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Direction of launches



 
 
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  #1  
Old April 24th 10, 06:19 PM posted to sci.space.history
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Default Direction of launches

Do all satellites travel the same direction as the earth spins when in orbit? My
understanding is that they are launched in that direction to get added speed
from the earths rotation? I know there are satellites in polar orbit, but do any
travel from east to west and if so, what would be the advantage? Thanks.
  #2  
Old April 24th 10, 11:37 PM posted to sci.space.history
Fevric J. Glandules
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Default Direction of launches

Pat Flannery wrote:

The Israelis launch their satellites into east-to-west orbits so that
the spent rocket stages fall into the Mediterranean Sea rather than over
Arab countries.


Interesting factoid, thanks Pat! Do you happen to know what percentage
payload loss is involved?
  #4  
Old April 25th 10, 01:27 AM posted to sci.space.history
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Default Direction of launches

On Apr 24, 12:19*pm, wrote:

, but do any
travel from east to west and if so, what would be the advantage? Thanks.


Ooh! A chance to self-reference myself! Probably illegal in many
states, but here it is:

http://www.fas.org/spp/military/prog.../at_950411.htm

http://www.fas.org/spp/military/prog.../at_950415.htm


  #5  
Old April 25th 10, 03:15 AM posted to sci.space.history
Pat Flannery
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Default Direction of launches

On 4/24/2010 2:37 PM, Fevric J. Glandules wrote:
Pat Flannery wrote:

The Israelis launch their satellites into east-to-west orbits so that
the spent rocket stages fall into the Mediterranean Sea rather than over
Arab countries.


Interesting factoid, thanks Pat! Do you happen to know what percentage
payload loss is involved?


At the equator, Earth rotates at just over 1,000 mph, so you lose that
velocity and need to compensate for the backwards orbit as well, so you
will need to add over 2,000 mph total for a retrograde orbit at the
equator over that of a eastwards launch.
As far as specifics of payload lost by the westwards launch from Israel,
I haven't been able to dig up any info on that.
It would depend on the orbital inclination they were launching into, but
their available inclinations are fairly limited if they want the stages
to fall into the Mediterranean Sea.
According to this, a proposed reusable launch vehicle that can carry
60,000 pounds into a posigrade orbit can carry only 26,592 pounds into a
retrograde one:
http://www.spacefuture.com/archive/r..._spac e.shtml
So, going by that, you lose around half your payload, but payload loss
decreases as you get further north or south of the equator.

Pat

  #6  
Old April 25th 10, 08:41 AM posted to sci.space.history
Pat Flannery
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Posts: 18,465
Default Direction of launches

On 4/24/2010 4:27 PM, wrote:
On Apr 24, 12:19 pm, wrote:

, but do any
travel from east to west and if so, what would be the advantage? Thanks.


Ooh! A chance to self-reference myself! Probably illegal in many
states, but here it is:

http://www.fas.org/spp/military/prog.../at_950411.htm

http://www.fas.org/spp/military/prog.../at_950415.htm


What's the orbital period on these spysats?
Also, I don't know how friendly Israel is with South Africa since the
fall of the apartheid government and the ending of the South African
nuclear weapons program.
I imagine there are still ties due to the diamond mining, but that's not
as pressing as the cooperative nuclear bomb program was.

Pat


  #7  
Old April 26th 10, 05:50 PM posted to sci.space.history
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Posts: 157
Default Direction of launches



What's the orbital period on these spysats?


The nodal period is about 95 minutes.


Also, I don't know how friendly Israel is with South Africa since the
fall of the apartheid government


I expect that, if it ever were true (a possibility I still think
likely), the spysat cooperation ended with the fall of apartheid.
  #8  
Old April 26th 10, 06:02 PM posted to sci.space.history
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Default Direction of launches


The nodal period is about 95 minutes.


However, that said, the earth's eastward rotation takes targets at
around 30 degrees latitude (think Iran) to meet the westward-traveling
Ofeqs in a bit less than the nodal period:

http://tinyurl.com/2cz9nam

"Ofeq-5 is capable of revisiting critical targets every 90 minutes."


  #9  
Old April 27th 10, 01:09 AM posted to sci.space.history
Pat Flannery
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Posts: 18,465
Default Direction of launches

On 4/26/2010 9:02 AM, wrote:

The nodal period is about 95 minutes.


However, that said, the earth's eastward rotation takes targets at
around 30 degrees latitude (think Iran) to meet the westward-traveling
Ofeqs in a bit less than the nodal period:

http://tinyurl.com/2cz9nam

"Ofeq-5 is capable of revisiting critical targets every 90 minutes."


Yeah, I thought that would be the case with the retrograde orbit in
regards to ground targets.
Their Shavit booster uses three solid fuel stages in its basic form,
with a liquid fueled fourth stage if desired - that would probably mean
stages one and two would fall into the Mediterranean Sea, and stage
three...where? North Atlantic?

Pat
  #10  
Old April 27th 10, 02:11 AM posted to sci.space.history
Pat Flannery
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Posts: 18,465
Default Direction of launches

On 4/26/2010 4:09 PM, Pat Flannery wrote:

Yeah, I thought that would be the case with the retrograde orbit in
regards to ground targets.
Their Shavit booster uses three solid fuel stages in its basic form,
with a liquid fueled fourth stage if desired - that would probably mean
stages one and two would fall into the Mediterranean Sea, and stage
three...where? North Atlantic?


I was just checking great circle launch trajectories from Israel
westwards into orbit on Google Earth, and there's no way they can do it
without passing over someone else's country. Assuming they are trying to
shoot it over the Straits of Gibraltar, and it goes over northern
Tunisia and Algeria.
Thread it between Sicily and Tunisia, and they end up going over
southern Spain.

Pat
 




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