The Juno spacecraft, which left Earth in 2011, is now safely in orbit around Jupiter!
The orbit insertion marks the third and fourth time Juno’s on-board engine was used in space. The first two times occurred during its long flight to adjust its trajectory. This last two burns, at a little over 30 minutes each, slowed the craft just enough to be snagged by the gravity of Jupiter.
The engines were fired twice because a single burn over an hour in length exceeded the burn time over which its engines had been tested. Although it probably would have performed fine for a longer burn, basic safety rules dictated that two shorter burns were preferable.
During orbit insertion, scientific instrumentation on the craft was powered down, as Juno was running entirely on internal batteries. This was necessary because during the process it would pass through the shadow of Jupiter.
NASA scientists were able to detect successful orbital insertion by Doppler shift in the received signal. The change in frequency of the signal indicated the correct and expected change in velocity. Additionally, Juno sent specific tones to indicate success of the operation.
Once the craft is settled into its polar orbit of Jupiter, it will always be illuminated by the sun and will power itself from its large solar arrays. At this point, all scientific instrumentation will once again be powered on and active.
Interesting side note: There are three small passengers aboard. NASA collaborated with Lego to make three Lego men; Galileo, Juno (Hera) and Jupiter (Zeus). The reasons for the choice of tiny passengers relate to both history and mythology.
The inclusion of Galileo is obvious. Juno (Hera) and Jupiter (Zeus), however, were included because of Juno’s ability to see through clouds to see what Jupiter was up to. This is exactly what the instrumentation on the Juno spacecraft are designed to do; pierce Jupiter’s cloud layer to see what’s going on deep within the gas giant.