First ASU-built space instrument ready for final lab tests

The first space instrument to be built at Arizona State University has just received the electronics it will use in flight. This starts the final laboratory tests leading to its launch next year on a NASA rocket.

The electronics for the OSIRIS-REx Thermal Emission Spectrometer, or OTES for short, arrived in a cleanroom at ASU's School of Earth and Space Exploration. The electronics are the final of three subsystems making up the instrument. The other two are the spectrometer's optical and mechanical systems.

On March 31, NASA gave a green light for the OSIRIS-REx mission to transition from development to bringing instruments and their components together. This will be followed in the months ahead by integrating and testing the spacecraft's combined systems.

Flight instrument with engineering model sunshade.  Flight instrument with engineering model sunshade.

The OSIRIS-REx mission will launch in September 2016 and fly to an asteroid, 101995 Bennu. There it will collect a sample of its rocks and dirt and bring them back to Earth in 2023. (OSIRIS-REx is short for Origins Spectral Interpretation Resource Identification Security Regolith Explorer; the University of Arizona in Tucson leads the mission.)

OTES plays a key part in the mission to Bennu. Its task is to use long-wavelength infrared light to map the asteroid's minerals, which will help mission scientists select where to collect samples. ASU is one of only a handful of universities in the United States capable of building NASA-certified space instruments.

"We have already built the spectrometer part of OTES and attached it to the telescope that collects light so it can work," said Philip Christensen, OTES' designer and principal investigator. Christensen is a Regents' Professor of geological sciences in SESE. "The final element is the electronics that will control the instrument. OTES has now received its brain and nervous system."

Next come tests as engineers working in a cleanroom in the Interdisciplinary Science and Technology Building 4 on the Tempe campus work to integrate the electronics with the optical and mechanical parts of OTES.

Testing will include placing OTES in a chamber where it is subjected to the same conditions it will experience during the mission. Aerospace engineers call this process "shake and bake" because it reproduces the vibrations of a rocket launch as well as the extremes of heat and cold that OTES must survive to do its job.

"NASA's rules for testing flight instruments and other space hardware are detailed and thorough," Christensen said. "They need to be. Once the spacecraft leaves Earth, there are no repair calls. Everything has to work perfectly."

Primitive target
Scientists chose asteroid Bennu as the target for the OSIRIS-REx mission because it has undergone relatively little change since it formed early in the solar system's history. Thus samples from Bennu may give us a better look at how the solar system formed.
With an orbit that brings it inside Earth's orbit, Bennu is the most accessible asteroid rich in organic materials. It is about 575 meters (1,900 feet) wide, roughly spherical and spins once every 4.3 hours. Reflecting only 3 percent of the sunlight falling on it, Bennu is about as dark as a charcoal briquette.

The flight plan calls for the OSIRIS-REx spacecraft to launch in September 2016 and rendezvous with Bennu in November 2019. It will spend up to 15 months surveying Bennu's mineralogy with OTES and another spectrometer working at shorter visible and infrared wavelengths. A suite of three visible-light cameras and a laser altimeter will draw a complete picture of the asteroid.

Mission scientists will then select a target area. The spacecraft will approach Bennu, touch it briefly and collect at least 60 grams (2 ounces) of dust, soil and rubble from its surface. Then OSIRIS-REx will cruise back to Earth and deliver the encapsulated sample to a landing site in Utah in September 2023. After dropping off the sample as it flies past Earth, the spacecraft may go on to survey other asteroids, although it will not be able to collect samples from them.

"As we put all its flight parts together and start on this final series of testing, it's very exciting to see OTES come to life in our hands," Christensen said.