RBE 595: Space and Planetary Robotics Lecture 8

1. RBE 595: Space and Planetary RoboticsLecture 8 Professor Marko B Popovic A term 2019

2. Acomparison of three generations of Mars rovers developed at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL's Mars Yard testing area. Front and center is the flight spare for the first Mars rover, Sojourner, which landed on Mars in 1997 as part of the Mars Pathfinder Project. On the left is a Mars Exploration Rover Project test rover that is a working sibling to Spirit and Opportunity, which landed on Mars in 2004. On the right is a Mars Science Laboratory test rover the size of that project's Mars rover, Curiosity, which landed on Mars in 2012. Sojourner and its flight spare, named Marie Curie, are 2 feet (65 centimeters) long. The Mars Exploration Rover Project's rover, including the "Surface System Test Bed" rover in this photo, are 5.2 feet (1.6 meters) long. The Mars Science Laboratory Project's Curiosity rover and "Vehicle System Test Bed" rover, on the right, are 10 feet (3 meters) long.

3. Curiosity Curiosity is a car-sized robotic rover exploring Gale Crater on Mars as part of NASA's Mars Science Laboratory mission (MSL). As of September 30, 2019, Curiosity has been on Mars for 2542 sols (2619 total days) since landing on August 6, 2012. Curiosity was launched from Cape Canaveral on November 26, 2011, aboard the MSL spacecraft and landed on Aeolis Palus in Gale Crater on Mars on August 6, 2012,. The Bradbury Landing site was less than 2.4 km (1.5 mi) from the center of the rover's touchdown target after a 563,000,000 km (350,000,000 mi) journey. The rover's goals include: investigation of the Martian climate and geology; assessment of whether the selected field site inside Gale Crater has ever offered environmental conditions favorable for microbial life, including investigation of the role of water; and planetary habitability studies in preparation for future human exploration. https://www.youtube.com/watch?v=Q-uAz82sH-E https://www.youtube.com/watch?time_continue=107&v=UUweNrpFTwA

4. Curiosity comprised 23 percent of the mass of the 3,893 kg (8,583 lb) Mars Science Laboratory (MSL) spacecraft, which had the sole mission of delivering the rover safely across space from Earth to a soft landing on the surface of Mars. The remaining mass of the MSL craft was discarded in the process of carrying out this task. Dimensions: Curiosity has a mass of 899 kg (1,982 lb) including 80 kg (180 lb) of scientific instruments. The rover is 2.9 m (9.5 ft) long by 2.7 m (8.9 ft) wide by 2.2 m (7.2 ft) in height. Curiosity is powered by a radioisotope thermoelectric generator (RTG), like the successful Viking 1 and Viking 2 Mars landers in 1976. Radioisotope power systems (RPSs) are generators that produce electricity from the decay of radioactive isotopes, such as plutonium-238, which is a non-fissile isotope of plutonium. Heat given off by the decay of this isotope is converted into electric voltage by thermocouples, providing constant power during all seasons and through the day and night. Waste heat can be used via pipes to warm systems, freeing electrical power for the operation of the vehicle and instruments. Curiosity's RTG is fueled by 4.8 kg (11 lb) of plutonium-238 dioxide supplied by the U.S. Department of Energy.

5. Curiosity is powered by a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), designed and built by Rocketdyne and Teledyne Energy Systems under contract to the U.S. Department of Energy, and assembled and tested by the Idaho National Laboratory. Based on legacy RTG technology, it represents a more flexible and compact development step, and is designed to produce 125 watts of electrical power from about 2,000 watts of thermal power at the start of the mission. The MMRTG produces less power over time as its plutonium fuel decays: at its minimum lifetime of 14 years, electrical power output is down to 100 watts. The power source will generate 9 MJ (2.5 kWh) each day, much more than the solar panels of the Mars Exploration Rovers, which can generate about 2.1 MJ (0.58 kWh) each day. The electrical output from the MMRTG charges two rechargeable lithium-ion batteries. This enables the power subsystem to meet peak power demands of rover activities when the demand temporarily exceeds the generator’s steady output level. Each battery has a capacity of about 42 ampere-hours. The temperatures at the landing site can vary from −127 to 40 °C (−197 to 104 °F); therefore, the thermal system will warm the rover for most of the Martian year. The thermal system will do so in several ways: passively, through the dissipation to internal components; by electrical heaters strategically placed on key components; and by using the rover heat rejection system (HRS). It uses fluid pumped through 60 m (200 ft) of tubing in the rover body so that sensitive components are kept at optimal temperatures. The fluid loop serves the additional purpose of rejecting heat when the rover has become too warm, and it can also gather waste heat from the power source by pumping fluid through two heat exchangers that are mounted alongside the RTG. The HRS also has the ability to cool components if necessary.

