Starshade would take his training by flying to the extreme

Anyone who has ever seen aircraft flying in formation can appreciate the fact of staying perfectly synchronized in flight. As part of the work sponsored by NASA's Exoplanet Exploration Program (ExEP), engineers from the Jet Propulsion Laboratory in Pasadena, California, are pushing flight training to a new extreme .

Their work marks a milestone in a larger program to test the feasibility of a technology called starshade. Although the starshades have never flown in space, they have the potential to allow groundbreaking observations of planets beyond our solar system, including images of planets as small as the Earth.

A future Starshade mission would involve two spaceships. One would be a space telescope looking for planets orbiting our solar system. The other spacecraft flew in front of him, at a distance of 40,000 kilometers, carrying a large flat shadow. The shadow would unfold like a blooming flower – complemented by "petals" – and block the light of a star, allowing the telescope to better see the planets in orbit.This would only work if the two spacecraft remained in place, despite the A great distance separates them, aligned within 1 meter (3 feet) of distance.Furthermore, the starlight would flow around the lampshade at the sight of the telescope and would overwhelm the weak exoplanets.

"The distances we're talking about for starshade technology are rather hard to imagine," said JPL engineer Michael Bottom. "If the star was reduced to the size of a drinking glass, the telescope would be about the size of an eraser and would be about 60 miles apart. [100 kilometers]. Now imagine that these two objects float freely in space. They both experience these small brainstorms and shots due to gravity and other forces, and on this distance, we try to keep them both perfectly aligned, at a distance of less than 10 feet. about 2 millimeters. "

The researchers discovered thousands of exoplanets without using starry shadows, but in most cases scientists have discovered these worlds indirectly. The transit method, for example, detects the presence of a planet when it passes in front of its parent star and causes a temporary drop in star brightness. Scientists have very rarely taken direct images of exoplanets.

It is essential to block starlight for more direct imaging and, possibly, to conduct in-depth studies of planetary atmospheres or to obtain insights into the surface features of rocky worlds. Such studies have the potential to reveal signs of life beyond the Earth for the first time.

Looking for shade

The idea of ​​using a space astrolargure to study exoplanets was originally proposed in the 1960s, four decades before the discovery of the first exoplanets. And while the ability to direct a single spacecraft to a distant object is not new, keeping two satellites aligned one towards the other towards a background object represents a different type of challenge.

Researchers working on the Starshade technology development of ExEP, known as the S5, have been tasked by NASA to develop Starshade technology for possible future space telescope missions. The S5 team attacked three technological gaps that would have to be filled before a Starshade mission was ready to go into space.

The work done by Bottom and his JPL engineer colleague, Thibault Flinois, corrects one of these shortcomings by confirming that engineers are able to realistically produce a sunshade mission that meets these strict requirements for "detection and detection". training control ". Their results are described in the S5 Milestone 4 report, available on the ExEP website.

Enter the training

The particularities of a given mission, including the exact distance between the two spacecraft and the size of the shadow, would depend on the size of the telescope. The S5 Milestone 4 report focused on a separation distance of 20,000 to 40,000 kilometers (12,500 to 25,000 miles) with a diameter of 26 meters (85 feet). These parameters would work for a mission the size of NASA's Wide Field Infrared Survey Telescope (WFIRST), a telescope with a 2.4-meter diameter primary mirror expected to be launched in the mid-2020s.

WFIRST will feature a different stellar light blocking technology, called a coronagraph, located inside the telescope and offering its own strengths in the study of exoplanets. This technological demonstration will be the first high-contrast stellar coronograph to go into space, allowing WFIRST to directly image giant exoplanets similar to Neptune and Jupiter.

The Starshade and Coronagraph technologies work separately, but Bottom has tested a technique by which WFIRST could detect the day a hypothetical starhade drifts subtly from its alignment. A small amount of stellar light would inevitably bend around the star's umbrella and form a bright, dark pattern at the front of the telescope. The telescope would see the motive with the help of a student camera, which can take a picture of the front of the telescope from the inside, which amounts to photographing a windshield of the camera. Inside a car.

Earlier investigations by starshade had considered this approach, but Bottom made it a reality by building a computer program that could recognize when the light and darkness pattern was centered on the telescope and when it was off-center. Bottom found that the technique worked extremely well to detect the motion of star shading.

"We can feel a change of stellar position from stars up to an inch even over these huge distances," said Bottom.

But detecting the alignment of the starry star is a totally different proposition from keeping it aligned. To this end, Flinois and his colleagues have developed a set of algorithms that use the information provided by Bottom's program to determine when star-shaker thrusters need to fire to put it back into position. The algorithms were created so that the star-star stays aligned autonomously on the telescope for days.

Combined with Bottom's work, this shows that it is possible to maintain the alignment of both spacecraft with the help of sensors and automated thruster controls. In fact, the work of Bottom and Flinois demonstrates that engineers can reasonably meet the alignment requirements of an even larger parashade (associated with a larger telescope), positioned more than 74,000 kilometers from the telescope.

"With such an unusually wide range of ranges involved here, it can be very counterintuitive as it's possible at first glance," said Flinois.

A starshade project has not yet been approved for the flight, but we could eventually join WFIRST in space in the late 2020s. Responding to flight requirements in training is just a step forward to demonstrate that the project is feasible.

"For me, it's a fine example of how space technology is becoming more and more amazing by building on its previous successes," said Phil Willems, head of Starshade's technology development activities. at NASA. "We use space training flights every time a capsule is docked at the International Space Station." But Michael and Thibault went well beyond that and showed a way to keep the training on track. scales larger than the Earth itself. "

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