PUBLIC AFFAIRS CONTACTS

                                

              For Information on the Space Shuttle

                                

Ed Campion                 Policy/Management                       

202/358-1778

  Headquarters, Wash., D.C.

James Hartsfield           Mission Operations/EVA                  

713/483-5111

  Johnson Space Center,    Astronauts

  Houston

Bruce Buckingham           Launch Processing                       

407/867-2468

  Kennedy Space Center, Fla.                                        

KSC Landing Information

June Malone                External Tank/SRBs/SSMEs                

205/544-0034

  Marshall Space Flight

  Center, Huntsville, Ala.

Nancy Lovato               DFRF Landing Information                

805/258-3448

  Dryden Flight Research Facility, 

  Edwards, Calif.

               For Information on STS-61 Payloads

Sarah Keegan               HST Program/Science                     

202/358-1547

  Headquarters, Wash., D.C. 

Debra Rahn

  Headquarters, Wash., D.C. HST International Elements              

202/358-1639

Jim Elliott                HST Project/Science                     

301/286-6256

  Goddard Space Flight Center                                       

STOCC Operations

  Greenbelt, Md.

Michael Finneran           HST Project/Science                     

301/286-5565

  Goddard Space Flight Center                                       

STOCC Operations

  Greenbelt, Md.

Bob MacMillin              Wide Field/Planetary Camera-II          

818/354-5011

  Jet Propulsion Laboratory

  Pasadena, Calif.

Jean Paul Paille           European Space Agency                   

011 33 1 42 73 72 92

  ESA, Hq., Paris

Ray Villard                HST Science, COSTAR                     

410/338-4514

  Space Telescope Science Institute

  Baltimore, Md.

                            CONTENTS

GENERAL BACKGROUND MATERIAL

General Release                                                  

3

Media Services Information                                       

4

Quick-Look Facts                                                 

5

Shuttle Abort Modes                                              

7

Vechicle And Payload Weights                                     

..................................................................

..........................8

Summary Timeline                                                 

10

Orbital Events Summary                                           

12

CARGO BAY PAYLOADS & ACTIVITIES

HST Servicing Mission-01 (HST/SM-01) Overview 

             History of HST                                      

14

             Mission Objectives And Success                      

................15

             First Corrected Image Availability                  

15

              Science Accomplishments                            

16

             ESA Role in HST Program                             

17

     Servicing Mission Orbital Verification                      

17

     Key Hubble Scientific Goals Following the First Servicing 

Mission                                                          

19

      Hubble Space Telescope Rendezvous and Retrieval            

19

     Commands to Hubble                                          

20

     STS-61 Extravehicular Activities                            

20

     Replacement Hardware and Instruments                        

21

      Primary Servicing Tasks                                    

25

      Secondary Servicing Tasks                                  

35

     HST Tools and Crew Aids                                     

35

Imax Camera                                                      

43

IN-CABIN PAYLOADS

Imax Camera                                                      

43

Air Force Maui Optical System (AMOS)                             

44

DTO-667 Pilot Inflight Landing Operations Trainer (PILOT)        

44

STS-61 CREW BIOGRAPHIES

Richard O. Covey, Commander (CDR)                                

45

Kenneth D. Bowersox, Pilot (PLT)                                 

45

Tom Akers, Mission Specialist 5 (MS5)                            

45

Jeffrey A. Hoffman, Mission Specialist 3 (MS3)                   

45

Kathryn C. Thornton,  Mission Specialist 1 (MS1)                 

46

Claude Nicollier, Mission Specialist 2 (MS2)                     

46

F. Story Musgrave, Mission Specialist 4 (MS4)                    

46

ACRONYMS AND ABBREVIATIONS                                       

47

Release:  93-204

FIVE SPACEWALKS TO SERVICE HUBBLE SPACE TELESCOPE HIGHLIGHTS 

SHUTTLE MISSION STS-61

     The December flight of Endeavour on Space Shuttle Mission 

STS-61 will see the first in a series of planned visits to the 

orbiting Hubble Space Telescope (HST).  The 11-day mission has 

been designed to accommodate a record five spacewalks with the 

capability for an additional two if needed.

     The first HST servicing mission has three primary 

objectives:  restoring the planned scientific capabilities, 

restoring reliability of HST systems and validating the HST 

on-orbit servicing concept.  These objectives will be 

accomplished in a variety of tasks performed by the astronauts in 

Endeaour's cargo bay.  

     Replacement of the spacecraft's solar arrays _ HST's source 

of electrical power _ tops the primary servicing task list.  This 

is because solar array jitter, or excessive flexing which happens 

when the telescope passes from cold darkness into warm daylight, 

may be compromising the structural integrity of the arrays. 

     The objective to restore the HST's science capabilities will 

be accomplished with the installation of the Wide Field/Planetary 

Camera-II and the Corrective Optics Space Telescope Axial 

Replacement, both of which will compensate for the spherical 

aberration of the primary mirror.

     The installation of new gyroscopes, which are required to 

point and track HST, along with fuse plugs and electronic units 

will increase the reliability of the HST system.

     Leading the seven-person STS-61 crew will be Mission 

Commander Dick Covey.  Pilot for the mission is Ken Bowersox.  

The mission specialists for the flight are Kathy Thornton, Claude 

Nicollier, Jeff Hoffman, Story Musgrave and Tom Akers.  Working 

in pairs, Hoffman and Musgrave and Thorton and Akers, all of whom 

have previous EVA experience, will perform the five spacewalks 

scheduled for flight days 4-8.

     Launch of Endeavour on the STS-61 mission is currently 

scheduled for no earlier than Dec. 1, 1993 at 4:57 a.m. EST.  The 

planned mission duration is 10 days, 22 hours and 36 minutes.  An 

on-time launch on Dec. 1 would produce a 3:33 a.m. EST landing on 

Dec. 12 at Kennedy Space Center's Shuttle Landing Facility.

     STS-61 will be the 5th flight of Space Shuttle Endeavour and 

the 59th flight of the Space Shuttle system.  The Hubble Space 

Telescope is an international cooperative program between NASA 

and the European Space Agency.

                             - end-

                                     

                   MEDIA SERVICES INFORMATION

NASA Select Television Transmission

     NASA Select television is available on Satcom F-2R, 

Transponder 13, located at 72 degrees west longitude; frequency 

3960.0 MHz, audio 6.8 MHz.

     The schedule for television transmissions from the orbiter 

and for mission briefings will be available during the mission at 

Kennedy Space Center, Fla; Marshall Space Flight Center, 

Huntsville, Ala.; Ames-Dryden Flight Research Facility, Edwards, 

Calif.; Johnson Space Center, Houston and NASA Headquarters, 

Washington, D.C.  The television schedule will be updated to 

reflect changes dictated by mission operations.

     Television schedules also may be obtained by calling COMSTOR 

713/483-5817.  COMSTOR is a computer data base service requiring 

the use of a telephone modem.  A voice update of the television 

schedule is updated daily at noon Eastern time.

Status Reports

     Status reports on countdown and mission progress, on-orbit 

activities and landing operations will be produced by the 

appropriate NASA newscenter.

Briefings

     A mission press briefing schedule will be issued prior to 

launch.  During the mission, status briefings by a Flight 

Director or Mission Operations representative and when 

appropriate, representatives from the science team, will occur at 

least once per day.  The updated NASA Select television schedule 

will indicate when mission briefings are planned.

                       STS-61 QUICK LOOK

                                

Launch Date/Site:   Dec. 1, 1993/Kennedy Space Center, Fla., Pad 

39B

Launch Time:        4:57 a.m. EST (approximate)

Orbiter:            Endeavour (OV-105) 5th Flight

Orbit/Inclination:  320 nautical miles/28.45 degrees

Mission Duration:   10 days, 22 hours, 36 minutes (approximate)

Landing Time/Date:  3:33 a.m. EST (approximate)/Dec. 12, 1993

Primary Landing Site:    Kennedy Space Center, Fla.

Abort Landing Sites:     Return to Launch Site - KSC, Fla.

                    TransAtlantic Abort Landing -

                         Banjul, The Gambia

                         Moron, Spain

                         Ben Guerir, Morocco

                    Abort Once Around - Edwards AFB, Calif.

Crew:               Dick Covey, Commander (CDR)

                    Ken Bowersox, Pilot (PLT)

                   Kathy Thornton,  Mission Specialist 1 

                   (MS1/EV3)

                    Claude Nicollier, Mission Specialist 2  (MS2)

                    Jeff Hoffman, Mission Specialist 3 (MS3/EV1)

                   Story Musgrave, Mission Specialist 4 

                   (MS4/EV2)

                    Tom Akers, Mission Specialist 5 (MS5/EV4)

Cargo Bay Payloads: HST SM-01 (Hubble First Servicing Mission)

HST Replacements:   SA (Solar Arrays)

                   WF/PC-II (Wide Field/Planetary Camera-II)

                   RSU-1, 2 & 3 (Rate Sensor Units 1, 2 and 3)

                   ECU-1 & 3 (Electronic Control Units 1 and 3)

                   MSS-1 & 2 (Magnetic Sensing Systems 1 and 2)

                   COSTAR (Corrective Optics Space Telescope

                      Axial Replacement)

                   SADE (Solar Array Drive Electronics)

Cargo Bay Equip:         HST FSS (HST Flight Support System)

                    ORUC (Orbital Replacement Unit Carrier)

                    SAC (Solar Array Carrier)

                    SIPE (Scientific Instrument Protective 

Enclosures)

                    ICBC (IMAX Cargo Bay Camera)

In-Cabin Payloads:  IMAX (IMAX In-Cabin Camera)

                    

Other:              AMOS (Air Force Maui Optical Site)

DTOs/DSOs:     DTO 648:  Electronic Still Camera

               DTO 656:  PGSC Upset Monitoring

               DTO 700-2:  Handheld Laser Ranging Device

               DTO 700-8:  Global Positioning System Flight Test

               DTO 1211:  Water Dumps at 10.2 psi Cabin

               DSO 326:  Window Impact Observation 

               DSO 469:  Inflight Radiation Dose/Distribution

               DSO 483:  Back Pain in Microgravity

               DSO 485:  Inter-Mars Tissue Equivalent Counter

               DSO 487:  Immunological Assessment of Crew

               DSO 489:  EVA Dosimetry Evaluation

               DSO 604:  Visual-Vestibular/Function of Adaptation

               DSO 617:  Skeletal Muscle Performance

               DSO 624:  Cardiovascular Response to Exercise

               DSO 901:  Documentary Television

               DSO 902:  Documentary Motion Picture

               DSO 903:  Documentary Still Photography

                   SPACE SHUTTLE ABORT MODES

     Space Shuttle launch abort philosophy aims toward safe and 

intact recovery of the flight crew, orbiter and its payload.  

