The Design and Engineering of Curiosity

by Emily Lakdawalla

  The decision to use a nuclear power supply for MSL was not yet official. It couldn’t be finalized until NASA and the Department of Energy went through a process required by the National Environmental Policy Act to document the potentially harmful environmental impacts of developing the nuclear power supply, including environmental effects of a potential launch disaster. NASA dutifully analyzed both nuclear and solar options as part of the environmental documentation process. They found that MSL could accomplish its full science objectives as a solar-powered mission only at a latitude of 15° north of Mars’ equator; but it could achieve minimum science objectives between 5° south and 20° north. Also, without the waste heat provided by the MMRTG, the rover would need numerous additional radioisotope heater units to maintain the rover’s temperature, offsetting the environmental benefit of avoiding a launch accident with an MMRTG.

  On December 27, 2006, NASA finally issued a formal Record of Decision that the mission would use nuclear power. In internal documents, however, the mission never spent much effort developing solar power as an option, because the limitations of solar power would render it far less feasible.

  1.3 BECOMING MARS SCIENCE LABORATORY (2003–2004)

  1.3.1 Defining the science objectives

  NASA chartered a Project Science Integration Group, headed by Mars scientists Dan McCleese and Jack Farmer, to further develop possible mission scenarios for the 2009 mission. They set about defining objectives and capabilities for the mission, while keeping its development cost (that is, the cost of designing and building the rover, but not including launch, operations, or nuclear power system) under $1 billion.

  The Project Science Integration Group had a lot of new science to integrate into the mission plans. Mars Global Surveyor continued its productive mission, while 2001 Mars Odyssey arrived at Mars in February 2002. Almost immediately, its neutron spectrometer revealed that vast regions of Mars held near-surface ground ice, hidden under only centimeters of soil.13 Present-day ground ice led to speculation that there could be extant life surviving beneath the surface in underground aquifers.

  The Project Science Integration Group advocated a mission focus on the habitability of ancient (not recent) Mars. Their proposed science objective: “Explore and quantitatively assess a potential habitat on Mars.” To accomplish that objective, they proposed three scientific investigations, listed in Box 1.1. The group held open the possibility of the sampling system being used on icy targets at high latitudes in order to study a recently habitable zone on Mars. That meant the ability to access, drive on, drill into, and examine ice. It would require a landing site at a very high latitude (poleward of 60°) and a sample handling system that could handle ice without melting it, except where melting was wanted. Such a spacecraft would have to be stringently sterilized to prevent contamination of the Mars environment with Earth microbes, imposing substantial costs and complexity on the mission.

  Box 1.1. Mars Science Laboratory scientific investigations.

  Assess the biological potential of at least one target environment (past or present).°Determine the nature and inventory of organic carbon compounds.

  °Inventory the chemical building blocks of life (C, H, N, O, P, S).

  °Identify features that may record the actions of biologically relevant processes.

  Characterize the geology of the landing region at all appropriate spatial scales.°Investigate the chemical, isotopic, and mineralogical composition of Martian surface and near-surface geological materials.

  °Interpret the processes that have formed and modified rocks and regolith.

  Investigate planetary processes that influence habitability.°Assess long-timescale (i.e., 4-billion-year) atmospheric evolution processes.

  °Determine present state, distribution, and cycling of water and carbon dioxide.

  For cost and complexity reasons, the Project Science Integration Group questioned the need for “go-to” capability. Designing and verifying a system that would be capable of driving tens of kilometers would be very expensive, blowing the billion-dollar mission development cap. Also, the beginning of a go-to mission – land, and then spend months driving – would be boring. As a result of these discussions, the requirement of go-to capability went away, and so did the related verification and validation requirements for long-distance driving.

  The group issued their report in June 2003, allowing a cooling-off period after the work ended so that scientists who had participated in the Group could propose instruments to the mission without a conflict of interest. In the meantime, JPL produced and released the first concept artwork of Mars Science Laboratory (Figure 1.2). It showed no instruments and appeared like a scaled-up Mars Exploration Rover, with two robotic arms and a high-gain antenna nearly a meter in diameter for direct-to-Earth communications.

