Countdown to Curiosity: today’s the day!

26 11 2011

Weather update: Looking good! Low wind, partly cloudy.


This morning Cosmoboy realized that one important piece of equipment hadn’t been covered in the “Countdown” series: the Alpha Particle X-ray Spectrometer (APXS). This is Canada’s contribution to Curiosity’s instrument suite! APXS was built in Richmond B.C. by MacDonald, Dettwiler and Associates Ltd and the Principle Investigator is Dr Ralph Gellert at the University of Guelph. Dr Gellert actually designed a previous version of the instrument for Spirit and Opportunity, so he’s a bit of a star of the Canadian space instrumentation scene!

OK, so what does APXS actually do? Basically, APXS is an instrument for determining precisely what elements are present in a given sample. To do this APXS will rely on two techniques, Particle-Induced X-ray Emission (PIXE) and X-ray Fluorescence (XRF). PIXE relies upon the fact that fast moving alpha particles can knock electrons from the lowest energy levels of atoms right out of the atom itself. This leaves an atom with an unstable configuration of electrons, and one of the electrons in the high energy levels of the atom will now drop down to the low level one, emitting an X-ray as it does so. APXS has a detector to capture these X-rays and we can determine the elements in the sample by looking at the energy of the X-rays – each elements emits X-rays with very specific energies, an energy signature if you like. PIXE is good for detecting lighter elements, essentially sodium through to calcium.

APXS contains Curium 244 as a source of alpha particles. But it also decays into Plutonium 240 (one of the tracer elements people have looked for in tracking Fukushima emissions) which emits X-rays that can in turn excite X-ray emission in other atoms. This is called X-ray Fluorescence and the idea is pretty much the same as PIXE, accept instead of alpha particles causing the excitation, this time it is incoming X-rays. The two methods turn out to be very complementary though as XRF is good for detecting heavier elements, calcium through to zirconium.

OK, so that’s the science behind APXS. For it to work effectively you have to be able to get close to the sample. So the emitter and detector part of APXS sits on the end of Curiosity’s robotic arm while the main electronics are back in side the body of the rover. The APXS on Curiosity is also 3 to 6 times better than the ones on Spirit or Opportunity. It will take data much more rapidly, and quick tests for a few specific elements can be done in as little as 10 minutes – it used to take several hours. It can even take data during the day as well, because a special active cooler has been added.

The main science goals of APXS are similar to that of CheMin – to understand the elemental composition of Martian geology, what elements are present and in what concentrations? The high precision of APXS will also allow it to look for any local anomalies in elemental abundances, which will help pinpoint interesting areas for further sampling with SAM. There is also a possibility of combining results with CheMin to find X-ray invisible compounds like bound water or carbonates.

How expensive was APXS to build? I’ll present this in a way that puts the investment in context. Curiosity’s overall budget is about 2.5 billion dollars. Canada’s gross domestic product is about 1/10th that of the US. So if we collaborate on a project with the US, you would anticipate that we might contribute about 10% of the overall cost, or around $250 million. Well, we didn’t do that, so about half that, say $100 million? Nope, I may as well cut to the chase, we spent $17.8 million. OK, so that’s still a good sum of money, but from an international perspective it’s a pretty minimal investment: 0.6% of the overall mission cost. I’ve written at length about the funding for the Canadian Space Agency and how low it is, and that’s true regardless of which party is in power. Although things are about to get notably worse as the CSA budget is to be cut by almost 25% beginning in 2013. But at least we’re involved, it could be worse.

APXS is a great instrument, and you can be sure that once it starts taking data on Mars there’s going to be a lot of interesting new discoveries!

T-minus one hour and counting…. Go Curiosity!


Why “Curiosity” and Mars go together

15 11 2011

Curiosity might kill the cat, but it’s what keeps scientists in a career. So it’s pretty appropriate that the next generation Mars Rover, scheduled to launch on November 25th, is named Curiosity. But more importantly than its name, Curiosity is the most interesting mission to Mars since the Viking landers of the 1970s.

