Monday, May 14, 2018

Thruster Firings Boost Healthy TESS Planet Hunter over Halfway to Final Science Orbit Prior to Critical May 17 Lunar Flyby: Interview

Artist’s concept of NASA’s Orbital ATK-built Transiting Exoplanet Survey Satellite (TESS) planet hunting satellite orbiting the Earth-Moon system. Credit: NASA/Orbital ATK
Ken Kremer  --  --   13 May 2018

KENNEDY SPACE CENTER, FL – NASA’s recently launched TESS planet hunting probe is healthy, operating very well, and more than halfway through the demanding regimen of on board thruster firings required to carry out the preplanned series of six orbit raising maneuvers setting up this weeks do or die Lunar Flyby trajectory adjustment on May 17 – absolutely critical to reaching its intended science perch, Orbital ATK TESS program manager Robert Lockwood told in an interview.
The goal of TESS is to carry out an all sky survey and discover dozens of new Earth and Super Earth sized exoplanets beyond our Solar System that may be capable of supporting life, and possibly answer one of humanities most profound questions – “Are We Alone?”

“Everything is as expected with the spacecraft systems,” Orbital ATK TESS program manager Robert Lockwood told in an exclusive interview.   Lockwood is based at the TESS mission operations center at Orbital ATK headquarters in Dulles, VA. 
“We are all green. We have done four of the six [orbit raising and adjustment] thruster firing maneuvers.” 
Then we have the flyby of the Moon on Wednesday night /early Thursday May 17 … that will change the orbit significantly ..  and get in position    … to do a period adjustment to get into the special ‘goldilocks’ orbit - the P/2 lunar resonant orbit.”
P/2 is the name of the TESS missions final science orbit. 
The lunar flyby takes place at 06:31:52.180 UTC on 17 May 2018 at a distance of approximately 8000 kilometers altitude above the surface.
“We are very excited about the lunar flyby!” gushed Lockwood.

NASA’s TESS Exoplanet hunter being processed by technicians inside the Payload Hazardous Servicing Facility clean room on Feb 20, 2018 at the Kennedy Space Center.  Launch on SpaceX Falcon 9 occurred on April 18, 2018. Credit: Ken Kremer/
The $240 million spacecraft was built by prime contractor Orbital ATK.
TESS is NASA’s second exoplanet mission and a follow up to the hugely successful Kepler probe which discovered over 2300 exoplanets of all sizes. 

The TESS spacecraft systems are in excellent health and the engineering and science teams are diligently working through the middle of the commissioning phase activities. 
“Everything is clicking off per planned so far in the commissioning timeline,” Lockwood told me. 
“The science phase will begin on June 12!”
The kitchen table sized probe weighs 770 pounds (350 g) and measures 12 x 4 x 5 ft (3.7 x 1.2 x 1.5 m).

Roughly 1 month after the beautiful sunset blastoff to space from the Florida Space Coast on April 18 aboard a SpaceX Falcon 9 rocket NASA’s newest exoplanet hunting spacecraft is in fine shape and on course to achieve its very special mission enabling P/2 lunar resonant orbit. 

NASA’s next planet-hunter, the Transiting Exoplanet Survey Satellite (TESS), successfully launched on a SpaceX Falcon 9 rocket on April 18, 2018 from Space Launch Complex-40 on Cape Canaveral Air Force Station, FL - in this view from a pad camera. TESS will search for new worlds outside our solar system for further study.   Credit: Ken Kremer/
The Transiting Exoplanet Survey Satellite (TESS) successfully blasted off on a two stage SpaceX Falcon 9 rocket at 6:51 p.m. EDT, April 18, from seaside Space Launch Complex-40 on Cape Canaveral Air Force Station, Florida.

After liftoff TESS uses six thruster burns to travel in a series of progressively elongated orbits to reach the Moon - which will provide a gravitational assist so that TESS can transfer into its 13.7-day P/2 lunar resonant final science orbit – a highly elliptical orbit around Earth.

Graphic of NASA’s Transiting Exoplanet Survey Satellite orbit raising maneuvers. Credit: NASA
After approximately 60 days of check-out and instrument testing, the spacecraft will begin its important work.

What is the current spacecraft status?

