Unmanned System Data Protocol and Format

            NASA’s Mars Exploration Program has an evolving science strategy to discover past or present life on Mars.  Since 1965, NASA has sent spacecraft to orbit or land on the red planet. Every time new discoveries are made to better understand the planet and try to answer the question if life existed.  All this work is the preface for human exploration of the planet. 

            Early Mars missions focused on finding the presence of water, either in ancient time or present.  There are plenty of signs that water did exist on the planet.  NASA’s current Mars Science Laboratory mission with the remote operated vehicle, Curiosity is embarked on the process to find signs of life on Mars.  Curiosity has numerous sensors that require a specific data protocol so that data can be transmitted efficiently, and received by engineers and scientists around the world. (Overview, n.d.). 

            In order to fully understand the complexity of the capture, transfer and storage of the sensor data, the paper will discuss the communications and data support architecture, specific sensors onboard Curiosity, and propose an alternative data treatment strategy.

Communication and data support architecture

Deep Space Network

            To support spacecraft and rover programs, NASA has built an extensive communications array that includes ground stations, satellites, orbiters and radios for rovers, such as Curiosity.  The Deep Space Network is an array of giant radio antennas that support interplanetary spacecraft missions and include satellites that act as relays to ground stations on earth.  There are three ground stations equally spaced around the earth to receive communications from NASA spacecraft, orbiters, satellites and the rover. It is the largest and most sensitive scientific telecommunications backbone that makes effective data transfer between the rover, orbiters, ans satellite to support the scientific communities throughout the world (Deep Space Network, n.d.)

            In the case of Curiosity, it can communicate directly to the Deep Space Network (DSN) system or through the orbiting spacecraft around Mars, which include the Mars Reconnaissance Orbiter, 2001 Mars Odyssey and Mars Global Surveyor.  Two of these orbiters were part of previous Mars mission and are still vital to the success of Curiosity.  The advantage of using the orbiters is that they can communicate with the rover for longer periods of time, than the DSN.  Likewise, being much closer to orbiters, Curiosity does not need to use too much power to transmit the data (Communications, n.d.).

Primary communications frequency and data rates

            The primary frequency band for communications between Curiosity and earth is through X-band radios. The messages are send to earth via low-gain and high-antenna.  The low-gain antenna is an omni-directional that permits low rate communications with DSN.  The high-gain antenna sends a beam of information, which is steerable to ensure positive connectivity.  By having a steerable antenna, the rover can save energy by not having to reposition every time it need to communicate back to earth.  The rover communicates directly back to earth at a rate between 3 to 12 Kbit/s. The rover communicate to the orbiter for eight minutes a day at 128 Kbit/s. This means that the rover can pass a maximum of 60 Mbit of data per transmission to the orbiter (X-band, n.d; Data rates, n.d).

            Not all the transmission is in the form of preformatted messages.  During the entry, descent and landing of the rover on Mars, the intense maneuvering of the spacecraft required the use of special individual radio tones, which ring during different stages of the landing process.  The tones were sent for all major phases, such as parachute deployment, and landing.  In all NASA had 128 distinct tones it used to track Curiosity (Special Communications, n.d.). 

Data standards and protocol

            The data transmitted to earth is in the Consultative Committee for Space Data Systems (CCSDS) standard that was developed by a team of international space data communications specialists.  This standard reduces cost and risk to space missions, and offer rich ‘cross-support’ capabilities to collaborate. They use the CCSDS protocol to ensure a reliable and robust data transfer through there challenging communications links.  They also receive support from the cross support capability of using the European Space Agency’s (ESA) Mars Express Orbiter, via ESA’s deep space tracking network. These standards ensure that the maximum amount of data is transferred during the transmission windows. 

            There are two data communication standards used with Curiosity.  The first is for long-haul communications directly to and from Mars.  It uses the CCSDS “Packet Telemetry” and “Packet Telcommand.”   This protocol is designed for high performance over weak, long-delay radio channels.  The second is the Proximity communications using special radios on the orbiters to pass short-delay, short-contact data between Curiosity.  The protocol in the second case is the CCSDS Proximity-1 Space Link Protocol (Prox-1) (Tongson, 2012).

