Countdown to Curiosity: 3 days to go

23 11 2011

While yesterday we focused on radiation measurements on Mars, and the RAD experiment, today we’ll look how Curiosity is going to measure the Martian atmospheric conditions, or Martian weather if you want to think about it that way. The instrument(s) that will make these measurements form the Rover Environmental Monitoring Stations (REMS).

The Martian atmosphere is both very thin and much lower pressure than the Earths (the average pressue is about 150 times lower than at sea level on Earth). The elemental composition is very different too, Mars’ atmosphere is dominated by carbon dioxide (95%) and there is only a tiny fraction of oxygen (0.1%). Combined with a variation of surface temperature from -87 C through to (very localized) highs of 30 C in the southern regions (although mean surface temps are around -60 C), Mars is expected to have some quite unique planetary weather.

For our weather forecasts on Earth we like to know temperature, wind speed, humidity, atmospheric pressure and some times the UV levels. So it will come as no surprise that’s pretty much what Curiosity is going to measure. In fact, Curiosity will measure the following six atmospheric parameters: wind speed/direction, pressure, relative humidity, air temperature, ground temperature, and ultraviolet radiation.

Anyone who has worked at a weather station knows that you need to put sensors measuring wind speed (for example) slightly above the ground to get away from surface effects. The two wind speed sensors thus sit on Curiosity’s Remote Sensing Mast (on two separate booms, one pointing forward and another at 120 degrees to the first), along with humidty and air & ground temperature sensors. Placing the booms at different angles ensures that at least one of them will record accurate wind data for any given wind direction. Note, even on the mast the wind measurements will still be slightly impacted by air flow around the mast itself. The wind speed measurements will be pretty accurate, with a resolution of around 0.5 m/s. The directional measurements are anticipated to be accurate to within 30 degrees or so, and it will even measure vertical variation in wind direction to within 10 degrees.

Even though the ground temperature sensor is up on the mast, it can still measure the temperature of the ground by pointing toward a patch to the side of the rover. The temperature sensor is an electrical one, a thermopile, and can record in a temperature range of 150-300K with an accuracy of around 10K. The air temperature measurements made on the boom itself will be twice as accurate (to within 5K) over the same temperature range. The pressure and humidity sensors complete the instrument suite on the mast.

Since the UV sensor is designed to measure the incoming UV from above the rover, it sits on top of the rover deck to the back. Much like the radiation assessment detector (RAD) the UV sensors are sensitive to incoming radiation across about a 60 degree cone above the rover. The sensor itself will be able to detect UV in six different wavelength ranges, (from UVA through to UVE, plus a “total dose” across the entire range) and will thus characterize the UV environment in great detail.

But really the great “value add” behind all these measurements is that Curiosity will make them systematically every hour. So for each hour of each Martian day, Curiosity will record 5 minutes of data from all the sensors. To do this REMS has been set up to work independently of the main power sources on Curiosity and can take data even when the rover is in a sleep mode.

From all this data we’ll be able to develop detailed models of Martian weather patterns, with a detailed focus both on large scale fronts and smaller, so called microscale weather systems. The microscale systems include small whirlwinds like dust devils. We’ll also uncover precisely how the Martian water cycle works, and it’s going to be seriously different from the Earth’s!

And to whet your appetite for all this new Martain weather data, here’s a beautiful Martian sunset taken by the Spirit Rover. Tomorrow: DAN.

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Countdown to Curiosity: 4 days to go

22 11 2011

With 4 days to go, we can start to ask the question: What will the weather be like on Saturday? At the moment there’s a 70% chance of suitable launch weather on either Saturday or Sunday. So things are looking good…

Yesterday we talked about the Sample Analysis at Mars (SAM) instruments. Today we’ll talk about a simpler, but nonetheless important piece of equipment: the Radiation Assessment Detector (RAD). Data from RAD will provide the first measurements of radiation on the surface of Mars (it will also operate during the flight to Mars) and allow us to answer a very important question for any human missions: What would be the radiation dose on the surface? Knowing this answer is a big deal: unlike the Earth, Mars does not have a big magnetic field to shield it, or a thick atmosphere to shield against cosmic rays.

