How much of an advantage do equator-proximal launch sites provide?

Question

Comparing ESA's Kourou (5° off) with NASA's Cape Canaveral (28°) and JAXA's Tanegashima (30°) launch sites, how advantageous is proximity to the equator? Considering the fact that the ESA and all of Arianespace's clients are happy to transport equipment and payloads all the way to French Guiana, why don't NASA and JAXA relocate to a more suitable station?

In the case of the US, which has a number of overseas territories, there are a number of options. For a start the US Virgin Islands are 10° closer to the equator and not too far away from Florida either. Then there are possessions like the Palmyra Atoll which is on par with Kourou in terms of latitude.

So, why doesn't NASA use a site closer to the equator as a launch site? Is it for security reasons? Or is Kourou preferred purely for historical reasons as well as safety? Setting aside safety and political issues, how beneficial is Kourou to the ESA purely in terms of launch metrics?

Answer 1

The question should be broken in several parts.

• Why was Cape Canaveral chosen?
• Why does NASA not relocate somewhere else?
• What is the gain in terms of payload mass when launching from Kourou?

I will not answer the third part since for each launcher and inclination the answer will be slightly different.

From Moonport:

Cape Canaveral, better known as "the Cape," had been earmarked as a missile testing range in 1947. An elbow of land jutting out into the Atlantic midway between Jacksonville and Miami, the Cape covers about 60 square kilometers. Early Spanish sailors, marking it down as the only major feature of the long Florida coast line, named it for its abundance of cane reeds. Its choice as a missile range was dictated by several factors: the planners could set up a line of tracking stations stretching southeasterly over the Atlantic to provide the longest range necessary for missile testing; the Banana River Naval Air Station could serve as a support base; and the launch area was accessible to water transportation.

The selection was made by a Joint Chiefs of Staff committee. When the armed services went into rocketry in 1945, the Army stationed its launch team of German V-2 experts at White Sands, New Mexico - near the scene of Robert Hutchings Goddard's pioneering work in the 1930s. The southwestern desert proved too small for rockets, On 29 May 1947, a modified V-2 went the wrong way and landed in a cemetery south of Juarez, Mexico - one of the factors that decided the Joint Chiefs to move rocket experiments to the east coast of Florida.

Factors not mentioned above:

• Access by road and railroad from elsewhere in the CONUS
• Availability of land to set up oxygen (later - hydrogen) production

Historical curiosities:

• "Historical precedent" - Florida was "chosen" by Jules Verne in 1865

Other factors that came into play later:

• Launch ranges need a lot of uninhabited or sparsely inhabited land/sea in the direction of useful launch azimouths, especially where spent stages fall.
• The likely list of inclinations to launch into.
• Conversion of the Atlantic range into an operational ICBM base (and you simply don't build ICBM bases on tiny coral atolls in the middle of nowhere).

So, did NASA consider changing sites? YES, there was one particularly stubborn person out there.

Moonport:

A Saturn Launch Site

With better than 20 years' experience, the von Braun team preached and practiced that rocket and launch pad must be mated on the drawing board, if they were to be compatible at the launching. The new rocket went hand in hand with its launching facility.

The short-lived plan to transport the Saturn by air was prompted by ABMA's interest in launching a rocket into equatorial orbit from a site near the Equator; Christmas Island in the Central Pacific was a likely choice. Equatorial launch sites offered certain advantages over facilities within the continental United States. A launching due east from a site on the Equator could take advantage of the earth's maximum rotational velocity (460 meters per second) to achieve orbital speed.

The more frequent overhead passage of the orbiting vehicle above an equatorial base would facilitate tracking and communications. Most important, an equatorial launch site would avoid the costly dogleg technique, a prerequisite for placing rockets into equatorial orbit from sites such as Cape Canaveral, Florida (28 degrees north latitude). The necessary correction in the space vehicle's trajectory could be very expensive - engineers estimated that doglegging a Saturn vehicle into a low-altitude equatorial orbit from Cape Canaveral used enough extra propellant to reduce the payload by as much as 80%.

