Russians in South America
Published on Mar 10, 2007 at 12:17 pm.
No Comments.
Filed under rockets.
A while back, I read a news story about the Russian Federal Space Agency’s plans to build a launch site in French Guiana at the Centre Spatial Guyanais (Guiana Space Center). Construction has now started. I grew up during the Cold War, and back in those days even a hint of the possibility that the Soviet Union would build a launch site anywhere in the Americas would have been a major news event with serious worldwide ramifications. But, today the Soviet Union is gone, and we are cooperating with the Russians in space exploration. My how the world has changed!
But, why do they want to build a launch facility so far from home? After all, transporting people and equipment all the way to South America has got to be expensive. So, why do this at all?
Well, it’s quite simple, really. In order to launch something into orbit, you need to achieve a minimal speed. For a 400km high orbit, that is about 7.6 kilometers per second (17,000 mph). Achieving this speed is in addition to just lifting the payload to an altitude of 400km in the first place.
Most people tend to not think about the fact that Earth is rotating. Standing on the equator of the Earth, the rotation of the Earth carries you around a circle of about 40,000 kilometers every day. That works out to a speed of nearly 464 meters per second. So, you would be moving eastward at that speed. But, if you were to launch a rocket towards the east from the equator, you’d only have to increase its speed about 7140 meters per second to put it into an orbit moving eastward. Now, that is still a lot, but it is still less than you’d have to do so otherwise. Importantly, kinetic energy increases as the square of the velocity, so this corresponds to about 12% less kinetic energy that you have to impart to the payload to put it into orbit. As expensive as rockets are, this is a significant savings, and can result in larger payloads. But, the farther from the equator that you go, the smaller the circle that you go around each day, until you reach the poles, and there you just spin around rather than moving around a circle at all. The speed that you are moving works out to be about
where θ is your latitude. The French Guiana site is at 5° latitude, so that makes it nearly ideal. This is about 4% better than the Baikonur site that the Russians normally use, which is located at about 46° latitude. That 4% doesn’t sound like much, but it adds up really fast. Furthermore, the inclination of the orbit is always going to be equal to or greater than the latitude of the launch site. The most useful orbits are often geosynchronous orbits, and most of them are best if they are situated right over the equator (and inclination 0° orbit). But, it takes a lot of energy to change inclination of the orbit, so that results in a far greater benefit than just the 4% difference in kinetic energy needed for orbit. I should also point out that that 4% figure is for the payload energy. To get that, you need more fuel, and then more fuel to carrry that fuel, and then more rocket structure to carry the additional fuel. So, it turns out to be considerably more than 4% savings in the end, even without worrying about the orbital inclination. Also, that 4% figure is only for one special case, that of a 400km altitude orbit. That is about the least savings that they get from launching at this site. The savings can be much bigger for other orbits. The Soyuz launch vehicle that they want to launch from French Guiana will be able to carry nearly 3 metric tons of payload from French Guiana rather than the 1.8 metric tons when launched from Baikonur. That is a major difference in payload mass. And, that is why the Russians want to launch from South America.
Also, there is already a successful launch facility in French Guiana. The French spaceport there, the Centre Spatial Guyanais, already is a major spaceport for the European Space Agency. So, the Russians only have to build launch facilities for the Soyuz. That saves cost from building all new infrastructure for a spaceport. This is a good deal for everyone.
-Astroprof
