MSL instrument host (Curiosity rover)
During the MSL mission, data are collected by instruments on the rover and those data are relayed directly to stations of the NASA Deep Space Network (DSN) on Earth or indirectly to the DSN using the orbital relay capability of Mars Reconnaissance Orbiter (MRO) or 2001 Mars Odyssey (ODY). The following sections provide an overview of the MSL spacecraft, DSN ground system, and MRO and ODY orbiters.
The Mars Science Laboratory (MSL) mission landed a mobile science laboratory on Mars to assess the biological potential of the landing site, characterize the geology of the landing region, investigate planetary processes that influence habitability, and characterize the broad spectrum of radiation. For more detailed information about the MSL spacecraft, see [GROTZINGER2009, GROTZINGERETAL2012].
Spacecraft Configuration for Cruise and Approach
Following launch of the MSL flight system, the cruise stage separated from the launch vehicle and headed to Mars. On its way, the spin-stabilized spacecraft performed 4 trajectory correction maneuvers (TCMs) and underwent a series of checkout and maintenance activities. A health checkout of each of the science instruments plus the engineering cameras was carried out from March 12 to 22, 2012, beginning 108 days after launch. The one exception to this is RAD, which was checked out and began routine science observations on December 6, 10 days after launch. Additional late cruise checkouts were performed on Mastcam, MARDI, MAHLI and the engineering cameras on April 20, 2012; Mastcam, MARDI and MAHLI plus the engineering cameras and REMS were checked again on June 14, 2012; the SAM instrument was checked on June 28, 2012.
Spacecraft Configuration for Entry, Descent, and Landing
After separation from the cruise stage, the 2559 kg entry vehicle, consisting of the backshell and heat shield enclosing the descent stage and rover, performed a series of guided maneuvers. Cruise balance masses separated to adjust the center of mass of the entry vehicle. At 3522.2 km from the center of Mars, the vehicle entered the atmosphere. This was followed by peak heating, peak deceleration, supersonic parachute deploy, and heat shield separation. At the appropriate time, the descent stage engines started, the backshell and parachute separated, and the MARs Descent Imager (MARDI) started recording video. As the descent stage approached the surface using powered descent, at an altitude of about 18.6 m, the rover was lowered on a descent rate limiter and bridle umbilical device to 7.5 m below the descent stage, and its wheels were deployed into the touchdown configuration. The descent stage continued descending until the rover touched down on the surface of Mars. The rover landed in Gale Crater at 15:03 Local Mean Solar Time on Mars (August 6, 2012, 05:18 UTC Spacecraft Event Time). Upon successful touchdown, the descent rate limiter and bridle umbilical device were cut. The descent stage flew away and impacted the surface 650 meters away from the rover.
Rover on the Surface of Mars
After landing, the instrument host is the rover. Overall characteristics of the rover include a total mass of ~900 kg, 2.8 m width, 3 m length (4.7 m long with robotic arm extended), 1.1 m top deck height, 2.2 m total height, and 84 kg instrument payload. The rover is a vehicle for remote operation on the Martian surface with the following capabilities: (1) supports the science instrument payload investigations, (2) can traverse up to 100 to 200 meters per sol, depending on the terrain, (3) provides high- speed computational capability and substantial data storage, and (4) provides X-band for Direct-to- Earth (DTE) and Direct-from- Earth (DFE) telecommunications, and the ability to communicate via UHF with Mars Reconnaissance Orbiter and Mars Odyssey (which will store and relay data to the Earth).
The rover is a scaled version of the 6-wheel drive, 4-wheel steering system from the Mars Exploration Rover (MER). Based on the center of mass, the vehicle is required to withstand a static tilt of at least 50 deg in any direction without overturning. Fault protection will limit the rover from exceeding 30 deg tilts while driving. The design of the rocker-bogie allows the wheels to move over objects approximately as large as the wheel diameter (0.5 m). Clearance under the rover's body on flat ground is 66 cm. Each wheel has cleats and is independently actuated and geared, providing for climbing in soft sand and scrambling over rocks. Each front and rear wheel can be independently steered, allowing the vehicle to turn in place as well as execute arcing turns. The rover has a top speed on flat hard ground of ~4 cm/s but under autonomous control with hazard avoidance, the vehicle achieves an average speed of ~1.5 cm/s.