In higher orbits, the penalty was less severe but still involved at least a 20% loss of payload. There were also significant disadvantages to an equatorial launch base: higher construction costs (about 100% greater), logistics problems, and the hazards of setting up an American base on foreign soil. Moreover in 1959 there was a question as to how many U.S. space missions would require equatorial orbits. The only definite plans for equatorial orbits were in connection with communications and meteorological satellites operating at 35,000 kilometers. (6)

While there was disagreement over the merits of an equatorial base for future Saturn operations, the Atlantic Missile Range was the clear choice for the developmental launchings. At the range's launch site, Cape Canaveral, the Air Force Missile Test Center provided administrative and logistical support. The range's ten tracking stations, stretching into the South Atlantic, gave good coverage of test flights. Moreover, ABMA's launch team, the Missile Firing Laboratory (MFL), had launched missiles from Cape Canaveral since 1953. Cost and time considerations agreed. As an MFL study noted, the Atlantic Missile Range met "the established [launch] criteria in the most efficient, timely manner at a minimum cost. (7)

(6) NASA Special Committee on Space Technology, Recommendations Regarding a National Civil Space Program (Stever Committee Report), Washington, 28 Oct. 1958; ABMA, Juno V Development, pp. 19-20, 65; Army Ordnance Missile Command (hereafter cited as AOMC), Saturn Systems Study, by H. H. Koelle, F. L. Williams, and W. C. Huber, report DSP-TM-1-59 (Redstone Arsenal, AL, 13 Mar. 1959), pp. 16-19, 61- 63. 183-89; House Committee on Science and Astronautics, Equatorial Launch Sites - Mobile Sea Launch Capability, report 710, 87th Cong., 1st sess., 12 July 1961, pp. 1-5 (see hearings of same committee and topic, 15-16 May 1961, for fuller discussion): Mrazek interview. The debate over the merits of an equatorial launch site or a mobile sea launch capability continued for several years with congressional hearings in the spring of 1961. Vice Adm. John T. Hayward was a leading advocate of shipboard launches.

(7) Missile Firing Laboratory, "Project Saturn, Facilities for Launch Site," n.d.

Why does NASA not relocate someplace else now? The answer is simple - first, and foremost, COST. Building the whole supporting infrastructure from the ground up at a new place is very very costly and will not bring any money since NASA does not do commercial launches.

References:

• Moonport: A History of Apollo Launch Facilities and Operations. By Charles D. Benson and William Barnaby Faherty. NASA SP-4204. http://www.hq.nasa.gov/office/pao/History/SP-4204/contents.html

Answer 2

I would like to add my own answer based purely on math, which is not as complex as you may think (but I explain each term and everything else so it looks long). We only need a couple equations.

First the Tsiolkovsky Rocket Equation:

$V_f = V_e \ln(\displaystyle \frac{m_i}{m_f})$

(Soon, we'll need this rearranged for $m_f$, which is $m_f = \displaystyle \frac{m_i}{e^\frac{V_f}{V_e}}$)

$V_f$ is the final velocity, or delta v, or change in velocity. If you're going from 0 to 10 km/s, then 10 km/s will be your final velocity.

$V_e$ is the effective exhaust velocity, which is basically how fast the exhaust is propelled out the engine. The faster, the better. $V_e$ is equivalent to the specific impulse (in seconds) multiplied by g (9.80665 m/s/s).

$m_i$ and $m_f$ are the initial and final masses of the whole rocket. These are both total masses.

(The $\ln$ part is a natural logarithm, which is log base e (2.718...). If you don't know what those are, don't worry, just use a calculator. It's noteworthy, though, that this logarithm makes the equation exponential.)

Second, we need to know the tangential velocity of Earth's surface, based on latitude.

