(Note: the majority of this text was derived from that in[MALINETAL1991])

Instrument Overview
===================
The Mars Observer Camera (MOC) was initially developed as part of the Mars Observer instrument complement. After the loss of MO, the MOC flight spare was completed and flown on the Mars Global Surveyor spacecraft. To avoid a confusing change of acronym, the instrument on MGS is called the Mars Orbiter Camera, but is often referred to internally to the MOC project as MOC2. Regardless,the two instruments are essentially identical.

MOC is a three-component imaging system (one narrow-angle and two wide-angle cameras) designed to take high spatial resolution pictures of the surface and to obtain lower spatial resolution, synoptic coverage of the surface and atmosphere [MALINETAL1992, MALINETAL1998]. The cameras are based on the 'push broom' technique, acquiring one line of data at a time as the spacecraft orbits the planet. Using the narrow-angle camera during the Mapping Phase of the mission, areas ranging from 2.8 x 2.8 km to 2.8 x 25.2 km (depending on available internal digital buffer memory) can be imaged at about 1.4 m/pixel. Additionally, lower-resolution pictures (to a lowest resolution of about 11 m/pixel) can be acquired by pixel averaging; these images can bemuch longer, ranging up to 2.8 x 500 km at 11 m/pixel.

The following table summarizes MOC characteristics.

Camera Min wave- Max wave- Focal Aperture F number Reso- length length length lution (nm) (nm) (cm) (380 km, m/pixel)---------------------------------------------------------------- ------
Narrow angle 500 900 350.0 0.35 m 10 1.5 Wide angle red 600 630 1.1 1.7 mm 6.4 230 Wide angle blue 420 450 1.14 1.8 mm 6.3 230----------------------------------------------------------------------


Scientific Objectives
=====================
High-resolution data will be used to study sediments and sedimentary processes, polar processes and deposits, volcanism, and other geologic/geomorphic processes. The MOC wide-angle cameras are capable of viewing Mars from horizon to horizon and are designed for low-resolution global and intermediate resolution regional studies. Low-resolution observations can be made every orbit during the Mapping Phase, so that in a single 24-hour period a complete global picture of the planet can be assembled at a resolution of at least 7.5 km/pixel. Regional areas (covering hundreds of km on a side) may be imaged at a resolution of better than 250 m/pixel at the nadir. These images will be particularly useful in studying time-variable features such as lee clouds, the polar cap edge, and wind streaks, as well as acquiring stereoscopic coverage of areas of geological interest. The limb can be imaged at vertical and along-track resolutions of better than 1.5 km. Color filters within the two wide-angle cameras permit color images of the surface and atmosphere to be made to distinguish between clouds and theground and between clouds of different composition.


Calibration
===========
MOC is fixed to the nadir panel of the spacecraft, and therefore cannot view any spacecraft-mounted calibration targets. Through a combination of pre-launch calibration over temperature ranges anticipated at Mars, and occasional coordinated observations with TES, especially during regional or global dust storms when the atmosphere obscures the surface and presents a relatively featureless target, it is anticipated that MOC data can be calibrated photometrically to about <=10% in an absolute sense, although the relative photometric precision of the data (pixel topixel) should be better than 3%.


Operational Considerations
==========================
The pre-mapping MOC observations were taken while MGS was in its elliptical capture and aerobraking orbits. Imaging was only done for a few minutes immediately after periapsis, when the spacecraft was either tracking the nadir or performing the so-called 'rollout', a reorientation maneuver that returned it from the aerobraking drag pass to an Earth-pointed attitude. (A handful of images were taken when the spacecraft was explicitly slewed to point at targets of interest, including the Viking and Pathfinder landing sites, Phobos, and the 'Face on Mars'.) Altitudes were at times lower than those expected in mapping, but the high velocity of the spacecraft usually precluded clocking the line array fast enough to produce images with a 1:1 pixel aspect ratio. In this period, a wide variety of summing modes and line times were used to address imaging goals in the best way possible. Global coverage with the wide angle cameras was not possible in this period; typically a small fraction of the MOC buffer was devoted to reduced-resolution WA images for regional monitoring, while the lion's share of the buffer was used tostore targeted NA images.