Abort modes include:

    * Abort-To-Orbit (ATO) - Partial loss of main engine 

    thrust late enough to permit reaching a minimal 

    105-nautical mile orbit with orbital maneuvering system 

    engines.

    

    * Abort-Once-Around (AOA) - Earlier main engine 

    shutdown with the capability to allow one orbit around 

    before landing at Edwards Air Force Base, Calif.

    

    * TransAtlantic Abort Landing (TAL) - Loss of one or 

    more main engines midway through powered flight would 

    force a landing at either Banjul, The Gambia, Moron, 

    Spain, or Ben Guerir, Morocco.

    

    * Return-To-Launch-Site (RTLS) - Early shutdown of one 

    or more engines, and without enough energy to reach 

    Banjul, would result in a pitch around and thrust back 

    toward KSC until within gliding distance of the Shuttle 

    Landing Facility.

    

     STS-61 contingency landing sites are the Kennedy Space 

Center, Edwards Air Force Base, Banjul, Moron or Ben Guerir.

               STS-61 VEHICLE AND PAYLOAD WEIGHTS

                                

Vehicle/Payload                                        Pounds

Orbiter (Endeavour) empty and 3 SSMEs             173,014

Flight Support System (FSS)                            4,200

Imax Cargo Bay Camera (ICBC)                      608

Imax (in cabin)                                        329

Orbital Replacement Unit Carrier (ORUC)           6369

Solar Array Carrier (SAC)                              3829

Solar Array II                                    702

Rate Sensor Units (3)                                  73

Wide Field/Planetary Camera II                         613

Corrective Optics Space Telescope Axial Replacement    660

Electronic Control Units (2)                           35

Magnetic Sensing System (2)                       30

Co-processor                                      140

Goddard High Resolution Spectrograph Redundancy Kit    7

Changeout complement total (launch)                    2300

High-Speed Photometer                             603

WF/PC I                                           624

Solar Array I                                     668

RSU (3)                                           73

ECU (2)                                           35

Changeout complement total (Earth return)              2135

DSOs/DTOs                                    104

Total Vehicle at SRB Ignition                     4,511,115

Orbiter Landing Weight                            209,383

                                     

             space shuttle cargo configuration art

                                     

                                     

                    STS-61 SUMMARY TIMELINE*

Flight Day One*

Ascent

OMS-2 burn (310 n.m. x 297 n.m.)

ICBC activation

NC-1 burn (310 n.m. x 302 n.m.)

Flight Day Two*

Remote Manipulator System checkout

Cabin pressurization to 10.2 psi

Space Support Equipment checkout/survey

Configure Flight Servicing Structure

NPC burn (310 n.m. x 302 n.m.)

NSR burn (310 n.m. x 304 n.m.)

Extravehicular Mobility Unit checkout

NC-2 burn (317 n.m x 305 n.m.)

Flight Day Three*

HST rendezvous operations

NH burn (320 n.m. x 305 n.m.)

NC-3 burn (320 n.m x 310 n.m.)

NCC burn (320 n.m. x 310 n.m.)

TI burn (320 n.m. x 312 n.m.)

HST grapple (320 n.m x 313 n.m.)

HST berth

HST survey

Group B powerdown

Flight Day Four*

HST Extravehicular Activity 1

(Hoffman and Musgrave:  Two Rate Sensor Units/Secondaries)

Flight Day Five*

HST Extravehicular Activity 2

(Thornton and Akers:  Solar Arrays)

Flight Day Six*

HST Extravehicular Activity 3

(Hoffman and Musgrave:  Wide Field/Planetary Camera; Two Magnetic 

Sensing Systems)

Flight Day Seven*

HST Extravehicular Activity 4

(Thornton and Akers:  Corrective Optics Space Telescope Axial 

Replacement/Secondaries)

Flight Day Eight*

HST reboost burns (320 n.m. x 313 n.m.)

HST Extravehicular Activity 5

(Hoffman and Musgrave:  Solar Array Drive 

Electronics/Secondaries)

Flight Day Nine*

Group B power up

HST grapple

HST unberth

HST release (320 n.m. x 313 n.m.)

Separation burns 1, 2 and 3 (320 n.m. x 311 n.m.)

Group B power down

Flight Day Ten*

Cabin pressurization to 14.7 psi

Off-duty half day (MS1, MS3, MS4, MS5)

Off-duty half day (CDR, PLT, MS2)

Flight Day Eleven*

Group B power up

Flight Control Systems checkout

Reaction Control System hot fire

Cabin stow

Flight Day Twelve*

Space Support Equipment power down

Deorbit preparations

Deorbit burn

Entry

Landing

*SPECIAL NOTE ON STS-61 SUMMARY TIMELINE

     On every Shuttle mission, some day-to-day replanning takes 

place to adjust crew and event timelines according to unforeseen 

developments or simply to optimize the use of time in orbit.

     During STS-61, the bulk of the daily replanning will be 

undertaken, while the crew sleeps, by the planning shift in 

mission control.  During the EVA days, this team will play a 

crucial role in making the most of the astronauts time in 

Endeavour's payload bay.

     To maximize crew productivity and to adapt to any unexpected 

challenges, the planning team will have the ability to reorder 

the sequence of individual tasks within any given spacewalk or to 

shift tasks from one day's agenda to another.

     Each day's replanning effort will produce an execute plan 

defining the approach for the next day's activities in space and 

on the ground.

                 STS-61 ORBITAL EVENTS SUMMARY

                                

EVENT          START TIME     VELOCITY CHANGE     ORBIT

               (dd/hh:mm:ss)  (feet per second)   (n.m.)

OMS-2          00/00:45:00         461            310 x 297

NC-1           00/05:33:00         8              310 x 302

    (adjusts the rate at which Endeavour is closing on HST)

NPC            00/23:12:00         .5             310 x 302

    (fine-tunes Endeavour's ground track to be exactly in line 

with HST track)

NSR            01/03:57:00         5.5            310 x 304

    (adjusts Endeavour's closing rate on HST)

NC-2           01/04:32:00         12             317 x 305

    (adjusts Endeavour's closing rate on HST)

    

NH             01/17:22:00         4              320 x 305

    (adjusts altitude of Endeavour's orbital high point, 

fine-tunes course to arrive at a point 40 nautical miles behind 

HST at same altitude)

NC-3           01/18:10:00         10             320 x 310

    (fired at 40 n.m. behind HST, begins closing in on HST; 

initiates closing rate of about 16 n.m. per orbit aimed to arrive 

at a point 8 n.m. behind HST, at same altitude as HST, two orbits 

later)

NCC            01/20:23:00         TBD            320 x 310 

   (first burn calculated by onboard computers using onboard 

navigation derived from orbiter star tracker sightings of HST; 

fired while orbiter is about closing on point 8 n.m. behind HST 

to fine-tune course)

TI             01/21:23:00         3              320 x 312

   (fired upon arrival at point 8 n.m. behind HST; begins 

terminal interception of HST) 

MC1-MC4        TBD                 TBD            TBD

   (mid-course corrections; calculated by onboard computers, 

double-checked by ground; fine-tune final course toward HST, may 

or may not be required)MANUAL      01/22:57:00         TBD   

     TBD

   (Begins about 45 minutes prior to HST grapple, less than 1 

nautical mile from HST.  Commander takes manual control of 

orbiter flight, fires braking maneuvers to align and slow final 

approach)

GRAPPLE        01/23:42:00         n/a            n/a

   (HST captured with mechanical arm)

HST REBOOST    06/17:45:00         TBD            TBD

   (Performed only if amount of available propellant allows, 

lifts Endeavour's orbit to reboost HST's orbit while HST is in 

cargo bay)

     

HST REBOOST    06/18:33:00         TBD            TBD

   (Performed only if amount of available propellant allows, 

lifts Endeavour's orbit to reboost HST's orbit while HST is in 

cargo bay)

HST RELEASE    08/00:43:00         n/a            n/a

   (HST is released from Endeavour's mechanical arm)

SEP-1          08/00:44:00         1              320 x 313

   (Begins a slow separation of Endeavour from vicinity of HST)

SEP-2          08/01:08:00         2              320 x 313

   (Increases rate at which Endeavour is departing vicinity of 

HST)

SEP-3          08/01:32:00         3              320 x 311

   (Puts Endeavour on final course departing vicinity of HST)

DEORBIT        10/20:31:00         508 

 

LANDING        10/21:45:00 

     NOTE:  All planned burns are recalculated in real time once 

the flight is underway using the latest information for the 

position of HST and will likely change slightly.  Depending on 

how accurate the orbiter's navigation and course is at certain 

times, some smaller burns listed above may not be required.  

However, the times for major burns and events are unlikely to 

change by more than a few minutes.

          HUBBLE SPACE TELESCOPE/SERVICING MISSION-01

                          (HST-SM-01)

OVERVIEW OF MISSION

History

     Launched on April 24, 1990, NASA's Hubble Space Telescope 

was designed to be the most powerful astronomical observatory 

ever built.  And indeed, HST far surpasses the capabilities of 

ground-based optical telescopes for many types of research.  The 

keys to Hubble's power are its operation in space, far above the 

interference of the Earth's atmosphere, and to the unique 

instruments it carries as it orbits the planet.  In addition HST 

was the first observatory designed for extensive on-orbit 

maintenance and refurbishment.

