This slide presentation reviews the Space Shuttle electromagnetic compatibility (EMC). It includes an overview of the design of the shuttle with the areas that are of concern for the electromagnetic compatibility. It includes discussion of classical electromagnetic interference (EMI) and the work performed to control the electromagnetic interference. Another area of interest is electrostatic charging and the threat of electrostatic discharge and the attempts to reduce damage to the Shuttle from these possible hazards. The issue of electrical bonding is als reviewed. Lastly the presentation reviews the work performed to protect the shuttle from lightning, both in flight and on the ground

Scully, Robert C.

NASA Technical Reports Server

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Agenda 
Introduction 
Classic EMI 
Electrostatic Charging 
Electrical Bonding 
Radar Monitoring 
Lightning Protection 
Future Work 
Summary & Closing 
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Wing(s) 
EMC Zones of the Orbiter 
Vertical Stabilizer 
Payload Bay 
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Avionics Bays 
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Flight Deck 
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Fuselage 
Crew Compartment 
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Orbiter Structures 
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Classic EMI 
We provide electromagnetic compatibility and 
interference control engineering expertise 
- Identification, definition and/or tailoring of 
EMI/EMC requirements 
- Assistance with mitigation of known or 
suspected failure(s) to meet EMI/EMC 
requirements 
- Areas of expertise include lightning protection, 
control of electrostatic discharge and corona, 
power supply filter design, signal routing and 
integrity, grounding, bonding, and shielding 
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Classic EMI 
We also offer advanced electromagnetic modeling 
capabilities, and can perform computation using 
approaches such as: 
Finite Difference Time Domain (EMA3D) 
Method of Moments (NEC-BSC, GEMACS) 
radar cross section calculation (X-Patch) 
Finally, we collaborate with EMI/EMC groups located 
at other NASA centers, such as Marshall Space 
Flight Center and Kennedy Space Center, to ensure 
we provide the best overall products and services 
possible. 
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Classic EMI 
Space Shuttle Electromagnetic Interference limits 
and test methodologies were originally derived from 
Mil-Std-461A. Recently, the requirements were 
completely revised to reflect the current version, 
Mil-Std-461 E. Although the Mil Spec was used as a 
basis, the limits were heavily tailored specifically for 
the Shuttle application. 
In contrast, Space Station uses limits and test 
methodologies derived from Mil-Std-461 C, whereas 
the Russian segment uses limits and test 
methodologies similar to both Programs. 
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REIQUIREMENT AJ'PLICABILITY 
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Classic EMI 
As an example of specific tailoring, Space Shuttle 
employs a Bulk Cable Emissions (BCE) test from 
150 kHz to 200 MHz as a part of the more familiar 
RE102 radiated emissions requirement. 
The BCE test utilizes a CISPR 16 absorbing clamp, 
calibrated as a current probe, to measure common 
mode radiated emissions associated with cable 
harness currents. 
The intent of this measurement is to characterize 
possible crosstalk interference related to cable 
harness currents. 
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Classic EMI 
Another example of a unique test methodology 
created for Space Shuttle is the CS106 test, which 
replaces the obsolete eS06 limit and methodology 
in earlier versions of MIL-STD-461. 
This test measures the EUT response to negative 
going transients on the power bus associated with 
equipment turn-on, and is an accurate simulation of 
load-induced power-line switching transients 
expected to occur on the Shuttle power bus. 
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Classic EMI 
An intentionally complimentary test methodology to 
CS106, modified from a previous unique Space 
Shuttle test, is the TT101 test, which also has no 
equivalent counterpart in MIL-STO-461. 
This test measures the emitted negative going 
transient associated with equipment turn-on, and 
provides specific information regarding bus sag as 
a function of both time and magnitude, as well as 
insight into potential inrush current problems. 
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Electrostatic Charging 
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Electrostatic Charging 
Electrostatic discharge is a constant threat to the 
Space Shuttle and its various components and 
equipments, whether on the ground during 
preparation for flight, or in Low Earth Orbit 
approaching the International Space Station. 