The remainder of this discussion describes observations planned from the mapping orbit. Low resolution observations can be made every orbit, so that in a single 24-hour period a complete global picture of the planet can be assembled at a resolution of at least 7.5 km/pixel. Of course, because the Mars Global Surveyor orbit is sun synchronous, this global picture shows how each part of Mars appears at approximately 2:00 PM local time. From an imaging perspective, this global map also illustrates two principal limitations in the Mars Global Surveyor orbit: the absence of diurnal coverage (it samples Mars only at two times of day, one of which is unsuitable for visible imaging) and the poor illumination angle (chosen prior to the selection of a camera for the mission). Relief will be less apparent in images taken at low incidence angles near the equator, but at higher latitudes (i.e., nearer the terminator), relief shading will become moreprominent. Shadows will be visible near the poles.

The fields of view of both the NA and WA cameras, the nature of the Mars Global Surveyor spacecraft and mission, and specific aspects of the MOC design place certain constraints on viewing Mars. The width of MOC NA frames is limited by the camera FOV to be about 2.9 km. Even if MGS orbits were uniformly spaced, it would take over 600 days for the same location near the equator to be viewed twice. Given the 687 nominal mission duration and the vagaries of the Mars Global Surveyor orbit that result from gravitational perturbations and atmospheric drag, MOC will be fortunate to pass over each equatorial area once. At higher latitudes, of course, the number of opportunities to image a given location increases. Unfortunately, the along- and cross-track orbit prediction uncertainties are larger than the NA FOV owing to mission operational constraints on Earth. Thus,targeting a given feature will be a probabilistic activity.
Contiguous 'mosaics' of NA images are not possible. The WA FOV covers approximately 1300 km on the surface from nadir to each limb. At the equator, MGS orbits are spaced about 1500 km, so the limb on one orbit is at the nadir on the subsequent orbit, and again at the limb on the orbit after that. There is therefore good overlap at the equator, and excellent overlapcloser to the poles. Contiguous WA mosaics are possible.

MOC image sizes are determined by the camera FOV (cross-track dimension, as noted above) and by the size and utilization of the 12 MB digital buffer (along-track). Using realtime compression, it is possible to acquire an image longer than the orbit determination along-track uncertainty. However, other contents of the buffer may prevent its use in this manner. Buffer spaceis thus an important resource that requires close management.
For this reason, MOC images can vary in size and compression factor. For the NA, areas ranging from 2.9 km X 2.9 km to 2.9 km X 25.2 km (depending on available buffer memory) can be imaged at about 1.4 m/pixel. Additionally, lower resolution pictures (to a lowest resolution of about 11 m/pixel) can be acquired by pixel averaging. Contingent as well upon available power, these imagescan be much longer, ranging up to 2.9 X 500 km at 11 m/pixel.

Since payload selection and the Mars Observer project 'new start' in 1986, the data return from the MOC has grown significantly with better understanding of the spacecraft and ground telecommunication system. Mission data rates, and the MOC data rate allocation, vary substantially over the course of the MGS mission, owing to Deep Space Network link performance. They include recording at 3.5, 7, and 14 Kbps, and transmitting in realtime at 34.2 Kbps. MOC data rates vary from 0.7 Kbps during the lowest record rate to 9 Kbps during the highest record rate, and 29 Kbps during realtime transmissions. These rates permit the daily transmission of roughly 2, 4, and 8 uncompressed 2048 X 2048 images during 'record only' days and, once every three days, 14 such images during an eight hour realtime pass. These numbers can be larger or smaller, depending on the compression factors used and the resolution of the global map that is being acquired at the same time. MOC is capable of simultaneously sending data to both the record and realtime streams, and is further capableof matching any data rate available on-board the spacecraft.


Detectors
=========
To minimize mass and complexity, and to increase reliability, all three MOC camera heads are line-scan imagers. This allows the detectors to be electronically shuttered, eliminating the need for a mechanical shutter. The substantial advantages ofline-scan systems comes at the cost of fixed exposure times.
This is not a problem for the WA (f/6, 13 lines per second), but is a substantial problem for the NA (f/10, 2200 lines per second). In order to meet the signal to noise requirement of 20:1 over an appreciable part of the planet, the overall signal chain noise performance must be better than 100 electrons. This performance must be met at the raw acquisition pixel processingrate of 5 million pixels per second.

In order to meet the noise and other performance requirements, two custom CCDs were fabricated for the MOC by Ford Aeronutronics (now Loral Aeronutronics): one for the MOC NA (2048 13 um pixels, two outputs) and one for the MOC WA (3456 7 um pixels, one output). Development work also resulted in devices with thinner polysilicon layers than used in Ford's standard process,increasing their quantum efficiency in the blue (400 to 450 nm).

