Emily Lakdawalla

by The Design

  The international community of space image processing enthusiasts at the online forum

  unmannedspaceflight.com contributed many of the beautiful mosaics you’ll see in this

  book and helped me monitor ongoing rover activity. I want to single out Mike Howard and

  Joe Knapp for developing valuable software tools for browsing raw images (midnightplan-

  ets.com and curiosityrover.com); Thomas Appéré, Damia Bouic, Seán Doran, and James

  Sorenson for their exceptional image processing work; and Nick Previsich for singlehand-

  edly administering the forum after I and the rest of the admins got too busy.

  I’m deeply grateful to the members, staff, and board of The Planetary Society, repre-

  sented by chief operating officer Jennifer Vaughn and chief executive officer Bill Nye, for their generous support of my time to perform the research and writing necessary to produce this book.

  Thanks to the teachers and mentors who raised me, especially Ms. Foster, Mr. Killion,

  Ms. Hamilton, Dr. Aldridge, Mr. Atkison, Ms. Koeppe, Tekla Harms, Jack Cheney, Jim

  Head, Geoff Collins, Louise Prockter, Sasha Basilevsky, and Charlene Anderson. Finally,

  thanks to my husband Darius, my daughters Anahita and Sanaya, and my parents Karen

  Stewart, Rick and Murfy Stewart, and Rhoda and Noshir Lakdawalla for supporting my

  writerly ambitions – and to Concepción Peña for supporting me in supporting them,

  enabling this wife, mom, and daughter to be a writer, too.

  Preface

  The book you are holding is not quite the one I intended to write. I embarked on this project in 2013, with the working title Curiosity on Mars - Design, Planning, and the First Mars Year of Operations. I thought two years was a reasonable timeline, as I’d already done a lot of writing about the mission. I had been covering the Mars Science Laboratory mission as

  senior editor for The Planetary Society’s blog since the mission’s announcement, and

  attended most of the landing site selection meetings. Five times I had visited the gallery

  above the clean room where all the mission hardware came together at the Jet Propulsion

  Laboratory, and I returned to “the Lab” (as those in the know call it) for the landing and every press briefing. I’ve written three feature stories about it for Sky and Telescope. I’m an admin-istrator of an online discussion forum full of armchair geologists and engineers who follow the daily motions of the rover, so I was cognizant of every twist and turn of the mission. It seemed possible that with steady work I should be able to write this book relatively rapidly.

  It didn’t turn out that way. I decided that understanding how the hardware worked was

  crucial to narrating the mission, because holey wheels, “Florida air,” contaminated drill

  bits, and balky sampling mechanisms loomed large in the story of the rover’s daily opera-

  tions. I set to work researching rover engineering. The more I learned about Curiosity, the more rabbit holes I fell down. It had so many subsystems, and most had complicated histories, fascinating stories worth telling. Many of those stories hadn’t been told in print, at least not in any document that the public can access. The publications that did describe

  Curiosity’s engineering had mostly been written before launch, and contained inaccura-

  cies that were corrected for me by helpful engineers. I came to understand that this machine was the most complicated thing ever sent beyond our planet and that no one person on

  Earth understands all of its parts and functions. I wrote and wrote about its design, its

  engineering, and its journey. Many mission engineers and scientists have contributed to

  making this text describe the actual spacecraft as accurately as possible.

