Quick Facts: Time History of Events of Macroscale Interactions During Substorms (THEMIS)

Mission Introduction

THEMIS spacecraft

THEMIS employs five identically-instrumented spacecraft in carefully chosen orbits whose apogees line up once every 4 days over a dedicated array of ground observatories located in Canada and the northern United States. (Courtesy UCB/SSL)

THEMIS is a constellation mission consisting of 5 satellites in different orbits together with a ground array of magnetometers and auroral cameras located in North America. The outer-most satellites will be as far away as 30 Earth radii (200,000 km). THEMIS answers fundamental outstanding questions regarding the magnetospheric substorm instability, a dominant mechanism of transport and explosive release of solar wind energy within geospace. Every fourth night, all five satellites will line up above North America. While the ground-based instruments monitor the space environment by watching the aurora (Northern Lights), the satellites will directly observe the processes that drive it.

LASP Roles

THEMIS Electric Field Instrument

The THEMIS Electric Field Instrument (EFI) measures the electric fields in three directions. One pair of sensors is deployed to 20 meters, the other pair to 25 meters. Two stiff telescopic booms extend sensors perpendicular to the four spinning cables and along the probe's spin axis. (Courtesy UCB/SSL)

LASP provides:

  • LASP designed and built the Digital Fields Board (DFB)
  • Co-Investigators, Xinlin Li and Bob Ergun
  • Data processing for the Electric Field Instrument

LASP Instrument

LASP designed and built the Digital Fields Board (DFB) for the THEMIS mission (5 flight-units plus 1 spare). The THEMIS DFB performs the spectral processing for the Electric Fields Instrument (EFI) and the Search Coil Magnetometer (SCM). The resulting data represent the electric and magnetic wave power in bands from DC up to 8 kHz, plus a high-frequency electric field band from 30 kHz to 500 kHz. Additionally, the DFB filters and digitizes the analog signals from the EFI and SCM instruments.

The DFB creates two types of spectral products: filter bank data (FBK) and Fourier power spectra (FFT). The filter bank data are meant for survey-type monitoring of wave power. They have broad frequency bands and relatively low time resolution, and are usually available whenever the instruments are on. The FFT data are meant for detailed event studies, and have much narrower and sharper spectral bands as well as higher time resolution. The FFT data are available only when the spacecraft is in burst mode.

Quick Facts

Launch date: February 17, 2007
Launch location: Kennedy Space Center, Cape Canaveral, Florida
Launch vehicle: Delta II 2425-10
Mission target: Earth orbit
Mission duration: 2 years planned; currently on extended mission phase
Other organizations involved:

  • University of California, Berkeley/Space Sciences Laboratory