RAD will measure the three main types of radiation, alpha, beta and gamma. Alpha radiation, which is the easiest radiation to shield against, corresponds to particles containing two neutrons and protons (the same as a helium nuclei). Beta radiation, which is slightly harder to shield against than alpha particles, corresponds to high energy electrons or positrons. While gamma radiation corresponds to high energy photons, and, depending upon the energy of the photons, can need inches of lead to provide adequate shielding. In addition to these forms of radiation, RAD will also detect cosmic rays which are made of high energy atomic nuclei stripped of their electrons as well as other particles such as neutrons. For the experts, here is a graph of the energy coverage for each of the different particles RAD will detect:

RAD will sit on top of the body of Curiosity. It isn’t very big, roughly the size of coffee can, and at first take isn’t all that impressive looking. It’s essentially a very short and “stubby” telescope with detectors behind it that will capture the various particles associated with the radiation. The particles are detected by essentially two methods: The first is through a process called scintillation, whereby the energetic particles in the radiation cause a target material to undergo luminescence when hit (the light is then detected). The second method is through striking a semi-conducting material which creates an electric current that can be detected. It’s also possible to use these interactions to determine the overall energy of the incoming particle. In all, RAD contains five separate detectors which combine to give it both an excellent coverage in terms of the energies of incoming particles, and also the specific types of radiation. RAD is sensitive to particles coming in from above through about a 65 degree cone of coverage.

While RADs measurements will enable us to determine how hazardous the Martian environment is for humans, this data can also be used to determine what kind of life could survive on the surface now, and also in the past as well (it’s even possible to calculate how far down into the Martian surface life would have to be to avoid any lethal radiation levels). The radiation levels can also be used to infer what kind of mutation risks the environment presents for lifeforms based on DNA. Lastly, from all the new data it will be possible to determine how much of an impact the radiation background has had on the chemistry and isotopes in the Martian environment.

Bottomline: from the human exploration persepective, RAD well tell us just how inhospitable the Martian environment is!

Tomorrow: the Rover Environmental Monitoring Station (REMS).





Countdown to Curiosity: 5 days to go

21 11 2011

Following a 1-day hiatus because of the launch delay, we’re back on the countdown trail. Last time in this series of blog posts we looked at the CheMin experiment and what it will tell us about the mineralogy of Mars. Today we’ll focus on Curiosity’s Sample Analysis at Mars (SAM) system. In a nutshell, SAM will help us to look for the organic compounds that are necessary for life.

SAM is actually a suite of three main instruments plus some sub-systems that sit within the body of the rover. It has an inlet on the top that is fed by the robotic arm part of the sample acquisition system, but it can also sample the atmosphere directly through a pair on inlet tubes.

The first instrument we’ll talk about is QMS, the Quadrupole Mass Spectrometer. Mass spectrometers work on the principle that the deflection of a particle in an electric field is determined by the ratio of its mass to its electrical charge. Notice that the particles must have an electric charge, which means that the particles in the sample need to be ionized (i.e. have electrons removed from them). The stream of particles is passed through the electric field and only particles of a certain mass to charge ratio then reach the collector. With a little effort the exact masses of the atoms can then be determined. The Quadrupole name of the system comes from the electric field geometry being a quadrupole between four rods.

The TLS instrument (Tunable laser spectrometer, sometimes called TDLAS) is another type of spectrometer that is specially designed for handling gases. This type of spectrometry measures the amount of molecules present by essentially determining how much light of given wavelength is absorbed. The wavelength of the light is determined beforehand to correspond to a specific molecule. If you have more absorption, you have more of that molecule present. The TLS on Curiosity will target measurements of methane (CH4), water (H20) and carbon dioxide (CO2), and will be able to measure their concentrations to levels of parts per billion in some cases.

The last main instrument in SAM, is the GC for gas chromatography. Gas chromatography applies to organic compounds that will evapourate into a gas (in this case Helium) and then rise up through that gas. Different compounds will “rise”, strictly speaking the gas passes through a wound spiral tube so perhaps “travel” is better, at different rates allowing them to be separated. If the rates are known beforehand then the molecules present can be determined. This process can also be used to feed into the QMS to provide combined “CGMS”. GCMS is a very powerful method because it combines the best of GC, i.e. separating different compounds, with the ability to determined the pieces that make up the compound itself (through mass spectroscopy).

