Satellite-spotting in the Outback
A special sight for many visitors to Broken Hill is the “fast moving star” – the glint of light that seems to move amongst stars.
This is how many city people are introduced to satellites!
The skies above cities are too bright to detect these specks of light that become apparent when sunlight reflects to Earth from the satellite’s solar powerhouse.
Every now and again we see a bright flash. Wow! This gets even more attention.
These are also satellites, flashing back sunlight to us, possibly because they were manoeuvred into an improved orbit position by their Earth - based remote controllers, or perhaps they were tumbling for other reasons.
These artificial objects pervade our lives yet they’re still mysterious commodities.
When sighted for the first time with human eyes as they glide through the stars above, many folks are unaware they are satellites.
We hear “What’s that?” during most sky shows on dark evenings.
It is from this very low base of awareness that people view the night sky. Outback Astronomy helps to fill knowledge gaps for the busy person who is otherwise too distracted with life to bother with data that does not directly affect them. But if you are interested, people anywhere on Earth can track satellites overhead using an app or PC programme.
In Broken Hill on any given dark evening, using naked eyes alone, we’ll see many satellites overhead in just a relatively short time, if patient enough to look.
Understanding the stories behind satellites makes satellite-spotting even more interesting.
Recently, engineers in Sydney and Adelaide built three small satellites, about the size of a shoe box and weighing less than 2 kg.
These were the first Australian-built satellites in 15 years. They were launched from the International Space Station in May 2017.
Soon after launch the satellites were lost!
However, with some creative thinking, a few shout outs for assistance and some waiting time for things to happen, two satellites were found again.
All this within a month or so. The third satellite has not been communicated with. It has a short in-orbit lifetime of about three months and may already be lost.
These tiny satellites orbit Earth at nearly 30,000 km/hr, about 400 km high. Why were they put there?
They are part of a group of 50 or so small satellites taking measurements of the thermosphere, a large region that wraps about planet Earth from 90 km to perhaps 1,000 km. It is a part of our atmosphere with a very low air density and it’s often thought of as the place where space begins. One definition says space begins at 100 km altitude.
The thermosphere also hosts bigger and more expensive satellites to track weather and provide communication services. However, solar radiation can change the air density here. Engineers must account for this variability when calculating satellite orbits, eg satellites are manoeuvred into new positions to avoid orbit drag which may in turn cause a satellite flash!
Knowing more about the thermosphere is a really good idea since it shields us from dangerous space products like cosmic rays and intense UV and X-ray radiation from the Sun.
Being able to design, build and launch satellites like these mini-sats is also a good thing for Australia as it opens up new industry opportunities.
Let's hope this recent satellite work continues to evolve and grow into a new local industry. It is overdue. Australia should develop its own space industry!
Image: One of the small satellites made by UNSW, depicted as if in orbit. Source UNSW Engineering.