IRIS imaging system used inthe VMC camera

FAQ - Frequently asked questions

FAQ developed by the VMC team at ESOC. Please read below before contacting us, as we will regularly update responses to the most common questions here. Scroll down for general specifications and contact information; the links on the right give more technical information about the VMC and its use and history on Mars Express.


1. What is the 'VMC'?

The Visual Monitoring Camera (VMC) is carried on Mars Express, as well as several other ESA spacecraft, including Cluster, XMM-Newton and Herschel-Planck. On Mars Express, its formal role was to image the separation of the Beagle 2 lander, a one-time event in 2003. The camera was dormant between 2003 and 2007.

The VMC consists of a small CMOS-based optical camera, which can be fitted with an on-pixel RGB colour filter for colour images. The camera has a basic command interface that can be operated by ground controllers at ESOC; it does not offer advanced features such as updateable software as found on other instruments.

The VMC really is just a regular 'web cam' such as found attached to any home PC, except it is specially qualified to function in the space environment.

2. Who operates the VMC?

Mars Express VMC - the Mars Webcam
Box-type VMC camera similar to the one carried on Mars Express

The VMC is operated by the Mars Express Flight Control Team, based at ESOC, Darmstadt, Germany. This activity is conducted on a 'best-effort, last-priority' basis given the availability of planning time, command upload time and data down-link capacity.

This is a unique situation, as Flight Control Teams for ESA missions usually do not 'operate' payload instruments; this is done by dedicated, specialised science teams. But the VMC is different: it had a purely operational purpose (successfully completed in 2003 with Beagle's separation) and as such it is not operated by scientists, but by flight controllers.

3. What format are the images we get from the VMC?

The camera produces a 640x480-pixel array of 8-bit intensity samples. These are received in the Mars Express Dedicated Control Room (DCR) as binary packets from the spacecraft. From these, ESOC software extracts the raw image binary files from the packets and performs a direct conversion of that data into the PNG files published on the website.

Example of Bayer pattern

Within each raw image are 307,200 pixels of 8 bits each (640 lines of 480 pixels). The binary file stores each pixel as an unsigned integer representing a value between 0 (black) and 255 (white). The pixels are organised with the top left pixel of the image being at the start of the binary file, then running through the image line by line from left to right of each line.

Note that the original image files contain colour information in the form of a Bayer pattern RGB filter, but the Flight Control Team do not have the spare capacity (or software) to conduct colour processing; we only generate black & white images. The colour information can be seen on every image as a grid-like overlay - the classic form of a Bayer filter.

5. Why are some of the VMC images so blurry or otherwise of low quality?

Actually, they are of rather good quality - as is the camera itself - given the original intended usage. The VMC is not a scientific instrument per se and it was designed for relatively low-resolution, fixed-focus operation. Its images should therefore not be compared to those coming from other Mars Express instruments.

Sunburst at Mars (VMC artefacts indicated)

Further, since the camera was reactivated in 2007, at least two regions of artefacts now appear in all images (which may have been caused by debris scratching or being deposited upon the optics), and other artefacts intermittently appear.

The Mars Express Flight Control Team are still learning which exposure settings give the best results for any particular imaging series; illumination conditions and pointings vary dynamically from one orbit to the next.

6. Where was Mars Express when each image was taken?"

Most VMC images are captured close to apocentre, at around 10,000 km from Mars (this is due to a constraint preventing operation with other Mars Express instruments).

See Help us with the VMC for more details.

7. How often are images taken?

Images are recorded as often as possible, but this can vary widely. Sometimes we'll get image sets daily, and other times there may be only one new set in a month. VMC activities are last-priority and often must be delayed due to higher priority activities. Check the site often! (We should have an RSS feed available shortly.)

8. How can I help?

If you are a student, teacher, professor, scientist, photographer or a Mars fan of any age, we can use your help!

Since the VMC is operated on a best-effort basis, we would be delighted to have help from the general public with processing the images, removing artefacts, increasing sharpness and interpreting the images. Please see "Help us with the VMC" for more details.


Contact

For more information and if you have any specific questions, don't hesitate to send us a mail:

vmc [@] esa.int

VMC team coordinator:
Thomas Ormston, Mars Express Spacecraft Operations Engineer

VMC specifications

Lens
Focal length: 12.3mm
F-Number: 5
Elements: 5 (1 BK7G18 infrared filter, 3 Suprasil lenses, 1 Suprasil detector window)
Focus: Fixed, sharp from 3 m to infinity
Distortion: <0.4%
Total Transmission (including filters): 0.745
Field of View: 40 x 31 degrees
Wavelength range: 400-650 nm
Diffraction spot size: 9 µm
Sensor
Sensor Type: IMEC IRIS-1 integrating CMOS APS
Colour: Bayer pattern RGB filter on chip
Image size: 640x480 pixels
Shutter: Electronic
Sensor size: 10x8 mm
Pixel depth: 8 bits
Individual pixel size: 14 µm
Spectral response: 400-900 nm
Signal-to-Noise ratio: 65 dB
Image acquisition duration: 200 ms + exposure time
Unit
Size: 65x60x108 mm
Mass: 430 g
Operating temperature: -50 degrees to +65 degrees
VMC internal image buffer capacity: 1 full VMC image
Image transfer duration (to Mars Express mass memory): 38s
Power input: 28 V
Power consumption: 2.8 W average, 5 W peak
Interface to spacecraft: serial

More information can be found on the manufacturer's website and via the links at right.

Last update: 26 August 2008

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