Vital signs: the Disaster Monitoring Constellation

28 February 2011 | By Ellie Zolfagharifard

Last week, an urgent alarm was activated at the International Charter for Space and Major Disasters. A powerful 6.3-magnitude earthquake had hit Christchurch on New Zealand’s South Island, leaving 200 people missing and 98 dead as The Engineer went to press.

The charter, set up to provide emergency access to information from space, instantly triggered all available satellites to zoom in on the shattered city. What came back was detailed imagery of the area showing collapsed buildings and damaged infrastructure. Over the next few weeks, the satellites will continue to provide updated images to emergency teams on the ground. When compared with past maps of the affected area, these images could provide vital information on where to focus relief efforts.

’Without this ability, we really wouldn’t have been able to fully understand the consequences of a disaster,’ said David Williams, chief executive of the UK Space Agency. ’About 50 years ago, the information getting to the general public would have varied hugely, but today satellites are vital to planning fast and effective relief operations.’

The capability to image at such speed and scale is largely thanks to the Disaster Monitoring Constellation (DMC), founded in 2000 to record natural and man-made activities. Led by Surrey Satellite Technology (SSTL), the constellation is made up of six satellites co-funded by the UK, China, Algeria, Nigeria, Turkey and Spain. The satellites are small - about the size of a washing machine - but together they are capable of providing detailed daily images of any part of the world.

The satellites are about the size of a washing machine but are able to provide detailed images of any part of the world

Relief agencies have access to five per cent of the images during an emergency and can tap into them by contacting the Reuters Foundation’s Alert Net. The pictures are typically wide-area views collected over a 600km swath width. When superimposed onto aerial photographs, they provide valuable assistance to relief teams who would otherwise rely on more basic maps. According to SSTL chief executive Martin Sweeting, the DMC could make a detailed map the size of Europe in just five days.

’The key is that the international co-operation has been kept straightforward, and this is the absolute essence of its success,’ he said. ’While individuals can own one spacecraft, they can take advantage of all the satellites in the constellation to provide rapid re-visit applications - not only for disaster monitoring but for agriculture, environmental monitoring, pollution and climate change.’

For countries such as Nigeria, environmental monitoring and agriculture are significant reasons to be involved in the constellation. Dr Seidu Mohammed, director-general of Nigeria’s National Space Research and Development Agency, said that the DMC could help solve some of the country’s major issues. ’Some people ask why the developing world should get involved in a space programme,’ he said. ’I would say that it is absolutely vital. As well as disasters, it is helping us monitor our rural areas.’

“This is absolutely vital. As well as disasters, DMC is helping us monitor our rural areas.”

Seidu Mohammed, Nigerian Space Agency

The basic DMC structure uses the low-cost SSTL-100 microsatellite platform, designed with off-the-shelf components and compatible for batch launch on rockets such as Dnepr, Athena and Taurus. The DMC-2, which went into orbit in July 2009, carries two X-band transmitters that operate at 20 or 80Mbps, allowing it to download images up to 10 times faster than previous DMC spacecraft. Storage capacity has increased from 1 to 1.5GB on the first generation of satellites, with up to 12GB available.

But engineers at SSTL are hoping to go one better. Their plan is to dramatically improve the data-handling capacity of their satellites to provide rapid streaming of large amounts of information. SSTL has named the concept satellite Earthmapper; an ’always-on’ spacecraft that will image the entire sunlit landmass that enters its field of view. Because it can constantly observe a larger area, six Earthmappers would be able to provide 22m ground sampling of the entire landmass of the world every day, providing pre-emptive imaging of an area before a disaster happens.

To achieve this, engineers first need to expand the downlink data rate, onboard data storage and power generation. ’These improvements are now attainable,’ said Luis Gomes, SSTL’s head of Earth observation. ’The same technology that you use in your laptop to provide seven hours of lifetime can be put into satellites and we can use spectral bands to increase imaging resolution.’ Developing a synthetic-aperture radar (SAR) payload is one of Gomes’ goals over the next two years. Adding this capability to the constellation would overcome its inability to collect images due to cloud cover.

’That has its own problems,’ said Gomes. ’For years we were grappling with the difficulty of getting enough amplification. You need to get a lot of power onto the ground with SAR, but the efficiencies of amplifiers can be quite poor. The idea has always been to use transistors, but they were at the time limited in the amount of amplification they could achieve. Since 2006, high-power versions have started appearing in telecommunications and I believe we can make use of them in space.’

Both the Earthmapper and the SAR payload will need improvements in the way they handle and store data in order to be feasible. Flash memory systems, similar to those used in smart phones and cameras, are in development to provide larger amounts of storage that can be switched off when not in use. If an increase in power generation can also be achieved, engineers could double the data downlink rate from DMC-2’s 80Mbps to 160Mbps using more powerful X-band transmitters. Switching to a 105Mbps downlink is also being considered as an option.

Whatever solution is chosen, the next few years will be crucial in the development of the DMC. With six nations on board, many more countries are waiting in the wings to see how far the UK can push the capabilities of its satellites. The SSTL project has proven that a collaborative approach can outdo the efforts of singular space agencies. If it can continue its success, satellites in space will become even more crucial to our survival.