  Years passed. By 2015 Curiosity had traveled more than 10 kilometers across Mars and

  still the full depth of its scientific promise hadn’t been realized. I changed my working

  title, dropping the “First Mars Year” bit, as the rover drove into its second Mars year and had only just reached the base of the mountain its science team hoped to study.

  xiii

  xiv Preface

  I asked my boss at The Planetary Society for permission to take a three-month sabbati-

  cal at the beginning of 2017 to finish up the project. It wasn’t until the end of that sabbati-cal that I realized why I’d had so much trouble finishing the work. I hadn’t written my

  book yet because I had, by now, nearly written two. I had to write a book about how the

  rover worked in order to be able to write the book I had intended to write about what it did on Mars. Fortunately, my editors at Springer-Praxis were amenable to splitting the project

  into two books. The one you’re holding is the first of these: how and why the spacecraft

  was designed, the function of every system, and the engineering of every instrument. It’s

  a reference work designed to answer your – and my! – questions about how the rover

  works and why it was built that way. It answers the same questions for all the other Mars

  Science Laboratory hardware, from cruise stage to Earth testbeds.

  Of course, the mission has continued operating all this time, so parts of this book will

  be out of date immediately. It is certain to be complete as of sol 1514, and as complete as possible through sol 1800.

  Now that I’ve written the reference book I needed, I can proceed with the second book,

  which will cover the mission’s science, from landing site selection, through pre-landing

  mapping, the operational adventure, and the science results. Look for Curiosity and Its Science Mission: A Mars Rover Goes to Work in 2019.

  1

  Mars Science Laboratory

  1.1 INTRODUCTION

  Curiosity began in the wreckage of NASA’s Mars hopes. Two spacecraft launched to Mars

  in 1998. Neither survived arrival. The twin disasters could have doomed NASA’s Mars

  program – again. But the American public enthusiastically supported a NASA search for

  Martian life following the announcement of possible fossils in a Mars meteorite recovered

  from Antarctica.

  NASA had enjoyed early success at Mars with the Mariners and Vikings, though the

  Viking landers’ powerful (and expensive) life-detection experiments had failed to reveal

  signs of biologic activity on Mars. A lengthy hiatus in Mars exploration followed Viking

  in the 1980s, and the 1990s were mostly cruel to Mars missions. NASA’s Mars Observer,

  launched in 1992, failed just days before arrival. Mars 96, a Russian mission, failed to

  leave Earth parking orbit. But things had been looking up at the end of the decade. Mars

  Global Surveyor successfully entered orbit in 1997 and began its mapping mission in

  1999. And the world fell in love with a little six-wheeled robot named Sojourner that had

  trundled around NASA’s Pathfinder lander for three months in the summer of 1997, shar-

  ing daily reports and Mars photos on the new medium of the Internet. The American

  public was willing to support another try at Mars.

  A year after Mars Polar Lander and Mars Climate Orbiter failed, NASA announced a

  reformulated Mars program.1 Their goal: to search Mars’ geologic present and past for the kinds of environments that could support life. The search would require a “sustained presence in orbit around Mars and on the surface with long-duration exploration.” Joining Mars

  Global Surveyor in orbit would be two orbiters, 2001 Mars Odyssey (to be launched in 2001)

  and Mars Reconnaissance Orbiter (2005). NASA also announced two rover missions: the

  twin Mars Exploration Rovers (2003) and a “mobile science laboratory,” to be launched “as

  early
as 2007,” which would eventually become Mars Science Laboratory, or MSL.

  1 NASA (2000b) press release dated October 26, 2000

  © Springer International Publishing AG, part of Springer Nature 2018

  1

  E. Lakdawalla, The Design and Engineering of Curiosity, Springer Praxis Books,

  https://doi.org/10.1007/978-3-319-68146-7_1

  2 Mars Science Laboratory

  From the start, MSL was an ambitious mission. It would deliver a Viking-sized suite of

  science instruments to the surface of Mars. But that huge science capability could move

  around the surface on wheels. NASA promised a precision landing, close to a very inter-

  esting geologic site on the surface of Mars. They also proposed a lifetime of two Earth

  years, much longer than the proposed one-month life for Pathfinder or three months for the

  Mars Exploration Rovers. Finally, the intent to carry analytical laboratory instruments that could ingest Martian rock required entirely new sample handling technology.

