Apparently NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, thinks that what space exploration in the 21st century needs is spacecraft that are a bit more botanical. The center has released a video showing off its starshade spacecraft that opens up like a blossom. Bearing a resemblance to a cosmic sunflower, it’s designed to help astronomers to directly study exoplanets, including taking the first actual pictures of planets beyond our Solar System.
It was over 15 years ago that the first exoplanets were discovered and in five years the Kepler space telescope alone discovered 961 new planets. The problem is, almost everything we know about these planets came indirectly. The basic method for finding planets orbiting stars other than our Sun is known as the transit method.
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This involves observing the light coming from a star over a period of time and waiting for the brightness to dip, thereby indicating that a planet passed in front of the star. That can tell you a lot about a planet, such as its orbit, its size, and other things, but at some point, you need to look directly at the planet if you want to learn if that Earth-like planet really is like Earth.
The problem is that looking at an exoplanet directly is like trying to study a fly sitting on top of a floodlight. The light emitted by the star easily swamps the reflected light of any planets orbiting it by a factor of a billion to one, particularly for small, Earth-like planets. Therefore, in order to learn more about the planets, it’s necessary to do something about all that starlight.
The starshade’s function is to act as a shield to block out starlight so astronomers can get a look at any planets in its vicinity. The principle is the same as that of a solar eclipse when the Moon blocks the light of the Sun, allowing stars that normally wouldn’t be visible in the daytime to be seen.
In its current design, the starshade is closed up like a flower bud and bundled in a payload fairing with a space telescope for launch. After orbit insertion, the starshade and the telescope separate and the shade unfolds into a disk with petals on the rim. The petals are not aesthetic, they are a key to the shade working effectively by keeping light from bending around the edges of the disc.
"The shape of the petals, when seen from far away, creates a softer edge that causes less bending of light waves," says Dr. Stuart Shaklan, JPL’s lead engineer on the Starshade project. "Less light bending means that the starshade shadow is very dark, so the telescope can take images of the planets without being overwhelmed by starlight.”
The shade is equipped with thrusters, allowing it to maneuver independently of the telescope. The space telescope and the starshade move in formation to line up on any desired star. By blocking the light of the star, the telescope can look directly at its planets with enough clarity to take pictures of them, as well as perform spectroscopic analysis of their atmospheres with an eye toward seeing if any of the planets are habitable.
“One of the starshade’s strengths is simplicity,” says Professor Jeremy Kasdin, Principal Investigator of the starshade project. “Light from the star never reaches the telescope because it’s blocked by the starshade, which allows the telescope system to be simpler.”
The starshade is now undergoing testing at Princeton University, where a small-scale version is under construction to test the light-blocking design against computer models. Meanwhile, a near-full scale version is being tested at JPL to make sure its able to deploy its petals with the necessary millimeter accuracy.
The video below shows how the starshade works.