Real sustainable expenditure on space projects can only be from the private sector. What governments do are generally boondoggles, which sometimes show pretty results.
The space shuttle, for instance, persisted not for the scientific or technical advances, but that it sent money to lots of political constituencies, which alone made it viable. The Hubble, while giving us spectacular images, was still horribly overpriced and NASA ended up paying for it twice over (once to send it up and twice to send the shuttle after it).
There wasn't a lot of opposition to the shuttle and the ISS from within NASA (for 'eating up the budget') because they were aware that budget only existed because of these high-value items. They might have liked to have the money for other things, perhaps, but political money doesn't work that way.
The space shuttle, for instance, persisted not for the scientific or technical advances, but that it sent money to lots of political constituencies, which alone made it viable. The Hubble, while giving us spectacular images, was still horribly overpriced and NASA ended up paying for it twice over (once to send it up and twice to send the shuttle after it).
There wasn't a lot of opposition to the shuttle and the ISS from within NASA (for 'eating up the budget') because they were aware that budget only existed because of these high-value items. They might have liked to have the money for other things, perhaps, but political money doesn't work that way.