundancies are such that no degrading first-order effects will result from the lightning.
c. The automatic abort system has been designed to provide an adequate safety margin and no changes are necessary.
d. The probability of initiating launch vehicle ordnance by means of a lightning strike is virtually nonexistent while the probability of dudding is deemed negligible.
7. Review of the present launch complex design and past analyses relative to lightning protection shows that the design concept is adequate.
Whew, I guess that's all taken care of, and spaceflight is now reasonably safe:
There is no practical procedure to eliminate the mechanism which led to the platform tumbling. However, because there is no requirement to align during launch, and the coarse-align mode inhibits the manual takeover of the S-IVB guidance, a software change is planned for Apollo 13 to prevent activation of the coarse-align mode during launch.
Good thing nothing else could go wrong on that next flight! Uh, anywayz, that's all I got. Just geeking out a bit on a foggy Sunday morning.
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