  MSL occupies a pivotal position in NASA’s Mars Exploration program. An advisory

  group stated in 2003 that MSL “both concludes the currently planned missions and…

  initiates the paths of exploration in the next decade.” Mindful of the number of Mars mis-

  sions that would be active in the years prior to its landing, NASA tasked the project with

  being able to respond to discoveries made while the spacecraft was being prepared for

  launch.2 To be so flexible, the mission had to be able to achieve success at a wide variety of landing site locations: from equatorial sites to near-polar ones, and from sites where

  ancient geology and hard rocks would be the target, to sites where it might be possible to

  sample ice and search for recently habitable zones. This wide envelope of possibility

  meant that the spacecraft and landing system that were ultimately built had capabilities

  that were never used.

  MSL would eventually become the most complex mission ever launched beyond Earth.

  Its development required a gargantuan effort spanning more than a decade. Its success

  depended on the invention of new technologies. Challenges in the development program

  forced NASA to delay the launch, at great financial cost. Originally proposed for the 2007

  launch opportunity, MSL would finally depart for Mars in November, 2011.

  1.2 DESIGNING A BIGGER LANDER (2000–2003)

  1.2.1 “Rover on a Rope”

  Chief engineer Rob Manning traces the origin of MSL’s landing system to the terrible

  failures of 1999, particularly Mars Polar Lander. “We came to realize that we did not

  know how to land anything on Mars reliably, let alone something large,” he wrote in a

  2014 mission memoir.3 NASA’s Jet Propulsion Laboratory (JPL), which had built Mars Polar Lander, formed a team to identify the technology they needed to develop in order to

  be able to precisely land a large rover on Mars. They began work in early 2000.

  Mars is one of the hardest places in the solar system to land. The problem is its atmo-

  sphere: there is too much to ignore, and too little to slow a spacecraft for a safe landing.

  On bodies lacking atmospheres, like the Moon or an asteroid, spacecraft land using rock-

  ets alone. On Earth, Venus, or Titan, which have dense atmospheres, a spacecraft deceler-

  ates from supersonic speeds with a blunt-nosed heat shield, and then drops speed nearly to

  zero with a parachute. On Mars, a spacecraft needs all three: heat shield for high-speed

  2 Mars Program Synthesis Group (2003) Mars Exploration Strategy 2009-2020

  3 Manning and Simon (2014) Mars Rover Curiosity

  1.2 Designing a Bigger Lander (2000–2003) 3

  entry, parachute for slowing during descent, and rockets for landing. The entire procedure

  required to land on Mars is referred to as Entry, Descent, and Landing, or “EDL” for short.

  (Engineers delight in abbreviating frequently-used phrases into acronyms and initialisms,

  turning their writing into alphabet soup. In this book I refrain from using most such abbreviations for clarity.)

  All Mars landers to date have used a capsule, also known as an aeroshell, to shelter the

  lander during entry; the capsule is a clamshell that consists of a heat shield and a back-

  shell. The design is similar to the capsules used by Mercury, Gemini, and Apollo astro-

  nauts to return to Earth. Astronauts in capsules usually used maneuvering rockets to guide

  the capsules during entry, steering them toward a landing zone where they could be picked

  up quickly. Mars landers, lacking human pilots, passively fell through the Martian atmo-

  sphere on a ballistic entry, like meteors. The lack of human guidance led to large uncer-

  tainty about where the spacecraft would end up landing. Achieving a precision landing

  required guidance, but Mars is too far away for humans on Earth to steer in real time.

  To make a precision landing possible, Manning and his teammates advanced an idea

  that JPL had been developing since the 1990s: autonomous guidance for a Mars entry

  vehicle. The capsule could use accelerometers and gyroscopes to determine its position

  relative to its intended target as it flew. Software would command banking turns to fly the aeroshell closer to the target. Guided entry could dramatically shrink the size of a Mars

  landing ellipse, placing a rover closer to interesting geology.

