Aligning spacecraft: Virtual telescopes

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  • Published: Nov 1, 2014
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Aligning spacecraft: Virtual telescopes

Stars aren't aligned

Semper (left), Calhoun, and Shah are advancing the technologies needed to create a virtual telescope that they plan to demonstrate on two CubeSats. Image Credit: NASA/W. Hrybyk

Aligning two spacecraft to focus on a single astronomical target creates a single or "virtual" telescope and paves the way for extreme ultraviolet imaging of the Sun and X-ray imaging of solar flares, according to research by NASA scientists.

A team led by aerospace engineer Neerav Shah of NASA's Goddard Space Flight Center in Greenbelt, Maryland is developing the guidance, navigation, and control technology necessary to bring two CubeSats into concert so that these tiny satellites can be used to create a high-resolution solar coronagraph. Such an instrument might then be used to observe our nearest star's outermost plasma layer, the corona, where powerful eruptions called coronal mass ejections take form. The phenomenon, while of intrinsic scientific interest to those studying stars also has implications for telecommunications, power supply and other systems that can be disrupted by these enormous and energetic outpourings.

The same skills acquired in aligning these two satellites for solar observations might also be useful in experiments using dual spacecraft to detect Earth-like planets beyond our solar systems and even to image activity close to the event horizon of a black hole. "Many virtual-telescope mission concepts have been conceived and proposed," explains Shah. "One of the main reasons they are not selected for funding is because the systems-level capability to align two spacecraft to an inertial source isn't mature enough for projects to take the risk. Now is the time to advance the technology's readiness so that we can confidently propose and win these types of missions, which, I believe, will revolutionize astrophysics and heliophysics."

Low-cost and virtual

With support from Goddard's Internal Research and Development (IRAD) program, the team hopes to develop and test a prototype system, the Virtual Telescope Alignment System (VTAS). Ultimately, however, they hope to successfully demonstrate VTAS on two CubeSats, relatively low-cost platforms after which the techniques and technology would be ready for use with a dual-spacecraft mission.

The proposal would be to launch both tiny satellites into a high low-Earth orbit. One spacecraft would be equipped with a communication crosslink, thrusters, software, and an occulter to block the main disc of the Sun so that the fainter corona can be seen. The second spacecraft would be positioned 20 metres behind the first and carry the coronagraph, a laser beacon, and communications equipment. Aligned towards the sun, this virtual telescope could study the corona at high resolution and so give us new insights into solar eruptions that cause severe space-weather events.

Magnitude

Shah is working with Joe Davila, a senior scientist in Goddard's Heliophysics Science Division and principal investigator on an instrument flying on NASA's Solar Terrestrial Relations Observatory (STEREO), and Phil Calhoun, a Goddard senior aerospace engineer, who conceived the solar-coronagraph mission. The solar coronagraph will be easier to demonstrate than an exo-planet mission although the technology and techniques will be almost identical with the occulter mask blocking starlight in the latter. It is all about resolution, where imaging the sun's corona is three orders of magnitude less demanding than observing exo-planets which requires milli-arcsecond precision.

Enabling the solar coronagraph paves the way for the more demanding missions," such as X-ray imaging of solar flares and extreme ultraviolet imaging of the sun, Shah adds. "Once you fly a virtual telescope with looser formation requirements, you open up the space for others to follow and improve on the accuracy.

Related Links

NASA Technology, 2014, online: "Featured Technologies"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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