Minimize ISS Utilization: NightPod

ISS Utilization: NightPod - Motion compensation mechanism for ISS-based long-exposure imaging

ISS night photography: The Cupola on board the ISS (International Space Station) provides a unique vantage point for remote sensing of the Earth. There has been a steadily increasing awareness of the potential for high resolution global photography of the night side of the Earth ever since the Earth observation group from the defense meteorological satellite program started releasing coarse resolution photographs of the night side of the Earth. Because a dedicated satellite is not foreseen in the near future, the most likely candidate suppliers of high resolution, global, nocturnal imagery is the crew on board the ISS. 1) 2)

The NightPod has been commissioned as a crew-attended and operated device. The mission objective was to assist the crew in taking high-resolution (long exposure) pictures of Earth targets at night from the Cupola, using on-board available cameras and lenses.

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Figure 1: NightPod observation concept: the image motion blurring effect during long exposures is reduced by rotating the camera so that the LOS (Line Of Sight) points to the same target on the ground during exposure (image credit: Cosine Research, Astro-und Feinwerktechnik)

The main design drivers identified were:

• Crew safety

• Easy-to-use interfaces to allow the astronaut to quickly mount/dismount the NightPod, accurately align it, point and shoot

• High accuracy on alignment and pointing

• Structural strength to withstand all load cases (including launch and crew “kick-loads”) and double fault-tolerant mechanical interfaces

• Maximum 10 kg total launch mass (including launch packaging)

• Compact volume for stowage on orbit and to comply with the Soyuz cargo constrains

• Capability to interface cameras and lenses ranging from 10.5 mm to 800 mm focal lengths (and similar physical lengths).

The NightPod project is the result of an efficient collaboration between Cosine Research BV (The Netherlands) as prime contractor, Astro-und Feinwerktechnik GmbH (Berlin-Adlershof, Germany) as subcontractor, and the directorate of ESA's HSO (Human Space Flight and Operations. The project is managed by ESA under GSTP (General Support Technology Program). The NightPOD project was funded by the Netherlands Space Office and the German government.

The NightPod is a state-of-the-art electro-mechanical system which accommodates commercial optical cameras and compensates for the orbital motion and attitude of the ISS. The compensation is achieved by a non-linear motorized rotation of the camera with arcsecond accuracy. The NightPod computer directly controls the camera and synchronizes the non-linear rotation of the pointing axis and the integration time of the camera. The NightPod allows rotation in 4 axes. Two axes are used to align the NightPod to the ISS local nadir direction. The third motorized axis rotates during operation keeping the desired target steady in the camera's FOV (Field of View) for the several seconds integration period. The fourth axis is used to manually point at off-track targets.

Instrument design:

The NightPod instrumentation has been conceived as a combination of custom built parts and ISS compatible COTS items. The instrument is comprised of:

• the “head”, providing 3 manually adjustable axes, single motorized rotary stage with micro-stepper motor controlled by a single board computer, electronics enclosure (the Control Box), camera interface, USB port and Crew interfaces

• two “legs”, providing 4 seat track interfaces to Cupola, and the interface to the NightPod “head”

• a lens support (for the Nikkor 400 mm lens only).

The design is optimized to accommodate a Nikon D3s camera mounting a Nikkor 400mm lens. Shorter lenses can be used as well.

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Figure 2: Exploded view of the main NightPod components and the Nikon D3s assembly (image credit: Cosine Research)

The NightPod is powered by two batteries connected in series and placed on the side of the control box (Figure 3) which contains the control electronics. The batteries have internal over-current protection and are qualified by NASA for flight on-board the ISS and the Space Shuttle. The custom battery I/F is verified against all the safety requirements for battery usage on board the ISS. Fully charged batteries allow continuous operation for more than 6 hours in worst case conditions.

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Figure 3: Control box of NightPod (image credit: Cosine Research)

The control box also accommodates the buttons to control the payload, the OLED (Organic Light Emitting Diode) display to show the information, and the USB data interface used to communicate with the camera and to upgrade the control software. The interface to the camera is located on top of the control box, and accommodates the captive tripod mounting screw to mount the camera itself.

The non-linear rotation of the camera to compensate for the ISS orbital motion is actuated by a rotary stage. The rotary stage is composed by a gear box, a micro-stepper motor, a motor controller and an optical encoder. The encoder is also used as stall warning system, in case any force is applied to the camera lens while rotating. 3)

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Figure 4: Illustration of the NightPod axes (image credit: Cosine Research)

Gear drives are used to set and lock the orientation of the NightPod axes as shown in Figure 4. The gears are adjusted via an enumerated dial and their gear ratio provides high adjustment accuracy and ensures the correct alignment during operations.

