Planck and Herschel en route for L2

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MeteorWayne

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I posted this in the other Herschel/Plank thread yesterday, but I guess we can leave this thread here for at least the 10 week commisioning period for both craft.
 
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montmein69

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Good news from the two spacecrafts
Herschel and Planck talk to Earth

14 May 2009
At 15:49 CEST today, just under 40 minutes after liftoff, Herschel and Planck sent their first radio signals to Earth, confirming that they separated successfully from the launcher and are alive.

Herschel, the upper passenger, was the first to separate from the upper stage of the Ariane 5 at 15:38 CEST at an altitude of about 1150 km over the east coast of Africa. About 1.5 minutes later, the Sylda support structure that enclosed Planck came off and separated. It was followed by Planck at 15:40 CEST at an altitude of about 1700 km slightly East of the east coast of Africa.

The satellites switched on their attitude control and telecommunications systems right after separation, to re-orient themselves and establish contact with Earth for the first time from space. The signals were received by ESA’s 35-m deep space antenna at New Norcia in Australia.



Herschel separation
The mission control teams will continue to receive telemetry from Herschel via New Norcia, and for Planck via ESA’s antenna at Perth, also in Australia. Spacecraft Operations Engineers at the Mission Control Centre will use these data to assess the overall health of the satellites after launch.

Almost immediately after telemetry reception starts, engineers will determine the actual trajectory of each satellite so that it can be fine-tuned for planned trajectory correction manoeuvres.
from : http://www.esa.int/esaSC/SEMFBDZVNUF_index_0.html
 
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paultrafalgar

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I have a problem:
I don't understand why Herschel and Planck are taking so long to get to L2.
I read that the craft are traveling at about 10km/sec
That the L2 point is about 1.5 million kilometers away.
My calculation says that that should take 1.73 days!
i.e.
1500000/(10*60*60*24) days
What am I doing wrong?
I read that it will take 2 months!
 
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MeteorWayne

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Welcome to Space.com.

I don't know the exact path, but can speculate a little. First of all, they are slowing down, because the earth's gravity is still pulling on them, and they are just coasting. All their motions was imparted during the launch phase, they are slowing down in relation to earth since then.

Second, you need them to slow down because if they were moving at 10 km/sec when they got to L2, they'd shoot right past. They don't have any engines for braking purposes. They do have propellant for station keeping purposes, and to refine they're orbits around the L2 point, but that is limited. So the path would be chosen to have them arrive at the L2 point at close to zero speed.

I'll see if I can find out more detail.

Good question.
 
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paultrafalgar

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Thanks MeteorWayne for a prompt reply. Forgot about gravity slowing the things down. Was thinking of Newton's 1st(?) Law - things remain stationary or travel at a constant velocity unless acted upon by an external force. Gravity is that external force here.
 
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MeteorWayne

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Yeah, ain't Newton (with Einstein tweaking over his shoulder) wonderful.

After the hubble spacewalk ends I'll try and look for an accurate desciption of the paths, but it's just too much fun to watch them work now...
 
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Tom_Scrace

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I wonder if somebody could help to clarify an issue regarding Herschel's orbit? I understand that this will be what is called a Lissajous orbit around L2, but what I cannot understand is how it can orbit around a point where there is no object, no mass and therefore, I assume, no gravitational pull. Is this some odd effect created by the L2 point that creates a 'virtual' body because of the interplay of the gravitational fields of the Earth and the Sun?

Thanks for your help.
 
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scottb50

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Tom_Scrace":wuds5kmq said:
I wonder if somebody could help to clarify an issue regarding Herschel's orbit? I understand that this will be what is called a Lissajous orbit around L2, but what I cannot understand is how it can orbit around a point where there is no object, no mass and therefore, I assume, no gravitational pull. Is this some odd effect created by the L2 point that creates a 'virtual' body because of the interplay of the gravitational fields of the Earth and the Sun?

Thanks for your help.
It's not so much it's orbiting a point in Space as it is maintaining a point in reference to the earth the moon and the Sun, it still has to maneuver every three months to maintain it's path around the point the gravitational effect of the three bodies nullify each other. The best way to look at is a bean, an elliptical path that keeps it in a null point of external gravitational forces. That it can maintain this position with relatively little energy expenditure lets it see specific areas of Space for longer periods of time then it could if it was in an Earth or Solar orbit.
 
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centsworth_II

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scottb50":rtj03epv said:
It's not so much it's orbiting a point in Space as it is maintaining a point in reference to the earth the moon and the Sun...
I wonder if it's helpful (and accurate) to envision the telescopes as bobbing up and down as they orbit the sun. As they bob up, a point is reached where the combined pull of Sun and Earth pull them back down. After they reach a certain point on the down side, the Earth and Sun pull them back up.
 
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