So those are instruments, what are the experiments going to address? Direct from the Goddard website, the goals can be summarized as follows:

    1. Question 1: What does the inventory of carbon compounds near the surface of Mars tell us about its potential habitability?
      1. Goal 1: Survey carbon compound sources and evaluate their possible mechanism of formation and destruction.
      2. Goal 2: Search for organic compounds of biotic and prebiotic importance expecially methane.
    1. Question 2: What are the chemical and isotopic states of the lighter elements in the solids and atmosphere of Mars and what do they tell us about its potential habitability?
      1. Goal 3: Reveal the chemical and isotopic state of elements (i.e., N, H, O, S and others) that are important for life as we know it.
      2. Goal 4: Evaluate the habitability of Mars by studying its atmospheric chemistry and the composition of trace species that are evidence of interactions between the atmosphere and soil.
  1. Question 3: Were past habitability conditions different from today’s?
    1. Goal 5: Understand atmospheric and climatic evolution through measurements of noble gas and light element isotopes.

SAM is the experiment that will follow up on the questions posed by the Viking landers: even if there isn’t life now, are the building blocks for life there?

Tomorrow: the radiation assessment detector (RAD).





Countdown to Curiosity: launch delay by 1 day

20 11 2011

This is Ecogirl & Cosmoboy’s 100th blog post! Thanks to everyone who’s been reading and there’s more to come!

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Curiosity’s launch has been delayed from Friday November 25th to 10:02 am Saturday the 26th. The delay is due to a battery change in the Flight Termination system of the Atlas V launch vehicle. Flight Termination systems are a key part of range safety (rockets frequently do veer off course!) so this is a pretty big deal.

So rather than writing about an experiment today, let’s take a closer look at some of the launch details and any dangers that might be lurking there.

What if it all blows up? Well other than being a huge disappointment for thousands of people that have worked on the project, there are a number of hazardous materials on the rocket. From the press perspective, I’m sure the most play would be given to the 3.5 kg of Plutonium 238 that is actually Curiosity’s main power source.

But there’s really very little cause for concern. 238Pu is what’s known as an alpha emitter – it emits alpha particles (essentially helium nuclei, containing two protons and two neutrons). From a particle physics perspective, these are comparatively large objects that will interact easily with material around them. Thus they don’t penetrate far, even a few inches of air or paper is enough to protect against small sources of alpha particle radiation. That’s considerably different to say gamma radiation emitters which can penetrate inches of lead (depending on their energy).

In short, NASA estimates there’s about a 1 in 400 chance of material being released during the launch. Anyone who was exposed to this material would actually receive a radiation dose far below that we receive in a year from natural sources. For the experts, the maximum dose expected for an individual in the launch range is 0.23 rem (as compared to 0.14 rem/day being average exposure from solar and cosmic radiation). For the dose to be fatal, it would need to be over two hundred times higher, and that is simply not going to happen – there isn’t enough material on board, and it’s type of radiation is easily shielded.

It’s worth pointing out that NASA launches have to undergo an environmental assessment (here is the one for Curiosity). These issues are taken very seriously and each launch has a list of hazardous materials that are on board. According to NASA documentation each Atlas V launcher (i.e. neglecting the payload) includes 4.7 tons of hazardous waste. In case you were wondering, here’s the list!

Material                                                                         Quantity
Petroleum, oil, lubricants                                    2177 kg (4790 lb)
VOC-based primers, topcoats, coatings            145 kg (320 lb)
Non-VOC based primers, topcoats, coatings   86 kg (190 lb)
VOC-based solvents, cleaners                             627 kg (1380 lb)
Non VOC-based solvents, cleaners                    432 kg (950 lb)
Corrosives                                                                2500 kg (5500 lb)
Adhesives, sealants                                                1036 kg (2280 lb)
Other                                                                         291 kg (640 lb)
Electron QED cleaner                                            5.7 liter (5 qt)
MIL-P-23377 primer                                              2.8 liter (5 pt)
Silicone RTV-88                                                      45 liter (10 gal)
Electric insulating enamel                                    0.1 kg (5 oz)
Acrylic primer                                                          22 liter (5 gal)
Conductive paint                                                     45 liter (10 gal)
Chemical conversion coating                                0.3 kg (10 oz)
Cork-filled potting compound                              5.7 liter (5 qt)
Epoxy adhesive                                                        5.7 liter (5 qt)

So how likely is a launch problem? Looking at the statistics of the Atlas V rocket, it’s had 27 launches and 1 failure. That’s close to a 4% failure rate, which is actually pretty good. The probability of anything going wrong on the range itself is low – thankfully!

