Mars Pathfinder
Frequently Asked Questions

General Topics

Why (in your opinion) was this mission chosen for the Discovery program versus other proposed missions?

Mars Pathfinder and the Near Earth Asteroid Rendezvous (NEAR) mission were not chosen by the same process as the later Discovery missions. Pathfinder was originally designedto demonstration technology for inexpensive entry and landing on Mars, as a precursor to a network of landers called Mars Environmental Survey, or MESUR. Because Pathfinder was the first mission it fell into what was then considered a "Discovery" mission class - that is it had to be done for less than $150M in 1992 dollars. The MESUR Network missions were never funded, but Pathfinder is now a technology demonstration for landers in the Mars Surveyor program. Later Discovery missions are being chosen through Announcements of Opportunity and are being developed by teams headed by scientists.

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Pathfinder is a "Discovery" mission. The Mars Surveyor Program is separate from Discovery and will launch one or two missions to Mars at every opportunity (every 26 months). Mars Global Surveyor launches in November 1996, Mars Surveyor 98 will launch an orbiter and a lander in December 1998 and January 1999. The 98 Surveyor missions are both using Pathfinder components, especially the computer and software. The Mars Surveyor 98 lander is using much of the entry and descent technology demonstrated by Pathfinder, including the aeroshell and the parachute. The science from Pathfinder will be completely complementary with the Surveyor Program science. In fact, the Mars Surveyor 98 lander is using the same camera and weather station technology that Pathfinder is using.

In addition to the U.S. missions, Russia will launch Mars 96 in November 1996. It comprises an orbiter, two small landers, and two penetrators. There is a U.S. experiment on the landers and the landers and penetrators will relay data through the Mars Global Surveyor orbiter. Pathfinder carries instruments provided by several different countries. The Mars Surveyor 98 missions also have international payloads, including Russian contributions to the U.S. Infrared Radiometer on the orbiter, and to the lander payload. The Japanese will fly an aeronomy orbiter in 1998 to study the upper atmosphere of Mars. A U.S. instrument is scheduled to be on board this Japanese mission.

We are currently studying the feasibility of a joint U.S.-Russian mission called Mars Together in 2001. One option for this mission is for the U.S. to launch an orbiter, and to provide a "carrier" spacecraft to be launched with a Russian lander on a Russian launch vehicle. We are also studying a sample return mission which could be made affordable by partnering with other countries.

--Donna Shirley, Mars Exploration Program Manager

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The Mars Pathfinder spacecraft is quite different from other missions built at JPL. First of all, as a lander mission, the prime focus is on getting the lander/rover instrument package safely to the surface of Mars. This means that this spacecraft must be able to electro-mechanically transform itself autononmously from a "cruise" configuration much like a Galileo (without the cruise science observations of course) into a stable science platform on the surface of Mars. All of this must be done on a budget quite small compared with previous planetary missions. This adds considerably to the technical challenge.

These challenges were met by first taking maximal advantage of past work: we "inherited" hardware from the Cassini mission to Saturn; we utilized designs of equipment flown to Mars on the Viking missions of the 70's; and we have an improved understanding of the environmental uncertainties from science observations obtained over the last 2 decades. Secondly, improvements in computer technology have allowed us to model, design and test aspects of our system that were impossible 20 years ago. Finally, we have built a small "Skunkworks-like" team that has accomplished only that work necessary to do the mission, with little red tape nor redundancy in effort.

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No one can build a complex spacecraft that is absolutely guranteed to work. Embarking on unique, first-of-a-kind enterprises, by their very nature, invoke risk taking. However we can go to great lengths within the limits of our budget to minimize technical risk. Much like the design process leading to a passenger jet, spacecraft designers must ensure that design margins conservatively exceed the uncertainty in the expected environment and that the spacecraft is tested to those environments. Much work then must be placed in understanding the environment, followed by as much testing as money and time will allow. We feel quite certain (and many independent reviewers have agreed) that although Mars Pathfinder is about 1/10th total mission cost of Mars Observer, that we have struck an appropriate balance between cost and risk.

