# Presentation: 095302

## Shuttle Lightning Protection

**Shuttle Lightning Protection**

## Straight to the Chase

- The truth of the matter is that the Shuttle elements have varying degrees of lightning protection, almost all of which are inadequate in some sense to fully protect from the so-called “MIL-SPEC” 200 kA attachment. Because of this, for most of the life of the Program, the Shuttle has used weather restrictions and lightning activity avoidance as its primary means of lightning protection.The elements of the Shuttle include 1) the External Tank, 2) the Orbiter, 3) the Solid Rocket Boosters, which include the Reusable Solid Rocket Motors and the forward and aft skirts that contain the engine nozzles, parachutes, and assorted electronics, 4) the Space Shuttle Main Engines, and last but by no means least, 5) Ground Operations.The Program does have a lightning protection requirements document, NSTS-07636, which is currently in Revision F. The history of this document may provide some clues as the manner in which lightning has been dealt with in the past by the Program. The next few charts will attempt to summarize some of the more important aspects of this document’s colorful past.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- JSC-07636 was initially released by the Program in September of 1973. In the introduction, it stated“The Space Shuttle vehicle may experience lightning in flight even though launch restrictions will be imposed. In addition, the system will be exposed to lightning on the ground and possibly during other mission phases.” ... “This document defines the lightning environment for design and imposes the requirements that the design must satisfy to ensure the protection of the Space Shuttle vehicle system from the direct and indirect effects of lightning.”The original intent appears to have been to build a vehicle robust enough to survive and operate through a lightning attachment. The maximum threat level identified in this initial release was a two stroke event, with the first stroke of amplitude 200 kA, the second stroke being 100 kA in amplitude, with no distinction between flight phases, including ground operations.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- Revision B was released in 1979. A number of changes were introduced into this revision. The waivers for the ET DFI were removed. Waivers were added to require the LO2 and the LH2 tanks and the LO2 pressurization line to meet only the second and subsequent return strokes, and only at a minimum vehicle velocity of 64 ft/sec. Also,  ET cables were allowed to have splices in the shields. The lightning model definition was also changed to indicate the second stroke not always being present, and if so, at only 1⁄4 the amplitude of the first stroke.

- Revision A was released in November of 1975. Two waivers were added at that time to exempt external tank developmental flight instrumentation (ET DFI). The lightning model used in the basic release and in Rev A is shown at left.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- In 1976, Rockwell specification MF0004-002, Electrical Design Requirements for Electrical Equipment Used on the Space Shuttle, *deleted* indirect effects requirements, because vendors said they were incapable of testing to the requirements. Several changes were accordingly written into 07636 to remove testing of flight and ground hardware for indirect effects, *and* some direct effects testing as well. Detailed analysis was substituted for test.