Equatorial tangential speed will be $\displaystyle \frac{2\pi*6,371,000}{86,164}$ = 464.58 m/s. (radius of earth = 6371 km, siderial rotational period = 86164 seconds, which is actually 23 hours, 56 minutes, 4 seconds, not 24 hours even.)

For other latitudes, multiply by the cosine of the latitude. At 45 degrees north (or south for that matter), ground tangential speed will be $464.58 * \cos(45°)$ = 328.51 m/s. (be careful your calculator is in degree mode, not radian mode).

One more thing we need to know is the orbital speed our satellite needs. This is typically 7.8 km/s, HOWEVER: Due to air drag, gravity drag, and some obvious vertical acceleration, the typical carrier rocket needs to send its payload to something like 9.7 km/s. This is the figure I will use.

So for prograde orbits, the actual delta v your rocket needs is 9.7 km/s minus the ground speed. Obviously, the larger the ground speed, the less work our rocket needs to do. This is what drives launch sites towards the equator.

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Now let's pick some figures for our rocket's final stage. I'll choose some based on the Soyuz' final (3rd) stage.

Let's say this final stage can take a 7-ton payload up to 4 km/s. Its total mass is 30 tons (including the payload), while its empty mass is 9.3 tons (including the payload). This implies that the empty 3rd stage without the payload is always 2.3 tons, and the effective exhaust velocity is 3.415 km/s.

Now with a boost from ground speed at the equator, the final stage only need to take this payload 3.535 km/s. Therefore, we can remove some fuel and add some payload mass. This will keep the total mass constant, because we're just trading fuel for payload.

This is the benefit of ground speed boost: increasing payload mass by reducing needed delta v.

So now it's time for a giant chart:

$$\begin{array}{|c|c|c|c|c|} \hline \text{site} & \text{latitude} & \text{ground speed} & \text{final stage needed speed} & \text{Final Stage Masses}\\ \hline \text{Equator} & 0° & \text{465 m/s} & \text{3.535 km/s} & \text{mf = 10.655 t, payload = 8.355 t}\\ \hline \text{Korou} & 5° & \text{463 m/s} & \text{3.537 km/s} & \text{mf = 10.649 t, payload = 8.349 t}\\ \hline \text{US Virgin Islands} & 10° & \text{458 m/s} & \text{3.542 km/s} & \text{mf = 10.633 t, payload = 8.333 t}\\ \hline \text{Cape Canaveral} & 28° & \text{411 m/s} & \text{3.589 km/s} & \text{mf = 10.488 t, payload = 8.188 t}\\ \hline \text{Tanegashima} & 30° & \text{403 m/s} & \text{3.597 km/s} & \text{mf = 10.464 t, payload = 8.164 t}\\ \hline \text{Baikonur} & 46° & \text{323 m/s} & \text{3.677 km/s} & \text{mf = 10.221 t, payload = 7.921 t}\\ \hline \text{Plesetsk} & 62° & \text{218 m/s} & \text{3.782 km/s} & \text{mf = 9.912 t, payload = 7.612 t}\\ \hline \text{North Pole} & 90° & \text{0 m/s} & \text{4.000 km/s} & \text{mf = 9.300 t, payload = 7.000 t}\\ \hline \end{array}$$

So comparing your two cases, Korou and Cape Canaveral, we see that we can get up to an additional 161 kg of payload. It may not seem like a lot, but keep in mind, we are paying tens of thousands of dollars for every pound we put into space.

By the same token, a reduction of 52 m/s may not seem like a lot either, but the exponential nature of the Tsiolkovsky Rocket Equation means that this is nothing to sneeze at.

In case you're wondering about the very small differences at first, but the larger differences later, see this graph, because the cosine function is exponential too. 45 degrees is halfway between pole and equator (50 percent), but take the cosine of it and you get something closer to 71 percent.

