Mars Pathfinder Current Position

To those of you who have sent questions in your e-mail, I am working on responses. It may take me a while due to the large volume of e-mail I've received. Please be patient since I do intend to reply to all of your messages eventually. But if you get tired of waiting, check out Mars Team Answers Your Questions and see if you can find your question there.

Robin Vaughan, Mars Pathfinder navigator

What time is it on Mars? Check out the tables of local time on Mars at the Pathfinder landing site in the Mars Pathfinder Trajectory Data (Technical) Page. (This now include links to some other web sites with Mars time information.)

How far from Earth are Mars and the Pathfinder spacecraft? How far are they from the Sun? How fast are they going?

Now that the spacecraft is on the Martian surface, the distances in the table reflect the orbital motions of the Earth and Mars about the Sun. The velocity listed in the table is the velocity of the spacecraft relative to the Sun. This is a combination of Mars's orbital velocity as it revolves around the Sun and its rotational velocity as it spins around its axis every Martian day.

The information on Mars and Earth orbits used for this page is taken from the DE403 or DE405 planetary ephemerides developed by the Solar System Dynamics Group at JPL. For more information, see JPL Planetary and Lunar Ephemerides or HORIZONS.

If you'd like more technical details than are given here, please go to the Mars Pathfinder Trajectory Data (Technical) Page. This now includes tables of local time on Mars at the Pathfinder landing site as well as information about our interplanetary cruise trajectory.

Curious about how our pre-landing navigation solutions mapped 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.

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 (from Earth to Mars) 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. A standard golf hole on Earth is 4 1/4 inches in diameter. Then, if we tee'ed off from JPL here in Pasadena, CA, the hole 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 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 carried the option for another (fifth) maneuver to be executed within the last 24 hours before arrival in case we had a bad game and need another stroke beyond the 4th.

The navigation team is happy to report that we made par! The fifth maneuver was not required and we successfully landed in the hole on July 4, 1997 :-)

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

To those of you who have recently sent questions via e-mail, I am working on responses. It may take me a while due to the large volume of e-mail I've received since our landing on July 4th. Please be patient since I do intend to reply to all of your messages eventually. But if you get tired of waiting, check out Mars Team Answers Your Questions and see if you can find your question there.