Emily Lakdawalla
Page 5
operations in October, included a camera named HiRISE (for High-Resolution Imaging
Science Experiment) that could map the surface in unprecedented detail. Perhaps more
importantly for MSL, Mars Reconnaissance Orbiter carried an upgraded radio for commu-
nicating with surface missions and a 3-meter dish for high-rate communications with Earth.
That dish gave Mars Reconnaissance Orbiter the ability to relay much more data to Earth
than Odyssey did for the Mars Exploration Rovers (Figure 1.4). The successful arrival of Mars Reconnaissance Orbiter meant that the MSL mission could get rid of the enormous
radio dish and related power requirements that had been part of the earliest design
concepts.
By mid-2006, the rover concept was taking a shape that looks much more recognizable
(Figure 1.5). 18 Instead of two arms, there was just one, along with the sample preparation hardware bolted to the deck. The mast and arm were configured to support the instruments
that had been selected in 2004. The high-gain antenna had shrunk. There was only one,
rather than two, MMRTGs. (Because the environmental review process described in sec-
tion 1.2.3 was not officially complete by this time, the publicly released version of the artist’s concept shown in Figure 1.5 had no MMRTG.)
The EDL concept had matured more than the rover design (Figure 1.6). The active terrain hazard avoidance that had been scoped in the initial concept was gone, replaced with
a much longer powered-descent phase. The final concept of the flight system – a Dagwood
sandwich of a spacecraft consisting of cruise stage, aeroshell, descent stage, rover, and
heat shield – changed very little after this time (Figure 1.7). This lander would require a larger, flatter landing ellipse than had been promised for the Mars Smart Lander concept.
JPL presented these concepts at the MSL Preliminary Design Review in June 2006.
Manning “thought that the team was presenting designs that were rough, much less
18 Vasavada (2006)
1.4 Preliminary Design (2005–2006) 19
Figure 1.6. EDL timeline (top) and model of the rover (bottom) prepared for the Preliminary Design Review. Compare to Figure 1.3 .
developed than they should have been at this stage.” Still, the review board voted to give
MSL a passing grade, and NASA started writing checks. The biggest one was the first:
NASA immediately announced a contract with Lockheed Martin for an Atlas V rocket for
the fall 2009 launch, at a fixed price of $194.7 million.
20 Mars Science Laboratory
Figure 1.7. Components of the MSL flight system. NASA/JPL-Caltech.
1.4.3 First real cost estimate
Until the Preliminary Design Review, there had not been a solid cost estimate for MSL,
because there had not yet been a design to price. The NASA advisory panel that had ini-
tially identified MSL as a mission worth pursuing had scoped it out as a medium-class
1.4 Preliminary Design (2005–2006) 21
mission, costing under $650 million. Internal NASA bookkeeping accounted it at $865
million in November 2003, a number that did not include the radioisotope power source,
the launch vehicle, or the cost of the focused technology program needed to bring some
key landing technologies to maturity. The Preliminary Design Review revealed that,
despite years of effort to find ways to keep the mission’s cost down, MSL was going to be
much more expensive than outsiders had anticipated. Including development costs, new
technology, launch vehicle, operational costs, and reserves, project manager Richard Cook
estimated a total cost of $1634 million.
1.4.4 Where to send the mission?
At the same time as the Preliminary Design Review, the landing site selection process
began. On May 31, 2006, the Landing Site Selection Committee invited the world’s Mars
scientists to the first in a series of community workshops. Anyone could propose landing
sites, and explain how they would address the mission’s science objectives. To prepare for
the first landing site selection meeting, deputy project scientist Ashwin Vasavada trans-
lated the science objectives into more specific terms that would help guide the choice of
landing site (Box 1.5).
Box 1.5. Curiosity science objectives.
• To assess the biological potential of at least one target environment by deter-
mining the nature and inventory of organic carbon compounds, searching for
the chemical building blocks of life, and identifying features that may record
the actions of biologically relevant processes.
• To characterize the geology of the landing region at all appropriate spatial scales
by investigating the chemical, isotopic, and mineralogical composition of sur-
face and near-surface materials, and interpreting the processes that have formed
rocks and soils.
• To investigate planetary processes of relevance to past habitability (including
the role of water) by assessing the long timescale evolution of the atmosphere
and determining the present state, distribution, and cycling of water and car-
bon dioxide.
• To characterize the broad spectrum of surface radiation, including ultravio-
let light, galactic cosmic radiation, solar proton events, and secondary
neutrons.
The rover’s precision landing was aimed at an unprecedentedly broad swath of Mars.