The leg assemblies are connected to the head by two interfaces (Figure 5) that lock into position when the head is correctly inserted by the crew members. In order to dismount the system, release levers shall be operated and, once unlocked, a body release lever shall be used to disengage the three components completely.

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Figure 5: View of the NightPod legs and head interface (image credit: Cosine Research)

The interface to the Cupola is at the seat-tracks alongside the Cupola lateral windows (Figure 8). The NightPod seat-track interface consists of a custom designed mechanism equipped with a self-locking system as shown in Figure 6.

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Figure 6: NightPod seat track interface in the locked (left) and open (right) positions (image credit: Cosine Research)

Tracking accuracy

7 arcsec

Maximum integration time

10 seconds

Best ground resolution

10 m/ pixel

Tracking range

± 18º

Table 1: Summary of the main NightPod specifications - using the Nikon D3s camera and the 400 mm f 2.8 lens

Safety assessment: The NightPod has been designed and tested for compliance with the requirements for human spaceflight safety for pressurized payloads. These requirements cover a wide range of areas from interface definition to outgassing requirements.

The impact of different load cases, including launch, de-pressurization and crew-induced (kick) loads on structural integrity was analyzed with the FEM (Finite Element Method) model of the NightPod, and verified at later stage by qualification and acceptance testing. The mechanical and electrical interfaces are labelled, locking is visually verifiable and secured against inadvertent disengagement. The system has been designed to be operated with one hand, once installed, and is free from pinching points and sharp edges.

LEDs (Light Emitting Diodes) are used to indicate the power status of the main power line and of single battery low-voltage. Power is automatically cut-off when the voltage goes below the security margin set by the ISS safety policy.

Operational envelope limits are reported in Table 2. The motor speed and full swap angle has been analyzed (and mechanically constrained) to avoid impact and consequent injury to astronaut during operation.

Axis

Operational ranges for alignment / pointing

Ranges for non-main windows position

1st:Yaw

±20º

± 60º

2nd:Roll

±20º

+40º/-20º (constrained by NightPod geometry)

3rd:Pitch nodding

±20º

±20º

Table 2: NightPod operational ranges

Materials and components have been selected and verified in compliance with requirements for human spaceflight safety. Flammability and explosion assessments have also been supported by qualification test.

The control box is verified for structural integrity under the different load cases and provides containment for inadvertent flame (which would self-extinguish) and shatters (which would be contained). - A successful off-gassing test has been performed on the PFM (Proto-Flight Model).

Calibration: The NightPod (with the camera installed) must be calibrated in order to account for the current ISS attitude and altitude. The calibration is performed inserting the ISS orbit attitude information in terms of yaw pitch and roll in the NightPod computer, which then calculates how much each axis on the NightPod should be rotated so that the camera is pointing nadir. The crew member shall adjust the yaw and roll axis using the scales engraved on the axes. The motorized axis is then set by software. Once this calibration is complete the Nightpod is ready to be used and an operational mode can be selected. It is, however, possible to switch between all operational modes during a session.

Manual mode: The manual mode is intended to assist in manually pointing the camera to specific targets (either preselected by their latitude/longitude coordinates or hand-picked by the user), and making single-shot pictures of those targets. The motorised axis rotates to compensate the orbital motion of the ISS. The crew member decides when to take the picture.

Automatic mode: This mode is a semi-automatic mapping mode, the camera takes a number of pictures in a row, selecting the integration times and tracking axis reset times such that the entire swath covering the ISS ground track during one pass is imaged with minimum smear and distortion per image.

The idea behind the automatic mode is to use the mechanism to systematically take pictures of adjacent areas on the surface, so that combining these pictures results in large-scale but high resolution “maps” of the night side of the Earth. This principle is shown schematically in Figure 7. Given enough time and enough passes, equal areas can be imaged under a wide variety of angles and lighting conditions, increasing the quality of the resulting maps and increasing the number of areas of scientific research that can benefit from the data.

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Figure 7: Illustration of the NightPod automatic mode operation (image credit: Cosine Research)

NightPOD is a one-of-a-kind product for mounting and accurately tracking a camcorder (or single-lens reflex camera) in the Node-3/Cupola of the ISS. NightPOD compensates for the motion of the Space Station by tracking single points on Earth automatically. The subject stays centered in frame during a long exposure time so the final image is in focus.