  Figure 1.2. Concept art for MSL, late 2003. NASA/JPL-Caltech release PIA04892.

  1.3.2 The mission concept matures

  Three spacecraft successfully reached Mars in January 2004: ESA’s Mars Express Orbiter, and NASA’s two Mars Exploration Rovers, Spirit and Opportunity. Opportunity landed within easy reach of a scientific bonanza: inside a crater, facing an obviously layered bedrock exposed in the crater’s wall. A month later, the mission held a press briefing to announce that “Scientists have concluded the part of Mars that NASA’s Opportunity rover is exploring was soaking wet in the past.” Their mission to “follow the water” had succeeded in finding evidence for a different, wetter environment on an ancient Mars. MSL would be able to take the next step.

  Mars Exploration Rover project manager Peter Theisinger shifted to the MSL project. One of his first actions was to convene an informal panel of outsiders to evaluate the proposed rover-on-a-rope design for MSL’s landing. One member of the panel was a Sikorsky helicopter pilot, who “pointed out that experienced heavy-lift helicopter pilots can control both the speed and the position of their suspended loads with exquisite precision. This was a man who had extensive experience in one of the early heavy-lift helicopters, the Sikorsky sky crane,” Manning wrote. From that day forward, the landing approach was often referred to as the “sky crane maneuver.”

  Many development challenges remained, but the mission’s basic plan was fixed, and the project was ready to solicit proposals for science instruments. For flagship missions, NASA issues an Announcement of Opportunity detailing the goals of a mission, providing budget and timeline information, and seeking proposals for teams of scientists and engineers from all over the world to develop science instruments tailored to the planned spacecraft and its goals. NASA issued the MSL Announcement of Opportunity in April 2004, with proposals due in July.

  To support the Announcement of Opportunity, JPL described MSL in detail for the first time in the form of a Proposal Information Package issued on April 14, 2004. To begin with, the information package described a slightly modified primary objective for the rover mission (Box 1.2). It also detailed the design of the spacecraft components to be built at JPL (Box 1.3 and Figure 1.3), and specified the mechanisms, avionics, power, temperature conditions, and other aspects of the proposed rover design that would be available to support the instruments.

  Box 1.2. Primary objective of the MSL mission.

  The Mars Science Laboratory Mission will explore and quantitatively assess the habitability and environmental history of a local region on Mars. The mission has the primary objective of placing a mobile science laboratory on the surface of Mars to assess the biological potential of the landing site, characterize the geology of the landing region, investigate planetary processes that influence habitability, and characterize the broad spectrum of surface radiation. The MSL project aims to achieve this objective in a manner that will offer the excitement and wonder of space exploration to the public.

  Box 1.3. Components of the MSL flight system.

  A cruise stage to provide power, navigational capability, and thermal control to the spacecraft for the trip from Earth to Mars.

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nbsp; An aeroshell consisting of a heat shield and backshell with a parachute to protect the rover during its initial entry and descent in the Martian atmosphere. The aeroshell would also have the necessary hardware to provide communications during cruise, entry, and descent. The aeroshell would be able to maneuver in the air in order to reduce landing location errors caused by uncertainty in atmospheric conditions.

  A descent stage that would decelerate with rockets while scanning the landing area with radar, allowing the rover to generate a terrain map and identify a safe landing site. The descent stage would come to a hovering stop 5 meters above the landing site, then lower the rover on a tether to rest on its wheels. Once the rover was at rest, it would cut the tether to the descent stage, and fly away.

  A rover that would be capable of a mission lasting one Mars year (670 sols), driving 50 meters per sol at 5–10 centimeters per second on typical sols, with a total mission traverse capability of at least 6 kilometers. It would carry a 58-kilogram science payload, of which about 3 kg would be on an instrument arm, 9 kg on the mast, and 38 kg inside the rover. To accommodate this large payload, the rover’s body would be 1.2 meters long by 0.7 meters wide by 0.35 meters deep.

  Landing accuracy would be within a 5-by-10-kilometer ellipse.

  Two instruments were already included: a meteorology package contributed by Spain, and an active neutron spectrometer contributed by Russia.