6. The two identical on-board rover computers, called Rover Computer Element (RCE) contain radiation hardened memory to tolerate the extreme radiation from space and to safeguard against power-off cycles. Each computer's memory includes 256 kB of EEPROM, 256 MB of DRAM, and 2 GB of flash memory. For comparison, the Mars Exploration Rovers used 3 MB of EEPROM, 128 MB of DRAM, and 256 MB of flash memory. The RCE computers use the RAD750 CPU, which is a successor to the RAD6000 CPU of the Mars Exploration Rovers. The RAD750 CPU, a radiation-hardened version of the PowerPC 750, can execute up to 400 MIPS, while the RAD6000 CPU is capable of up to only 35 MIPS. Of the two on-board computers, one is configured as backup and will take over in the event of problems with the main computer. On February 28, 2013, NASA was forced to switch to the backup computer due to an issue with the then active computer's flash memory, which resulted in the computer continuously rebooting in a loop. The backup computer was turned on in safe mode and subsequently returned to active status on March 4. The same issue happened in late March, resuming full operations on March 25, 2013.

7. The rover has an Inertial Measurement Unit (IMU) that provides 3-axis information on its position, which is used in rover navigation. The rover's computers are constantly self-monitoring to keep the rover operational, such as by regulating the rover's temperature. Activities such as taking pictures, driving, and operating the instruments are performed in a command sequence that is sent from the flight team to the rover. The rover installed its full surface operations software after the landing because its computers did not have sufficient main memory available during flight. The new software essentially replaced the flight software. Curiosity is equipped with significant telecommunication redundancy by several means – an X band transmitter and receiver that can communicate directly with Earth, and a UHF Electra-Lite software-defined radio for communicating with Mars orbiters. Communication with orbiters is the main path for data return to Earth, since the orbiters have both more power and larger antennas than the lander allowing for faster transmission speeds. Telecommunication includes a small deep space transponder on the descent stage and a solid-state power amplifier on the rover for X band. The rover also has two UHF radios,the signals of which the 2001 Mars Odyssey satellite is capable of relaying back to Earth. An average of 14 minutes, 6 seconds is required for signals to travel between Earth and Mars. Curiosity can communicate with Earth directly at speeds up to 32 kbit/s, but the bulk of the data transfer is relayed through the Mars Reconnaissance Orbiter and Odyssey orbiter. Data transfer speeds between Curiosity and each orbiter may reach 2 Mbit/s and 256 kbit/s, respectively, but each orbiter is able to communicate with Curiosity for only about eight minutes per day (0.56% of the time).

8. Curiosity is equipped with six 50 cm (20 in) diameter wheels in a rocker-bogie suspension. The suspension system also served as landing gear for the vehicle, unlike its smaller predecessors.Each wheel has cleats and is independently actuated and geared, providing for climbing in soft sand and scrambling over rocks. Each front and rear wheel can be independently steered, allowing the vehicle to turn in place as well as execute arcing turns.Each wheel has a pattern that helps it maintain traction but also leaves patterned tracks in the sandy surface of Mars. That pattern is used by on-board cameras to estimate the distance traveled. The pattern itself is Morse code for "JPL" (·--- ·--· ·-··). The rover is capable of climbing sand dunes with slopes up to 12.5°. Based on the center of mass, the vehicle can withstand a tilt of at least 50° in any direction without overturning, but automatic sensors will limit the rover from exceeding 30° tilts. After 7 years of operation the wheels are visibly worn with punctures and tears. Curiosity can roll over obstacles approaching 65 cm (26 in) in height, and it has a ground clearance of 60 cm (24 in). Based on variables including power levels, terrain difficulty, slippage and visibility, the maximum terrain-traverse speed is estimated to be 200 m (660 ft) per day by automatic navigation. The general sample analysis strategy begins with high-resolution cameras to look for features of interest. If a particular surface is of interest, Curiosity can vaporize a small portion of it with an infrared laser and examine the resulting spectra signature to query the rock's elemental composition. If that signature is intriguing, the rover will use its long arm to swing over a microscope and an X-ray spectrometer to take a closer look. If the specimen warrants further analysis, Curiosity can drill into the boulder and deliver a powdered sample to either the SAM or the CheMin analytical laboratories inside the rover. It has 17 cameras: HazCams (8), NavCams (4), MastCams (2), MAHLI (1), MARDI (1), and ChemCam (1).