Of course there are mission risks far beyond the launch itself. The recent Phobos-Grunt problems serve as a good reminder that there are plenty of things that can go wrong on a mission to Mars – this is rocket science…

Tomorrow, provided there are no further delays :), Sample Analysis at Mars (SAM).





Countdown to Curiosity: 6 days to go

19 11 2011

Yesterday we talked about ChemCam, and how Curiosity will be able to sample rocks up to 7m away using a laser. Today we’ll look at CheMin, short for Chemistry and  Mineralogy. This is the first of the instruments we’ve looked at that is served by the sample acquisition system (I’ll talk about this more tomorrow when we look at the Sample Analysis at Mars (SAM) system), and is contained within the body of the rover.

While LIBS can tell you what elements are present in a rock, the vapourization process destroys the crystal structure created by the bonds between the atoms. So LIBS can’t tell you precisely what minerals (like hematite or magnetite) are present in a rock. That’s where CheMin comes in. Using X-rays it will be able to determine what mineral crystal structures are present, as well as being able to give a rough breakdown of the elements in a sample.

The technique used to determine the mineral structure is known as X-ray diffraction. When X-ray photons are fired at a material with a precise crystal lattice structure the X-rays will be scattered when they pass through the lattice in a very specific way (the basics of the theory were worked out by the Braggs around 1913 or so). For a given incoming energy (or wavelength) the spacing between atoms will determine the angle that the X-ray photons are scattered through. So from the angles you can then determine the type of lattice (actually it’s good to have two sets of angles from different incoming energies, and then a bit of sleuthing is required to figure out the precise minerals present on the basis of the lattice size and the elements present).

CheMin will perform a very specific type of x-ray diffraction commonly known as powder XRD (or often just XRD), where the sample is provided in a powder form. XRD produces what you might call an average signal that combines all the different lattice scatterings super-imposed on one another because the powder contains the minerals in random orientations. The result is just a series of rings that specify the lattice spacings (one for each dimension).

As well as using X-ray diffraction, CheMin will also use X-ray fluorescence (XRF). The physics behind this process is actually quite a bit simpler than the X-ray diffraction. In fluorescence, X-rays that strike atoms will often knock electrons entirely out of the atom, leaving behind an ionized atom (i.e. one missing an electron) and an unoccupied electron energy level. Importantly, the unoccupied energy level is usually one of the lowest ones and many other electrons will “want” to be in this state. Thus an electron with a higher energy will drop down to this lower energy and emit an X-ray photon as it does so – the source of the fluorescence.

The key part here is that the energy levels of atoms are very specific to each element. So the energies of the X-rays produced in the fluorescence precisely describe which elements are present. This is exactly the same idea as used in LIBS, just using X-rays.

CheMin thus gives you the atoms and the crystal lattice structure you need to figure out what minerals are present in the sample. From this information we’ll build up a picture of the role of water in the formation of minerals, how they were deposited, and how they have been altered through geological processes. It’s also possible to use this information to look for mineral signatures of life, whether there were environments in the past that were, at least at one time, habitable.

CheMin is thus really important part of Curiosity’s main mission goal, to determine the current and past habitability of Mars.

Tomorrow: Sample Analysis on Mars (SAM)





Countdown to Curiosity: 7 days to go

18 11 2011

Yesterday we talked about the cameras on Curiosity – and there’s plenty of them. Curiosity is going to document Mars in high resolution and send back some pretty amazing HD movies.

Today we’ll talk about another set of sensors (slightly confusingly also called a camera) namely, ChemCam. The “Chem” part is a dead give away, this package is designed for determining what elements are present on Mars. ChemCam contains two major instruments:

LIBS, short for laser-induced breakdown spectroscopy, will do what every science fiction buff wants to do – vapourize things with a laser. Yup, this is the first interplanetary mission with a laser! But before everyone gets too excited, LIBS will only focus its laser (on Curiosity’s mast) into a point 0.3 to 0.6mm in diameter. Although it will achieve a really high energy density within that spot, 10 MegaWatts per mm squared. Physics note: remember this is a power rating though, how much energy is expended per second. In fact the laser will typically only fire for 5 nano seconds so the total energy focused on the spot turns out to pretty small, about 14 milli Joules of energy (that’s about as much energy as it takes to pick up a pencil and get ready to write with it).