The custom CCDs are individually packaged and mounted on custom hybrid ceramic substrates. Each hybrid is attached to a small printed circuit board (PCB) that contains a small amount of pre-amplification circuitry inside the radiation shielding to minimize low level signal path lengths. The hybrid and PCB are mounted together in a focal plane assembly that provides mechanical alignment of the detector to the optics, radiation shielding of the detector (down to <1 kilorad for the NA, <2 kilorad for the WA), and thermal control. Each FPA has a heater to keep it warm during the cold cruise to Mars, and each incorporates a thermal path to conduct away heat produced during operation. In the case of the NA, the thermal path runs from the FPA to an 'internal radiator' behind the primary mirror. This radiator loses its heat by radiation to the back of the primary mirror which, in turn, loses heat by radiation to Mars during the nominal mission, or to space during interplanetary cruise. The focal plane assemblies are attached to the main analog circuitry through flex cables with multiple isolated return paths tominimize cross-talk.

Based on breadboard measurements, the NA signal chain has a readout noise is less than 70 electrons, and a dark current noise of less than 3 electrons rms at its operating rate. The WA signal chain has a readout noise of less than 15 electrons, and a dark current noise of less than 25 electrons at WA operating rates. In-band quantum efficiency for the NA detector (i.e., between 500-900 nm) is better than 35%, for the WA red detectors (575-625 nm) better than 35%, and for the WA blue detectors (400-450 nm) better than 10%. Both detector designs have chargetransfer efficiencies better than 0.999995.

Combined with the optics described previously, the 2048 X 1-element line array with 13 um pixels provides permits a NA resolution of 1.41 m/pixel from 380 km altitude and better than 1.5 m/pixel over the entire range of operational altitudes, while the WA cameras, using the 3456 X 1-element line array with 7 um pixels, achieve nadir resolutions of 233 m/pixel (blue) and 242m/pixel (red) from 380 km altitude.


Electronics
===========

Analog Electronics------------------
Separate but similar processing chains are used for the NA and WA cameras. Both chains provide control of gain to 3 db ('root 2') resolution. Offset control in 256 steps covering the range from 0 to 5 times the full scale of the analog-to-digital converter (A/D) is provided to subtract the effects of, for example, atmospheric scattering prior to A/D conversion. Allcamera outputs are digitized to eight bit resolution.

Correlated double sampling (CDS) is implemented in both cameras to attenuate reset and low-frequency noise. In the WA this is performed by the fairly conventional means of using two separate sample and hold circuits, one holding the reset level and the other the video level, both driving the inputs of a difference amplifier. Owing to the high speed of the NA (each of the two NA CCD outputs produces pixels at 400 ns intervals), a 200 ns delay line comb filter is used in each output chain to form the difference between the reset and video period, and this difference is further filtered and sampled before theoffset and A/D operation.

All variable gain is taken before the CDS, while the signal is effectively 'chopped,' providing immunity from offset drift in these amplifiers. Monolithic transimpedance amplifiers are extensively used in the NA for their compactness and high-frequency performance. A slow feedback loop maintains the average reset level of the signal at a fixed voltage, keeping the reset and video levels in a stable, linear range of the amplifiers while the clock feedthrough transients are removedby clipping stages to keep the amplifiers out of saturation.

For each of the NA and WA, dual-tracking linear field effect transistor-series regulators, operating with about 300 mV of headroom, provide overall post-regulation and ripple rejection for the analog 10 V power rails. L-C-R decoupling is used to isolate individual amplifiers. These regulators provide overcurrent power cycling and current monitoring to the housekeeping telemetry. They operate as switches to shut downthe analog load by microprocessor command, to conserve power.

Both NA and WA analog systems show long-term gain stability of better than 1% and gain stability over temperature excursions of better than 0.5% per 10 degrees C. The NA system uses about 700 parts and draws about 3 W; each of the WA systems uses about 450 parts and draws 1 W. Noise through the WA analog system is 25 electrons, while noise through the NA analogsystem is less than 80 electrons.


'Slow Digital' Electronics--------------------------
The MOC digital system is divided into two parts: that constrained to operate at the clock speed of the microprocessor (the 'fast' digital electronics) and that which is not so constrained (the 'slow digital' electronics). In order to isolate potential noise interactions between the 'slow' and 'fast' electronics, and to minimize the amount of circuitry that had to be placed on one face of a 35 cm diameter PCB, theyhave been placed on separate faces of two-sided PCB assemblies.

