Challenges and triumphs mark TESS’ first year on orbit

Joe Latrell

NASA’S Transiting Exoplanet Survey Satellite (TESS) recently celebrated one year of operational status with the discovery of one of the smallest exoplanets found to date. For those working on the project, its discoveries are just a small part of the mission’s success.

So far TESS has discovered hundreds of potential exoplanets within the skies above Earth’s Southern hemisphere. Additionally, the space telescope has confirmed the existence of twenty exoplanets. TESS’ “eyes” have now been turned toward the Northern hemisphere. Mission managers have focused the spacecraft’s instruments in a hyper-tight manner.

“The attitude on TESS is just exquisite, that’s what our Principal Investigator George Ricker calls it. We had a level one science requirement to slow down to what that pointing of the spacecraft should be (toward target stars). Pointing is a combination of using the instrument cameras and our attitude control system,” Robert Lockwood TESS’s Program Manager told SpaceFlight Insider. “When we are collecting science data, we only care where the instrument cameras are pointed.. The stability on the one hour time scale is an important time scale for detecting planetary transits. It’s 20 milliarcseconds. That’s a thousandth of the size of one pixel. It’s unbelievable it’s wildly beyond what I thought we could get and it’s just fantastic. To me, in terms of technical performance, that’s the most exciting thing on the vehicle.”

Just before the anniversary, the TESS mission team announced that TESS had discovered the tiniest exoplanet discovered so far. That planet, called L 98-59b has been estimated to be about 80 percent the size of Earth. It orbits around an M dwarf class host star (L 98-59). This star is no titan itself, measuring only one-third the mass of our Sun. L 98-59 is about 35 light-years away.

The TESS telescope uses four wide-field cameras to scan nearly the entire sky. The primary objective of the mission is to look for planets ranging from the size of Jupiter down to those about the size of Earth. It has the capability of looking for planets orbiting stars of different types and at varying distances from their parent star.

“The TESS observatory is exceeding expectations after just one year scanning the skies,” said Steve Krein, vice president, civil and commercial satellites, Northrop Grumman.

Northrop Grumman not only designed and built TESS but the company also handles mission operations for the observatory. Before the satellite was deemed operational it performed a series of maneuvers, including a high gravity assist flyby of the Moon, to place it into its final orbital position in high-Earth orbit. These maneuvers were completed on May 29, 2018.

As is the case with many satellites and spacecraft, TESS is based of an existing “bus.” In this case, that platform is Northrop Grumman’s LEOStar-2. This design has been used on a diverse array of spacecraft including the Landsat-9 and the JPSS-2, -3 and -4 weather satellites.

While the telescope might have been based off a familiar design, certain aspects of that design had to be altered to accommodate NASA’s requirements.

“We’ve built spacecraft based on the LEOStar-2 bus several times, but for this mission we added a ka band science mission transmitter, this ka band is a particular band NASA wants to use more of in the future. There are a couple of ka bands, there’s the 32 gigahertz ka band that a lot of people use on various missions. TESS uses a 26 gigahertz ka band. This is a band that the Deep Space Network is using and NASA wants folks to use it,” Lockwood said. “There were a handful of missions that used it before, like three or four, but none of them used it at the data rate we needed. We’re running at 109 megabits per second and this was the first time that DSN used ka band at 109 megabits per second. Working through that, with DSN and getting it fully tested out, just working out all of the bugs, working it through the ground processing and making sure the radio was compatible, all that, I think, was the most challenging technical item for us.”

TESS was launched on April 18, 2018 atop a Block 4 Falcon 9 rocket (B1045.1) from Cape Canaveral Air Force Station’s Space Launch Complex 40 in Florida. The telescope was declared operational and ready for science on July 16, 2018.

Video courtesy of SpaceFlight Insider