[meteorite-list] Bonus Fuel Could Change OSIRIS-REx Flight Plan

[Ron Baalke]

http://spaceflightnow.com/2015/02/05/bonus-fuel-could-change-osiris-rex-flight-plan/

Bonus fuel could change OSIRIS-REx flight plan
by Stephen Clark
Spaceflight Now
February 5, 2015

A NASA spacecraft under construction for launch in 2016 to retrieve samples 
from asteroid Bennu could benefit from an extra load of fuel, allowing 
an extended stay at the asteroid or a return to Earth a year early.

The $1 billion OSIRIS-REx mission is scheduled for launch from Cape Canaveral 
on Sept. 3, 2016, and a United Launch Alliance Atlas 5 rocket will send 
the probe on a two-year voyage to asteroid Bennu, a near-Earth object 
scientists say is made of primitive material from the ancient solar system.

The specimens collected from Bennu could help researchers better understand 
how the solar system's planets formed, and the material might contain 
the building blocks of life.

Engineers have come up with a plan to fill OSIRIS-REx with more hydrazine 
fuel, giving the spacecraft more propulsive ability on its interplanetary 
journey, according to Dante Lauretta, the mission's principal investigator 
at the University of Arizona.

The OSIRIS-REx spacecraft, being built at a Lockheed Martin facility in 
Denver, is coming in lighter than the lift capability of the Atlas 5 rocket, 
which will lift off in its "411" configuration with a four-meter payload 
fairing, a single-engine Centaur upper stage, and one strap-on solid rocket 
booster.

The proposal - described as a 'heavy launch option" - would add an extra 
341 pounds of fuel to the spacecraft's fuel tank.

"We are still planning to launch on the Atlas 5-411," Lauretta wrote in 
an email to Spaceflight Now. "The heavy launch option is a project-level 
decision based on increased confidence in our dry mass value."

The "411" version of the Atlas 5 rocket can lift up to 4,651 pounds of 
mass on the trajectory needed for the OSIRIS-REx mission, and the spacecraft 
is currently projected to weigh about 4,310 pounds when fueled for launch.

"Our main propellant tank has the additional capacity to accommodate the 
extra 155 kilograms of propellant - enabling both an early return and 
a late departure option from Bennu," Lauretta said.

A final decision on whether to fuel OSIRIS-REx with more propellant is 
still a couple of months away, according to Bill Cutlip, the mission's 
launch vehicle manager at NASA's Goddard Space Flight Center.

"The final decision will not be made until the spacecraft dry mass is 
measured and we receive the final performance evaluation from ULA," Lauretta 
siad. 'Once in space, we can make the decision to return early or depart 
late after arrival at Bennu."

NASA's Origins, Spectral Interpretation, Resource Identification, Security, 
Regolith Explorer, or OSIRIS-REx, is due to arrive at asteroid Bennu in 
late 2018 after a gravity slingshot flyby of Earth in 2017. After a close-up 
survey of the asteroid, scientists will select a sampling site where the 
OSIRIS-REx spacecraft will descend and snag a specimen of rock and dust 
from Bennu's surface.

The mission's original flight plan called for OSIRIS-REx to depart Bennu 
in March 2021 and cruise back to Earth, deploying a landing capsule containing 
the samples to parachute to touchdown in Utah in September 2023.

In a presentation last month to NASA's Small Bodies Assessment Group, 
Lauretta said navigators on the ground could use the extra propellant 
to keep OSIRIS-REx near asteroid Bennu longer than planned, and still 
return to Earth as scheduled in 2023.

OSIRIS-REx could also leave Bennu in January 2020 and make it back to 
Earth a year early in late 2022. Lauretta pitched the idea as a chance 
to reduce the mission's risk and enable an early start to the analysis 
of the asteroid's samples.

Under the current plan, OSIRIS-REx will loiter near asteroid Bennu for 
two-and-half years. More than 500 days of the timeline is set aside as 
margin for bonus scientific observations or in case the mission encounters 
problems.