A dramatic end to a STG1 billion ($A1.7 billion) space mission will see the Rosetta orbiter crashes on to comet 67P/Churyumov-Gerasimenko.
Scientists are hoping the European Space Agency (Esa) spacecraft will beam back high-quality images moments before the controlled impact on Friday.
If all goes well, Rosetta will take a series of close-up images as it plunges towards the comet's rugged surface.
The final photo before communication is lost should be captured from a height of just 15 metres.
Rosetta will also use its instruments to gather vital data on gas and dust.
The risk faced by scientists is that there will not be time for all the information to be "downlinked" to Earth.
The spacecraft reached comet 67P/Churyumov-Gerasimenk on August 6 2014, after a 10-year journey through the solar system.
