ECAMs
All of the Perseverance engineering cameras share the same detector and camera body designs. This approach helps reduce development costs and greatly simplifies integration and test activities, the software and image processing architecture, and camera operation. Table 2 lists the characteristics of the Navcam, Hazcam, and Cachcam cameras. A total of 23 cameras were built in the Perseverance engineering camera production run, including 9 flight model units (FM), 9 engineering model (EM) units, 4 flight spare (kits), and one qualification model (QM). The ECAM lenses were designed and manufactured by Jenoptik.
Detector
The Perseverance engineering cameras use a CMV-20000 detector (Fig. 11), a global shutter CMOS (Complimentary Metal Oxide Semiconductor) device with \(5120\times 3840\) pixels, built by AMS (formerly CMOSIS). The image array has \(6.4~\text{micron}\times 6.4~\text{micron}\) sized pixels, digitized at 12 bits/pixel. The detector has a full-frame optical size of 32.77 mm by 24.58 mm with a Bayer pattern color filter array (Bayer 1976). The CMV-20000 was chosen due to the large optical format, the relatively high dynamic range, and high frame rate capability. The Perseverance engineering cameras have a commandable exposure time range of 410.96 microseconds to 3.277161 seconds, in 50 microsecond steps. The detector has been radiation tested to 20 kRad, RDF (Radiation Design Factor) \(=2\) and meets total dose mission performance requirements.
A CMV-20000 detector undergoing prototype testing in 2014 at JPL. The active imaging area is \(32.77~\text{mm}\times24.58~\text{mm}\)
Electronics
The camera electronics consist of 3 electronics PWBs (printed wiring boards) connected via rigid flex polyimide film layers built into the inner layers of the boards. This integrated approach simplifies the design and manufacturing, and follows the approach used on MER and MSL. The three PWBs are folded into the camera body mechanical housing. The electronics are connected to the rover interface using a 37-pin microD connector. Figure 12 shows the functional block diagram for the ECAM electronics. The pixel transfer rate between the camera and the RCE was increased to 500,000 pixels/second without changing the heritage LVDS clock rate by inserting less space between pixel waveforms. The MER/MSL pixel transfer rate is \(\sim200{,}000\) pixels per/second.
Perseverance camera electronics block diagram
Hazcams
The Hazcam lenses have a focal ratio of f/12 and a best focus distance of approximately 0.9 meters, optimized for the robotic arm workspace and views of the rover wheels. Each Hazcam lens assembly contains 10 individual lens elements and a fused silica UV and IR blocking filter mounted inside the lens assembly between the third and fourth elements. The cameras are body-mounted to the fore and aft of the rover. The FOV of the Hazcams is \(136^{\circ}\) (horizontal) by \(102^{\circ}\) (vertical), with a \(173^{\circ}\) diagonal. Figure 13 shows a set of flight Hazcams.
Front Hazcams
There are four Hazcams hard-mounted to the rover front chassis (Fig. 14). The Front Hazcams form two stereo pairs: one pair is connected to RCE-A, and the second pair is connected to RCE-B. The Front Hazcam stereo baseline for each pair is 24.8 cm; the A/B cameras are interleaved to maximize the stereo baseline between the left and right cameras. The Front Hazcams are pointed downward \(28^{\circ}\) from the nominal horizon to allow better coverage in the area immediately in front of the rover. Additionally, the left and right Front Hazcam boresights are each angled outwards by \(10^{\circ}\) (the left cameras are angled \(10^{\circ}\) to the left and the right cameras are angled \(10^{\circ}\) to the right) to allow better viewing of the rover wheels.
Perseverance Front Hazcams. \(\text{L} = \text{left}\), \(\text{R} = \text{right}\), \(\text{A} = \text{RCE-A}\), \(\text{B}=\text{RCE-B}\). Also shown are the Left/Right Navcams
The Front Hazcams have a sun visor mounted above the cameras to prevent sunlight from falling directly onto the lenses. This helps reduce lens flare and other scattered light artifacts. To maximize sun shading during late afternoon imaging the visor extends into the top of the camera FOV slightly. These upper regions of the FOV will typically be cropped (subframed) out of the image before being sent for downlink.