  Figure 1.3. Initial design for MSL from the Proposal Information Package. Note the two arms, two RTGs, huge dish, and tall mast mounted at the center of the front of the rover. The landing sequence is substantially similar to Pathfinder’s (Figure 1.1 ).

  The design drawn in the 2004 Proposal Information Package was far from final. In actuality, the spacecraft design was in a state of extreme flux, with the mission being torn between reliability, capability, and expense.14 The 2004 rover concept differed from the final one in a number of ways. The originally planned mast was quite tall, reaching to 3.5 meters from the ground. It had a huge dish for direct-to-Earth data relay, as Odyssey wouldn’t have the capacity to relay all of MSL’s hoped-for data volume, even if the orbiter survived until the 2010 landing.

  The Sample Acquisition/Sample Processing and Handling (SA/SPaH) system on the original rover design included two robotic arms, separating the heavy, rattling, dust-raising activities of drilling and retrieving rock cores and the finer tasks of scientific analysis and soil scooping onto separate arms. Both arms could deliver material to a sample processing system mounted directly to the rover body. The sample processing system would have two rock crushers to smash and sieve the rock samples into pieces smaller than a millimeter in diameter. A sample delivery system would move these samples into the analytical laboratory instruments, and an ejection system would get rid of detritus. Both arms could acquire samples in icy material, though the rock crusher would not be expected to handle ice. If the corer failed, the scoop would presumably still be available to gather loose rock samples and deliver them to the crusher.

  But the biggest difference between proposed and final rovers was power. As originally planned, MSL would carry two Radioisotope Thermoelectric Generators to provide ample power and heat for operation at a wide range of latitudes.

  1.3.3 Instrument selection

  Teams of scientists and engineers responded to the Announcement of Opportunity by proposing 48 instruments to NASA. NASA turned around the proposals quickly, selecting eight (Box 1.4). Adding the already-accepted Russian and Spanish instruments brought the MSL mission payload to a total of ten. Some, the remote sensing instruments, would study the landscape from a distance, mostly from the top of the remote sensing mast. Others, the in situ instruments, would study rocks and soil from a turret at the end of the robotic arm, or measure the environment that the rover experienced. Finally, there were two analytical laboratory instruments buried within the body of the rover that would accept samples of rock, soil, and atmospheric gas for detailed study.

  Box 1.4. Mars Science Laboratory Instruments, as described in the 14 December 2004 press release announcing them.

  Remote Sensing Instruments:

  Mars Descent Imager (MARDI), located on the body of the rover. Principal investigator: Michael Malin, Malin Space Science Systems. The Mars Descent Imager will produce high-resolution color-video imagery of the MSL descent and landing phase, providing geological context information, as well as allowing for precise landing-site determination.

  Mast Camera (Mastcam), located on the mast. Principal investigator: Michael Malin, Malin Space Science Systems. Mast Camera will perform multi-spectral, stereo imaging at lengths ranging from kilometers to centimeters, and can acquire compressed high-definition video at 10 frames per second without the use of the rover computer.

  ChemCam: Laser Induced Remote Sensing for Chemistry and Micro-Imaging, located on the mast. Principal investigator: Roger Wiens, Los Alamos National Laboratory. ChemCam will ablate surface coatings from materials at standoff distances of up to 10 meters and measure elemental composition of underlying rocks and soils.

  In-situ Instruments:

  Mars Hand Lens Imager (MAHLI), located on the arm turret. Principal investigator: Kenneth Edgett, Malin Space Science Systems. MAHLI will image rocks, soil, frost and ice at resolutions 2.4 times better, and with a wider field of view, than the Microscopic Imager on the Mars Exploration Rovers.

  Alpha Particle X-ray Spectrometer (APXS), located on the arm turret. Principal investigator: Ralf Gellert, Max-Planck-Institute for Chemistry. APXS will determine elemental abundance of rocks and soil. APXS will be provided by the Canadian Space Agency.

  Radiation Assessment Detector (RAD), located on the rover body. Principal investigator: Donald Hassler, Southwest Research Institute. RAD will characterize the broad spectrum of radiation at the surface of Mars, an essential precursor to human exploration of the planet. RAD will be funded by the Exploration Systems Mission Directorate at NASA Headquarters.

