formation flying satellites

The world craves for more space. More details, see further: the instruments should be getting bigger and better. Satellites are expensive and larger than, and fit even more into the rocket. You should not think that such a giant breaks in space. The entire mission may be lost, and millions are discarded. No insurance that reimburses. The solution here is for Formation Flying Satellites: satellites in formation. In other words, chop the large satellite into pieces and these pieces together the job done.You can probably imagine you: to see more larger equipment is needed. Look at a telephoto lens of a photographer. With a giant lens is able to detail mapping from a great distance. This also applies to the space, only the distances are greater hundred kilometers. The instruments must therefore be even greater.
Until now, the only solution was to launch increasingly instruments. This has some major drawbacks. First, a larger instrument need more support. Think not only current, but also cooling and a stiffer structure so that the tool can work properly. This means that the satellite is still heavier, and thus there is again more propellant to be used.


Anyway, you now have a giant built and launched. Such satellite costs many millions. Despite this huge investment, there is still a chance that something breaks so maybe the whole mission in jeopardy. Away millions! So what is being done: more money for this chance as small as possible. However, how much money is also given to this certainty, there is always a chance that the mission fails.
Besides a lot of money, it takes a lot of time designing such a mission. The instruments are unique and therefore specially built for this satellite. But it takes a lot of time to demonstrate that the probability of failure is small enough for testing, testing and then only once testing. By the time the satellite can be launched, the design for years outdated.
The risks must therefore need to be reduced. One possibility is the use of multiple satellites that work together. This distinction can be made between two concepts:

    Constellation (Eng: Constellation): a cluster of satellites in which the distance between the satellites are not of importance for the success of the mission.
    Formation (Eng: Formation Flying Satellites): a group of satellites to be controlled so that the distance (more or less) fixed.
The two terms are quite often confused, but the distinction lies in the application of active control of the spacing. A constellation is actually nothing more than a collection of satellites, which in some time to watch a particular purpose. This relates more to the differences that the satellites show.

 
 A formation must cooperate. For example, a camera can exist in two parts from a satellite with a film and the other with a lens. With such a mission distance should be controlled, otherwise the correct distance between the lens and film not. XMM is such a camera in a whole. On the front is a "lens" (X-ray mirror) at the back of the "film" (Focal Plane Architecture). The lens and the film are connected by no more than a hollow tube as can be seen on a cross section of XMM. This tube is about ten feet long and barely fits into an Ariane 5. The successor, XEUS, still accurate. The tube was then fifty meters long should be, so it fits even less in a rocket. This satellite must be split.
By satellites in a formation to fly, we can see more details. The costs are also lower. The satellites in the formation are in fact often the same design, so not every satellite has to be individually designed. Also, the smaller satellites which two or three at a time can be launched. Is there a satellite broken, it can be replaced or can the same mission accomplished with fewer details. The risk that the mission (total) fails is much lower, making the cost even more can be printed. Also, the time required for design is shortened, so the risk of aging of the technique becomes smaller. Here is more, a satellite in the formation may be replaced by an improved version. This allows the formation literally grow, not only in number but also in its performance.
Finally, a formation has a big advantage: flexibility. The mutual distance between the satellites is controlled. This means that the formation of shape and size can be changed! This provides more options for achieving the objectives.
Unfortunately, there are still some problems to be solved. The important thing is the control of the distance between them. For the operation of the formation is of course of vital importance. The technology can make an accurate estimate of the distance is still insufficient. Thus, the distance between the two satellites of XEUS known to an accuracy of one millimeter, and at fifty meters! In doing so the satellites themselves can control: thus independent decisions, and certainly not collide.
 
Replacing a giant satellite by a formation has so many advantages. The probability of failure of the mission is not only smaller, but the effects if something breaks are also much less: a small satellite is easy to replace. A formation is flexible, allowing more goals can be achieved. But before that, there are still some hurdles to be overcome.