The Nuts and Bolts
|Mars Odyssey has found what appears to be subsurface ice near where new methane concentrations may also appear when measured by Mars Express.|
Image Credit: NASA
The Mars Reconnaissance Orbiter launched on August 12, and now is on its seven-month journey to the Red Planet. Once there, MRO will search for evidence for water in the martian atmosphere, surface, and subsurface. MRO also will provide detailed surveys of the planet, identifying any obstacles that could jeopardize the safety of future landers and rovers.
Jim Graf, Project Manager for the Mars Reconnaissance Orbiter, gave a talk where he provided an overview of the mission. In part 2 of this edited transcript, Graf describes the instruments that will provide a great amount of detail about martian climate and topography.
Read Part 1 of this transcript.
“The MRO spacecraft is huge. We are two to three times the size and mass of Mars Global Surveyor (MGS) and Mars Odyssey. What this really means is we have more power, greater capability, and we can sustain more instruments than the other great missions that are currently providing terrific data.
MRO weighs 2,180 kilograms at launch. From tip to tip, from solar array to solar array, it’s 14 meters. From thrusters up to the top of the high-gain antennae, it’s about seven meters. On Earth, the solar arrays can produce six kilowatts of power. But at Mars, which is farther away from the Sun, it can still produce two kilowatts. This will be the power source for the instruments in the payload.
|Perspective view. Ophir Chasm in northern Marineris Valley network.|
Credit: ESA/Mars Express
The high-gain antenna is three meters across — about 10 feet – and has a 100-watt amplifier. Together, the amplifier and the antennae enable us to return 5.6 megabits of data per second back to Earth. Essentially, the spacecraft that have gone before us are using something akin to a dial-up modem. What we’ve got is the equivalent of three DSL lines. This is critical when you want to start an intensive investigation of a planet. We’re trying to increase the spatial resolution, finding finer and finer details. To do that, we need to be able to send back more data, and so we’ve created this very large system to get as much back as we can.
The other thing to keep in mind is we will operate at a lower orbit. We will be at a 255 to 320 kilometer orbit, as opposed to 400 kilometers. By getting closer to the planet, we can have better data resolution. But in doing that we sacrifice something called Planetary Protection. The United States has treaties with countries all over the world to prevent us from migrating our bacteria to other planets. We want to find life there, and we want to find out if life started there, so we don’t want to take it there on a spacecraft. If you are orbiting 400 kilometers or above, you have one set of rules that you contend with, and you get to stay up there for 20 to 50 years. But we are dipping into the atmosphere every time we come by, so we had to clean the bacteria off our spacecraft. It’s called a ‘spore burden approach’. We had to estimate what kind of bioload we’re carrying, and clean it up.
|Perspective view. Solis Planum images were taken during orbit 431 in May 2004 with a ground resolution of approximately 48 meters per pixel. The displayed region is located south of Solis Planum at longitude 271° East and latitude of about 33° South.|
Credit: ESA/Mars Express
But orbiting at this lower level enables us to do ground sampling at 30 centimeters per pixel, 3/10 of a meter. With three pixels together, we have the capability to resolve one-meter objects. So we’ll be able to look at the rocks on the surface. We’ll be able to look at debris fields and try to understand whether they were created just by gravity or whether there was a fluid involved, depending upon the size of the rocks and their distribution. Compare that to Odyssey, which can do 18 meters per pixel, or MGS camera at 1.5 meters per pixel.
The MRO telecommunications system will allow us to return up to 90 times each day what these other missions are returning. That enables us to start really getting global coverage. Cassini, which is now at Saturn, is expected to return 2.5 terabits of data. Magellan, which flew to Venus, returned 3.7. If you add them all up and multiply them by three, you start approaching how much MRO is going to return in terms of its data. It’s an immense amount.
And so it’s an immense challenge for the ground stations – the Deep Space Network – to absorb all this data. We have to be able to process the data quickly; we cannot allow any delays. If we get a bottleneck, we’ll never be able to recover.
|A topview, high resolution image looking down on Eos Chasma, part of Valles Marineris|
Credit: ESA/Mars Express
MRO has a wonderful suite of instruments. The smallest one is MARCI, the color imager. It weighs only two kilograms. It has a fish-eye that looks 180 degrees in two directions, looking in five visible bands and two UV bands. When it looks down, it has a swath width that goes from horizon to horizon, which is effectively 3,000 kilometers. It’s able to resolve one- to 10-kilometer objects. It’s our weather instrument, looking for the changes in the atmosphere. It’s also telling us, on a macroscopic sense, what’s happening on the surface as a whole.
The Context Imager (CTX) has a smaller swath — 30 kilometers instead of 3,000 — but it has dramatically better resolution. Instead of a resolution of one to 10 kilometers, here we’re down to about 18 meters resolution, or six meters per pixel. So we’re starting to be able to resolve things the size of a school bus with this instrument. On almost any other spacecraft that’s flying to Mars, this camera would be considered high-resolution. But for us, this is moderate resolution.
