Spacewalks by four astronauts to highlight third servicing mission

Space Shuttle Discovery is poised to launch December 9 on the third visit to the Hubble Space Telescope that will include four spacewalks designed to install new equipment and replace old. The liftoff is set to occur at the beginning of a 42-minute launch window opening at 1:10 a.m. Eastern Standard Time. The launch time will be refined one final time closer to the launch when the flight dynamics team obtains updated trajectory data for Discovery's rendezvous with Hubble.

Seven astronauts are ready to pay this visit to Hubble a little sooner than originally planned so that its gyroscope complement can be restored to full capacity. In addition, other tasks will be completed that originally had been scheduled for next year. The mission will feature four spacewalks, or extravehicular activities (EVA's), to ensure the health of the first of NASA's Great Observatories launched nearly a decade ago. Each of the spacewalks is planned to last about six hours with specific tasks laid out to maximize the efficiency of the work to be done.

The primary objective is to replace all six gyroscopes that make up the three Rate Sensor Units. In addition, astronauts will install a new computer that will dramatically increase the computing power, speed, and storage capability of HST. They will change out one of the Fine Guidance Sensors and replace a tape recorder with a new Solid State Recorder. The EVA crew also will install a new S-band single access transmitter and voltage/temperature improvement kit for the telescope's nickel-hydrogen batteries. Finally the crew will begin repair of the insulation on the telescope's outer surface that has deteriorated in the years since it was launched.

Steve Smith services the Hubble Space Telescope during the STS-82 mission.

The STS-103 mission will be commanded by veteran astronaut Curt Brown (Col., USAF), who will be making a record-tying sixth voyage to space and third as commander. Making his first flight into space is pilot Scott Kelly (Lt. Cmdr.,USN).

Five mission specialists are assigned to the flight. European Space Agency (ESA) Astronaut Jean-Francois Clervoy is Mission Specialist 2 serving as the flight engineer and primary robot arm operator. He will be making his third flight on the shuttle. The four remaining crewmembers will form two teams to perform the four spacewalks. Mission Specialist 1 and Payload Commander is Steven Smith. He's flying on the shuttle for the third time and will team with John Grunsfeld on the first and third EVAs. Grunsfeld, Mission Specialist 3, also will be making his third flight into space. Mission Specialist 4, Michael Foale, and Mission Specialist 5, Claude Nicollier of the European Space Agency, will team on the second and fourth spacewalks. Foale will be going to space for the fifth time and Nicollier for the fourth.

Though the four spacewalking astronauts began training for this mission more than a year ago, the remaining three crewmembers were not named until this past March when the Hubble project called for this earlier-than-scheduled visit to replace the ailing gyroscopes. The training consisted of underwater activity in the Neutral Buoyancy Laboratory near the Johnson Space Center; and hands-on training in the Goddard Space Flight Center's 12,500 square-foot cleanroom.

As was the case with the previous servicing missions, the crew practiced every task it will have to perform during the four scheduled spacewalks. More than 150 special tools and crew aids have been developed for the servicing missions.

STS-103 will be the 27th flight of Discovery and the 96th mission in the history of the Space Shuttle Program.

HST Servicing Mission 3A -- COST TO TAXPAYERS

NASA's Hubble Space Telescope is the first observatory designed for routine maintenance, upgrade, and refurbishment on orbit. The program is planned as a 20-year mission with periodic servicing by Shuttle astronauts. Hubble's modular design allows for more than 90 spacecraft components and all of its scientific instruments to be replaced on orbit. Servicing maintains the spacecraft, ensures operation at maximum scientific efficiency and allows for incorporation of new technology.

Hubble was launched on April 24, 1990 with a full complement of six scientific instruments. At that time, an inventory of spare HST hardware was available to support future servicing missions. Since launch, HST budgets have been sized to develop new instruments, to maintain the spare hardware, to sustain hardware expertise, to plan and develop servicing activities, and to test and integrate the payloads with the Shuttle.