     While the launch on the Space Shuttle Discovery more than 3 

years ago was flawless, Hubble was not.  Two months after HST was 

deployed into orbit 370 miles (595.5 km)  high, Hubble produced a 

disquieting discovery not about space, but about itself.  The 

curvature of its primary mirror was slightly _ but significantly 

_ incorrect.  Near the edge, the mirror is too flat by an amount 

equal to 1/50th the width of a human hair. 

     A NASA investigative board later determined that the flaw 

was caused by the incorrect adjustment of a testing device used 

in building the mirror.  The device, called a "null corrector," 

was used to check the mirror curvature during manufacture.

     The result is a focusing defect or spherical aberration.  

Instead of being focused into a sharp point, light collected by 

the mirror is spread over a larger area in a fuzzy halo.  Images 

of extended objects, such as stars, planets and galaxies, are 

blurred. 

     NASA has been coping with Hubble's fuzzy vision with 

computer processing to sharpen images.  For bright objects, this 

technique has yielded breathtaking detail never seen from the 

ground.  NASA also has been concentrating on the analysis of 

ultraviolet light, which ground-based telescopes cannot see 

because of the Earth's intervening atmosphere. 

     To realize the full potential of HST, however, the 

spacecraft must be serviced.  The telescope mirror itself cannot 

be fixed or changed.  However, corrective optics can be applied 

to the HST instruments to compensate for the aberration, much the 

same as glasses or contact lenses correct human sight.  The new 

optics should allow Hubble to accomplish most, if not all, of 

it's originally planned objectives.

     The mission, though, will accomplish much more than improved 

vision.  Hubble was designed to spend 15 years in space.  Even 

before the spherical aberration was known, several servicing 

missions, including one in 1993, had been planned so that failed 

parts could be replaced and others improved with better 

technology.  This mission will perform that type of servicing in 

addition to installing corrective optics. 

     Endeavour will carry some 16,000 pounds (7,257 kilograms) of 

servicing hardware into space.  During nearly 2 weeks in orbit 

around the Earth, astronauts will use the Shuttle as a kind of 

orbiting service station from which they will venture to work on 

the 12.5-ton (11.34-metric ton) telescope as it hurtles around 

the planet at 18,000 miles (28,968 km) an hour. 

     The crew will spend some 30 hours in space during at least 

five separate spacewalk periods, undertaking a series of tasks 

more complex than any ever attempted in orbit, to ensure that 

Hubble remains a viable and productive national resource 

throughout its planned 15-year lifetime.

 Mission Objectives and Success

     The three objectives of the first Hubble servicing mission 

are to restore the planned capabilities of the telescope by 

correcting the optics, to restore reliability of the spacecraft 

and to validate that the concept of Hubble on-orbit servicing is 

viable.

     The top priorities are installation of the replacement solar 

arrays; two rate sensing units, one with an electronics control 

unit; the Wide Field/Planetary Camera II (WF/PC-II) and fuses; 

the Corrective Optics Space Telescope Axial Replacement (COSTAR); 

at least one new magnetometer; and a new Solar Array Drive 

Electronics unit.  

     For the first servicing mission to be considered fully 

successful, these top priority items must be accomplished.  In 

addition, other tasks may be performed on a time-available basis.  

The minimum criteria for mission success are to leave Hubble with 

three newer-design gyroscope systems and either an operational 

WF/PC-II or COSTAR.

First Corrected Image Availability

     The first fully corrected Hubble images are estimated to be 

available 6 to 8 weeks after the servicing mission.  This time is 

necessary for adjustments to ensure telescope stability and the 

best possible focus.  During this period, telescope operators on 

the ground will remotely calibrate the gyros, which help keep the 

HST fixed on its targets, and position the corrective mirrors in 

the Corrective Optics Space Telescope Axial Replacement (COSTAR) 

and the Wide Field/Planetary Camera 2 (WF/PC-II).  

     COSTAR is being installed to remedy the blurred vision of 

three observing instruments on HST.  The WF/PC-II is a 

replacement camera that has its own corrective optics.

     More information on activities after STS-61 necessary to 

produce a fully corrected Hubble image can be found in the 

section on Servicing Mission Orbital Verification.

Science Accomplishments

  Despite the flaw in the primary mirror, the bus-size Hubble 

still has been able to gather a wealth of scientific data, most 

of which would have been impossible to collect if the telescope 

did not exist.  In the last 3 years, HST has conducted a variety 

of scientific investigations that have rapidly expanded knowledge 

of what lies beyond the Earth, from the relatively nearby planets 

in Earth's solar system to the most distant reaches of the 

universe. 

  Hubble's studies have ranged from Earth's neighbor Mars, to 

the evolution of stars from birth to death, to the 

characteristics of galaxies beyond, and finally to a field known 

as cosmology, which probes the fundamental nature of the universe 

itself.

  The following is a small sampler of some of Hubble's 

discoveries and work in progress:

    The Planets

  Even prior to the servicing mission, Hubble conducted and 

continues to conduct long-term observations of global weather 

changes on Mars. 

Hubble has observed the development of a rare, planet-wide storm 

on Saturn.  The telescope also resolved, as two distinct objects, 

the most distant planet in the solar system, Pluto and its moon 

Charon.  Previously, no telescope had been able to separate 

clearly the two bodies. 

  HST also has been studying long-term weather changes on 

Jupiter and its auroral activity.  Hubble also has been measuring 

the extent of the atmosphere of the Jovian moon Io and also has 

looked for changes in the satellite's surface.

    Stellar Evolution

  Hubble uncovered the strongest evidence yet that many stars 

form planetary systems.  This evidence was the discovery of disks 

of dust around 15 newly formed stars in the Orion Nebula, a 

starbirth region 1,500 light-years away.  Such disks are 

considered a prerequisite for the formation of solar systems like 

Earth's. The HST images confirm more than two centuries of 

speculation, conjecture and theory about the genesis of a solar 

system. 

    Star Clusters

  HST discovered young globular star clusters at the core of a 

peculiar galaxy.  The discovery of these stars early in their 

evolution was the equivalent of finding a "Jurassic Park" in 

space.  

  The space telescope found "blue straggler" stars in the core 

of globular cluster 47 Tucanae, providing evidence that some 

stars "capture" others and merge with them.

    Gallaxies

  HST uncovered circumstantial evidence for the presence of a 

massive black hole in the core of the neighboring galaxy M32 as 

well as the giant elliptical galaxy M87.  Both galaxies have a 

central concentration of starlight that probably is shaped by the 

gravitational field of the black hole.  This implies that massive 

black holes may be quite common among "normal" galaxies, perhaps 

even Earth's.

  Hubble yielded direct evidence for galaxy evolution by 

resolving the shapes of galaxies that existed long ago.  HST 

revealed that many ancient spiral galaxies have since 

disappeared, possibly through fading or collisions and mergers 

with other galaxies.

    Cosmology

  The space telescope allowed astronomers to take a major first 

step in determining the rate at which the universe is expanding.  

HST detected 27 stars called Cepheid variables.  These stars are 

"standard candles" for estimating distances to galaxies.  The 

expansion rate, known as the Hubble Constant, is one of two 

critical numbers needed for making a precise determination of the 

size, age and fate of the universe.

  HST discovered boron, the fifth lightest element, in a very 

ancient star.  This star would have been one of the earliest 

formed after the Big Bang explosion that most scientists believe 

began the universe.  If boron was produced in the first few 

minutes of the birth of the universe, it implies that the Big 

Bang was not a uniform explosion.

  Hubble precisely determined the ratio of deuterium to hydrogen 

in interstellar gas clouds.  This value shows that the universe 

has only 6 percent of the observable matter required to prevent 

itself from expanding forever.

European Space Agency (ESA) Role in HST

                                     

     The Hubble Space Telescope is a program of joint cooperation 

between NASA and ESA.  ESA provided Hubble's deployable solar 

arrays, the major source of electrical power, which collects 

energy from the sun to recharge the spacecraft's six 

nickel-hydrogen batteries.  ESA's second contribution was the 

Faint Object Camera (FOC), which was intended for imaging of the 

faintest objects in the visible and ultraviolet spectral regions 

at very high spatial resolution.  These elements are discussed 

further in the section addressing replacement hardware and 

instruments.

     Claude Nicollier, a mission specialist on this flight, is an 

ESA astronaut.

         SERVICING MISSION ORBITAL VERIFICATION (SMOV)

     The purpose of SMOV is to "recommission" HST so that it can 

begin science operations as soon as possible following the first 

servicing mission.  This involves a thorough engineering checkout 

of all serviced subsystems; optical alignment and initial 

calibration of all science instruments; and the phasing in of 

astronomical observations.  SMOV begins when HST is released from 

the Shuttle and is expected to last approximately 13 weeks.

Key Activities During SMOV

    Activation and engineering checkout of the science 

instruments.

    Optical alignment and focusing of WF/PC-II and COSTAR.

    Initial calibration of WF/PC-II and the COSTAR-corrected 

science instruments.

    Early science observations.

Engineering Checkout Activities

    Decontaminate the WFPC II detectors (charge-coupled devices 

or CCDs) of any foreign substances by heating the detectors to 

"drive-off" contaminants.

    Establish proper operating temperature of WFPC II CCDs by 

monitoring ultraviolet (UV) light from a calibration star.

    Monitor pressure drop (due to outgassing) until it is safe 

to turn on high voltage to the COSTAR-corrected science 

instruments.

    Determine the effects of the servicing mission on the basic 

(pre-COSTAR) optical performance of the science instruments.

Steps in Focusing the Science Instruments

    Check out the first generation instruments and conduct 

prefocusing tests.

    Adjust the secondary mirror in HST's Optical Telescope 

Assembly to set focus for WF/PC-II and correct for residual coma 

in the Optical Telescope Assembly.

    Deploy COSTAR arms.

    Adjust COSTAR and WF/PC-II optics and mirrors, including 

mirror tilt, coarse adjustment, fine alignment and focus.

