NASA's next Mars probe is poised for launch Monday, weather permitting, to kick off a $671 million mission to find out why a good portion of the red planet's atmosphere leaked away ages ago in an extreme case of climate change that turned a once wet and hospitable world into the dry, frigid wasteland it is today.
The Mars Atmosphere and Volatile Evolution -- MAVEN -- spacecraft, perched atop a United Launch Alliance Atlas 5 rocket, is scheduled for takeoff from the Cape Canaveral Air Force Station at 1:28 p.m. EST (GMT-5) Monday to begin a 10-month voyage to Mars for at least a year of science observations using a suite of sophisticated instruments.
"After all these years we're just a few days away from going to Mars," said David Mitchell, MAVEN project manager at NASA's Goddard Space Flight Center in Greenbelt, Md. "We're poised to launch on day one of what we submitted as our final proposal five years ago."
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Forecasters, however, are predicting a 40 percent chance of possibly thick clouds and isolated showers that could trigger a launch delay. The odds worsen to 60 percent "no-go" Tuesday with a 70 percent chance of flight rule violations on Wednesday.
But given a brief work stoppage during the early days of the government shutdown, a subsequent exemption to continue processing and the disruption the turmoil caused, Mitchell was clearly pleased to have only the weather to worry about.
"Weather and other things can set you back, but to be there launch ready gives us time to deal with anything downstream," he told reporters Friday. "So kudos to the team. It's not only on time, it's on budget, it has the full capability that we proposed years ago and it's been fully checked out."
Unlike recent NASA Mars missions that have primarily focused on the surface to determine the past and present habitability of the planet, Maven will concentrate on the Martian atmosphere, repeatedly flying through its upper reaches to sample its constituents, probe its structure and measure how solar radiation and charged particles blasted away by the sun affect its evolution.
Mars does not have an active magnetic field to shield the planet from the effects of high energy radiation and electrically charged particles streaming by, which may act to carry away atoms and molecules in the upper reaches of the martian atmosphere.
Researchers hope to gain insights into how much of the atmosphere may be leaking into space today, how much might have been carried away over the past few billion years, what mechanisms were responsible, and how those mechanisms might compare to others that apparently locked up some amount of atmospheric carbon dioxide in the martian crust.
"It's clear that major questions about the history of Mars center on the history of its climate and atmosphere and how that influenced the surface, the geology, and the possibility for life," Bruce Jakosky, MAVEN principal investigator at the University of Colorado's Boulder Laboratory for Atmospheric and Space Physics, said last month.
"MAVEN is going to focus on trying to understand what the history of the atmosphere has been, how the climate has changed through time and how that's influenced the evolution of the surface and potential habitability, at least by microbes, of Mars."
Jakosky said here is no question water once flowed on the surface of Mars and that the planet once had a much thicker atmosphere, "but somehow that atmosphere changed over time to the cold, dry environment that we see today, one that is too cold with an atmosphere too thin to be able to support liquid water. What we don't know is what the driver of that change has been."
"There are two places the atmosphere can go," he said. "It can down into the crust, it can go up to the top of the atmosphere and be lost to space. I think these questions of where did the water go, where did the CO2 go, from that early atmosphere are driving our exploration of Mars."
Tipping the scales at 5,410 pounds at launch, the MAVEN spacecraft measures 37.5 feet across its two solar panels, which provide between 1,150 and 1,700 watts of power. The orbiter is equipped with eight scientific instruments and a UHF communications package that can relay data back to Earth from rovers on the martian surface.
Six of the instruments will characterize particles and fields, measuring the interaction of the atmosphere with electrically charged particles from the sun and the impact of solar radiation. Two other instrument packages will carry out remote sensing and chemical analysis of particles in the martian atmosphere.
Assuming an on-time launch, it will take MAVEN 10 months to reach Mars, braking into an elliptical orbit around the red planet on Sept. 22, 2014. The parameters will vary throughout the mission, but the initial orbit will have a high point of some 3,860 miles and a low-point of 93 miles.
In addition, MAVEN will carry out five "deep dip" sessions lasting about five days each, dropping to a low point of around 78 miles to sample the atmosphere in regions where it is 30 times more dense than the regions studied during normal operations.
Guy Beutelschies, MAVEN project manager for spacecraft builder Lockheed Martin Space Systems Co., said the orbiter will not drop as deep into the atmosphere as NASA's Mars Reconnaissance Orbiter, which used a technique called aerobraking to achieve orbit. But it will still feel the wind rushing by.
"If you put your hand out when you were going through (the low point of the orbit) you'd feel a light breeze," he said. "It's really a modest amount of pressure. But it is of tremendous value to the scientists, being able to go down and get that in situ measurement of the atmosphere."
Maven is the 10th NASA spacecraft built to orbit Mars. If all goes well, it will join three other operational satellites now circling the red planet: NASA's Mars Odyssey, launched in 2001; the European Space Agency's Mars Express, launched in 2003, and the Mars Reconnaissance Orbiter, launched in 2005.
In addition, NASA currently operates two rovers on the surface, the Mars Exploration Rover Opportunity, launched in 2003, and the Mars Science Laboratory, or Curiosity, launched in 2011 and now in its second year of surface operations.
The rovers currently use Odyssey and MRO to relay science data back to Earth and to receive commands from flight controllers. MAVEN is equipped with similar relay gear and will serve as a backup for use as needed by the rovers.
"There's quite an interest in this mission, and you wouldn't think so in that it's not as sexy as the rovers," said Omar Baez, NASA's launch director. "This is kind of like a weather satellite for Mars. ... It's an interesting mission, and it's captured the imagination."