Data storage

            Data is stored onboard Curiosity during periods that the rover is not in sight of the orbiters or earth.  The data is stored in two “The Rover Compute Element”, which contains a special memory able to tolerate the extreme radiation environment and during times when the rover may be in an off power cycle.  The memory includes 356MD of DRAM and 2GB of flash memory with error detection and correction and 256kB of EEPROM.  It also has a central memory storage for mission data and telemetry of 32 Gbits via a non-volatile memory and camera (NVMCAM) card. The Rover Electronics Module (REM) inside the rover module has a communications interface bus named the Versa Module Europa (VME), which enables the main computer to exchange data with the instruments and sensors (Makovsky, Ilot, and Taylor, 2009; Brains, n.d.). 

            The orbiters can see earth for about 16 hours a day.  Otherwise, they store the data until earth comes into view again.  The Mars Reconnaissance Orbiter (MRO) employs a 133 MHz PowerPC processor supported by a solid state recorder with a total capacity of 160 Gbits. This device using an array of more than 700 memory chips, each with 256 Mbits of capacity to store MRO data (Command & Data, n.d.).

Curiosity sensors

Curiosity has numerous sensors used to confirm the presence of water or to establish whether the planet can sustain life.  The sensors are divided into are four main types of sensors.  The following is a list of the major sensor systems and the purpose for each sensor. 

Contact instruments

a.     APXS (Alpha-Particle X-ray Spectrometer) determines the elemental chemistry of rocks and soils using alpha particles and X-rays. 

b.     MAHLI (Mars Hand Lens Imager) on the robotic arm, also referred to as the Microscopic Imager, it is a combination of a microscope and CCD Camera. The microscope is used to analyze sedimentary rock, which is important to determine if water existing on the planet. 

                                               i.     It is a 2 MP color camera with focusable macro lens to investigate stratigraphy and grain-scale texture.

c.     Rock Abrasion Tool (RAT) is a grinder able to create holes into the ground.

d.     Magnet Arrays are used to reveal clues about the mineralogy and the planet’s geologic history by measuring magnetic properties of dust. 

Remote sensing

a.     ChemCam (Chemical Detection Camera) is an instrument suite that includes the Laser Induced Breakdown Spectrometer and the Remote Micro Imager used to obtain major element compositions for rocks and soils within seven meters of the rover.

                                                        i.     The Data Processing Unit (DPU) carries out the function of taking command from the rover, performing commands, storing data, and sending data to the rover.

                                                      ii.     It communicates via two links that run at 9.6, 19.2, 38.4 and 1115.2 kbaud. The images from the unit run at 8.25 Mbps.

b.     Mastcam (Mast Cameras) on the mast.  The mast cameras are a pair of high resolution stereo pair of CCD cameras to image the surface and sky.  They have 360 degree of movement and swing down to 180 degrees.  They can use the camera to map areas.  The camera has a ‘pin-wheel’ that gives the camera a multispectral capability. 

a.     Miniature Thermal Emission Spectrometer (Mini-TES).  It is a infrared spectrometer of rocks and soil from a distance by detection the patterns of thermal radiation.

c.     Environmental instruments

d.     DAN (Dynamic Aibedo of Neutrons) is an active and passive spectrometer that measures the abundance and depth distribution of H- and OH- bearing materials associated with absorbed water or hydrated minerals in a shallow level.

e.     MARDI (Mars Decent Imager) is a fixed-focus color camera, which points to the ground.  Primarily used during the landing sequence, it is used to provide geologic and engineering-geologic framework of the landing site for early operations.

a.     The pictures are written to a permanent flash memory in real-time during the acquisition for later transmission. 

b.     The 8 GB internal buffer permits the storage of over 4,000 raw frames, which covered the entire descent phase of the operation.

f.      RAD (Radiation Assessment Detector) is used to detect and analyze the most biologically-significant energetic particle radiation. 

g.     REMS (Rover Environmental Monitoring Station) is intended to provide in situ near surface measurement of air and ground temperatures, wind speed and direction, pressure, humidity, and ultraviolet radiation.

h.     Analytic Laboratory instruments

a.     CheMin (Chemistry and Mineralogy) is designed to perform mineralogical analysis of rocks and soils to pursue the identification and classification of habitable environments on Mars.