  Dynamic Analysis of Neutrons (DAN), located in the rover body. Principal investigator: Igor Mitrofanov. DAN will perform an in situ analysis of the hydrogen content of the subsurface.

  Rover Environmental Monitoring Station (REMS), in various locations on the rover. Principal investigator: Luis Vázquez. REMS will measure temperature, pressure, wind speed and direction, humidity, ultraviolet dose, atmospheric dust, and local fluctuations in magnetic field.

  Laboratory Instruments:

  CheMin, located in the rover body. Principal investigator: David Blake, NASA’s Ames Research Center. CheMin is an X-ray Diffraction/X-ray Fluorescence (XRD/XRF) instrument that will identify and quantify all minerals in complex natural samples such as basalts, evaporites and soils.

  Sample Analysis at Mars (SAM), located in the rover body. Principal investigator: Paul Mahaffy, NASA’s Goddard Space Flight Center. SAM consists of a gas chromatograph mass spectrometer and a tunable laser spectrometer. SAM will perform mineral and atmospheric analyses, detect a wide range of organic compounds, and perform stable isotope analyses of organics and noble gases.

  This was a huge and exciting instrument package. Some of the instruments looked familiar. Mastcam, MAHLI, and APXS all had direct parallels on the Mars Exploration Rovers (Pancam, Microscopic Imager, and APXS), but in each case the proposed MSL instrument had major improvements. Mastcam promised the possibility of color, stereo, high-definition video of rover traverses across Mars. APXS would have higher spatial resolution and speedier data acquisition than ever before.

  The novel instruments were just as exciting. ChemCam would provide remote elemental analysis capability unlike anything seen on a Mars mission before, and would do it with a high-powered laser zapping rocks. RAD would make measurements that would pave the way for human exploration of Mars. DAN would bring to the surface the neutron-detection capability that had led to the Odyssey discovery of ground ice.

  But the pièce de résistance was the analytical laboratory comprising CheMin and SAM. Geologists salivated over t
he prospect of performing X-ray Diffraction/X-Ray Fluorescence (XRD/XRF) on Mars with CheMin. All previous methods of mineral identification on the surface of Mars were indirect; XRD/XRF measurements are diagnostic, as long as the samples contain crystals. And SAM would sensitively study atmospheric gas isotopes, could follow up on the possible discovery of methane, and would be capable of detecting organics, dangling the possibility of finding direct evidence for Martian life.

  The selected instrument package contained many items from the wish list the Science Definition Team had drawn in 2001 (see section 1.2.2). The final science package lacked a dedicated mast-mounted thermal infrared spectrometer like the Mini-TES on the Mars Exploration Rovers and significantly, a near-infrared spectrometer that could follow up on discoveries from OMEGA on Mars Express and CRISM on Mars Reconnaissance Orbiter that played a major role in landing site selection. (ChemCam can be used in a passive spectroscopic mode, but its sensitivity barely reaches into the near-infrared.) There was no arm-mounted mineralogical analyzer, no ground-penetrating radar, and no seismology package. But everything else was there.

  One group was both excited and dismayed by the list of instruments: the engineers, who would have to find space, mass, and power to accommodate them all in their rover, never mind operating a machine with so many capabilities.

  1.4 PRELIMINARY DESIGN (2005–2006)

  A developing NASA mission faces many hurdles on the way to its destination, but there are five formal ones. First is the Preliminary Design Review, which usually takes place about four years (give or take) before launch. At the Preliminary Design Review, the mission team has to demonstrate that they have a sound concept for the mission and all its technically challenging components. Passing a Preliminary Design Review unlocks NASA’s coffers, allowing a mission to spend money turning concepts into detailed designs. About a year later comes the Critical Design Review, when the mission has to present blueprints to the review panel. Passing the Critical Design Review allows a mission to transition to the third phase, Assembly, Test, and Launch Operations (ATLO), usually about two years before launch. The final hurdles are launch and arrival. MSL’s Preliminary Design Review was scheduled for June, 2006. The project had a lot of work to do before then.