Due to gyroscope failures, a servicing mission was needed as soon as replacement hardware could be ready. Servicing Mission 3 (scheduled for June 2000) was divided into two flights --- servicing mission 3A (SM3A), and servicing mission 3B (SM3B), scheduled for no earlier than the Spring of 2001. Much of the hardware planned for servicing mission 3 will not be ready in time for the first flight, and will therefore be installed on SM3B.

The cost to carry out this mission is $136 million. This includes $19 million of HST costs for the additional servicing mission, $7 million of HST costs to switch from Columbia to Discovery, and $110 million for the Shuttle to carry out the mission and replace Space Shuttle flight hardware previously assigned to another mission. NASA has also spent approximately $69 million on Servicing Mission 3A, in addition to the $136 million, reflecting the costs of building and testing the planned replacement hardware, ground operations and other related activities.

All six gyroscopes will be replaced during the STS-103 (SM3A) mission. The fourth of the sixth existing gyroscopes failed on Nov. 13, forcing Hubble to suspend scientific operations until the servicing mission is completed.

In addition, the crew will replace a guidance sensor (a unit brought back to the ground after the last mission and refurbished) and the spacecraft's computer. The new computer will reduce the burden of flight software maintenance and significantly lower operating costs. A voltage/temperature kit will be installed to protect spacecraft batteries from overcharging and overheating in certain, infrequent spacecraft modes of operation. A new radio frequency transmitter will replace a failed spare one currently aboard the spacecraft, and a spare solid state recorder will be installed to allow more efficient handling of high-volume data.


HST Program & STS-103 Costs

Servicing Mission Costs - HST
Planned Servicing Mission Hardware & Software
Gyroscope	$8 Million
Fine Guidance Sensor	$13 Million
Advanced Computer	$7 Million
Other Flight Hardware	$11 Million
Simulators/Testing	$6 Million
Ops/Software Development	$24 Million
Sub-total	$69 Million
Costs for Flight Changes
HST Cost for Additional Servicing Mission	$19 Million
HST Cost for Switching from Columbia to Discovery	$7 Million
Sub-total	$26 Million
HST Total	$95 Million
Servicing Mission Costs - Shuttle
Shuttle Flight Costs	$110 Million
Total STS-103 Mission Costs
Shuttle	$110 Million
HST	$95 Million
Total	$205 Million

Plans for the Future

The Hubble Space Telescope's purpose is to spend 20 years probing the farthest and faintest reaches of the cosmos. Routine servicing missions will continue to refine and enhance the telescope's capabilties. Two additional servicing missions and a close-out mission are planned.

Three instruments are currently in active scientific use on Hubble - the Wide Field and Planetary Camera 2, the Space Telescope Imaging Spectrograph, and Fine Guidance Sensor 1R, which has been designated as the prime Fine Guidance Sensor for astrometric science. Other instrument bays are occupied by the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), which is now dormant due to the depletion of its solid nitrogen cryogen, the Faint Object Camera, which has been decommissioned, and the corrective optical device called COSTAR, which is no longer needed.

Servicing Mission 3B -- Spring 2001

The next servicing mission will focus on installing the Advanced Camera for Surveys and more efficient rigid solar arrays. Astronauts also will install the aft shroud cooling system. In addition, an advanced cooling system will be installed on NICMOS, which became dormant after its solid nitrogen coolant was exhausted in January 1999. The application of new external thermal coverings will be completed, if necessary.

Advanced Camera for Surveys

During this mission, scheduled for Spring 2001, astronauts will install a new science instrument, the Advanced Camera for Surveys (ACS). The Advanced Camera for Surveys will physically replace the Faint Object Camera. This new instrument is designed for survey mode imagery and discovery. It is estimated that the survey capability of the Telescope will be increased tenfold. A major objective for the ACS is mapping the distribution of dark matter throughout the universe. Several other maintenance activities are planned over four EVA days. A few of the activities are discussed below.

