Chinese space station falling soon

The Chinese space station Tiangong-1 was blasted into orbit in 2011. In March 2016 control was lost, and since then the 10 metre long station has been gradually losing altitude. It is expected to burn and possibly crash in the next day or two, but it is uncertain exactly when, and where.

Image result for tiangong 1

The possibilities:

It sounds like we are safe as far south as Dunedin, and most and probably all people around the world will be unaffected.

It is unprotected by heat shields so will mostly or completely burn as it drops into the Earth’s atmosphere. This could be spectacular if you can see it – and with streaming telescopes that should be easy wherever it happens.

Thanks to the Virtual Telescope Project and the Tenagra Observatory, people can see it live –click here to watch.

LiveScience: Here’s How to Watch the Chinese Space Station’s Uncontrolled Plunge to Earth

The Chinese space station Tiangong-1 is plummeting back to Earth this weekend, and anyone with an internet connection can watch the fiery demise live online.

Tiangong-1 is expected to re-enter Earth’s atmosphere sometime between late Saturday (March 31) and late Sunday (April 1).

With our time difference in New Zealand add half a day or so to that, so Sunday-Monday.

It also remains true that it is not a danger to you or anyone else, because the Earth is very big and still mostly pretty empty, and the station is very small in the scheme of things. And the odds of getting hit by a piece of the space lab that manages to survive the fiery re-entry into our atmosphere are incredibly low.

The Conversation: Tiangong-1 crash: why it’s so hard to predict where space debris will land and what can be done about it

While experts have been aware that this would happen for more than a year, there has been huge uncertainty around the exact timing. As the station’s orbital altitude has decreased, however, this uncertainty has gradually reduced and it is now possible to determine that it will deorbit within a few days.

Most of the 8.5-tonne station will burn up and disintegrate as it passes through the atmosphere, though some debris may hit Earth.

We cannot actually predict the time and place of Tiangong-1’s potential impact on Earth, despite it being only 200km above us.

Why is it so difficult, and will science one day help us nail such predictions?

Newton’s laws tell us that satellites orbit the Earth in perfectly circular or elliptical orbits, repeating their path again and again (assuming that gravity is the only force acting on them). However, this is not true at low altitudes, say below 1,000km, because the satellite is then moving through the Earth’s atmosphere. This causes “aerodynamic drag” (air resistance) – a force that opposes the satellite’s velocity, which effectively turns the orbit into a downward spiral towards the Earth’s surface.

The spacecraft’s velocity is easy to measure fairly accurately using observations. However, the other parameters are highly uncertain – making it difficult to determine Tiangong-1’s path. For vehicles such as cars and aircraft, C can be estimated theoretically or with computational fluid dynamics and measured experimentally in a wind tunnel. The main problem here is that Tiangong-1’s shape is complex, and the object is uncontrolled and tumbling chaotically, resulting in a constantly changing airflow.

The other unknown is the density of the atmosphere, which decreases with altitude. However, particularly at high altitudes, this varies due to a number of unpredictable factors – the most important of which is solar activity.

Another important factor is that the satellite will disintegrate and burn during the final phases of reentry, adding further uncertainty to all terms of the drag formula.

One thing is certain – there will be plenty of coverage of the burn online and on TV, and if any remnants crash the location is likely to be known and closely examined.