Science Instruments Calibration

    A series of tests and measurements to establish the actual 

performance of the science instruments in the areas of 

sensitivity, resolution and detector response characteristics.

KEY HST SCIENTIFIC GOALS FOLLOWING THE FIRST SERVICING MISSION

    Hubble will determine, precisely, the expansion rate of the 

universe by measuring the light curve of Cepheid Variable stars 

in galaxies out to the distance of at least 50 million 

light-years.

     Cepheids are pulsating stars that become alternately 

brighter and fainter with periods (duration of the states of 

brightness or faintness) ranging from 10 to 50 days.  Astronomers 

have known for over 50 years that the periods of these stars 

precisely predict their total luminous power, which allows their 

distance to be measured.

     In the expanding universe, the Hubble Constant (Ho) is the 

ratio of the recession velocities of galaxies to their distance.  

(Recession velocity is the speed at which the galaxy is moving 

away from Earth.)  The age of the universe can be estimated from 

the Hubble Constant.  The age currently is estimated to be 

between 10 and 20 billion years, but a more precise measurement 

of the Hubble Constant is required to narrow this range to an 

accuracy of 10 percent.

    HST will look for the gravitational signature of massive 

black holes in the cores of normal and active galaxies.  A black 

hole is a theoretical object that is so compact and dense, 

nothing can escape its gravitational field.  The HST 

spectrographs will measure precisely the velocities of gas and 

stars orbiting the center of a galaxy.  If the stellar velocities 

increase rapidly toward the galaxy center, it would be the 

signature of a massive, compact central object.

    Hubble will be able to determine the shapes of galaxies that 

are very distant.  Because remote objects also are relics of the 

early universe, HST will be able to study how galaxies have 

evolved since the beginning of the universe.  Nearby galaxies 

have spiral, elliptical and irregular shapes, however, these 

shapes should have changed over time because the universe is 

evolving.

    Hubble will be able to precisely measure the ages of 

globular clusters by observing the faintest stars in the 

clusters.  Globular clusters are considered to be the oldest 

objects in the universe, and their ages provide insights into how 

stars evolve and also provide an independent estimate of the age 

of the universe.

        HUBBLE SPACE TELESCOPE RENDEZVOUS AND RETRIEVAL

     The rendezvous and retrieval operations associated with 

Hubble Space Telescope will be similar to those conducted on 

previous missions requiring capture of a free-flying satellite in 

orbit.

     For the HST mission, Endeavour's crew will perform many 

orbit adjust burns to catch up with and retrieve the telescope on 

flight day three of the mission using the Shuttle's robot arm.

     Once the Shuttle is safely in orbit and the payload bay 

doors opened, the space support equipment activation is 

performed. This includes activating the flight support system and 

orbital replacement unit carrier heaters.  Other pre-rendezvous 

activities will include checkout of the robot arm, the orbiter 

Ku-band dish antenna used as a radar system during rendezvous and 

the ground command system.

     The terminal initiation burn occurs about 2 hours prior to 

capture at a distance of approximately 40,000 feet (12,192 m) in 

front of the telescope.  Several small mid-course correction 

burns follow before the Commander takes over manual control of 

the Shuttle about 1,200 feet (366 m) below and 500 feet (152 m) 

behind the telescope.

     The orbiter approaches Hubble from underneath, just after 

orbital sunset.  This approach technique is designed to minimize 

potential contamination from the Shuttle's thruster firings.

     Prior to capture, a ground-commanded maneuver of the 

telescope will be performed to align the grapple fixture on the 

HST with Endeavour's robot arm.  The size of the telescope 

maneuver will depend on the angle to the Sun and ranges from 

about 70 degrees to 180 degrees.

     When the telescope is grappled, using the robot arm's end 

effector, it will be lowered into the payload bay and berthed in 

the flight support system, a turntable likened to a lazy susan 

for its rotation and tilt ability to assist in the servicing 

tasks.  An electrical cable is remotely attached to provide 

orbiter power to the telescope.

                       COMMANDS TO HUBBLE

     Commands to HST are issued from the Space Telescope 

Operations Center (STOCC) at Goddard Space Flight Center, 

Greenbelt, Md., which manages the orbiting observatory.  The 

STOCC has been the nerve center for Hubble operations since the 

telescope was launched.  Commands to Hubble are issued from the 

STOCC and data gathered by the spacecraft arrive there first.

     The STOCC is responsible for most commanding of the HST 

during 

STS-61, although the crew can send a limited number of commands 

from Endeavour.  The STOCC will send commands configuring the 

space telescope for retrieval by the orbiter; integrate commands 

with crew activities during extravehicular activities (EVAs) to 

configure various spacecraft hardware and perform hardware 

checkouts and send commands to configure the space telescope for 

deployment from Endeavour.

                STS-61 EXTRAVEHICULAR ACTIVITIES

     A total of five spacewalks are planned on STS-61 to service 

the HST.  Unlike past Shuttle repair work performed on satellites 

such as Intelsat on STS-49, HST was designed with the objective 

of servicing it in orbit through Shuttle spacewalks.  As such, it 

has two grapple fixtures for the Shuttle's mechanical arm, many 

handholds for spacewalkers and bolts and electrical connections 

designed to be serviced by a spacewalker.

     However, the amount of work to be performed on STS-61 has 

increased above what originally was projected for the first 

servicing flight to the telescope due to deficiences and 

equipment problems that have occurred or been discovered since 

HST was launched.  Since there is such a large amount of work to 

be accomplished on STS-61, the various tasks have been 

prioritized by the HST program officials.

     The primary tasks on STS-61 will be to install two Rate 

Sensor Units, one with an Electronics Control Unit, the Solar 

Arrays, the Solar Array Drive Electronics, the Wide 

Field/Planetary Camera and four instrument fuse plugs, the 

Corrective Optics Space Telescope Axial Replacement and one 

Magnetic Sensing System.

     Secondary tasks that may be performed during the spacewalks 

if time permits include installing the Goddard High Resolution 

Spectrograph Redundancy Kit, a 386 Coprocessor, a second Magnetic 

Sensing System, four gyro Fuse Plugs and one Electronic Control 

Unit.  A third Rate Sensor Unit is being carried in the payload 

bay for use if needed.

     The spacewalks will be peformed by STS-61 extravehicular 

crew members Jeff Hoffman, Story Musgrave, Kathy Thornton and Tom 

Akers.  Each spacewalk will be performed by two crew members, one 

of whom will be in a foot restraint mounted at the end of 

Endeavour's mechanical arm.  During all EVAs, the crew member 

mounted at the end of the arm will be referred to as 

Extravehicular Crew Member 2, or EV2, while the other spacewalker 

will be designated EV1.

     The EVA crew can be distinguished by markings on the legs of 

their spacesuits.  Hoffman will have a solid red stripe around 

the legs of his suit; Musgrave will have no stripes on the legs 

of his suit; Thornton will have a dashed red stripe around the 

legs of her suit; and Akers will have a diagonal, broken red 

stripe around the legs of his suit.

     In planning for the mission, the EVAs have been designed to 

take into account the possibility that crew members may encounter 

unforeseen difficulties either in tasks or equipment that could 

cause the preplanned schedule for installation of various 

equipment to change. All four EV crew members have cross-trained 

so that any one is capable of performing any given task. 

     For all of the various tasks, the Flight Support Structure 

in Endeavour's cargo bay on which HST will be mounted, once it is 

retrieved, will be rotated so the area being worked on faces 

forward to allow better visibility.  Those specific tasks and the 

EVA work required to complete them are described in the following 

sections.

              REPLACEMENT HARDWARE AND INSTRUMENTS

     While the servicing mission is complex, steps have been 

taken to make the spacecraft as straightforward to work on as 

possible.  Since HST was designed for servicing in space from 

it's inception, many of its subsystems are modular, standardized 

and accessible. 

     Hubble has 49 different modular subsystems designed for 

servicing, ranging from small fuses to large scientific 

instruments.  The space telescope, which is 43.5 feet (13.25 

meters) long, also has 225 feet (69 meters) of handrails and 31 

footholds to aid astronauts in servicing tasks. And more than 200 

tools _ from screwdrivers to hardware designed specifically for 

HST servicing _ are available for use on this mission.

     NASA's Goddard Space Flight Center, Greenbelt, Md., is 

responsible for the components that will be serviced or replaced 

on Hubble.  The components make up a primary servicing task list 

that will be carried out during the mission, followed by a 

secondary task list to be undertaken if time and conditions 

allow.

     The mission's primary objective is to restore the HST's 

science capabilities with the Wide Field/Planetary Camera-II and 

the Corrective Optics Space Telescope Axial Replacement, both of 

which will compensate for the spherical aberration of the primary 

mirror. 

     However, the replacement of the spacecraft's solar arrays _ 

HST's major source of electrical power _ tops the primary 

servicing task list.  This is because solar array jitter, or 

excessive flexing, may be compromising the structural integrity 

of the arrays.  By replacing the arrays first, the observatory 

still will be able to perform science even if an emergency causes 

the mission to be called off and forces astronauts to release the 

telescope from the Space Shuttle before installing the optics 

packages

     Likewise the replacement of one gyro pair is second on the 

task list, because if more gyros fail, the pointing of the 

spacecraft at science targets cannot be accurately controlled.

     The primary servicing task list includes:

    Solar Array II (SA II).

    Gyro Pair 2.

    Wide Field Planetary Camera 2 (WFPC2) and four instrument 

fuse plugs.

    Corrective Optics Space Telescope Axial Replacement 

(COSTAR)

    Magnetometer System 1.

    Gyro Pair 3 with Electronics Control Unit (ECU).

    Solar Array Drive Electronics 1 (SADE).

  

  The secondary servicing task list includes:

    A redundancy kit for the Goddard High Resolution 

Spectrograph 

          (GHRS).

    The 386 co-processor on the spacecraft's primary computer, 

called the 

          DF-224.

    Magnetometer System  2

    Four gyro fuse plugs.

    Electronics Control Unit for Gyro Pair 1.