                                                        i.     Up to 2730 individual frames can be stored on the instrument, which correspond for 11 hours of data collection.

b.     SAM (Sample Analysis at Mars) is used to address the present and past habitability of Mars by exploring molecular and elemental chemistry relevant to life.

c.     Mossbauer Spectrometer (MB)  Used to determine the composition and abundance of iron bearing minerals at a high level of accuracy.

Additionally, there are 12 engineering cameras, 4 Navcams and 8 Hazcams.  There is a Sample Acquisition, Processing and Handling (Sa/SPaH) with a robotic arm and turret-mounting devices with includes tools (MSL Instruments (n.d.), MSL Instrument data set, n.d.; Rover instruments, n.d.).

Although there are data sheets for each sensor onboard Curiosity, there are no specific specifications regarding power requirements of each individual sensor (MSL Instrument data sets, n.d.).

Support Systems

The main source of power for Curiosity are two solar arrays.  The rover’s solar arrays generate about 140 watts of power for up to four hours a Martian day. The rover need only 100 watts to drive. The power systems include the two batteries previously mentioned that provide energy when recharging the battery is not possible, such as night time.  They anticipate that after 90 days on Mars, the solar arrays would only operate at 50% capacity because of the dust on Mars surface. 

The two RCEs previous mentioned, are connected to the power switching and analog input and output is provided by the redundant Rover Power and Analog Assembly. Battery charge management is provided to both batteries.  The Rover Motor Control Assembly (RMCA) contains the drivers for controlling all the actuators.  It can handle up to eight actuators at a time.  The main software in the RCE’s executes the command signals and monitors the status of the systems during all phases of operation, making sure all the functions and check maintain the rover in good health (MSL Instruments (n.d.). 

Alternative data treatment strategy

            Among all of NASA programs, the agency collects approximately one gigabyte of data a minute (Cooney, 2013). To be able to store or process that that data, new strategies approaches need to be implemented. One approach is to process more onboard the rovers and orbitals before transferring the information via the Deep Space Network back to earth.  A second approach is to utilize more modern data centers on earth to process the data faster to make better use of the information. Both need to be done in parallel.

            The Air Force and NASA are asking industry to develop new computers for spacecraft, which include the orbitals and rovers. These new computers will permit the use of advanced software solutions so that more processing can be done at the collection site and less needs to be sent back to earth for processing and analysis (Cooney, 2013).  When this occurs artificial intelligence and neural network software similar to what we are seeing being used on new cars could be used to make the rovers more autonomous.  They would become more efficient in carrying out their missions and less data would have to be transfer between the rover and orbiters with earth.   

            NASA’s use of modern data centers is occurring at a rapid pace.  This will also allow the efficient processing of critical data to optimize command and control of the rovers and orbitals (Cooney, 2013).  In addition to use of modern data center, NASA is starting to use advanced visualization tools, such as Obong’s Mezzanine (Oblong, n.d.).  This visual collaboration tool will be NASA’s immersive collaboration solutions transforming the way NASA communicates among themselves. This technology should be rolled out to those involved in the Mars Exploration Program so that scientist and engineers can be interpret the data that is being collected from Curiosity and the Mars Orbiters in an effective manner.  This collaboration will assist in enhancing the data protocols, treatment strategy and better use of data storage. 

References

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Cooney, M. (2013, April 11). NASA, Air Force define cutting-edge next-generation space computer. Retrieved June 24, 2016, from http://www.networkworld.com/article/2165277/data-center/nasa--air-force-define-cutting-edge-next-generation-space-computer.html

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Markovsky, A., Ilot, P., & Taylor, J. (2009, November). Mars Science Laboratory Telecommunications System Design [PDF]. Pasadena, CA: NASA: Jet Propulsion Laboratory.

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Oblong to Bring Immersive Collaboration to NASA Aeronautics - Oblong Industries. (n.d.). Retrieved June 24, 2016, from http://www.oblong.com/blog/posts/oblong-to-bring-immersive-collaboration-to-nasa-aeronautics/

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Tongson, N. (2012, August 22). NASA's Curiosity Rover Maximizes Data Sent to Earth by Using International Space Data Communication Standards : The American Institute of Aeronautics and Astronautics. Retrieved June 24, 2016, from https://www.aiaa.org/SecondaryTwoColumn.aspx?id=13350