Rover power is provided by the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), which generates ~110 W of electrical power at the start of the landed mission. Peak power demand from the rover activities easily exceeds this however, and the rover has two Li-Ion rechargeable ~42 amp-hour batteries to allow for all activities. The batteries go through multiple charge/discharge cycles per Sol, with maximum allowed depth of discharge of ~53%.
The surface telecommunications system uses three antennas, two for X-Band DTE/DFE (Direct to/from Earth), and a UHF antenna for relay to an orbiting asset. The X-band antennas are the Rover Low Gain Antenna (RLGA) and the High Gain Antenna (HGA). The HGA is used for either direct-to-Earth (DTE) or direct-from-Earth (DFE), while the RLGA is used primarily for DFE. The basic telecom requirement for surface operations on the HGA is to transmit at least at 160 bits per second to a 34-meter Deep Space Network (DSN) antenna, or 800 bits per second to a 70-meter DSN antenna. In safe mode, commands from the Earth are received via the LGA, which does not require pointing. Limited capability for communications exists via the LGA (15 bits per second uplink at max range). Typical daily uplink of commands is done via the HGA, taking approximately 15 minutes for a total volume of 225 kilobits. The HGA sits on a 2 degree-of-freedom gimbal, with 5 degree system pointing accuracy (including rover attitude knowledge), and is 0.28 meters in diameter.
The primary data return path for surface operations is via the UHF relay system, using the Mars orbiting assets, Mars Odyssey and Mars Reconnaissance Orbiter (MRO). The project intends for primary communications to go through MRO, with two passes a day primarily used to return data from the surface. Typically, it is expected that science decisions will be supported by returning a minimum of 50 to 100 megabits of low-latency decision-supporting data for the tactical process, and up to 800 total megabits of data per sol. The mission is designed to work with a minimum of 250 megabits per sol using two UHF passes. Communications with Odyssey are subject to necessity and available energy. The UHF subsystem has a pair of redundant Electra-Lite radios. If for any reason DTE/DFE via X-Band is not possible, the UHF passes can be used to command the rover instead. A single quad-helix antenna called the RUHF is mounted to the rover deck and used for either of the radios.
The computing, command, data handling, power regulation, and power distribution functions of the rover (for all phases of the mission including cruise and EDL) are supported by two identical computers (two for redundancy backup) called Rover Compute Elements (RCEs). Each computer has a 32-bit RAD750 processor which is capable of up to 400 MIPS. Each RCE contains a central processor (a radiation hardened PowerPC 750 architecture system) that communicates with peripheral devices using other cards connected on a compact PCI backplane interface, and provides central memory storage for mission data and telemetry of 32 Gb via a Non-Volatile Memory / Camera (NVMCAM) card. In addition to the RCEs, power switching and analog input/output is provided by the redundant Rover Power and Analog Modules (RPAMs) connected to the RCEs. Battery charge management is provided via the two Battery Control Boards (BCBs) with one BCB for each battery. The Rover Motor Control Assembly (RMCA) contains drivers for controlling all engineering actuators. Up to eight actuators can be driven simultaneously. The software in the main computer of the rover executes a control loop which monitors the status of the flight system during all phases, checks for the presence of commands to execute, maintains a buffer of telemetry for transmission, performs communication functions, and checks the overall health of the spacecraft.
On the surface, activities such as imaging, driving, or instrument operations are performed under commands transmitted in a command sequence to the rover from the flight team. The rover generates constant Engineering, Housekeeping and Analysis (EH&A) telemetry and episodic Event Reports (EVR) that are stored for eventual transmission.
