The March of TESS

The Transiting Exoplanet Serve Satellite (TESS) is slated on the launch from Earth, no earlier than mid-April 2018, from Cape Canaveral Air Force Station. From this amazing mission, we hope to find thousands or Earth-sized worlds.

Published by Tony Darnell on 2nd Mar, 2018

The Transiting Exoplanet Serve Satellite (TESS) is slated on the launch manifest of NASA and SpaceX to leave Earth no earlier than mid-April, from Cape Canaveral Air Force Station. This observatory’s small size hides the tremendous contribution it will make to the golden age of astronomy. The significance of finding 20,000 new exo-planets, 50 of which astronomers’ estimate will be Earth-sized cannot be understated.

Dr. Stephen Rinehart, TESS project scientist at NASA’s Goddard Space Flight Center. Explains why the data TESS will provide is so significant;

“The data TESS will gather will help us find new exoplanets around bright, nearby stars — these will be the best targets for future follow-up observations and will be important for the efforts to characterize and understand planets.”

Dr. Rinehart goes on to say

“In its two-year mission, TESS will search ~20 million stars for transiting exoplanets orbiting essentially every star brighter than 16th magnitude. The expected yield will be ~20,000 planets in the solar neighborhood. These planets—because of the brightness of their stellar hosts—will likely include the best candidates for follow-up characterization by all future exoplanet missions.”

The magnitude of an object like a star is a logarithmic measurement of its brightness. The brighter the object, the lower it is on the scale. This means TESS will look at stars that are as bright or brighter than Pluto’s moon Charon appears to us.

However, first TESS must get to its parking orbit. It will have to weather the fires of launch, the radiation of cislunar space and a delicate dance with the Moon.

Right now, TESS is getting ready to start its journey to Florida. Dr. George Ricker of MIT’s Kavli Institute for Astrophysics and Space Research said, “TESS is on schedule” and “The environmental testing is complete, and the TESS observatory is being prepared for shipment to Cape Canaveral in February.” Dr. Ricker is the TESS Principal Investigator, and the Kavli Institute is one of NASA’s primary partners on the mission, handling all the data from TESS.

After launch, TESS will take an interactive path to its parking orbit.
After launch, TESS will take an interactive path to its parking orbit.

The SpaceX Falcon 9 will sling TESS into a highly eccentric orbit where it will use the Moon’s gravity to whip it into its final operational orbit. The green represents TESS’s initial orbit, the blue its path represents TESS’s path after interacting with the moon and the red is TESS’s mission orbit.

The final orbit of TESS will be highly eccentric and inclined. After interacting with the Moon, TESS will be tilled 47 degrees from the ecliptic plane. Which is the line the sun draws in the sky. Also, for every two orbits the Moon makes, TESS will orbit the Earth once. When it is low, it will transfer its data to the Kavli Institute. As an idea for how much data there will be NASA planners looked at the Kepler and K2 missions. To house the data for those missions, the servers held 15 Petabits of Memory.

More than an amicable download point, TESS’s orbit provides a haven from oscillations that can accumulate over time in complex orbital systems. With the Earth and Moon pulling on the telescope the orbit could change drastically enough over the course of the mission to hamper observations. Work performed at the Goddard Space Flight Center mapped an orbit which TESS will traverse to mitigate this effect. Known as the Kozai mechanism, it explains the interactions between two objects with a third, in TESS’s case the Moon, giving the smaller object a destabilizing tug. With a 210 meter per second delta V sling from the Moon TESS will be placed into its orbit which will remain stable from these interactions well over its two-year mission time period.

The challenge, in the optical design for the camera, was to get as much as light as possible onto the detector focal plane, given the constraints on volume, weight and image performance: volume, because the four cameras have to fit in the diameter and depth available on the satellite’s camera platform, weight, to meet the overall budget for the satellite, and image performance, so that the light gathered from a star is concentrated on a small number of pixels. - NASA report Optical Design of the Camera for Transiting Exoplanet Survey Satellite (TESS)
The hybrid Petzval design presented here, with no vignetting, proved to have the best light gathering for the given volume and weight constraints.
James Webb Continuous Viewing Zone
James Webb Continuous Viewing Zone
TESS Viewing Zone
TESS Viewing Zone

All of this is in place to afford TESS one thing: A nearly month-long uninterrupted view of a 24-by-96- degree section of the sky. Dr. Ricker of MIT’s Kavli Institute puts it another way, “Extended unbroken observations of more than 300 hours per orbit, Earth/Moon stray light reduction [of] about 106 times less than low Earth orbit and no gravity gradient, which means excellent pointing stability. All of these factors combine to provide for a number of advantages for the survey mission.”

The data will yield new possibilities for both ground-based and future space-based observations. TESS’s survey of the stellar neighborhood and the bright stars in it will help ground based telescopes firmly categorize the makeup and locations of the exoplanets TESS discovers. The observation patterns will coincide with the James Webb Space Telescope’s viewing area.

TESS is meant to pave the way for detailed observations of the rocky exoplanets it finds and helps to answer fundamental questions about how common Earth-like planets are.

As its name implies, TESS finds traces of these worlds through the process of transit photometry. The detectors of TESS will sense the brightness of nearby dwarf stars, and if they dim at regular intervals, it could mean humanity found another planetary neighbor in our region of space.

The hunt for new worlds is on, and March is fast approaching. Soon our hopes for discovery will rest on the shoulders of a small telescope sent to space to map the sky. We indeed are on the shores of a cosmic ocean. What lies across it will only be found if we keep looking up.


The TESS Science Writer’s Guide
Trajectory Design for the Transiting Exoplanet Survey Satellite (TESS), Donald Dichmann, Joel Parker, Trevor Williams, Chad Mendelsohn

Optical Design of the Camera for Transiting Exoplanet Survey Satellite (TESS) Michael Chrisp, Kristin Clark, Brian Primeau, Michael Dalpiaz, Joseph Lennon
Lessons Learned from Developing and Operating the Kepler Science Pipeline and Building the TESS Science Pipeline; Jon M. Jenkins (2017)
Dr. Stephen Rinehart, TESS project scientist at NASA’s Goddard Space Flight Center.
Dr. George Ricker MIT Kavli Institute for Astrophysics and Space Research
Dr. Sara Seager TESS Deputy Science Director

Published by Tony Darnell

Tony Darnell Profile Picture

Tony Darnell is the creator of Deep Astronomy, LLC, a company dedicated to sharing the wonders of the universe and providing perspective of our place in the cosmos. For most of his life, Tony has been interested in science communication and education and has dedicated the best part of his life towards that interest. While embarked on that mission, for 30 years Tony has also worked as a software engineer and worked on writing code for telescopes, astronomy data pipelines, image processing and data analysis. His last gig was the goal of a lifetime: working on data from the Hubble Space Telescope.