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Film and HSD Imaging | Visible and Infrared Imaging | Stereoscopic 3D Imaging

Engineering Imagery - Film and High Speed Digital

Engineering imageryImagery has played an important engineering role throughout the history of human spaceflight. It is examined to determine if the launch vehicle and ground support systems operate properly during launch. It also serves as a valuable tool for identifying the cause of anomalous events. The importance of engineering imagery cannot be overstated as it has played a vital forensic role in determining the root cause of both the Challenger and Columbia Shuttle accidents. Lessons learned from the imagery during those investigations were applied in upgrading systems and processes, resulting in safer launches. Imaging systems and processes were also upgraded, improving the data available for analysis of subsequent launches.

Since the earliest days of the space program, engineering imagery has been acquired using high speed motion picture film cameras. Film is still the primary sensor used to acquire engineering imagery of Shuttle launches. However, film's status as the sensor of choice for engineering analysis is facing a challenge from high speed digital sensors. As the digital technologies continue their relentless advance, it seems inevitable that high speed digital imagery will eventually take over film's role as the imagery of choice for engineering analysis. A number of film and high speed digital camera attributes relevant to engineering imagery are considered in the table below.

Note: Several examples of Shuttle engineering imagery are shown in the NASA video Ascent.

Attribute High speed motion picture film cameras High speed digital cameras
Track record Proven track record. Used throughout history of human space flight. Have become more prevalent at Test Ranges in recent years.
Image Quality Considerations
Sensor quality Every frame is a new sensor, though processing issues can potentially adversely affect entire reels.

Vendors require film stock be ordered in large batches. Emulsion shelf life is of concern.
One sensor for the lifetime of the camera.

Sensor can degrade over time.

Sensor is likely to become obsolete relatively quickly as a result of rapidly advancing technology.
Frame rate / temporal resolution High frame rates. Greater frame rates achievable for 16mm film (smaller load to advance) than for 35mm film.

Frame rate can vary somewhat as mechanical load shifts from the feed reel to the take-up reel.
Higher frame rates than for film of comparable spatial resolution.

Very consistent frame rate.
Spatial resolution (depends on lens and atmospherics as well) Film and 2K HSD sensors have roughly comparable spatial resolution. (Some evidence that HSD may have recently surpassed film for certain applications) Film and 2K HSD sensors have roughly comparable spatial resolution. (Some evidence that HSD may have recently surpassed film for certain applications)

Spatial resolution not as good for color imagery as is implied by array size. Single chip sensors use pattern of filters in front of pixels and demosaicing algorithms to assign three colors to each pixel. The effective resolution is thus less than the array size would suggest.
Dynamic range Film superior to HSD.
Film is an analog sensor.
Improving dynamic range, though film is still superior. Special techniques are often implemented to expand the effective dynamic range of the digital sensor.
The digital HSD sensor has a limited bit-depth.
Artifacts Dirt/filaments seen occasionally in film frames. But each new frame is a new sensor, and features are thus typically transient.

Telecine process (conversion to digital) can introduce artifacts in sequential frames.
Dust is often seen in digital imagery as the energized sensor attracts dust. Care must be taken to avoid getting dirt on the sensor window when changing lenses.

Artifacts due to noise, bad pixels, and demosaicing for color sensors (improving situation as technology advances)
Operational Considerations
Setup / Operation Procedures Setup and operation procedures, finely tuned over long history of use, provide consistently high quality results. Not currently used operationally to cover launches. Instead, many different models are used infrequently in testing capacity. Hence, results are not as consistent. Setup and troubleshooting involve skills not involved in setup of film cameras.
Power Motor advances film only for the short duration of the film run.

Power required for only limited time during acquisition. Exposed film reel removed following launch.
Pixels must be energized and the sensor cooled for significant time prior to launch.

Power required to retain imagery recorded in on-board volatile memory until it can be offloaded onto non-volatile memory. Power loss prior to offload will result in complete loss of imagery. Some cameras now have options for recording directly to non-volatile memory. Some come with backup battery.
Thermal Overheating is not major concern as little power is dissipated when motor is not advancing film. Overheating concern resulting from need to keep pixels energized and ready for acquisition. Cameras have on-board cooling, but if camera is housed inside enclosure, it is necessary to dissipate this heat outside the enclosure.
Humidity / Coastal marine environment Corrosion concern, but ability to maintain and repair in-house helps mitigate this concern Corrosion concern since in-house maintenance and repair is not generally an option for internal electronics. High quality workmanship during manufacture is necessary to avoid problems.
Dust In-house maintenance and repair limit concerns. Of concern since in-house maintenance and repair is not generally an option. High quality workmanship during manufacture is necessary to avoid problems with internal electronics.
Turnaround time / Time required to get imagery to the analyst Relatively long turnaround time. Includes travel time back and forth to processing facility (likely in a different state), processing time, and time to convert to digital format used for initial review. Relatively short turnaround time. Though time to offload imagery, convert it to non-proprietary format desired by analysts, and distribute it to analysis facilities will take a few hours per camera. If supported by the distribution infrastructure, this could be accomplished in parallel for multiple cameras to minimize turnaround time.
"Quick Look" / Backup imagery High Definition (HD) cameras are used in addition to film cameras at many camera sites.

These cameras provide a "Quick Look" capability since imagery from these cameras is available a few hours after launch while the film is not yet processed.

In addition, the HD imagery serves as backup imagery should there be a problem with the film. The HD imagery has poorer resolution and a narrower dynamic range than the high speed film imagery.
The short turnaround time for HSD imagery means that the analyst can begin reviewing the imagery quickly, though not as quickly as if it were HD imagery.

In addition, many HSD cameras now provide an output for HD imagery that can be used for "Quick Look" and as backup to the high speed digital imagery.
Other Considerations
Device type Primarily a mechanical device Primarily an electronic device
Maintenance / Repair In-house maintenance and repair Cameras typically returned to vendor for repair. Turnaround time can be extensive, especially if the vendor has other customers deemed more valuable to accommodate.
Archival Considerations Well-established long-term storage procedures. Film stored in environmentally controlled facilities to avoid degradation. Digital storage technologies evolve rapidly. Obsolescence is a concern.

Also concern about long-term stability of digital storage media.
Infrastructure requirements Need facilities for: Camera and film storage. Maintenance and repair. Loading / unloading film. Film archive.

Digital storage and distribution infrastructure to accommodate imagery that has been transferred from film to digital format.
Need facilities for: Camera storage.

Digital storage and distribution infrastructure to accommodate HSD imagery.

As HSD technologies continue to advance, digital storage and distribution infrastructure will need to expand to accommodate larger array sizes, greater dynamic range, longer record times, etc.
Camera lifetime Extremely reliable. Readily maintained and repaired. Long camera lifetimes. Rapid advancement of industry. Cameras become obsolete relatively quickly (few years). Vendors stop providing technical support for a camera model after a few years.
Longevity of technology Has enjoyed a long, fruitful life, but is facing numerous challenges.

Economic challenges: Large entertainment and consumer imaging markets are embracing digital technologies. Manufacturers are discontinuing some film stocks and are limiting production runs of others.

Environmental challenges: Environmental concerns have resulted in fewer vendor options for film processing.
Expanding market for high speed digital imaging systems as technologies continue to advance.
Information Assurance / IT Security Well-established procedures. Rapidly evolving procedures.


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