The little spacecraft that struggled
Last week’s Nature had a series of stories about the feature by Eric Hand. My reaction on reading it was a sense that he’d got it absolutely right, hitting a tone that is best described as qualified success.
There is no doubt that Phoenix was a success. It was a cheap (especially when compared to the next generation of Mars landers, the American MSL and European Exomars) spacecraft, and yet in landed and produced results from each of its instruments. The headlines were taken by the chemistry of the soil – perfect for growing asparagus, if only it weren’t sprinkled with oxidising perchlorates – but there were other, ground-breaking results too. Flying an atomic force microscope to another planet and getting it to work is breathtaking, for example, and I’m sure we’ll be surprised again and again as the teams publish their results.
And yet, and yet…Phoenix was beset with problems. The team did manage to get icy soil into Phoenix’s ovens, but never a pure sample of ice. As a result, what was for me the most important single result expected from the mission – a measurement which would have told us whether the ice that Phoenix was sitting on had melted recently or whether it had been frozen in place for billions, not millions of years – will never come. According to the article, there are hints in the data that might be the signature of organic materials, but as the team ran out of time to run their blank, comparison sample we will probably never know for sure.
The fact that these problems were avoidable – the Nature article mentions that the problems with TEGA could have, should have been spotted before launch – is ultimately irrelevant. All problems with spacecraft should probably have been foreseen and corrected, but 100% success is achievable only in the dreams of bureaucrats. What matters is the overwhelming need for the mission to be seen, and talked about, as a resounding success and nothing but that. What Phoenix was trying to do was hard, it put in a huge amount of work in a very nasty environment and we know more about Mars than we did. We shouldn’t be afraid to admit that it didn’t quite deliver everything it could have.
Where does this fear come from? It’s pervasive, and it’s not necessarily NASA’s fault. I know that when reporting on Phoenix my instinct was to tell the positive story, and I felt guilty for mentioning the problems that the team – some of the nicest people I’ve met in the five years I’ve been doing Sky at Night – were having.
In an accompanying editorial, Nature have an answer. They point out that because even cheap missions are rare and (compared to, say, funding an Earth-based research project or experiment) expensive, the cost of failure is too large. A single mishap can derail a program for years. Their solution is for there to be more recycling of material between missions – shared landing systems, for example.
The amazing rovers, Spirit and Opportunity, they point out, bounced to the surface in an airbag, whereas Phoenix touched down, and MSL, the next in line, will land via something very scary called a sky crane. (If you haven’t seen it, it’s found it’s way onto youtube).
Why didn’t all the missions use the same technology? What Nature is missing is that they couldn’t have done; if I understand the situation correctly, the trajectory needed to land Phoenix in the martian arctic wouldn’t have slowed the lander enough in the atmosphere to allow airbags to be used, and MSL is simply too heavy for airbags to support it. The spirit of their call is right, though – more probes, costing less (and therefore each individual mission doing less) and a more honest approach to success or failure is exactly what’s needed. And not just on Mars, either.
Hat tip : Emily at the Planetary Society.
