Understanding how fire spreads in a microgravity environment is critical to the safety of astronauts who live and work in space. And while NASA has conducted studies aboard the space shuttle and International Space Station, risks to the crew have forced these experiments to be limited in size and scope. Fire safety will be a critical element as NASA progresses on the journey to Mars and begins to investigate deep space habitats for long duration missions.
The first Spacecraft Fire Experiment (Saffire-I) was the beginning of a three-part experiment to be conducted over the course of three flights of Orbital ATK’s Cygnus vehicle to investigate large-scale flame spread and material flammability limits in long duration microgravity.
The Saffire-I experiment enclosure was approximately half a meter wide by 1 meter deep by 1.3 meter long and consisted of a flow duct and avionics bay. Inside the flow duct, the cotton-fiberglass blend burn sample measured 0.4 m wide by 1 meter long. When commanded by Orbital ATK and Saffire ground controllers operating from Dulles, Virginia, it was ignited by a hot wire. Previous to this experiment, the largest fire experiment that had been conducted in space is about the size of an index card.
After the experiment was ignited, the Cygnus continued to orbit Earth for six days as it transmitted high-resolution imagery and data from the Saffire experiment. Following complete data transmission, the Cygnus spacecraft completed its mission with a destructive entry into the Earth’s atmosphere.
Saffire-I launched inside the Cygnus spacecraft atop the United Launch Alliance (ULA) Atlas V launch vehicle on March 22, 2016. Space Station Crew members successfully grappled Cygnus to the space station on March 26. The Saffire experiments were developed at NASA Glenn Research Center by the Spacecraft Fire Safety Demonstration Project and sponsored by the Advanced Exploration Systems (AES) Division of NASA’s Human Exploration and Operations Mission Directorate. AES pioneers new approaches for rapidly developing prototype systems, demonstrating key capabilities, and validating operational concepts for future human missions beyond low-Earth orbit. AES activities are uniquely related to crew safety and mission operations in deep space, with a strong focus on future vehicle development.
High above the surface, Earth’s magnetic field constantly deflects incoming supersonic particles from the sun. These particles are disturbed in regions just outside of Earth’s magnetic field – and some are reflected into a turbulent region called the foreshock.
New observations from NASA’s THEMIS – short for Time History of Events and Macroscale Interactions during Substorms – mission show that this turbulent region can accelerate electrons up to speeds approaching the speed of light. Such extremely fast particles have been observed in near-Earth space and many other places in the universe, but the mechanisms that accelerate them have not yet been concretely understood.
The new results provide the first steps towards an answer, while opening up more questions. The research finds electrons can be accelerated to extremely high speeds in a near-Earth region farther from Earth than previously thought possible – leading to new inquiries about what causes the acceleration. These findings may change the accepted theories on how electrons can be accelerated not only in shocks near Earth, but also throughout the universe. Having a better understanding of how particles are energized will help scientists and engineers better equip spacecraft and astronauts to deal with these particles, which can cause equipment to malfunction and affect space travelers.
“This affects pretty much every field that deals with high-energy particles, from studies of cosmic rays to solar flares and coronal mass ejections, which have the potential to damage satellites and affect astronauts on expeditions to Mars,” said Lynn Wilson, lead author of the paper on these results at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The results, published in Physical Review Letters, on Nov. 14, 2016, describe how such particles may get accelerated in specific regions just beyond Earth’s magnetic field. Typically, a particle streaming toward Earth first encounters a boundary region known as the bow shock, which forms a protective barrier between the solar wind, the continuous and varying stream of charged particles flowing from the sun, and Earth. The magnetic field in the bow shock slows the particles, causing most to be deflected away from Earth, though some are reflected back towards the sun. These reflected particles form a region of electrons and ions called the foreshock region.
This image represents one of the traditional proposed mechanisms for accelerating particles across a shock, called a shock drift acceleration. The electrons (yellow) and protons (blue) can be seen moving in the collision area where two hot plasma bubbles collide (red vertical line). The cyan arrows represent the magnetic field and the light green arrows, the electric field. Credits: NASA Goddard’s Scientific Visualization Studio/Tom Bridgman, data visualizer
Some of those particles in the foreshock region are highly energetic, fast moving electrons and ions. Historically, scientists have thought one way these particles get to such high energies is by bouncing back and forth across the bow shock, gaining a little extra energy from each collision. However, the new observations suggest the particles can also gain energy through electromagnetic activity in the foreshock region itself.
