Physics would constrain space-to-space engagements. These five key concepts help explain how:
- Satellites move quickly.
- Satellites move predictably.
- Space is big.
- Timing is everything.
- Satellites maneuver slowly.
Warfighting on Earth typically involves competitors fighting to dominate a physical location:
Opposing military forces fight to control the land, sea, and air over a certain part of Earth to expand influence over people or resources. Space warfare does not follow this paradigm; satellites in orbit do not occupy or dominate a single location over time. Instead, satellites provide capabilities, such as communications, navigation, and intelligence gathering, to Earth-based militaries. Therefore, to “control space” is not necessarily to physically conquer sectors of space but rather to reduce or eliminate adversary satellite capabilities while ensuring one retains the ability to freely operate their own space capabilities.
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Objects orbiting Earth have a strict relationship between altitude and speed. Orbital mechanics dictate that objects at lower altitudes will always move more quickly than those at higher altitudes. Any attempt to add or reduce a satellite’s speed will always lead to a change in altitude. Compare this relationship between speed and altitude to an aircraft, which often changes speed without affecting its altitude, and vice versa.
And that speed is fast. Satellites in commonly used circular orbits move at speeds between 3 km/s and 8 km/s (6,700 mph and 18,000 mph), depending on their altitude. In contrast, an average bullet only travels about 0.75 km/s (1,700 mph).
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Also, because a satellite’s speed is tied to its altitude, a satellite will return to approximately the same point in its orbit at regular intervals (known as its period), regardless of the orbit’s shape and absent a maneuver to change the orbit.
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To deviate from their prescribed orbit, satellites must use an engine to maneuver. This contrasts with airplanes, which mostly use air to change direction; the vacuum of space offers no such option.
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Getting two satellites to the same altitude and the same plane is straightforward (though time and delta-V consuming), but that does not mean they are yet in the same spot. The phasing — current location along the orbital trajectory — of the two satellites must also be the same. Since speed and altitude are connected, getting two satellites in the same spot is not intuitive. Therefore, it requires careful planning and perfect timing.
One way to get close to another satellite is to perform a flyby. A flyby occurs when one satellite nearly matches the other satellite’s position without matching its orbit. Because the satellites are in different orbits, they will appear to speed past each other. These maneuvers are useful for inspection missions where the goal is not to destroy the target but to image it. Flybys often require minimal delta-V for an attacking satellite to perform since it can use natural intersection points of the two orbits to come close to its target. A related operation, known as an intercept, involves intentionally trying to match positions with the target, leading to the destruction of both satellites.
For two satellites in the same orbit, a common maneuver known as a phasing maneuver is required for one satellite to catch the other satellite. A phasing maneuver involves changing the satellite’s position in its orbit plane, either moving it ahead or behind of where it would normally be, similar to a train increasing or decreasing its speed to arrive at a destination sooner or later. Unlike a train, which can speed up or slow down without changing tracks, a satellite that changes speed also changes its altitude. This leads to the satellite entering into a new orbit known as a transfer orbit, an orbit used temporarily to move a satellite from an original orbit to a new orbit.
Ground-based ASATs are missiles that rely on a rocket to deliver a small warhead to impact with a satellite. Because the rocket has a large delta-V capacity, the warhead itself is placed in the correct intercept trajectory and requires little propellant to reach its target — this makes them more intuitive as they behave more like traditional missiles.
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In contrast, an orbital ASAT is basically a satellite that purposefully destroys other satellites. This can be done either with an RPO intercept or with onboard weapons. Unlike the ground ASAT missile, which can be launched without warning and at a moment’s notice, an orbital ASAT may be launched months to years ahead of a potential conflict.
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Some counterspace threats utilize the electromagnetic spectrum to inflict either temporary (reversible) or permanent (irreversible) harm. These threats are attractive because the attacks happen from a distance, which adds a measure of deniability and lessens the burden of getting physically close. Intentional jamming can also be quite difficult to distinguish from unintentional interference, making attribution more challenging.
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While there has never been a battle in space, we can still gauge what a war in space might look like. It would not be like the movies with intense dogfights. Instead space-based threats would be un-crewed and require slow and deliberate planning to get into position. Compared with the timing and flexibility limitations of on-orbit weapons, ground-based threats afford substantially shorter engagement execution timelines and the prospect of more numerous shots. The more we can internalize these insights, the better we can understand the stakes of a geopolitical fight in space.
