– Delayed several months by a launch vehicle problem, five small NASA satellites are ready to lift off in mid-February to find out where and when aurora-boosting magnetic storms begin.
The identical spacecraft comprise NASA’s THEMIS mission to pinpoint the origins of substorms – geomagnetic disturbances visible in the northern hemisphere as a sudden brightening of the aurora borealis, or Northern Lights. The two-year mission also is expected to provide insight into the role substorms play in severe space weather.
The speed at which substorms develop and strike the Earth’s upper atmosphere makes finding their point of origin all but impossible with a single spacecraft, THEMIS mission officials said.
“Finding the elusive substorm point of origin is a question almost as old as space physics itself,” THEMIS Principal Investigator Vassilis Angelopoulos, a
scientist, told reporters in a Jan. 17 teleconference. He characterized THEMIS as “a stepping-stone towards understanding space weather phenomena that affect our lives.”
THEMIS is short for Time History of Events and Macroscale Interactions during Substorms. The $200 million mission was selected in 2003 to be the fifth mission to fly under NASA’s medium-class Explorers Program of competitively selected astrophysics and heliophysics science investigations.
The spacecraft were built by Swales Aerospace of Beltsville, Md., under a $48 million subcontract to the
‘s Space Sciences Laboratory, which is managing the project.
The THEMIS satellites are only the second set of spacecraft built by Swales Aerospace, a 900-person company better known as an engineering services contractor. Swales’ first spacecraft was Earth Observer-1, an experimental NASA satellite launched in 2000 and still in operation today.
Mike Cully, the THEMIS program manager at Swales, said the square-shaped satellites, measuring about 1 meter on each side, weigh 128 kilograms apiece fully fueled.
NASA officials said the mission constitutes the largest number of scientific spacecraft that the agency has ever launched aboard a single rocket.
A United Launch Alliance Delta 2 rocket equipped with nine solid-fuel strap-on boosters is slated to loft the probes Feb. 15 from Cape Canaveral Air Force Station,
, during a 19-minute window that opens at
6:07 p.m. EST.
The spacecraft were to have launched last October, but a manufacturing defect in the second stage of the Delta 2 rocket assigned to the mission forced the delay.
During routine testing last July, engineers from Boeing, which built the rocket, discovered that the second stage leaked. The problem was traced back to an oxidizer tank supplied by a unit of Alcatel Alenia Space in
United Launch Alliance spokesman
said in a Jan. 17 e-mail that engineers concluded “the tank issue occurred because of re-work by the supplier using a tool that was inappropriate for the application.”
United Launch Alliance is a joint venture of Boeing Co. of Chicago and Lockheed Martin Corp. of
, that markets rockets to
The faulty oxidizer tank was removed and replaced. Since identifying the root cause of what Shores said was an isolated problem, United Launch Alliance has successfully launched four Delta 2 rockets, including the Dec. 14 launch of a classified National Reconnaissance Office payload.
Willis Jenkins, the THEMIS program executive at NASA headquarters here, said the launch delay cost about $3 million, a sum the project was able to absorb without exceeding its $200 million budget.
THEMIS Project Manager Peter Harvey, also of the
, described the launch delay’s impact on the mission as minor.
He said the delay drove some changes to the mission profile to ensure that the spacecraft will be optimally positioned to observe the peak period of northern hemisphere substorm-related activity that begins each February.
The first two weeks following the launch will be spent checking out the spacecraft and turning on their suite of instruments,
said. After that, mission controllers in
will send the spacecraft to their designated orbits, spacing the probes thousands of kilometers apart.
Every four days, THEMIS officials said, the satellites will line up along Earth’s magnetic tail. Working in combination with ground stations placed at schools throughout
, the THEMIS probes will help researchers track disturbances from their point of origin to the ground.
“We look forward to some terrific scientific discoveries,”
Because only four satellites are needed for the mission to succeed, a fifth will be reserved as an on-orbit spare should one of the others fail. “We’re flying five to increase our reliability,” Angelopoulos said.
Should more than one THEMIS probe go out of service during the nominal two-year mission, Angelopoulous said the team could complete its science objectives with the help of satellites already in orbit, including the 15-year-old U.S.-Japanese Geotail spacecraft.