Why is it difficult to drop a probe like Galileo? How did engineers solve this problem?

Galileo spacecraft was sent to orbit around and study Jupiter. It was launched on October 18, 1989 and entered into Jupiter's orbit on December 7, 1995. It had a lot of firsts in its name and most important of them was the first probe that entered in Jovian atmosphere. The spacecraft carried a probe named Galileo which separated from the spacecraft 5 months before it was to reach Jupiter. The separation was done in such a way that the rendezvous of probe and spacecraft with Jupiter coincided.

The mission was very challenging. Some of them are listed below:

1. Because of Jupiter's immense gravity the speed of the probe reached up to 47 KM/Sec as it approached Jupiter, but to enter into Jupiter's atmosphere it had to be brought down to subsonic level (0.34 KM/Sec). Due to this it had to withstand 228G deceleration.

2. Also, the time of probe entry had to be synchronized with that of the rendezvous of spacecraft with Jupiter. Very precise calculations were needed to achieve this.

3. Jupiter has a very thick atmosphere which would result in very high pressure and temperature for anything entering into it atmosphere. A very strong heat shield was needed to withstand such high pressure and temperature. Out of the 339 kg of the probe 152 kg was just the weight of the heat shield. Around 80 kg of the heat shield was lost during the entry. Its instruments were so sturdy that they worked till a pressure of 23 atm and temperature of 153°C.

4. The deceleration of the probe was further aided by using a parachute during the entry.