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TomQ
2014-Aug-24, 01:20 AM
Hi,
I'm aware that NASA launches its rockets toward the east to take advantage of the "slingshot" effect of the earth's rotation and thus save fuel. Occasionally rockets are launched from the West coast and consequently need more fuel. I have absolutely no expertise about this so my question is probably a no-brainer to everyone else but, even if a rocket is launched from the West coast, why can't they slant it eastward as it goes up? the fact that it's being launched on the West coast doesn't mean it has to be angled west so why would it use more fuel. Thank you.

Jens
2014-Aug-24, 01:43 AM
Hi,
I'm aware that NASA launches its rockets toward the east to take advantage of the "slingshot" effect of the earth's rotation and thus save fuel. Occasionally rockets are launched from the West coast and consequently need more fuel. I have absolutely no expertise about this so my question is probably a no-brainer to everyone else but, even if a rocket is launched from the West coast, why can't they slant it eastward as it goes up? the fact that it's being launched on the West coast doesn't mean it has to be angled west so why would it use more fuel. Thank you.

I think it's more like this, that you have the cause and effect reversed: if you are planning to launch eastward, you launch from the east coast because if the rocket fails, it will fall into the ocean rather than on populated land. And if you are planning to launch it westward, then launch it from the west coast so that it will go over the ocean. So the ones that are launched from the west coast are launched from there because they are going westward, not the other way around. People generally try to launch rockets so that they go over the water.

Hornblower
2014-Aug-24, 02:02 AM
If I am not mistaken, typical launches from the west coast are southward into polar orbits from Vandenberg AFB in California. A trajectory slightly west of south gives a steeply inclined retrograde orbit that precesses in sync with the Sun and thus can be kept continuously in daylight. Such an orbit is chosen when the mission requirements justify the expense of the additional fuel. The only more westward launches I have heard of are from Israel, where that is the only way to stay over the Mediterranean Sea for any great distance.

Noclevername
2014-Aug-24, 02:03 AM
People generally try to launch rockets so that they go over the water.

IIRC, Russian launches usually pass over Siberia, since their East coast is still fairly remote and unindustrialized.

Van Rijn
2014-Aug-24, 02:37 AM
Vandenberg launches can go a little bit eastward in a southeast trajectory and still stay over water, though I don't know if they use that trajectory.

Jeff Root
2014-Aug-24, 05:05 AM
I've seen maps showing the directions in which launches are
permitted from Canaveral and Vandenberg. I think they have
been included in at least some launch press kits. Googling for
the launch site and "launch direction" or "ground track" will
probably find such a map.

-- Jeff, in Minneapolis

NEOWatcher
2014-Aug-25, 12:03 PM
I'm aware that NASA launches its rockets toward the east to take advantage of the "slingshot" effect of the earth's rotation...
You probably couldn't find the right word to say, so let me...
Angular momentum. Because the rocket is sitting on the ground, it's already travelling around 1000mph to the East. (less, the higher latitudes you go)
Slingshot is normally used for gravity assist.


I've seen maps showing the directions in which launches are
permitted from Canaveral and Vandenberg.
I found some over here (http://www.hobbyspace.com/SpacePorts/spaceports3.html).

OnePlus
2014-Aug-26, 01:49 AM
Hi,
I'm aware that NASA launches its rockets toward the east to take advantage of the "slingshot" effect of the earth's rotation and thus save fuel. Occasionally rockets are launched from the West coast and consequently need more fuel. I have absolutely no expertise about this so my question is probably a no-brainer to everyone else but, even if a rocket is launched from the West coast, why can't they slant it eastward as it goes up? the fact that it's being launched on the West coast doesn't mean it has to be angled west so why would it use more fuel. Thank you.

They'd use more fuel because the west coast launch sites are farther north (all of California is north of all of Florida), and therefore have less angular momentum, since the rotation of the earth is slower the farther you get from the equator. So even if you pointed the rocket east, it would take more fuel, not because it is launched from farther west, but because it is launched from farther north.

Your set of feasible orbits is also more restricted from farther north. You have the option of launching into a polar orbit from Florida if you choose, but you don't have to. If you were launching from northern Canada, it would be required, unless you want to put your rocket into orbit, wait until it cruises farther south, and then expend a lot of fuel to change direction.

NEOWatcher
2014-Aug-26, 11:45 AM
They'd use more fuel because the west coast launch sites are farther north (all of California is north of all of Florida), and therefore have less angular momentum, since the rotation of the earth is slower the farther you get from the equator.
True, but it isn't really that much at those lower latitudes. The difference is about 57mph. 1000mph*(cos(34.7325)-cos(28.5239)). It would be important to launches with a tight weight budget, but it's not the only concern.

As you get to higher latitudes it starts to get much worse. If you're talking about the Russians, it's a difference of about 184 mph.

Another large factor is the inclination. With a near equator launch, you have a wider variety of inclinations since they all pass through the equator. As you move away, you start to miss the lower inclination orbits.

Hornblower
2014-Aug-26, 12:46 PM
They'd use more fuel because the west coast launch sites are farther north (all of California is north of all of Florida), and therefore have less angular momentum, since the rotation of the earth is slower the farther you get from the equator. So even if you pointed the rocket east, it would take more fuel, not because it is launched from farther west, but because it is launched from farther north.

Your set of feasible orbits is also more restricted from farther north. You have the option of launching into a polar orbit from Florida if you choose, but you don't have to. If you were launching from northern Canada, it would be required, unless you want to put your rocket into orbit, wait until it cruises farther south, and then expend a lot of fuel to change direction.

My bold. Nobody ever said that you would lose eastward velocity by launching from farther west at the same latitude. As has been pointed out before, the reason for not launching due east from Vandenberg is the hazard of sending the launch vehicle over populated areas. The Soviets launched over land in Kazakhstan because they had plenty of flat, sparsely populated land in that area, and not much infrastructure on their Pacific coast.

NEOWatcher
2014-Aug-26, 12:56 PM
My bold. Nobody ever said that you would lose eastward velocity by launching from farther west at the same latitude.
The OP did but didn't specify why. Just that it needs more fuel from the West coast. So; I can see how that can be interpreted that way.

Jeff Root
2014-Aug-26, 01:20 PM
Reading the whole OP, TomQ does say the reason more fuel is
used launching from the west coast is that the direction of launch
is different from the direction of Earth's rotation. So Hornblower
is right that OnePlus didn't really need to say anything about
launching from farther west. Meh.

-- Jeff, in Minneapolis

NEOWatcher
2014-Aug-26, 04:18 PM
Exactly, he may not have needed to say it, but it wasn't wrong either. If there were any doubt, it was a clarification.