Use when verify that every unit and cable run mounted outside the main-structure envelope carries its own individual shield under ECSS-E-ST-20-07C clause 4.2.12.2: categorize each inventory item by mounting-location and kind, derive the attenuation it needs from the local field-strength and its own field-susceptibility threshold, read the declared shield's measured attenuation-versus-frequency curve at the assessment frequency, derate that curve for braid-optical-coverage and for shield-termination technique (circumferential-backshell, partial-backshell, pigtail, unterminated), compare provided against required, and flag a shield-identifier credited to two externally-mounted items. Trigger: ecss, e-st-20-07c, externally-mounted-unit, external-cable-run, individual-shield, shielding-effectiveness-derate, braid-optical-coverage, shield-termination, pigtail-derate, main-structure-envelope.
---
name: e2007-external-unit-shielding
description: "Use when verify that every unit and cable run mounted outside the main-structure envelope carries its own individual shield under ECSS-E-ST-20-07C clause 4.2.12.2: categorize each inventory item by mounting-location and kind, derive the attenuation it needs from the local field-strength and its own field-susceptibility threshold, read the declared shield's measured attenuation-versus-frequency curve at the assessment frequency, derate that curve for braid-optical-coverage and for shield-termination technique (circumferential-backshell, partial-backshell, pigtail, unterminated), compare provided against required, and flag a shield-identifier credited to two externally-mounted items. Trigger: ecss, e-st-20-07c, externally-mounted-unit, external-cable-run, individual-shield, shielding-effectiveness-derate, braid-optical-coverage, shield-termination, pigtail-derate, main-structure-envelope."
license: Apache-2.0
compliance: STANDARDS-REF
standards:
- id: ecss
reference-only: true
gated: false
domain: space-systems
pack: space-systems
compatibility: "agentskills.io SKILL.md; any SKILL.md host (Claude Code, Hermes, OpenClaw)"
metadata:
domain: space-systems
subdomain: ecss
tags: [ecss, e-st-20-electrical-scope, e2007-external-unit-shielding, externally-mounted-unit, external-cable-run, individual-shield, shielding-effectiveness-derate, shield-termination]
version: 0.1.0
author: Aero Agent Skills
---
# ECSS Electromagnetic Compatibility — External Unit Shielding (space-systems/ecss/e2007-external-unit-shielding)
Use when the task is the individual-shield check of ECSS-E-ST-20-07C
clause 4.2.12.2 -- confirming that each unit and each cable run
carried outside the main-structure envelope has its own shield, and
that the shield attenuates enough at the assessment frequency once the
braid-optical-coverage and shield-termination derates are taken.
## Domain quick reference
- The clause is scoped by mounting location. Hardware inside the
main-structure envelope is already enclosed by the primary structure
and its conductive skin, so it is out of scope here; hardware
outside that envelope -- an externally mounted unit, a cable run
crossing an appendage, a boom-mounted sensor -- sits directly in the
incident field and must bring its own shield. Categorizing by
location first is what keeps the assessment honest: an item is
either an external-unit, an external-cable-run, or out of scope.
- Required attenuation is not a fixed number, it is the gap between
the local field-strength and the item's own field-susceptibility
threshold, expressed in decibels as twenty times the base-ten
logarithm of their ratio. An item whose threshold already exceeds
the incident field needs no attenuation, and the requirement floors
at zero rather than going negative.
- Provided attenuation starts from the shield's measured
attenuation-versus-frequency curve, read at the assessment
frequency. A measured curve is a handful of points, so the value in
between is interpolated linearly against the base-ten logarithm of
frequency, and outside the measured span the nearest endpoint is
held rather than extrapolated.
- Two derates then reduce that measured value. Braid-optical-coverage
below the reference value leaks through the braid apertures and
costs a penalty linear in the coverage gap. The shield-termination
technique costs more: a circumferential backshell keeps the measured
performance, a partial backshell costs a fixed penalty, a pigtail
costs a large one because the pigtail wire puts an inductance in the
return path, and an unterminated shield is credited with nothing at
all.
- "Individual" is a real requirement, not a wording flourish. One
shield identifier credited to two externally mounted items means the
two share a return path and an aperture set; the clause asks for a
shield per item, so a shared identifier is a finding regardless of
how much attenuation it provides.
## Workflow
1. Inventory every unit and cable run in the electromagnetic-effects
baseline with its mounting location, its kind, and its
field-susceptibility threshold. Reject an unknown location or an
unknown kind before it enters the assessment.
2. Categorize each item. Drop the items inside the main-structure
envelope from the numeric check and count them as out of scope;
keep the external-unit and external-cable-run items.
