The recent flyby of Pluto brought back memories of Nasa at its best. But is the space agency's effort to explore the Solar System with robotic spacecraft in trouble?
Among Nasa's greatest achievements was sending astronauts to the Moon and returning them safely. An American flag was planted on the lunar surface. It marked a triumph for the US in the space race with the Soviet Union. But Neil Armstrong's step on the Moon was a moment for the entire planet, briefly bringing together a divided and war-torn world.
Forty-six years later, almost to the day, the Stars and Stripes was waved and there were chants of "USA!" at mission control as the New Horizons spacecraft flew past an unexplored world.
America's space agency and those working on the mission deserve to be congratulated on yet another great moment. No one should begrudge the scientists involved their celebration, but why such patriotic fervour this time?
Coming just a year after Europe setting down a lander on a comet, India orbiting Mars and not long after China sending a rover to the Moon, could those who work for Nasa be feeling a little insecure? If so, say observers, they may have good reason to be.
Since the New Horizons spacecraft was launched, the US space agency has faced upheaval and a funding crisis.
And some of the agency's robotic exploration projects have been mismanaged and over budget, leading the space agency to cut some of its planetary exploration missions.
Nasa's James Webb telescope is the successor to its beloved and very successful Hubble Space Telescope and will be able to image some of the most distant objects in the Universe. It was supposed to have cost $1.6bn and to have been launched in 2011. The current projected cost is $8bn with a launch date of 2018. The scientific journal Nature called it "the telescope that ate astronomy".
The most recent rover mission to Mars, Curiosity, landed successfully three years ago and has performed admirably. But the mission was around a billion over budget and three years late.
These events were monitored by former Nasa scientist Keith Cowing in his blog Nasa Watch.
"As upset as Nasa proclaims to be when these overruns happen, they just go off and do another one. It is an ongoing chronic issue with Nasa," he told BBC News.
"Nasa's financial management system is still a mess. After doing Nasa Watch for 20 years it is almost like I have a key on my keyboard that I press and it says: 'Nasa doesn't understand what things cost'."
A number of factors, including the US financial crisis, have caused the collapse of some collaborations between Nasa and the European Space Agency (Esa) in recent years. These missions included a plan called EJSM/Laplace to explore the icy moons of Jupiter that might be hospitable to life and a joint Mars mission called ExoMars.
In all these cases Esa either has or will go ahead on its own according to Prof Andrew Coates of the Mullard Space Science Laboratory which is part of University College London. Prof Coates is one of the principal investigators on ExoMars and a successor to EJSM/LaPlace the mission, called Juice, which is due for launch in 2022.
"What this has done is that it has provided a fantastic opportunity for Europe to take a really leading role in space exploration, which it is doing with ExoMars and Juice," he told BBC News.
The Russian space programme has also experienced financial difficulties. Even so, it has plans to begin a series of robotic missions to the Moon with a view to developing a long term presence on the lunar surface and a proposal for a probe to Venus.
China has had a series of robotic missions to the Moon and has plans for a new orbiting space station. It also has ambitions to send a probe to Mars.
India too is now arriving at the top table of those exploring space with the arrival of an orbiter at Mars last year. It has plans for a follow-up. Meanwhile, Japan continues to have a strong scientific programme.
According to Prof John Logsdon, of George Washington University, rival space agencies are catching up fast.
"Nasa has had a series of successes, notably the landing of rovers on Mars, particularly Curiosity. But the planetary exploration programme has struggled for adequate funding. Its funding has been cut by between 10% and 15% and no flagship missions seem to have been put in place under Obama," he told BBC News.
Nasa's focus over the last decade has been on Mars. And although the Spirit and Opportunity missions and the Curiosity Rover have been scientific triumphs, Keith Cowing says other interesting worlds have been ignored.
"There are a lot of people that think we have spent too much time on Mars and that Europa, Ganymede and Enceladus (moons of Jupiter and Saturn that could be hospitable to life) are worthy of our financial attention," he says.
Nasa has reportedly been cajoled by Congress into reviving plans to explore Europa as one of its next big missions.
Two decades ago, Nasa administrator Dan Goldin embarked on an effort to develop missions that were faster, better and cheaper - FBC in Nasa jargon.
Typically, a Nasa programme can take between 10 and 15 years to develop from approval to launch. The Hubble Space Telescope, for example, took 20 years. Goldin's aim was to have the turnaround for missions reduced to four years and their cost cut by a quarter.
But questions were raised about FBC following high profile blunders in two low-cost missions to Mars: Mars Climate Orbiter and the Mars Polar Lander, both in 1999. There were no further FBC missions following these losses. But according to Richard Holdaway, former director of RAL Space, that was a mistake.
"The cost overruns on the James Webb Space Telescope and the Curiosity mission became a significant problem. 'Faster, better cheaper' was the right approach, as we have seen with the success of the New Horizons mission," he said.
"But Nasa didn't implement it properly, with its full authority or stick to the criteria it set to cancel projects that were over-running."
Instead, Nasa seems to have lurched from bargain basement space missions back to gargantuan projects where costs have spun out of control - with the exception of the low-cost Discovery class and medium-cost New Frontiers class missions (of which New Horizons is one). According to Prof Coates, the European Space Agency has - generally speaking - a more balanced approach.
"Nasa learned the hard way that you can do two of those (faster, better, cheaper) at the same time but not three. Europe stayed the course on the larger missions such as Rosetta, ExoMars and Juice as well as small ones."
So could it be time for Nasa to rethink the "faster, better, cheaper" plan?
"Dan Goldin was prophetic," says Mr Cowing. "But the way his idea was put into practice was flawed and inconsistent and insincere," he says.
"It's like having the archetypical pictures of the little mammals running around as the dinosaurs are dying. There is always the seed of the next wave of doing things that emerges from the current way of doing things."
However, Prof Logsdon believes that following a difficult period of transition, Nasa is starting to get back on track.
"Congress has forced it to develop a big new rocket which has constrained the funds available for ambitious new projects.
"The James Webb is a big hiccup in the progress of robotic science missions - we are in this period of re-establishing our human space flight capability and getting ready to explore. Nasa is recovering and doing well in the missions that it is involved with. So I think the outlook is more positive than not."
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