The Front Hazcams are protected during EDL by a camera cover assembly. The camera covers have transparent Lexan windows, which allow useable images to be acquired while the covers are closed. The covers are released shortly after touchdown on Mars using a non-explosive actuator (NEA). Once released, the covers flip open using a spring loaded-mechanism and stay in the open position for the remainder of the mission.
Rear Hazcams
There are two Hazcams mounted on the rear of the rover, one on each side of MMRTG (Multi-mission Radioisotope Thermoelectric Generator). The stereo baseline between the two Rear Hazcam cameras is 93.4 cm. Unlike the Front Hazcams, the Rear Hazcams are connected to both RCEs. The Rear Hazcams are pointed \(45^{\circ}\) below the nominal horizon. Each of the Rear Hazcams has a deployable cover assembly similar in design to the Front Hazcams. The Rear Hazcam covers are opened shortly after touchdown on Mars in a similar fashion to the Front Hazcams. Unlike the Front Hazcams, the Rear Hazcams do not have sun visors. Figure 15 shows a picture of the Rear Hazcams mounted on the rover. The proximity of the Rear Hazcams to the RTG exposes these cameras to a slightly higher radiation dose than the Navcams and Front Hazcams. Over the course of the prime mission, the cumulative effects of radiation on the Rear Hazcam detectors will result in higher dark current levels. Additionally, waste heat from the RTG warms the Rear Hazcams by \(10~^{\circ}\text{C}\) to \(20~^{\circ}\text{C}\) relative to the Front Hazcams, further raising the Rear Hazcam dark current levels. Both of these effects are also seen with the Curiosity rover Rear Hazcams. As with the Curiosity Rear Hazcams, these effects are not expected to impact the useability of the Perseverance Rear Hazcam images in any appreciable way during the prime mission. As the dark current increases over time, operational considerations may be made to acquire Rear Hazcam images during the cooler times of the day to reduce thermal dark current effects.
Perseverance Rear Hazcams
Navcams
The Navcam lenses have a focal ratio of f/12 and a best focus distance of approximately 3.5 meters. Each lens assembly contains six individual lens elements and a fused silica UV and IR blocking filter mounted between the powered elements and the detector. The Navcam field of view is \(96^{\circ}\) (horizontal) by \(73^{\circ}\) (vertical), with a diagonal FOV of \(120^{\circ}\). The Navcam cameras are shown in Fig. 16. The Navcams are mounted to the underside of the camera plate on the Remote Sensing Mast (RSM) (Fig. 17).
Closeup view of the Navcams mounted on the Remote Sensing Mast (RSM), a pan/tilt mast that points the cameras to targets of interest. The Navcams have a 42.4 cm stereo baseline. Also shown in the picture are the Mastcam-Z cameras (Bell et al. 2020, this issue) located between the Navcams, and the SuperCam (Wiens et al. 2020, this issue), located above the Navcams
Cachecam
The Cachecam has a fixed focus, 0.51 magnification lens with a depth of field of \(\pm5~\text{mm}\) and a pixel scale of 12.5 microns/pixel. The Cachecam FOV forms a 50 mm diameter circle at the plane of focus. The Cachecam lens contains six individual lens elements. The Cachecam has no IR blocking filter because the LED illuminator has no output in the IR. At the end of the lens is an integrated illuminator assembly, which contains a mirror that redirects incoming light at an angle of \(90^{\circ}\). The front of the illuminator is sealed with a fused silica window. The illuminator has a set of three light emitting diodes (LEDs) which allow the sample to be illuminated during imaging. The LEDs are powered whenever camera power is applied. The LEDs are made by Luxeon, part number LXZ1-4070, are white light LEDs with a CCT (correlated color temperature) of 4000 K.
Figure 18 shows the flight Cachecam camera. The Cachecam is integrated into a sub-assembly called the Vision Assessment Station (Fig. 19). The Vision Assessment Station (VAS) contains a cylindrical shaped baffle sub-assembly. The VAS is placed into a larger assembly, the Adaptive Cache Assembly (ACA), which is inside the rover body (Fig. 20).
