K9322_Sec02M.new 8/26/99 4:46 PM Page 2-1 HUBBLE SPACE TELESCOPE SERVICING MISSION 3A he Hubble Space Telescope (HST) is the 2.1 Reasons for Orbital Servicing first observatory designed for extensive maintenance and refurbishment in The Hubble Telescope is a national asset and an Torbit. While other U.S. spacecraft have been invaluable international scientific resource that retrieved or repaired by astronauts, none was has revolutionizedmodern astronomy. To so thoroughly designed for orbital servicing as achieve its full potential, HST will continue to HST. Its science instruments and many other conduct extensive, integrated scientific obser- components were designed as Orbital vations, including follow-up work on its many Replacement Units (ORU) – modular in con- discoveries. struction with standardized fittings and acces- sible to spacewalking astronauts. Features such Although the Telescope has numerous redun- as handrails and foot restraints are built into dant parts and safemode systems, such a com- the Telescope to help astronauts perform ser- plex spacecraft cannot be designed with vicing tasks in the Shuttle cargo bay as they sufficient backups to handle every contingency orbit Earth at 17,500 mph. likely to occur during a 20-year mission. Orbital servicing is the key to keeping Hubble For Servicing Mission 3A(SM3A), the Discovery in operating condition. NASA’s orbital servic- cargo bay is equipped with several devices to ing plans address three primary maintenance help the astronauts. The Flight Support scenarios: System (FSS) will berth and rotate the Telescope. Large, specially designed equip- •Incorporating technological advances into ment containers house the ORUs. Astronauts the science instruments and ORUs can work and be maneuvered as needed from •Normal degradation of components the Shuttle robot arm. •Random equipment failure or malfunction. SM3Awill benefit from lessons learned on Technological Advances.Throughout the NASA’s previous on-orbit servicing missions, Telescope’s 20-year life, scientists and engineers ranging from the 1984 Solar Maximum repair will upgrade the science instruments. For mission to the 1993 HST First Servicing example, when Hubble was launched in 1990, it Mission (SM1) and the 1997 Second Servicing was equipped with the Goddard High Mission (SM2). NASAhas incorporated these Resolution Spectrograph and the Faint Object lessons in detailed planning and training ses- Spectrograph. Asecond-generation instrument, sions for astronauts Curtis Brown, Jr., Scott the Space Telescope Imaging Spectrograph, Kelly, Jean-François Clervoy, Steven Smith, took over the function of those two instruments John Grunsfeld, Michael Foale, and Claude – and added considerable new capability – Nicollier. All of NASA’s planning and the when it was installed during the Second astronauts’ skills will be put to the test during Servicing Mission in February 1997. This left the SM3Amission in 1999. Four extravehicular open a slot for the Near Infrared Camera and activity (EVA) days are scheduled for the Multi-Object Spectrometer (NICMOS), which servicing. expanded the Telescope’s vision into the K9322-02M 2-1 K9322_Sec02M.new 8/26/99 4:46 PM Page 2-2 infrared region of the spectrum. Additionally, 2.2 Orbital Replacement Units on SM2 a new Solid State Recorder (SSR) replaced an Engineering/Science Tape Advantages of ORUs include modularity, stan- Recorder (E/STR). dardization, and accessibility. Component Degradation. Servicing plans take Modularity. Engineers studied various tech- into account the need for routine replacement nical and human factors criteria to simplify of some items, for example, restoring HST sys- Telescope maintenance. Due to the limited tem redundancy and limited-life items such as time available for repairs and the astronauts’ tape recorders and gyroscopes. limited visibility, mobility, and dexterity in the EVA environment, designers simplified the Equipment Failure. Given the enormous sci- maintenance tasks by planning entire compo- entific potential of the Telescope – and the nents for replacement. investment in designing, developing, building, and putting it into orbit – NASA must be able The modular ORU concept is key to success- to correct unforeseen problems that arise from fully servicing the Telescope on orbit. ORUs random equipment failures or malfunctions. are self-contained boxes installed and removed The Space Shuttle program provides a proven using fasteners and connectors. They range system for transporting astronauts to the from small fuses to phone-booth-sized science Telescope fully trained for its on-orbit servicing. instruments weighing more than 700 lb (318 kg). Figure 2-1 shows the ORUs for SM3A. Originally, planners considered using the Shuttle to return the