Use when verify the external-ground-connection-provisions that ECSS-E-ST-20-07C clause 4.2.11.3 requires for charge-equalization before a handling-or-mating operation: qualify each attachment point for its bond back to structure, its current-limiting bleed-resistance and its reachability in the configuration where it is used, then for every operation compute the resistance-capacitance decay of the item's stored potential, check the residual-potential after the planned dwell against the electrostatic-susceptibility threshold, check the peak equalization-current against the soft-ground limit, and derive the bleed-resistance window that satisfies both. Trigger: external-ground-connection-provisions, charge-equalization, soft-ground-bleed-resistance, residual-potential-decay, equalization-dwell-time, electrostatic-susceptibility-threshold, grounding-stud-provision, handling-and-mating-operations.
---
name: e2007-external-ground-connection-provisions
description: "Use when verify the external-ground-connection-provisions that ECSS-E-ST-20-07C clause 4.2.11.3 requires for charge-equalization before a handling-or-mating operation: qualify each attachment point for its bond back to structure, its current-limiting bleed-resistance and its reachability in the configuration where it is used, then for every operation compute the resistance-capacitance decay of the item's stored potential, check the residual-potential after the planned dwell against the electrostatic-susceptibility threshold, check the peak equalization-current against the soft-ground limit, and derive the bleed-resistance window that satisfies both. Trigger: external-ground-connection-provisions, charge-equalization, soft-ground-bleed-resistance, residual-potential-decay, equalization-dwell-time, electrostatic-susceptibility-threshold, grounding-stud-provision, handling-and-mating-operations."
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-ground-connection-provisions, charge-equalization, soft-ground-bleed-resistance, residual-potential-decay, equalization-dwell-time, electrostatic-susceptibility-threshold, grounding-stud-provision]
version: 0.1.0
author: Aero Agent Skills
---
# ECSS Electromagnetic Compatibility -- External Ground Connection Provisions (space-systems/ecss/e2007-external-ground-connection-provisions)
Use when the task is the charge-equalization provision of
ECSS-E-ST-20-07C clause 4.2.11.3 -- the attachment points that let an
external cable bring a spacecraft, an item of ground-support-equipment
or a handling fixture to a common potential before anyone touches or
mates it, and the dwell and bleed-resistance that make the equalization
real rather than nominal.
## Domain quick reference
- The provision is hardware on the vehicle: a grounding-stud, a
banana-jack-receptacle or a clamp-lug, solidly bonded to structure
and marked so an operator finds it without a drawing. Its own bond
back to structure must sit inside a low-milliohm allowance (10
milliohm here) -- a provision that is itself poorly bonded equalizes
nothing.
- Equalization is a resistance-capacitance decay, not an event. The
item's stored potential falls as V(t) = V0 x exp(-t / (R x C)), where
R is the series bleed-resistance in the lead and C the item's
capacitance to its surroundings. The dwell is what turns a touched
stud into an equalized item.
- Both ends of R are constrained, which is why the provision has to be
sized rather than picked. Too little resistance and the initial
equalization-current V0/R is a discharge through the very hardware
being protected; too much and the decay is slower than the time the
operation allows. The acceptable window is R >= V0 / I_limit and
R <= t_available / (C x ln(V0 / V_target)); a soft-ground lead
typically lands near one megaohm.
- The residual target comes from the item's electrostatic-susceptibility
category -- withstand 250 V for category-0, 500 V for category-1a,
1000 V for category-1b, 2000 V for category-2 -- derated to a tenth
of the withstand so the residual is not sitting at the limit when the
operator makes contact.
- A provision is only usable in the configuration where it is reachable.
A stud under an already-mated fairing is not a provision for the
mating operation, whatever the drawing says.
## Workflow
1. Qualify each provision independently of any operation: recognised
attachment style, bond-to-structure inside the milliohm allowance, a
current-limiting bleed-resistance in the lead rather than a hard
short, and a marking. Reject an unrecognised style, a negative
resistance and a missing identifier as input defects.
2. For each handling-or-mating operation, resolve the provision it
names. A named provision that is not in the catalogue is an input
defect -- never silently substitute a nearby stud.
3. Check reachability: the operation's configuration must appear in the
provision's reachable set.
4. Compute the time constant R x C, then the residual-potential after
the planned dwell, and compare it with a tenth of the withstand
voltage for the item's susceptibility category.
5. Compute the peak equalization-current V0 / R and compare it with the
soft-ground current limit. Report it even when it passes; it is the
number that decides whether the bleed-resistance may be lowered to
buy dwell time.
6. Derive the bleed-resistance window from the current limit and the
available dwell. Report the window as infeasible when its lower
bound exceeds its upper bound -- that means no resistor value can
satisfy both constraints and the dwell or the initial potential has
to change instead.
7. Aggregate per provision and per operation; the provision set is
compliant only when both finding lists are empty.
## Pitfalls
- Treating contact with the stud as equalization. Without the dwell
the item is connected, not equalized, and the residual can still be
hundreds of volts when the connector mates.
- Bonding the lead straight to structure with no bleed-resistance. The
equalization then happens as a single discharge through the item,
which is the event the provision exists to prevent.
- Sizing the bleed-resistance from the current limit alone. That fixes
only the lower bound; the upper bound comes from the dwell the
operation can actually hold, and a one-sided size can be an order of
magnitude too large.
- Comparing the residual with the withstand voltage itself. The
residual is derated to a fraction of the withstand precisely so the
item is not at its limit at the moment of contact.
- Widening the residual threshold because a dwell set exactly at the
computed requirement lands a hair above it. An exponential decay
evaluated at a logarithm-derived dwell overshoots in the last place
-- absorb that in the comparison tolerance, never by relaxing the
threshold or shortening the required dwell.
## Behavior contract (gate 3)
The provision-qualification, decay, residual-potential, peak-current,
resistance-window and aggregate logic is exercised by the gate 3
contract test:
`scripts/test_e2007_external_ground_connection_provisions.py` against
`scripts/e2007_external_ground_connection_provisions_logic.py` (stdlib
unittest, offline). Run:
python3 scripts/test_e2007_external_ground_connection_provisions.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 the external-ground-connection-provisions that 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.
---
