Aim of The Pathfinder
We, as in humans, do not know much about the Martian planet, even though two Viking Landers have sent back images in the 1970's. Pathfinder's images ar much more detailed, and hopes are high that much will be learnt about the geology of the planet and whether it may have supported life and water.
    The main aim of these missions to Mars, is to discover if life has ever existed on Mars, or indeed if life could be maintained on Mars. We, on Earth, have a great thirst for discovering if there is life in the universe and satisfying our basic need to explore.
    The main quest is to discover if Mars was ever warm enough for a time to keep water from freezing. Rock studies would reveal this. The sojourner would explore the Martian surface, taking close up photos of rock and shifting out chemicals that could tell if conditions were suitable for life.
    The Mars Pathfinder will be the second of NASA's low-cost planetary Discovery missions. The mission consists of a lander and a surface rover known as the Sojourner, launched in December, 1996. It landed on the martian surface on July 4th, 1997, USA's Independence Day.
    The mission is intended to develop technology and capabilities for low-cost landings on and exploration of the Martian surface rather than being driven primarily by specific science goals.
    The scientific objectives are quite broad including atmospheric entry science, and detailed characterisation of the landing site by an advanced imaging system and a chemical analysis experiment mounted on the rover.
    The rover is primarily a technology experiment itself, designed to determine micro rover performance in the poorly understood Martian terrain so that future rovers may be designed to be effective in navigating and moving about the surface of Mars.
    In landing on the "Red Planet" the Mars Pathfinder set several firsts
~ It was the first spacecraft to land on a planet without orbiting it.
~ It was the first to deploy a parachute at a supersonic speed of 1600 km/h, and
~ It was the first to use airbags, similar to but larger than those used in cars, to cushion the impact of the landing. This was a risky but money-saving maneuver that had never been tried before.

            Features of the Mars Pathfinder
    The Mars Pathfinder is an amazing machine. There are two parts to the Pathfinder - spacecraft and Sojourner.
The Mars Pathfinder begins with a spacecraft. The design of this craft involves it's cruise stage platform, the aeroshell heat shield and back shell, solar panels, antennas, the lander and rover, parachute and air bag system, and contains about 110L of fuel. It also carries a heater unit that is vital in sub-zero temperatures.
    The spacecraft stands at about 105m tall, measuring 2.4m in diametre, and weighs about 1000 kg at launch. The pyramid shaped Pathfinder lander stands about 90 cm, weighing about 400 kg upon landing, and costing $171 million to build.
    The spacecraft uses an IBM R6000 computer with a VME bus. It is a considerably powerful system, executing anywhere from 2.5 to 20 million MIPS (millions of instructions per second). The R6000 has 128 MB of memory that was radiation hardened to survive the hazards of space flight. For propulsion, the spacecraft carries eight 4.4 Newton thrusters.
    Electric power is supplied during the day by solar cells, which also feed a bank of rechargeable batteries for night time power needs. The lander is designed to last for at least 30 days, but could operate for more than a year.

    The second part of the Mars Pathfinder is the Sojourner, also known as the Rover which is about the size of a microwave oven. The Rover, (It's official name is Micro rover Flight Experiment) weighs less than 14 kilograms, which includes it's mounting and deployment equipment. It's mobile mass is only 11.5 kilograms, which does include the Alpha Proton X-ray.
    The Rover is powered by 25 square centimetres of solar panels, which produces a peak power of 16 watt hours. Its primary battery provides 150 watt hours. This power also has to power three heater units, which are necessary for temperature control.
    The Rover can move approximately 41 centimetres a minute. The design feature that makes the Mars Pathfinder Rover perfect to move freely on the Martian landscape is the six 13 cm high wheels. Each wheel is independently controlled.
    A NASA expert navigates the Mars Pathfinder Rover. Each signal sent out to the Rover takes 11 minutes, so does the signal to get back to Earth, sent from the Rover. The Rover's wheels can be used to get valuable information about the properties of the Mars dust, by scraping molding and stirred it up.
 