The observations that led to this discovery were taken from one of the THEMIS – short for Time History of Events and Macroscale Interactions during Substorms – mission satellites. The five THEMIS satellites circled Earth to study how the planet’s magnetosphere captured and released solar wind energy, in order to understand what initiates the geomagnetic substorms that cause aurora. The THEMIS orbits took the spacecraft across the foreshock boundary regions. The primary THEMIS mission concluded successfully in 2010 and now two of the satellites collect data in orbit around the moon.
Operating between the sun and Earth, the spacecraft found electrons accelerated to extremely high energies. The accelerated observations lasted less than a minute, but were much higher than the average energy of particles in the region, and much higher than can be explained by collisions alone. Simultaneous observations from the additional Heliophysics spacecraft, Wind and STEREO, showed no solar radio bursts or interplanetary shocks, so the high-energy electrons did not originate from solar activity.
“This is a puzzling case because we’re seeing energetic electrons where we don’t think they should be, and no model fits them,” said David Sibeck, co-author and THEMIS project scientist at NASA Goddard. “There is a gap in our knowledge, something basic is missing.”
The electrons also could not have originated from the bow shock, as had been previously thought. If the electrons were accelerated in the bow shock, they would have a preferred movement direction and location – in line with the magnetic field and moving away from the bow shock in a small, specific region. However, the observed electrons were moving in all directions, not just along magnetic field lines. Additionally, the bow shock can only produce energies at roughly one tenth of the observed electrons’ energies. Instead, the cause of the electrons’ acceleration was found to be within the foreshock region itself.
“It seems to suggest that incredibly small scale things are doing this because the large scale stuff can’t explain it,” Wilson said.
High-energy particles have been observed in the foreshock region for more than 50 years, but until now, no one had seen the high-energy electrons originate from within the foreshock region. This is partially due to the short timescale on which the electrons are accelerated, as previous observations had averaged over several minutes, which may have hidden any event. THEMIS gathers observations much more quickly, making it uniquely able to see the particles.
Next, the researchers intend to gather more observations from THEMIS to determine the specific mechanism behind the electrons’ acceleration.
The primary mirror of NASA’s James Webb Space Telescope consisting of 18 hexagonal mirrors looks like a giant puzzle piece standing in the massive clean room of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Appropriately, combined with the rest of the observatory, the mirrors will help piece together puzzles scientists have been trying to solve throughout the cosmos.
Webb’s primary mirror will collect light for the observatory in the scientific quest to better understand our solar system and beyond. Using these mirrors and Webb’s infrared vision scientists will peer back over 13.5 billion years to see the first stars and galaxies forming out of the darkness of the early universe. Unprecedented infrared sensitivity will help astronomers to compare the faintest, earliest galaxies to today’s grand spirals and ellipticals, helping us to understand how galaxies assemble over billions of years. Webb will see behind cosmic dust clouds to see where stars and planetary systems are being born. It will also help reveal information about atmospheres of planets outside our solar system, and perhaps even find signs of the building blocks of life elsewhere in the universe.
The Webb telescope was mounted upright after a “center of curvature” test conducted at Goddard. This initial center of curvature test ensures the integrity and accuracy, and test will be repeated later to verify those same properties after the structure undergoes launch environment testing. In the photo, two technicians stand before the giant primary mirror.
These two natural color images from NASA’s Cassini spacecraft show the changing appearance of Saturn’s north polar region between 2012 and 2016.
Scientists are investigating potential causes for the change in color of the region inside the north-polar hexagon on Saturn. The color change is thought to be an effect of Saturn’s seasons. In particular, the change from a bluish color to a more golden hue may be due to the increased production of photochemical hazes in the atmosphere as the north pole approaches summer solstice in May 2017.
Image Credit:NASA/JPL-Caltech/Space Science Institute/Hampton University
Researchers think the hexagon, which is a six-sided jetstream, might act as a barrier that prevents haze particles produced outside it from entering. During the polar winter night between November 1995 and August 2009, Saturn’s north polar atmosphere became clear of aerosols produced by photochemical reactions — reactions involving sunlight and the atmosphere. Since the planet experienced equinox in August 2009, the polar atmosphere has been basking in continuous sunshine, and aerosols are being produced inside of the hexagon, around the north pole, making the polar atmosphere appear hazy today.
Other effects, including changes in atmospheric circulation, could also be playing a role. Scientists think seasonally shifting patterns of solar heating probably influence the winds in the polar regions.
Both images were taken by the Cassini wide-angle camera.
The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.