Previous landers were limited by their solar power systems to regions near the equator. But MSL, with its nuclear power source, could access latitudes as far as 60° away from the
equator, including regions where there is modern-day ground ice within reach of a scoop
or wheel scuff. The mission also planned for the ability to reach elevations up to 2500
22 Mars Science Laboratory
meters above the Martian mean, opening up Mars’ southern highlands to exploration for
the first time. 19
MSL’s ellipse was smaller than that of previous missions, so landings could be squeezed
into tighter spaces (Figure 1.8). At the beginning of the landing site selection process, MSL’s landing ellipse was taken to be 25 kilometers in the down-track direction, and 20 in
the cross-track direction. Four main factors affected MSL’s landing precision:
• Navigational uncertainty. The navigation of MSL and other deep-spacecraft is
highly precise, but there are limits. The spacecraft could miss the target by as much
as 2 or 3 kilometers both down-track and cross-track.
• Attitude knowledge. The mechanical alignment of MSL’s gyroscope relative to the
star scanner on the cruise stage might be imperfect, potentially introducing error dur-
ing guided entry of as much as 4 to 6 kilometers both down-track and cross-track.
• Atmospheric and aerodynamic variability. The final 75 to 100 kilometers of MSL’s descent would be flown without guidance, in order to maximize altitude. Variability
in the atmosphere, and resulting variability in the aerodynamics of the aeroshell,
can cause the spacecraft to miss by 5 to 7 kilometers in the down-track direction.
• Winds. Once MSL’s parachute opens, guidance is no longer possible, and winds can divert the spacecraft from its intended path, resulting in as many as 1 to 2 kilometers of positional error.20
More than 100 scientists attended the workshop. Scientists participated not only out of
a desire to contribute to the landing site selection, but also because proposed locations
would be short-listed for early scienti
fic observations by Mars Reconnaissance Orbiter.
The outcome of the workshop was a list of 33 potential landing sites, of which 11 were
voted to be top-rank possibilities. All of the favored 11 were below Martian mean eleva-
tion, and all were within 30° of the equator. 21 The fact that no high-elevation landing sites were among the top-ranked locations presented an opportunity of some relief to the engineers developing the entry, descent, and landing systems. In July 2006, NASA’s Mars
Exploration Program made this relief official, setting a new requirement for the MSL
landing to lie below 1000 meters’ elevation.
Shortly after the workshop, on November 2, 2006, NASA lost contact with Mars Global
Surveyor, and the mission was declared over on November 22. The remaining orbiters at
Mars – 2001 Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter – got to
work performing detailed observations of the proposed sites. The committee scheduled a
second workshop for October 2007, after a year of Mars Reconnaissance Orbiter’s pri-
mary science mission.
1.4.5 Plans for planetary protection
We go to Mars in part because we are interested in searching for past or present life there, so it’s crucially important that we avoid forward-contaminating the planet with Earth
19 Golombek et al (2012)
20 Wallace (2012)
21 Golombek et al (2012)
1.4 Preliminary Design (2005–2006) 23
Figure 1.8. Comparison of historic Mars landing ellipse dimensions with Gale crater. Gale is about 154 kilometers in diameter. The base image is Viking orbiter data. Map by Emily Lakdawalla.
microbes. Although Mars is more clement than the rest of the planets beyond Earth, it is
not a particularly kind environment to Earth microbes. It’s cold, the atmospheric pressure
is very low, it’s incredibly arid, and it’s bathed in ionizing radiation. But Earth life is tena-cious. There are some places on Mars warm enough for microbial activity. There are Earth
microbes that can survive very low pressures. Some scientists argue that Mars may possess
limited present-day liquid water (though likely very salty); and a mere 1 millimeter of
Martian soil is enough to shield microbes from damaging ionizing radiation, so life could
theoretically be hiding in briny aquifers buried beneath the surface. 22
Preventing forward contamination (and also preventing the backward contamination of
Earth with alien microbes) is the role of NASA’s Office of Planetary Protection. One of
the central concepts in planetary protection is that of “special regions.” A special region is defined by the International Council for Science’s Committee on Space Research as “a
region within which terrestrial organisms are likely to propagate” or “a region which is
interpreted to have a high potential for the existence of extant Martian life forms. ”23 In 22 Rummel et al (2014)
23 Rummel (2006)
24 Mars Science Laboratory
practice, there are no places on Mars that have yet been identified as having high potential for extant life, so it’s the first definition that applies to planetary protection.
Because MSL is not a life detection mission, it was not planned to target a special
region. However, a catastrophe on landing day could actually create a “spacecraft-induced
special region.” If MSL crash landed at a place with modern near-surface ground ice, the
hot plutonium power source would melt that ice to water and keep it nice and warm. Any
microbes that hitched a ride could potentially propagate in such an oasis.
Because MSL had the potential to create such a spacecraft-induced special region, in
August 2005, NASA’s Planetary Protection office classified the mission as “Category
IVc”. This categorization required either complete sterilization of the spacecraft, or a
landing site restriction to regions where water ice is no shallower than 1 meter from the
surface, plus sterilization of the parts of the rover that were expected to penetrate below the surface: the wheels and drill bits.24 The 1-meter number was based on estimates of how deeply large hardware fragments could be buried upon impact.
