Mars Pathfinder
Frequently Asked Questions

Surface Operations

When can we expect to see the first picture from the surface of Mars and who will be taking it, the lander camera or the rover? (Please give us PDT/EDT).

First we take some science images which are important for recording the state of the magnetic targets as early as possible in the mission. These are not downlinked right away. Then we take the ramp deploy pan to see which direction we want to deploy the ramps, and downlink it immediately. The resolution will be probably poor, but it will be interesting, including rover, lander parts, airbags, and of course terrain. Then we take a good-resolution 3-color pan of lander, rover, and terrain and send it right after. The lander camera works nearly all day the first sol, and we deploy the camera mast at sunset. The rover takes a lot less pictures, but we do get pictures of the soil, and the lander the first sol. But they aren't downlinked until very late on the first sol and could easily be delayed until the second sol.

One caveat is, since the spacecraft has the ability to generate some high-priority telemetry autonomously, planned image downlink can be interrupted and the exact arrival time of each image cannot be forecasted.

--William Dias, Surface Mission Operations Planner

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Almost! The real time data that we get is somewhat indecipherable to nearly everyone. However, individual image frames that we get from our cameras on the lander will be posted on this website almost immediately after we get them down. We will also post the image data that JPL's image processing lab produces from the raw images. These images are corrected for true color and warp. Also these images will be mosaics of multiple image frames, so the field of view will be considerably larger than we get from a single 14 degree wide image frame. These processed images will be posted onto the Web within an hour or two after we get the images down.

--Rob Manning, Chief Engineer, Mars Pathfinder Flight System

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We expect the lander's solar arrays to be sitting some distance above the surface, atop the airbag material that has been gathered beneath the lander during the deployment operation. Of course, this still leaves the arrays open to any blowing dust that might settle on them over time. We have planned for some dust to accumulate on the solar arrays of both the lander and rover and have factored that into our daily activities. There are even a couple of experiments on both the rover and lander which are designed to measure the amount and characteristics of the accumulated dust.

We also do not believe that dunes will be a problem in Ares Vallis where we are landing. There is little sign of dunes in this area from the Viking orbiter images that we have studied. Also dunes on Mars do not move very rapidly according to most Mars aeolian process experts. The wind blows fast, but at only 1/110th the density of Earth's it takes a long time to move a dune. They think we will not have to worry much if we get the bulk of our mission done within a month or so. Of course, we need to be prepared for nearly anything.....

--David Mittman, Surface Mission Operations Planner
--Rob Manning
--Tim Parker, Mars Pathfinder Science Team

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The nominal expected life (the "prime mission") is 30 days for the lander and 7 days for the rover. However there is no known absolute maximum system life for either the lander or rover. Those numbers were chosen because the lander's rechargeable battery was qualification tested for 30 discharge/recharge cycles, and the duration of thermal testing applied to the rover's electronics box. The project has programmed funding for a year on the surface, in case it lasts that long.

It really will be "against the odds" for the system to survive that long. But if the spacecraft is still functioning at that time, or if we run out of money before that for some reason, I for one would certainly hope that more money could be allocated. It is hard to believe that ANYONE would turn off a functioning spacecraft on the surface of Mars, especially since it gets cheaper and cheaper to run it the more time goes by. Now, it is true that some parts of the mission objectives are completely satisfied very early in the mission. For instance, we can take a picture of all the terrain features using every filter in the lander camera and send all that data in the first month, and there is probably no reason to take those pictures again. However more time will always add more value in other areas of investigation. The weather (including data from atmospheric imaging) could be profitably measured for years, and so long as the rover can move, new photo angles are always possible. These would include not just new terrain, but also pictures of the lander, so see what parts were damaged in landing, the airbags, the landing path ground imprints, etc. But, I hope we have this problem! It really will be "against the odds" for the system to survive that long.

--William Dias, Surface Mission Operations Planner

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I can understand how we can receive and transmit adequately from Earth to Pathfinder, given the power of our transmitters and gain of our antennae, but how does Pathfinder communicate with Earth? It seems to me it would be difficult for a small probe on the surface of mars to receive and transmit with enough gain to establish a robust data connection. Do you use a very low bandwidth?

The one quantity that most people overestimate is the amount of man-made and natural noise that exists at microwave communication frequencies. We use very sensitive low noise microwave receivers and large antennas here on Earth to receive the signal from Mars Pathfinder. At the 8 gigahertz radio frequency that Mars Pathfinder uses to talk back to Earth, the ratio of signal power to noise power is 6000 to 1, or about 37 decibels. This allows us to receive data from the spacecraft 190 million kilometers away at a modest data rate of 1 or 2 kilobits per second. Compare that to your computer modem which probably operates at 14.4 or 28.8 kilobits per second!

