SDO, (Solar Dynamics Observatory) Options

[Guest_PhilCo126_*]

So it's fingers crossed for the Solar Dynamics Observatory, destined to help the predictions of "space weather".
SDO promises to become an exciting mission as an orbiting solar observatory with multiple high-definition telescopes has never been attempted before…

The prelaunch readiness press conference will be held at 1 p.m. EST, on Monday, 8th February 2010 from the Kennedy Space Center News Center. It will be immediately followed by the SDO science briefing, both briefings will be
broadcast live on NASA Television. Launch is set for 9th February 2010 (10:30 – 11:30 a.m. EST).

[kwan3217]

On the press conference and EVE instrument:

The solar image on the EVE spectrum image is not a mistake. We designed the instrument almost from the beginning to use an otherwise unused portion of one of the spectrometer CCDs as a pinhole camera - we call it SAM, the Solar Aspect Monitor. SAM has its own hardware including a precision 26 micron pinhole, filter wheel, and its own optical path with a door (one of four on the instrument) that we had to open to get first light.

The unexpected thing about it is that we are able to see the sun as well as we do. The SAM image was apparent in the very first CCD image we got down. We weren't expecting to be able to see the limb or active regions this well until years from now, well up into solar max.

-- A concerned EVE data processing engineer

[elakdawalla]

The solar image on the EVE spectrum image is not a mistake.

What exactly was said about that? It surprised me when I heard it but I was busy writing down other things so I didn't get what the P.I. said. It seemed weird to me that an image of the Sun showing up so beautifully on a detector would be a "mistake."

[kwan3217]

What exactly was said about that? It surprised me when I heard it but I was busy writing down other things so I didn't get what the P.I. said. It seemed weird to me that an image of the Sun showing up so beautifully on a detector would be a "mistake."

From the report on Spaceflightnow.com: http://spaceflightnow.com/news/n1004/21sdoimages/

"Our first image from EVE doesn't look anything like it should," Pesnell said.

I may have misinterpreted this, but I remember thinking at the time that it sounded like he said this was a mistake.

[stevesliva]

I may have misinterpreted this, but I remember thinking at the time that it sounded like he said this was a mistake.

But, is it? Is there worry that at solar max the pinhole image will obscure the spectrum? (Or some such thing?)

It's "unexpected," but is it okay?

[kwan3217]

But, is it? Is there worry that at solar max the pinhole image will obscure the spectrum? (Or some such thing?)

It's "unexpected," but is it okay?

We don't expect the SAM image to cause a problem, even at solar max. There is plenty of space on the CCD between the solar image and the spectrum. If it does somehow cause a problem, we can turn the SAM filter wheel to 'dark' and effectively turn SAM off. SAM is a lower priority measurement -- EVE is primarily a spectrometer, and there are five other cameras on SDO, all higher-resolution than SAM.

SAM isn't even really an imager - we plan on using it to get a spectrum as well. The main EVE measurement is a spectrum from about 7nm, right on the edge between ultraviolet and x-rays, out to about 120nm, at the Lyman Alpha line. We use SAM to fill in the spectrum from 7nm down to almost zero, in the soft x-ray band.

It's really hard to build a diffraction grating that works for x-rays. The smaller the wavelength is, the smaller the lines on the grating have to be. It's hard enough to get a grating that works well in extreme ultraviolet. Also, x-rays being x-rays, they have a tendency to pass through the grating rather than be diffracted by it.

So, SAM doesn't use a grating at all. We collect the image of the sun, and then analyze that image pixel-by-pixel. SAM is designed with a small-enough pinhole and short-enough exposure that we expect only one x-ray photon to hit any one pixel. When a pixel does get hit, its brightness is directly proportional to the energy of the photon that hit it. Then we can use Planck's constant to get the wavelength of each photon, then count and bin the photons to get a spectrum.

It's a really neat concept, and one that hasn't to my knowledge been tried in space. The theory is good, but in theory, theory and practice are identical, while in practice, they are not. We are treating it as an engineering experiment. We have a long way to go before we see this work, but initial signs are good.