ICE / ISEE-3, First comet encounter September 1985 |
ICE / ISEE-3, First comet encounter September 1985 |
Guest_PhilCo126_* |
Jan 24 2007, 06:43 PM
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Guests |
Any weblinks where we can learn something about the where-abouts of ICE/ISEE ( International Comet Explorer / International Sun Earth Explorer ) as the craft was expected to return to Earth in 2014?
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Jul 9 2014, 12:38 AM
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#2
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Member Group: Members Posts: 723 Joined: 13-June 04 Member No.: 82 |
Mechanical 'hiccups' complicate satellite reboot mission
QUOTE Is NASA's forsaken ISEE-3 satellite finally headed home? On Tuesday a private team of engineers initiated a series of propulsive bursts intended to return the aging spacecraft to Earth orbit. However, several mechanical "hiccups" occurred that prevented the spacecraft from completing the maneuver and raised questions about the condition of the spacecraft's fuel system. The team will attempt to refire the spacecraft's thrusters on Wednesday. "The good news is the propulsion system works -- when it wants to," said Keith Cowing, a former NASA astrobiologist and a spokesman for the ISEE-3 Reboot Project. QUOTE On Tuesday, ISEE-3 completed the first of its seven burn sessions without a hitch. When engineers commanded the satellite to begin its second session however, it quickly became clear there was a problem.
"We could tell the valves and things were working, but we did not see that the spacecraft was changing its trajectory or speed, which told us something was going on," Cowing said. ISEE-3 is equipped with a dozen monopropellant hydrazine thrusters. Hydrazine, an extremely toxic substance, freezes at roughly the same temperature as water, so a series of heaters are used to liquefy the propellant before executing maneuvers. The hydrazine is kept in eight fuel tanks, which also contain pressurized gas. When the spacecraft receives a command to open a fuel valve, the pressurized gas forces the hydrazine through a fuel line and into a catalyst. The catalyst causes the hydrazine to break down, which produces a propulsive blast of hot gas. Unlike rockets taking off from Earth, the hydrazine blast is invisible to the human eye. Before executing the first burn on Tuesday, the reboot team turned off the fuel line heaters to save power, raising the possibility that the fuel had become frozen and thus unable to come in contact with the catalyst. "That's the first thing you think of," Cowing said. "But it could be something else. There may not be enough fuel for that to be an issue, or it's possible that the pressurant may have run out, or that there's a valve not doing its thing." Like most spacecraft, ISEE-3's propellant system contains numerous redundant elements, and Cowing said he was confident that the team would determine the cause of the firing failure and figure out a work-around solution. The window for ISEE-3's course alteration will remain open for several days. "Ideally, we would have done it today, but if we do it in the next day or two or three, we’re good to go," Cowing said. |
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