Don’t remember the Viking landers? OK, no problem, here’s the background.

In the late 1960s with the space race in full swing, the US was planning a suite of ambitious planetary missions. By the end of the decade engineers and scientists from the Langley Research Centre of NASA had outlined the Viking mission – an ambitious plan centered on placing landers on Mars to look for evidence of life. With numerous important scientists, such as Harold Urey and a young Carl Sagan, supporting this kind of mission the project had significant political capital. The mission parameters were not easy, the lander design was far more complex than lunar landers NASA had designed previously.

But to cut an incredibly interesting story short, the Viking landers were one the most successful missions flown by NASA in the 1970s. Aside from their experiments (more on that in a sec) they sent back images from the Martian surface. I remember thinking as a six year old, “WOW! These are the first pictures from another planet!” Actually that wasn’t true because the Russian’s had images of the Venusian surface, but I didn’t know that at the time. As far as I’m concerned those first images were just as good as the ones taken by Spirit and Opportunity almost 30 years later, and heck, the Vikings were the first landers to show us frost on another planet!

But for all the amazing images, it was the science experiments that really excited me. The landers were designed to scoop up soil and then test it for signs of alien life! That isn’t as easy as it sounds. There isn’t any one single chemical or biological test that can be done to look for life. So the Vikings carried a suite of four experiments. One to examine the chemical compounds present (after baking the sample) and three others to look for signs of biological processes: photosynthesis, metabolism and respiration. Despite some really interesting preliminary results, it turns out that Mars didn’t have any signs of life in these tests. Although 40 years later, the data remain under scrutiny and there is an outside possibility that something was missed. So Mars still has plenty of secrets to be unlocked….

Enter Curiosity. With a scientific payload weighing ten times that carried by any other rover, and being a similar size and weight to a Mini-Cooper, it will bring Mars science truly into the 21st century. Unlike the Viking landers, Curiosity’s mission profile is best described as assessing whether the right conditions for life could have existed on Mars, rather than looking for life directly. But it will revisit one of the Viking tests: do the chemical compounds in samples include organic (carbon including) compounds that are necessary for life? In an advance over the Viking missions it will also do it in two ways, the first being similar to the Viking approach of testing a baked sample, while the other approach will use liquids in the analysis. Many scientists believe the liquid method will in fact find the organic molecules that the baking method essentially destroys.

But these chemical tests are just one part of Curiosity’s 2-year mission (actually 1 Martian year of 686 Earth days, or 668 Martian “sols”). Curiosity (or Mars Science Laboratory as it was originally known) will also examine Martian geology and atmosphere, while sending back the first high definition movies of the Martian surface. Nothing quite beats a high-def movie for giving a feeling of being there, and NASA isn’t missing a trick on this one – it will be incredible! Over the next few days I’ll outline the scientific payloads.

For all the excitement,  one thing makes Curiosity just a little bit scary – its landing. At close to one ton in weight, it can’t just be dropped on a parachute – the gravitational field of Mars is too strong. So a deft powered descent is part of the mission profile. Anyone who recalls the Moon landings knows that finding the right place to land can be pretty difficult (Apollo 11 got perilously close to running out of fuel while Neil Armstrong found the right place to land). To solve this problem Curiosity will actually be lowered by crane from a hovering descender onto one of the smoothest pieces of Martain soil we know. This will be the first time a “sky crane” has been used in any mission.

And Canada’s involved too! The Alpha Particle X-ray Spectrometer (APXS) was funded by the Canadian Space Agency and will allow Curiosity to determine the elements in a sample by shining a beam of alpha particles on the target. The APXS science team includes members from The University of Guelph and the University of New Brunswick.

If you haven’t guessed already, I can’t wait for Curosity to begin its journey. It will take over 8 months to get there, but the science it will produce is the most exciting event on Mars in almost 40 years. And it has a face for fame, anyone remember Johnny 5 from “Short Circuit”? Separated at birth?