The MOC 'slow digital' electronics include the power supply, bus interface unit (BIU), housekeeping/engineering measurement circuitry, and power switching elements (PSE). The power supply consists of two flyback-type switching converters, each capable of operating asynchronously at approximately 45 KHz but normally synchronized to a common 50 KHz clock. Both converters share a common input filter. One converter (the 'digital' converter) operates whenever the spacecraft-provided 28 VDC bias is present. It provides +5 V to the digital logic and +20, +10 and -10.5 V to various sensitive analog loads (for which separate return lines are maintained). The second converter (the 'analog' converter) also draws from the spacecraft 28 VDC power, but may be turned off using secondary control logic. It supplies only analog referenced voltages:+22.5, +10.5, -10.5, +12, -5, and -20 V.

Voltages from each of two 'slow digital' boards are 'diode or'd' to provide power redundancy to the analog and digitalsystems.

The bus interface unit is Mars Global Surveyor Project-provided hardware that acts as the link between the MOC and the spacecraft Payload Data Sub-System (PDS). Three functions are accomplished by the BIU: 1) it receives MOC uplink commands from the PDS (in the form of a serial bit-stream that is converted by the BIU to a 16-bit parallel format at the BIU/MOC interface), 2) it requests and receives from the MOC science and engineering data in 16-bit words on specific polling schedules, and 3) it provides a spacecraft timing referencesignal (the Real-Time Interrupt, RTI) eight times a second.
The PDS to BIU link is Manchester II encoded, and the BIUincorporates a custom encoder/decoder chip to decode commands.
All three signals are carried over shielded differentialtwisted wire pairs.

MOC housekeeping/engineering monitoring occurs for 48 points within each redundant system--34 voltages and currents and 14 temperatures. Test points are selected using analog switches; the voltage from a selected test point is fed to a voltage controlled oscillator (VCO) which is allowed to settle for two output cycles. VCO cycles are counted by an A/D converter, with sampling initiated on an integer RTI and completed one RTIlater. The final count may be read immediately thereafter.
Housekeeping telemetry is sampled four times each second.

Owing to power constraints, the MOC implements power management circuity. Power switching elements permit various sections of the MOC digital and analog electronics to be power-cycled to reduce orbit-average power consumption. Some of these elements also incorporate circuitry to sense overcurrents that resultfrom cosmic-ray induced single-event latchups (SEL).
Power-cycling these sections enables the MOC electronics toavoid the deleterious effects of such latch-ups.


'Fast Digital' Electronics--------------------------
The MOC digital electronics incorporate many advanced technologies. Three aspects of the all-CMOS digital electronics are highlighted here: the microprocessor, the threecustom ASIC designs (on two chips), and the DRAM buffer memory.
Figure 5 shows the layout of the 'fast digital' board, illustrating the relationships between the main elements of thedigital design.

The MOC control system is based on a radiation-hard version of the National Semiconductor 32C016 microprocessor developed by Sandia National Laboratories (the Sandia SA3300). The SA3300 is a 32-bit microprocessor with a 16-bit bus and a 24-bit address space. The MOC operates its SA3300 at 10 MHz, giving a computational performance of just under 1 MIPS. Among the advantages of this processor is that all flight software could be written in a high level programming language ('C'). All memory and control registers are located in the logical address space of the microprocessor. All of its address space is also directly accessible by ground command through the PDS by directmemory load.

All of the MOC digital design except the microprocessor, memory, and BIU is implemented in gate arrays. Three basic designs are used, with two occurring on the same chip. The three designs are called the Control Gate Array (CGA), the Buffer Gate Array (BGA), and the Narrow Angle Gate Array (NAGA). Four parts (1 CGA, 2 BGA, and 1 NAGA) are used in eachof the redundant half-systems.

The CGA provides the link between the SA3300 microprocessor and the rest of the system by performing all address decoding and memory mapping. It incorporates interfaces to the program memory and operational memory, three direct memory access (DMA) channels to the BIU, and the housekeeping/engineering VCO. It also includes the reset/bootstrap controller and 'deadman' timer. The CGA permits direct memory/register access without CPU intervention, allowing the MOC to continue to function should its microprocessors fail during the mission, albeit in adegraded fashion.

