The precision manufacturing and integration of the 21.5 foot telescope structure allow it to withstand the pressure and weight of the launch loads when stowed inside the 15-foot-diameter fairing of the Ariane 5 rocket. The cutting-edge design and transformer like capabilities of the telescope structure allow it to fold-up and fit inside the launch vehicle, and then deploy once the Webb telescope reaches its ultimate destination, one million miles away from earth. Furthermore, throughout travel and deployment, the telescope simultaneously maintains its dimensional stability while also operating at cryogenic or extremely cold temperatures, approximately 400 degrees below zero Fahrenheit. The telescope is the world's first deployable structure of this size and dimensional stability ever designed and built.
"The significant milestone of completing and delivering the OTE to NASA's Goddard Space Flight Center, marks the completion of the telescope, and attests to the commitment of our hardworking team," said Scott Texter, telescope manager, Northrop Grumman Aerospace Systems. "The telescope structure is one of the four main elements of this revolutionary observatory. The other elements include: the spacecraft, sunshield and the Integrated Science Instrument Module (ISIM), the latter of which is also complete. All of the elements require a collaborative team effort. We are all committed to the cause and excited about the upcoming phases of development as we prepare for launch in October 2018."
The next step in the progress of the telescope structure includes its integration with the ISIM to combine the OTE and ISIM, referred to as the OTIS. The OTIS will undergo vibration and acoustic testing by the end of this year, and then travel to NASA's Johnson Space Center in Houston, to undergo optical testing at vacuum and operational cryogenic temperatures, around 40 kelvin. The OTIS will be delivered to Northrop Grumman's Space Park facility in Redondo Beach, towards the end of 2017, where it will be integrated with the sunshield and spacecraft.
The James Webb Space Telescope is the world's next-generation space observatory and successor to the Hubble Space Telescope. The most powerful space telescope ever built, the Webb Telescope will observe the most distant objects in the universe, provide images of the first galaxies formed and see unexplored planets around distant stars. The Webb Telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
At a Goddard cleanroom, technicians unveil the James Webb Observatory’s segmented mirror in preparation for an alignment test this summer. The tool used to determine the segments’ alignment has inspired Goddard technologists to create another that offers picometer accuracy for next-generation observatories. (Photo Credit: Chris Gunn)
Credits: NASA/Chris Gunn
To date, NASA has yet to launch an observatory with such demanding stability requirements. However, the scientific community is studying the possibility. Last year, the Association of Universities for Research in Astronomy endorsed the High-Definition Space Telescope. It found that with proper stability and instrumentation, a 33-39 foot (10-12 meter) telescope could find and characterize Earth-like planets. Another study group evaluating a similar concept known as the Large Aperture Ultraviolet-Optical-Infrared Space Telescope, or LUVOIR, has reached similar conclusions.
“If the agency wants to search for and analyze Earth-like planets in other solar systems, the telescope it designs and builds will have to be orders of magnitude more stable than anything launched to date, including the James Webb Space Telescope,” said Babak Saif, a Goddard optics specialist.
New Tool to Assure Picometer-Level Stability
To help NASA reach this next level of precision, Saif and his Goddard colleague, Lee Feinberg, have begun working with 4-D Technology, of Tucson, Arizona, to develop the instrument.
Like all interferometers, the instrument would split light and then recombine it to measure tiny changes, including motion. With this tool, technicians would measure distortions in mirror segments, mounts, and other supporting telescope structure primarily during thermal, vibration, and other types of environmental testing.
Displacements and movement occur when materials used to build the optics shrink or expand due to wildly fluctuating temperatures, such as those experienced when traveling from Earth to the frigidity of space or when exposed to fierce launch forces more than six-and-a-half times the force of gravity.
If optics must conform to a specific prescription to carry out a challenging mission, even nearly imperceptible, atomic-size movements caused by thermal and dynamic changes could affect their ability to gather and focus enough light to distinguish a planet’s light from that of its parent star — to say nothing of scrutinizing that light to discern different atmospheric chemical signatures, Saif said.
Leveraging Instrument Developed for Webb Testing
The effort leverages a similar instrument that 4-D Technology created to test the optics of the Webb Observatory, which will be the most powerful observatory ever built once it launches in October 2018. From its orbit 930,000 miles from Earth, it will study every phase in the history of our universe, from the first luminous glows after the Big Bang to the evolution of our own solar system. Among many other firsts, Webb will carry a 21-foot primary mirror made of 18 separate ultra-lightweight beryllium segments that unfold and adjust to shape after launch.
