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Emily LakdawallaAugust 4, 2007

Phoenix wrapup

Just watching the post-launch press conference now, and as of 11:00 a.m. Phoenix is already halfway to the Moon. The spacecraft is power-positive, which my friend Doug remarked in a chat room early this morning is "more than we can say for all Mars spacecraft at the moment."

I'll do my best to write down what people are saying as they say it...

An interesting detail: there is only 10 kilograms of trajectory correction propellant on Phoenix, so getting the spacecraft onto exactly the right course was very important.

"Today, we know what the landing ellipse is." So the team that is investigating the landing site can now focus on an ellipse that is much smaller than the box they've been investigating to this point.

Possible landing ellipses for Phoenix

NASA / JPL-Caltech / Washington Univ. St. Louis / JHU APL / Univ. of Arizona

Possible landing ellipses for Phoenix
Where Phoenix will land on Mars depends slightly on its launch date. If it launches early in its August 3-24 launch period it will most likely land somewhere within the black ellipse oriented northwest to southeast. If it lands toward the end, its most likely landing spot will be somewhere within the ellipse oriented southwest to northeast.
The spacecraft is now in an "inertial hold mode," with the solar arrays off-pointed from the Sun by 54 degrees (something they have to do because the arrays are designed to operate much farther from the Sun than Earth, so while closer to the Sun they need to tilt so as to receive less solar energy). On the star tracker they have one "red alarm" of a bright spot -- which is the Earth in the star tracker's field of view, so that is expected. The star tracker -- which is part of the spacecraft's navigational system -- has had only 23 "bad solutions" out of 23,000 attempted trackings. These probably result from there being some amount of debris on the same trajectory as the spacecraft. This is "unusually clean." The batteries dipped to an 84% state of charge, but with the solar arrays providing power they're now up to 98%. They used up 9 grams of propellant for "initial acquisition," and 43 grams to slew attitude, out of a total load of 64 kilograms. (The 10 that I mentioned earlier is what they have to spare to correct their trajectory; they also need some to slow as they approach landing.)

Peter Smith is a happy man. It'll be 10 months, he points out, until he can report any science results' so he decided to describe how the launch impressed him instead. "From the position I was in, it was headed directly toward Mars, which was in the Pleiades. And then it arcs away from Mars, because it has to orbit the Earth first. So as it turned toward the horizon, it crossed right across Orion's belt, and then it dropped its solids, which dropped down like little twinkling stars, like another constellation. When I returned back outside, the gases from the solid rocket were still there in a cloud. The winds were very benign. You could still see the stars and you could see this white sheet morphing around. I was watching those clouds, and you know how it is when you're watching clouds, and I began to see a beak and wings and a tail. And I thought, the Phoenix has risen! I feel tremendously relieved that our spacecraft, after four years of development, is now on its way to Mars and ready to do its job."

He was asked by the AP reporter where he had watched from. "As Principal Investigator I was inside the mission control center, but as it got down to T minus 2 I couldn't stand it, I had to go outside."

That's it for my Phoenix launch coverage. And I'm taking a three-day vacation now, from Sunday through Tuesday, so I'll be back again with more news about more places and spacecraft on Wednesday. Thanks for reading!

Phoenix Lifts Off


Phoenix Lifts Off
A Delta II rocket lit up the early morning sky over Cape Canaveral Air Force Station in Florida as it carried the Phoenix spacecraft on the first leg of its journey to Mars. The powerful three-stage rocket with nine solid rocket motors lifted off on August 4, 2007 at 5:26 a.m. EDT.

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
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