Emily Lakdawalla

by The Design

  there are few locations that are flat enough over such a broad area, and even fewer that are geologically interesting.

  For Mars Smart Lander, the landing ellipse would be dramatically smaller: the initial directive was for an ellipse only 6-by-3 kilometers in extent, achieved using entry guidance to steer the entry capsule along its intended path. The charter also stipulated a lander with “active terminal hazard avoidance,” meaning that it should be capable of detecting large rocks or

  steep slopes and steering around them. Finally, the rover would have “surface mobility com-

  mensurate with landing precision errors.” In other words, if the landing ellipse was 6 kilometers in extent, then the vehicle should be able to drive at least 6 kilometers in its lifetime.

  It’s that last requirement – a roving range of the same size as the landing ellipse – that

  opened up the possibilities for exciting science on the proposed rover mission. The mission would not be limited to scientific exploration of sites that were also safe for landing. They could plan to explore a site with steep topography, as long as there was a safe landing zone sufficiently close by. They called these “go-to” sites, because the rover would land away from the intended scientific goal, and then go to the site before starting its scientific investigation.

  NASA directed the Mars Smart Lander science definition team to set science goals

  consistent with the highest priorities of the Mars Exploration Payload Analysis Group, an

  advisory panel of Mars scientists. The number one goal of the Mars Exploration Payload

  Analysis Group was the search for present and past life on Mars, so the team debated

  whether the mission should attempt to search for extant life on Mars.

  In the end, the Science Definition Team argued against Viking-like attempts at direct

  life detection experiments. Emboldened by the recent discovery of widespread layered

  sedimentary rocks across Mars by the Mars Global Surveyor camera team,9 they suggested an oblique approach that avoided the challenge of defining what life on Mars is

  expected to look like:

  The most promising place to explore for evidence of life on Mars is in lacustrine or

  marine sedimentary rocks that accumulated rapidly under reducing conditions and

  where subsequent diagenesis did not obliterate the original textural and compositional

  8 NASA (2001) Mars Exploration Program Mars 2007 Smart Lander Mission Science Definition Team Report

  9 Malin and Edgett (2000)

  6 Mars Science Laboratory

  (isotopic, organic, and mineralogic) evidence for the environment of deposition and

  associated biomes…[The] strategy for searching for evidence of life on Mars is to

  maximize the probability of landing on sedimentary deposits in which reducing condi-

  tions have been preserved, to use mobility to explore and characterize the deposits…

  Direct life detection experiments are not needed to implement this strategy for the

  Smart Lander Mission. Rather, positive signs of biosignatures would be used to help

  focus locations for sample return missions and/or follow-on missions with direct life

  detection experiments. 10

  Through all of the twists and turns of the development of the mission that followed, this

  strategy would remain constant. The strategy has two parts: first, search for habitable

  environments, places where life could thrive (now or in the past). Second, seek out rocks

  that have a high potential to preserve carbon-containing materials trapped within them.

  The Science Definition Team responded to the charter in October 2001. Mars Smart

  Lander would take one of two forms. It would either be a Mobile Geobiology Explorer – a

  large rover that could carry a heavy instrument package beyond the confines of its landing

  ellipse – or a Multidisciplinary Platform with a deep drill and a small rover that could

  explore the site and return samples to the stationary lander.

  As initially conceived, the Mobile Geobiology Explorer would carry a 100-kilogram

  science payload, powered either by solar panels or a radioisotope power supply, although

  the team argued strenuously for the latter. They suggested that in a 180-sol11 primary mission, the rover should be able to traverse at least 5 kilometers and preferably 9 kilometers, to perform in-situ science at 3 locations, sampling multiple geologic units. (In hindsight, this list is comically optimistic.) The team proposed a payload consisting of up to 14 different science instruments:

  • A descent imaging system.

  • A mast-based remote sensing system including color cameras, infrared spectrom-

  eter, and a laser-induced breakdown spectrometer.

  • Ground-penetrating radar.

  • Arm-based contact science package with rock abrasion tool, elemental and miner-

  alogical analyzers, and microscope.

  • Long-duration radiation experiments (relevant to future human exploration).

  • Drill/corer and sample acquisition system.

  • Sample preparation and delivery system (for grinding and partitioning sample

  cores).

  • Laboratory instruments to determine inorganic and organic chemistry, oxidation

  state, mineralogy, and high-resolution images of samples.

