What if we could unite the top 5 GDP nations and have each contribute 1% of their GDP to a non-government space agency that had a board of randomly selected advisors from the heads of industry for various tech sectors that served say 5 year terms (adequate time for serious project/mission development) before new were randomly selected. Stagger these random draws though starting with the first batch so every 6 months a certain percent are replaced so existing projects can continue to run seemlessly.
If we took 1% of the GDP from the top 5 nations, we could have 408 billion a year for space.
NASA'S budget in 2015 was 18 billion. The DoD had a budget of 585 billion in 2015. This would be a tiny sacrifice for each of the top 5 GDP nations and they'd not even notice.
All technology developed from this new space agency would be 100% open source to any participating nation, any nation that wished to join would be required to contribute 1% of their GDP for no less than 3 years to also be granted access to all of the technology, however they could be included in helping to manufacture/develop/include personnel.
Think of what could be achieved. Can we say Starfleet 0.5?