Remember to look up at the stars and not down at your feet — Stephen Hawking, Brief Answers to the Big Questions.
The Artemis II mission is an emotive event and offers a unique opportunity. Our vision was to show the spacecraft flying over deep-sky objects. This would be a very unusual picture for one reason: the capsule's distance from Earth allows for long-exposure photography. By comparison, this is impossible with the ISS. Therefore, the image would show the crewed spacecraft diving among the nebulae.
You can see the picture in full resolution at the PixInsight gallery. The image shows the Orion spacecraft's trail below Antares and M4. It can be seen just left of the two Antares diffraction spikes at the bottom:
The image was acquired from our observatory at the AstroCamp telescope-hosting facilities using a PlaneWave DeltaRho 350 telescope, a Moravian 150-megapixel camera, and a red filter. It has a total exposure time of 75 x 30 seconds.
There are some key points to keep in mind to appreciate the image fully. Firstly, the imaging conditions. The Moon was only 22 degrees away, and the capsule was less than 20 degrees above the horizon. The Moon was directly illuminating the telescope's mirrors, and slight movements of the telescope produced very bright reflections:
At right, the same field 48 minutes later than the image at left. The Moon moved only 25 arcminutes towards the telescope's field of view.
Even after minimizing reflections, we still had strong gradients in the image. MultiscaleGradientCorrection performed splendidly using the MARS-u database. We used a gradient scale of only 384 pixels. The result can be seen below:
The image still shows reflections of the Moon. However, in our opinion, these reflections give the photograph additional significance, since the spacecraft was indeed heading for a close encounter with the Moon.
The second important point about this image is how we control the spacecraft's signal. Generating a master by averaging the pixel values would drastically reduce its signal's strength: since it spans 75 subframes, its light would be mixed with 74 images containing pure noise. On the other hand, we should also consider that a pixel rejection would obviously produce a master without the Orion spacecraft.
The right way to integrate the trail is by changing the Combination parameter of ImageIntegration to Maximum:
This option generates a master where each pixel is set to the maximum value in its integrated set. Below we can see a comparison of three different masters:
At left, the average master with pixel rejection, where the trail is almost rejected. In the middle, the average integration produces a loss of signal on the trail. At right, the maximum integration, where the brightness is well preserved. However, as expected, the increase in noise of the maximum integration is very significant.
For this image, we produced an average master and superimposed the maximum master only on the pixels containing the trail. To select these pixels, we used the master's high-rejection map with pixel rejection. Once processed, the mask selects perfectly the pixels we want to superimpose:
The resulting master has the noise level of the average master without any signal loss on the spacecraft:
Finally, a small detail about the framing of this image is worth mentioning. We decided to present it in a vertical format, with the spacecraft positioned below the celestial objects. This places the astronauts in a position of humility before nature. We believe this is a necessary message for our time.