10. Mission Moon Ranger The goal of the seven Ranger missions during the early 1960's was to obtain the first close-up U.S. pictures of the Moon. Each spacecraft was to fly straight down to the Moon's surface and return photographs until being destroyed on impact. Only the Ranger 7, 8, and 9 missions were successful, each returning thousands of photographs of the lunar surface. The photos were highly detailed, with resolution 1000 times better than that of Earth-based observations. Neither Ranger 3 or 5 were able to impact the Moon, while Rangers 4 and 6 reached its surface but didn't return any images. The Ranger missions were useful for the planners of the Surveyor and Apollo programs, showing them that a safe landing site on the Moon would be hard to find.

11. Lunar Orbiter During 1966 through 1967, five Lunar Orbiter spacecrafts were launched, with the purpose of mapping the Moon's surface in preparation for the Apollo and Surveyor landings. All five missions were successful. The first three Lunar Orbiters were mostly dedicated to obtaining detailed photographs of 20 areas preselected as possible future landing sites. Lunar Orbiters 4 and 5 concentrated on more general mapping, covering 99% of the lunar surface including most of the farside. Also, much was learned about the Moon's gravitational field. After orbiting the Moon and returning hundreds of photographs, each Lunar Orbiter spacecraft was commanded to crash into the surface, destroying itself.

12. Surveyor The Surveyor missions of 1966 through 1968 were the next step in space travel to the Moon, following the Ranger missions. Their goal was to perform "soft" landings on the lunar surface, meaning that the spacecrafts would not crash and be destroyed. Five of seven Surveyor missions were successful, landing safely on the moon and conducting the first soil analysis. From the Surveyor program we learned that the lunar surface is firm and can be walked on by astronauts, a feat accomplished by the Apollo missions, just a few years later.

13. Apollo 1 The Apollo space program, scheduled for its first launch on Feb. 21, 1967, started in tragedy. On Jan. 27, 1967, astronauts Gus Grissom, Ed White, and Roger Chaffee were executing a dress rehearsal when fire was smelled in the command module. Caused by a spark due to faulty electrical wiring, the fire spread quickly within the capsule. It then burned the walls of the command module, releasing toxic fumes. Meanwhile, technicians outside needed more than five minutes to open the elaborate escape hatch, only to find that the astronauts trapped inside had already died because they couldn't breathe. The investigation which followed showed that poor planning and design were to blame for the Apollo 1 disaster. Further Apollo missions had to be postponed for over a year, as these problems were resolved and safety improvements, such as a rapid releasing escape hatch, were made.

14. Apollo 7 The Apollo 7 mission was launched on Oct. 11, 1968, carrying astronauts Walter Schirra, Jr., DonnEisele, and Walter Cunningham on board. It successfully accomplished all its objectives, giving NASA and the Apollo space program much confidence following the Apollo 1 disaster. Apollo 7 spent eleven days making 163 orbits around Earth, proving that its command module would last long enough to make a trip to the Moon possible. Although the astronauts all developed unpleasant colds, and complained about food, they enjoyed the large cabin size, bigger than those of the Gemini spacecrafts. Apollo 7 also returned the first live television pictures from space. It earned public and government support for a mission to the Moon, accomplished by the Apollo 8 mission, only months later.

15. Apollo 8 Originally planned as another Earth orbiting mission like Apollo 7, Apollo 8's objectives were changed due to pressure of beating the Soviet Union in the race to the Moon. Powered by the Saturn V rocket, later used by Apollo 11, Apollo 8 was launched on Dec. 21, 1968 as the first manned lunar mission. Astronauts Frank Borman, James Lovell, Jr., and William Anders became the first humans to travel to the Moon and see its farside, successfully accomplishing all their mission objectives during their six days in space. On Christmas Eve, Apollo 8 completed 10 orbits around the Moon returning live television pictures back to our planet. Over half a billion people watched as Earth rose on the Moon's horizon, realizing the limitless possibilities of space exploration. Apollo 8 provided astronauts with more experience in space travel, and brought us one step closer to the Apollo program's goal of safely landing humans on the Moon.

16. Apollo 9 The major goal of the Apollo 9 mission was to conduct the first tests of the Lunar Module and other new space equipment. The Lunar Module was the latest piece of hardware designed to safely carry astronauts to the Moon's surface, and would be used repeatedly by future Apollo missions. Apollo 9 lifted off on Mar. 3, 1969, with astronauts James McDivitt, David Scott, and Russell Schweickart on board, becoming the first flight with all the equipment necessary for a lunar landing. During 152 orbits of Earth, they released the Lunar Module and later reattached it to the Space Module, in conditions similar to those around the Moon. The astronauts also tested a new space suit designed with a built-in life support system. Apollo 9, though not as famous as other Apollo missions, was a success, giving scientists much valuable information about safely reaching the Moon, a goal finally achieved by Apollo 11.