The BGAs provide DRAM interfaces to each of two separate 'banks' consisting of 6 MByte each. Each BGA also provides WA CCD clocking, analog setting control, and downtrack summing for one of the two WA cameras, as well as WA data DMA. Each BGA allows data DMA for both the Mars Balloon Relay (MBR) link andthe NA camera, and applies ECC to the MBR data.

The NAGA provides acquisition control and image processing capabilities for the NA camera. It generates the NA clocking and acquisition control signals. Image processing capabilities include cross-track summing, and one- and two-dimensional predictive compression, resampling, and Huffman encoding. All data acquired through the NAGA may be optionally impressed with a 16-bit polynomial ECC syndrome capable of correcting 2 biterrors in 256.

Each of the MOC's two half-systems incorporates more digital memory than has cumulatively flown on planetary missions: ninety- six 1 Mbit DRAMs arranged in two banks of 3 million 16-bit words each. The primary use of this memory is image storage and downlink data rate buffering, although approximately 1 MByte is allocated for flight software use (e.g., command sequences, scratch space, etc.). Access bandwidth to the RAM buffer is sufficient to accommodate NA, WA, and MBR acquisitions, and memory refresh and PDS DMA transfers, all simultaneously and at their maximum rates. CPU accesses are given lower priority and are delayed as necessaryto allow other system activities the access they require.

The DRAM devices are susceptible to both cosmic-ray induced single event upset and latchup (SEU and SEL). Based on tests performed by the MOC design team, SEUs will probably occur less than 100 times each day under normal solar conditions. The ECC applied to information stored in the DRAM was designed to repair such data corruption; the software refresh rate is selectable to match the actual upset rate. Such procedures will not work during energetic solar flares, but these areexpected to occur rarely during the Mars Observer mission.
Additionally, every set of three devices (i.e., one bit in the 16-bit word) has a separate power sensing element capable of detecting SEL-induced overcurrent, and power-cycling those parts. As these devices use capacitive storage, the short- duration power-cycles are non-destructive (i.e., the memoriesretain their contents).

The MOC includes two other memory banks--one each for program memory and operational memory. The program memory consists of 128 KBytes of ultraviolet-erasable programmable read-only memory (UVEPROM), while the operational memory consists of 192KBytes of radiation-hard static random access memory (SRAM).
The flight software is stored in the UVEPROM, with ECC. It is copied into the SRAM for execution. A small amount of SRAM isalso used as a high- speed line buffer for the NAGA.


Flight Software---------------
The MOC flight software is very sophisticated. It is capable of establishing the acquisition parameters of many different data types, while simultaneously conducting routine housekeeping and data compression tasks. Among its housekeeping tasks is the continual refreshing of the DRAMbuffer ECC.

WA commanding constitutes the most complicated task of the flight software. Owing to the desire to simultaneously acquire global monitoring, NA context, and local and regional WA coverage, a schema of 'virtual cameras' was implemented. The BGA incorporates a 16-line 'ring buffer' into which WA observations are continuously acquired on each sun-lit pass; the flight software routes lines from this buffer to separate addresses, each representing a different acquisition or 'camera.' Downtrack and cross-track summing can be performed separately from full- resolution acquisitions. Different pixel positions along the detectors may also be selected so that, for example, both nadir 'context' frames and limb observations can be acquired at the same time without returning to Earth thefull 3456 pixel FOV.


Data Compression----------------
MOC has considerable capabilities to compress images tooptimize use of its buffer and downlink bandwidth allocation.
Three different forms of compression are available. During acquisition of images (i.e., in realtime), a predictive compression technique can be employed, in either lossless or 'lossy' form, to acquire more data than would otherwise fit in the MOC buffer. As noted above, predictive compression is implemented in hardware for the NA camera; the same algorithm can be applied in software to WA data. Depending on scene content, lossless compression factors from 1.5 to 2.5 are possible; with loss, the factors are larger but image quality degrades rapidly, primarily by contouring that results frominsufficient bits to represent the actual image gray levels.
Once otherwise uncompressed data are in the buffer, they can be compressed using two transform compression techniques: Walsh- Hadamard (WH) and Discrete Cosine (DC). WH transform compression, which uses square-wave approximations of spatial frequency content, can be used to compress images by factors of 3 to 5 with acceptable degradation, that appears mostly in the form of 'blockiness' associated with the loss of high frequency information. DC transform compression, using cosine representation of spatial frequencies, provides the highest compression factors with the least degradation, but takes about30 minutes to compress a typical image (2048 X 2048).
Compression factors of 10:1 show little visual evidence of degradation, although they may have increased radiometric noise (in the 1-3 DN range) within each 16 X 16 pixel transform block. Visual degradation of DC transformed images typically focuses on the boundaries between the transform blocks, which become more obvious when these blocks contain different information owing to requantization of the higher frequencycomponents.


