L.L. syzygia • Gk. syzygia "yoke, pair, union of two, conjunction" • syzygein "yoke together"
Recent events with interesting connections to other things got my attention. See if you agree. |
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The Phobos-Grunt spacecraft was put in orbit on November 9, but failed to fire the engine that was designed to take it on to the Red Planet. Engineers have attempted to talk to the probe and diagnose its problems, but without success. Phobos-Grunt was to reach Mars' orbit next year, touch down on the larger of its two tiny moons in 2013, collect a sample from the surface and fly back to Earth in 2014. Dust from Phobos would shed light on the genesis of the solar system and Mars' enduring mysteries. More can be read in this diary by Something the Dog Said and in this from Space Review.
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Another attempt to launch a spacecraft to Mars will occur in late November or early December. That mission is the highly anticipated
Mars Science Laboratory containing the latest roving vehicle
Curiosity. Why are there two major missions to Mars in this time period?
Is there something special about the alignment of Mars and Earth at this time? The answer is yes. That is the yoke between these two Mars mission stories happening so close in time.
Join me below the squiggle for more of this story.
The Mars Launch Window Opportunity |
Earth is in a smaller orbit around the Sun, and is going faster, than Mars. About every 25 or 26 months, Earth orbits the Sun and catches up to Mars. It is when Earth is approaching Mars that we are nearing our closest distance with each orbit. It is more economical and takes less time for a spacecraft to reach Mars then. This short video will give you an idea of this catching up perspective. It is when we are approaching Mars that we have the few weeks of opportunity to actually launch in the correct direction and with enough speed to reach Mars. It is a lot like riding a merry-go-round and you want to toss a ball to a friend who is walking around the ride in the same direction as you are going. There is a relatively short time when you can actually toss the ball to the person so they can catch it. At other times, you are too far away or going in the wrong direction.
This is called a launch window opportunity. It is during this window of time that missions must be ready to execute their launch. If they don't succeed, there is another wait until the next opportunity arrives. In this case, it would be over two years. Launch windows come at different times and durations depending on the mission. Windows to rendezvous with the Space Station are short when the station passes over a launch site. Here is more detailed explanation from an Air & Space article about Shuttle launches.
Earth moves an average of nearly 30 km/s with respect to the Sun. Mars moves about 24 km/s. Rocket engineers use this extra 6 km/s to their advantage to get the spacecraft to coast in a transfer orbit away from Earth and toward Mars. The rocket coasts in an independent orbit with respect to the Sun which intersects the orbit of Mars in about 8 months of time.
Rockets need to reach a speed of about 8 km/s in order to place a spacecraft into a low Earth orbit. To escape Earth orbit and begin the coasting journey to Mars, the rocket must reach a speed of about 11 km/s. This additional 6 km/s of relative speed provided by the speed of the Earth is a significant amount. It is a tremendous cost and time saver if you consider trying to reach Mars at any other time besides this few weeks of launch window.
There have been many Mars missions. Some notable successes are described briefly below.
NASA has a comprehensive web site with mission details about these and many others
at this link. These brief summaries are taken from that site.
Viking 1 and Viking 2 - 1976
The Viking landers took 4,500 unprecedented images of the surrounding surface and radioed more than 3 million weather-related measurements back to Earth, while their two companion orbiters took 52,000 images of sections of the Martian globe.
Mars Global Surveyor - 1997
The spacecraft returned detailed information that has overhauled our understanding of Mars. Major findings include dramatic evidence that water still flows in short bursts down hillside gullies, and identification of deposits of water-related minerals leading to selection of a Mars rover landing site.
Mars Pathfinder/Sojourner - 1997
Mars Pathfinder demonstrated a number of innovative, economical, and highly effective approaches to spacecraft and mission design. The wagon-sized Sojourner rover was the forerunner of more advanced rovers such as Spirit, Opportunity and Curiosity. The Carl Sagan Memorial Station also used an innovative petal design that unfolded after landing, exposing its science instruments and releasing the rover to explore surrounding rocks. In addition to its engineering accomplishments, Pathfinder made significant contributions to what was known about Mars' geology and meteorology at the time.
Here is a view of Sojourner rover packed inside the airbag-petal design before being deployed. Next, is the rover right after it left the airbag assembly. The third image shows the surroundings near Sojourner.
Mars Odyssey - 2001
Mars Odyssey is still providing stunning images and crucial science far beyond its planned 917-day mission. The orbiter made valuable global observations of Martian climate, geology and mineralogy. It mapped the elemental distribution of hydrogen, silicon, iron, potassium, thorium and chlorine on the Martian surface. Odyssey also determined that radiation in low-Mars orbit -- an essential piece of information for eventual human exploration because of its potential health effects -- is twice that in low-Earth orbit. The orbiter's maps helped guide the selection of landing sites for the Mars Exploration Rover Opportunity and the Phoenix polar lander.
