Mars Pathfinder Current Position

NOTE: The data in these latest (and possibly last) trajectory tables are taken from the 6/23/97 navigation solution used to design TCM 4. There will be no further updates of these numbers before July 4 due to the frantic level of activity for the NAV team as we go into the last few days before Mars arrival. Although we will continue to do solutions quite frequently, there will be no time for us to format the data and post it to the web site.

We will will continue to post new images of our predicted landing ellipse on the surface which you can find in the Landing Footprint Plots section of the Mars Pathfinder Trajectory Data (Technical) Page. During the last 24 hours before atmospheric entry (just before 10 AM PDT on July 4), the latest footprint plots may be posted to a different spot on our web page. The NAV team will be passing the lastest images along to our web master to insure that they are posted ASAP. We'll do our best to keep you informed on our progress.

How far from Earth is the Pathfinder spacecraft? How far is it from Mars? How fast is it going?

Curious about how our current navigation solution maps to our target landing area on Mars? See the landing footprint plots in the trajectory figures section of the Mars Pathfinder Trajectory Data (Technical) Page. Stay tuned for updates of these plots as we close in on our destination!

If you'd prefer to see the spacecraft location in a graphical form, plots are available in the trajectory figures section of the Mars Pathfinder Trajectory Data (Technical) Page. Orbital elements for Mars Pathfinder's cruise trajectory are also listed in the Mars Pathfinder Trajectory Data (Technical) Page.

When you play golf, you start by teeing off at the edge of a long green that's far away from a small hole in the ground. You get a certain number of shots to move your ball from the tee off point into the hole. You first try to get the ball to the green - another small area around the hole. If you're a good player, you figure you're home free once your ball is on the green. Surely you can make it to the hole from there!

Let's suppose that the tee off point for Mars Pathfinder navigation is the Earth at the time of launch in December 1996. And our "hole" is certain spot above the atmosphere of Mars on arrival day, July 4, 1997. We have two requirements for the accuracy with which we have to hit that spot above Mars. These are the criteria that determine the size of our "hole" and the size of the "green" around it that constitutes safe atmospheric entry conditions for the spacecraft.

Our safety and survival requirement for navigation is to get the spacecraft within a corridor that is 42 km (26 mi) wide centered at a radius of 3522.2 km (2189 mi) from the center of Mars at arrival. (For you technical types out there, this corresponds to a deviation in our nominal flight-path angle of +/- 1 degree.) We'll use 42 km (26 mi) as the diameter of our green. Our target zone on the surface is +/-100 km (62 mi) downtrack of a specified latitude and longitude. This corresponds to a corridor that is 24 km (15 mi) wide at the top of the atmosphere. We'll use this as the diameter of our hole.

Now the spacecraft will travel a total of 497418887 km (309081764 mi) from launch to arrival at Mars. (That's the distance measured along the spacecraft's trajectory - NOT the distance between Earth and Mars at launch or arrival or the distance from the spacecraft to Mars). Let's use that as the length of our golf course from tee off to the hole. And let's assume that a typical golf hole on Earth is 6 inches in diameter. Then, if we tee'ed off from JPL here in Pasadena,CA, the hole would be located in Atlanta, GA! And the 42 km (26 mi) safety requirement would be a green of 10.5 inches in diameter around that hole in Atlanta! If the hole is only 4 inches in diameter, then it would be located on the outskirts of Houston, TX. And the safety requirement would be a green of 7 inches in diameter around the hole in Houston.

And if you're not bored with this analogy yet, we can go even further and say that our MPF navigation golf game is a "PAR 4". The 4 trajecory correction maneuvers that we have planned between Earth and Mars are like strokes in the golf game. We'd like to make it onto the green - and into the hole - with just these 4 changes to the trajectory. We are carrying the option for another (fifth) maneuver to be executed within the last 24 hours before arrival in case we turn out to have a bad game and need another stroke beyond the 4th.

Robin Vaughan (rvaughan@mpfnav2.jpl.nasa.gov)

Note: If you send e-mail during the week of June 30 to July 4, 1997, I may not answer you until after landing! The NAV team will be very busy during this last week and I must give priority to flying the spacecraft. Thanks in advance for your patience during this time.