PUBLIC INFORMATION OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Analysis of data received following Galileo's successful course change last month shows that one of two check valves in the helium pressurization system apparently remains open. However, project engineers have determined that the problem can be managed by carefully controlling the spacecraft's propellant temperatures.
The purpose of these valves -- one on the fuel side and one on the oxidizer side of the propellant system -- is to limit the amount of propellant vapor that can flow upstream and potentially condense and subsequently react and, in a possible but very unlikely scenario, damage the propellant feed system. Galileo project engineers plan to manage the propellant temperatures and pressures to minimize the possibility of reaction. Even without this additional propellant temperature and pressure management, project officials say, Galileo's propulsion system design makes the potential for any harmful interaction of the propellants very low. "With temperature management," says Project Manager Bill O'Neil, "Galileo's maneuvers and mission will be unaffected by open check valve."
After studying the detailed data received during and in the days following the July 27 orbiter deflection maneuver, Galileo propulsion engineers now estimate the steady-state thrust level of the 400-newton engine is 3 percent below the pre-flight performance prediction, and this is well within the 6 percent tolerance on that value.
On August 28 (Pacific Daylight Time), Galileo performed a small trajectory correction maneuver to fine-tune its flight path for a close flyby of Jupiter's satellite Io on December 7. The maneuver also put Galileo in position to collect data from the recently released probe that will enter Jupiter's atmosphere on December 7. Galileo is on course for the main engine burn that will bring it into orbit around Jupiter. The trajectory correction maneuver changed the spacecraft's velocity by less than 1 meter per second (2.2 miles per hour), slowing the spacecraft on its current trajectory by about 4 minutes in order to move it 1,950 kilometers (about 1,200 miles) to its targeted Io flyby point.
Galileo's dust detector has been observing an intense interplanetary dust storm apparently emanating from the Jovian system during much of August. The current event, generating more than 20,000 particle impacts per day, is one of several storms of increasing intensity observed since about a year ago. The normal interplanetary dust count is less than one particle per day. The first of these interplanetary dust streams were detected by the Ulysses spacecraft in 1992, when it flew by Jupiter on its way to study the poles of the Sun. Galileo has been commanded to collect and transmit dust data as often as three times daily instead of twice a week.
In further preparations during August for Galileo's Jupiter arrival and operations, the flight team deployed the relay radio antenna, which will track the probe and receive its telemetry during the atmospheric descent. The plasma instrument was also turned on and checked out.
The Galileo spacecraft is operating normally, spinning at about 3 rpm and transmitting at 10 bits per second. It is more than 760 million kilometers (470 million miles) from Earth, and 792 million kilometers (492 million miles) from the Sun. It still has nearly 55 million kilometers (34 million miles) to go before reaching Jupiter's system on December 7, 1995.
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