The following sections describe the phases of the MSL mission, from launch through the end of surface operations. The timeline and primary activities are summarized for each phase. For the surface phase, these are accompanied by an overview of the various constraints on science operations and a description of mission scenarios that exemplify how science return can be optimized under them.
Launch, Cruise, Approach, and EDL Phases; Surface Initial Checkout Activities
MSL and the Curiosity rover successfully launched on 26 November 2011. Entry, descent, and landing will occur late in the evening of 5 August 2012, Pasadena time. During the cruise to Mars, the spacecraft will perform trajectory correction maneuvers (TCMs) and undergo a series of checkout and maintenance activities. An initial payload health checkout, assessing postlaunch health and functionality, occurs as part of the first spacecraft engineering checkout. In addition, there likely will be at least one window for more comprehensive payload tests, including examples of routine instrument sequences, collection of calibration data, and limited cruise science observations (e.g., RAD). The last 45 days before landing comprise the approach phase, involving additional trajectory correction maneuvers. Entry, descent, and landing activities occur within ~15 minutes prior to touchdown on Mars. MARDI acquires its data set from heat shield separation through touchdown (< 2 minutes). For landing, MSL uses a propulsive descent “sky crane” to lower the tethered rover beneath it onto the Martian surface, setting its wheels directly on the ground. After rover landing, the connection with the descent stage is severed and the descent stage flies away to fall elsewhere, 150 m or more away from the rover. Surface science operations begin upon landing, though the first few (< 10) sols will include critical hardware deployments, spacecraft and payload checkout activities, and possibly a drive out of the region contaminated by the landing engines’ effluents.
Surface Operations Phase: Overview
MSL's primary mission spans one Mars year (669 sols or 687 Earth days) after touchdown. Science team activities would terminate six months after the end of the surface mission, whether it ends after one Mars year or after any number of extensions. Nominal science operations will occur throughout this period with some exceptions due to the ~10 sol post-EDL rover checkout, a ~20-sol period of minimal operations centered on superior solar conjunction (18 April 2013), ~10 sols dedicated to software updates throughout the primary mission, and a few other maintenance activities.
MSL is intended to be a discovery-driven mission, with the science operations team retaining flexibility in how and when the various capabilities of the rover and payload are used to accomplish the overall scientific objectives. One major partition in the rover's activities is between driving and “sampling,” where the latter represents a series of environmental, remote sensing, and contact science measurements that lead to the acquisition, processing, and analysis of a sample of rock or soil in the analytical laboratories. The nature of the landing site will influence the ratio of driving to sampling, especially if the site is a “go to” site, where the primary science targets are some distance from the center of the landing ellipse.
Science activities on any particular sol are governed by a number of constraints that are measured or predicted for that sol, such as the Earth-Mars geometry and local time phasing, timing of telecom windows, downlink data volume capability, the time profile of energy available for science, and any thermally driven operational constraints or energy needs of the payload, rover subsystems necessary for payload operations (e.g., robotic arm actuators), or the rover. Science activities generally require more power than is available from the RTG and rely on drawing down the rover batteries. Battery capacity, RTG output, overnight battery recharge, and management of the state-of-charge over multiple sols, are all critical to science planning. The thermal limitations, including significant time and energy required to heat mast, arm, and mobility actuators, vary with both local time and season, and are more severe at higher-latitude landing sites, especially in the southern hemisphere which experiences winter at aphelion.
Most science activities will occur during daylight hours on Mars. Commands for the sol's activities are sent via the overnight orbiter telecom pass or direct-from-Earth at local midmorning on Mars. The rover would complete its tactical science activities (i.e., those that influence planning for the next sol) in time to return the data via an orbiter telecom pass in the midafternoon. Between midafternoon and the next morning on Mars, the science operations team on Earth would assess the downlink, plan the next sol's activities, and prepare the commands. Data that are not essential for next-sol planning would be returned during the overnight orbiter telecom pass. This basic framework allows approximately five hours for tactical science activities on Mars, though additional payload or rover operations can occur outside of this window if they are not critical to the next sol's planning.
For the first ~90 sols after landing, MSL project personnel will live on "Mars time", allowing the above framework to be executed every sol. For the rest of the mission, however, the start time of the prime shift on Earth will track Mars time, sliding forward from 6 AM until it reaches 1 PM. After this point, the downlink from Mars arrives too late in the day on Earth to allow commands to be generated before a reasonable end of shift. In these cases the ground cycle is postponed until next available Earth shift. From a tactical standpoint, every other sol is lost during this period. However, science activities can be performed by the rover on every sol as long as they can be planned in advance and/or their results are not required immediately for future planning. This period of every-other-sol (or multiple-sol) commanding is expected to span about 12 sols of every 36-sol Earth-Mars phasing cycle.
During winter the time available each sol for science operations may be reduced because of the need to use a greater share of energy to heat the rover actuators. Also, the largest actuators may not warm sufficiently until after the afternoon orbiter telecom pass. For this reason, winter operations may use every-other-sol commanding for more than 12 out of every 36 sols.
The following table summarizes some of the key resources affecting operations and the required capability for each.
A few of the resources that drive science operations and the required minimum capabilities during the design stage of MSL.
Example Mission Scenarios
There exists an enormous variety of ways in which the mission may unfold, because of the unknown nature of the discoveries, the flexibility of the scientific payload, and the capabilities of the rover. However, in order to understand how science operations can be optimized given the constraints listed above, a set of example mission scenarios has been developed. These scenarios contain typical science activities that address the scientific goals of the mission, including driving and the use of all instruments. The goal is to demonstrate a representative surface mission that fits within the mission constraints, not to examine every conceivable use of the payload or rover.
