Without an additional Hubble Space Telescope (HST) Servicing Mission (SM4), the HST Project will face numerous challenges to keep the telescope operating for as long as possible. As part of SM4, the HST Project planned to install various upgrades to the telescope including the installation of new batteries and new rate integrating gyros. Without these upgrades, reliability analyses and trend projections indicate that the spacecraft will lose the capability to conduct science operations later this decade. The HST team is being challenged to maximize the telescope's remaining operational lifetime, and also maximize its science output and quality.
The two biggest areas of concern are the age and condition of the batteries and gyros. Together they comprise the largest risk to telescope productivity and safety and present the biggest challenges to the HST team. The six nickel-hydrogen (NiH2) batteries on HST are the original batteries from launch. With fourteen years of operational life, these batteries have -lasted longer than those on any comparable mission. Yet as with all batteries, their capacity has been declining. Engineers are examining various methods to prolong the life of these mission critical batteries, and retard the rate of degradation.
In addition to the batteries, the National Aeronautics and Space Administration (NASA) scheduled all six gyros to be replaced on SM4. Two of the six gyros have already failed, leaving four available for operational use. To be able to conduct science operations, the telescope currently needs three gyros. Efforts are underway to enable a guiding mode that will require only two gyros. In this mode, however, science target scheduling will be strongly driven by new factors (such as star tracker availability), which may ultimately reduce science gathering efficiency. The status on this effort and its potential impact on science operations will be discussed.
This paper will focus on these and other efforts to prolong the life of the HST, thus enabling it to remain a world-class observatory for as long as possible.
Older spacecraft missions, especially those in low Earth orbit with telemetry intensive requirements, required round-the-clock control center staffing. The state of technology relied on control center personnel to continually examine data, make decisions, resolve anomalies, and file reports. Hubble Space Telescope (HST) is a prime example of this description. Technological advancements in hardware and software over the last decade have yielded increases in productivity and operational efficiency, which result in lower cost. The re-engineering effort of HST, which has recently concluded, utilized emerging technology to reduce cost and increase productivity. New missions, of which NASA's Transition Region and Coronal Explorer Satellite (TRACE) is an example, have benefited from recent technological advancements and are more cost-effective than when HST was first launched.
During its launch (1998) and early orbit phase, the TRACE Flight Operations Team (FOT) employed continually staffed operations. Yet once the mission entered its nominal phase, the FOT reduced their staffing to standard weekday business hours. Operations were still conducted at night and during the weekends, but these operations occurred autonomously without compromising their high standards for data collections. For the HST, which launched in 1990, reduced cost operations will employ a different operational concept, when the spacecraft enters its low-cost phase after its final servicing mission in 2004. Primarily due to the spacecraft’s design, the HST Project has determined that single-shift operations will introduce unacceptable risks for the amount of dollars saved. More importantly, significant cost-savings can still be achieved by changing the operational concept for the FOT, while still maintaining round-the-clock staffing. It’s important to note that the low-cost solutions obtained for one satellite may not be applicable for other satellites. This paper will contrast the differences between low-cost operational concepts for a satellite launched in 1998 versus a satellite launched in 1990.