Beyond our solar system, there are more than 3,900 confirmed planets. Most of them were discovered due to their "transits" – cases in which a planet crosses its star and blocks its light for a moment. These burglaries in the starlight can tell astronomers about the size and distance of a planet to its star.
To learn more about the planet, including whether it contains oxygen, water, and other vital signs, far more powerful tools are needed. Ideally, these would be much larger telescopes in space, with light levels as wide as those of the largest ground observatories. NASA engineers are currently developing designs for such next-generation space telescopes, including "segmented" telescopes with multiple small mirrors that could be assembled or rolled up into a very large telescope once it was launched into space.
NASA's upcoming James Webb Space Telescope is an example of a segmented main mirror with a diameter of 6.5 meters and 1
A challenge for segmented space telescopes is to keep the mirror segments stable and together aim at an exoplanet system. Such telescopes would be equipped with coronagraphs – instruments that are sensitive enough to distinguish between the light emitted by a star and the much weaker light of a orbiting planet. However, the slightest shift in any part of the telescope could affect the measurements of a coronagraph and interfere with measurements of oxygen, water or other planetary features.
Now, MIT engineers suggest that a second spaceship the size of a shoebox equipped with a simple laser could do so at a distance from the large space telescope and act as a "guiding star". They provide a uniform, bright light near the target system that the telescope could use as a reference point in space to keep itself stable.
In a paper The researchers published today in the Astronomical Journal show that the design of such a laser guide star is possible with today's technology. The researchers say that using the second spacecraft's laser light to stabilize the system loosens the need for precision in a large segmented telescope, saves time and money, and allows for more flexible telescope designs.
"This paper suggests that in the future we might be able to build a telescope that is a bit more floppy and less intrinsically stable, but it could serve as a reference source to maintain its stability," says Ewan Douglas, Postdoc in the Department of Aerospace of the MIT one main author on the paper.
The paper also includes Kerri Cahoy, Associate Professor of Aerospace at MIT, and students James Clark and Weston Marlow at MIT and Jared Males, Olivier Guyon and Jennifer Lumbres from the University of Arizona.
In the Crosshair
For over a century, astronomers have been using star stars as "guides" to stabilize groundscopes.  "If imperfections in the telescopic motor or gears cause your telescope to be tracked a little faster or slower, you could use a crosshair to observe your guide star with the eye and slowly center it while taking a long exposure," says Douglas ,
In the 1990s, scientists began to use lasers as artificial guide stars on the ground by exciting sodium in the upper atmosphere and directing the lasers into the sky to create a spot of light about 40 miles from the ground. Astronomers could then stabilize a telescope with this light source, which could be generated wherever the astronomer wanted to align the telescope.
"Now we are broadening this idea, but instead of directing a laser from the ground into space, we are" "It seems from space to a telescope in space," says Douglas to counteract atmospheric influences, but space telescopes for exoplanet imaging have to counteract minute changes in system temperature and possible movement disorders.
The idea of a space-based laser guide star came from a project that was already funded by NASA Considering segmented telescopes in space, researchers are tasking them with finding ways to reduce the cost of huge observatories. "The reason is that NASA has to choose the next pair will be a priority for the next decades, "says Douglas is now happening, as well as decision-making for the Hubble Space Telescope in the 1960s, but it was not started until the 1990s. "
Star Fleet  Cahoys laboratory has developed laser communications for CubeSats. These are shoebox-sized satellites that can be launched into space at a fraction of the cost of conventional spacecraft.
For this new study, researchers investigated whether a laser integrated into a CubeSat or a slightly larger SmallSat could be used to maintain the stability of a large, segmented space telescope modeled on NASA's LUVOIR (for Large UV Optical Infrared Surveyor) was modeled. This concept includes multiple mirrors to be assembled in space.
Researchers have estimated that such a telescope would need to remain completely still within 10 picometres – about one quarter of the diameter of a hydrogen atom – so that a coronagraph on board could be accurately taken measurements of a planet's light, except for its star.
"Any disturbance of the spacecraft, such as a slight change in the angle of the sun or an electronic element that turns on and off and alters the heat radiation. The spacecraft will cause a slight expansion or contraction of the structure," says Douglas. "If you get perturbations larger than about 10 picometers, you will see a change in the pattern of the starlight in the telescope, and as a result of these changes you can not subtract the starlight perfectly to see the reflected light of the planet."
The team developed a general design for a laser guide star that was far enough away from a telescope to be considered a solid star – tens of thousands of miles away – and that would point to the back and its light in Direction of the sky send telescopic mirrors, each of which would reflect the laser light towards a camera on board. This camera would measure the phase of this reflected light over time. Any change of 10 picometers or more would compromise the stability of the telescope, which could then be quickly corrected by on-board actuators.
Douglas and Cahoy Collaborate with Colleagues To see whether such a laser guide star design is feasible with today's laser technology. At the University of Arizona, various sources of brightness are to be found, for example, to find out how bright a laser should be to produce a particular laser To provide quantity of information about the position of a telescope or to ensure stability using large scale models of segment stability. They then designed a series of existing laser transmitters and calculated how stable, strong and far from each telescope each laser must be to act as a reliable guide-star.
In general, they found that laser beacon designs are feasible with existing technologies, and the system could fit completely into a SmallSat about the size of a cubic foot. Douglas says that a single beacon could possibly track the "gaze" of a telescope as it travels from star to star as the telescope changes its observation targets. However, this would require the smaller spacecraft to travel hundreds of thousands of miles away with the telescope because the telescope repositions itself to look at different stars. Instead, Douglas says that a small guide star fleet could be deployed cost-effectively and spread across the sky to stabilize a telescope when surveying multiple exoplanetary systems. Cahoy points out that the recent success of NASA's Marcos CubeSats, who supported the Mars Insight Lander as a communication relay, proves that CubeSats can operate with propulsion systems in interplanetary space for extended periods of time and over long distances.
We analyze existing propulsion systems and find out how this is optimal and how many space probes we want to skip in space, "says Douglas." Ultimately, we believe that this is one way to lower the cost of these large, segmented space telescopes . "