Science Planning

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 launch is scheduled for the fall of 2011. Entry, descent, and landing will occur in the summer of 2012. During the cruise to Mars, the spacecraft will perform trajectory correction maneuvers and undergo a series of checkout and maintenance activities. In addition, there are three windows for payload checkouts. The first occurs prior to December and primarily assesses the health of the payload. Two more comprehensive checks, in early 2012 and just before the approach phase, will include instrument functionality tests and data acquisition/downlink, as requested. The last 45 days before landing comprise the approach phase, involving additional trajectory correction maneuvers. Entry, descent, and landing activities occur within ~25 minutes prior to touchdown on Mars. MARDI acquires its data set from heat shield separation through touchdown (< 2 minutes). 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 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 post-EDL checkout, a 15-sol period of minimal operations centered on superior solar conjunction, ~10 sols dedicated to software updates, 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 target is 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 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 mid-morning 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 mid-afternoon. Between mid-afternoon 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 due to 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.

Key Resources Affecting Operations

• Energy Available for Science Activities
• Downlink Volume
• Rover Awake Time
• Traverse Distance

Example Mission Scenarios

There exists an enormous variety of ways in which the mission may unfold, due to 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 the 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., the contact analyses suggest the target is not worth sampling). Groups of activities with a similar goal, and which are uninterrupted by a decision 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-min 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 an arm deployment (requiring Hazcam imagery from a previous sol), a short APXS integration and a MAHLI 3-D product, and 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 the same contact science as in Traverse Sols. The remaining activities collect Mastcam and Navcam panoramas.

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 ChemCam acquiring targeted observations 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 Mastcams 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 due to the required time, energy, and data volume. As a rule of thumb, sample acquisition, CheMin analyses, and SAM analyses each require one sol's worth of resources.

Mission Performance

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.

The MSL mission will have to operate efficiently in order to meet its goal of analyzing between 28 and 75 samples with its analytical instruments. Of the 669 sols during the primary mission, ~40 are budgeted for checkout, solar conjunction, and software updates. Of the remaining sols, about 1/6, or ~105, will not be "commandable" due to Earth-Mars phasing. Driving 10 km over the mission (a modest total) would require ~100 to ~200 sols. This leaves ~424 to ~324 sols for sample-driven science operations. Scenario modeling shows that between 5 and 8 sols are required per target, suggesting that between 40 to 85 samples could be analyzed over the mission.

The above numbers may be significantly smaller in practice. A number of sols may be used to accomplish scientific investigations not captured by the scenarios, such as sols dedicated to atmospheric chemical and isotopic analyses, weather observations, DAN subsurface mapping, or other campaigns. Other sols will be "lost" due to activities not being executed as planned, poor thermal conditions during winter, or by decisions by the science team to abandon a particular target before a complete analysis. Finally, many of the candidate landing sites are "go to" sites. For such sites, ~100-300 sols may be required to reach the primary scientific area.