Pale Blue Dot 2.0?
Question: "Can @NASANewHorizons reproduce the famous "Pale Blue dot" image? @AlanStern: Yes we think we can but there is a risk of burning the cameras out – permanently – so we would want to do all flybys first. #UltimaThule pic.twitter.com/Rzmreuo1af
— NASA Watch (@NASAWatch) December 31, 2018
Makes sense.
In addition to the risk, it might also take some special commanding for New Horizons to take a picture of the Earth. I know Cassini had flight software that would just say no (trigger fault protection) if commanded to point the camera at the Sun (or within 18 deg. of it.) We did get Earth and Venus, when the Sun was blocked by Saturn. But that required sending up some custom commands that amounted to “don’t worry, it’s ok” and “yes, I’m sure.” I think most modern spacecraft are similar. The computer on the spacecraft is smart enough not to do things that will break something.
Guess I’m surprised that at that distance there is a risk of doing damage to the camera… wonder what specifically the risk is.
Although it wasn’t mentioned I would guess that there is also a hesitancy to reorient the spacecraft for the photograph, which besides using a small amount fuel I assume it temporarily breaks communication with Earth. Then after the photograph the spacecraft has to automatically reorient itself to establish communication again. Some risk involved doing that for a photo that can be taken at any time, so I would think they would at least want to get all of their data downloaded, and as mentioned also find out first if they will be attempting another flyby.
Yes, that would be my take on it… just curious that Stern specifically mentioned “burning the cameras”. Maybe just a little melodrama…
Think of it as an eight-inch telescope, not a camera. Yes, sunlight is very faint that far from the Sun. But so are surfaces illuminated by sunlight. LORRI and the other instruments were designed to observe under those lighting conditions and with reasonable exposure times. That means looking at the Sun is still a problem.
Yes, understood (that the “cameras” are essentially telescopes). Just wondering if the risk is to the CCD, cooling system, support electronics, etc…. or something that wouldn’t occur to me.
Honestly, answering that would take more digging into the instrument papers than I care to do. But it might not even be LORRI, the visible light imager. CCD detectors could be damaged if they were on. (I’d think they would be pretty safe if you turned the voltage off. I know that’s mostly true of MCP detectors. But then what’s the point?)
New Horizons has several telescopes, all pointed in the same direction. Ralph includes a near infrared spectrometer, and those sorts of instruments have serious thermal issues when pointed at anything warm and bright.
My point was just that everything about those instruments was scaled to the brightness of surfaces illuminated by a Sun which is 40 AU away. That means that, relative to their sensitivity, the Sun at 40 AU is really bright.
As I understand it, from that distance you have to point directly at the sun and hope to find that partial pixel to the right of the sun which would be us. I also assume that for the reasons others have mentioned, they would wait the 20 months for the fly-by data to be transmitted to earth in its entirety before attempting the shot.
Even at 43 AU, the Sun and the Earth are 1.3 deg apart at greatest elongation. The 1024×1024 pixel field of view of LORRI is only 0.3 deg. The concern would either be scattered light or another instrument with a wider field of view. Just to put this in perspective, The Cassini imagers (the NAC and WAC) had 0.3 and 3 deg. fields of view, but the solar avoidance angle was 18 deg.