“We are all green. We finished all spacecraft checkouts at L plus 5 days after launch,” Lockwood explained.
Describe the spacecraft checkout? Is everything going as planned?
“Yes everything is clicking off per planned so far in the commissioning timeline.”
“We took about 5 days to check out all the basic spacecraft functionalities including power, thermal control, attitude control, propulsion, etc.” 
Thus the spacecraft systems checkout has concluded.
“So then we turned TESS over to the instrument team. That’s primarily to do their part to check out the cameras and make the measurements they want to make on orbit.”
The four cameras were powered on on April 30. They were slowly cooled to their operating temperature of -85°C.

How long will the camera checkout require?
“There is plenty of time for checkouts of the science instrument. We have about 7 weeks until we are in the final science orbit.”
To carry out its daunting task, the spacecraft is equipped with 4 identical wide-field science cameras.  Their combined field of view will enable the spacecraft to image some 85% of the entire sky during the full sky survey over the first two years of the primary mission phase. 

Each of the four cameras is equipped with four 16.8 megapixel CCD’s and a seven element optical system. 

The cameras are located on the top of the kitchen table sized spacecraft inside a protective sunshade to shield the instruments.

As part of the calibration phase the cameras were collecting data as of May 9. 

So the camera check-out phase has started! 

Please describe the six orbit raising thruster maneuvers and lunar flyby? 
“There were a series of maneuvers to get in position to fly by the Moon and then do a period adjustment to get into the special ‘goldilocks’ orbit, P/2 lunar resonant orbit,” Lockwood explained. 
“We have done four of the six thruster firing [orbit raising] maneuvers.”
“First we did a calibration maneuver 3 days after launch. Then we raised the apogee to the level of the moon about a week after launch.”
“Then we did a small timing adjustment maneuver about 2 weeks after.”
The first two firings were called the first apogee maneuver (A1M) and the first perigee maneuver (P1M) and were conducted on 22 and 25 April respectively. 
A1M was a 50 second checkout burn to characterize the performance of the TESS thrusters.
“Then we have what’s called a B plane targeting maneuver to get to a specific spot to flyby the moon – [completed Sunday].”
“Then we have the flyby of the Moon Wednesday night/early Thursday May 17.”
“Then in 3 weeks time we have the period adjust maneuver to get into the P/2 orbit.”
“Then we go through one P/2 orbit for commissioning.”
“After that we begin the science phase in the P/2 orbit on June 12.  It’s all gone very well.” 
Describe the impact on the mission and how important is the lunar flyby?
“The lunar flyby will change the orbit significantly.  That’s really part of the whole elegance of the mission design. The lunar flyby will put us in an orbit that’s inclined to the ecliptic by about 35 degrees,” Lockwood stated.
“It will also raise our Perigee up to double the distance of GEO. So we’ll be at about 17 Earth radii for the perigee and 70 Earth radii for the apogee.”
“The we will do the period adjust maneuver after that to lower the apogee to about 59 Earth radii.”
“That period adjust maneuver which lasts about 15 minutes will put TESS in exact resonance with the Moon.” 
“We are very excited about the lunar flyby!”
Will any science be collected during the lunar flyby?
“No science will by gathered during the flyby.”

Watch this video explaining the orbit raising maneuvers:

Video Caption:  TESS Orbit Insertion 1.  Credit: NASA
Can you describe the engine firings in detail?
“The thruster firings are typical delta V maneuvers using one central delta V thruster on the spacecraft,” Lockwood elaborated. 
“The largest maneuver was the apogee raising maneuver. It lasted 449 seconds and that raised the apogee from 275,000 km to 350,000 km.”
“The short 7 second timing maneuver [P2M or Perigee 2 Maneuver], and 26 second targeting maneuver were both very short firings.”
“The other substantial maneuver is the period adjust maneuver, after we have flown past the moon [lunar flyby]. It will be about a 15 minute burn on May 30.” 
Describe the thruster? 
“We do these all with the one main delta V engine which is a 22 newton thruster.”
What is TESS current orbit now?
“We are currently in the highly eccentric phasing orbit, which has an apogee of 350,000 km. So its out at the distance to the moon about 57 Earth radii.  The perigee is about 800 km altitude.” 
When does the spacecraft become operational and the science begin? 
“The first science orbit starts on June 12 – which is in about 7 weeks.”

“The spacecraft will be declared operational on June 12- when the science gathering begins.”
But before that, the entire team will conduct a thorough mission checkout review.

“The team will conduct a post launch assessment review at NASA Goddard in Maryland on June 4 of the spacecraft, instruments and associated ground systems. They will check that all three of those elements are ready to proceed into mission operations.”

