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Mars Journal - Mars Exploration Rover Mission
Journal for Michael Watkins

December 31, 2003 - Looks like no TCM-A5

We continue to be very close to the center of the target, and the only changes are small ones due to scientists modifying the atmosphere data as they learn more by using Mars Global Surveyor orbital data. There's some question about whether the dust storm heats up the atmosphere and makes it less dense, which means we don't slow down as fast as we planned.

As far as the targeting goes, it looks like we won't need to do TCM-5 (the fifth trajectory correction maneuver). Tonight is another all-nighter for the Nav team, though, as we watch the orbit to make sure everything continues to look fine and we can keep TCM-5 as a no-go.


December 28, 2003 - Perfect

More data has now gone into the solution, and we're now within 200 meters (about 219 yards) !! of the target. This is without a doubt the best navigation in history. Absolutely incredible. I am so happy and proud of the team. It's really amazing.

Because we now know exactly where we're going, we have to update the Entry, Descent, and Landing parameters, so we're now reviewing in a big meeting how all the parachute deploy timers, etc, should be set. Then we'll upload to Spirit later today.


December 27, 2003 - Looking good

We've gotten the first solutions post-TCM-A4 (the fourth trajectory correction maneuver), and we are within 500 meters (about 547 yards) of the target, but we had to make certain assumptions about the maneuever execution. We'd like more data. By tomorrow, we should know even better.

I'm going to do one of my only 'holiday' activities during this crazy period, going to dinner with some friends tonight on a rare free evening.


December 26, 2003 - TCM-A4 is Go

Delivered the final solution early this morning for the fourth trajectory correction maneuver (TCM-A4), using the Orbit Determination (OD) solution with the plasma delay solution, and the very long arc. I think it's right on. We've been working closely with some of the spacecraft team members who are most knowledgeable about how Spirit will actually react during the maneuver (like Steve Collins and Miguel San Martin), and we've decided to do the maneuver in a way that will be most accurate ('lateral only' for those who are interested in the details of these things).

TCM-A4 was just executed. Looks perfect. We have to wait for additional tracking data for us to see how perfect, and exactly where we're now headed. Hopefully it's in the bullseye.


December 25, 2003 - A Nav Team Christmas

Today is Christmas. The Mars Exploration Rover Navigation team is working today because we are doing trajectory correction maneuver number 4 (TCM-A4, we call it) tomorrow, and we need to know exactly where Spirit is and where it's headed in order to design the maneuver correctly. This afternoon it's me, Lou, Brian and Geoff. We got a nice surprise when Dr. Charles Elachi, the Director of JPL, stopped by to visit us with some cookies.

The trajectory solutions continue to look great, only changing by a couple of hundred meters in what we navigators call 'the B-plane,' which is really just a fancy way of talking about the navigation of Spirit just before it hits the Martian atmosphere. We talk about that separately from where exactly it's going to land on the surface of Mars inside Gusev crater because the atmosphere of Mars is hard to predict and the scientists change their models sometimes, which moves the most likely landing site a few kilometers.

It turns out that the Stardust Navigation Team is also here on Christmas day trying to process optical navigation pictures of Comet Wild-2, so I went down to work a little with them and get a progress report.

The Mars Exploration Rover Orbit Determination solutions continue to look excellent today. It sometime moves around a tiny bit that doesn't matter much, but we're always a little paranoid, plus I really want to get it perfect. Since we think we understand Spirit's orbit very well, we think one of our error sources is plasma delay on our radio tracking from the big solar flares that have been going on.


December 24, 2003 - Our Colleagues at the European Space Agency

Tonight we will watch Mars Express attempt to insert into Mars orbit, and also hopefully hear Beagle-2 transmit to Mars Odyssey. We've been working with the European Space Agency for several years on Mars Express, and I think all of us in the space exploration community share a kind of comraderie, a common goal, and occasionally common disappointment, so we wish the best to our European colleagues.

It's now about 10:00 at night and Mars Express is safely in orbit around Mars, but Mars Odyssey didn't get a transmission from Beagle-2. We're keeping our fingers crossed for later attempts.


