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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
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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? |
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#4
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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 |
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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 |
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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
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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
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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
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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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