What's Up With Ulysses?, alive? dead? cancelled soon? |
What's Up With Ulysses?, alive? dead? cancelled soon? |
Sep 27 2005, 04:05 AM
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Member Group: Members Posts: 356 Joined: 12-March 05 Member No.: 190 |
What is up with the tiny Ulysses spacecraft that was launched in 1990 to study the solar whatever at high lattitudes? Last I heard it was in danger of dying because the RTG power was running low and at aphelion there was a risk of the hydrazine freezing/exploding in its propulsion system. Well that was like a year ago and I haven't heard anything since. It looks like it should've passed aphelion by now and should be out of danger.....
Its been going up there for over a full solar cycle, is it one of the missions on the chopping block because of the new humans on moon/mars thing? |
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Feb 25 2008, 09:42 PM
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Junior Member Group: Members Posts: 55 Joined: 1-May 06 From: Cincinnati, Ohio Member No.: 758 |
Thermal Constraints of the Reaction Control Subsystem
From: http://ulysses-ops.jpl.esa.int/ulsfct//spa...ft/scframe.html Fuel-bearing components are specified to be kept above 5°C. This is to prevent the fuel, hydrazine, from freezing, which would cause two problems. Firstly, the fuel would not flow to the thrusters and no manoeuvres would be possible. Secondly, if the fuel were to subsequently thaw, pockets of expanding liquid could form possibly rupturing RCS sections. During the prime mission (1990-1995), meeting this requirement was not difficult, but with RTG power levels becoming so low it is no longer possible to keep remote RCS components above (5+margin)°C, particularly when the margins have been made particularly generous. In order to keep as much of the payload operating as safely possible, it is necessary to trim thermal margins to the lowest level. This in turn necessitates careful calibration of the spacecraft Thermal Model against in-flight temperature data. The Reaction Control Subsystem (RCS) has several thermistors that measure component temperatures directly, shown on the right. There are also thermistors elsewhere on the spacecraft that can be used to infer RCS component temperatures. Early in the mission, the available telemetry and generous thermal margins were sufficient to ensure compliance, however with steadily decreasing power availability, greater scrutiny of margins and more insight on the thermal behavior of all RCS components was necessary. - - - Sounds as if since 1995 things have been dicey when themal heating was low... Hydrazine freezes at 34 F (4 C) so holding temps above 5 C is a minimum requirement. Rob |
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