To carry out its job, the Webb Observatory also must be highly stable. However, the movement of its materials is measured in nanometers — the unit of measure that scientists use to determine the size of atoms and molecules.
“What we did was measure the surface of each mirror after each environmental test to see if we could see changes,” Saif said. “I started questioning, what if something behind the mirror moves. Just measuring the surface isn’t enough.”
To assure nanometer-level stability — 4-D Technology worked with the Webb Observatory team at Goddard to develop a dynamic laser interferometer that instantaneously measured displacements in the mirror segments as well as those in their mounts and other structural components, despite vibration, noise, or air turbulence.
“The high-speed interferometer actually enables you to do nanometer dynamics for large structures,” Saif said. “This is absolutely new. The instrument is four orders of magnitude more sensitive than other measurement tools and it measures the full surface of the mirrors.” That instrument now is used in laboratories, manufacturing areas, clean rooms, and environmental-testing chambers operated by the project’s major contractors.
LUVOIR-Type Mission Ups the Ante
However, a next-generation LUVOIR-type mission will demand even greater stability, and consequently an instrument capable of quickly measuring picometer displacements, which are two orders of a magnitude smaller than an atom. Although it is possible to calculate picometer movements with existing tools, the physics are non-linear and the resulting calculations might not accurately reflect what actually is going on, Saif said.
“Every subsystem needs to be designed on a picometer level and then tested at picometers,” Saif explained. “You need to measure what you’re interested in and the instrument needs to calculate these motions quickly so that you can understand the dynamics.”
The team is developing the tool with $1.65 million in funding from NASA’s Cosmic Origins Strategic Astrophysics Technology program. It expects to complete the work in four years.
A Mechanical Harmony to NASA's Webb Telescope Sunshield
NASA's Webb telescope sunshield, opened for inspection. In this photo, engineers and scientists examine the sunshield layers on this full-sized test unit.
Credits: Northrop Grumman Corporation/Alex Evers
NASA's James Webb Space Telescope has a giant custom-built, kite-shaped sunshield driven by mechanics that will fold and unfold with a harmonious synchronicity 1 million miles from Earth.
Like a car, many mechanical pieces in the Webb telescope's sunshield will work together to open it from its stored folded position in the rocket that will carry it into space.
According to car manufacturers, a single car can have about 30,000 parts, counting every part down to the smallest screws. Like getting all of the parts in a car to operate together, the mechanical parts of the sunshield have to work in the same way.
The sunshield support structure contains well over 7,000 flight parts, including springs, bearings, pulleys, magnets, etc. In addition, the sunshield has hundreds of custom fabricated pieces. Most mechanical pieces were developed exclusively for the sunshield, with a few from existing designs.
There are about 150 mechanism assemblies that have to function properly to fully deploy the sunshield. Within those mechanism assemblies, there are numerous small parts that work in harmony. The smaller parts include about 140 release actuators, approximately 70 hinge assemblies, eight deployment motors, scores of bearings, springs and gears, about 400 pulleys and 90 cables. These mechanisms release the sunshield membranes from their folded and stowed launch configuration, deploy the supporting structures, and unfold and tension the membrane layers. In addition there are hundreds of magnets and clips to manage the membrane shape and volume during deployment, and many sensors to tell engineers that each deployment step has been completed.
"The process of opening or deploying the sunshield in space is a multi-step process," said James Cooper, Webb telescope sunshield manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Each step of the deployment will be manually initiated from engineers on Earth. That sequence runs automatically to its completion (with automated stoppage in case of a fault), then the system waits for the next command.
It will be like conducting an orchestra from a million miles away. "Thousands of components work together to deploy the sunshield," Cooper said.
The mechanisms that separate each of the sunshield's five layers do so with precision. Near the center of the sunshield each layer is separated by only a couple inches, but the layer-to-layer gap increases as you move away from the center, to about a foot between layers around the edges. It will take nearly two days to fully deploy the sunshield system when in orbit.
The Webb telescope state-of-the-art composite structure that supports the sunshield “operates with Swiss watch-like precision," said Paul Geithner, Webb telescope technical manager at Goddard. "The engineering of the sunshield is an intricate system with a simple but not easy-to-do purpose."
The stowed sunshield fits inside of a 5-meter (16.4-foot) rocket fairing, folded up against the sides of the telescope. When deployed in space it’s about the size of a tennis court (about 21 meters by 14.5 meters, or 68.9 feet by 47.5 feet).
"There has never been a composite structure this large and complex (for a NASA mission)," Cooper said.