But guess what. It's not over:

• This only holds for launches due east. If you're at 46 degrees north and launch due east, your sputnik ends up in an orbit inclined 46 degrees. But Baikonur launches in a 51.6 degree orbit, and used to launch in a 63 degree inclined orbit! This is to keep the sputnik over Russia, not China, for the early phase in case the rocket fails and the sputnik (or Soyuz with people aboard) comes back down. For these other inclinations, you'll need to do a vector subtraction in only one dimension to find the rocket needed speed.

• Spy sputniks typically go into polar orbit (about a 90 degree inclination). So large ground speed is actually a bad thing. This actually drives launch sites towards the poles, if it's a launch site intended for spy sputniks, like the Plesetsk Cosmodrome.

• There's an alternate way to apply benefits: keeping the payload mass constant, but sending it to a higher orbit.

• If you're launching into a retrograde orbit (opposite of the way the Earth turns), then being closer to the equator is a disadvantage. Israel faces this problem as the only safe direction to launch their orbital rockets is to the west. I believe they orbit things in an approximately 120 degree inclination.

• Latitude is not the only factor in choosing sites. Other factors include weather, security (USSR chose a central inland area for this), and transportability (Cape Canaveral is transportable by sea barge, so they can ship huge rockets without a problem).

• Don't assume that the ratio of masses for any two examples in the chart will be the same ratio for the same latitudes of a different rocket. You really need to look at the rocket's final stage, see what it's Ve is and other parameters. Then use those numbers in the equations and make your own chart.

• Earth isn't a perfect sphere. Equatorial radius is actually a bit more than 6371 km. There may also be a mountain or plateau somewhere that would give a decent boost by extra radius (which yields extra ground speed) and extra height above mean sea level (which yields less vertical acceleration needed). Of course, remote and inhospitable areas incur their own expenses if you're really thinking about building there, but these sort of boosts once spawned the concept of balloon-launched rockets, and still today there is talk of rockets launched from airplanes as well as those exotic launch systems like the Launch Loop which can run up a mountainside for the same "Newton's Cannonball" physical boost.

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Alright. There's my answer based purely on math. If you dare, you can plug in your own example and figure out the exact benefits for your specific case.

Answer 3

From DrZ214's answer

So comparing your two cases, Korou and Cape Canaveral, we see that we can get up to an additional 161 kg of payload. It may not seem like a lot, but keep in mind, we are paying tens of thousands of dollars for every pound we put into space.

So, from NASA's point of view, they might be able to add several million dollars of payload value to a launch if they launched from, for example, the Marshall islands (only a few degrees off the equator, where some American rockets have been launched) or Puerto Rico (18 degrees North) But this cost advantage is negated by the cost of logistics and communications with a remote launch site.

I will not get into NASA's historical issues as they have already been discussed by Deerhunter, but I will give an account of the ESA's situation.

There are two ESA countries (Spain and Italy) which have easy to reach territory at 36 degrees North in the Mediterranean region. 36 degrees is slightly worse than Cape canaveral, but better than Baiknour. The bigger issue is that the Mediterranean region is both a busy shipping lane and a region containing many different and often densely populated countries, which would make approval extremely difficult.

When the ESA was formed in 1975, France had already launched several rockets from Kourou in French Guiana. It has open ocean to the East so is ideally sited from the point of view of range safety (which was a huge issue in times when countries were much less trusting of one another.)

France offered the site for use by the ESA. It ought to have been a no-brainer to select Kourou as the ESA's site, as it would avoid all the regulatory and national security issues (as well as any national pride arguments as to which country the launch site should be in) which (given the slowness of European multigovernmental collaborations) could have paralysed the programme for decades.

In conclusion France's / The ESA's choice of Kourou in French Guiana was driven partially by the issue of deltaV but it had more to do with politics and range safety. It should also be noted that in 1975 the Iron Curtain was not far from the Italian Border, and Spain was transitioning from dictatorship to democracy, so neither of these countries was really a viable option at that time.