Friday, 24 October 2014
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Satellite, or salty chip?

The sky is full of junk. Over half a million bits of space debris less than 10cm in diameter currently orbit the Earth, their unpredictable movements causing daily worries for space traffic controllers trying to protect their expensive equipment.

So adding thousands if not millions of tiny microchip satellites to the mix might not seem like an obvious step forward. But for advocates of so-called ChipSats, this is the future of satellite technology and their size and high recurrence is their big appeal.

Complex satellites have been getting smaller for decades and the miniaturised CubeSat design (10cm in diameter and typically less than 1kg in weight) has brought the term pico-satellite into use.

However, the idea behind ChipSats is different. ‘It’s all a matter of designing from the bottom up, not trying to shrink a traditional design down to this size,’ says Dr Mason Peck of Cornell University, who’s about to trial the first circuit-board satellite technology in space.

Turning something very small into a satellite is a different challenge and requires new research into how these objects move in space, especially because the effects of phenomenon like solar radiation have a much greater impact than on larger objects.

And it’s these movements that could give ChipSats one of their key advantages and allow them to address the criticism that they will just add to the space debris, says Strathclyde University’s Professor Colin McInnes.

‘If we can balance air drag and pressure for sunlight, we can design them so the spacecraft stay in roughly stable orbits for a period of months or years and then very quickly decay and they’ll be removed so you don’t leave long-term debris.’

Their high surface-area-to-mass ratio and low ballistic coefficient means they would likely flutter down through the atmosphere rather than burn up at high speeds.

This could make them ideal for studying previously unreachable parts of the atmosphere or for dropping onto alien planets.

Millions of satellites falling out of the sky sounds a bit scary but Peck says if they hit anyone on the way down it would feel like a raindrop. And if they were made of a degradable material like salt then pollution would be limited to trace amounts of materials like gold and silicon.

Where there is no atmosphere, such as on the Moon, ChipSats would also rely on their size to play a role, but this time because you could afford to manufacture and launch so many of them.

You can’t land on the Moon without rockets and if these chips were dropped onto the surface they’d travel at the speed of a bullet and most would likely be destroyed.

‘But that’s where the large number principle comes in,’ says Peck. Say we had thousands, maybe millions of chips, I’m virtually certain that some would survive, maybe one in 1000.

‘Rather than building a single satellite that’s very reliable and costs billions of dollars, let’s use the statistics to ensure some fraction survive and accept that some won’t.’

The problem with ChipSats is it won’t be as simple as sticking a box of microchips onto a space shuttle and pushing them out the hatch.

Firstly, how do you deploy them so that they don’t damage each other on the way up and can be distributed evenly when in orbit? Peck says one idea could be to encase them in a gel or foam that would gradually degrade in UV light and drift into space.

Another problem is radiation. Physical shielding is one option but it adds to the weight, and building radiation hardening into their chemical design would make them expensive. So perhaps it could come back to relying on large numbers and accepting that some will be destroyed quickly while others survive.

But the immediate issue is integrating a solar array that can provide enough power, says Dr Tanya Vladimirova of the University of Surrey Space Centre, who has been conducting research on microchip and circuit board satellites for over a decade.

Peck says the answer comes back to the idea of designing from the bottom-up. ‘We have integrated 5.5mm squared solar cells that are roughly 28 per cent efficient into a new 3cm by 2cm prototype.

‘Even more mass-efficient efficient cells and energy storage are likely possible, and every few months someone comes up with an even lower-power IC that might be used to replace what we have baselined.’

Despite over fifteen years’ work in this field and some funding from the US Air Force and the EU, it’s still early days and the space agencies haven’t yet got behind the idea.

But with potential applications ranging from monitoring solar weather to studying the Earth’s magnetic field, perhaps we can hope this first experiment will lead to bigger and better things for this smallest of ideas.


Readers' comments (2)

  • Ok, you have your millions of ChipSats in space, all self powered by solar cells, with appropriate sensors for their task and data storage. How do you retrieve the data from them?

    I cannot see how you can either power or control wireless on this scale, so are you relying on members of the public posting them back to you when they flutter back to earth?

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  • If a flake of paint can take out a Shuttle window (if memory serves me right) then I'd be a bit wary about this.

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