3. For each in-scope item, compute the required attenuation from the
local field-strength and the item's threshold.
4. For each in-scope item, read the declared shield's measured curve
at the assessment frequency, subtract the braid-optical-coverage
derate and the shield-termination derate, and floor the result at
zero. An item with no declared shield is a finding on its own and
needs no further arithmetic.
5. Record the margin as provided minus required. Treat a margin that
is negative only by the decibel-subtraction representation error as
satisfied -- the named tolerance absorbs it, the engineering limit
is never widened.
6. Cross-check shield identifiers across the in-scope items and flag
every item whose shield is shared. The inventory is compliant only
when no item carries a shortfall, a missing shield, or a shared
shield.
## Pitfalls
- Crediting the primary structure to an externally mounted unit --
the item sits outside that enclosure, which is the whole reason the
clause exists; only the item's own shield counts.
- Reading the measured curve at the wrong frequency, or extrapolating
past the measured span. A shield curve outside its measured range is
unknown, and holding the endpoint is the defensible reading.
- Taking the braid-optical-coverage derate and forgetting the
shield-termination derate. Termination usually dominates: a superb
braid ended in a pigtail performs far worse than a modest braid on
a circumferential backshell.
- Reading a large attenuation figure as compliance when the shield is
shared between two externally mounted items -- individuality is a
separate finding, and a shared shield fails even with margin to
spare.
- Letting an unterminated shield inherit its measured attenuation. An
open-ended shield is a conductor, not an enclosure, and must be
credited with zero until it is terminated.
## Behavior contract (gate 3)
The item-categorization, curve-interpolation, coverage and termination
derate, required-attenuation, margin and shield-individuality logic is
exercised by the gate 3 contract test:
scripts/test_e2007_external_unit_shielding.py against
scripts/e2007_external_unit_shielding_logic.py (stdlib unittest,
offline). Run: python3 scripts/test_e2007_external_unit_shielding.py
## Compliance
- ECSS standards are freely downloadable (ESA); cite the source and
paraphrase per standards-map.yaml.
- compliance: STANDARDS-REF, gated: false.
When Claude will use it
Use when verify that every unit and cable run mounted outside the main-structure envelope carries its own individual shield under ECSS-E-ST-20-07C clause 4.
---
name: added-mass-coefficients-potential-flow
description: Use when you must determine the added-mass-coefficients-potential-flow virtual mass (apparent mass) of a body accelerating through an inviscid irrotational fluid from the kinetic energy of the irrotational flow it sets up: the 2-D circular cylinder rho pi R^2 and normal flat plate rho pi a^2 per unit span, the 3-D sphere two-thirds rho pi R^3, the elliptic cylinder and the prolate and oblate spheroid coefficients, plus the kinetic-energy and acceleration-reaction relations. Produces the added mass of the requested shape, its ratio to the displaced fluid mass, the fluid kinetic energy at a translation speed, the virtual mass with the body mass, and the acceleration-reaction force for the fluid inertia of unsteady motion. Trigger: added mass coefficients, virtual mass, apparent mass, acceleration reaction force, kinetic energy of irrotational flow, body accelerating in fluid, airship hull added mass, ditching float added mass, spheroid added mass.
---
---
name: aeroelastic-gust-response
description: Use when you must compute the dynamic aeroelastic response of a flexible two-degree-of-freedom typical wing section to a discrete gust with indicial unsteady aerodynamics: run the Wagner and Kussner lag-state lift model in the time domain, produce the plunge and pitch response histories for a one-minus-cosine gust, and report the dynamic magnification factor of the peak lift over the quasi-steady value plus the peak-load verdict against a limit. Produces response histories, the dynamic magnification factor, and load margin. Trigger: aeroelastic gust response, dynamic gust response, kussner function, wagner function, indicial aerodynamics, dynamic magnification factor, typical section gust, gust response history.
---
---
name: divergence-speed
description: Use when you must compute the static aeroelastic divergence condition of a lifting surface: calculate the divergence dynamic pressure from the torsional stiffness, the reference area, the chord, the lift curve slope, and the aerodynamic-center-to-shear-center offset ratio, convert it to the divergence speed at sea level, and assess the divergence margin against the design dive speed, flagging risk when the margin falls below the required 1.15 threshold. Produces the divergence dynamic pressure, the divergence speed, and a margin verdict that feed torsional stiffness sizing for divergence clearance. Trigger: divergence speed, divergence dynamic pressure, torsional stiffness, aerodynamic center, shear center, divergence margin, static aeroelastic divergence.
---