  The descent phase begins when the spacecraft has been slowed to something close to

  twice the speed of sound. All Mars landers have deployed a parachute for descent.

  Supersonic parachutes for Mars were first developed in the early 1970s for Viking, with

  expensive high-altitude tests. As long as the mass of a Mars lander could be kept similar

  to or less than that of Viking, they could stick with the same parachute design for the

  descent phase without performing new, expensive tests.

  For the final, landing phase, JPL had successfully used two different approaches. The

  Vikings employed retrorockets that slowed the descent to a near-standstill, and then the

  spacecraft dropped to a hard landing atop three legs that crushed to absorb some of the

  force of the impact. Pathfinder (and, later, the Mars Exploration Rovers) worked differ-

  ently (Figure 1.1). The triangular lander was folded into a tetrahedral shape and the outside of the tetrahedron fitted with airbags. This contraption dangled on a rope beneath a rocket pack that was itself connected to the parachute. At the last possible moment, a mere 100

  meters above the ground, the airbags inflated, the rocket jetpack fired to zero out the downward velocity, and the rope tether cut. The lander dropped and bounced repeatedly, rolling

  nearly a kilometer inside its airbags, before finally coming to a rest.

  Neither lander design would work for MSL. If the rover were perched atop a Viking-

  like lander platform, the top-heavy design would tip over in a wide variety of landing

  scenarios. But Pathfinder’s airbag design had a maximum payload capacity of 200 kilo-

  grams; anything larger, and the airbags would shred.4 Manning thought that elements of

  the two could be combined into a successful landing strategy. If a Viking-like descent

  stage could dangle a Pathfinder-like lander on a tether, the descent stage might be able to 4 Caffrey et al (2004)

  4 Mars Science Laboratory

  Figure 1.1. Illustration of the successful Mars Pathfinder entry, descent, and landing. Based on Golombek et al (1999 ).

  lower the lander close enough to the ground to enable it to make a soft touchdown. 5 In fa
ct, they might be able to make the landing so soft that they could put a rover down directly on

  its wheels.6 Manning called this idea the “rover on a rope.” The concept became Mars Smart Lander in late 2000, when NASA announced it as part of the reformulated Mars

  program, with a launch “as early as 2007. ”7

  As the reformulation proceeded, Mars Global Surveyor generated a bounty of science

  results. Its spectrometer instrument discovered gray hematite on the surface, a mineral that probably required liquid water to form. The spectrometer also mapped dust on the surface,

  allowing mission planners to seek out less-dusty landing sites with good access to bed-

  rock. Its sharp-eyed camera proved that sedimentary rocks existed on Mars, a second line

  of evidence to a lengthy water-rich geologic history. And the mission generated a dramati-

  cally improved global topographic map of Mars, crucial for planning safe landings.

  5 Manning and Simon (2014)

  6 Rob Manning credits Dara Sabahi with that realization

  7 NASA (2000a) Mars Program Independent Assessment Team Summary Report

  1.2 Designing a Bigger Lander (2000–2003) 5

  1.2.2 Mars Smart Lander

  NASA chartered a Science Definition Team for the planned 2007 rover in April, 2001. 8

  The charter identified three ways in which the Mars Smart Lander concept would improve

  on past landers’ ability to explore interesting scientific sites. Most of them related to landing precision, specified in the dimensions of a “landing ellipse.”

  What is a landing ellipse? Mars missions target a specific latitude and longitude spot on

  Mars, but a variety of factors can cause the lander to miss the target. By modeling these

  factors, engineers can estimate the area within which the rover is about 99% likely to land.

  The region is usually shaped like an ellipse with its long axis oriented in the direction of the incoming lander’s trajectory.

  Landing ellipses for Viking were 280 kilometers long and 100 kilometers across.

  Pathfinder’s was smaller, but not by much, at 200-by-100 kilometers. Large landing

  ellipses drastically limited the locations on Mars where spacecraft could land, because