Wesley's Tool-Box

After observing the ISS last year, I was waiting for some interesting changes on board the space station. And this came in the form of the Boeing Starliner spacecraft docking on June 6 as a part of the Crew Flight Test. This test was originally planned to last about a week, but thruster issues kept preventing its return to Earth. This meant that when I finally got the opportunity to make an observation in Daejeon after the monsoon season was over, I could photograph it with the ISS.

Weather in August was still unstable, and forecast for August 15 was cloudy with a chance of rain in many places. But outlook for Daejeon was clear, so drove my car there to make an attempt. And as forecasted, I could see the Sun onobstructed and was able to make a satisfactory observation, as you can see in the composite photo above. The docked Starliner is easily visible as a bump on the left-hand side of the space station's main modules. You can also see the large sunspot named AR3784 near the center of the Sun.

For those who are not familiar with the space station's structure, here's an enlarged photo showing where the Boeing Starliner is currently located within the space station. It's docked to the IDA-2 at Harmony module's forward port. SpaceX Dragon spacecrafts have docked at this location before, so some of my previous observations show that at the same spot instead.

Device: Nikon P1000
Settings: 3000mm - ISO 125 - 1/2000s - f/8
Filters: ICE N100000 (Neutral Density 16.5 Stop)
Time: 2024-08-15 14:20 KST
Location: Daejeon, Korea
17 photos processed with Pixelmator 3.6.6, RegiStax 6.1.0.8, and PIPP 2.5.9

The two biggest objects orbiting the low earth orbit, International Space Station (ISS) and the Tiangong Space Station (a.k.a. Chinese Space Station or CSS) can be seen transiting the Sun every now and then. But because their orbital characteristics are different, it's hard to see the two like that on the same day within the 200 km range. And it's much rarer for the two to be seen in front of the Sun at the same time. But earlier this month, I found out that I could see the next best thing - seeing the two make the transit from the same location within 14 minutes of each other.

The result of this observation is shown here as a multiple-frame composite. Thanks to the weather, both space stations were photographed clearly and you can make out their distinct shapes - the less dense one is Tiangong. And because the observations occurred within a short timeframe, it's easy to gauge the relative apparent size difference between each other.

Close-ups of the two space stations make this more apparent. The ISS was 53 arc-seconds wide at 521 km away, while Tiangong was 37 arc-seconds wide at 460 km away. The difference in distance shows that Tiangong's orbit is lower than that of ISS. In fact, Tiangong's nominal orbit is around 375 km, while ISS is at about 420 km.

If the ISS was observed at the same distance, it would have been 60 arc-seconds wide. This means that Tiangong, which was fully built a few months ago, is roughly 60% as wide as the ISS and much bigger than what the transit finder website claims. I think that it's showing the size of just the core module (Tianhe), not the entire structure.

Maybe if I get lucky I will be able to spot the two making the transit at the same time in the future. Until then, I'll keep looking.

Device: Nikon P1000
Settings: 3000mm - ISO 200 - 1/1000s - f/8
Filters: ICE N100000 (Neutral Density 16.5 Stop)
Time: 2023-04-07 11:00 - 11:14 KST
Location: Dangjin, Korea
28 photos (14 each) processed with Pixelmator 3.3.2, RegiStax 6.1.0.8, and PIPP 2.5.9

Tiangong is a Chinese space station which was initially launched on April 29, 2021. It is built upon the experience gained from its preceding prototypes, Tiangong-1 and Tiangong-2. It only has the core module (Tianhe) at the moment, but two additional modules (Wentian and Mengtian) are planned to be added this year. Because Tianhe is much smaller and simpler than the ISS, I wasn't sure what to expect when photographing it. Once I did catch it crossing in front of the Moon, I noticed that it looked longer and resembled a candy in a wrapper. That was due to the cargo spacecrafts Tianzhou 2 and Tianzhou 3 docked to the ports.

To see the solar panels on the space station and the spacecrafts, I needed to observe it crossing in front of the Sun. Fortunately, a sighting opportunity took place just two days later and I was able to get a good look. Both the large panels on the core module and the smaller ones on the spacecrafts were visible.

With the shots zoomed in and stacked, you can see the individual parts more clearly. The length of the object is about 38 meters (Tianhe: 16.6m, Tianzhou: 10.6m each), which came out to be about 30 pixels long when I shot it on February 8 at 413km away. This is roughly 1/3 the size of the ISS. If there were no spacecrafts docked, it would have looked much smaller and less distinct. On February 10, it was 576km away, so it came out to be smaller at about 20 pixels. I may be able to get larger Sun-crossing shots in Summer when the maximum altitude of the Sun is higher.

Device: Nikon P1000
Settings: 3000mm - f/8 (ISO 800 - 1/800s / ISO 200 - 1/1250s)
Filters: None
Time: 2022-02-08 19:03:59 / 2022-02-10 12:11:53 KST
Location: Haenam / Gangjin, Korea
20 / 23 video frames processed with Pixelmator Pro 2.3.5
10 / 14 video frames stacked with RegiStax 6.1.0.8