--Rob Manning, Mars Pathfinder Flight System Chief Engineer

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The major impact of the planetary protection requirements on Pathfinder is that we must carefully clean the spacecraft before launch in order to keep from contaminating Mars. Although scientists now believe that it would be difficult to sustain and cultivate life on Mars, they would prefer that we not take any chances. They have developed a system for rating different missions by the potential impact that they could have. The most stringent missions are those which will be returning samples from Mars or are performing life detection experiments there. In both cases, complete sterilization is required. In our case (and MGS), we are allocated a specific number of biologic spores which are deemed acceptable. We have to clean the spacecraft (or perform mission design tricks - I write about below) to reduce the number of spores below this level (I am glad to say that we are well below the acceptable number). The only parts of the spacecraft which we actually need to clean is the part that will come in contact with the Martian atmosphere and surface. The other parts (meaning the third stage and cruise stage) do not have to be cleaned because they will either not hit Mars (we specifically bias the aim point of the Delta away from Mars so that upper stage does not hit the planet) or will burn up during entry (we had to perform a break-up re-entry analysis of the cruise stage to prove this will occur). MGS did not have to do any planetary protection related cleaning because they can guarantee that the spacecraft will not enter the Martian atmosphere for a long time with high probability.

--Richard Cook

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The computer is a Radiation Hardened IBM Risc 6000 Single Chip (Rad6000 SC) CPU. It is the same as the IBM R6000 workstation. Lockeed-Martin Federal Systems in Manassas, VA, is responsible for doing the radiation hardening of the Rad6000 SC as well as developing the complete Mars Pathfinder Flight Computer (MFC).

The MFC contains 128 MBytes of DRAM memory and runs at speeds of 2.5, 5, 10 and 20 MegaHertz. This translates to approximately 2.7, 5.5, 11, and 22 MIPS (this does vary, depending on which benchmark is being used). The code was developed using VxWorks as the real-time OS and "C" and assembly languages. It utilizes object-oriented constructs.

On the system there is only one computer to control the spacecraft throughout all phases of the mission. The Rover has a very small CPU that it uses once we have landed and the rover is released. All communications to Earth from the spacecraft and rover come through the Rad6000 SC.

--Lloyd Keith, MFC (Mars Pathfinder Flight Computer) Chief Engineer

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The Mars Pathfinder is powered during cruise by a non-deployable solar array that uses Gallium-Arsenide solar cells. This provides all of the power during nominal cruise conditions. During Launch and the Entry, Descent and Landing on the surface of Mars the spacecraft will be powered by a rechargeable battery. The rechargeable battery has silver cathode, zinc electrode, and potassium hydroxide electrolyte.

Once, the lander has landed and the petals have been opened the lander is powered by another solar array that uses the same type of gallium-arsenide solar cells. During the night time and for peak power loads the spacecraft is powered using the same rechargeable battery used during cruise.

The rover similarly is powered by a fixed array on gallium-arsenide solar cells. Again peak power loads and night-time loads are supported by using a battery. The battery for the rover isn't rechargeable and thus uses a different chemistry.

--Richard Ewell, Mars Pathfinder Power Subsystem Engineer

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The Mars 96 failure had little direct impact on the U.S. program. We lost two small instruments that were to measure the chemistry of the surface. But the loss of science for the earth's Mars exploration is severe. There were 20 instruments on the orbiter plus two small landers and two penetrators, so it would have been a very informative mission if it had succeeded.

There was a meeting last week of all the countries involved in exploring Mars to talk about how to recover the Mars 96 science. The ability of the Russians to fly another mission is very unclear, but many countries will offer instruments to fly on future U.S. missions, if we can accomodate them.

--Donna Shirley, Mars Exploration Program Manager

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The speed of the Pathfinder computer is limited by the clock oscillator speed. The clock is divided down by 2s to get the next lower increment, hence the speeds of 2.5, 5, 10, and 20. We can't run slower than 2.5 MHz because we can't service the refresh rate on the 128 MBytes of DRAM and still have enough CPU to do useful work. During tests (with an external oscillator that can be minutely adjusted) we have tested the CPU at 2.5 to over 25 MHz in increments of less than 0.1 MHz.

--Lloyd Keith, MFC Chief Engineer

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When will a human stand on Mars?

When depends on the budget and on what we find with our robotic missions. Is Mars safe to land on? Is it interesting? Are there things for people to do?

Some people believe that we could technically land people on Mars in the first decade of the next century. Others think it would be 2019 at the earliest.

--Donna Shirley, Mars Exploration Program Manager

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Are there easy and tough plants that you are experementing with to go to Mars with? What would they be? If food and water were low, are there methods that could produce the necessary food and water on Mars? If you were to live on Mars for 1 year, what 10 things would you bring?

At the Jet Propulsion Laboratory we don't work on sending people to the planets, we send robots. But at the Johnson Space Center they are working on growing plants that can live in space and make oxygen and food for astronauts on the way to Mars.