        The Journey to Mars
Launch and Injection
    The Mars Pathfinder mission begins with a successful launch atop at Delta II rocket from the Kennedy Space Centre in Florida in December of 1996. Once in orbit, the spacecraft is given a final boost with the help of a solid fuel rocket motor, which gives the spacecraft just the right amount of velocity increase it needs to escape Earth's gravity and enter it's own orbit around the sun. The third stage is jettisoned and it's officially on the way to Mars.
    At separation from the upper stage, the spacecraft is in the Earth's shadow and spinning at 20 rpm. An onboard sequence of events is activated once the separation micro switch detects that separation is completed. The Deep Space Network (DSN) initiates spacecraft acquisition and lockup activities using a 34m antenna located in the Californian desert. As soon as acquisition has occurred, the engineering telemetry broadcast by the spacecraft is received on the ground at a rate of 40 bits per second (b/s). This telemetry is a combination of real time engineering data and stored data from the launch, separation, and Earth/Sun acquisition sequence is executed autonomously by the spacecraft.
    The spacecraft automatically determines its orientation in space by first determining the location of the Sun with respect to the spin of the axis of the spacecraft using a Sun sensor located on the top of the cruise stage. This procedure, known as Sun acquisition, will provide the spacecraft with the information it needs to reduce the spin rate from 20 rpm to nominal 2 rpm. After the spacecraft has cleared the moon's orbit and safely spun down to 2 rpm, the star scanner will be activated. After star identification has been confirmed, the Attitude and Information Management (AIM) computer will then calculate the spacecraft orientation. Once the attitude is determined, the spacecraft can be commanded to change its attitude and move the spin axis closer to Earth if needed.

During the Cruise
    A number of activities are performed to maintain the health of the entry vehicle, lander and rover. Activities commence once safely out of Earth's orbit. After the attitude is established and the spacecraft is determined to be healthy, the flight team begins a two-week initial characterisation and calibration period. Systems to be characterised include the solar array and battery, thermal control, attitude determination and control, and the communication subsystems.
    The primary spacecraft activities during the first month of the cruise are collection and downlink of relevant engineering maneuvers to maintain the correct Earth/Sun geometry. A health check of the rover and the science instruments occurs at 15th day after launch. Measurements of the spacecraft range to Earth and the rate of change of this distance are collected during every DSN station contact and sent to the navigation specialists of the flight team for analysis. They use this data determine the true path the spacecraft is flying, and determine corrective maneuvers needed to maintain the desired trajectory (The first of four Trajectory Correction Maneuvers - TCMs - was scheduled on January 4th, 1997 to correct any errors collected from launch. Two more are performed in early February and early May to further reduce navigation guidance errors.)
    After TCM1 - the flight team transfers from a 'spacecraft checkout mode' to a more routine 'spacecraft monitoring mode'. DSN tracking coverage is reduced from 3 contacts a day to 3 per week. Spacecraft health and performance telemetry is downlinked at 40b/s or greater during each tracking pass.
    A key activity during the cruise is the designing and building of command sequences that dictate to the spacecraft how it is to perform each of the activities required. Each cruise command sequence is generated and uplinked approximately once every four weeks during one of the regularly scheduled DSN passes. The uplink generation process requires 14 days for planning, sequence generation, verification, and commanding.

Approaching Mars
    Five days prior to entry, tracking is increased to 3 day passes and the flight team steps up its preparation for atmosphere entry and landing. A final health and status check of the instruments and rover is performed at Mars - 30 days. A forth and final trim maneuver is performed at Mars - 10 days (June 24th), requiring less than 0.5 m/s. At mars - 5 days, the spacecraft performs a turn to the entry attitude, where it will remain until atmosphere entry. The roll thrusters increase the spacecraft spin rate from 2 to 10 rpm for entry. At that time, the cruise phase ends and the flight team transitions to the entry, landing, and surface operations.
    During the final day of approach, the navigation team is producing orbit solutions on a regular basis, and adjustments are made to the computer programs that determine when the parachute should be deployed. At 6 hours out, the final adjustment is made, and the flight team makes final preparations for atmosphere entry.
 

            Science Instruments and its Activities on
            Mars / Operations - Second Journey
    The spacecraft will enter the Martian atmosphere directly without entering orbit and, after losing most of it's energy in the upper atmosphere, will land on Mars with the aid of parachutes, rockets and airbags. After landing, the spacecraft will unfold itself from within a tetrahedral structure that has three triangular solar panels.
    The lander will first transmit the engineering and science data collected during entry and landing after which the stereo/colour imaging system will obtain a panoramic view of the landing area and transmit it to earth. Finally, the rover will be deployed to examine and measure the composition of individual rocks near the lander. Much of the lander's task will be to support the rover by imaging rover operations and relaying data from the rover to Earth.
    The rover, "Sojourner", is a six wheel vehicle, mounted on a "rocker bogie" suspension. The rover is stowed on the lander at a height and roll down a deployment ramp. The rover will be controlled by an Earth based operator, who will use images obtained by both the rover and lander system. Note that the time delay will be between 6 and 41 minutes depending on the relative position of the Earth and Mars, requiring some autonomous control by the rover. The rover is equipped with black and white and colour imaging systems which were used to image the lander in order to asses its condition after touchdown. The goal was to acquire three black and white images spaced 120 degrees apart of the lander. Images of the surrounding terrain were also acquired to study size and distribution of soils and rocks, as well as locations of larger features. Imaging of the rover wheel tracks will be used to estimate soil properties. Imaging of the rover by the lander was also done to asses rover performance and soil and site properties. The rover's performance was monitored to determine tracking capabilities, driving properties, thermal behavior, and sensor performance. UHF Communication between the rover and the lander were studied to determine the effectiveness of the link between the rover and the lander. Assessments of rock and soil mechanics will be based on abrasions of the wheels and adherence of dust. An APXS is on board the rover to asses the composition of rocks and soil. Images of all samples tested are transmitted to Earth. The primary objectives were scheduled for the first seven sols, all within about 10 metres of the lander. The extended mission included slightly longer trips away from the lander, and even longer journeys were planned. Images were taken and experiments performed by the lander and rover until 27th September 1997 when communications were lost for unknown reasons.
 