The price tag for system-level sterilization was expected to be between $60 and $170
million – more than the project could afford.25 The project elected to go with the cheaper option, accepting the restriction of avoiding near-surface ground ice, which Odyssey
mostly mapped poleward of 45° north and south latitude. The project would sterilize the
drill bits and wheels, and closely evaluate landing ellipses late in the landing site selection process to ensure that there were no hints of near-surface ground ice.26 In the end, 89% of the spacecraft’s surface area, and 61% of its volume, were subjected to heat sterilization, making it the cleanest NASA spacecraft launched since the Viking landers.27
1.5 THE COST OF COMPLEXITY (2007–2008)
It didn’t take long for the development effort to run into trouble. The main problem was
schedule. Everything seemed to take longer than it should, but the 2009 launch date was
fixed and immovable, and complexity cropped up everywhere. Engineers took shortcuts,
moving quickly to final designs without time to test early ones, risking that problems would crop up later on, which they did.28 Avionics development continued to be slowed by its complexity. A suite of sensors called the Mars Science Laboratory Entry Descent and Landing
Instrument (MEDLI) – essentially another science instrument – was added to the heat shield
late in 2006; the project would benefit future Mars landing efforts by supplementing models of entry with actual data, but created another interface to incorporate. The sample acquisition and handling mechanism design was completely scrapped and design effort restarted in
2007. On top of all of this, the mission suffered two particularly huge setbacks in 2007,
involving the design of the motors and the heat shield. Solving these problems required massive redesigns, imposed major costs, and resulted in huge schedule delays.
24 Golombek et al (2012)
25 Rummel (2006)
26 Golombek et al (2012)
27 Benardini et al (2014)
28 Manning and Simon (2014)
1.5 The Cost of Complexity (2007–2008) 25
1.5.1 Sample handling restart
Mars Smart Lander had been initially scoped with two arms, one for coring and one for
sample processing. At the time of the Preliminary Design Review, Mars Science Laboratory
had had a single arm with a driller/corer and scoop, and a deck-mounted piece of sample
preparation and handling hardware to crush, sieve, and portion the sampled rock. While
intact cores would provide insight into near-surface layering or weathering, neither of the two analytical laboratory instruments, SAM or CheMin, needed intact cores. In fact, techniques available to crush the cores for the instruments had difficulty in achieving the fine particle sizes the instruments required.
After the Preliminary Design Review, the sample handling approach changed again. A
drill would simultaneously penetrate into and powder the rock, augering it into a sample
chamber. Then the drill would transfer the material from the sample chamber into a device
on the arm that could sieve, portion, and deliver the right kind of sample to the waiting
science instruments. The approach was simpler than the two-arm core-crushing solution,
but the development effort started very late. Also, the switch from coring to percussive
drilling and the addition of sample handling hardware to the end of the arm increased the
weight of the turret from 15 to 34 kilo
grams. 29 The 2-meter-long arm and its 5 motors would need to be much more robust than planned to support all of that weight.
1.5.2 Motor problems
MSL’s design included a total of 31 motors, not counting the ones in the science instru-
ments: 6 to rotate the wheels, 4 to steer them, 2 for the high-gain antenna, 3 for the mast, 3 for the instrument inlet covers, 5 for the robotic arm, and 8 for the drilling, sampling, and dusting hardware in the arm turret. The MSL mission had sought to reduce the rover’s
power demands by using dry-lubricated motors that could operate at very low tempera-
tures without being heated for all but 4 of these. The effort had started off well: JPL successfully developed titanium-geared motors lubricated with powdered molybdenum
disulfide that operated perfectly under Martian conditions, down to a minimum tempera-
ture of –135°C, colder than the Mars minimum of –127°C (the freezing point of carbon
dioxide).30 But the motors failed later lifetime tests that checked how they would cope with the demands of operating under Martian conditions for millions and millions of revolu-tions. Over time, the titanium gears fatigued and cracked, their teeth falling out.
With schedule pressing, they had no choice but to return to the old way of doing things:
steel motors with wet lubricant, based as much as possible on the titanium motor designs
that had been worked on to date. These motors could not operate under most Martian con-
ditions without heaters. Mars Exploration Rover motors had such heaters, thin strips that
were elegantly incorporated into flat surfaces planned for that purpose in the motor design.
MSL motors had been designed without these interior surfaces, so there was no choice but
to add them to the exteriors of the motors. Furthermore, the MSL motors were dramati-
cally larger than the Mars Exploration Rovers’, and took correspondingly longer to heat.
In order to heat them up in a reasonable 1 to 2 hours, they would require larger heaters,
29 Billing and Fleischner (2011)
30 Novak et al (2008)
26 Mars Science Laboratory
consuming more power, than they would have if they had been planned into the design