If I were to live on Mars for 1 year I would bring (in no particular order):

1. Oxygen
2. Water (I could make oxygen out of water, of course).
3. Food
4. A way to land (a lander that I could live in on the surface).
5. A spacesuit so I could go outside.
6. Tools to collect and analyze samples.
7. Medicine
8. A radio for communicating with Earth.
9. Solar arrays for making power.
10. Books and computer games.

--Donna Shirley, Mars Exploration Program Manager

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It is stated above that the MFC "....runs at speeds of 2.5, 5, 10 and 20 MegaHertz". Why the different speeds instead of just running it at the maximum speed?

The MFC runs at different speeds to save power. There is a direct correlation between the speed of the processor and the amount of power consumed and the processing capability. At 20 MegaHertz, the processor can process about 22 Million Instructions Per Second (MIPS) while at 10 MegaHertz it can process only about 11 MIPS. At 20 MegaHertz, the processor uses about 9 watts of power. Dropping the speed in half to 10 MegaHertz will reduce its utilization to about 5.5 watts and at 2.5 MegaHertz it will use about 2.5 watts. This capability to run at different speeds allows us to tailor the speed and power utilization of the MFC to match the tasks we are processing and minimize the power used.

Power is a critical resource for any space mission and any reductions in power utilization can aid in making the spacecraft lighter (by using smaller batteries and solar arrays) or capable of allocating power to be used to do more scientific work or take more pictures, or conduct a longer mission, etc.

--Lloyd Keith, Mars Pathfinder Flight Computer Chief Engineer

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Actually UTC stands for Universal Coordinated Time (the acronym coming from the French "Universel Temps Coordonne"). It is ALMOST exactly the same as GMT, they only differ by a fraction of a second. UTC counts the number of SI unit (atomic clock) seconds so it is synchronized with International Atomic Time (TAI or atomic time). TAI is simply a count of atomic seconds that have occurred since the instant of midnight January 1, 1958 at the Royal Observatory in Greenwich, England.

GMT is tied to the true rotation of the Earth and is related to the prime meridian angle. It is derived from the mean sidereal time at the Greenwich Observatory and determined by astronomical observations of stars and radio sources. Although it is angular in nature, it can be expressed using a calendar system having the familiar six components of year, month, day, hours, minutes, and seconds that specify an instant of time. Midnight is defined as 0 hours, minutes, and seconds, or 00:00:00. However since the rotation of the Earth varies a bit, a GMT second is not quite the same length as an atomic second.

UTC is also represented in 00:00:00 format with all zeros representing midnight in Greenwich England. UTC is an attempt to have a time where 00:00:00 is midnight AND still have it count atomic seconds. So that UTC and GMT don't drift too far apart, the International Earth Rotation Service (IERS) in Paris, France occasionally announce the introduction of leap second, usually at the beginning of the year.

Why did you chose to use pyrotechnic devices? Are they very simple/reliable/light?

Pyrotechnically activated devices have been in use on space vehicles since the beginning of the space age, especially on launch vehicles. They are reasonably lightweight, simple and remarkably reliable. There are drawbacks, most notably the "one-shot" nature of these devices and the fact that they pose potential hazards to those who handle them. On Mars Pathfinder, we require that 42 of these devices (including several varieties) work in order for the entry, descent and landing process to be successful. That may sound like a lot, but it is less than half the number required for a typical expendable launch vehicle (rocket).

On Mars Pathfinder, we used two sizes of pyro cable cutters which are used to disconnect electrical and mechanical cables and tubing between the big pieces of the spacecraft (cruise stage, backshell, heatshield, lander and rover) just prior to physical separation. We also use pyro separation nuts to disconnect bolts that hold some of these pieces together. We also utilize pyrotechnically initiated thermal batteries that are used during the entry descent and landing process to provide electrical power to other pyro squibs. Of course the parachute mortor, the three solid rocket motors and the three airbag gas generators (an unusual form of rocket motor) must all be electrically initiated at just the right time by sending electric current into squibs (called "NSI's" or NASA standard initiators). There are two factors that primarily govern the system reliability of pyrotechnic applications; the reliability of the electrical system which delivers current to the NSI and the manner in which the device is used (the NSI's will fire if current is delivered to them - what happens after is up to the spacecraft designer). We were very fortunate to have responsive pyro device manufacturers and experienced engineers at JPL who could work the design and test details for all these pyro applications. We also extensively tested every application in as close to the flight conditions we could.

--Rob Manning, Mars Pathfinder Chief Flight Engineer

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