December 23, 2003 - Spacecraft All Over the Solar System

One of the most challenging parts of my job is that our section is simultaneously navigating a bunch of spacecraft around the solar system. We've got Spirit and Opportunity headed for Mars which takes up most of my time now, but we've also got two orbiters already at Mars (Mars Global Surveyor and Mars Odyssey both of whose orbits we tweaked to put them in the best position to relay information from Spirit and Opportunity), plus Stardust headed for a flyby of Comet Wild-2 on Jan 2nd, Genesis at the libration point, Cassini headed for Saturn, Topex/Poseidon orbiting the Earth, and so on. We're also working with the European Space Agency to make sure Mars Express and the Beagle-2 lander are on course. With so many missions having critical events in the month between now and Opportunity's arrival at Mars in January, sometimes I feel like I'm just running from one meeting to the next. Luckily, we have great navigation teams for each of these missions and things are going remarkably well.


December 20, 2003 - 1000 solutions every day

Over the next days in this journal you'll hear me talk mostly about how the orbit determination (OD) is going and what that means for the maneuvers we need to make to get Spirit into Gusev crater. OD is a difficult job because you can never be certain you have it right. We have to mix in a lot of statistics and a little intuition. We run about 1000 solutions every day that cover all the possible ways we could analyze the data to make sure we get it right. We review those every day together in a meeting we call 'The Daily show' so we can all discuss the range of cases and pick the best one. Although it's stressful to have to get things exactly right and we only get a maximum of 6 chances to change Spirit's direction, the daily show usually turns out to be a fun meeting, with a lot of jokes thrown in to break the tension (almost none of which I can repeat in this journal!).


December 18, 2003 - Navigating Spirit and Opportunity

Hi, my name is Mike Watkins, and I'm the Manager of the Navigation and Mission Design Section at JPL. We are responsible for finding the trajectories (or orbits) that essentially all the NASA planetary spacecraft, like Spirit and Opportunity, should travel along to get to their destinations. We call that Mission Design.

Then, after the spacecraft is launched, we have to make it actually fly along the planned trajectory. We call that Navigation and it involves two main parts. The first part is determining where Spirit and Opportunity currently are headed. We call that 'Orbit Determination' or 'OD' for short, and it's done using radio tracking from the Earth with NASA's huge Deep Space Network Antennas (the DSN). Some of the antennas are almost as big as a football field, and they have to be big in order to collect the signals all way from Mars and beyond. It may be hard to believe, but we can measure the velocity of the spacecraft to less than a tenth of a millimeter per second (that's less than a thousandth of a mile per hour). We put all those measurements together with models of the forces acting on the spacecraft, like the gravitational effect of the Sun and the planets, the radiation pressure from the Sun, and of course anything the spacecraft has been doing like firing thrusters, to get our best estimate of where Spirit is headed. The OD part of the Nav Team is Tim McElrath, Brian Portock, Geoff Wawrzyniak, Eric Graat, and Darren Baird.

Then we do the second step in Navigation, which we call Maneuver Design or Flight Path control. The maneuver part of the Nav team is Chris Potts, Julie Kangas, and Behzad Raofi. In that step, we decide that if Spirit is not headed exactly where we want it to go, we have to fire the engines to put us back on course. We've done that 3 times so far, and we're almost exactly on course. But 'almost exactly' isn't good enough for Spirit to land in the tight confines of Gusev Crater, so we'll do a tiny adjustment on Dec 26th.

Part of the maneuver process that is unusual for the Mars Exploration Rover mission is that not only do we have to get the orbit back on course to Mars, we have to get it through the Martian atmosphere and onto the ground through the Entry, Descent, and Landing (EDL) sequence. So we have to be able to predict the trajectory through the atmosphere, including things like the effect of the parachute. In most cases, we also decide whether to change parts of the EDL sequence, like the time the parachute is deployed. We have special software to do that, and several Nav team members have specialized in that area, like Phil Knocke, Prasun Desai (visiting from NASA Langley Research Center), and Ralph Roncoli.


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