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Unaffordable and Unsustainable, NASA’s failing Earth-to-orbit Transportation Strategy
Guest_DonPMitchell_*
post Aug 2 2006, 10:30 PM
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The most efficient orbital launch is made eastward with engine burnout at perigee. That leaves you with an orbit inclined at the same angle as the latitude of the launch site. And if you don't care what the orbital plane is, then you get the most boost from the Earth (0.46 km/sec) by launching from the equator. At Cape Canaveral, you get 0.41 km/sec. Not a big deal. Kourou wasn't built to get an extra 50 m/sec. It was built to launch geosynchronous communications satellites with a big simple rocket.

The equator is a bad place to launch to polar orbit. You have to spend energy to cancel that 0.46 km/sec, because the angular momentum is entirely in the wrong direction. Furthermore, to make that big change in orbital plane needs tricky and expensive technology -- a Centaur, Briz or Fregat stage. The best places to get into polar orbit are Plesetsk or Kodiak.
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David
post Aug 3 2006, 12:20 AM
Post #47


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QUOTE (DonPMitchell @ Aug 2 2006, 05:27 PM) *
The white paper suggests that servicing ISS is ready for privatization. In theory I agree, but I doubt if the EU would stop subsidizing the Ariane/ATV plan -- even though it is not a great idea to go from Kourou to the highly inclined ISS orbit. But now who would ever pay for the real cost of a launch? This is why, if there is a viable market, you want the government to stay out.


I can't really follow your argument. You seem to be saying that the government is outcompeting private industry in providing a service that, as far as I know, only the government needs or wants. Perhaps to make it more clear you could identify:
What exactly is the product/service being provided?
Who are the customers?
Who are the providers?
Where's the competition?
How is a privatized system cheaper overall than the current system?
Does even more money end up coming out of my (or any taxpayer's) pocketbook to pay for the same things that I'm already paying for?
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Guest_DonPMitchell_*
post Aug 3 2006, 12:59 AM
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QUOTE (David @ Aug 2 2006, 05:20 PM) *
I can't really follow your argument.


Flying supplies to ISS from Kourou is subsidized, so there is no market opportunity for anyone to develop a cheaper scheme.
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Guest_DonPMitchell_*
post Aug 3 2006, 03:19 AM
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QUOTE (Analyst @ Aug 2 2006, 11:50 AM) *
If you launch from the equator you are never worse off (for any inclination) than launching from another place north or south. You are better or the same, but never worse.

Analyst


Hmm, I think you are right about ISS, now that I think about it some more. It is very tricky to get into an orbital plane that is less inclined than the latitude of the launch site. That takes something like a centaur stage doing several powered maneuvers, and it's why a Proton can send more payload to Mars than it can to GSO!

For going into more-inclined orbits, there seems to be some practical issues that place an upper bound. I'll ask some people I know who are experts on this for more details.
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Jim from NSF.com
post Aug 3 2006, 04:26 AM
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QUOTE (remcook @ Aug 2 2006, 03:38 PM) *
then why do the russians launch polar satellites from Plesetsk?


Because it first was an ICBM base and close to the US, and it has a clear impact area for stages
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Jim from NSF.com
post Aug 3 2006, 04:34 AM
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QUOTE (Analyst @ Aug 2 2006, 02:50 PM) *
If you launch from the equator you are never worse off (for any inclination) than launching from another place north or south. You are better or the same, but never worse.

Analyst


Not true. It takes more energy to fly at 90 degrees inclination at the equator than at a pole. A launch from the equator due south (180 degree azimuth) would not be become 90 degrees inclination due to the earth rotatation. The azimuth has to be slightly retrograde to cancel out this velocity. The further north, the less velocity to cancel out.
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Guest_Analyst_*
post Aug 3 2006, 06:30 AM
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Interesting, Jim. I should be more careful with absolute statements. What does this tell us about efficiency in gerneral? Is there a different optimal launch site for any given inclination, e.g. 57 degress inclination best from x degrees latitude, 28 degrees inclination best from y degree latitude?