Solar Array III

Two large flexible solar array wings provide power to Hubble. During Servicing Mission 1, the original European Space Agency arrays were replaced with a new upgraded set of solar arrays. These arrays consist of silicon cells installed on a thin layer of Kapton blanket. When these arrays are replaced they will have powered the Telescope for nearly 7 years.

The newest arrays are rigid arrays, which do not roll up and therefore are more robust. They are also smaller and more efficient and will slightly reduce the effects of atmospheric drag on the spacecraft. The arrays to be installed on that servicing mission have several enhancements and incorporats new technology: The cells are made from gallium arsenide which is more efficient than the original silicon cells. The frames are made of lightweight Lithium Aluminum alloy tubes, in an "H"-shaped configuration. Each wing can be folded for transport, and then easily locked into place when fully deployed.

NICMOS Cooling System

The NICMOS Cooling System, an experimental mechanical cooling system, will be connected to NICMOS to return it to normal operation.

Aft Shroud Cooling System

This new system is designed to carry heat away from scientific instruments in the Aft Shroud area of the Telescope assembly and to allow the instruments to operate better at lower temperatures. The cooling system allows multiple instruments to operate simultaneously, helping the science team maintain the program's high productivity

Possible Reboost

Although the atmosphere is quite thin at satellite altitudes, it is not a perfect vacuum. Over time, all low Earth orbiting satellites feel the effects of atmospheric drag and lose altitude. If the altitude is not restored, the Telescope eventually will reenter Earth's atmosphere. Hubble has no on-board propulsion, so the only way to restore lost altitude is by the creative use of shuttle jets. If necessary, Hubble will be reboosted to a higher altitude. This was done on both Servicing Missions 1 and 2.

Servicing Mission 4 -- 2003

Plans for the fourth servicing mission are very preliminary at this time, but two Science Instruments are in development. The corrective optics package installed on the first servicing mission will be removed during this mission to make room for the Cosmic Origins Spectrograph. Wide Field Camera 3 will replace the Wide Field Planetary Camera 2. Also a refurbished Fine Guidance Sensor will be in-stalled leaving Hubble in optimum condition.

Cosmic Origins Spectrograph

The Cosmic Origins Spectrograph (COS) is a medium resolution spectrograph specifically designed to observe into the near and mid ultraviolet. COS coupled to Hubble's optics will be the most sensitive spectrograph ever flown in space. The ultraviolet region is particularly interesting for observing hot objects such as new hot stars and quasars. It is also a good region for viewing the composition and character of interstellar and intergalactic gas. COS will measure the chemical composition of the gas between the galaxies at great distances, as it was when the universe was very young.

Wide Field Camera Three

Wide Field Camera Three (WFC3) will be the last imaging camera mounted on HST. WFC3 will replace the current workhorse of Hubble, Wide Field and Planetary Camera 2. WFC3 will be a "panchromatic" camera, extending Hubble's imaging capability over an enormous range of wavelengths from the ultraviolet to the near-infrared. It will provide important backup to the ACS in visible light and will supersede the near-infrared capability of the aging NICMOS. This upgrade will allow Hubble to maintain good imaging capa-bilities throughout the remainder of its mission.

Fine Guidance Sensor

The Fine Guidance Sensors are systematically refurbished and upgraded. In "round-robin" fashion, one FGS per servicing mission is being replaced. The returned FGS is disassembled and refurbished, and then taken back to Hubble on the next servicing mission to replace the next FGS. By the conclusion of SM4 all three FGS's will have been brought up to optimum condition in this manner.

Closeout Mission -- 2010

NASA will determine the best approach to secure the Telescope, upon the completion of Hubble's 20-year mission. Currently there are several options being considered, ranging from staying in orbit indefinitely through a large reboost, to a return to ground.