Space shuttle: The darker view of the end of an era
As space shuttle Atlantis's wheels touched down in Florida on Thursday, the shuttles' epoch of defining manned spaceflight came to a close. What comes next for the US space agency is a new way of running things - but not everyone is happy about it.
For now, American astronauts and their long-time partners in Canada, Europe and Japan will depend on Russian Soyuz vehicles to get to orbit and the job of developing the shuttles' successors will be carried out in the private sector.
Much of the news coverage of the end of this era has looked wistfully back on the shuttles' accomplishments, principal among them the development of the International Space Station.
As for what's next, Nasa administrator Charles Bolden is just one of many at the agency insisting that the "future of human spaceflight is bright".
However, those rosy views of both past and future are not shared by everyone.
One concern is the sweeping job cuts at the agency. But former Nasa administrator Mike Griffin and space policy expert John Logsdon say that Nasa's grip on leadership in space has this week been lost - possibly forever.
"When you push aside all the puffery and high-flying political announcements, with the landing of Atlantis, the human spaceflight programme of the US will come to an end for the indefinite future," Professor Griffin told BBC News.
"The Obama administration has made the decision that the primary means of transporting crew to orbit will be with fledgling commercial firms, who have yet to build and deliver a product."
What has been pitched by Nasa as a brief pause in US manned spaceflight "business as usual" is a catastrophe, Prof Griffin says - possibly an unrecoverable one.
Professor Logsdon, a former director of the Space Policy Institute at George Washington University, agrees.
"We've gotten ourselves into a rather stupid situation of ending shuttle flights without a clear path to a replacement and without a sense of the long-range future of the programme. It's really rather deplorable," he told BBC News.
"I was a member of board that investigated the Columbia accident in 2003 and we said in our report the lack of a shuttle replacement was a failure of national leadership. Here we are eight years later and we still don't have a shuttle replacement," Prof Logsdon said.
"That's a failure, an embarrassment, that we have to depend on Russian taxi services [to ferry astronauts to the ISS] for a number of years, but my complaint is that we've seen this coming for years and haven't done enough about it. We put ourselves into this situation."
Although Prof Logsdon issued a scathing account of leadership issues in a recent essay in the Washington Post, he said the whole heritage of the space shuttle may have contributed to the current situation.
"The mistake was building a particular design for the shuttle that cost too much to operate and became a burden on the programme... and then building a 30-year programme around that particular design," Prof Logsdon told BBC News.
"This design was chosen while we were still doing Apollo - and there was a kind of hubris that Nasa could do anything and do it successfully. I think it became clear within the first three or four years of operating the shuttle that it was going to be extremely fragile, extremely expensive and carry with it very high risks."'Shaping the game'
For Prof Griffin, the most insidious aspect of Nasa's current situation is a strategic one. He said current rank-and-file Nasa employees shared that view even as Atlantis was being launched on her final journey.
"They're obviously out of jobs when the shuttle lands - a lot of them are already gone. But most of the people I spoke to at the launch were not actually concerned about their own prospects; their thoughts were of dismantling the teams, the loss of capability. I share those feelings, I think it's upsetting. I regard it as a mistake."
He argues vehemently that a clear technical superiority in space confers a tremendous geopolitical advantage back home.
"Very few investments on the part of society yield as much impact as an investment in human spaceflight. Our capability to operate on the frontier - in fact to define that frontier - shapes the game in ways that redound to our advantage in the future."
He imagines a future scenario in which the US and Western powers may not have the capability to return to the Moon, or go further - but countries such as China do.
"Who then exerts power and influence? Who do you think other nations will want to do deals with, which nation will be regarded as technologically superior, the most advanced, the most capable, the one that holds sway in world affairs?
"It's impossible to conclude anything other than the fact that the capability to accomplish great things in human spaceflight is in fact strategic."
For his part, Prof Logsdon said that hope for leadership in space may not yet be lost.
"America might lose its position, but that's still a choice to be made," he said.
"The alternative is to take the actions now and in the next few years to get over this embarrassing period, re-establish good US access to low-Earth orbit - but more importantly develop the systems that put us in a leadership position in the 2020s and beyond."
The irony is that the space shuttles, for all their accomplishments, may have painted Nasa and the US into the corner that it now finds itself.
Prof Logsdon said: "[The shuttle] did remarkable things, it's a remarkably capable technological achievement, but we used it too long, failed to replace it when its problems became evident, and so it leaves in my mind a very mixed heritage."