                 Overall HST Configuration art

                                     

              Light Path for the main telescopeart

                                     

                    PRIMARY SERVICING TASKS

                                     

Gyroscope Pairs (Rate Sensing Units) and Electronics Control Unit

     Three gyroscopes (or gyros) are required to point and track 

HST.  Three more gyros are onboard as backups.  The total of six 

gyros are packaged in pairs of two, called Rate Sensing Units 

(RSU).  One gyro failed in December 1990; a second failed in June 

1991 and a third in November 1992.  

     Two of these three gyros, one located in pair 2 and the 

other in pair 3, contain hybrid electronics that are suspected of 

causing the failures.  Gyro pairs 1 and 3 also have experienced a 

failure in one channel of their Electronics Control Unit (ECU), 

the cause of which is suspected to be a random electronic part 

failure.  While these failures have not affected HST's 

performance, replacing the failed hardware will increase system 

reliability. 

     The Rate Sensor Units are inside the housing of HST.  To 

begin the replacement work, the spacewalking astronaut, standing 

in a foot restraint mounted on the end of the Shuttle's 

mechanical arm, will first back out several bolts to open doors 

covering the star tracker near the base of HST.  One of the four 

bolts holding the doors, called the star tracker seal, must be 

completely removed to unlatch the doors. 

     A programmable power wrench will be used to loosen and 

tighten all bolts during the RSU replacement.  While the 

arm-mounted astronaut unlatches the doors, his fellow 

spacewalker, mounted on a foot restraint attached to a support 

structure in the Shuttle's bay, will assist.  Once the doors are 

unlatched, they will be swung open to provide access to the bay 

area.

     The Rate Sensor Units are located behind the cone-shaped 

star tracker shades in the bay area of the telescope.  To replace 

an RSU, these shades may have to be removed.  If so, three bolts 

must be loosened and the shade pulled off.  The shade then can be 

temporarily stowed outside the work area.  The shades are 

reinstalled by pushing them back into place and then retightening 

the three bolts.

     To remove an RSU, the spacewalker, standing in an adjustable 

foot restraint attached to the telescope, will loosen three bolts 

and disconnect two electrical plugs.  The RSU then may be removed 

by holding a handrail located at the top of the unit. 

     During these activities, the astronaut standing on the end 

of the arm will assist his partner from behind.  The new RSU, 

carried aloft in an Orbital Replacement Unit Carrier (ORUC) in 

the Shuttle's bay, will be installed by sliding it into place and 

then retightening the three bolts and hooking up the two 

electrical plugs.

     The time required to set up, remove two RSUs, install two 

RSUs and then clean up the area during training has been around 

3.5 hours, including the possible removal and reinstallation of 

the star tracker shades.

Electronic Control Units

     The Electronic Control Units are the electrical brains for 

the Rate Sensor Units and are located in a service bay on the 

Hubble Space Telescope.  Once the compartment door is opened, two 

of the three ECUs will be replaced by removing four bolts and 

disconnecting each one's electrical cable.  The new units, which 

are retrieved from a protective container in the payload bay, 

will be installed in a similar fashion.

Solar Array II

     The Solar Arrays were built in Europe under the auspices of 

ESA.  The solar arrays provide the telescope and its instruments 

with 5kW of electrical power at the start of their lifetime.  

They constitute the spacecraft's two "wings" and consist of 

50,000 silicon photoelectrical cells, covering a surface area of 

84 square yards/6.6 x 39.6 x 9.24 ft (70 square meters/2 x 12 x 

2.8 m).  

     The arrays are the flexible "roll-out and roll-up" type and 

are made of huge sheets of plastic (fiberglass-reinforced Teflon) 

held in place by horizontal metal struts, which also unroll.  

Each wing weighs about 352 pds (160 kg).

     But the arrays create a jitter that interferes with 

spacecraft stability and affects its pointing capability.  The 

arrays now on Hubble were supposed to accommodate the expansion 

and contraction caused by heating and cooling as the space 

telescope moves in and out of daylight during its 96-minute 

orbits.  However, a compensation device that allows for the 

expansion and contraction of the solar array blankets does not 

expand and contract as smoothly as expected. 

     As a temporary fix, engineers created software that 

commanded Hubble's pointing system to compensate for the jitter 

automatically.  This procedure occupies a large portion of the 

on-board computer memory, though, and to truly fix the problem, 

the solar arrays must be replaced.

     ESA redesigned and provided to NASA a set of spare solar 

arrays to reduce the jitter to an acceptable level.  This set 

will be installed on the HST after the existing arrays are 

removed; the arrays now on the spacecraft will be returned to 

Earth.  To significantly reduce jitter, the new arrays have 

thermal insulation sleeves on the array supports, called 

bi-stems, to minimize heating and cooling of the support during 

each orbit.  Springs that work like shock absorbers also will 

take up tension at the array ends.

     To replace the HST Solar Arrays, first the old arrays are 

retracted by commands from the Space Telescope Operations Control 

Center.  Once they have been retracted and stowed, the 

arm-mounted spacewalker will release three latching points on the 

first array to be removed.  Once the three latches have been 

released, the array can be removed and handled using a transfer 

handhold mounted to the array. 

                  Solar array wing detail art

                 Solar array carrier (SAC) art

     The array then is carried by having the mechanical arm moved 

to position the astronaut within reach of a temporary stowage 

bracket for the old arrays, mounted on the right-hand side of the 

Solar Array Carrier in Endeavour's cargo bay.  While being moved 

from place to place at the end of the arm, the crew member also 

may evaluate the handling characteristics of the array to prepare 

for carrying the new array up to its installation position.  

Thoughout the removal operation, the arm-mounted astronaut will 

be assisted by his counterpart, who will be moving about via 

handholds on the telescope and Shuttle. 

     The new solar array is removed from the SAC by disconnecting 

a power and a data connection and then unlatching three latch 

points exactly like the latch points on the telescope.  A 

temporary transfer handle allows the arm-mounted astronaut to 

carry the new array up to the installation location. His 

counterpart will assist with the installation by standing in a 

foot restraint mounted to the telescope near the work area.  

     While the array is being transported, the power and data 

connectors are secured in temporary holding brackets on the 

array.  To install the new array, first it is moved into position 

and once seated, the three latch points are locked in place and 

the connectors plugged in.  The second array is removed and its 

replacement installed in exactly the same fashion.

     During training, the time required to perform a changeout of 

the solar arrays was about 5 hours, and one full spacewalk is 

dedicated to this task.  The new arrays are not planned to be 

deployed during the spacewalk performed to install them.

Wide Field/Planetary Camera-II (WF/PC-II)

     The current WF/PC has been used to study bright, 

high-contrast objects, such as major solar system planets and 

nearby star clusters and galaxies. Spherical aberration, however, 

has hampered the ability of the camera to provide high-resolution 

images of the very faintest objects, or objects in a field 

crowded with other objects. 

     The WF/PC-II is a spare instrument developed, beginning in 

1985, by the Jet Propulsion Laboratory (JPL) team, Pasadena, 

Calif., that built the first WFPC.  When Hubble's mirror was 

found to be flawed, NASA and the WFPC science team immediately 

began working on an optical correction that could be built into 

WFPC2.  The new design incorporates an optical correction by the 

refiguring of relay mirrors already in the optical train of the 

cameras.  Each relay mirror is polished to a new "prescription" 

that will compensate for the incorrect figure on HST's primary 

mirror.  Small actuators will fine-tune the positioning of these 

mirrors on orbit, ensuring the very precise alignment that is 

required.

     Through a servicing bay door built into the side of HST, 

astronauts will slide out the 610-pound (277-kilogram), 

wedge-shaped WFPC, as they would a giant drawer, and replace it 

with WFPC2.  The removed WFPC will be returned to Earth. 

               Wide Field/Planetary Camera-II art

     The WFPC2 will have three wide-field cameras and one 

planetary camera instead of the original total of eight.  The 

WFPC2 team chose to reduce the number of cameras to four in order 

to develop a system to align the corrective relay mirrors 

on-orbit.  Improved Charged Coupled Devices (CCDs) are 

incorporated into WFPC2 to improve its sensitivity, particularly 

in the ultraviolet.

     To remove and replace the Wide Field/Planetary Camera 

(WF/PC), the doors to the service bay at the base of the 

telescope are opened and specially designed guide rails are 

installed to assist with removal of the instrument.

     A temporary handhold then is installed on the WF/PC.  Using 

this handhold, the arm-mounted spacewalker pulls the WF/PC out of 

its installed position while his counterpart watches the 

alignment of the WF/PC on the rails and ensures it is level as it 

is removed.  Once removed from the telescope cavity, the 

arm-mounted astronaut is positioned within reach of a temporary 

parking fixture for the old WF/PC in Endeavour's cargo bay, where 

it is stowed.

     A temporary handhold is installed on the new unit, WF/PC-II, 

in its Scientific Instrument Protective Enclosure (SIPE) in 

Endeavour's cargo bay.  The WF/PC-II is pulled from the SIPE by 

the arm-mounted crew member, who is later moved to the 

installation site by the arm operator.  Meanwhile, the SIPE door 

is temporarily latched by his crew mate.

     Before sliding the WF/PC-II into place inside the telescope, 

a cover over its mirror is removed.  Then, the arm-mounted 

spacewalker slides it into the telescope slot while his fellow 

spacewalker checks to ensure that it is aligned on the guide 

rails.  Once inserted in place, the handhold is removed from the 

instrument and the guide rails are detached. 

     Finally, the old WF/PC is removed from its temporarily 

stowed postion in the parking fixture and inserted into the SIPE 

that carried WF/PC-II, where it is secured for Endeavour's trip 

home.

     Removal of the old WF/PC and the installation of WF/PC-II 

has taken about 4 hours and 15 minutes during training.

Coorective Optics Space Telescope Axial Replacement (COSTAR)

     COSTAR is designed to optically correct the effects of the 

primary mirror aberration on three instruments besides the WFPC:  

the Faint Object Camera (FOC), the Faint Object Spectrograph 

(FOS) and the Goddard High Resolution Spectrograph (GHRS). 