Analyst
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The Messenger
post Aug 3 2006, 08:51 PM
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QUOTE (Analyst @ Aug 3 2006, 12:30 AM) *
Interesting, Jim. I should be more careful with absolute statements. What does this tell us about efficiency in gerneral? Is there a different optimal launch site for any given inclination, e.g. 57 degress inclination best from x degrees latitude, 28 degrees inclination best from y degree latitude?

Analyst

There are many logistics: High altitudes are great for launching, but windy and very cold. How many people want to become rocket scientist and live in a miserable climate? What about the effects of rust and corrosion? The probability of tropical storms tearing up the place? Bugs and storms making flights in and out of the launch area risky? Where do you want your workforce located? how secure is a jungle location, where do you plug in the airconditioner...
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Jim from NSF.com
post Aug 4 2006, 12:50 AM
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QUOTE (Analyst @ Aug 3 2006, 02:30 AM) *
Interesting, Jim. I should be more careful with absolute statements. What does this tell us about efficiency in gerneral? Is there a different optimal launch site for any given inclination, e.g. 57 degress inclination best from x degrees latitude, 28 degrees inclination best from y degree latitude?

Analyst


It works out that you want to launch at the same latitude as the desired inclination
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Guest_Analyst_*
post Aug 4 2006, 07:35 AM
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QUOTE (The Messenger @ Aug 3 2006, 08:51 PM) *
There are many logistics: [...]


I am well aware of logistics. But this has not been the point in my (theoretical) question if there is an ideal launch site latitude for a given inclination if all you worry about is the most efficient trajectory.

Jim, after your answer I have to rethink this completely. Are you sure you are correct? DonPMitchell, if Jim is right I stand corrected.

Analyst
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Jim from NSF.com
post Aug 4 2006, 01:00 PM
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By default, a launch going due east (90 degrees azimuth) will be at the inclination equal to the latitude
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Guest_DonPMitchell_*
post Aug 4 2006, 07:27 PM
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The perigee of the orbit will be approximately where the launch site was (where engine burnout occured actually). Consider the velocity vector at that point on the orbit. The magnitude of that vector must be 7.9 km/sec to sustain orbit. At the equator, the Earth gives you a free eastward component of 0.49 km/sec, and the rest of the velocity vector has to be supplied by the rocket.

So I believe as long as the inclination is less than Arccos(0.49/7.9), then it is most efficient to launch from the equator. That's about 86 degrees. To get a true polar orbit (90 degree inclination) then you have to fight the Earth's motion by launching the rocket somewhat westward. So I think Analyst was right, except for the case of an orbit that is greater than 86 degrees of inclination.

The oldest equatorial launch site is the Kwajalein Missile Range, a complex of island radar, telemetry and launch facilities operated by the US Army. SpaceX is planning to launch their Falcon rockets from there. Like Kourou and the island Sea Launch site, there are no logistic constraints on the direction of launch, from east to north.
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tty
post Aug 4 2006, 07:51 PM
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The ideal launch site should be:

1. On the Equator
2. As high as possible
3. Have ocean or sparsely inhabited territory to the east

So, disregarding logistics, Mount Kenya, Chimborazo or Sangay would seem to be the best places.

tty
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Guest_DonPMitchell_*
post Aug 5 2006, 09:06 AM
Post #59





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Some of these effects are more important than others. At sea level on the equator, you get a tangential velocity of 0.464 km/sec from the Earth's rotation. If you started on a mountain 8 kilometers high, you would only get 0.5 m/sec more velocity. So altitude is irrelevant. Also, google reveals that Sangay is a very active volcano, which I think we would catagorize as a "logistic concern". :-)

Cape Canaveral is at 28 degrees latitude, so it gets 0.410 km/sec of velocity boost. Only 50 m/sec less than the Equator, which isn't really very important. What is important is that you cannot launch into an initial orbit with an inclination less than 28 degrees.

The Russians and Americans do multiple-burn maneuvers to get into less inclined orbits. Evidently the most efficent maneuver is to increase the apogee, then at apogee fire perpendicular to the orbital plane to change its angle, and then reduce the apogee.
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djellison
post Aug 5 2006, 01:56 PM
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QUOTE (DonPMitchell @ Aug 5 2006, 10:06 AM) *
So altitude is irrelevant.


So why didn't the fire Space Ship One from the ground then wink.gif

Doug
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