For many years, Shuttle relied on Mil-Std-1686 and 
Mil-HOBK-263 for guidance and requirements for 
protection of equipment. These documents have 
now been superseded within NASA by ESO 
Association Standard ANSI/ESO 520.20-1999. As 
additional reference, the ESO Association Technical 
Report TR20.20-Handbook is also available. 
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Electrostatic Charging 
Electrostatic charging can generally be reduced to 
three primary mechanisms: 
triboelectric charging 
exogenous charging 
ionic charging 
Of these, triboelectric charging is probably the most 
familiar, and presents the most ubiquitous threat to 
Shuttle equipment. 
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Electrostatic Charging 
Triboelectric charging results from the separation of 
material surfaces. The amount of charge transfer is 
dependent on the surface roughness, and the 
difference in their respective work functions. A work 
function describes the amount of energy necessary 
to liberate an electron from its orbit about the 
nucleus of an atom. Clearly, different materials will 
exhibit different work functions. 
Surface separation can occur from frictional contact 
between one's feet and the floor surface, or the flow 
of a gas contaminated with slight amounts of 
particulate matter. 
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Electrostatic Charging 
In Low Earth Orbit, the Orbiter is in contact with the 
plasma environment, and is potentially subject to 
current collection. Negative surfaces collect ions; 
positive surfaces collect electrons. 
The charge process is governed by the Poisson 
Equation 
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Experiment has shown the Orbiter main engine bells 
collect sufficient ion current to achieve balance with 
the surrounding plasma at a low potential difference, 
as long as the main engine bells are not in the 
Orbiter wake. 
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Electrostatic Charging 
Exogenous charging results from near proximity to a 
strong concentration of electric charge, and is 
thought to playa role in triggered lightning events. 
This type of electrostatic charging is not generally a 
threat to Shuttle. 
So, how do we control all this transfer of electric 
charge? 
In the case of ionic vehicle charging, we try to keep 
the main engine bells out of the Orbiter's wake so we 
can balance Poisson's Equation. Space Station uses 
a device known as a Plasma Contactor, which uses 
Xenon gas as an ion source. 
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Electrical Bonding 
TYPICAL ELECTRICAL BONDING OF DETAILS WHICH ARE 
ELE.CTRICALlY BONDED BY ADHESIVES 
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Electrical Bonding 
Space Shuttle currently uses Mil-B-5087B as the 
source for its bonding criteria. Several classes of 
. electrical bonding are described in Mil-B-5087B, 
among them Class A, C, H, L, Rand S. 
Recently released NASA-Std-4003, titled Electrical 
Bonding for Launch Vehicles, Spacecraft, Payloads 
and Flight Equipment, combines requirements 
contained in Mil-B-5087B and SAE ARP 1870, and 
the experience of NASA EMC engineers from 
several NASA centers. This new standard includes 
bonding classes C, H, L, Rand S (A is included in 
R), provides general and specific requirements, and 
a section containing design guidance. 
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Electrical Bonding 
Electrical bonding is the process we use to 
electrically and mechanically join two or more 
materials together to minimize electrical potential 
differences. 
In the electrostatic case, we want to control the 
accumulation and distribution of electrical charge. 
That's true, whether the charge is on your body, or 
covering the surface of a Space Station solar array 
upon which an astronaut is about to perform routine 
maintenance. 
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Electrical Bonding 
One of the largest bonding challenges for Shuttle is 
to control electrostatic charging on multilayer 
insulated blankets and related materials. 
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Lightning Protection 
The primary protection for Space Shuttle from the 
effects of lightning is avoidance. 
Stringent weather avoidance criteria are in place to 
ensure the Shuttle vehicle is not exposed to 
lightning events. 
During launch, the Shuttle is exposed for about 80 
seconds as it ascends into orbit; during landing, the 
exposure time is a bit longer, only about 5 minutes 
as it passes through the lower atmosphere where 
lightning might be expected to occur. 
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protected by the 
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Instrumentation System 
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Lightning Protection 
Since lightning is ultimately unpredictable even with 
strict weather controls in place, NASA still uses 
design criteria, analysis, and protective measures to 
provide protection form both direct and indirect 
effects of lightning. 
