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Why Are Space Probe Photographs in B&W?

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Hi, my dears;

It would seem I’ve been neglecting you, but I have been terrifically busy with other projects. I know that isn’t an excuse, but i did want to let you know. But onto the subject matter for today:

Space Probe Photographs

Cassini-HuygensI subscribe to several tech astronautic websites. You know, the ones that report on ongoing space missions, new developments, future projects; that sort of thing. I was reading through an article about the Cassini-Huygens mission to the moons of Saturn which has been sending back photos and data since its arrival in 2004. Simply amazing stuff. As is my habit, I scanned through some of the comments and one caught my attention, mostly because I’ve seen similar comments in numerous other articles. As I intend to refute everything in the comment, I’m not going to give out the gentleman’s name, nor the article to which his comment was submitted. Here is his comment:

“How is it possible that in 2013 when even the cheapest phone has a color camera, all the public gets is a black and white photo from a mission funded by tax payers!”

 
It appears that many people assume that since a spacecraft is performing a mission in 2013 that it is equipped with 2013 technology. But let’s look at a few facts. Cassini is not on a pleasure drive through the park. Since the Earth and Saturn are moving through space and orbiting the sun at different velocities (Saturn takes 29.1 earth years to complete 1 orbit of the sun), you cannot get from the Earth to Saturn by traveling in a straight line. I’m not going to give a lesson in Celestial Mechanics, but all you really need to know is that as in the American sport of Football, the Quarterback does not throw the ball to where the wide receiver is, but to where the receiver will be when the ball gets there. So while Saturn is, on the average, 868 Million miles from the Earth, Cassini has racked up 3.6 Billion miles in it’s journey.
Cassini_interplanet_trajectory.svg
Huygens_ImageThat journey took Cassini almost 8 years. It has been orbiting Saturn and visiting its moons for the last 9 years. During that time, it has sent back to mission control at JPL, 444 Gigabytes of scientific data and 300,000 hi-resolution photographs, all the while traveling in different orbits around Saturn, visiting dozens of its 60 moons. The Cassini spacecraft also launched the Huygens probe which landed on Titan in January of 2005. Huygens survived its plunge through the huge moon’s thick atmosphere and sent data back to Earth for about 90 minutes after landing. But let’s get back to the issue at hand. Why are all the photographs in black and white?

Cassini-Huygens_AssemblyCassini was launched 16 years ago, in 1997. So your iPhone today can take great colour photographs, right? How well did your cell phone do that in 1997? Oh, wait. Cell phones didn’t HAVE cameras in 1997. Back then, cell phones had enough trouble making phone calls. But Cassini doesn’t even have 1997 technology. That was when it was launched, NOT when it was engineered and built.

The engineering design began in 1979 and wasn’t finalized until 1986, due to budget cuts along the way. By canceling another planned deep space probe, NASA was able to build the 3.8 Billion dollar, 22 foot long spacecraft by 1995, although the launch window wasn’t until October of 1997. (Remember all that nasty little Celestial Mechanics stuff and the Quarterback?).

saturnmethaneSo basically, due to a combination of Cassini being designed using 40 year old technology and colour photographs needing many times the bandwidth to transmit than does black and white, we get black and white photographs.

The system that controls the taking of the photographs, the collection and analysis of dust particles and the flight trajectories, is a 1970s era 16-bit MIL-STD-1750A computer designed by the USAF for flight and weapons control systems of aircraft during the Vietnam war. A 16-bit computer address bus can address a maximum of 64-Megabytes of memory. That’s it. My laptop computer has 8-Gigabytes of memory. A typical smartphone has at least 1-Gigabyte of memory. (Keep in mind that 1-Gigabyte = 1,000-Megabytes.) Also, the 1750A has a single CPU running at a speed of 1Mhz. My desktop system has 2 quad core CPUs, which is 8 CPUs, each running at 2.4Ghz, or 2,400 times faster than the 1750A CPU. The USAF discontinued use of the MIL-STD-1750A computer in 1996.
cassini-orbits-15-years
True_Colour_SaturnI can hear the faint echoes of readers saying “What the Fuck? I’ve SEEN colour photographs of Saturn!” Ummm. you have and you haven’t. When NASA and JPL want to release a colour photo, a black and white image is taken 4 times. First, a full B&W image, then an image through a red filter, an image through a blue filter and lastly, an image through a green filter. The computers at JPL the examine the B&W image, followed by each filtered image. The data missing from each filtered image that is in the B&W image represents the colour data blocked by that filter. Using this data, the computer then creates a RGB composite colour photograph. To further complicate things, they sometimes arbitrarily select colours to make the images easier to see, or to intentionally highlight a particular aspect, such as a storm.

False_Colour_SaturnIf you look at the colour images on the NASA or JPL website, they are religiously marked as ‘True Colour” or “False Colour”. The problem arises when the media publishs these photographs leaving this little detail out so that people believe they are seeing something real when what it does depict is a technician’s idea of a pretty colour purple. I’ve even seen ‘latest photograghs’ shown on news shows that are clearly marked on the JPL website as an ‘artist rendition’. Do yourself a favour; go to the source and be sure.

Saturn_Tilt_NASASo before making wisecracks about why the pictures aren’t in colour, give a little thought about how much you could get done at work if your system were to be replaced with a 40 year old computer that has 1/125th the memory capacity and runs 2400 times slower. Sort of puts things into perspective, doesn’t it?

Love ya, Poppy xxxxx

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