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The radio signal strength from the Mars Pathfinder high gain antenna on the July 4, 1997 landing day will be -146 dBm (decibels referenced to a milliwatt) or 2.5e-18 watts as received at our Deep Space Network 34 meter diameter antenna on Earth.

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We use digital modulation to send commands to and receive data from the Mars Pathfinder spacecraft. Both the uplink and downlink use a residual carrier binary phase shift keying (BPSK) modulation scheme.

Our command uplink data rate has several settings between 7.8125 bits per second (bps) and 500 bps. Our telemetry downlink data rate has 20 settings between 5 bps and 11060 bps. Currently, we are commanding the spacecraft at 250 bps and receiving data from the spacecraft at 1185 bps. As the spacecraft moves further away from the Earth, we will lower our data rates to compensate for the weaker signal. When the spacecraft arrives at Mars, we will be commanding at 7.8125 bps and sending 40 bps on the downlink.

There is only one "channel" of data on both the uplink and the downlink. On the downlink, we use packet time-division multiplexing to send both engineering data (i.e., hardware status bits) and science data (i.e., camera picture bits) in the same data stream.

--Leif Harcke, Telecommunications Systems Analyst

How will the quality of the images from the Martian surface compare with what was beamed backed from the Viking mission? I imagine that with 20 extra years of technological improvements, imaging must have made significant advancements.

The Mars Pathfinder mission was originally conceived to demonstrate a low-cost way of getting to the Martian surface. The original guidelines for the camera were to provide a simple (monoscopic) panorama of the surface. When NASA asked for proposals to build the camera we specified that the resolution should be comparable to the Viking lander cameras and listed stereo coverage and color as desirable capabilities if they could be provided within a very limited cost cap. I am pleased to say that an ingenious team from the University of Arizona, supported by the Max Planck Institute in Germany has delivered a camera with 1 milliradian resolution (Viking black and white was 0.7; color, 1.4) that includes 24 filter positions and stereo capability. Thus Pathfinder has an unprecedented multispectral capability with 12 distinct spectral filters for geology, eight for atmospheric studies and a closeup lens position for viewing dust accumulations on a magnetic target (some filter positions are duplicated for the camera's two eyes for the purpose of stereo imaging). The camera has 12-bit encoding (compared to Viking's 6-bit), so that the radiometric accuracy is greatly enhanced. Finally, the camera software includes several data compression algorithms to take maximum advantage of the telemetry rates available.

Pathfinder is expected to return a complete panorama of the surface in color and in stereo. In addition, its scientific capabilities will be used to study the spectra of surface rocks and minerals, the optical characteristics of the atmosphere and the magnetic properties of wind-blown dust.

As the questioner correctly asserts, this improved set of imaging capabilities was made possible at very reasonable cost by technology improvements, most notably,the use of a high-quality imaging charge coupled device (CCD) detector.

--John Wellman, Mars Pathfinder Science and Instruments Manager

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Does the Pathfinder Lander's imager perform well under low light conditions? Would it have the ability to image the Martian skies when the Sun has set, perhaps to take a long distance snapshot of Earth low in its horizon?

The camera can expose for up to 32 seconds, which gives it a respectable low-light capability. Peter Smith reports that the University of Arizona have recently imaged Orion (the constellation, not the nebula) and gotten good results. We expect to image bright stars and planets during the mission and can probably image Earth as well. Please note however, Earth is less than a pixel wide in the IMP.

Why didn't you use the Martian winds to provide additional electric energy to the lander/rover?

That's a good question. Mars often does have high speed winds. But even in the fiercest gales on Mars, the pressure that the winds can generate (and therefore the ability to perform work) is surprisingly small. This is because the Martian atmosphere is only 1/100th as dense as Earth's. To "feel" the equivalent of a 10 mile per hour "Earth" breeze (enough to turn a windmill), a Martian wind must be 10 times the speed, or 100 mph! It is a very rare day on Mars when the winds get anywhere close to that speed! Most of the time the winds are less than 20 m/s (50 mph) which is comparable to only a light Earth-breeze of 5 mph. Not much power there! To get energy out of a breeze like that would require large windmills (bigger that Pathfinder) much like those that are built on giant windmill farms in places with lots of wind on Earth. For Pathfinder, we decided that we cold get more "bang" for our buck by using arrays of Gallium Arsenide solar cells.

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