Since the middle of the sixties I have been involved in satellite observing. Apart from the official observers program, as coordinated by e.g. Satellite Orbits Group, I saw several bright objects during my sky presentations to the public and also during nightly walks. Especially in the seventies I noticed that many objects followed about the same track and sometimes even close to each other. Then I started looking for similarities in their orbits. I really "dicovered" groups of satellites having about the same orbital characteristics. These groups are briefly described in order of appearance in the past.
The oldest group of similar satellites, that sometimes are visible to the naked eye started with (possibly) Kosmos 44 (64- 53 A). The orbital plane is inclined 65 degrees to the equatorial plane and the nodal period was around 96 minutes. Kosmos 58 (65- 14 A) and its rocket (65- 14 B) were certainly members of this group.
The A-objects, the payloads were 5 m long cylinders and 1.5 m diameter and provided with two vanes with solar cells as shown in many books. The B-objects were the upper stage of the A-2 or Vostok rocked being cylinders with 3.8 m length and 2.6 m diameter. Shortly after launch these B-objects had a nice flashing periods of pattern AA_Aand sometimes a sharp flash instead of the missing maximum. This group of satellietes has no more members left in orbit: they all decayed.
This group started with a triple launch of Kosmos 54..56 (65- 11 A..C) in a 56 degrees inclination orbit. But this orbit was rather eccentric, an altitude between 250 and 1800 km. Only the rocket was bright enough to be seen with the naked eye. At apogee however it was also invisible. Near perigee it could be a mangitude 1 object, moving rather fast.
The next lauch in this group delivered 5 objects at about 500..640 km. It was the rocket again being the only naked eye object.
Another two launches followed that year but all 5 payloads were placed above 1300 km making even the rocket almost invisible. At the end of that year Kosmos 103 was lauched as a single payload. (65- 112 A) with its rocket for me the first fast tumbling object I ever saw (many would follow).
In 1967 and 1968 two Kosmos 103 like orbits were achieved by Kosmos 151 (67- 27 A) and Kosmos 236 (68- 70 A). I never looked for a possible connection of the orbital planes.
This group is comparable to group 1 except for the inclination that is 81.2 degrees. The group started with Kosmos 144 (67- 18 A), and probably finished with Kosmos .... (83- 10 A). At first I thought all the members within this group were meteorological satellites, as 69- 29 A was named Meteor 1 and had a similar orbit. Moreover the next object in such an orbit 69- 84 A was named Meteor 2, Meteor 3 (70- 19 A) was the next and Meteor 4 (70- 37 A) the following. But with Meteor 5 (70- 47 A) a higher orbit was reached. Meteor 6 however had the traditional altitude. Some confusion arose when 70-113 A had a Meteor-like orbit but was named Kosmos 389. After that other Kosmosses have been launched with similar orbits. They were apparently electronic intelligence satellites with however the same payload shape and size as the Meteors.
Study of the planes with respect to each others should have shown a certain regularity. But I was not yet interested in these during the period of their launching (till 1983).
This group consisted of rockets only, the C-1 rocket, now also known as the Kosmos-rocket. From 67-108 B on it appeared to be used several times a year to launch an electronical intelligence satellite. These rockets had also a short flashing period shortly after launch. A remarkable feature was that their nodal period was about 95.2 minutes and with 74.0 degrees inclination they had about the same tracks along the sky on successive days.
The last member of this group was probably Kosmos 1215 rocket (80- 83 B). All rockets have decayed.
Another interesting group with 65 degrees inclination is still existing. It concerns the EORSAT's. The first member was Kosmos 699 (74-103 A) and was followed by many more. During the last ten years there are most of the time three objects present in the same plane but 120 degrees saparated. Before 1986 these objects had a nodal period of 93.3 minutes. From that year they had a bit lower orbit with a period of 92.8 minutes. With this period and their inclination these objects have a nice visibility as one object has the same trajectory as another one the day before and the third one had the day before and so on until the whole constellation of satellites shifts into daylight or earth shadow.
After their active life these objects are manoeuvred into different orbits, mostly resulting in a rapid decay. However sometimes they reach a much higher orbit and are still visible at present. Such objects are e.g. Kosmos 1220 (80- 89 A) and Kosmos 1461 (83- 44 A).
Nowadays this group is the easiest as it consists of the Zenit rockets that are intrinsically bright by their large dimensions: 10.4 x 3.8 m. Even with their altitude of approximately 850 km they are easily visible to the naked eye and very interesting in most cases in the year after their launches when they are the brightest flashing satellites ever. There is also some regularity between the planes. With their 71 degrees inclination these objects tend to move SSW-NNE or NNW-SSE on our latitudes. Another nice feature is that these objects use almost the same trajectory at the sky on successive days.
In fact this group does not consist of members of one family but belong to different mission-types, even different launch agencies and launch organisations. Their common property is the fact that they all have a sunsynchronous orbit, resulting in a summer visibility in our regions, moving from S to NNW. Their inclination is higher the more their altitude is and ranges between 97 and 100 degrees. As they are mostly visible in the summer their maximum brightness occurs when they are in SE.
The members of this (unnatural) group are USA-satellites like of KH-11 if not too close to their apogee (84- 122 A, 88- 99A and 92- 86 A). Then the Landsat 4 (82- 72A) and Landsat 5 (84- 21 A) may sometimes be visible to the naked eye.
European members are all launched by the Ariane rocket that will be reasonably visible itself. Of the payloads the SPOT and ERS are visible to the naked eye if suitable placed with respect to the sun (so in fact in SE).
At last some Kosmosses are in this group and are Meteor-like but in fact they are Earth Resource Satellites. They resemble the Meteor a bit. Their lauchers happen to be the A-2 rocket and with their altitude of about 600 km both payload and rocket are visible to the naked eye. Due to the very small planedrift either in eastern or western direction these planes become more spread in space, so also in time and some planes cause their respective objects to be visible in winter now or in the early morning in the summer.