17. Apollo 10 Apollo 10 was launched on May 18, 1969, carrying astronauts Thomas Stafford, John Young, and Eugene Cernan. It served as a "dress rehearsal" for the Apollo 11 lunar landing mission which followed a month later. While in orbit around the Moon, the astronauts of Apollo 10 released a lunar module which descended to within 14 km (9 miles) of the lunar surface, before returning to the Command Module. They successfully performed other tests in the lunar gravitational field, proving that humans were ready to attempt a safe landing on the Moon. Another task of Apollo 10 was to take close-up pictures of the anticipated Apollo 11 touchdown location. While in flight, it also made possible the first color television broadcast from space, allowing audiences back on Earth to see their planet as never before. https://www.youtube.com/watch?time_continue=179&v=_QYRVCqwuYI

18. Apollo 11 Driven by a recent surge in space research, the Apollo program hoped to add to the accomplishments of the Lunar Orbiter and Surveyor missions of the late 1960's. Apollo 11 was the name of the first mission to succeed in landing a person on the surface of the moon. On July 16, 1969, the U. S. rocket Saturn 5 was launched and three days later successfully deployed the lunar landing module Eagle which landed in the Moon's Sea of Tranquility. On July 20, millions of people back on Earth watched and listened as astronaut Neil Armstrong prepared to walk on the lunar surface. "One small step for man, one giant leap for mankind". With these historic words, Armstrong became the first human to set foot on the Moon, leaving his footprint etched in the lunar soil. Over the next 2 1/2 hours, he and astronaut Edwin Aldrin took color photographs, collected soil and rock samples, and raised the American flag, while walking around on the Moon. They also conducted several experiments to learn more about the dusty surface, geologic activity, and solar wind effects on the lunar environment. Apollo 11 returned to Earth on July 24, 1969, meeting President Kennedy's challenge earlier that decade to safely send a human to the Moon and back. Today, the Apollo 11 mission remains one of the greatest technological achievements of all time.

19. https://www.youtube.com/watch?v=OCjhCL2iqlQ https://www.youtube.com/watch?v=AcmeiYhclJY

20. Space suit A space suit must perform several functions to allow its occupant to work safely and comfortably, inside or outside a spacecraft. It must provide: A stable internal pressure. This can be less than Earth's atmosphere, as there is usually no need for the space suit to carry nitrogen (which comprises about 78% of Earth's atmosphere and is not used by the body). Lower pressure allows for greater mobility, but requires the suit occupant to breathe pure oxygen for a time before going into this lower pressure, to avoid decompression sickness. (At altitudes above the Armstrong limit, around 19,000 m (62,000 ft), water boils at body temperature and pressurized suits are needed.) Mobility. Movement is typically opposed by the pressure of the suit; mobility is achieved by careful joint design. Supply of breathable oxygen and elimination of carbon dioxide; these gases are exchanged with the spacecraft or a Portable Life Support System (PLSS) Temperature regulation. Unlike on Earth, where heat can be transferred by convection to the atmosphere, in space, heat can be lost only by thermal radiation or by conduction to objects in physical contact with the exterior of the suit. Since the temperature on the outside of the suit varies greatly between sunlight and shadow, the suit is heavily insulated, and air temperature is maintained at a comfortable level. A communication system, with external electrical connection to the spacecraft or PLSS Means of collecting and containing solid and liquid bodily waste (such as a Maximum Absorbency Garment)

21. Generally, to supply enough oxygen for respiration, a space suit using pure oxygen must have a pressure of about 32.4 kPa (240 Torr; 4.7 psi), equal to the 20.7 kPa (160 Torr; 3.0 psi) partial pressure of oxygen in the Earth's atmosphere at sea level, plus 5.3 kPa (40 Torr; 0.77 psi) CO2 and 6.3 kPa (47 Torr; 0.91 psi) water vapor pressure, both of which must be subtracted from the alveolar pressure to get alveolar oxygen partial pressure in 100% oxygen atmospheres, by the alveolar gas equation. When space suits below a specific operating pressure are used from craft that are pressurized to normal atmospheric pressure (such as the ISS), this requires astronauts to "pre-breathe" (meaning pre-breathe pure oxygen for a period) before donning their suits and depressurizing in the air lock. This procedure purges the body of dissolved nitrogen, so as to avoid decompression sickness due to rapid depressurization from a nitrogen-containing atmosphere. The human body can briefly survive the hard vacuum of space unprotected, despite contrary depictions in some popular science fiction. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. No snap freeze effect occurs because all heat must be lost through thermal radiation or the evaporation of liquids, and the blood does not boil because it remains pressurized within the body. Human skin does not need to be protected from vacuum and is gas-tight by itself. Instead, it only needs to be mechanically compressed to retain its normal shape. This can be accomplished with a tight-fitting elastic body suit and a helmet for containing breathing gases, known as a space activity suit (SAS).