Flight Cachecam camera assembly, including the lens, illuminator, and camera body. This photo shows the view looking directly into the Cachecam entrance aperture
The Perseverance Vision Assessment Station, which includes the Cachecam camera and cylindrical baffle. Sample tubes are presented to the camera by a Sample Handling Assembly (SHA), a small robot arm that brings sample tubes into the baffle from the bottom (the SHA is not shown in this picture). The illuminator assembly contains 3 LEDs that shine down onto the sample tube from the top. The camera looks down into the tube and acquires images of the top of the material within the tube
Location of the Cachecam within the Adaptive Caching Assembly (ACA), looking upwards from below the rover chassis. A portion of the Front Hazcam cover mechanism spring assembly can be seen in the upper right of the image
Due to the small depth of field of the Cachecam, the sample tube must be moved in and out of the plane of focus of the camera in small mm-sized vertical steps, with an image acquisition occurring at each step. The small depth of field was chosen to help estimate the height of the sample in the sample tube. The movement of the tube is done with the Sample Handling Assembly (SHA) robot arm. The SHA robot arm brings the tube over to the Vision Assessment Station and moves the sample tube through focus. The resulting set images form a Z-stack data set. The individual images are downlinked to Earth and processed. Information about the sample is extracted from this data set, including sample depth within the tube, sample texture, and estimates of the sample volume.
Camera Hardware Processing
ECAM Readout Modes
The MER/MSL camera data interface supports an image size of \(1024\times 1024~\text{pixels}\), and the available image buffer sizes in the RCE RAM are limited to the MER/MSL heritage sizes. In order to use the heritage interface and memory allocation, a 20 Megapixel Perseverance ECAM image must be sent to the rover as a series of smaller sub-images (tiles). After an ECAM camera acquires an image, it stores the entire 20 Megapixel image temporarily in camera memory and returns individual, smaller sub-images to the rover upon command. The individual sub-image tiles are nominally \(1280\times960\) pixels in size, and a total of 16 tiles must be transferred to copy an entire \(5120\times3840\) pixel image into the rover computer. Smaller-sized sub-image tiles can be requested if desired. Larger tiles can also be requested, but they cannot be larger than \(1296\times976\) pixels due to memory limitations in the RCE. The tile starting location can be arbitrarily placed within an image as long as the entire tile fits within the boundaries of the larger image and the starting locations are even multiples of 8.
The Perseverance cameras are also capable of reducing the pixel scale of an image prior to transmission by performing a pixel summing operation. There are four possible pixel scales available: full-scale (\(1\times1\), or no spatial downsampling), half-scale (\(2\times2\) spatial downsampling), quarter-scale (\(4\times4\) spatial downsampling), and one-eighth scale (\(8\times8\) spatial downsampling). In all modes the resulting subimage tiles are nominally \(1280\times960\) pixels, with the exception of the \(8\times8\) downsampling mode, which always produces \(640\times480\) pixel images.
In addition to spatial downsampling modes, the Perseverance ECAMs also allow the separate readout of individual red, green, and blue color channels. Depending on the requested mode, the camera either subsamples the Bayer cells by sending only the requested color, or it averages all of the pixels of the same color together. The camera can also average all of the pixels together and return a panchromatic image. In the \(8\times8\) mode, the camera always returns a panchromatic image by averaging all 64 pixels together into a single pixel. Table 3 lists all 10 available hardware processing modes, and Fig. 21 depicts the modes schematically.
Schematic representation of the 10 available ECAM readout modes: a) full-scale (\(1\times1\), upper left), b) half-scale (\(2\times2\), upper right), c) quarter-scale (lower left), and d) 1/8th scale (lower right). In modes 0 through 8, all image tiles returned from the cameras are nominally \(1280\times960\) pixels in size. In mode 9 the image tiles are \(640\times480\) pixels in size. In the above figure the \(1\times1\) and \(2\times2\) tiles are shown aligned on even multiples of \(1280\times 960\) for simplicity. In actuality the location of tiles can be located anywhere on the sensor as long as the entire tile is inside the larger source image and the starting locations are even multiples of 8
Image Co-adding
The ECAM hardware allows in-camera co-adding of 2, 4, 8, or 16 images to improve the signal to noise ratio of the image. This capability may be useful when imaging shadowed surfaces and acquiring images under low-light conditions such as nighttime imaging of the surface, nighttime atmospheric imaging, and astronomy observations. During a co-add operation, the camera exposes an image, adds it to an image accumulator buffer, acquires the next image, and continues until the desired number of images have been co-added. In all cases the camera returns the final co-added image and discards the intermediate images. During the transmission of the image data to the RCE, the camera divides the image by the number of co-added images by performing a bit-shift operation and returning the most significant 12-bits of the co-added pixel data.
