Max Planck Institute for Astronomy - Annual Report 2005
Max Planck Institute for Astronomy - Annual Report 2005
Max Planck Institute for Astronomy - Annual Report 2005
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Earth = Launch (L)<br />
Trajectory correction<br />
maneuver 1<br />
L + 15 hrs<br />
Sunshield<br />
deployment<br />
L + 2 days<br />
384 000 km<br />
Telescope<br />
deployment<br />
L + 4 days<br />
Observatory<br />
available <strong>for</strong><br />
ISIM activities<br />
L + 70 days<br />
Observatory<br />
»first light« (ISIM at safe<br />
operating temp)<br />
L + 59 days<br />
Moon<br />
Fig. IV.1.9: Timetable <strong>for</strong> the flight of JWST to its orbit around<br />
the Lagrangian Point L2. After 119 days (launch � 109 days)<br />
the final orbit is reached. A few days later the test operation of<br />
the instruments will begin.<br />
� 1500000 km<br />
impacts of micro-meteorites, the solar wind, cosmic rays,<br />
extreme temperature variations and manifold mechanical<br />
stresses in order to ensure the millionfold radiation reduction<br />
over the entire duration of the mission.<br />
The cameras of Miri, however, have to be cooled to<br />
– 268 °C (about 5 K). Here a decisive modification in<br />
the development took place in <strong>2005</strong>. Up to then work<br />
on a cryostat with solid hydrogen was in progress. With<br />
this simple and well-proven technique a just sufficient<br />
operating temperature of – 267 °C could be achieved.<br />
But in view of the desired weight cuts the cryostat<br />
soon appeared to be too heavy. There<strong>for</strong>e a mechanical<br />
cooling machine was chosen. The motor-driven first<br />
compressor stage will be placed on the satellite part of<br />
JWST and linked to the cooling head in Miri by flexible<br />
pipes. In principle this technique has advantages: lower<br />
temperatures, lower masses, almost unlimited operation<br />
times … . On the other hand there are risks concerning<br />
time, costs <strong>for</strong> development and testing, and the use of<br />
this new technique <strong>for</strong> a flagship mission without any<br />
possibility <strong>for</strong> maintenance or replacement. If this active<br />
cooling proves a success with JWST it probably will be<br />
used in many future missions.<br />
The involvement in the JWST mission offers the MPIA<br />
the chance to carry on in its tradition of interesting technological<br />
developments in infrared instrumentation, and<br />
guarantees participation in the most exciting scientific<br />
IV.1 Instruments <strong>for</strong> the James Webb Space Telescope 95<br />
L2 orbit<br />
achieved<br />
L + 109 days<br />
Trajectory<br />
correction<br />
maneuver 2<br />
(if required)<br />
L + 25 days<br />
L2<br />
Initiate ISIM<br />
testing and<br />
certification<br />
L + 113 days<br />
� 374000 km<br />
Lissajous-loops<br />
Fig. IV.1.10: For launch, the 6.5 m-telescope and its multi-layered<br />
radiation shield more than 30 m across have to be folded<br />
many times in order to be stowed within the 5 m wide nose<br />
cone of the ariaNe 5 rocket. Two days after launch, during the<br />
journey to L2, the unfolding process is started.