Key decisions on Europe's capability and activity in space will be taken by research ministers on Tuesday.
They will come together in Luxembourg to resolve the future of the Ariane rocket and the continent's involvement in the International Space Station.
The European Space Agency's (Esa) Council Meeting at Ministerial Level also has the Red Planet on its agenda.
Money must be found to fill a budget hole in the flagship ExoMars mission due to leave Earth in 2018.
But it is an agreement on a next-generation Ariane launcher that will be pivotal to the outcome of the gathering.
Ministers look set to approve the full development of a new rocket to replace the continent's existing workhorse.
The Ariane 5 has come to dominate the market for putting up big commercial satellites, but it is now under pressure from competitor services offering lower prices.
A new Ariane 6 concept has been proposed, and ministers must sanction the way ahead and fund it.
They are being asked to commit 3.8 billion euros (£3bn; $4.7bn), which will cover not only the A6's development but also an upgrade to Esa's small Italian-built Vega rocket.
It has taken months of negotiation to get to this point, involving government and industry.
France, which has been most keen to move to a next-generation launcher, will be putting up most of the money on Tuesday.
But it needs Germany's support financially and programmatically.
The Germans had wanted a two-step project involving an upgrade to the existing Ariane 5, but they are now ready to forego this demand - provided their interests are also satisfied on the space station.
Johann-Dietrich Woerner, who heads the country's national space agency (DLR), told the BBC: 'We will participate in A6 with a big amount of money, up to 20% if necessary for the overall programme, but it depends also that France and Italy are going ahead with ISS.
'They said that if Germany participates in A6, if it agrees in A6 - then they will participate in the ISS. Now that Germany agrees, I expect France and Italy to confirm their proposal.'
An Ariane 6 concept for the decade's end
- Next-generation rocket will be modular in design, offering two variants
- Vehicles will lean on their Ariane 5 heritage but cost less to build
- A new upper-stage engine (Vinci), already in development, will be used
- Solid fuel boosters from the Vega rocket will provide additional power
- A62 will tend to launch medium-sized government/science missions
- A64 will launch the big commercial telecoms satellites, two at a time
- They will carry 5 or 11 tonnes into geostationary transfer orbit (GTO)
Germany has long been the leading Esa member state on the ISS.
It has borne most of the financial burden and will again make the largest contribution to the 820 million euros being requested on Tuesday.
This money will support Esa activities on the orbiting platform through until 2017.
Of major interest at the meeting will be the position taken by the UK.
For years, it refrained from any ISS involvement even though it was an original signatory to the treaty that brought the orbiting platform into existence.
Then, at the last ministerial meeting in Napoli in 2012, Britain made what it described at the time as a 'one-off, 20m-euro' contribution.
The desire was that this would lead to industrial work on the ISS - which has happened. More widely, it was seen as a gesture of thanks to Esa for recruiting the Briton Tim Peake into its astronaut corps.
But other member states are now banking on the one-off payment being turned into an ongoing contribution.
There is a financial profile for funding of the ISS that was agreed in 1995 at an Esa ministerial conference in Toulouse, France.
Germany's space minister Brigitte Zypries says that the UK's support - as modest as it is - could be instrumental in helping Europe stick to this funding trajectory.
'Germany will fulfil its commitments on the basis of the Toulouse 'key', but we also expect this from our partners in Europe, especially the big countries. France, Italy and Great Britain should shoulder responsibility together with us for a stable ISS,' she told the BBC last month.
David Parker, the head of the UK Space Agency, would not discuss British strategy ahead of the meeting, adding only: 'We're interested in ensuring a really successful mission for Tim Peake in 2015.'
The third main element of the Luxembourg meeting concerns the ExoMars rover, which will be sent to scour the surface of the Red Planet in 2018 for signs of past or present life.
It is a project with a troubled history that has come within a breath of being cancelled on more than one occasion.
Its persistent woe is a shortfall in the money needed to carry the venture through to completion. This gap is on the order of 200 million euros. Ministers will be asked to plug the hole.
How much they will have left to offer after matching the needs of the expensive Ariane 6 and ISS programmes is highly uncertain, however.