     The FOC, provided by ESA, is designed to detect very 

low-luminosity celestial bodies and to provide the most detailed 

images on HST.  It consists of an electronic conventional 

scanning camera (of the television type), whose front part is a 

powerful image intensifier tube.  Its performance has been 

degraded by the spherical aberration, but the sharp image cores 

still allow the camera to detect details not seen by ground-based 

telescopes.

             Corrective Optics Space Telescope art

     The FOS analyses the light from very faint objects in the 

visible and ultraviolet spectral regions.  While the faintest 

objects now cannot be reached, observations of brighter sources 

are only moderately degraded. 

     The GHRS is intended for very detailed analysis of 

ultraviolet radiation. The instrument now loses spectral 

resolution on the faintest objects, but observations of brighter 

sources are only moderately degraded.

     COSTAR was invented by the Hubble Space Telescope Strategy 

Panel, a group of scientists and engineers brought together at 

the Space Telescope Science Institute, Baltimore, Md., in the 

fall of 1990 to consider how to fix HST.  Built by Ball 

Aerospace, Boulder, Colo., under contract to NASA, COSTAR has no 

detectors or cameras.  It will use precisely shaped mirrors, 

ranging from about the size of a dime to a quarter, to correct 

for the spherical aberration.

     Through a servicing bay door, astronauts will pull out the 

487-pound (221-kilogram), phone booth-size High Speed Photometer 

(HSP) and install in its place the identically sized COSTAR.  

Once in place, COSTAR will deploy a set of mechanical arms, no 

longer than a human hand, that will place corrective mirrors in 

front of the openings that admit light into the Faint Object 

Camera, the Faint Object Spectrograph and the Goddard High 

Resolution Spectrograph.  COSTAR's corrective mirrors will 

refocus light relayed by HST's primary mirror before it enters 

these three instruments.  COSTAR will restore the optical 

performance of these instruments very close to the original 

expectations.

     To install COSTAR, the spacewalkers first will open doors to 

the bay, that enclosed the HSP, by loosening several bolts.  Once 

the doors are open, latches that hold the HSP in place will be 

loosened and then four electrical connectors and a ground strap 

will be disconnected from the instrument. 

     Then the HSP is lowered from its position to guide rails for 

the unit. The arm-mounted spacewalker and his crew mate, standing 

in a foot restraint attached to the telescope, will coordinate 

efforts to remove the device.  The arm-mounted crew member will 

slide HSP out while his fellow spacewalker ensures that it is 

aligned with the guide rails.

     Once removed, the HSP is held by the crew member standing on 

the end of the arm while the arm is positioned so the HSP can be 

placed in a temporary parking fixture mounted in the cargo bay.  

After it is temporarily stowed, a handhold is attached to COSTAR 

and it is lifted from its protective enclosure.  A ground strap 

is disconnected and, while the arm-mounted astronaut is lifting 

COSTAR out, his crew mate is assisting by ensuring COSTAR is 

squarely aligned with the enclosure as it is extracted.

     The arm-mounted crew member then is positioned up to the 

installation area while his fellow spacewalker moves to the site 

via handrails on the telescope.  COSTAR then is aligned with the 

guide rails, with the arm-mounted spacewalker watching the 

alignment of a rail at the upper left-hand corner of COSTAR and 

his counterpart checking the alignment of a rail at the lower 

right corner.  

     Once COSTAR slides into place, the four electrical 

connections, disconnected from HSP, are connected to COSTAR along 

with the grounding strap, and the latches are tightened to hold 

COSTAR in place.

     In training, removal of the HSP and installation of COSTAR 

has taken about 3 hours and 15 minutes.

Solar Array Drive Electronics 1 (SADE)

     Each solar array wing has an electronics control assembly 

that includes a drive electronics unit.  These units transmit 

positioning commands to the wing assembly.  One of these Solar 

Array Drive Electronics units has failed due to transistor 

overheating.  A replacement SADE, provided by ESA, will restore 

that lost capability and provide better heat protection for the 

transistors.

     The Solar Array Drive Electronics are mounted on the inner 

side of one of the doors to an HST service bay.  Two electronics 

boxes are mounted on the inside of the door, but only one is 

being replaced.  Once the door is opened, the two spacewalkers - 

one mounted on the arm and one holding handrails on the telescope 

- will loosen six bolts to free the old SADE unit and disconnect 

electrical connectors attached to the unit.  The new SADE unit is 

installed in the reverse of this process.

Magnetometer System 1

     The HST's two magnetometers (also known as magnetic sensing 

systems) measure the spacecraft's relative orientation with 

respect to the Earth's magnetic field.  Neither magnetometer is 

functioning at full capability.  Both replacements have improved 

electronics and thermal blankets added.  The replacement 

magnetometers will be snapped into place over the existing 

magnetometers, which will not be removed from the HST.

     Both of the magnetic sensing systems are located near the 

top of the telescope near the aperture door.  The new units will 

be installed using four rotating knob connectors and will be 

attached directly on top of the old units by removing some 

insulation and removing and reinstalling the electrical cable.  

These units are used to help measure the observatory's position 

relative to Earth's magnetic field.

Fuse Plugs

     Fuses for both the gyros and instruments will be replaced to 

correct sizing and wiring discrepancies.

     The fuses that will be replaced on the HST are located on 

the inside of a compartment door.  Eight of the fuse plugs will 

be removed and replaced by the spacewalking astronauts.  Once all 

have been replaced, checks will be made to ensure they are 

working properly.

                   SECONDARY SERVICING TASKS

Co-Processor

     The DF-224 is the HST's flight systems computer.  One of the 

computer's six memory units has failed and another has partially 

failed.  Hubble requires only three memory units to fully 

function, so the failures have not affected telescope operations.  

However, to restore the memory redundancy and augment the 

telescope's memory capacity and speed, a co-processor, based on 

386-computer architecture, will be integrated into the flight 

systems computer, which will increase both flight computer memory 

and the speed of some operations.

     The DF-224 co-processor will be installed on top of the HST 

computer located in a compartment on the telescope.  The memory 

upgrade is installed using handles on the computer and attaching 

four bolts using a power tool.

Goddard High Resolution Spectrograph Redundancy Kit

      The GHRS has two detector systems.  Because of the 

anomalous behavior of a low-voltage power supply, the side-one 

detector no longer is used.  The redundancy kit consists of an 

externally mounted relay box that enhances system redundancy so 

that the side-one detector can be used and the side-two detectors 

will not be compromised if the anomaly recurs. 

     Made up of four cables and a relay box, the Goddard High 

Resolution Spectrograph redundancy kit is designed to bypass an 

erratic detector system on the science instrument located in an 

instrument bay on the lower portion of the HST.  The relay box is 

installed first using a power tool similar to an electric drill.  

This is followed by attachment of the four cables.

           HUBBLE SPACE TELESCOPE TOOLS AND CREW AIDS

     The crew of STS-61 has more than 200 tools and crew aids 

with them for the servicing of the Hubble Space Telescope.  The 

tools and crew aids, known as Space Support Equipment (SSE) 

hardware, range from a simple bag for carrying some of the 

smaller tools to sophisticated, battery operated power equipment.  

These tools will be used by the EVA crew members servicing the 

spacecraft.

Crew Aids

     Crew aids are defined as those that are fixed in place and 

those that are portable equipment items but not hand tools, used 

to assist crew members in accomplishing servicing mission tasks.  

SSE equipment crew aids permit the crew members to maneuver 

safely or to restrain themselves, transfer Orbital Replacement 

Units (ORUs) and other portable items, protect equipment and 

themselves during changeout activities and temporarily stow or 

tether equipment during EVAs. 

     Examples of crew aids are handrails, handholds, translation 

devices, transfer equipment, protective covers, tethering 

devices, grapple fixtures, foot restraint sockets and stowage and 

parking fixtures.

Tools

     Tools are hand-operated or manipulated devices that allow 

the EVA astronauts to increase the efficiency of performing 

intricate, labor-intensive tasks. 

Stowage

     The tools and crew aids will be stowed on or in the Solar 

Array Carrier (SAC), Orbital Replacement Unit Carrier (ORUC), 

Flight Support System (FSS), HST Tool Box, Sidewall-mounted 

adapter plates, Provisions Stowage Assembly (PSA), an Adaptive 

Payload Carrier (APC), middeck lockers, aft flight-deck and 

airlock.  Tools and crew aids are provided by Johnson Space 

Center, Houston, and Goddard Space Flight Center, Greenbelt, Md.

Uses

     Tools and crew aids considered "general," with a wide 

variety of uses, include the Power Ratchet Tool (PRT), 

Multi-setting Torque Limiter (MTL), adjustable extension with 

7/16th-inch sockets, ingress aids, portable work-light receptacle 

and a locking connector tool.  More specific, but still 

considered general, items are a low-gain antenna (LGA) cover, 

umbilical connector covers, a flight support system (FSS), 

berthing and positioning system (BAPS), support post and a 

multi-layer insulation (MLI) repair kit.

    To be used on the changeout of the Wide Field Planetary 

Camera 2 (WFPC2) are the WFPC handholds, WFPC guide studs, 

quick-release zip nuts, WFPC pick-off mirror cover, forward 

fixture, aft fixture and the HST radial bay cover.

     For the High Speed Photometer (HSP) replacement with the 

Corrective Optics Space Telescope Axial Replacement (COSTAR), 

tools and aids to be used will be the COSTAR contamination cover, 

a COSTAR handling aid, an HSP handling aid, forward fixture, aft 

fixture and an axial Science Instrument Protective Enclosure 

(SIPE) safety bar.

     For the solar array replacement, the astronauts will use 

articulating foot restraints, solar array primary drive mechanism 

handles, solar array temporary stowage brackets (TSBs), solar 

array transfer handles, solar array jettison handle, solar array 

spines, Portable Flight Release Grapple Fixture (PFRGF) and a 

Marmon clamp. 