But once the laser has vapourized the small amount of material (and it can choose spots up to 7m away) the light from that event will be captured and analyzed using a spectrometer. By looking for different wavelengths of light associated with different atoms it will then be possible to determine precisely what elements were in the vapourized sample. We can expect to find Na, Mg, Al, Si, Ca, K, Ti, Mn, Fe, H, C, O, Li, Sr, Ba, S, N, P, Be, Ni, Zr, Zn, Cu, Rb, and Cs (at least these are all found in rocks on Earth). From the data collected by LIBS we’ll start to understand Mars geology far better than we do right now (both at local and regional levels) and we’ll also learn more about trapped water in rocks and minerals on Mars. Oh and whether there are any materials that are potentially hazardous.

RMI, the Remote Micro-Imager, provides imaging of the spots that LIBS vapourizes. It will help provide a geological context for the data that LIBS gathers – did we vapourize the rock, or something that was actually sitting on top of it? This isn’t as simple as it sounds because rocks often have layers of dust on top of them and RMI will help determine when that dust has been removed (it might need a number of shots from the laser). RMI will also be able image farther out than the 7m limit of LIBS and will be able to resolve features 1mm in diameter at 10m away (see picture at right for an example from laboratory testing).

So that’s ChemCam! A suite of tools to let us determine what Martian rocks are made of (and it can do it remotely, no need to pick up samples or anything like that) — pretty cool.

Tomorrow: Chemin (for chemistry and mineralogy).





Countdown to Curiosity: 8 days to go

17 11 2011

Here’s a quick series of posts on Curiosity (or as it’s still known by many, Mars Science Laboratory). For each day prior to the launch Cosmoboy will write a short piece on Curiosity’s scientific instruments and/or design. For many people the most fun is going to come from the movies and images Curiosity sends back, so let’s start with a quick overview of the cameras onboard – and there are plenty!

The cameras break into two separate groups, those designed specifically for taking pictures and those designed to do a job, such as help navigate. The three imaging cameras are:

MastCam is actually two cameras, one with a 15 degree field or view and another with a 5 degree field of view. Both cameras take images that are about 1200×1200 pixels in size (so a bit less than your standard digital camera) using a CCD sensor (note many consumer digital cameras now use “CMOS” sensors). the images can be “tiled” together to create even bigger images (it takes about an hour to aquire the entire panorama around Curiosity). Both cameras can also take 720p high definition video (1280×720 pixels) at 10 frames per second. More importantly (at least for the science!) these cameras are sensitive across a wide range of wavelengths of light and can take images through filters in the visible through to near infra-red.

MAHLI, short for Mars Hand Lens Imager, will allow Curiosity to get a close up look at things around it the way we might use a magnifying glass or microscope. MAHLI will be mounted in a turret on the end of Curiosity’s robotic arm so that it can be moved in close to interesting features on the ground. At its closest focus MAHLI will be able to resolve features 0.0006 inches or 0.015 mm in size, i.e. microscopic. The sensor in this camera will be the same as the two Mastcams, and it will also have a small LED light so that it can take images at night. 3-d views will be taken by slightly moving the camera between two separate positions. Seeing as this camera will operate close to the ground, it also has a carefully designed dust cover!

MARDI, the MSL Mars Descent Imager, will be the first camera to provide images. For about 100 seconds, from the time the heat shield is jettisoned until touch down, MARDI will aquire 4 images per second of what is happening to Curiosity. As well as the obvious interest of seeing the landing, the images captured by MARDI will be use in assess geological features on the ground and to plan the initial rover path. These images will be balanced to provide “natural colours” as the human eye will see them.

So that’s the list of imaging cameras, what about the navigation and hazard avoidance cams?

Two pairs of hazcams are located in fixed positions on the front and rear of the rover. Since the cameras come in pair separated to the left and right of the rover, Curiosity can take forward and aft 3-d images. From this information a detailed map of the upcoming terrain (out to about 10 feet in front, in a patch up to 13 feet wife) is made. Then from these images, software running on Curiosity’s onboard navigation system will determine the best path to take. Unlike the imaging cameras, the hazcams work in black and white only.

To complement the hazcams, there are two additional navcams mounted on Curiosity’s mast. This pair of images will provide additional 3-d imagery for the navigation software from a higher vantage point (complementing the data from the hazcams). The navcams will also be able to take 3-d panoramas.

That’s the cameras! Tomorrow: ChemCam.