EXPReS: Development of Earth-Sized Telescope Furthers Grid Computing

EXPReS (Express Production Real-time e-VLBI Service) is an FP6 funded project that aims to improve what astronomers can “see” using a radio astronomical technique called “electronic very long baseline interferometry” (e-VLBI). e-VLBI observations rely on a global network of radio telescopes. The telescopes gather information about celestial objects and send the data in real time over fiber optic networks to the “correlator”, a purpose-built supercomputer operated by the Joint Institute for VLBI in Europe (JIVE; www.jive.nl/) in the Netherlands. Connecting the telescopes in this way creates a virtual telescope of continental dimensions, almost 11,000 kilometers in diameter. The correlator processes the data and produces information used to create an image of the object observed. In this way, by transferring data electronically and correlating it in real-time, weeks of waiting can be eliminated: the old method required posting boxes of hard disks to the correlator.

Enabling new science: supernova flares
e-VLBI is more than just a way to bypass the “snail mail” postal system; it also enables new types of science. For example, EXPReS has developed tools that support rapid response observations, such as those involved in short duration events like supernova flares. Historically a supernova flare could only be observed long after it had occurred. This was due to the time required to ensure an observing telescope was pointing in the correct direction: the telescope had to record data, send it to the correlator, and an astronomer needed to analyse the data to determine if redirection was necessary. If the time cycle between observation and analysis was weeks, then a short-lived event could not be seen. However, since e-VLBI’s real-time data transfer and analysis provides immediate feedback, astronomers can now dynamically adjust telescope observations, allowing telescopes to respond quickly and see the most interesting, early stages of short-lived events. 

1024 Mbps: why bother?
Over the course of EXPReS, operational e-VLBI has improved from 128 Mbps to 1024 Mbps (just a bit faster than a gigabit per second). Achieving 1024 Mbps means that e-VLBI now performs at the same speed as the older disk-based system. So why bother with the effort to move from disk to network? Because the foundational network infrastructure improves over time, and the tools we build now will easily evolve to to take advantage of the improved infrastructure. And although the old disk-based systems will also evolve, the costs and benefits are not shared, since the equipment is not shared across different research communities or geographies. Attentive readers will immediately wonder: what of your “purpose-built” correlator? How can it benefit from e-Infrastructures? EXPReS is now researching how this correlation could be conducted on distributed computer systems. The final product will rely on network, computational and storage infrastructures that are being developed both by EXPReS and other projects.

Looking to the future
Without the rich mesh of existing continental and international networks, e-VLBI would not be possible. Looking to the future, as e-Infrastructures continue to develop, faster network connections will allow more telescope data to be sent to the correlator, which will allow more detail in observed objects. For this to be possible, the correlator must then run more calculations, which in turn will increase the load on computing infrastructure, exposing the limits of our current systems. EXPReS is confident that the future of astronomy will continue to rely on and benefit from the shared e-Infrastructures being developed around Europe.