A good example of such protective measures is the 
incorporation of aluminum mesh in the outer mold 
line of the composite payload bay doors. This 
technique has been proven in many aircraft designs 
using composite materials, such as the Bell-Boeing 
V-22 Osprey, and the Beech Starship. 
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Future Work 
Measurement of the RF attenuation of aircraft has 
been a problematic issue for several years 
Older methods utilized a very time consuming, 
direct illumination process that required many 
antenna positions to be used 
- Often the results were questionable, thus 
leading to high cost for low return on the 
investment 
NIST has been working to develop a ,direct 
illumination method in the time domain, and has 
recently been successful with this approach 
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Other new methodologies have been developed in 
the recent past that utilize reverberation chamber 
theory 
- The statistical basis of these methodologies 
has been carefully explored and verified by 
multiple tests on large aircraft 
- These new methodologies require fewer 
antenna positions, and generate a lot of 
accurate and reliable data in a (relatively) short 
time 
Both Patuxent River NAWC and Dahlgren NSWC 
have successfully utilized this approach 
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Two major Orbiter vehicle tests are currently in 
planning: 
- RTF (quick look) test to validate aft 
compartment shielding 
- Full Orbiter EMI characterization 
The RTF test is planned to utilize the AFRL Mobile 
Diagnostics Lab (MOL) and drag on instrumentation 
in the Orbiter aft compartment. Testing will occur 
during transfer of the Orbiter from the OPF to the 
VAB prior to flight. 
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Small transmitting antennas will be placed in near 
proximity to the aft avionics bays and the three 
SSMEs. These antennas will be adjusted such that 
they do not radiate more than a 1 VIm electric field 
strength on any avionics equipment located in the 
aft compartment. 
The measurements will be made in a 180 degree 
semicircle around the aft end of the vehicle. The 
receiving antennas on the AFRL MOL can be 
adjusted to various heights, so that we can take 
data on a quasi-cylindrical surface as we move 
around the vehicle. 
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The AFRL MOL will be used to 
collect the radiated data from 
transmitters located inside 
the aft compartment of the 
Orbiter. 
The instrumentation will be "drag on", and can be 
placed well before the actual test start time. 
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Future Work 
A test stand will need to be constructed such that 
the transmitting antennas described above can be 
placed in the same geometric position as if they 
were mounted in the aft compartment. 
This will enable us to collect data for these 
transmitters with and without the Orbiter structure 
in between the transmitting antennas and the AFRL 
MOL receive antennas. 
That measured delta represents the attenuation of 
the vehicle. 
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The Full Orbiter test will be conducted inside an 
electromagnetically reflective enclosure and will 
characterize the vehicle RF attenuation as a 
function of internal location for the entire Orbiter 
vehicle. 
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Our current plan is to modify an existing purge tent 
structure by replacing the tent's exterior covering 
with conductive cloth, and extending the structure 
so that it covers the forward section of the vehicle. 
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Future Work 
Personnel from the National Institute of Standards 
and Technology, Denver, Colorado will be collecting 
data from below 6 GHz, using a direct pulse 
technique. These measurements are similar in 
nature to those proposed for the aft compartment of 
the vehicle. 
US Navy personnel from the E3 Division, Naval Air 
Warfare Center Aircraft Division, Patuxent River, 
Maryland will be collecting data from 6 GHz to 18 
GHz, using reverberation chamber methods. 
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Summary 
Introduction 
Classic EMI 
Electrostatic Charging 
Electrical Bonding 
Radar Monitoring 
Lightning Protection 
Future Work 
Summary & Closing 
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Contact Information 
Robert C. Scully, (281) 483-1499 
JSC EMC Group Lead Engineer 
Bldg 14, Rm 118, MIS EV41 
2101 NASA Road 1 
Building 14, MIS EV41 
Houston, Texas 77058-3696 
(281) 483-1499 vox 
(281) 483-5830 fax 
robert.c.scully@nasa.gov 
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Electromagnetic Compatibility for the Space Shuttle

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