In May, astronauts travelled into space to install new instruments and other components on the Hubble Space Telescope during Servicing Mission 4. But before these components were cleared for launch, they had to go through a final check up in the world’s largest cleanroom at NASA’s Goddard Space Flight Center.
Space shuttle Atlantis with its seven-member crew launched at 2:01pm EDT on Monday 11 May, 2009 from NASA’s Kennedy Space Center. The 11-day mission included five spacewalks to refurbish the Hubble Space Telescope with state-of-the-art science instruments designed to improve the telescope’s discovery capabilities by up to 70 times while extending its lifetime until at least 2014.
The mission was successful and the space shuttle Atlantis and its crew landed safely at Edwards Air Force Base, California, having completed the final servicing mission to the Hubble Space Telescope.
An operation like this requires massive planning and pre-checks to ensure all the components are working prior to launch. For sensitive components and instruments a cleanroom environment is essential, according to Mike Weiss, Hubble’s technical deputy programme manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, US.
“The High Bay Cleanroom is to Hubble what hospital operating rooms are to patients,” says Weiss. “Surgeons wear sterile gowns, gloves and masks during surgery, and operating rooms must be kept free of germs to keep patients healthy. In our case, Hubble is the patient.”
Before entering, workers pass through a set of “lobbies,” all responsible for keeping the cleanroom clean. In the first lobby, or vestibule as engineers call it, walking across the floor feels like walking inside a movie theatre. But that sticky texture doesn’t come from spilled soft drinks. Adhesive floor mats trap loose dirt from employees’ shoes.
The next stop is a small glass box a little larger than a phone booth where employees receive a forced-air shower. Dozens of air jets on the walls blow away loose debris from hair, skin and clothing. A green light indicates when it is safe to enter the last station, a larger area with lockers and benches. It is in this area where anyone intending to enter the cleanroom must don sterile bodysuits, head covers, gloves, boots and face masks, a painstaking process that can take upwards of 10–15 minutes.
The cleanroom and the elaborate steps taken before entering it are vital to the success of every Hubble mission. Even a speck of dust or a fingerprint could severely damage the sensitive telescope components and instruments, so the cleanroom must filter out these harmful contaminants.
Unlike personal digital cameras, a smudge or speck of dust on Hubble’s optics and sensors cannot be easily cleaned, especially once the instruments have reached orbit, Weiss says.
Besides being extremely clean, this facility is also the only place large enough to house Hubble’s components and simulators, as well as all the equipment needed to prepare the components for launch. In fact, the Goddard cleanroom is big enough to house two space shuttle payloads at the same time.
Because of its size and sanitary conditions, Weiss says all the components taken to Hubble on the four previous servicing missions (SM1, SM2, SM3A and 3B) made their way through Goddard’s cleanroom.
The entryway vestibules and suit-up process help counteract particulate debris, one of two contaminating offenders. Particulate debris includes tiny bits of dirt or dust workers might track in, such as loose fabric lint or flakes of dead skin. A robust ventilation system and an entire wall of air filters provide further protection.
The cleanroom ventilation system circulates almost one million cubic feet of air every minute through 9,000ft2 of HEPA filters located along one wall. The filters are not of the typical off-the-shelf HEPA variety but are specially designed to last several decades, Weiss says.
In combination, all these features afford the Goddard cleanroom a Class 10,000 rating. That means any cubic foot of air in the cleanroom has no more than 10,000 particles floating around in it larger than 0.5µm.
Molecular contaminants, the second offender, are a little more difficult to describe. Most people are familiar with “new car smell”. Over time that smell fades away because molecules in the car’s plastics and leather vaporise, or “boil off.” Exposure to the heat of a summer day speeds up the process.
The optics and sensors inside Hubble and other spacecraft go through a similar process. Orbiting Earth every 97 minutes, Hubble passes through the intense heat of the sun 15 times a day. Those higher temperatures can cause materials inside Hubble to boil-off molecules. The loss of some molecules poses no threat to a car, but this molecular damage can devastate sensitive optical equipment.
To prevent this, all Hubble’s new components and instruments are put into a vacuum chamber and literally baked at high temperatures. This process eliminates potentially damaging molecules in one fell swoop, so they do not cause problems after the components are installed.
Because the Goddard cleanroom does an excellent job of filtering out con-taminants, it is the perfect place to assemble and test Hubble’s components. Technicians spend hours running system compatibility tests to make sure all of the telescope’s new instrument electronics and software will work correctly, a key step in pre-flight preparations. Hubble’s new instruments are connected to an exact duplicate, or simulator, of Hubble’s electrical system – the Vehicle Electrical System Test facility, or VEST.
Instruments also go through a mechanical test to ensure components will fit and operate properly once they are installed in the telescope. Engineers mount the instruments inside an exact mechanical replica of the telescope’s optical end: the High Fidelity Mechanical Simulator, which was built from the same blueprints as Hubble. Using this simulator, astronauts have the opportunity to see how hardware will look once installed on Hubble.
The cleanroom also contains a structure called the Flight Support System. When reconfigured for the Hubble mission, the FSS will provide structural, mechanical and electrical interfaces between Hubble and the space shuttle. It serves as a maintenance platform, holding Hubble securely in place as astronauts work on the telescope. After servicing is complete, the support system enables astronauts to return Hubble safely to its orbit.
Only after ground testing is completed and fit checks had been performed were Hubble’s new instruments and components carefully packed for shipment to NASA’s Kennedy Space Center in Florida ready for the mission to the Hubble Space Telescope.
Contact
Goddard Space Flight Center Procurement site
T +1 301 286 7522
F +1 301 286 1706 .(JavaScript must be enabled to view this email address) www.nasa.gov www.nasa.gov/centers/goddard
Footnote This article is adapted from a piece written by Robert Garner, NASA’s Goddard Space Flight Center.