There are four main types of science instruments on the rover: (1) the contact instruments APXS (Alpha-Particle X-ray Spectrometer) and MAHLI (Mars Hand Lens Imager) on the end of the robotic arm; (2) the remote sensing instruments ChemCam (Chemical Camera) and Mastcam (Mast Cameras) mounted on the mast; (3) the environmental instruments DAN (Dynamic Albedo of Neutrons), MARDI (Mars Descent Imager), RAD (Radiation Assessment Detector), and REMS (Rover Environmental Monitoring Station); and (4) the analytical laboratory instruments CheMin (Chemistry and Mineralogy) and SAM (Sample Analysis at Mars), which are inside the body of the rover.
In addition to the science cameras, the MSL rover carries 12 engineering cameras (4 Navcams and 8 Hazcams), all of which share the same design as those on the Mars Exploration Rovers Spirit and Opportunity (see [Makietal2003]). The primary set of engineering cameras is a Navcam pair near the top of the mast, a front Hazcam pair mounted on the front panel of the rover body and a rear Hazcam pair mounted on the back panel. Three pairs of the cameras provide redundant backups (an extra Navcam pair and an extra Front and Rear Hazcam pair). The redundant backup cameras are connected to the backup rover computer and are not expected to be used unless there is a problem with the primary rover computer and/or primary cameras.
The Remote Sensing Mast (RSM), provides a tall geologist's eye- level view from the cameras mounted at the top, ~2 meters above the Martian surface. The RSM head includes the ChemCam, Mastcams, and Navcams, with the ChemCam sitting inside of the remote warm electronics box (R-WEB). The R-WEB is a thermally controlled enclosure atop the mast. The RSM has the ability for azimuth and elevation control, and can slew at 5 degrees per second. The RSM allows for full 360 degree (plus or minus 181 degree) azimuth and plus or minus 91 degree elevation (zenith to nadir) range of motion. Mounted along the shaft of the mast are two booms for the REMS investigation.
The Sample Acquisition, Processing, and Handling (SA/SPaH) subsystem is responsible for the acquisition of rock and soil samples from the Martian surface and the processing of these samples into fine particles that are then distributed to the analytical science instruments, SAM and CheMin. The SA/SPaH subsystem is also responsible for the placement of the two contact instruments, APXS and MAHLI, on rock and soil targets. SA/SPaH consists of a Robotic Arm (RA) and turret-mounted devices on the end of the arm, which include a drill, brush, soil scoop, sample processing device, and the mechanical and electrical interfaces to the two contact science instruments, APXS and MAHLI. SA/SPaH also includes drill bit boxes, the Organic Check Material (OCM), and an observation tray, which are all mounted on the front of the rover, and inlet cover mechanisms that are placed over the SAM and CheMin solid sample inlet tubes on the rover top deck.
The Robot Arm (RA) is a 5 degree-of-freedom manipulator that is used to place and hold the turret-mounted devices and instruments on rock and soil targets, as well as manipulate the turret-mounted sample processing hardware. The 5 degrees of freedom are provided by a set of rotary actuators known as the shoulder azimuth joint, the shoulder elevation joint, the elbow joint, the wrist joint, and the turret joint. The joints are connected by structural elements with long links connecting the shoulder and elbow joints (known as the upper arm link) and connecting the elbow and wrist joints (known as the forearm link). When fully extended straight ahead in the rover forward drive direction, the center of the turret of the robotic arm is 2.3 m from the front of the rover body.
At the end of the RA is the turret structure on which 5 devices are mounted. The outer diameter of the turret plus the installed devices is 60 cm. Two of these devices are the science contact instruments APXS and MAHLI. The remaining three devices are associated with sample acquisition and sample preparation function: the Powder Acquisition Drill System (PADS), Dust Removal Tool (DRT), and the Collection and Handling for Interior Martian Rock Analysis (CHIMRA). The robotic arm can meet its positioning requirements for targets inside a volume called the robotic arm workspace. The workspace volume is an upright cylinder 80 cm diameter, 100 cm high, positioned 105 cm in front of the front body of the rover, and extending to 20 cm below the surface when the rover is on a smooth flat terrain.