EDLCAMs
EDLCAM Cameras
The EDLCAM camera bodies were manufactured by FLIR (formerly Point Grey). They have CS type lens mounts, which mate with custom lenses designed and manufactured by Universe Kogaku America. The PUC, RUC, and RDC lenses are identical in design and each contain 6 lens elements, including a front window, have a focal ratio of f/2.8, and a focal length of 9.5 mm. The DDC lens assembly contains 7 lens elements, including a front window. The DDC lens has a focal ratio of f/5.6 and has a focal length of 8 mm. See Table 4 for a summary of the EDLCAM camera types. The EDLCAM hardware is shown in Fig. 22, and the locations of the DDC, RUC, and RDC on the rover are shown in Figs. 23, 24 and 25.
Location of the DDC on the descent stage
Location of the RUC on the rover
Location of the RDC on the rover
Microphone
The EDLCAM system contains an omnidirectional microphone capsule for the capturing of sound during EDL. The microphone capsule was manufactured by DPA Microphones, part number MMC4006. The microphone capsule is connected to a DPA digitizer electronics board (part number MMA-A) that was repackaged into a custom aluminum chassis by the EDLCAM hardware development team. The digitizer board has two audio channels but the EDLCAM system only has one microphone capsule. The only key requirement on the microphone system was that it provided a simple interface to the EDLCAM DSU. The acoustic performance of the microphone system was not a key requirement – it has a frequency response from 20 Hz to 20 KHz (\(\pm2~\text{dB}\)). The digitizer is connected to the EDLCAM subsystem rover DSU via a USB2 connection. The microphone has a custom field grid that was modified for the Martian acoustic environment. The grid controls the behavior of sound waves on the diaphragm of the microphone while also minimizing the penetration of Martian dust into the diaphragm. Figure 26 shows the microphone capsule and microphone digitizer assembly. The microphone is mounted externally on the rover (Fig. 27).
The EDLCAM microphone (left, with bracket) and digitizer assembly (right). The microphone is approximately \(42~\text{mm}\times40 \times 19~\text{mm}\) and weighs 52 grams. The digitizer assembly is approximately 56 mm in diameter and weighs approximately 50 grams
Location of the EDLCAM microphone on the Perseverance Rover. The microphone is located on the port side (Y-axis, rover coordinate frame) of the rover body, above the middle wheel
Because the EDLCAM microphone is attached to the rover body, it will be commandable after landing. If the microphone survives the diurnal temperature cycles, it could be used to record Martian ambient sounds on the surface, mechanism movements such as wheel motions and coring operations, and other items of interest. The microphone could also be used in collaboration with the SuperCam microphone described in Murdoch et al. (2019), Chide et al. (2019), and Maurice et al. (2020).
Data Storage Unit (DSU)
In addition to six cameras and a microphone, the EDLCAM system includes two data storage units (DSUs) and two USB3 hubs. The DSU is an off-the-shelf computer-on-module (CoM) from CompuLab Ltd with an Intel Atom processor and solid-state memory. The DSU runs the Linux operating system, along with additional software to communicate with the EDLCAM sensors, perform the EDL data collection sequence, manage the data storage and compress the collected data files. The DSU uses a high-density connector to provide connectivity to the high-speed USB3, USB2, gigabit ethernet and SATA interfaces.
The main DSU is located inside the rover body. A second DSU, the descent stage DSU, is located on the descent stage. In both DSUs the CoM is connected to a custom electronics board that provides connectivity for all the USB devices. The two DSUs are almost identical to each other and communicate with each other through a gigabit ethernet link. The rover DSU includes a 480 GB solid-state flash memory drive (SSD) for data storage, provides a gigabit Ethernet link between both DSUs, and implements the high-speed serial communication protocol to communicate to the rover computer.
The DDC streams data to the descent stage DSU over USB3, and the descent stage DSU streams data back to the rover DSU in real time over the ethernet link. The three Parachute Uplook Cameras (PUCs) connect to two USB3 hubs in series, which merge the USB3 stream into one port on the rover DSU and also acts as a USB repeater, allowing the data signals to travel beyond 5 meters. The RUC, RDC, and the microphone are USB2 devices and connect directly to the rover DSU. After the rover touches down on Mars, data saved on the rover DSU are available to be copied from the 480 GB NVM SSD into the RCE for subsequent downlink. Figure 28 shows a functional block diagram of the EDLCAM system.