Telescope to Earth Standardization. Standardized bolts and con- approximately every five years for mainte- nectors also simplify on-orbit repairs. Captive nance. However, the idea was rejected for both bolts with 7/16-in., double-height hex heads technical and economic reasons. Returning hold many ORU components in place. To Hubble to Earth would entail a significantly remove or install the bolts, astronauts need higher risk of contaminating or damaging del- only a 7/16-in. socket fitted to a power tool or icate components. Ground servicing would manual wrench. Standardization limits the require an expensive clean room and support number of crew aids and tools. facilities, including a large engineering staff, and the Telescope would be out of action Some ORUs do not contain these fasteners. for a year or more – a long time to suspend When the maintenance philosophy changed scientific observations. from Earth-return to on-orbit-only servicing, other components were selected as replaceable Shuttle astronauts can accomplish most units after their design had matured. This maintenance and refurbishment within a added a greater variety of fasteners to the ser- 10-day on-orbit mission – with only a brief vicing requirements, including non-captive interruption to scientific operations and 5/16-in.-head bolts and connectors without without the additional facilities and staff wing tabs. Despite these exceptions, the high needed for ground servicing. level of standardization among units reduces K9322-02M 2-2 K9322_Sec02M.new 8/26/99 4:46 PM Page 2-3 K9322_201 Fig. 2-1 Hubble Space Telescope Servicing Mission 3A Orbital Replacement Units the number of tools needed for the servicing Telescope. The foot restraint sockets and mission and simplifies astronaut training. handrails greatly increase the mobility and sta- bility of EVA astronauts, giving them safe Accessibility. To be serviced in space, worksites conveniently located near ORUs. Telescope components must be seen and reached by an astronaut in a bulky pressure Crew aids such as portable lights, special tools, suit, or they must be within range of the appro- installation guiderails, handholds, and port- priate tool. Therefore, most ORUs are mounted able foot restraints (PFR) also ease servicing of in equipment bays around the perimeter of the the telescope components. In addition, foot spacecraft. To access these units, astronauts restraints, translation aids and handrails are simply open a large door that covers the appro- built into various equipment and instrument priate bay. carriers specific to each servicing mission. Handrails, foot restraint sockets, tether attach- 2.3 Shuttle Support Equipment ments, and other crew aids are essential to effi- cient, safe on-orbit servicing. In anticipation of To assist the astronauts in servicing the servicing missions, 31 foot restraint sockets Telescope, Discovery will carry into orbit several and 225 ft of handrails were designed into the thousand pounds of hardware and Space K9322-02M 2-3 K9322_Sec02M.new 8/26/99 4:46 PM Page 2-4 Support Equipment (SSE), including the • Capture, berth, and release the Telescope Remote Manipulator System (RMS), FSS, and • Transport new components, instruments, ORU Carrier (ORUC). and EVA astronauts between worksites • Provide a temporary work platform for one 2.3.1 Remote Manipulator System or both EVA astronauts. The Discovery RMS, also known as the robotic 2.3.2 Space Support Equipment arm, will be used extensively during SM3A. The astronaut operating this device from Ground crews will install two major assem- inside the cabin is designated intravehicular blies essential for SM3A – the FSS and ORUC – activity (IVA) crew member. The RMS will be in Discovery’s cargo bay. Figure 2-2 shows a used to: cargo bay view of these assemblies. K9322_202 Fig. 2-2 Servicing Mission 3A Payload Bay configuration K9322-02M 2-4 K9322_Sec02M.new 8/26/99 4:46 PM Page 2-5 Flight Support System. The FSS is a mainte- 2.3.3 Orbital Replacement Unit nance platform used to berth the HST in the Carrier cargo bay after the Discovery crew has ren- dezvoused with and captured the Telescope The ORUC is centered in Discovery’s cargo bay. (see Fig. 2-3). The platform was adapted from A Spacelab pallet modified with a shelf, it has the FSS first used during the 1984 Solar provisions for safe transport of ORUs to and Maximum repair mission. It has a U-shaped from orbit (see Fig. 2-4). In the SM3A configu- cradle that spans the rear of the cargo bay. A ration: circular berthing ring with three latches secures the Telescope to the cradle. The berthing • The Fine Guidance Sensor (FGS) #2 is stored ring can rotate the Telescope almost 360 degrees in the Fine Guidance Sensor Scientific (176 degrees clockwise or counterclockwise