The PADS is the device that is responsible for acquiring powdered rock samples from up to 5 cm inside the surface of a rock. The drill both penetrates the rock and powders the sample to the appropriate size for analytical instrument use. The powder travels up an auger in the drill and into a chamber with a transfer tube connection to the CHIMRA processing unit. Movement of the powder through CHIMRA is driven by gravity (by changing the position and orientation of the robotic arm) and vibration.
The diameter of the hole in a rock after drilling is 1.6 cm in diameter and up to 5 cm deep, depending on the surface topography of the rock. Material from the upper ~1.5 cm of the drill hole is deposited on top of the rock surrounding the drill hole and does not make it into CHIMRA.
The grain size distribution of the drilled powder and the temperatures to which the powder is heated during drilling will depend on the nature of the rock being drilled, the final drill design and performance, and operating parameters selected for use on Mars (rotation and percussion parameters, on-off cycles, etc). Pre-landing tests on prototype drills over a range of operational parameters and rock types have yielded samples with ~90% of the bulk material generated by the drill capable of passing through a 150 um sieve and 100% passing through a 1 mm sieve. Heating of the drilled sample in pre-landing tests was minimal.
Soil samples are acquired with CHIMRA's clam-shell scoop mechanism, which can collect loose soil material from depths of up to 3.5 cm. The volume of a scooped soil sample is expected to be between 1 and 30 cm3.
The CHIMRA provides mechanisms for sieving particles to less than 150 um, mixing the samples that pass through the 150 um sieve, and portioning the samples into the appropriate volume (~76 mm3 per portion) for distribution to the SAM and CheMin instruments. The CHIMRA also provides the capability for sieving particles to less than 1 mm and portioning that material into an appropriate volume for distribution to the SAM instrument (45-130 mm3 per portion).
The MSL rover surface navigation coordinate frame is right-handed, orthogonal, and defined by axes Xr, Yr, and Zr.
- +Zr axis is normal to the rover top deck plane and points down, from the top deck toward the wheels;
- +Xr axis is parallel to the rover top deck plane and points from the center of the top deck toward the RSM assembly;
- +Yr completes the right hand frame.
The origin of the MSL rover navigation frame is centered directly between the centers of the two middle wheels.
The Deep Space Network (DSN) is a telecommunications facility managed by the Jet Propulsion Laboratory of the California Institute of Technology for the U.S. National Aeronautics and Space Administration (NASA).
The primary function of the DSN is to provide two-way communications between the Earth and spacecraft exploring the solar system. To carry out this function it is equipped with high-power transmitters, low- noise amplifiers and receivers, and appropriate monitoring and control systems.
The DSN consists of three complexes situated at approximately equally spaced longitudinal intervals around the globe at Goldstone (near Barstow, California), Robledo (near Madrid, Spain), and Tidbinbilla (near Canberra, Australia). Two of the complexes are located in the northern hemisphere while the third is in the southern hemisphere.
Each complex includes several antennas, defined by their diameters, construction, or operational characteristics: 70-m diameter, standard 34-m diameter, high-efficiency 34-m diameter (HEF), and 34-m beam waveguide (BWG).
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter (MRO) was designed and built by Lockheed Martin Space Systems.
To meet its science objectives, MRO has seven scientific instruments: Mars Color Imager (MARCI), Mars Climate Sounder (MCS), High Resolution Imaging Science Experiment (HiRISE), Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), Context Imager (CTX), and Shallow (Subsurface) Radar (SHARAD).
An Electra UHF Communications and Navigation Package on MRO allows the spacecraft to act as a communications relay between the Earth and landers and rovers on the martian surface.
2001 Mars Odyssey
The 2001 Mars Odyssey (ODY) spacecraft was designed and built by Lockheed Martin Astronautics (LMA). To meet its science objectives, Mars Odyssey has three primary instruments: Thermal Emission Imaging System (THEMIS); Gamma Ray Spectrometer (GRS), which includes the High Energy Neutron Detector (HEND); and Mars Radiation Environment Experiment (MARIE). In addition to transmitting data collected by ODY instruments and systems, the telecommunications system is used to relay data from Mars surface assets and measure their relative motion radiometrically in the 400 MHz frequency range. For more information, see [JPLD-16303].