How a close pass can change an orbit
Two satellites do not need to touch to affect one another. As they pass close by, each pulls on the other with gravity. That pull bends their paths and can change their speeds relative to Earth. The timing and direction of the encounter determine which satellite speeds up and which slows down.
A satellite that gains speed in the right direction can move into a higher, more elongated orbit. It has not been lifted directly upward: it has gained orbital energy, which changes the size and shape of its path. The partner gives up some energy in the exchange and may end up in a lower or otherwise altered orbit.
The trade has to balance
This is a close cousin of a gravity-assist maneuver, in which a spacecraft gains or loses speed by passing a moving planet. Here, the moving body doing the tugging is another satellite. The energy is not created from nothing; it is redistributed between the pair, with their mutual gravitational interaction contributing during the encounter.
The outcome depends on mass as well as geometry. A much lighter satellite can undergo a larger change in speed than a heavier one, while the heavier satellite’s change is comparatively small. For ordinary spacecraft, their weak gravity makes the effect tiny unless the encounter is extraordinarily close. A useful, controlled exchange would therefore demand precise timing and a safe trajectory—because the same close pass that transfers energy can also end in a collision.
The striking part is that “higher orbit” need not require a rocket burn: in principle, one satellite can climb by taking orbital energy from another, leaving the other with the bill.