The Falcon 9 launch itself went extremely well and injected TESS into its intended orbit using so little fuel that the science gathering can go on for “decades” if the spacecraft survives.
Spacecraft checkout began soon after launch.
Just how good was the launch injection and propellent fuel usage?
“The launch was very accurate to 1 sigma accuracy. We needed only 1/3 of the fuel on board,” Lockwood told me.

“So there is enough fuel on board for many decades of use!”

“It is good enough for decades of operation.” 
“Everything is as expected with the spacecraft systems. It’s all gone very well.”

NASA’s next planet-hunter, the Transiting Exoplanet Survey Satellite (TESS), successfully launched on a SpaceX Falcon 9 rocket on April 18, 2018 from Space Launch Complex-40 on Cape Canaveral Air Force Station, FL - in this view from a pad camera. TESS will search for new worlds outside our solar system for further study.   Credit: Ken Kremer/
The SpaceX Falcon 9 delivered TESS to the highly elliptical Earth orbit never used before by a science mission, said George Ricker, TESS principal investigator at the Massachusetts Institute of Technology’s (MIT) Kavli Institute for Astrophysics and Space Research in Cambridge Ricker at a prelaunch media briefing.

TESS will orbit Earth in 13.7 days in a 2:1 resonance orbit with the moon. The moon orbits earth every 28 days.

The TESS science orbit is extremely stable as a result, thus requiring minimal fuel to maintain.  The spacecraft was intentionally loaded with enough propellants to continue its observations for 20 years or more if all goes well with the spacecraft systems.  

During those hoped for decades of exploration, TESS will search for new Earths beyond the confines of our Solar System on a first-of-its-kind mission to find worlds that could potentially support life. 
TESS is expected to find thousands of new exoplanets orbiting nearby stars.

Scientists plumbing the data gathered by TESS hope to discover on the order of 300 to 500 Earths and Super Earths alone, orbiting in their habitable zones compared to a dozen or so by Kepler.

TESS observations will yield the orbits and sizes of these exoplanets.  They will also provide the specific targets for follow up high resolution investigations by NASA’s James Webb Space Telescope and other telescopes to determine the exoplanets masses, compositions and atmospheric constituents. 

In turn researchers will use these observations to determine if any of the newly discovered Earths and Super Earths are actually Earth-like possessing water, oxygen and carbon based molecules for example that can potentially support life.

“We are thrilled TESS is on its way to help us discover worlds we have yet to imagine, worlds that could possibly be habitable, or harbor life,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate in Washington, in a statement. 
“With missions like the James Webb Space Telescope to help us study the details of these planets, we are ever the closer to discovering whether we are alone in the universe.”
 “One critical piece for the science return of TESS is the high data rate associated with its orbit,” said Ricker in a statement. “Each time the spacecraft passes close to Earth, it will transmit full-frame images taken with the cameras. That’s one of the unique things TESS brings that was not possible before.”
For this two-year survey mission, scientists divided the sky into 26 sectors. TESS will use its four unique wide-field cameras to map 13 sectors encompassing the southern sky during its first year of observations and 13 sectors of the northern sky during the second year, altogether covering 85 percent of the sky.
TESS is a NASA Astrophysics Explorer mission led and operated by MIT and managed by Goddard. George Ricker, of MIT’s Kavli Institute for Astrophysics and Space Research, serves as principal investigator for the mission. TESS’s four wide-field cameras were developed by MIT’s Lincoln Laboratory. Additional partners include Orbital ATK, NASA’s Ames Research Center, the Harvard-Smithsonian Center for Astrophysics, and the Space Telescope Science Institute. More than a dozen universities, research institutes and observatories worldwide are participants in the mission.
Watch for Ken’s continuing onsite coverage of NASA’s TESS, SpaceX, ULA, Boeing, Lockheed Martin, Orbital ATK and more space and mission reports direct from the Kennedy Space Center and Cape Canaveral Air Force Station, Florida.
Stay tuned here for Ken's continuing Earth and Planetary science and human spaceflight news: – – twitter @ken_kremer - ken at

Ken Kremer/SpaceUpClose with the TESS spacecraft inside the Payload Hazardous Servicing Facility clean room on Feb 20, 2018 at the Kennedy Space Center.  Launch on SpaceX Falcon 9 occurred on April 18, 2018. Credit: Ken Kremer/

Up close view of NASA TESS exoplanet hunter encapsulated inside the nose cone atop SpaceX Falcon 9 rocket poised for liftoff from Space Launch Complex-40 on Cape Canaveral Air Force Station, FL, on April 18. Credit: Ken Kremer/

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