22. DCS is best known as a diving disorder that affects divers having breathed gas that is at a higher pressure than the surface pressure, owing to the pressure of the surrounding water. The risk of DCS increases when diving for extended periods or at greater depth, without ascending gradually and making the decompression stops needed to slowly reduce the excess pressure of inert gases dissolved in the body. The specific risk factors are not well understood and some divers may be more susceptible than others under identical conditions. DCS has been confirmed in rare cases of breath-holding divers who have made a sequence of many deep dives with short surface intervals; and it may be the cause of the disease called taravana by South Pacific island natives who for centuries have dived by breath-holding for food and pearls. Two principal factors control the risk of a diver suffering DCS: 1) the rate and duration of gas absorption under pressure – the deeper or longer the dive the more gas is absorbed into body tissue in higher concentrations than normal (Henry's Law); 2) the rate and duration of outgassing on depressurization – the faster the ascent and the shorter the interval between dives the less time there is for absorbed gas to be offloaded safely through the lungs, causing these gases to come out of solution and form "micro bubbles" in the blood. Even when the change in pressure causes no immediate symptoms, rapid pressure change can cause permanent bone injury called dysbaric osteonecrosis (DON). DON can develop from a single exposure to rapid decompression.

23. Other requirements: Shielding against ultraviolet radiation Limited shielding against particle radiation Means to maneuver, dock, release, and/or tether onto a spacecraft Protection against small micrometeoroids, some traveling at up to 27,000 kilometers per hour, provided by a puncture-resistant Thermal Micrometeoroid Garment, which is the outermost layer of the suit. Experience has shown the greatest chance of exposure occurs near the gravitational field of a moon or planet, so these were first employed on the Apollo lunar EVA suits (see United States suit models below).

24. Apollo/Skylab A7L EVA and Moon suits. The Block II Apollo suit was the primary pressure suit worn for eleven Apollo flights, three Skylab flights, and the US astronauts on the Apollo–Soyuz Test Project between 1968 and 1975. The pressure garment's nylon outer layer was replaced with fireproof Beta cloth after the Apollo 1 fire. This suit was the first to employ a liquid-cooled inner garment and outer micrometeroid garment. Beginning with the Apollo 13 mission, it also introduced "commander's stripes" so that a pair of space walkers will not appear identical on camera. Extravehicular Mobility Unit (EMU) used on both the Space Shuttle and International Space Station (ISS). The EMU is an independent anthropomorphic system that provides environmental protection, mobility, life support, and communications for a Space Shuttle or ISS crew member to perform an EVA in Earth orbit. Used from 1982 to present, but only available in limited sizing as of 2019.

25. Homework 4 Here, you will try to save the world by diverting large asteroid from impacting Earth. This is time (and accuracy/precision) critical mission. Your robot could carry 40 warheads with each being the 320-kT () strategic bomb. They are packaged inside metal structure (to simplify imagine just Fe atoms, and each is heavy with ).To further simplify imagine that after the explosion the entire fusion/fission energy is in the form of Fe kinetic energy. The Fe atom average speed is The total momentum released over blast sphere is The asteroid can be imagined as billiard ball with radius of and mass of moving directly toward Earth with speed of . This corresponds to or ‘bomb’. (By comparison, the "Little Boy" atomic bomb dropped on Hiroshima during World War II yielded roughly 15 kilotons TNT. The "Fat Man" bomb dropped on Nagasaki was about 20 kilotons TNT.) Also the asteroid momentum is

26. It is only 6 hours from impacting the Earth at the moment when you lunch rocket with warheads, see Figure below. Let’s imagine the rocket will be moving with constant speed of and it is up to you to control its direction. The change of direction is maximally per minute. The exact moment when you ignite the bomb will affect how much momentum and in which direction will be transferred onto asteroid. The direction will be aligned with rocket and center of asteroid position and amount of momentum transfer will be equal to with being the distance between rocket and center of asteroid. Design automatic angular control of your robot rocket and explosion trigger. Plot robot rocket and asteroid trajectories relative to Earth before and after blast (Earth radius is ). Can you save us? Btw, can you save us if asteroid consists of two identical hemispheres and you can explode the bomb in between?