Paul Birch and Mass Stream applications for the real world

[Dalex]

Well I can't speak for the time of the Viking landers as space science was more popular but yeah it wouldn't surprise me if history progressed pretty much the same for the reasons I've stated above. Why would you think it would be different? Space exploration, especially manned, is very very hard and very very expensive. Despite hundreds of billions of dollars over the last several decades technologies haven't developed to the point where those two statements aren't true.

Well for starters USSR and USA would have reason for another space race. Technology for interplanetary travel already existed even if only in prototype phase (NERVA) also launch vehicles that could deliver parts for said mission existed unlike now.

As for cost of manned space exploration consider this: some industries (car manufacturing for example) show what is called economies of scale.
For example making one car in your garage will cost you much more per unit produced than if you had factory.
Same goes for spaceships. Once you start making these things on "assembly line" cost will get lower.
In addition astronaut can stay in orbit longer and do more work if he lives in space station with artificial gravity. We don't have that kind of space station but we could if we made sufficient investment into production facilities. You also have to think about in situ manufacturing which would be possible with enough people and automatiization, that would get costs lower too.

Don't forget about space tourist industry (yes I know it would be marginal compared to costs but it could provide some money).
Eventually importation of certain metals (like platinum in reasonable quantities because we don't want the market to collapse) would became possible.
Technologies developed as direct result of said efforts would enhance our lives significantly. For example flight control and automation of space industry would lead to better electronics, material science would need to answer new challenges arising from hostile environment and so on.

Yes I know it would require long term effort but if life on Mars was discovered by Viking probes then space industry would not stagnate at least not for so long.

As for feasibility, this is report of Space Task Group chaired by Spiro Agnew Report

In report cost of $8-10 billion is mentioned per year in 1969 dollars for Mars mission to happen in eighties. Of course there would be overruns so I guess 20 billion puts us in save territory yes it is much but that is cost for space station, moon base and several landings on Mars.