Optics and Filters
==================
The NA camera is a 3.5 m focal length (f/10) Ritchey-Chretien telescope, filtered to operate in the 500-900 nm bandpass. The WA system consists of two cameras with the same FOV, one optimized in the 400-450 nm ('blue') bandpass and the other in the 575-625 nm ('red') bandpass. The blue WA camera (f/6.3) has an on-axis focal length of 11.4 mm, while the red WA camera(f/6.4) has an on- axis focal length of 11.0 mm.

The MOC structure is approximately 88 cm in length and 40 cm in diameter, including four major components. The largest component of the camera is the NA tube (called the Secondary Mirror Support Assembly or SMSA), which holds the secondary mirror spider and acts as both an optical baffle and the primary/secondary distance metering bench. The SMSA is fabricated of pseudo-isotropicP75S/ERL1962 graphite/epoxy in a (0, 45, 90, 135) layup.
P75S/ERL1962 graphite/epoxy was selected as the main structural material within the MOC primarily for its high strength and stiffness per unit mass and low density (leading to a low mass) and low coefficient of thermal expansion over a large temperature range (allowing it to maintain focus without active mechanisms or complicated matched-material thermal metering). Attached to the side of the SMSA is the WA assembly, consisting of a mechanical support tube (the Wide Angle Support Assembly, or WASA) also made of P75S/ERL1962 graphite/epoxy with Invar fittings, the two WA optics and focal planes, and a WA baffle. Beneath the SMSA is the P75S/ERL1962 graphite/epoxy Main Body Structural Assembly (MBSA), which supports the primary mirror, NA focal plane and associated electronics, and connects these to the SMSA. Below the MBSA is the electronics assembly, housing three 2-sided electronics boards within an aluminum chassis/radiator assembly, connected to the MBSA by a T300/934 graphite/epoxy conical 'flexure skirt.'
Owing to the high magnification on the secondary mirror (7.75X) required to fold a 3.5 m focal length into 45 cm (17.8 inches), the NA optics are extremely sensitive to focus: a 1 um shift between the primary and secondary mirrors results in a 60 um movement of the plane of best focus, and the relatively fast optics provides only a 115 um depth of field. Thus, the NA design is extremely sensitive to gravitational, vibrational, and thermal loads, and to moisture absorption, which arises from the hygroscopic nature of the epoxy. Great care has been taken tominimize the effects of temperature variations on the camera.
For example, the secondary spider vanes are arranged such that expansion or contraction of their lengths will rotate rather than despace, decenter or tilt the secondary mirror. Adoption of a passive, graphite/epoxy-based structural metering system, and the uncertainties in its performance prior to actual testing of the Flight system, led to the inclusion of a bakeout heater todehydrate the structure during cruise to Mars.

Owing to their short focal lengths and compact design, the WA optics (each is a 9-element all refractive design) and their titanium housings are relatively insensitive to gravitational,vibrational, and thermal loading.

The MOC optics/structure weighs 9.5 Kg, the primary mirror and its mechanical assembly accounting for 3.4 Kg (36%). The primary mirror has been lightweighted and sags slightly under its own weight in a one-g field. The WA lenses and housings, and the NA secondary mirror and its housing, together weigh 0.6 Kg. The graphite/epoxy structures and associated fittings weigh 3.5 Kg, and the aluminum electronics housing and radiator andmiscellaneous hardware, weigh 2.0 Kg.


Operational Modes
=================
The Narrow Angle system has:
16 gain settings 2 56 offset settings 8 summing settings (1 to 8) 128 crosstrack size settings (16 to 2048 by 16) 3 2768 downtrack size settings 256 data compression settings
The Wide Angle systems have:
20 gain settings 2 56 offset settings 32 summing settings (1 to 32) 128 crosstrack size settings (16 to 2048 by 16) 3 2768 downtrack size settings 256 data compression settings 4 crosstrack summing modes
The modes in effect for each image are described in keyword-valuepairs in the header of each image.