The Constant Watch: Planetary Orbiter Missions Quiz

If a mission arrived at Saturn in 2004 and performed extensive long term planetary monitoring of the rings and the moon Titan until 2017, then that specific mission was Cassini.

If NASA sent a mission in 1989 specifically to "see" through the Venusian atmosphere using synthetic aperture radar, then the name of that successful mapping mission was Magellan.

If there is no air to cause friction (a vacuum), and if the balance between speed and gravity is perfect, then the laws of inertia mean the object will continue in its path indefinitely without needing extra thrust.

If there is no fuel left to change the path or keep the altitude stable against tiny forces, then gravity or atmospheric drag will eventually pull the craft down; for safety, scientists often plan for the craft to crash or burn up.

If the craft flies over the poles while the planet spins on its axis, then eventually every part of the planet will pass beneath the cameras; this is the most efficient way to achieve a global map.

If a mission is currently orbiting Jupiter in a highly elliptical "polar" path to avoid radiation and measure gravity and magnetism, then that mission is Juno.

If we only see a planet once (flyby), we miss changes; if we use an orbiter to watch the same atmosphere for months, then we can see how weather patterns like Martian dust storms develop and fade.

If sunlight becomes too weak to provide enough energy for a spacecraft's instruments at great distances, then the mission must use a reliable internal heat source like radioactive decay; this is commonly called nuclear power.

If a planet like Venus or Titan is covered in clouds that block visible light, and if radar waves can pass through gas and bounce off solid ground, then orbiters studying planets use radar to "see" the hidden surface.

If a craft is to stay in a circular or elliptical path, then the inward gravitational force must be perfectly countered by the outward tendency created by its high horizontal velocity; other forces are usually too small to affect the basic path.

If a spacecraft is designed to perform a "capture maneuver" by firing its engines to slow down near a planet, and if that speed reduction allows the planet's gravity to hold it in a loop, then the craft has transitioned into an orbiter.

If gravity is stronger closer to a planet (1/r^2 law), and if the spacecraft needs to balance that pull to avoid falling, then the craft must maintain a higher orbital velocity at lower altitudes.

If an instrument measures the time a signal takes to travel to the ground and back, and if that time is used to calculate the height or "altitude" of mountains and craters, then the technique is known as altimetry.

If a rover has a small antenna that cannot reach all the way to Earth, and if an orbiter is much larger and has a clear view of both the rover and Earth, then the orbiter can receive the rover's data and "relay" it across space.

If a planet has areas of higher density (like mountains or metal deposits), then the gravity is slightly stronger there; if the orbiter passes over that spot, the extra pull will speed it up slightly, allowing scientists to map the planet's interior.

If a mission's primary goal is to act as a high-powered "eye in the sky" for Mars, and if the Mars Reconnaissance Orbiter carries the HiRISE camera, then it is the mission responsible for those specific high-resolution images.

If an orbiter stays above the planet, it can scan the whole surface as the planet rotates; it can also act as a radio bridge between a rover and Earth. However, if it stays in orbit, it cannot physically touch or return soil samples.

If an orbit is elliptical (oval-shaped), then the distance between the craft and the planet varies; if we are naming the specific point of minimum distance, then that term is the periapsis.

If an orbiter stays in a stable loop for years, and if it passes over the same regions repeatedly, then it can record changes in dust storms or ice caps over time, which defines the process of long-term monitoring.

If a flyby spacecraft simply zooms past a target, it uses most of its fuel for the initial launch; if an orbiter must also carry enough fuel to fire large engines for "braking" into a stable path, then it naturally requires a higher fuel mass.