Stratospheric setback

NASA’s attempts to develop a solar and fuel cell-powered stratospheric communications platform suffered a setback this week, after engineers were unable to switch on back-up power during a test flight.

Using airships or fixed-wing aircraft to carry transponders to broadcast mobile, TV, digital radio and internet signals could do away with the need to build unsightly masts whose effects on public health are still being debated.

Following a 15-hour flight Helios, the remotely piloted electrically powered aircraft, landed earlier than planned after recording anomalies with its fuel cell system. This was to have been Helios’s first flight using fuel cell technology, but according to project manager John Del Frate from California’s Dryden Flight Research Centre the fuel cell was not brought online.

Helios uses wing-mounted solar panels to power its 10 electric motors for take-off and during daylight portions of its planned flight. At night it should switch to a proton membrane exchange fuel cell using gaseous hydrogen from on-board tanks and atmospheric oxygen to generate 15kW of power.

The eventual aim is for Helios to fly slow, fairly stationary orbits at 65,000ft in the next step towards stratospheric communication relays that will stay aloft for months. In July the aircraft is scheduled to fly for just under two days, 50,000ft above Hawaii, though more work to correct problems will be needed.

The aircraft is one of several High Altitude Platform Station (HAPS) systems under development. ‘Such systems have an advantage over satellite systems as these are very expensive to deploy and must be useful for a long time,’ said Ian Rose, technical area leader for satellite systems at BT Exact. ‘Upgrading satellites is difficult.’

Helios’s competition includes Anglo-Russian company Geoscan, which offers mast-free communications coverage using Russian- made M-55 stratospheric aircraft. The aircraft act as a base station by flying in a circular corridor 20km above the Earth, creating a cone of high-speed wireless communications over an area up to 400km in diameter. A relay of four or five planes ensures constant coverage, while the system can be deployed at very short notice following natural disasters. Geoscan is operational and ready for deployment, and the firm questioned whether NASA’s 15kW system would be sufficient for future applications.

‘Other developers want to use solar power to provide the energy to maintain airship positions and broadcast signals,’ said Hemant Patel, managing director of Geoscan’s UK office. ‘However, solar technology is not very well developed and so is not efficient. Our aircraft can easily remain in a set corridor. We offer 40kW of power, which is more than enough for communications needs.’

The Bedford-based Advanced Technologies Group is developing an airship design with a similar power capacity to Geoscan’s system. It is powered by solar panels and a back-up diesel engine and is designed to stay in place for up to five years. Systems are being readied for deployment in Malaysia and Japan, where they will be used for communications and possibly surveillance activity. A prototype is due next year.