            Investigations on Mars & their Results
The major scientific goals of this mission were:
1. Mapping the terrain and morphology of the landing site
2. Determine the mineral in the rocks, soil and dust at the landing site
3. Observe the weather at the landing site including wind velocity and direction, frost and cloud information
4. Observe the atmosphere including measuring the amount of water in it
5. Study the magnetic properties of the dust
6. Study Mars at night, including the study of the moon, Phobos and Deimos

Distribution of rocks/composition of local rock and how it compares to Earth
    The images showed a series of 4 metre high ridges and valleys near the landing site which the scientist think were carved by a great water deluge.
    The landing site surface had a reddish hue, and five whitish rocks were found which was of a great interest because it implied that its material was repeatedly heated, cooled and reheated to form a quality like material. The rock named "Barnacle Bill" appeared to be volcanic in origin and resembled rocks on earth - something that was unexpected.

Evidence of water existing on Mars
    Evidence of dried up channels and puddles also suggested that Mars was warm enough for a time to keep its water from freezing. There is evidence of many flooding on Mars as the area included many "Round rocks transported by water." Water ice clouds are found around the planet as well as ice in the Polar Regions. There is great evidence to show the role water has played in the erosion of the landing site and the formation of iron oxides.

Weather, Temperature and Air Pressure
    With days of about 24 hours, at least 2 and perhaps 4 seasons, lots of carbon and a thin cold carbon dioxide atmosphere shows that Mars is not too different from Earth.
    The Pathfinders weather station recorded unexpected, huge swings of as which as 40 degrees F (about 6 - 7 degrees C) within seconds or minutes of each other. At midday the sensor recorded temperatures of about 70 degrees F at ground level, but a chilly 10 - 15 degrees C just 5 ft about the same spot. Temperatures also change dramatically between days and night: -120 degrees C to -15 degrees is not uncommon swings of temperature. There are spectacular sunrises and sunsets - the dust mixing with the atmosphere to give the sky its red colouring. The winds show to be mild with the occasional 200 kmp/h wind gust - mostly from the west.

How much dust is in the atmosphere
    The Rovers' wheels can be used to get valuable information about the properties of the Mars dust by scraping, molding and stirring it up. There is a great deal of dust in the atmosphere - the sky stays bright for 5 hours after sunset indication the dust extends to high altitudes.
    The cameras aboard the Rover use stereoscopic glasses and different colour blocking filters and shows much about the landscape, dust and atmosphere because the blocked colours can represent different chemicals. Scientists now need to study the analysis of the exact composition of the dust particles.

Final Thoughts
    What an exciting time for space exploration. During the next decade Mars will be the most popular travel destination. Pathfinder is only the first of many missions by USA, Russia and Japan. NASA has plans to launch crafts during every available "Launch Windows" between now and 2005.

    The remarkably successful Mars Pathfinder spacecraft, part of NASA's discovery program of fast track, low-cost missions with highly focused science objectives, was the first spacecraft to explore Mars in more than 20 years.
    In all, during its three months of operations up till October '97, the mission returned about 2.6 gigabits of data, which included more than 16000 images of the Martian landscape from the lander camera, 550 images from the rover and about 8.5 million temperature, pressure and wind measurements.
    The rover travelled a total of about 100 metres in 230 commanded maneuvers, performed more than 16 chemical analyses of rocks and soil, carried out soil mechanics and technology experiments, and explored about 250 square metres of the Martian surface.
    The flight team lost communication with the lander on September 27, after 83 days of daily commanding and data return. In all, the lander operated nearly three times its design lifetime of 30 days, and the small, 10.5 kg rover operated 12 times its design lifetime of 7 days.