- Finally, the lightning model itself was altered, to indicate that the second stroke did not always occur, and if it did, its amplitude would be only 1⁄4 of the initial 200 kA stroke.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- Having eliminated testing as a requirement, criticality 1 and 1R LRUs were analyzed over the time period from 1976 to 1980 to assess the indirect effects of a 200 kA attachment to the vehicle.In 1980, simulated lightning tests were performed on OV-101 to assess the magnetic fields induced by a lightning attachment to the vehicle, and to determine the associated induced voltage and current levels.Then, in 1982, McDonnell Douglas performed an atmospherics operations constraints study. In this study, 20kA was indicated as the average lightning stroke current. During this same period of time, the remainder of the commercial and military lightning community was slowly accumulating data to show the maximum lightning stroke model should be close to 200 kA, with an average of 50 kA. Then, in 1983, the Orbiter End Item Specification, document number MJ070-0001, changed its stated requirements to indicate the Orbiter would meet the requirements of JSC 07636, except that the levels would be 20 kA for ascent and 50 kA for descent.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- With at least simulated data now available to work with, from 1981 through 1984  all criticality 1 and 1R LRUs were re-analyzed to assess their susceptibility to the indirect effects of 200 kA, 100 kA, 50 kA, and 20 kA amplitude attachments.In 1984, revision C of 07636 was released. In addition to the two waivers in revision B, five new waivers for ET were added to this revision. The engine cut-off sensors could use single-shielded wire; the eccobond lightning protection bands were to be removed for STS-2, -3, -4, -5, and -7; phenolic material could be used for the cable tray intertank forward fairing for STS-2 and -3; bonding for the same cable tray was not required; and finally the lightning protection band at station 536 could be removed on LWT-1 through LWT-6.The maximum threat levels were reduced, and for the first time made applicable on a flight phase basis, to 100 kA on the ground, and to 50 kA first stroke, possibly followed by a 25 kA second stroke, in flight. The lightning model retained the same shape as in revision B, with the levels altered as indicated.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- For the first time, the document states explicitly that equipment shall be designed to withstand the direct effects produced by lightning without endangering the crew. At the same time, all references to impact to mission success or launch delay are removed.The indirect effects requirements compliance is restricted to only criticality 1 or 1R circuits contained inside equipment.Testing to show compliance of protection of pyrotechnic circuits and devices is removed!All of the verification test and/or analysis techniques, information, et cetera, is removed to a new document, JSC 20007, the Space Shuttle Lightning Protection Verification Document (released in February, 1985).Specific weather restrictions, suspiciously similar to launch commit criteria, show up for the first time.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- Revision D was released in October 1986. One new waiver was added for ET, this time for the GH2 pressline bonding jumper.This revision introduced no less than *three* models for lightning. The first model was intended for flight and ground hardware not protected by facility or other structures. This model reintroduced the 200 kA stroke, but with no mention of a second stroke. The second model was intended for flight and ground hardware protected by facility or other structures. This model reintroduced the 100 kA stroke, but with no mention of a second stroke. The third model was intended for vehicles inflight. This model introduced a 50 kA first stroke, with a possible 25 kA second stroke. The lightning model retained the same shapes as in revision C, with the levels altered as indicated.Interestingly, this revision also for the first time acknowledges (in paragraph 4.1) that additional protection in the form of Faraday cages and weather restrictions may be required to protect flight and ground hardware from direct effects.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- In 1987, NASA tasked Rockwell to perfrom a re-evaluation study of the lightning criteria for the National Space Transportation System (Shuttle). Four primary observations/recommendations came out of this effort, to whit:	1) Shuttle requirements should be updated to adopt SAE AE4L lightning	standards to ensure incorporation of the state-of-the-industry knowledge,	and to incorporate standardized test waveforms, voltages, and currents	2) Shuttle and ground facilities appeared to meet proposed new	requirements, as referred to in (1)
- 	3) Previous lightning protection design requirements had been	implemented, and compliance was by either analysis or test	4) Operational constraints (e.g., weather restrictions, LCC) minimized risk

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## 07636 Revisited

- So, revision E, change 22 to 07636, was duly released in September 1990. Almost immediately, change 23 to 07636 was released in November of 1990, with no less than 44 waivers, essentially exempting all elements from all requirements in the document. Most of these waivers were based on 1) the presence of the catenary wire system at Pads 39 A & B; 2) weather related move restrictions; 3) post-lightning strike requirements; 4) launch commit criteria; 5) operational and crew procedures.Revision F, change 24 to 07636, was released almost exactly a year later, in November of 1991. The 44 waivers were removed and replaced by 21 exceptions to the requirements, obviating compliance to most requirements by any of the Shuttle elements for the remainder of the Program.Revision G was released in April of 1994. Most of the changes from revision F were related to document formatting, with one new waiver and a few additional exceptions added to the list.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## Protection per Element

