The countdown has resumed and there are four minutes remaining until the 7:05 p.m. liftoff of the United Launch Alliance Atlas V rocket carrying NASA’s OSIRIS-REx spacecraft.
The switch to internal power is complete. Standing by to pick up the countdown at 7:01 p.m.
Launch Conductor Scott Barney has checked in with his ULA team members and they confirmed they are go to resume the countdown at the T-4 minute mark.
The hold will be released at 7:01 p.m. Liftoff is on schedule for 7:05 p.m. EDT.
OSIRIS-REx is switching from ground-based to internal power.
Countdown clocks are holding for 15 minutes in the final built-in hold of the night.
Although the countdown will pause at the T-4 minute mark, the team’s work will not. During this 15-minute planned hold, we can expect to hear final readiness polls as NASA Launch Manager Tim Dunn and ULA Launch Conductor Scott Barney verify OSIRIS-REx, the Atlas V rocket and the Eastern Range are ready to proceed.
Weather conditions remain favorable for liftoff at 7:05 p.m. EDT.
“All [launch commit criteria] are ‘go’ and expected to remain ‘go’ for the remainder of the countdown,” Launch Weather Officer Clay Flinn told controllers.
OSIRIS-REx is headed to Bennu, a roughly spherical asteroid measuring about 1,614 feet (492 meters) in diameter. All asteroids represent remnants of the building blocks of our solar system, so why did scientists decide to send a mission to this one?
Location, location, location. For a sample return mission, accessibility is key. Bennu travels in an Earth-like orbit that varies between .9 and 1.4 astronomical units from the sun (an astronomical unit, or AU, is the average distance between Earth and the sun, about 93 million miles). This puts it within the ideal range of .8 AU to 1.6 AU.
Larger diameter means slower rotation. Smaller asteroids – those measuring less than 650 feet in diameter – tend to rotate faster, ejecting surface materials and making it difficult for a spacecraft to get close enough for a sample. With its larger diameter, Bennu completes its day in just over four hours, slow enough for OSIRIS-REx to approach and do its work.
Carbon-rich composition. Measurements taken from telescopes indicate Bennu is carbon-rich. This is important because primitive asteroids like these may contain volatiles and organic molecules that could trace the origins of life on Earth and the potential for life elsewhere.
Image credit: NASA’s Goddard Space Flight Center Conceptual Image Lab
Overall mission management for OSIRIS-REx, including systems engineering as well as safety and mission assurance, is provided by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Dante Lauretta is the mission’s principal investigator at the University of Arizona, and the spacecraft was built by Lockheed Martin Space Systems in Denver.
Launch management is the responsibility of the Launch Services Program, or LSP, at NASA’s John F. Kennedy Space Center in Florida. LSP selects the appropriate launcher for the agency’s science missions, provides oversight as the rocket and spacecraft come together, and conducts the countdown.
“Working alongside our United Launch Alliance colleagues, the engineers and analysts of NASA LSP take great pride in launching OSIRIS-REx,” NASA Launch Manager Tim Dunn said earlier in the week.
OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.
In the image above from NASA TV, viewers can clearly see gaseous oxygen venting away from the Atlas V booster. This is normal and is caused when small amounts of cryogenic liquid oxygen boil off and are vented away.
“All the fueling operations have gone perfectly fine today,” NASA Launch Commentator Mike Curie reported.