View Full Version : james webb telescope
2010-Oct-04, 11:20 PM
I have a question about the Webb telescope. I know it will be positioned at L2 point (I even know what's that and why it is positioned there...), I just found out on its site that the telescope will orbit the L2 point. I'd like to say that I'm just a lay man who finds astronomy and astrophysics fascinating, but not much else, so please, be gentle..! why does it orbit the L2 instead of being positioned exactly where L2 is? my little understanding of the Lagrange points is that the gravities of the sun, earth and, I assume moon, cancel each other at those points, so what will keep the telescope in orbit around the point?
2010-Oct-05, 12:44 AM
Welcome to the board.
The answer is to put JWST in an orbit around the L2 point. (http://www.jwst.nasa.gov/orbit.html)Implies:
The answer is to put JWST in a Solar orbit around the L2 point.
Not an orbit orbiting the L2 point.
ETA: The exact point might not be suitable and or might be reserved for some other project, hence the term "around" (not as in orbiting it).
ESA has a number of missions that will make use of this spot in the coming years. L2 will become home to ESA missions such as Herschel, Planck, Gaia and the James Webb Space Telescope. (http://www.jwst.nasa.gov/orbit.html)
2010-Oct-05, 01:40 AM
The L2 point itself is only neutrally stable, a "saddle point" in the gravitational potential, which means not stable in the presence of such perturbing influences as the Moon. However, a"halo" orbit around it can be maintained for a long time (years) with minimal station-keeping. For this reason (and inserting it into the halo orbit), JWST has maneuvering thrusters, unlike HST. Here (http://map.gsfc.nasa.gov/mission/observatory_l2.html) is a bit more detail from the WMAP team on the L2 halo orbit, and a more tailored discussion for JWST (http://www.stsci.edu/jwst/overview/design/orbit.html). Typical periods for the halo orbit are 0.5 year.
2010-Oct-05, 02:45 AM
Thanks for the correction.
2010-Oct-05, 04:42 AM
thank you so much ngs3314 (which looks magnificently .... not your "fault" of course...) thanks again
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