Reports from the United States last week highlighted the potential of stratospheric balloons to become part of the space in which the satellite industry operates. The Defense Advanced Research Projects Agency, known as DARPA, which is part of the Department of Defense is testing a balloon which floats above the same position on the Earth, in a similar manner to a geo-stationary satellite.
The obvious difficulty of maintaining a balloonâ€™s position in the stratosphere is the changes in wind speed and direction, the effects of which are of particular concern when trying to keep a balloon steady at altitudes of 23 – 28 km. The Adaptable Lighter-Than Air (ALTA) programme is testing wind sensors which can identify changes in wind speed and direction over long distances. The sensor being tested is called Strat-OAWL, or the Stratospheric Optical Autocovariance Wind LiDAR. The sensor works by sending out pulses of light through a laser, and gathers any reflected light via a telescope. From changes in wavelength of the reflected light, the sensor can calculate both wind speed and direction allowing the balloons to automatically adjust their altitude and maintain their position. Unlike other wind sensors, Strat-OAWL sends pulses of light in two directions at once, which when teamed with advances in machine learning, have allowed the balloon to have flights of up to three days, with longer ALTA test flights already planned
There is still a long way to go, but if successful these balloons could offer a cheaper alternative to launching satellites, and have the potential to be deployed relatively quickly in disaster areas. In addition to the other obvious military surveillance type applications, it is hoped that the balloons could also take passengers in the future.
Similarly, High-Altitude Pseudo-Satellite, also known as HAPS were on the agenda again at the European Space Agencyâ€™s Î¦-week in Friscati. HAPS are unmanned platforms â€“ airships, planes or balloons â€“ that float, or fly, in the stratosphere.
They operate best at around 20 km up where they can maintain their position over a specific area of interest for long periods of time â€“ it has been suggested that this could even be years. It is hoped that they can provide a link between data collection from drones and satellites.
Recognising this potential, ESA is working on a HAPS programme, while a number of prototype pseudo-satellites have already been successfully tested. In 2010, Airbus developed the Zephyr, achieving a continuous flight of 14 days and claiming the official endurance record for an unrefuelled, unmanned aerial vehicle flight. Continued development of this programme has produced the Zephyr-S, designed to accommodate small payloads of tens of kilograms, and the Zephyr-T for larger payloads. While Zephyr-T is still in development, in the summer of 2018, Zephyr-S took its maiden flight, remaining aloft for 25 days 23 hours 57 minutes, doubling its predecessorâ€™s record. Away from Airbus, Thales Alenia Space is meanwhile preparing the lighter-than-air Stratobus, which will be able to carry payloads of 250 kg and is expected to launch in 2021. Stratobus is being designed to carry both radar and optical imaging technologies, allowing for day, night and all weather observations, ideal for Earth Observation applications. Itâ€™s anticipated that operational services could occur in the early part of the next decade.
HAPS could offer a relatively low cost solution compared to satellites, with potential applications include the normal Earth Observation data collection and environmental monitoring; offer telecommunication services in remote or difficult to reach places; surveillance; rapid deployment to support disaster relief or supporting security at major events, such as the Olympics, by providing a secure communications.
It will be interesting to see how these new technologies will develop over the coming years and what new potential they offer.