The mission scenarios envision a logical sequence of scientific operations that repeats multiple times as the rover explores the region around its landing site. The rover performs a detailed examination of a number of distinct locations; specifically, targets occur 10 m apart in clusters separated by 1.5 km. The analysis of a target is assumed to consist of a traverse to a site of interest, remote sensing measurements to identify a target, a short approach drive to place the target within the robotic arm workspace, contact analyses to triage the target and determine whether to sample it, a set of activities that acquire rock or soil samples, process them, and deliver them to the analytical laboratory instruments, and finally, the analysis by those instruments.
For the purpose of the scenarios, each target is assumed to undergo the full set of activities, though in practice, each step is a decision point that can go forward or restart the process (e.g., if the contact analyses suggest the target is not worth sampling). Groups of activities with a similar goal, and which do not require any intermediate decisions from the science operations team, are collected into representative Sol Types. Overlain on these sols are systematic and opportunistic measurements by the environmental instruments. For example, on every Sol Type, REMS collects 1-Hz data for 5 minutes periodically throughout the day and night, while RAD observes for 15 min every hour, day and night. Most sol types also include one hour of passive DAN measurements and one additional hour-long block of REMS observations.
Traverse Sols are sols in which roving is the dominant activity. The scenarios use Traverse Sols to move the 1.5 km between clusters of targets. The roving capability is assumed to be 50 m/sol, but will vary with terrain, thermal constraints, and available energy. Traverse Sols begin with a set of targeted ChemCam observations. The roving goal is determined from engineering camera data (from a previous sol) as well as HiRISE imagery. Mastcam panoramas and DAN measurements are taken at intervals along the traverse. At the end of the traverse, the rover acquires Mastcam and Navcam panoramas, Hazcam stereo pairs, and a set of untargeted ChemCam observations.
Reconnaissance Sols initiate the detailed study of a site by returning remotely sensed "survey" observations that allow the science team to plan the next steps. Reconnaissance Sols begin with a set of targeted ChemCam observations, followed by an arm deployment (requiring Hazcam imagery from a previous sol), and acquisition of a MAHLI 3-D product. The remaining activities collect Mastcam and Navcam panoramas. The APXS remains deployed overnight for a long integration.
Approach Sols are used to place a target (e.g., part of a rock or a patch of soil) within the robotic arm’s workspace and to prepare for workspace activities. The target is identified on a previous sol and can be reached in a single sol if it is less than ~10 m distant. Approach Sols begin with targeted ChemCam observations, a short APXS integration, and a MAHLI 3-D observation before the approach. After roving, Navcam and Hazcam images, and Mastcam spectral data, are collected within the workspace. DAN acquires active measurements during the approach and at the new location.
Contact Sols conduct scientific observations of a target with the arm-mounted instruments. A specific target selected from the approach data is analyzed with MAHLI and APXS. The target is then brushed and the measurements are repeated, though with a longer APXS integration. ChemCam and Mastcam take spectral observations to provide context to the target, while Hazcam images document the activities.
Sampling and Analysis Sols contain a set of activities with the end goal of placing solid sample material within CheMin and SAM. While it may be deemed unnecessary at some point, the scenarios presently assume that cross contamination is reduced in the drill and sample processing hardware by acquiring a "cleaning" sample before the "science" sample. First, a sample is acquired by the drill from a spot near the science target and fed through the appropriate sieve. Next, the primary sample is obtained, sieved, and delivered to CheMin and SAM. Remaining sample material, if available, is placed on the observation tray for analysis by MAHLI and APXS. Finally, CheMin and SAM complete their analyses. Unlike the other Sol Types that have activities thought to fit within a single tactical window on Mars, these activities will span 3 to 5 sols because of the required time, energy, and data volume. As a rule of thumb, sample acquisition, CheMin analyses, and SAM analyses each require at least one sol's worth of resources.
In addition to the activities in the above Sol Types oriented toward selecting and analyzing solid samples, there are many additional activities critical to achieving the mission's science objectives. Examples include the analysis of atmospheric gases by SAM, meteorological imaging, dedicated campaigns for REMS, RAD, and DAN, and calibration or cleaning activities for all instruments. These activities will be performed at the direction of the Science Operations Working Group, in some cases taking advantage of sols not available for tactical commanding because of Earth-Mars phasing.
Quantitative models of the above scenarios incorporate the operational constraints, the energy and data volume usages of the instruments and rover, and the time required to perform the activities. Nominal cases have been run along with special cases that assume high southern latitude, a go-to site, or resource limitations that are tighter or looser than presently expected. The modeling exercise has yielded insights on how to optimally plan each sol and how to exploit trades among resources to increase the science return. The modeling results quantify the scientific productivity of the rover at various sols throughout the year, and as integrated over the mission.
Two key measures of mission performance are the number of solid samples analyzed by the analytical laboratory instruments and the total distance traversed. The nominal mission performance model includes 25% margin (i.e., 1 in 4 sols) to account for potential increases in required time or energy, sols that fail to achieve planned outcomes, and communication problems. In addition, 40 sols are not available to science operations because they are used for health/maintenance activities or occur during solar conjunction. Finally, 150 sols are not commandable because of Earth-Mars phasing, occur during weekends after sol 180, and/or are dedicated toward science activities not involving the solid-sample-oriented Sol Types. The remaining 311 sols are used to perform the Sol Type scenarios at a reference landing site at 27°S. Given these assumptions, over its one Mars year primary mission, MSL is expected to be capable of selecting and analyzing 30 solid samples with a traverse of 4.5 km, or alternatively, selecting and analyzing 10 solid samples with a long "go-to" traverse of 15 km.