Now what kind of images is this going to take? We will be able to see tornadoes moving across the surface, and other kinds of atmospheric phenomena. We will see sand dunes, layered terrain, and bedrock.
The spectrometer, CRISM, doesn’t just look in one spectral band like the other cameras. It looks from 0.4 to four microns — from the visible all the way into the infrared. Its swath is always 11 kilometers, but it can work in a mode in which you’ve got resolution of 200 meters, and you can get 60 channels. Or you can go into a high-resolution mode where you get 512 channels at 20-meter resolution. Twenty meters is the size of the Eagle Crater. So we can start homing in on that size of phenomena, looking for compositional diversity on the surface. This camera works like a prism. It divides the light into its original constituents, which can be translated into absorption features and reflective features that are in the light that’s coming from the surface. So we can start seeing the clay; we can start seeing the water.
|Shadow cast by Spirit over Gusev tire tracks.|
Image Credit: NASA/JPL
And now we get to the big guy: HiRISE. It is 65 kilograms, and uses 60 watts. It has a swath width that’s only six kilometers wide, but it gets a resolution that’s down to about one meter. With this instrument, at our altitude, we can start looking at fine details on the surface, such as layering. We can also dovetail these one-meter resolution measurements with the 20-meter resolution CRISM measurements, providing different spatial resolution to better understand features in the surface.
In 1998 we sent a spacecraft called the Mars Polar Lander to the surface, but it didn’t make it. HiRISE can do 30 centimeters per pixel, so we can start looking for that spacecraft. The Europeans asked if we could look for Beagle, and we can certainly try to look for it, but it’s smaller than the Polar Lander.
|Tracks in the Martian soil made by the Spirit rover. Image Credit: NASA/JPL/OSU/Cornell|
When we put HiRISE, CHRISM and CTX together, turning them on at the same time, we get a high-resolution band down the middle. We can then extrapolate out to the 30 kilometers that CTX shows. So we can make cooperative, synergistic measurements. The other thing to keep in mind is that as we travel along, we can roll the spacecraft 30 degrees, one side or another. That will allow us to access a lot of places on the planet that previously we were not able to see. Since we are able to look side-to-side, on different orbits, we can start getting stereo. And HiRISE, getting stereo, can detect differences in elevation down to about 20 centimeters. So now we’re able to start seeing the hills and the little valleys. That’s especially critical if you are going to send a valuable lander there. You want to know if you’re going to run into a big crevasse or a big boulder.
Mars Climate Sounder (MCS) is a microwave instrument. It looks at the atmosphere: the water, carbon dioxide, airborne dust, and temperature. The most remarkable thing, from a technological point of view, is that this instrument has flown to Mars before. It was unsuccessful because the spacecraft failed. But when it first flew to Mars, it was 40 kilograms. The microdevices lab here at JPL worked with our Division 38 and reduced the size down to nine kilograms, while getting more accurate measurements with it. That’s an amazing feat.
With MCS, we can start looking for the sources and sinks of water vapor. We can look at the atmospheric structure that transport the dust storms, and the seasonal cycles. We can also look at the radiation imbalance, such as how much sunlight is being reflected as opposed to absorbed in the poles.
|An artist’s rendition of 2001 Mars Odyssey as it entered orbit. On Oct. 28, 2003, during a period of intense solar activity, the radiation-detecting instrument stopped working properly.|
SHARAD, the Shallow Subsurface Radar, is, perhaps, the most different of all the instruments. It will probe underneath the surface, penetrating almost 500 meters down, looking for layers of ice and water. It is produced by the Italian Space Agency in a cooperative venture with NASA. It’s only 17 kilograms and takes 17 watts, which is pretty darn amazing for radar. That’s very efficient. It works at a very low frequency, about 20 megahertz. And because it’s at a low frequency, it will penetrate the surface until it strikes an ice or a water patch, in which case you get a reflection. Now, when it gets a reflection, is that a thin layer of ice, or is it the tip of the iceberg of a major aquifer? This instrument will help us to understand that.
Odyssey’s gamma ray spectrometer has shown that there is hydrogen in the high latitudes of the North and the South Pole. We believe that hydrogen is water ice. Theories now say that there is also ice around the equator, but it’s very deep underground. Then as you get closer to the poles, the water ice comes up closer to the surface, maybe within a meter of the surface. Phoenix will be landing in ’07, and it’s going to be looking for that water.
It is critical to understand the hydrology cycle on Mars to understand if there is life. The MRO suite of instruments is designed to do that. We have MARCI and we have MCS to look for where the water is going, and where the water is in the atmosphere. At the same time, we’ll have surface imagers looking at the landforms that have been formed and modified by flowing water. And, in the case of CRISM, we’ll be able to tell where the minerals are that have been created by interaction with water. That will tell us where the water may be, and certainly where it was in the past. And SHARAD will look under the surface, on the surface and in the atmosphere for the water. We’re going to follow that water, find out where it goes, and hopefully, one day, we’ll be able to find the life that goes with it.”