Research On Mars Curiosity Rover: Reliability And Redundancy

Introduction

For achievement standard 91360, we were required to research a technological system in order to gain a depth of understanding in redundancy and reliability. I chose the Mars Curiosity Rover as a research subject.

What is the Mars Rover?

A car-sized rover designed to explore the climate of Mars. Its mission was mainly to find out if Mars was capable of supporting life, and one day maybe for humans. The secondary purpose was to study the geological features and the natural climate of Mars. The $2. 5 US billion project ($3. 4 billion NZD today) launched on the 27th of November 2011 at 04:02 AM PST. After around 8 months later, on the 6th of August 2012 at 6:17 PM PST, the Mars Rover landed on Aeolis Palus, in the Gale Crater after a 560 million kilometre journey. The population of the US at that time was 313 million. This costs taxpayers roughly around $8 US ($11 NZ) each, over a period of 8 years. The total amount of taxpayer money plus 1. 8% of NASA’s yearly budget adds up to the fund of $2. 5 US billion ($3. 4 NZ billion).

The rover itself is about the size of a car. It is 2. 9 meters long x 2. 7 meters wide x 2. 2 meters high. It has a mass of 899kg (338kg on Mars). The Curiosity rover has found that Mars could have at one stage was capable of supporting life. More than 190GB of data has been collected in the 36, 700 full images as well as 35, 000 smaller images. More than 75, 000 laser blasts have been fired since too. All this happened during the Mars Curiosity rover’s first year.

The Importance of Reliability and Redundancy in the Mars Rover

a. Safety

Safety was a major concern and of great importance when it came to the reliability and redundancy of the Mars Curiosity Rover. As a result, the design was altered in order to provide a safer environment. For starters, the MMRTG (Multi-Mission Radioisotope Thermoelectric Generator) is capable of withstanding a strong impact. The MMRTG has a mass of 45 kilograms and is 65 centimetres in diameter by 66 centimetres high. The MMRTG is composed of eight GPHS (General Purpose Heat Sources) modules. Together, they create the MMRTG system. As seen through previous missions and similar power sources, there is no reason to suggest that they are the cause of any accidents that have occurred. The three missions that failed in previous years was due to other reasons, and not due to the MMRTG system. In fact, the MMRTG systems performed as specified and designed safely.

The MMRTG consists of 4. 8 kilograms of plutonium dioxide or Plutonium-238. This provides 2, 000 Watts of thermal power and 110 Watts of Electrical power when in unfamiliar environments in space. These last almost forever and have demonstrated its ability and reliability and redundancy through two previous systems to Mars (Mars 1976 Viking), as well as over 27 successful missions conducted by the US over the last 50 years. Having a lifetime power source is important as you would not have to replace or maintain the machine for a while. It has shown safety considerations throughout these missions due to the engineering, design, construction, and safety analysis and testing.

The contents of the MMRTG has been designed to safely keep the nuclear fuel (Plutonium-238) no matter the conditions. In normal conditions or extreme conditions, the container withheld and refrained from exposing the contents within. This is important and a great achievement as a leaking container would mean not only a lot less power available, but it would be harmful and dangerous due to the exposure to the surrounding environment. On Earth, the exposure to humans would be catastrophic. On Mars, it could affect research and test samples. These test scenarios the MMRTG were put under all surpassed the test and safety checks.

b. The Economy

The Mars Curiosity Rover needed to be reliable and redundant, and not contain any errors as this cost them $2. 5 US billion project ($3. 4 billion NZD today). The population of the US at that time was 313 million. This costs taxpayers roughly around $8 US ($11 NZ) each, over a period of 8 years. The total amount of taxpayer money plus 1. 8% of NASA’s yearly budget adds up to the fund of $2. 5 US billion ($3. 4 NZ billion).

c. The Environment

The environment is considerably different from that on Earth. Mars is 54. 6 million kilometers away from Earth. As such, sending the Rover back a forth for analysis would be unnecessary and too expensive. As a result, once the Rover lands on Mars, it must be reliable and redundant to continue its mission for ages and send the gathered data back. Also, the environment would be different. The gravity on Mars is different to that of Earth’s. Earths gravitational force is 9. 8m/s2, whereas, on Mars, it is 3. 711m/s2. This difference has different downward forces. Downward Force = Mass × Acceleration (or gravity). The Force acting downwards if 899kg × 9. 807m/s2. The downward Force (mg) acting down on the Mars Rover on Earth is equal to 8, 816. 5 Newtowns. However, on Mars, it is 899kg × 3. 711m/s2. This downward Force (mg) acting on the Mars Rover on Mars is 3, 336 Newtons. The downward Force is 2. 66 times less than on Earth. This means that most of the downward force acting on the Rover on Earth is not present on Mars. This means the Rover is subjected to less force keeping it grounded. It then must be reliable and redundant enough to keep itself grounded, or else it would not be able to test ground samples or take steady, upright images. If not grounded, there would be no need for 6 custom made tires and move wherever needed. If the gravity on Mars was too large, the rover would require a lot of Force to dive it forwards. The temperature is also different from that on Earth. On average, Earth is around 13. 8°C, compared to the average on Mars, which is around -62. 7°C. This drastic difference of temperature surrounding the Mars rover means the possibility of overheating is minimized. However, there is now a higher chance of the Mars Curiosity Rover freezing up in certain places. The motion of the Curiosity could be less smooth due to the increase of friction. Heat helps increase traction and reduce friction. This means if the Mars Curiosity Rover was subjected to heat, the movements of the Rover would be smoother compared to a much colder Rover. However, this is not the case. The Rover will be subjected to -62. 7°C conditions. Reliability and redundancy must then be considered to keep the rover going, despite these harsh conditions. As a result, the Mars Curiosity Rover was built to withstand conditions ranging from -127°C to 40°C. This means that the rover is able to survive another -60°C and still keep going. The components within contain two identical computers to fix the redundancy issue. If one were to fail, the other would replace it. This is important as the computer is the brains of the rover. Without it, it would not be able to process information, send data back to Earth, or even to the output components such as the arm or wheels. The data collected would also be lost. As a result, an unresponsive computer would instantly mean a failed mission. As a result, the computer is stored in a safe place. This safe place is called a WEB, or Warm Electronics Box.

Due to the rocky and harsh terrain on Mars, the wheels must be not only durable but also able to drive up and over the terrain and reduce the impact that would otherwise be absorbed by the components within.

d. Culturally

The Mars Curiosity Rover would be used as a stepping stone to help build a better design in reliability, redundancy, and efficiency for the next mission set for Mars in the year 2020. If successful, we may be able to find out if Mars is capable of supporting life and at the same time, find out more about this planet.