- The next few charts will attempt to summarize the salient features of lightning protection that each element possesses, similar to what was done for the requirements document. The level of detail is such as to provide an overview level of understanding. If very specific details are required, this will need to be addressed off-line. Much of the following information is taken from the recently completed Shuttle Vehicle Level Assessment, performed by the joint efforts of EMC Group members from JSC; MSFC; Boeing Huntington Beach & Houston; Lockheed Martin at the Michoud Facility, LA; Rocketdyne in Canoga Park, CA; ATK Thiokol, in Brigham City, Utah; and United Space Alliance, Houston & KSC.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## ET Protection Features

- ET has a lightning rod on the tip of the composite nose cap. The lightning rod is electrically bonded to the nose cap, which is in turn electrically bonded to the LO2 tank. The LO2 and LH2 tanks, and the intertank area, the Solid Rocket Booster (SRB) thrust panels, and the ET to Orbiter and ET to SRB attach fittings are all electrically bonded to each other. All bonds are less than 2.5 milliohms. The lightning rod to nose cap to LO2 to LH2 tank to the SRB and Orbiter interfaces defines the main conduction path through the ET for lightning.Cable trays protect externally mounted cables from direct effects. Cables in the cable trays also have electromagnetic shielding that is circumferentially bonded at terminating connectors, which are in turn electrically bonded to bulkhead metallic structure at either end. The cable trays have been tested to 25 kA attachment levels; the cable trays are exempt from a full threat level (i.e., 200 kA) attachment protection requirement.Nose cap internal wiring also has overbraid shielding; intertank wiring has no overbraid shielding. Propulsion and pressure lines, and vent ducts are all electrically bonded at entry/exit points.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## ET Protection Features

- The LO2 and LH2 tanks themselves are exempt from meeting requirements to prevent ignition points being attained in the event of a lightning attachment because the tank skin thicknesses range from 0.080 to 0.140 inches. Testing has shown that with expected cryogenic temperatures and pressures commensurate with flight operations, skins of 0.140 thickness are subject to skin penetration from exposure to coulomb content in 100 kA attachments.Portions of the tank are protected by their proximity to the Orbiter during launch (i.e., probability of initial attachment or swept stroke is low), while others derive their protection from the pad structures themselves until the vehicle has cleared the tower and is traveling at a speed greater than 64 feet per second. At this speed, the dwell time for an initial attachment or swept stroke is believed to be such that catastrophic damage (i.e., metallic penetration) will not occur.The ET is transported from the Michoud facility to KSC on a barge that is completely covered by a metal covering to prevent any lightning attachment to the ET itself. Once at KSC, the ET is located inside the Vehicle Assembly Building (VAB) until mated to an Orbiter and a pair of SRBs for flight operations.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## Orbiter Protection Features

- Main Orbiter structures are all metal and are electrically bonded together by large numbers of metal fasteners. Covered wire trays are used in the flight deck, payload bay and aft fuselage areas to provide shielding from lightning induced aperture and diffusion fields. Gross overbraid shielding is used in many areas where wiring is exposed, such as the wing trailing edge, in the Orbiter Maneuvering System (OMS) pods, between the Orbiter and ET, and in the Main Engine Compartment. Standard shielded wire is used extensively throughout the vehicle to provide shielding against internal and external electromagnetic fields, and associated induced voltages and currents. The payload bay doors a the OMS pods are composite, but they each have an aluminum mesh embedded in the outer mold line surface to provide lightning protection.The Reinforced Carbon Carbon wing leading edge material was demonstrated in 1973 to be able to withstand a 200 kA attachment with only minor damage. The thermal protection system (RSI-900) on other expected attachment points, such as the eyebrow, the vertical tail and the wingtips has been shown to be able to withstand a 50 kA attachment with only surface cracking. At 100 kA, two or three tiles may be ejected at the point of attachment.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## Orbiter Protection Features