 

NightPod on the ISS:

The challenging flight hardware design and development process, together with a full PFM (Proto-Flight Model) testing campaign, was successfully concluded in only five months in order to be on time for the launch of the Soyuz 29S to the ISS, on December 21, 2011. ESA astronaut astronaut André Kuipers took Cosine’s NightPOD camera on board to the ISS and installed the instrumentation. The commissioning of NightPod had been successfully completed on February 24, 2012. The NightPod is part of the Crew standard training and will be operated by all Crew Members flying to the ISS in the coming years (Ref. 1).

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Figure 8: NightPod installed in the Cupola with astronaut André Kuipers (image credit: ESA, NASA)

NightPOD is an intelligent tripod head that is used to accurately track a SLR (Single Lens Reflex) camera, potentially with a large SLR, to track objects. Extremely sturdy and user friendly, it can be used to take long exposure photographs or eliminate motion blur under demanding conditions. It can be used for accurate tracking of moving objects or track stationary objects from a moving platform, such as boats, airplanes and cars.

It has been confirmed that the NightPod helps in taking sharper high resolution images of the Earth at night. However, whereas Cupola is an outstanding location for optical observation, the windows (and in particular the protective panes) limit the use of high focal lengths. It has been observed that any picture taken using a lens with a focal length above 180 mm would result in “blurry” images.

The pictures produced during the first half of 2012 have already raised the attention of scientists from the Earth Observation community who expressed interest in further development of this project. 4)

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Figure 9: The Netherlands taken by André Kuipers with NightPod (image credit: ESA, NASA)

Legend to Figure 9: The largest cities of the Netherlands are clearly visible: Amsterdam, Utrecht, Rotterdam, and The Hague.

This is only the beginning for NightPod. The system has been designed to be adaptable, and astronauts on the Space Station are already thinking of using NightPod to look the other way, into space, taking images of stars.

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Figure 10: Naples area and the Vesuvius volcano, Italy (image credit: ESA, NASA). The black circle south of Naples is the volcano Vesuvius

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Figure 11: Melbourne, Australia, at night taken by ESA astronaut André Kuipers from the ISS with the NightPod camera aid (image credit: ESA, NASA)

 

Nighttime image with the Nikon D3S digital camera on ISS:

Astronaut photography of nighttime Earth is also acquired by other means than “NightPod-mounted“ cameras on ISS. The image of Riyadh (Figure 12) was acquired on November 13, 2012, with a Nikon D3S digital camera using a 400 mm lens. It is provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. 5)

 

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Figure 12: Nighttime image of Riyadh, the capital city of Saudi Arabia (image credit: NASA)

Legend to Figure 12: The population of Riyadh, the capital city of Saudi Arabia, has risen dramatically in the last half century—from 150,000 in 1960 to 5.4 million in 2012. The city appears as a brightly colored patchwork in this nighttime astronaut photograph. The brightest lights, apart from those on the old Riyadh Airbase, follow the commercial districts along King Abdullah Road and King Fahd Branch Road. Many of the darker patches within the built area are city parks.

University sectors stand out with different street and light patterns, including the King Saud University campus—which houses the Arabic Language Institute—and the Princess Nora Bint Abdul Rahman University—which is the largest all-female university in the world. Highways and various ring roads also stand out due to bright, regular lighting. Lighted developments beyond the ring roads mark the growth of the city (image lower left and lower right). Newer neighborhoods, set further from the city center, are recognizable by blue-gray lightning.


1) Luigi Castiglione, Simon Silvio Conticello, Marco Esposito, Rody Oldenhuis, Scott G. Moon, Anja Nicolai, Stephan Stoltz, Jan Dettmann, “The NightPod – An orbital motion compensation mechanism for ISS based imaging,” Proceedings of the 63rd IAC (International Astronautical Congress), Naples, Italy, Oct. 1-5, 2012, paper: IAC-12-B3.3.12

2) “ESA NightPod,” NASA Fact Sheet, Nov. 01, 2012, URL: http://www.nasa.gov/mission_pages/station/research/experiments/ESA_NightPod.html#overview

3) “Nodding Mechanism für den NightPod,” Astro-und Feinwerktechnik, URL: http://www.astrofein.com/astro-und-feinwerktechnik-adlershof/projekte/nightpod/

4) “Tracking cities at night from the Space Station,” ESA, April 5, 2012, URL: http://www.esa.int/SPECIALS/PromISSe/SEM3HNEWF0H_0.html

5) M. Justin Wilkinson, “Riyadh at Night,” NASA Earth Observatory, Dec. 3, 2012, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=79828


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.