11.26 - Understand the advantages and disadvantages of the major types of space probe:
b) orbiter

11.27 - Know an example of each type of space probe, including target body and major discoveries, including:
b) orbiter – Juno (Jupiter) or Dawn (asteroids Vesta and Ceres)

An orbiter is a probe that is sent to a body and continually orbits it for the duration of its mission life. When it arrives at the target it must slow down using fuel or aerobraking, using the upper part of an atmosphere to resist its speed. Orbiters sent to Jupiter and Saturn are usually sent to crash into the planets rather than risk any contamination from Earth to nearby moons.

  • Can observe the same area from different heights and at different times.
  • Usually the entire body can be observed.
  • Often, as happened with the Cassini Orbiter some changes to orbit can occur allowing controllers to change targets
  • They can only tell us so much about the surface features.
  • Slowing down the craft when it arrives at the target uses a large amount of fuel (as do changes to planned orbits)

Juno arrived at Jupiter in 2016 after a four-year journey and is expected to orbit until 2023. It is unique in that it largely has a polar orbit and is powered largely by solar arrays. It has equipment designed to measure the composition, magnetic field, mass and gravity of the planet as well as detect atmospheric water amounts, detect the nature of its core and study wind.


Dawn orbited Vesta from 2011 for 14 months and then travelled on to Ceres, arriving there in 2015. After using all its fuel by 2018 it remains in orbit there. Vesta is one of the largest asteroids in the solar system, Ceres is the smallest dwarf planet. Dawn used ion thrusters to move. Scientists aimed to map and study the surface and composition of the bodies aiming to understand their origin. It found organic molecules and bright areas composed of salt on the surface of Ceres. Evidence of water and carbon rich minerals were detected on Vesta's surface, likely delivered by comets.  


It is worth looking as this it is well-known for being a long lived and successful mission. As well as telling us more about the make up of Saturn and the rings, it enlarged our knowledge about its moons, even discovering new moons.


Juno at Jupiter
Fact Sheet

Juno Fact Sheet
(Opens in a new window)


Juno NASA Mission Page

Dawn NASA Mission Page

Cassini NASA Mission Page

Cassini at Saturn