- The air data probe is similar to that used by the B-1 bomber, which has been demonstrated insusceptible to a 200 kA attachment. Also, the probe is only extended during descent.All antennas are flush mounted under the TPS and are structurally desinged to withstand a 200 kA attachment.Closeout panels and metal wire mesh are in place in various locations in the Orbiter to provide shielding for vents and ducts, particularly on the flight deck.The Orbiter also claims some degree of protection from the proximity of the ET during launch, as well as the launch pad structures. Prior to launch, the Orbiter is kept inside one of the Orbiter Processing Facilities (OPFs). Movement from there to the VAB is controlled by weather restrictions. Movement of the entire stack (i.e., Orbiter, ET and SRBs) from the VAB to the pad is also controlled by weather restrictions. The stack has no lightning protection at all during this move, so is almost always performed during the evening or very early morning hours (lowest probability of lightning activity).

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## Solid Rocket BoosterProtection Features

- The outer skin of the SRBs was demonstrated in 1989 to be able to withstand a 200 kA attachment without penetration, although the TPS was destroyed in the local vicinity to the attachment during the test.Most external cabling is routed through a systems tunnel that provides a metallic enclosure for the cables. The tunnel floor plates and covers are electrically bonded to each other and to the Solid Rocket Motor case. The covers are also electrically bonded together using jumper straps. The cables themselves are covered by overbraid with a circumferential electrical bond at the terminating connectors.Internal LRUs and the associated cabling and wire harnesses are laid out, filtered, shielded, and electrically bonded to structure so as to minimize electromagnetic interference or indirect effects of lightning attachments.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## Solid Rocket BoosterProtection Features

- The Range Safety System (RSS) has two redundant antenna input channels, with a shorted 1⁄4 wave stub in each antenna transmission line that acts as a short to potential incoming lightning currents or voltages while still allowing the unhindered passage of RSS signals into the receiver/decoder string.
- RSS ET crossover cables carry only 28Vdc signals, and are overbraid shielded with circumferentially bonded terminations at all connectors.The Reusable Solid Rocket Motors (RSRMs) themselves have been tested to a full 200kA level without penetration. Also, the RSRMs are well protected in covered transport rail cars from Utah to KSC.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## Space Shuttle Main EngineProtection Features

- Space Shuttle Main Engine (SSME) wiring harnesses are constructed of twisted shielded pairs with a gross overbraid shield that is circumferentially terminated at connectors.
- The engine closeout has a Class R electrical bond, achieved through faying surface contact and electrical bonding strap connections. Main engine structure is designed to meet Class L bonding requirements for lightning protection. Interestingly, the engine bell itself on each main engine is exempt from meeting direct attachment requirements.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## Ground OperationsProtection Features

- Ground Operations are protected primarily by weather restrictions and avoidance. The pads do have a catenary system that provides good protection for the stack from higher amplitude strikes. However, a recent study was completed that indicates attachments to the pad surface itself have a fair probability (once every 3 years or so) in spite of the presence of the catenary.This study has been reported to the Program, with recommendations to proceed with additional fleet assessment studies and a risk assessment to determine whether physical changes should be made or not. Further details of this and related activity is outside the scope of this presentation.

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.

## My Last Chart(Hurray!)

- I hope the foregoing has answered some of your questions, and provided you all with at least some information you did not have before today.
- If anyone has questions, or would like more detailed information, my contact information is shown below.Bob ScullyJSC Lead EMC EngineerSpace Shuttle E3 Control Technical Panel Chair281 483 1499  vox281 483 5830  faxrobert.c.scully@nasa.gov

- Bob Scully, NASA JSC (281) 483-1499

- 17 November 2005

**Notes:**
Implementing these changes will result in enhanced reliability of electrical and electronic equipment installed/employed on Shuttle. ESD to poorly protected equipment most often causes latent damage that cannot be readily detected at the time the damage occurs. A serious loss of reliability follows, possibly resulting in premature failure. The associated time/cost for troubleshooting and root cause determination, and the cost of premature equipment replacement can all be reduced through implementation of this change.