Moog Celebrates 25th Anniversary of the Launch of the Hubble Space Telescope

24 April 2015

Moog Inc. (NYSE: MOG.A and MOG.B) Space and Defense Group is celebrating the 25th Anniversary of the launch of the Hubble Space Telescope (HST) but the story of Hubble begins nearly 50 years ago. Hubble launched in the payload bay of the Space Shuttle Discovery on April 24, 1990 (STS-31) but was conceived of over two decades previous before man had even landed on the Moon and the Space Shuttle even existed. The Large Space Telescope (LST), as it was called initially, was originally slated for launch in 1979 but funding was cut in 1974. Astronomers lobbied for this telescope that would help unlock the mysteries of the universe. In 1978 NASA resumed funding LST with conjunction of the European Space Agency (ESA) making this a truly international effort. The new launch date was planned for 1983 but later slipped to fall of 1986. The Challenger accident in January 1986 stopped Space Shuttle launches leaving the now named Hubble Space Telescope without a launch vehicle. Finally after two years of investigation the Space Shuttles were cleared to resume flight and Hubble got its launch date 11 years after the initially scheduled date. Hubble is the only space telescope designed to be serviced by astronauts and on five different occasions repairs were performed on-orbit. These repairs and upgrades are expected to extend the life of Hubble until 2020 if not longer.

Discovery Launch (STS-31) from Launch Complex 39B with Columbia at 39A in the foreground (courtesy of NASA)

Hubble Space Telescope in Orbit (courtesy of NASA)

In 1979 Moog, Schaeffer Magnetics at the time, received an order for 57 actuators to be used on what was called LST at the time. These actuators would be used for aperture door rotation and latching, High Gain Antenna deployment, solar panel latching, Primary Mirror optical figure control, Secondary Mirror pointing, optical filter selection for both guidance and observation, and even tape recorder drives (data storage at the time). Some of these actuators and assemblies were unique applications requiring specialized development. The Primary Mirror Optical Figure Control Actuator (FCA) was designed to provide slight corrections in the large 2.4 meter diameter Primary Mirror. Here 24 FCAs could provide slight pushing or pulling on the backside of the mirror to provide slight adjustments on orbit. The concern was the mirror would be made and tested on Earth in a 1g environment but operated in a 0g environment.  After launch it was discovered that the Primary Mirror had a manufacturing defect impairing the focus of HST. The FCAs were critical in adjusting the Primary Mirror until a modification could be made in late 1993.  

Primary Mirror Optical Figure Control Actuator (FCA)

Another critical piece of hardware designed specifically for HST was the Selectable Optical Filter Assembly (SOFA). This unique concept has been used on several other missions including the probe Cassini that is currently orbiting Saturn. SOFA contains twelve different rotor/stator motor combinations in a stack each with four filters and an open aperture. This provides 48 total filters but many possible filter combinations. SOFA was a key component of the Wide Field Planetary Camera (WFPC). The WFPC was replaced twice and the old version returned to Earth providing Moog engineers the opportunity to study SOFA after years of on-orbit service. The same unit was refurbished and recertified for flight.  This was installed as WFC3 during the final servicing mission.  Additionally a single wheel version was designed for the Fine Guidance Sensor (FGS) that provides high-precision pointing.  

Selectable Optical Filter Assembly (SOFA, left, and Fine Guidance Sensor (FGS) Filter Wheel, right

HST had a total of five different servicing missions between 1993 and 2009. Servicing Mission 1 (SM1) flew aboard Endeavour in December 1993 (STS-61) providing the critical correcting optics to account for a manufacturing defect in the Primary Mirror. The Moog FCAs had been used previously to effectively distort the Primary Mirror to provide useable images. SM1 also included the updated WFPC2 that included another Moog SOFA. Servicing Mission 4 (SM4) included the updated WFC3 including the refurbished SOFA that was launch initially in 1990 and was removed during SM1. This means WFC3 includes the same SOFA flying today as 25 years ago.

Servicing Mission 2 (SM2) in February 1997 and Servicing Mission 3B (SM3B) in March 2002 installed the Near Infrared Camera and Multi Object Spectrometer (NICMOS) and Advanced Camera for Surveys (ACS), respectively. Both of these payloads provided even more capability to HST. Due the sensitive nature of these instruments Moog, CSA Engineering at the time, was employed to use their vibration damping and suppression expertise.

Example Images from NICMOS and ACS (courtesy of NASA)

M-Strut Spring-Dampers in both Test at NASA-Goddard and Flight Configuration (courtesy of NASA)

In addition to installing the ACS instrument during SM3B, astronauts installed new solar arrays.  These new ‘rigid’ arrays required increase damping to reduce the impact of vibration on the telescope’s images.  Moog solar array damping technology has been used on recent observatories like Landsat Data Continuity Mission (LCDM).

HST Dynamic Response with and without Moog Solar Array Dampers

With the retirement of the Space Shuttle there are no reasonable methods to perform any HST repairs or updates. Currently the replacement observatory called the James Webb Space Telescope (JWST) slated to launch in 2018. JWST uses a different approach instead of one large primary mirror it uses 18 hexagonal segments that create an effective 6.5 meter diameter primary mirror yielding over 5 times more light collecting area. JWST will also operate much further away from Earth than HST away from the light and heat given off by the planet.

James Webb Space Telescope (courtesy of NASA)

Moog once again is supporting JWST just like HST before it. JWST will operate in a very cold environment requiring specialized equipment and testing. One instrument called the Near InfraRed Camera (NIRCam) includes Moog’s cryogenic instrument actuators. These actuators allow for positioning while operating at very cold temperatures. Moog is providing flight vibration dampen hardware in the Integrated Science Instrument Module (ISIM) used to isolate loads into the large radiator panels that are critical for the cold operation of the instruments. Another area is the validation that these 18 mirrors will work together on both the ground and in space. Moog provided a six degrees of freedom (6-DOF) micropositioning system used to validate the JWST Primary Mirror. Here the micropositioning system moves a large optical payload to provide ground testing and validation of the flight mirror. The system includes comprehensive software for position control, interference avoidance, and data logging all while operating in a vacuum and at very cold temperatures.

Moog Six Degrees of Freedom (6-DOF) Micropositioning System for JWST Validation

In addition to the components and equipment used to build HST and JWST, Moog supports many other aspects of these programs with NASA and their international partners like ESA and CSA. Moog provided hardware for the Space Shuttles that launched and serviced HST and is providing hardware for the Ariane 5 that will launch JWST. Both of these programs are part of the long history of supporting these critical national and international programs.

Moog Inc. is a worldwide designer, manufacturer, and integrator of precision control components and systems. Moog’s high-performance systems control military and commercial aircraft, satellites and space vehicles, launch vehicles, missiles, automated industrial machinery, wind energy, marine and medical equipment. Additional information about the company can be found at Additional information about Moog’s Space Sector can be found

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