  • If possible: seismology package.

  • If possible: climatology package.

  10 NASA (2001)

  11 A “sol” is a Martian day, about 3% longer than an Earth day

  1.2 Designing a Bigger Lander (2000–2003) 7

  Meanwhile, JPL was in the throes of preparing the Mars Exploration Rovers for launch.

  To cope with the ever-increasing mass of the twin rovers, JPL added throttleable rockets to their backshells, and cameras that would take one or two pairs of images and analyze them

  to detect the horizontal velocity of the lander. Both of these innovations made the “rover-

  on-a-rope” idea more feasible. 12

  Even though it was still on the drawing board, Mars Smart Lander rapidly ran into

  budget problems. “The Science Definition Team had defined a mission larger than NASA

  could afford,” recalls Mark Dahl, who was NASA Program Executive for the mission

  from 2002 until 2007. In order to fit this large rover into NASA’s budget, they would need

  to postpone it to a 2009 launch. The mission also drifted toward a name change. When

  Scott Hubbard developed NASA’s “follow the water” policy in 2002, he referred to the

  mission in different places as Mars Smart Lander; Mobile Surface Laboratory; and Smart

  Mobile Lab. Eventually, NASA decided that the name of the mission should describe its

  goals rather than its technology, and by 2003 it was being called Mars Science Laboratory.

  (Conveniently, its initials, MSL, remained the same through the name change.)

  1.2.3 Nuclear power

  In 2002, NASA determined that MSL would be able to do better science, accessing a

  wider band of latitudes and surviving longer, if it were nuclear-powered. That required a

  radioisotope thermoelectric generator (RTG), like the ones that powered Voyager, Viking,

  and more recently, Galileo and Cassini. A nuclear-powered rover would have lots of

  advantages over the solar-powered Spirit and Opportunity. It would be able to explore a

  much wider range of latitudes, and it would be able to operate year-round, rather than resting through the winter. However, the nuclear power design available in 2002 – the General

  Purpose Heat Source RTG used for Galileo, Ulysses, Cassini, and New Horizons – was

  not suitable for a Mars rover. It was too massive (more than a meter long and weighing 57

  kilogram
s). It produced more power than needed (285 watts). Most importantly, its

  electricity- generating thermocouples would fail if carbon dioxide from Mars’ atmosphere

  were to infiltrate its container.

  Anticipating these problems, the Department of Energy and NASA were already in

  discussions to develop a new type of radioisotope power supply that would be appropri-

  ately sized for the lower mass and power of modern spacecraft, one that could also func-

  tion in an atmosphere. The Department of Energy considered several designs and

  determined to develop two. One was the Multi-Mission Radioisotope Thermoelectric

  Generator (MMRTG), whose design would be based upon the RTG used on Viking lander

  and Pioneer missions. It would require 4.8 kilograms of plutonium dioxide fuel. The other

  proposed power source was a Stirling generator requiring only 1.2 kilograms of fuel.

  Either would deliver about 100 watts of power when first fueled. An MMRTG would

  throw off about 2000 watts of heat; the more efficient Stirling generator would produce

  about 500 watts.

  12 Manning and Simon (2014)

  8 Mars Science Laboratory

  NASA considered both options for MSL. They chose the MMRTG because of concern

  over the reliability of the Stirling generator’s moving parts. Also, the relatively inefficient design of the MMRTG would benefit Mars surface operations: the waste heat could be collected and put to use to maintain the temperature of the rover against the extreme swings of the Martian environment. On June 30, 2003, Boeing Rocketdyne Propulsion and Teledyne

  Energy Systems announced their partnership with the Department of Energy to develop the

  new MMRTG, specifically naming MSL as the first mission that would use the new technol-

  ogy. “An MMRTG-powered rover will be able to land and go anywhere on the surface of

  Mars, from the polar caps to deep, dark canyons, and will safely provide full power during

  night and day under all types of environmental conditions,” Boeing stated in a press release.

  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 mis-

  sion 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 centi-

  meters 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 13 Boynton et al (2002)

  1.3 Becoming Mars Science Laboratory (2003–2004) 9

  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 capa-

  bility 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.

  10 Mars Science Laboratory

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

  1.3.2 The mission concept matures

  Three spacecraft successfully reac
hed 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 suc-

  ceeded 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 pro-

  posed 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

  1.3 Becoming Mars Science Laboratory (2003–2004) 11

  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