HOPE for All Mankind
Scientists at Los Alamos National Laboratory are one step closer to putting a plasma analyzer in space that may provide critical information about how the sun affects Earth, life, and society. In late January, a Los Alamos team recently completed construction of the Helium Oxygen Proton Electron (HOPE) spectrometer, installing it into a vacuum chamber at Los Alamos for testing and calibration. Next, the spectrometer will be exposed to environmental tests such as vibration, temperature fluctuations, and electromagnetic interference.
The HOPE instrument is part of NASA's Radiation Belt Storm Probes (RBSP) mission, designed to help better understand the Sun's influence on Earth and near-Earth space by studying the Earth's radiation belts on various scales of space and time.
LANL's role is to build the HOPE plasma spectrometer (successfully accomplished in January), to set up and run the Energy Particle, Composition, and Thermal Plasma Suite (ECT) Science Operations Center, and to lead the ECT science analysis team.
The five instruments on NASA's Living With a Star Program's (LWS) RBSP mission will provide the measurements needed to characterize and quantify the plasma processes that produce very energetic ions and relativistic electrons—especially those that generate hazardous space weather effects, detailed below.
Making Life Better on Earth
According to NASA, understanding the radiation belt environment and its variability has extremely important practical applications in the areas of spacecraft operations, spacecraft and spacecraft-system design, and mission planning and astronaut safety. But the significance is far greater than space science; unpredictable changes in space weather greatly affect society via power grid problems, telecommunications, satellite malfunction, astronaut safety, oil pipeline leaks caused by corrosion as a result of charged particles, and even GPS accuracy, which greatly affects safe airline travel.
"During the last solar cycle, a dramatic change in our understanding of the Earth's radiation belts took place.…The radiation belts were found to be highly dynamic and full of new surprises," said Geoffrey Reeves, LANL scientist and a member of NASA's LWS team. "For reasons we still don't understand, the fluxes of relativistic electrons are seen to suddenly increase or decrease by factors of hundreds or more."
Ruth Skoug, a Los Alamos space physicist who coauthored the HOPE proposal in 2005, said changes in the radiation belt could be partially in response to geomagnetic storms, and scientists need to understand why energy particles change.
RBSP instruments will measure the properties of charged particles that comprise the Earth's radiation belts, the plasma waves that interact with them, the large-scale electric fields that transport them, and the particle-guiding magnetic field. Specifically, the goal of the NASA mission is to understand the acceleration, global distribution, and variability of energetic electrons and ions in the radiation belts.
The probes (i.e., spacecraft) will carry several instruments that support five experiments designed to address the mission's science objectives. Because it is vital that the two probes make identical measurements to observe changes in the radiation belts through both space and time, each probe will carry the following: the ECT, Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS), the Electric Field and Waves Suite (EFW), the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE), and the Relativistic Proton Spectrometer (RPS).
Containing HOPE, the two spin-stabilized RBSP probes will have nearly identical eccentric (deviating from a circle) orbits. The orbits cover the entire radiation belt region and the two spacecraft lap each other several times over the course of the mission. The RBSP in situ measurements discriminate between spatial and temporal effects, and compare the effects of various proposed mechanisms for charged particle acceleration and loss. The two spacecraft will be launched simultaneously at slightly different speeds to separate time and provide more accurate data from two different "views".
When space weather intensifies, the probes will not have the luxury of going into a safe mode, as many other spacecraft must do during storms. Consequently, these probes and instruments must be resilient enough to continue working even in the harshest conditions.
How it Works
The HOPE mass spectrometer instrument uses an electrostatic top-hat analyzer and time-gated coincidence detectors to measure electrons, protons, plus helium and oxygen ions with energies from less than or equal to 20 eV (electronvolts) or spacecraft potential (whichever is greater) to greater than or equal to 45 keV (kiloelectronvolts) while rejecting penetrating backgrounds.
Schematic of HOPE mass spectrometer.
Understanding the Magnetosphere
Earth has two regions—or belts—of trapped fast particles: electrons, protons, and heavier atomic ions that are trapped in our planet's magnetic field. The compact inner radiation belt extends about 4,000 miles above the equator, almost equal to our planet's radius. Further out is the large region of the ring current, and this belt fluctuates widely, rising when magnetic storms inject fresh particles from the tail of the magnetosphere, then gradually falling off again. The ring's current energy is mainly carried by the ions, most of which are protons.
here, a highly dynamic structure that responds dramatically to solar variations. The sun periodically releases billions of tons of matter in what are called coronal mass ejections; these immense clouds of material can cause large magnetic storms in the magnetosphere and the upper atmosphere.
The study of the region of space near the Earth helps to determine changes in the Earth's magnetosphere, ionosphere, and upper atmosphere in order to enable specification, prediction, and mitigation of their effects.
A Hopeful Prospect
The RBSP mission's instruments include LANL's HOPE spectrometer, which will measure the ion composition and plasma distributions in space that generate electromagnetic waves and control the dynamics of the Earth's magnetosphere and radiation belts.
The RBSP mission, LANL's traditional satellite nuclear-detection network, and the DREAM space weather model are being integrated to forecast hazards for national security. LANL scientists developed DREAM, the Dynamic Radiation Environment Assimilation Model, to understand and to predict hazards from the natural space environment and artificial radiation belts produced by nuclear explosions. DREAM was recently implemented for real-time space weather applications.
HOPE's other applications include analyzing the effects of a nuclear bomb detonation. "Could we mitigate the effects of a nuclear bomb? We're not there, but we're working to understand the effects," said Skoug.
The Los Alamos HOPE team is led by Herb Funsten, Arthur Guthrie, and Ruth Skoug. The spacecraft are being built by the Johns Hopkins University Applied Physics Laboratory. Many LANL scientists, engineers, and technicians are involved with the RBSP project, including researcher Geoff Reeves who heads the ECT suite and was part of a team that generated the first-ever images of changes in these radiation belts.
HOPE is projected to launch on RBSP spacecraft in May 2012.
HOPE team members Keith Kihara, Juan Baldonado, Rick Ortiz, and Ruth Skoug place the spectrometer into a vacuum chamber for testing.