Mars Exploration Rovers - 2004
Spirit: Described as a "wonderful workhorse," Spirit explored for years beyond its original 92 day mission. Spirit uncovered strong evidence that Mars was much wetter than it is now in a silica patch apparently produced by hot springs or steam vents. The rover captured movies of dust devils in motion, leading to a better understanding of Martian wind. Spirit continued to make discoveries even as it was stuck in deep sand at a spot dubbed Troy at Gusev Crater on Mars. On 25 May 2011, NASA ended efforts to contact the marooned rover and declared its mission complete. The rover had been silent since March 2010.
Opportunity: The second rover to land on Mars has returned dramatic evidence that its area of Mars stayed wet for an extended period of time long ago, with conditions that could have been suitable for sustaining microbial life. Scientists believe that Opportunity's Meridiani Planum landing site "was once the shoreline of a salty sea on Mars." Opportunity also has analyzed exposed rock layers recording how environmental conditions changed over time. Opportunity holds a Martian driving record and continues to explore.
Here are links to the mission home page and the mission overview page. Below are images of the rovers, some tracks left by one of them, Opportunity at the edge of a crater as viewed by an orbiting spacecraft, and the terrain traversed by Opportunity in the last few weeks.
Mars Reconnaissance Orbiter - 2006
Among the mission's major findings is that the action of water on and near the surface of Mars occurred for hundreds of millions of years. This activity was at least regional and possibly global in extent, though possibly intermittent. The spacecraft has also observed signatures of a variety of watery environments, some acidic, some alkaline, which increase the possibility that there are places on Mars that could reveal evidence of past life, if it ever existed. MRO also broke data transmission records, surpassing all other previous Mars missions. MRO continues on an extended mission.
Phoenix - 2008
Phoenix verified the presence of water-ice in the Martian subsurface, which NASA's Mars Odyssey orbiter first detected remotely in 2002. Phoenix's cameras also returned more than 25,000 pictures from sweeping vistas to near the atomic level using the first atomic force microscope ever used outside Earth. The findings advance the goal of studying whether Mars could ever have been favorable to microbial life.
Next Mission - Mars Science Laboratory - Curiosity |
The next NASA mission,
Mars Science Laboratory - Curiosity, is scheduled for liftoff on November 25 at 10:25 am EST. This date is within the launch window of Nov 25 - Dec.18. This mission is to deliver a rover named Curiosity. This rover is the size of a small car and is nuclear powered, instead of solar. The previous rovers, Sojourner and Spirit and Opportunity, are compared to Curiosity in the image below.
Clearly, this is a big step up in size and capabilities. The major challenge is getting the large rover to the surface safely. The previous smaller rovers were bundled inside of an airbag assembly for their final descent to the surface once they had safely parachuted to a slower speed. The airbags inflated and allowed them to bounce to a stop. They opened up like petals of a flower and out rolled the rover. A totally different approach will be taken for Curiosity.
Curiosity has been packaged within a protective capsule shown here just before closing. The tan colored portion is a heat shield for reentry into the Martian atmosphere.
The capsule was enclosed within a protective fairing which sits atop the launch rocket.
Once successful launch occurs and systems are checked, an engine burn will give the spacecraft the necessary boost in speed to escape Earth orbit on its way toward Mars. This video from JPLNews is narrated giving the highlights of the journey and landing in the first 2 minutes. The final 2 minutes describes some of the mission objectives.
I highly recommend that you watch at least the first 2 minutes. The Sky Crane technique is really an amazing thing to see. Mission scientists are very confident it will work well.
The sky crane method has never been used before for a spacecraft landing on another planet. It is similar to a sky crane heavy-lift helicopter. Curiosity will be over five times as heavy as and carry over ten times the weight of scientific instruments as the Spirit and Opportunity rovers. Using the airbag technique is not feasible. The Viking 1 and 2 landers used descent engines to successfully power them down to the surface. But, they were not able to move around to new locations after they landed. Curiosity could be brought down in the same way as Viking. The engineers felt the best approach was to lower the rover down from a descent engine which hovers above the surface. This technique allows the rover to be ready to function with the most economical and light weight approach. The video below shows a test drop of the Sky Crane technique.
Sky and Telescope magazine published a comprehensive article about Curiosity in the December 2011 edition. The article includes a 16 min audio interview with S&T editor in chief Robert Naeye and Curiosity deputy project scientist Joy Crisp. They talk about the goals and capabilities of the new rover. Dr. Crisp is a geologist at NASA’s Jet Propulsion Laboratory. A former project scientist for the Mars Exploration Rover project (Spirit and Opportunity). Dr. Crisp brings many years of experience working with rover teams and studying Mars’s surface and history.
The next mission milestone will be a successful launch within the constraints of the launch window. About 8½ months later, Curiosity arrives at Mars. We will be watching.