     For the changeout of the gyro rate sensor units, crew 

members will use a Portable Foot Restraint (PFR) socket converter 

(90-degree), Fixed-Head Star Tracker (FHST) light shade covers 

and a FHST delta plate cover.

              Orbital Replacement Unit Carrier art

                   Flight Support System art

                        HST Tool Box art

              Berthing and Positioning System art

                            IOBO art

Portable Foot Restraint

     There are two Hubble Space Telescope portable foot 

restraints built for use on the STS-61 mission.  These restraints 

are used by the spacewalking astronauts during the five 

extravehicular activities to provide a stable platform from which 

to work.  Both restraints are stowed in the payload bay, one on 

the left side and the other on the flight support system.

Tool Box

    The HST tool box is designed to stow individual tools, tool 

boards and tool caddies that will be used throughout the mission.  

The box is mounted on the right side of the payload bay.  Each 

tool inside the box is stowed in a specific location with 

markings to assist the astronauts in the retrieval and stowage.

Power Ratchet Tool (PRT)

     The Goddard-provided power ratchet tool (PRT) is powered by 

a 28-volt battery.  Made of titanium and aluminum, the 17-inch 

(43-centimeter) tool will be used for tasks requiring controlled 

torque, speed or turns and can be used where right-angle access 

is required.  It will provide 25 foot-pounds of pressure in the 

motorized mode and 75 foot-pounds of pressure in the manual mode.  

It has a speed of 10 to 30 revolutions per minute.  A spare power 

ratchet will be carried on the mission, as will spares for all 

other tools to be used by the astronauts.

HST Power Tool

    This tool is a modified, battery-operated power tool with 

torque and rpm control.  The design includes a 3/8-inch drive 

fitting, forward and reverse drive rotation, torque ranges from 

50 to 300 inch-pounds and a bracket for mounting the tool to the 

spacesuit.

Mini-Power Tool

     The mini-power tool is a battery-operated screwdriver 

intended for use when a larger power tool is not required and 

when work space is limited.  It can be used as a power tool or 

with the power off, the output shaft is locked automatically for 

use as a manual driver.

Multisetting Torque Limiter

     This tool is provided to prevent damage to hardware due to 

the application of torque which may exceed the design limits.  

Multisetting torque limiters are used in conjunction with the 

power tools or hand tools that interface with bolts and latches 

on the telescope.

Adjustable Extensions

     Several extensions were designed to be adjustable to ease 

the movement of the astronauts while reducing the time required 

for tool changeouts.  The adjustable extensions replace several 

fixed length extensions by providing adjustment from 12 to 16.5 

inches.  Another adjustable extension provides lengths from 15 to 

24 inches.  When retracted, these extensions reduce the potential 

for damage to other hardware.

                              IMAX

     THE IMAX project is a collaboration between NASA and the 

Smithsonian Institution's National Air and Space Museum to 

document significant space activities using the IMAX film medium.  

This system, developed by IMAX Systems, Corp., Toronto, Canada, 

uses specially designed 70mm film cameras and projectors to 

record and display very high definition large-screen pictures.

     An IMAX camera system will be flown on Shuttle Mission 

STS-61 and will be used by Endeavour's crew to collect material 

for upcoming IMAX productions.  IMAX cameras have flown on 

several Shuttle missions and film from those missions was used to 

form the IMAX productions The Dream is Alive  and The Blue 

Planet.

In-Cabin IMAX Camera Equipment

     The IMAX system consists of a camera, lenses, rolls of film, 

two magazines with film, an emergency speed control, a Sony 

recorder and associated equipment, two photographic lights, 

supporting hardware in the form of mounting brackets to 

accommodate the mode of use, two cables and various supplemental 

equipment.

     The IMAX and supporting equipment are stowed in the middeck 

for in-cabin use.  The IMAX uses two film magazines which can be 

interchanged as part of the operation.  Each magazine runs for 

approximately 3 minutes.  When both magazines are consumed, 

reloading of the magazines from the stowed supply of film is 

required.  Lenses are interchanged based on scene requirements.  

The IMAX will be installed in the orbiter middeck approximately 7 

days prior to launch.

IMAX Cargo Bay Camera (ICBC)

     During Shuttle Mission STS-61, an IMAX Cargo Bay Camera 

(ICBC) will be carried in the payload bay of Endeavour and used 

to document activities associated with the servicing of the 

Hubble Space Telescope.  The camera is mounted in a pressure 

sealed container with a viewing window.  The window has a sliding 

door which opens when the camera is in operation.  The camera is 

controlled from the aft-flight deck, exposing the film through a 

30mm fisheye lens.

                 AIR FORCE MAUI OPTICAL SYSTEM

     The Air Force Maui Optical System (AMOS) is an 

electrical-optical facility on the Hawaiian island of Maui.  No 

hardware is required aboard Discovery to support the experimental 

observations.  The AMOS facility tracks the orbiter as it flies 

over the area and records signatures from thruster firings, water 

dumps or the phenomena of "Shuttle glow," a well-documented 

fluorescent effect created as the Shuttle interacts with atomic 

oxygen in Earth orbit.  The information obtained by AMOS is used 

to calibrate the infrared and optical sensors at the facility. 

  DTO-667: PILOT INFLIGHT LANDING OPERATIONS TRAINER (PILOT)

     One of the challenges to flying long duration Shuttle 

missions is the issue of orbiter landing tasks requiring a high 

level of skill and proficiency yet data showing that a pilot's 

landing skills degrade after an extended absence from a landing 

trainer such as the Shuttle Training Aircraft.  During Shuttle 

Mission STS-61, a portable scientific workstation designed to aid 

the Shuttle commander and pilot in maintaining those landing 

skills will be demonstrated for the second time. 

     The PILOT system hardware, which flew on Shuttle Mission 

STS-58 in October 1993, consists of a portable scientific 

workstation, a high resolution color display and a hand 

controller with orbiter look and feel.  The software used in the 

system was transferred from the Shuttle Engineering Simulator 

software which is used to validate Shuttle flight software.  This 

provides PILOT with orbiter handling and guidance 

characteristics.

     The PILOT system is stowed in lockers on the flight deck and 

middeck areas of the Space Shuttle.  When a member of the crew 

wants to use the system, the workstation is mounted on a counsole 

directly in front of the pilot's seat on the flight deck and the 

PILOT system hand controller is attached to the orbiter's hand 

controller.

     In addition to evaluating the ability to maintain landing 

skills of a Shuttle crew in Earth-orbit, the PILOT system may be 

integrated into the standard training activities of all Shuttle 

crews at the Johnson Space Center in Houston.

                    STS-61 CREW BIOGRAPHIES

     Richard O. Covey, 47, Col., USAF, is Commander (CDR) of 

STS-61.  Selected as an astronaut in January 1978, Covey 

considers Fort Walton Beach, Fla., his hometown and will be 

making his fourth space flight.

     Covey graduated from Choctawhatchee High School, Shalimar, 

Fla., in 1964; received a bachelor of science degree in 

engineering sciences with a major in astronautical engineering 

from the U.S. Air Force Academy in 1968, and a master of science 

degree in aeronautics and astronautics from Purdue University in 

1969.

     Covey first flew as Pilot for Shuttle mission STS 51-I in 

August 1985.  He next flew as Pilot on STS-26 in September 1988.  

On his most recent flight, he was Commander for STS-38 in 

November 1990.  Covey has logged over 385 hours in space.

     Kenneth D. Bowersox, 37, Cmdr., USN, will serve as Pilot 

(PLT).  Selected as an astronaut in June 1987, Bowersox was born 

in Portsmouth, Va., but considers Bedford, Ind., his hometown and 

will be making his second space flight.

     Bowersox graduated from Bedford High School, Bedford, Ind.; 

received a bachelor's degree in aerospace engineering from the 

Naval Academy in 1978 and a master of science degree in 

mechanical engineering from Columbia University in 1979.

     Bowersox first flew as Pilot for Shuttle mission STS-50 in 

June 1992.  He has logged over 331 hours in space.

     Tom Akers, 42, Lt. Col., USAF, will serve as Mission 

Specialist 5 (MS5) and as one of the extravehicluar activity crew 

members.  Selected as an astronaut in June 1987, Akers was born 

in St. Louis, Mo., but considers Eminence, Mo., his hometown and 

will be making his third space flight.

     He graduated from Eminence High School and received bachelor 

and master of science degrees in applied mathematics from the 

University of Missouri-Rolla in 1973 and 1975, respectively.

     Akers served as a mission specialist on STS-41 in October 

1990.  His next flight was as a mission specialist on STS-49 in 

May 1992.  Akers was one of the EVA crew members of a 

three-person spacewalking team that successfully captured the 

stranded International Telecommunications Satellite.  He also 

performed a second EVA on STS-49 to evaluate space station 

construction techniques.  He has logged over 311 hours of space 

flight.

     Jeffrey A. Hoffman, 49, will be Mission Specialist 3 (MS3) 

and serve as one of  the extravehicular activity crew members.  

Selected as an astronaut in January 1978, Hoffman considers 

Scarsdale, N.Y., his hometown and will be making his fourth space 

flight.

     Hoffman graduated from Scarsdale High School, received a 

bachelor's degree in astronomy from Amherst College, received a 

doctorate in astrophysics from Harvard University and received a 

master's degree in materials science from Rice University.

     Hoffman first flew on STS-51D in April 1985, a mission 

during which he performed a spacewalk in an attempt to rescue a 

malfunctioning satellite.  He next flew on STS-35 in December 

1990.  Hoffman made his third space flight as Payload Commander 

and mission specialist on STS-46 in July 1992.

     F. Story Musgrave, 58, will be Mission Specialist 4 (MS4).  

He also will serve as Payload Commander and as a member of the 

extravehicular activity team.  Selected as an astronaut in August 

1967, Musgrave considers Lexington, Ky., his hometown and will be 

making his fifth space flight.