EDLCAM functional block diagram
Data Acquisition
A key feature of the design of the EDLCAM system is the requirement to not interfere with the safety of the vehicle during EDL. To meet this requirement the communication lines between the EDLCAM system and the rover are disabled at the hardware interface level during EDL to prevent spurious signals. The EDLCAM system runs autonomously once power is applied to the DSUs by the flight system. The application of power to the DSU and cameras is driven by external EDL events, as sensed by the flight system. Because the external triggering depends on the EDL system performance the exact number of images expected from each of the cameras is unknown in advance and can only be estimated. See Table 4 for the estimated number of images expected. The PUCs and DDC are jettisoned with the backshell and skycrane, but the RDC, RUC, and microphone remain on the rover and will continue to acquire data after touchdown.
PUCs
The three PUCs start to acquire image data immediately before parachute deployment at a frame rate of 75 fps (frames per second). After 30 seconds the frame rate drops to 30 fps until backshell separation, expected to occur approximately 98 seconds later. The total number of expected PUC images is \(\sim5{,}190\) images per PUC, or 15,570 total images.
DDC
The DDC will start acquiring image data just before the rover separates from the descent stage and continues acquiring data through rover touchdown on the surface. The DDC acquires data at 12 fps for \(\sim75\) seconds and is expected to acquire approximately 900 images.
RDC
The RDC will start acquiring data just before heatshield separation and will continue acquiring data through touchdown on the surface. The RDC acquires data at 30 fps for approximately 260 seconds and is expected to acquire approximately 7,800 images.
RUC
The RUC will start acquiring data just before the rover separates from the descent stage and continues acquiring data through rover touchdown on the surface. The RUC acquires data at 30 fps for approximately 140 seconds and is expected to generate approximately 4,200 images.
Microphone
The microphone will acquire data from immediately before parachute deployment through post-touchdown. The expected data acquisition duration is approximately 287 seconds. The microphone records at a sampling rate of 48 kHz, digitized at 24 bits.
LCAM
The LCAM characteristics are listed in Table 5.
An image of the flight LCAM is shown in Fig. 29. Figure 30 shows the LCAM mounting location on the Perseverance rover.
The LCAM flight unit, just prior to delivery to ATLO
Location of the LCAM on the rover
Optics
The LCAM lens is a 9-element, all-refractive lens with a nominal horizontal and vertical FOV of \(90\times90\) and an effective focal length of 5.785 mm. The nominal on-axis f/# is 2.7. The LCAM lens was fabricated at Collins Aerospace with design support from Synopsys Optical Design Services.
Detector
The detector is an On Semiconductor Python 5000, a global-shutter CMOS image sensor with \(2592\times2048\times4.8~\upmu \text{m}\) pixels and on-chip 8-bit or 10-bit digitization. LCAM uses the monochrome version of the sensor.
Electronics
The LCAM electronics design is derived from two previous camera designs by MSSS: the VSS (Vision Sensor System) camera on the NASA Goddard Space Flight Center (GSFC) Restore-L Mission and the P50 camera on the Naval Research Laboratory (NRL) Robotic Servicing of Geosynchronous Satellites (RSGS) Mission. Both of these cameras used the On Semiconductor Python 5000 detector. The LCAM electronics includes three printed circuit assemblies: the Interface Adaptor (IFA), Digital Module (DM), and Focal Plane Assembly (FPA).
The IFA connects to the LVS via a 25-pin Micro-D interface connector and communicates using asynchronous command and telemetry interface signals (LVDS), a discrete LVDS trigger, and a ChannelLink video interface. The DM contains a Microsemi RTAX FPGA and four NAND flash banks, which for LCAM are only used to store redundant copies of non-volatile operating parameters. The FPA contains three Line Current Limiter (LCL) modules that control the three power supplies to the sensor.
LVS Interface
In response to trigger signals, LCAM acquires each image, optionally sums it \(2\times2\), and transmits it to the Vision Compute Element (VCE) component of the LVS. Images are always summed \(2\times2\) and sent with 8-bit pixel depth. The ChannelLink clock is run at 35 MHz by default, with an optional mode at 17.5 MHz. Two pixels are sent in each ChannelLink cycle.
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