page_title: Optical Telescope Element
section_title: DTA
hierarchical_section_title: Optical Telescope Element / DTA
caption_attribution_description: Building a space telescope to see the light from the earliest stars of our universe is a pretty complex task. Although much of the attention goes to instruments and the giant mirrors on NASA's James Webb Space Telescope, there are other components that have big jobs to do and that required imagination, engineering, and innovation to become a reality. For example, engineers working on the Webb telescope have to think of everything from keeping instruments from overheating or freezing, to packing up the Webb, which is as big as a tennis court, to fit inside the rocket that will take it to space. Those are two areas where the "DTA" or Deployable Tower Assembly (DTA) plays a major role. The DTA looks like a big black pipe and is made out of graphite-epoxy composite material to ensure stability and strength with extreme changes in temperature like those encountered in space. When fully deployed, the DTA reaches ten feet in length. The DTA interfaces and supports the spacecraft and the telescope structures. It features two large nested telescoping tubes, connected by a mechanized lead screw. It is a deployable structure that is both very light and extremely strong and stable. The Webb telescope’s secondary mirror support structure and DTA contribute to how the telescope and instruments fit into the rocket fairing in preparation for launch. The DTA allows the Webb to be short enough when stowed to fit in the rocket fairing with an acceptably low center of gravity for launch. Several days after the Webb telescope is launched, the DTA will deploy, or separate, the telescope mirrors and instruments from the spacecraft bus and sunshield. This separation allows the sunshield to unfurl and shade the telescope and instruments from radiant heat and stray light from the sun and Earth. The DTA was designed, built and tested by Astro Aerospace - a Northrop Grumman Company, in Carpinteria, California. The James Webb Space Telescope is the scientific successor to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built. The Webb telescope is an international project led by NASA with its partners, the European Space Agency and the Canadian Space Agency. For more information about the Webb telescope, visit: www.nasa.gov/webb or jwst.nasa.gov NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram
context_page_description: Optical Telescope Element is a sub-section of the James Webb Space Telescope, a large infrared space telescope scheduled to be launched early 2021. The OTE consists of some major parts of the telescopes including the main mirror, the secondary mirrors, the framework and controls to support those mirrors, and various thermal and other systems to support the functioning of the telescope. The other two major sections of the JWST are the Integrated Science Instrument Module and the Spacecraft Element, which includes the Spacecraft Bus and Sunshield. The OTE collects the light and sends it to the science instruments in the ISIM. The OTE has been compared to being the "eye" of the telescope and the backplane of it to being the "spine".
  The primary mirror is a tiled assembly of 18 hexagonal elements, each 1.32 meters from flat to flat. This combination yields an effective aperture of 6.5 meters and a total collecting surface of 27 square meters. Secondary mirrors complete the f/20 anastigmatic imaging optics. The complete system provides an effective f/number of f/16.67 and focal length of 131.4 meters.
context_section_description: At the base of the OTE is a critical structural component that connects OTE to the Spacecraft Bus, it is called the Deployable Tower Assembly (DTA). It also must expand to allow the Sunshield (JWST) to spread out to allow the space between its five layers to expand. The Sunshield segment has various structure, including six spreaders at its outer edge to spread the layers out at its six extremities.
  During launch its is shrunk down, but at the right time in space the DTA must extend. The extended DTA structure allows the sun-shield layers to be fully spread out. The DTA must also thermally isolate the cold section of the OTE from the hot spacecraft bus. The Sunshield will protect the OTE from direct sunlight and reduce the thermal radiation hitting it, but another aspect is the OTE's physcially connection to the rest of the spacecraft. (see Thermal conduction and Heat transfer) Whereas the sunshield stops the telescope getting hot at a distance from a fire (near not in it), the DTA has to handle the heat flow like how a handle on a pan might get warm when its on the stove if not insulated enough.
  The way the DTA extends is that it has two telescoping tubes that can slide between each-other on rollers. There is an inner tube and an outer tube. The DTA is extended by an electric motor that rotates a ball screw nut that pushes the two tubes apart. When the DTA is fully deployed it is 10 feet long (~3 meter). The DTA tubes are made of graphite-composite carbon fiber, and it is intended that it will be able to survive the conditions in space.
caption: The Deployable Tower Assembly (DTA)  is where OTE connects with the rest of telescope such as the Spacecraft Bus. During stowage there is another attachment point for the folded sunshield higher up on the OTE
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