     Musgrave graduated from St. Mark's School, Southborough, 

Mass., in 1953; received a bachelor's degree in mathematics and 

statistics from Syracuse University in 1958; received a master's 

degree in operations analysis and computer programming from the 

University of California at Los Angeles in 1959; received a 

bachelor's degree in chemistry from Marietta College in 1960; 

received a doctorate in medicine from Columbia University in 

1964; received a master's degree in physiology and biophysics 

from the University of Kentucky in 1966 and received a master's 

degree in literature from the University of Houston in 1987.

     Musgrave flew as a mission specialist on STS-6 in April 

1983, on Spacelab-2 in August 1985 and on STS-33 in November 

1989.  More recently, he served aboard Space Shuttle Atlantis, 

STS-44 in November 1991.  He has logged more than 598 hours in 

space.

     Claude Nicollier, 49, will be Mission Specialist 2 (MS2).  

Under an agreement with the European Space Agency and NASA, he 

was selected as an astronaut in 1980.  Nicollier was born in 

Vevey, Switzerland, and will be making his second space flight.

     Nicollier graduated from Gymnase de Lausanne, Lausanne, 

Switzerland, received a bachelor's degree in physics from the 

University of Lausanne and received a master's degree in 

astrophysics from the University of Geneva.  Nicollier first flew 

as a mission specialist on STS-46 in July 1992 and has logged 

more than 191 hours in space.

     Kathryn C. Thornton, 41, will serve as Mission Specialist 1 

(MS1) and as one of the extravehicular activity crew members.  

Selected as an astronaut in May 1984, Thornton was born in 

Montgomery, Ala., and will be making her third space flight.

     Thornton received a bachelor of science degree in physics 

from Auburn University and a master of science degree and a 

doctorate in physics from the University of Virginia.  Thornton 

was awarded a NATO postdoctoral fellowship to continue her 

research at the Max Planck Institute of Nuclear Physics in 

Heidelberg, Germany.

     Thornton first flew as a mission specialist on STS-33 in 

November 1989.  On her second flight, she served on the crew of 

STS-49 in May 1992.  On STS-49, Thornton performed an 

extravehicular activity to evaluate space station assembly 

techniques.  She has logged over 333 hours in space.    

               STS-61 ACRONYMS AND ABBREVIATIONS

A-h       ampere-hour

ac        alternating current

ACE       actuator control electronics

ACP       astronaut control panel

AD        aperture door

AFD       aft flight deck

APS       antenna pointing system

AS        aft shroud

ATM       Apollo Telescope Mount

BAPS berthing and positioning system

BCU       bus coupler unit

BOD       bright object detector

BOL       beginning of life   

BOT       beginning of travel

BPRC battery protection and reconditioning circuit

bps       bits per second

BPRC battery protection and reconditioning circuit

BPSK biphase shift keyed

BREC body rate error check

C&DH communication and data handling

C/C       configuration control

CC        cargo control

CCC       charge current controller

CCTV closed-circuit television

CDI       command and data interface

CDU       command detector unit

CFRP carbon-fiber-reinforced plastic

CGG       contingency gravity gradient

CIF       computer interface 

CMD       command module

COM       communications module

CORU candidate orbital replacement unit

CPM       central processor module

CPU       central processing unit

CSM       cargo systems manual

CSS       coarse Sun sensor

CU/SDF    control unit/science data formatter

D/A       digital to analog

DAK       double-aluminized Kapton

DBA       diode box assembly

dc        direct current

DCE       deployment control electronics

DIH       discrete input high

DISP      display

DIU       data interface unit

DIUI      DIU interface module

DMS       data management subsystem

DMU       data management unit

DPC       direct power converter

ECA       electronics control assembly

ECU       electronics control unit

ED        engineering data

EDB       external data bus

EMI       electromagnetic interference

EOL       end of life

EOT       end of travel

EP/TCE    electrical power/thermal control electronics

EPS       electrical power subsystem

ES        equipment section

ESA       European Space Agency

ESTR engineering/science tape recorders

EU        electronics unit or expander unit

EVA       extravehicular activity

FEP       fluorinated ethylene-propylene

FGE       fine guidance electronics

FGS       fine guidance sensor

FHST fixed head star tracker

FHSTI     FHST interface 

FIFO      first in first out

FMDM flexible multiplexer/demultiplexer

FOC       faint object camera

FOD       Flight Operations Directorate

FOS       faint object spectrograph

FOV       field-of-view

F/S       filter/shaper 

FPA       focal plane assembly

FPDA focal plane deck assembly

FPSA      focal plane structure assembly

FS        forward shell

FSS       flight support system

FWH  flexible wire harness

GEA       gimbal electronics assembly

GG        gravity gradient

GGM       GG mode

GPC       general purpose computer

GSE       ground support equipment

GSFC Goddard Space Flight Center

GSTDN     ground spaceflight tracking and data network

HGA       high-gain antenna

HLD       high-level discrete

HOSC Huntsville Operations Support Center

HRS       high resolution spectrograph

HSP       high-speed photometer

HST       Edwin P. Hubble Space Telescope

HWL       hardware load

I&C       instrumentation and communication

ICAPC     increased capacity adaptive payload carrier

ICU       instrumentation control unit

IDB       internal data bus

IMU       inertial measurement unit

IOU       input/output unit

IPCU      interface power control  unit

IR        infrared

JSC       Lyndon B. Johnson Space Center

KA        keep alive

kbps      kilo bits per second

KSC       Kennedy Space Center

LGA       low-gain antenna

LLD       low-level discrete

LMU       logical memory unit

LS        light shield

LMSC Lockheed Missiles and Space Company

MA        multiaccess

Mbps megabits per second

MCC       Mission Control Center

MCC-H     MCC - Houston

MCE       monitor and control electronics

MCU       mechanism control unit

MDB       multiplexed data bus

MET       mission elapsed time

MLD       manual locking device

MLI       multilayer insulation

MMS  multimission modular spacecraft

MOD       Mission Operations Directorate

MR        main ring

MRA       main ring assembly

MSB       most significant bit

MSFC Marshall Space Flight Center

MSS       magnetic sensing system

MT        magnetic torquer

MTE       magnetic torquer electronics

MTP       master timing pulse

MTS       magnetic torquing system

MU        memory unit

N.m       Newton meter

NASA National Aeronautics and Space Administration

NASCOM    NASA communications

NGT       NASCOM ground terminal

nm        nanometer

NSSC-I    NASA Standard Spacecraft Computer, Model I

OAO       Orbiting Astronomical Society

OCE       optical control subsystem

OCS       optical control subsystem

OCXO ovencontrolled crystal oscillator

OLD       offload device

OPI       Orbiter payload interrogator

ORU       orbital replaceable unit

ORUC ORU carrier

OSO       Orbiting Solar Observatory

OTA       optical telescope assembly

OV        orbital verification

P-E       Perkin-Elmer Corporation

PC        planetary camera

PCM       pulse-code modulation

PCS       pointing control subsystem

          pointing control system

PCU       power control unit

PDI       payload data interleaver

PDM       primary deployment mechanism

PDU       power distribution unit

PI        payload interrogator

PI/KUSP   PI/Ku-band signal processor

PIT       process interface table

PLBD payload bay door

PLR       payload recorder

PM        primary mirror

PMA       primary mirror assembly

PMB       primary mirror baffle

PMT       photomultiplier tube

PMU       physical memory unit

PN        pseudorandom noise

POCC Payload Operations Control Center

PRCS primary react ion control system

PRI       primary

PRIPL     unregulated Orbiter power

PRLA payload retention latch assembly

PROM programmable read-only memory

PSEA pointing and safe-mode electronics assembly

psi       pounds per square inch

psia      pounds per square inch absolute

PSP       payload signal processor

PSP/PI    PSP/payload interrogator

QD        quick disconnect

RBM       radial bay module

RED       redundant

RF        radio frequency

RFI       radio frequency interface

RGA       rate gyro assembly

RGAI      RGA interface 

RIG       rate integrating gyro

RIU       remote interface unit

RMGA retrieval mode gyro assembly

RM        remote module

RMS       remote manipulator system

ROM       read-only memory

RPA       reaction plate assembly

RSOC Rockwell Shuttle Operations Company

RSU       rate sensor unit

RTC       real-time command

RWA       reaction wheel assembly

SA        solar array

SAD       SA drive

SADA SA drive adapter

SADE SA drive electronics

SADM SA drive mechanism

SD        science data or scientific data

SDM       secondary deployment mechanism

SI        scientific instrument

SIC&DH    scientific instrument control and data handling

SIP       standard interface panel

SIPE      scientific instrument protective enclosure

SISS      SI support structure

S/M       safe mode

SM        secondary mirror

SMA       secondary mirror assembly

SMB       secondary mirror baffle

SMC       safemode computer

SMCH standard mixed cargo harness

SMSA secondary mirror subassembly

SM4       safe-mode utility

SOC       state-of-charge

SPA       solar panel assembly

SPC       stored program command

SPG       single-point ground

SQPSK     staggered quadiphased, shift-keyed

SS        safing system

SSA       S-band single-access

SSC       Science Support Center

SSE       space support equipment

SSM       support systems module

SSM-ES    SSM equipment shelf

SSP       standard switch panel

SSS       star selector servo

STACC     standard telemetry and command components

STDN space flight tracking and data network

STINT     standard interface

STOCC     Space Telescope Operations Control Center

STS       Space Transportation System

STSCI     Space Telescope Science Institute

TAG       two-axis gimbal

TBD       to  be determined

TCE       thermal control electronics

TCS       thermal control subsystem

TCXO temperature controlled crystal oscillator

TDRS tracking and data relay satellite

TDRSS     TDRS system

TFC       TLM format control

TIM       timing interface module

TLM       telemetry

TRI       tape recorder interface

TTL       transistor-to-transistor logic

UDM       umbilical disconnect mechanism

ULE       ultralow expansion

URM       umbilical retraction mechanism

UV        ultraviolet

VATA Vehicle Assembly and Test Area

VCO       voltage controlled oscillator

VSS       vehicle support software

VSWR voltage standing wave radio

WF/PC     wide field/planetary camera

WFC       wide field camera

WSGT White Sands Ground Terminal

                            - end -