Emergency satellite decommissioning: scenarios

Unfortunately, recently the topic of various accidents during the removal of spacecraft does not lose its relevance, therefore (based on my own experience) I would like to tell you what tasks engineers solve when such an emergency situation occurs. The article describes possible scenarios in the case of abnormal launching of a spacecraft using the example of the completion of the operation of the telecommunications satellite Express-AM4 after the failure of the upper stage Briz-M. I will also talk a little about what is being done in the world to reduce the risks of collisions of spacecraft in case of abnormal launch.

Introduction

First you should say a few words about yourself. My main job is the ballistic support of the descent of manned and unmanned spacecraft to Earth. This includes both direct operational work and the development of software for it.



Now a few definitions:

Under abnormal launch, you need to understand the launch of a spacecraft into an off-design orbit in which it can exist for some time. The option when immediately "something went wrong" is meaningless to consider, since in this case nothing can be done.

Why do you need to do something with the device in case of an accident at the launch?

First of all, being in a spaceless orbit, a spacecraft may pose a threat of collision for other operating vehicles. And secondly, in the event of a spacecraft colliding with space debris (the number of which increases every day), the probability of detonation of the fuel remaining on board and the formation of a large number of fragments is high.

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One of the examples of non-standard launching into orbit was the Express-AM4 satellite. In August 2011, it was to be launched into a geostationary orbit (altitude 35786 km) to provide telecommunication services to the population. However, due to the crash of the upper stage, he remained in orbit with a minimum height of 655 km, and a maximum of 20,430 km. At this altitude, the satellite posed a threat to a large number of spacecraft, including the GPS and GLONASS constellations (their altitude 19,000– 20,000 km).

Variants of events

Depending on the type of accident during breeding, 3 main options for further developments are considered:

1. The continuation of the mission, taking into account the emergency situation.
2. Transfer of the apparatus to a safe orbit (burial orbit).
3. The flooding of the apparatus in a given area of ​​the oceans.

In the case of Express-AM4, the option of continuing the mission was impossible, since it was impossible to get to the geostationary orbit using our own engines. In this regard, the last two options were considered in detail.

Let's start with a safe orbit (here, literally in a nutshell). The essence of the task was to determine the orbital parameters using the orbital catalog, in which the satellite would pose the least danger to other spacecraft, and then calculate the flight pattern to this orbit with minimal fuel residues on board. As a result, the burial orbit was selected with the following characteristics: a minimum altitude of 12,000 km, a maximum altitude of 15,500 km. For the flight to this orbit, 3 engine start-ups were needed: the 1st to increase perigee, the 2nd to lower the apogee, and the 3rd to fully develop the fuel and make the final transition to a given orbit.



In theory, the burial orbit option was not bad, but from the point of view of practice it was rather difficult to implement (due to the specifics of the engine start up interval, vehicle orientation features, etc.), and to guarantee an accurate access to the specified orbit with full development fuel no one could. Therefore, the main option was the flooding of the satellite in a given area of ​​the oceans.



Here it is worth explaining a little: before reducing something from orbit, it is necessary to coordinate the area of ​​fall with various organizations, this is necessary, first of all, to ensure the safety of the local population. Russia has an agreement on the use of the Pacific region in the Southern Hemisphere to flood Progress trucks. Thus, when the “Express” was flooded, the options of aiming specifically in this area were primarily considered. But due to the characteristics of the orbit (the argument of the latitude of the perigee was located in the Northern Hemisphere) the use of this region was not possible. I had to look for an area in the Northern Hemisphere. There was nothing better than a place between the West Coast of the USA and Japan, so it was decided to sink the Express there.







A reserve area was also selected for insurance (it is smaller in the picture). To substantiate the possibility of satellite flooding in these areas, for different time intervals, the trajectory of the fall was calculated. As can be seen from the figure, they all met the condition of hitting a given area.

Operational work

Next was the most interesting - direct implementation. At once I will say that all the satellite control was carried out from the MCC of Toulouse, and all the work was carried out jointly with the French colleagues. The approved flooding pattern is shown in the figure.







I will explain a little: in order to bring a spacecraft from a highly elliptical orbit, it is necessary to slow it down at apogee, the perigee decreases, and the device enters the dense layers of the atmosphere. In this case, the thrust of the satellite engines did not allow the brake impulse to be developed quickly enough, so a scheme was chosen in which the satellite reached the apogee of the orbit in the middle of the propulsion system. This allowed the brake impulse to be worked out with maximum efficiency.



To increase reliability, any dynamic operations on spacecraft are attempting to be conducted in the radio visibility zone of ground points. Since the engine was turned on not over the territory of Russia, and the domestic orbital constellation of satellite repeaters was not so well developed, we had to use partner ground stations in Uralla (Australia) and in Beijing (China). According to them, March 25, 2012. during the calculated times the engine was turned on and off. After that, calculations were carried out, which confirmed the flooding of the satellite in a given area.

Conclusion

At this stage in the development of space technology, not every device can do anything in the event of an emergency situation during breeding. First of all, this is due to the high cost of each kilogram, put into orbit. For example, in order to increase the operating time of satellites in the geostationary orbit, electric rocket propulsion systems are installed on them, which have a very small load. In the event of an accident with a satellite with such engines, it becomes impossible to switch to a safe orbit or to flooding it.



At a meeting with French satellite manufacturers, they expressed interest in further exploring the possibilities of parrying abnormal situations during breeding. Now the work is being done in the direction of studying the possibility of additional installation of engines, development of the orientation system and many more other components of the satellite. It is possible that in the near future, equipment will be installed on the satellites that, in the event of abnormal derivation, can make autonomous decisions about their further actions.



Of course, one article does not fit all the features of the return of spacecraft to Earth, but for starters, I think that's enough.