Spaceflight Insider

Exoplanet-hunting TESS spacecraft ready for launch

Transiting Exoplanet Survey Satellite TESS photo credit Michael Howard / SpaceFlight Insider

NASA’s Transiting Exoplanet Survey Spacecraft (TESS) during a recent event at NASA’s Kennedy Space Center in Florida. Photo Credit: Michael Howard / SpaceFlight Insider

CAPE CANAVERAL, Fla. — NASA and SpaceX are set to launch the Transiting Exoplanet Survey Satellite (TESS) atop a Falcon 9 rocket. If everything goes according to plan, the observatory will conduct a two-year mission to survey more than 85 percent of the sky, searching for exoplanets around bright stars in the 300-light-year distance range.

TESS will be launched at 6:32 p.m. EDT (22:32 GMT) April 16, 2018, from Cape Canaveral Air Force Station’s Space Launch Complex 40. According to the 45th Space Wing, which manages the Eastern Range, there is currently an 80 percent chance of acceptable weather conditions during the 30-second launch window. The primary concerns for weather violation are high liftoff winds. Should the mission be postponed 24 hours, conditions are expected to improve to greater than 90 percent.

Artist's depiction of NASA's TESS spacecraft. Image Credit: NASA

Artist’s depiction of NASA’s TESS spacecraft. Image Credit: NASA

The 772-pound (350-kilogram) spacecraft is not very big. It measures about 4.9 feet (1.5 meters) tall and is 3.9 feet (1.2 meters) wide. With its solar panels deployed, its wingspan comes to about 12.8 feet (3.9 meters). With its four wide-angle telescopes, it will orbit high above Earth in a 2:1 lunar resonance orbit, meaning it will orbit the planet twice for every time the Moon orbits once. According to NASA, this orbit should remain stable for decades. 

Finding transiting exoplanets

Stars in the 300-light-year range are targeted for the survey, because brighter, closer stars lend themselves as better candidates for follow-up studies by ground-based observatories and, later, space-based telescopes such as Hubble or the James Webb Space Telescope (JWST) scheduled for launch in 2020. TESS will observe exoplanets by measuring the dip in a star’s light emission as a planet passes in front of, or transits, the star from Earth’s observational perspective.

TESS is following in the astrophysics “footsteps” of the Kepler Space Telescope, which gazed at a fixed spot in the constellations Cygnus and Lyra, and continually monitored main sequence stars out to a distance of 3,000 light-years. A “light-year” is the distance light travels in a single year—about 5.88 trillion miles (9.46 trillion kilometers). According to NASA, in many ways TESS is a bridge between Kepler and the JWST.  
“TESS is an Explorer mission,” TESS Principal Investigator George Ricker told the members of the media during a March 28, 2018, event at NASA Headquarters in Washington, D.C.
Ricker heads the mission from the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research (MKI), where his team has been working on the mission since 2006.
“There’s a huge discovery space that’s going to be opened up for the first time by TESS,” Ricker said. “Kepler looked at about a quarter of a percent of the sky. And that means that the discovery space is there for the other 99.75 percent of the sky. So I think that is the real promise that TESS actually has.”
The flight path from its initial insertion orbit to its final 2:1 lunar resonance orbit. Image Credit: NASA

The flight path from its initial insertion orbit to its final 2:1 lunar resonance orbit. Image Credit: NASA

TESS will conduct its survey with four cameras, each with a charge-coupled device (CCD) image sensor. The cameras aimed in such a way that they will observe a tiled vertical stack of the sky from the ecliptic to the celestial pole. The cameras will observe one such sector of the sky for 27 days before pivoting to the next of 13 observation sectors in each hemisphere, for a total of 26 sectors. The spacecraft will observe the southern hemisphere during its first year and the northern hemisphere during its second.

The CCD cameras at the heart of TESS were specially developed at MKI, and are definitely not the garden variety CCD of a backyard astronomer.
An example of one of TESS's camera lenses. Photo Credit: Jim Siegel / SpaceFlight Insider

An example of one of TESS’s camera lenses. Photo Credit: Jim Siegel / SpaceFlight Insider

“Those of an amateur astronomer are on the order of 2 or 3 microns thickness typically,” Ricker told Spaceflight Insider. “The TESS CCDs are 100 microns thick and that’s how we are able to get out into the near infrared and actually see the peak of the emission that occurs from the cool stars that TESS is going to be optimized for. The other difference is that these CCDs have very low noise. We’re able to push the noise down a factor of 10 below what Kepler actually had with the electronics that were available at the time that they were developing their instrument. And also the pixels are quite large on the wafers that we used.”

TESS will travel in a unique, highly inclined Earth orbit that is in a 2:1 resonance with the Moon. This 13.7-day “Goldilocks orbit” will keep the spacecraft in a safe thermal and radiation environment ideal for the sensitive transiting observations it is designed to make. Among these observations, the TESS team must learn to weed out some kinds of data that only masquerades as an exoplanet transit
“We monitor stars long enough to observe at least two dips in brightness so we can attribute that to a single planet,” said TESS Deputy Science Director Sara Seager. “We have actually been training a small team of people to work on simulated data that includes binary stars and instrument artifacts and other things that we would need to be able to recognize are not planet candidates. And we use humans and computers to look at the light curves and other data products to practice finding the very best planet candidates for further study. And that’s what we’ll be doing as soon as we get the real data.”
TESS will monitor the brightness of more than 200,000 stars, and is expected to catalog more than 1,500 exoplanet candidates. This will include a likely sample of at least 500 Earth-sized or “Super-Earth” planets nearly twice the size of Earth. It will be capable of detecting small rock-and-ice planets orbiting a diverse range of stellar types with a wide variety of orbital periods.
“TESS is helping us explore our place in the universe,” said Paul Hertz, Director of the Astrophysics Division at NASA Headquarters. “People have always wanted to know, ‘are we alone in the Universe?’ Well up until 20 years ago we didn’t know of any planets beyond our own solar system. Now we know that around nearly every star you look at in the sky, there’s probably a family of planets around it and most of them probably have rocky planets in the habitable zone. So we’ve expanded our understanding of our place in the Universe. Missions like TESS will help us keep learning so that eventually we can answer the question: ‘Are we alone? Or do we just have the best prime real estate in the galaxy?'”

Video courtesy of NASA 


Michael Cole is a life-long space flight enthusiast and author of some 36 educational books on space flight and astronomy for Enslow Publishers. He lives in Findlay, Ohio, not far from Neil Armstrong’s birthplace of Wapakoneta. His interest in space, and his background in journalism and public relations suit him for his focus on research and development activities at NASA Glenn Research Center, and its Plum Brook Station testing facility, both in northeastern Ohio. Cole reached out to SpaceFlight Insider and asked to join SFI as the first member of the organization’s “Team Glenn.”

Reader Comments

TESS is a worthless derivative mission cooked up by dumbasses at MIT. We should instead invest in designing, building, and testing interstellar spaceships, i.e. Elon Musk. TESS in a nosecone might have helped to aim an interstellar vehicle, but we already know the planets are out there, so we should just go, the sooner the better.

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