Key Takeaways

Michael Menzel delivered the College of Engineering’s Distinguished Speaker presentation on Nov. 10, 2022. Mr. Menzel is the mission systems engineer for the James Webb Space Telescope at NASA’s Goddard Space Flight Center in Greenbelt, Md. The theme was "Lessons Learned from the James Webb Space Telescope."

The James Webb Space Telescope: NASA’s Successor to the Hubble Space Telescope

Mission Objective: Study the origin and evolution of galaxies, stars, and planetary systems by providing infrared imagery and spectroscopy.

Team

• Mission Lead: Goddard Space Flight Center
• International Collaboration with NASA, European Space Agencies and Canadian Space Agency
• Prime Contractor: Northrop Grumman Space Technology with ball Aerospace as Telescope Subcontractor
• Ground Segment: Space Telescope Science Institute
• Additional instrument providers

Mission Description

• Deployable 6.5 meter diameter telescope
• Operates at cryogenic temperatures
• Deployable sunshield to allow passive cooling of telescope and all instruments
• Launched on Dec. 25, 2021 to Sun-Earth L2
• Required 5-year science mission (10-year goal – although enough fuel of 20 years)

Role of systems engineer

• Learn science objective
• Formulate mission requirements
• Design the system
• System analysis and performance assessment
• Risk management and technology development
• Verification of system (proof it will work in space)
• System operations

Science mission

• In 1994, scientists began developing basic themes the successor to Hubbell hold address.

• See first galaxies that turned on in the universe. 13.8 billion years ago big bang may have occurred followed 100 to 400 million years later, first galaxies appeared.
  • See how galaxies evolve over cosmic time
  • Birth of stars and proto-planetary systems
  • Learn how solar systems evolved
• Additional question: Explore exoplanets around stars for signs of biomarkers.
  • There are 2000 known planets around 1300 stars. The number is growing

Mission requirements: Telescope specs

• Spectral coverage: What colors to observe
  • Science requires Webb be an infrared telescope
  • Young stars emit blue light but after traveling through the expanding universe over 13 billion years, the light is stretched and becomes red or infrared.
  • Detect light that penetrates dust – requires a telescope that operates in mid infrared wavelengths
• Radiosensitivity: How faint are the objects the telescope must observe
  • Determine sensitivity requirements to capture faint objects
  • High signal collection
  • Low noise (minimize distractions)
  • Equation: Signal to noise for detecting a very faint source
    • Mirror is designed to collect the signal
    • Must mitigate background noise and dark current
  • Infrared observation must be very cold
    • Telescope must be cold to note interfere with data collection
    • Telescope must be cooled to 55 degrees above absolute zero
    • Requires intricate sunshield to allow passive cooling
• Field of view
  • Given sunshield at any point the telescope can observe 35% of celestial sphere.
  • Over course of year, scientists can see entire sky.
• Resolution and image quality
  • Webb must be able to sense objects as small as .084”
  • The wave nature of light sets a fundamental limit on the resolution of telescope. Diffraction prevents a telescope from focusing on a point source.
  • Sets requirement for design of mirror.

Systems Design

• Trade studies – balancing alternatives
• Trade options selected at the systems level for a highly integrated system
  • A set of optimized subsystems does not necessarily produce and optimized system.
  • Have subsystems present options and close out trades at the system level.
• Hierarchical list of major Webb trade studies
• Integrated modeling
• Observatory design summary
  • 6.6 meter telescope
  • Gold plated segments to give high reflectivity
  • 21.6 meters long sunshield
  • 14.6 meter wide sunshade
  • 4 science instruments
  • 6 metric tons
  • Must be folded up to deliver to space

• Verification, Integration and Testing
  • Mirror verification
  • Instrument integration
  • Telescope testing (temperature, vibration)
• Technical challenges
  • Deployment challenges
    • 344 single point failure items
  • Cryogenic challenges
  • Systems testing

Mission Operation

• Deployment
  • 14 days to unfold
  • 30-40 days to cool down
  • Science mission begins on time
• First Deep Field images
  • Shows massive gravity cluster
  • Short exposure time a positive sign.
  • Similar Hubbell image took 14 days of exposure. Webb took 12 hours.
  • “We built this thing to see first light. Whatever is our there we are going to see it."

Abstract

The James Webb Space Telescope (JWST), launched on December 25, 2022, is NASA’s successor mission to the Hubble Space Telescope.  JWST has been designed and developed to observe “first light” objects in the nascent universe, the evolution of galaxies over cosmic history, star birth within our own galaxy, planet formation and evolution both in our solar system and in solar systems around other stars and to make detailed observations of some of the recently discovered exoplanets.  The JWST telescope has an aperture greater than 6 meters in diameter, and along with its compliment of science instruments must be cooled to cryogenic temperatures below 50K.  It will be operated at the Sun-Earth L2 point to keep thermal sources such as the Sun and Earth in the same general direction so that their radiation can be shielded by a “tennis court sized” sunshield, allowing the payload to attain these temperatures passively. This presentation will give an overview of the JWST science and its systems design challenges.  The presentation will then discuss the lessons learned from this mission.