Orbital mobility is a satellite’s ability to change its orbit through manoeuvres. It is important for several key goals:
- carrying out the mission program;
- avoiding collisions;
- satellite deorbit at the end of the mission.
As the number of objects in orbit increases, satellite operators face more potential close approaches and more complex decisions about when to manoeuvre. However, a satellite can only perform an avoidance or deorbiting manoeuvre if it has sufficient propellant, power, propulsion capability, and accurate orbital information.
Therefore, mission managers and system engineers need to consider orbital mobility from the early stages of satellite design. This article examines how collision avoidance and deorbiting requirements affect satellite operations and why these capabilities should be planned before a mission begins. Specific regulatory requirements vary by country, orbit, and mission licence.
Why Orbital Mobility Is Becoming More Complex
Each year, more and more satellites are operating in orbit. On top of that, there are decommissioned satellites and debris nearby. At the moment, there are approximately 16,800 tracked satellites in Low Earth Orbit (LEO). The forecasts are different, but presumably about 20,000 to 58,000 new satellites will enter orbit by 2030. There is no doubt that LEO congestion will increase tremendously. As a result, operators have to check more frequently to make sure their satellite doesn’t come too close to another object.
“Even if no additional satellites were launched, the amount of debris in orbit would continue to grow because objects are fragmenting faster than debris naturally re-enters the atmosphere”, said Tim Flohrer, the European Space Agency’s Head of Space Debris. Source: The space boom has created a giant mess
A close-approach warning by itself does not always lead to an orbit change. First, experts evaluate the data and the probability of a collision, and then decide whether a manoeuvre is necessary. In doing so, it is important to take into account the satellite’s capabilities, such as its fuel supply and thruster performance.
More Objects in Orbit Create More Collision Avoidance Decisions
The number of objects in orbit increases; hence, operators receive recurrent alerts about potential close approaches. Each one must be reviewed to determine how accurate the data is, when the close approach might occur, and whether there is a real risk of collision.
After conducting an assessment, the team decides whether to change the orbit. If the risk is high, it’s important to make a decision quickly and ensure that the satellite is capable of performing the manoeuvre.
Satellite Constraints Limit Orbital Mobility
After a warning is received, it is not always possible for the satellite to change its orbit immediately. For a successful manoeuvre, the satellite needs propellant, a functioning thruster, and sufficient energy. In addition, the operators have to accurately determine the satellite’s position and check whether the satellite can manoeuvre.
Orbital Mobility and Collision Avoidance Decision-Making
When the team receives a warning about a potential close approach, it first verifies the data. Namely, where the objects are located and how accurate the calculations are. It then assesses the risk of a collision and determines whether the satellite can perform an evasive manoeuvre. For example, whether there is enough fuel and time.
After that, the team decides whether to change the orbit. A manoeuvre is not necessary every time a warning is issued. Sometimes calculations show that the danger is minimal. The verification procedure and decision-making criteria depend on the operator and the data sources they use.
As the number of objects in orbit increases, teams will likely receive more frequent warnings about potential close approaches. Thus, operators will have to process more of these messages and decide more quickly which ones require attention and which ones do not pose a serious threat.
Deorbiting Must Be Planned Before the Mission Ends
It is important to consider the end of a mission as early as the satellite design phase. Calculating safe deorbiting is a complex process that includes choosing the orbit and the right propulsion system. For example, the satellite can be directed to a lower orbit, where it will eventually re-enter the atmosphere, or it can perform a controlled re-entry into the atmosphere.
The decision has to be made in advance which method is suitable for a specific spacecraft and verify that there are sufficient resources for it. By the end of the mission, there must be enough fuel and power left for the final manoeuvre. If this is not taken into account during planning, the satellite may remain in orbit after the mission is complete.
Key Takeaways: Orbital Mobility, Collision Avoidance and Deorbiting
- Orbital mobility helps a satellite change its orbit to carry out tasks, avoid dangerous close encounters, and complete its mission;
- A collision warning does not always mean you need to change course. First, experts verify the data and assess the risk;
- A manoeuvre is possible only if the satellite has enough fuel and energy and its engines are functioning properly;
- The more objects there are in orbit, the more alerts operators have to check;
- De-orbiting must be planned during the satellite’s design phase. The requirements for this vary by country and license conditions.
About SteamJet Space Systems
SteamJet Space Systems is a leading UK-based provider of high-performance satellite propulsion solutions. We specialise in water-based propulsion solutions designed specifically for CubeSats and Small Satellites (SmallSats), prioritising operational safety and rapid launch integration.
By pioneering the use of green propellants and intelligent thermal engineering, SteamJet enables complex LEO (Low Earth Orbit) manoeuvres — including orbital maintenance, collision avoidance, and de-orbiting — without the risks associated with toxic hydrazine or high-pressure cold-gas systems, thereby advancing green propulsion for space missions.
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