Satellite abnormalities: development scenarios
Unfortunately, recently the topic of various accidents during the launch of spacecraft has not lost its relevance, therefore (based on my own experience) I would like to talk about what tasks engineers solve when such an emergency occurs. The article describes the possible scenarios in the event of an abnormal launch of the spacecraft on the example of the completion of the operation of the Express-AM4 telecommunications satellite after the failure of the Briz-M upper stage. I’ll also tell you a little about what is being done in the world to reduce the risks of a collision of spacecraft during emergency launch.
Introduction
First, a few words about yourself. My main work is the ballistic support of the descent of manned and unmanned spacecraft to Earth. This includes both immediate operational work and the development of software for it.
Now a few definitions:
By abnormal deduction, we need to understand the launch of a spacecraft into an off-design orbit, in which it can exist for some time. The option when “something went wrong right away” is meaningless to consider, since in this case nothing can be done.
Why do you need to do anything with the device in case of an accident at the launch?
First of all, being in non-calculated orbit, a spacecraft can pose a collision threat to other operating vehicles. Well, and secondly, in the event of a spacecraft colliding with space debris (the number of which increases every day), there is a high probability of detonation of the fuel remaining on board and the formation of a large number of fragments.
One example of abnormal orbiting was the Express-AM4 satellite. In August 2011, it was supposed to be launched into a geostationary orbit (altitude 35,786 km) to provide telecommunication services to the public. However, due to an accident in the upper stage, it remained in orbit with a minimum altitude 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 is 19,000 - 20,000 km).
Options for the development of events
Depending on the type of accident during recovery, 3 main options for the further development of events are considered:
- Continuation of the mission, taking into account the emergency situation.
- Transfer of the device to a safe orbit (burial orbit).
- Flooding apparatus in a given area of the oceans.
In the case of Express-AM4, the option to continue the mission was not possible, since it was impossible to reach 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 problem was to use the orbital catalog to determine the parameters of the orbit in which the satellite would pose the least danger to other spacecraft, and then to calculate the flight scheme to this orbit with the minimum remaining fuel on board. As a result, the burial orbit was chosen with the following characteristics: minimum altitude 12,000 km, maximum altitude 15500 km. For a flight to this orbit, 3 engine starts were needed: the first to increase the perigee, the second to lower the apogee and the third to fully generate fuel and the final transition to a given orbit.
In theory, the option with the orbit of the burial was not bad, but from the point of view of practice it was rather difficult to implement (due to the peculiarities of the interval for turning on the engines, peculiarities of the orientation of the apparatus, etc.), and to guarantee accurate access to a given orbit with full development no one could fuel. Therefore, the main option was the flooding of the satellite in a given area of the oceans.
Here it’s worth a little clarification:Before bringing anything from orbit, it is necessary to coordinate the area of impact with various organizations, this is necessary, first of all, to ensure the safety of the local population. Russia has an agreement to use the Pacific region in the Southern Hemisphere to flood Progress trucks. Thus, during the flooding of the “Express”, first of all, options for aiming in this area were considered. But due to the peculiarities of the orbit (the perigee latitude argument was 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 stoke the Express there.
Also, a reserve area was chosen for insurance (it is smaller in the picture). To justify the possibility of satellite flooding in these areas, trajectories of incidence were calculated for different time intervals. As can be seen from the figure, they all met the condition of falling into a given area.
Operational work
Then there was the most interesting - direct implementation. I must say right away that all satellite control was carried out from the MCC of Toulouse, and all work was carried out jointly with French colleagues. The approved flooding scheme is shown in the figure.
Let me explain a little: in order to bring a spacecraft from a highly elliptical orbit, it is necessary to slow it down at the peak, while lowering the perigee, and the spacecraft enters the dense layers of the atmosphere. In this case, the thrust of the satellite’s engines did not allow the brake impulse to be worked out quickly enough, therefore, a scheme was chosen in which the satellite reached the climax of the orbit in the middle of the propulsion system. This made it possible to work out the brake impulse with maximum efficiency.
To increase reliability, they try to carry out any dynamic operations on spaceships in the radio visibility zone of ground points. Since the engine was switched on not over the territory of Russia, and the domestic orbital constellation of relay satellites is not so well developed, it was necessary to use the partner ground stations in Uralla (Australia) and Beijing (China). According to them, March 25, 2012 at design times, the engine was turned on and off. After that, calculations were carried out that 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 case of an emergency during the launch. This is primarily due to the high cost of each kilogram put into orbit. For example, in order to increase the operating time of satellites in geostationary orbit, electric propulsion systems are installed on them, which have very low thrust. In an accident with a satellite with such engines, it becomes impossible to switch to a safe orbit or to flood it.
At a meeting with French satellite manufacturers, they expressed interest in further exploring the possibilities of parrying contingencies during hatching. Currently, work is underway to study the possibility of additional installation of engines, to work out an orientation system and many other satellite components. Perhaps in the near future, satellites will be putting equipment capable of autonomously making decisions on their further actions during an emergency shutdown.
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.