spore: failure
id: galileo-hga-1991
spore_version: 0.1
status: measured
org: nasa
title: Galileo high-gain antenna failed to fully open
mission: Galileo (Jupiter orbiter), launched October 1989 from Space Shuttle Atlantis
date: 1991-04
component: high-gain antenna rib alignment (standoff) pins
materials:
  - {role: pin, name: Ti-6Al-4V titanium alloy, treatment: Tiodize, category: metals, type: titanium}
  - {role: lubricant, name: Tiolube 460 bonded dry film, active_ingredient: molybdenum disulfide (MoS2), thickness_um: 25, category: tribology, type: dry-lubricants}
  - {role: counterface, name: Inconel 718 nickel superalloy, category: metals, type: nickel-superalloys}
environment: [vacuum, deep space]
tags:
  environments: [deep-space]
  stresses: [vacuum-and-outgassing, galling-and-cold-welding]
  applications: [mechanisms]
symptom: >
  When commanded open in April 1991, the umbrella-like main antenna opened only
  partly. JPL analysis concluded that 4 of its 18 ribs were stuck.
root_cause:
  summary: >
    High friction between a few rib pins and their sockets. The bonded MoS2 dry
    lubricant on those pins was most likely lost before launch, and the bare
    titanium pins galled (seized) against the Inconel sockets. The deployment
    motor then bent the pins during the first attempt.
  confidence: likely
  competing_explanations:
    - explanation: Lubricant shaken or worn off during pre-launch transport (cross-country truck trips).
      sources: [pds-galileo, spaceflightnow-2003]
    - explanation: Lubricant degraded during the long storage caused by launch delays.
      sources: [logbook]
      note: Unconfirmed; from a secondary source.
evidence:
  - measurement: friction coefficient, lubricated Ti-6Al-4V on Inconel 718, in vacuum
    value: 0.04
    source: nasa-tm-105355
  - measurement: friction coefficient, lubricated Ti-6Al-4V on Inconel 718, in air
    value: 0.13
    source: nasa-tm-105355
  - measurement: dry-film lubricant endurance life, vacuum vs air
    value: about 1000 times longer in vacuum
    source: nasa-tm-105355
  - measurement: friction coefficient, unlubricated Ti-6Al-4V on Inconel 718, in vacuum (galling)
    value: 1.2 (1.45 when wear debris clogged the interface)
    source: nasa-tm-105355
  - measurement: friction coefficient, lubricated pin run first in humid air then in vacuum (galling)
    value: 0.32 in humid air, 1.4 in vacuum
    source: nasa-tm-105355
consequence: >
  The mission ran on the small low-gain antenna. Without changes it would have
  sent only 8 to 16 bits per second from Jupiter. Software changes on the
  spacecraft and on the ground raised this to as much as 160 bits per second, and
  lossy compression shrank some image and plasma-wave data to as little as 1/80
  of its original size.
lessons:
  # Space Mushroom's reading of the sources, not a quote from them.
  - MoS2 dry-film lubricants wear far faster in air than in vacuum, so handling, transport and ground tests in air can use up lubricant life before launch.
  - Once a dry-film lubricant is gone, titanium sliding on nickel alloy in vacuum can gall and seize, with friction above 1.
  - Check lubricant condition after every transport and before final integration.
sources:
  - key: nasa-tm-105355
    title: Properties Data for Opening the Galileo's Partially Unfurled Main Antenna
    id: NASA TM-105355 (Miyoshi and Pepper, NASA Lewis Research Center, February 1992)
    url: https://ntrs.nasa.gov/citations/19920011418
    where: Summary and Introduction
  - key: pds-galileo
    title: Galileo spacecraft description (NASA Planetary Data System catalog file)
    url: https://pds-ppi.igpp.ucla.edu/volume/GOMW_5005/EXTRAS/CATALOG_FILES/GO_SPACECRAFT_DESC_INST.TXT
    where: High-gain antenna and low-gain antenna sections
  - key: spaceflightnow-2003
    title: The Galileo trials (Spaceflight Now, 2003)
    url: https://spaceflightnow.com/galileo/030921galileohistory.html
  - key: logbook
    title: Galileo's antenna problem (The Logbook)
    url: https://www.thelogbook.com/galileos-antenna-problem/
license: CC-BY-4.0