Oct 22 2015
From The Space Library
Release 15-030 (Goddard) NASA Study Shows That Common Coolants Contribute to Ozone Depletion
A class of widely used chemical coolants known as hydrofluorocarbons (HFC) contributes to ozone depletion by a small but measurable amount, countering a decades-old assumption, according to a new NASA study.
The paper, published Oct. 22 in Geophysical Research Letters, a journal of the American Geophysical Union, is based on the results of a NASA-derived atmospheric chemistry climate model that projected the impacts of HFC gases on the atmosphere by the year 2050.
The ozone layer comprises a belt of ozone molecules located primarily in the lower stratosphere. It is responsible for absorbing most of the sun’s harmful ultraviolet radiation before it reaches Earth’s surface. Research in the 1990s showed that HFCs, which have replaced more powerful ozone-depleting chemical coolants in recent years, destroy a negligible amount of ozone. But that conclusion was reached by examining only the gases’ ability to break down ozone molecules through chemical reactions that take place following the breakdown of these molecules in the atmosphere.
The new study, which focused on the five types of HFCs expected to contribute the most to global warming in 2050, found that the gases indirectly contribute to ozone depletion. HFC emissions cause increased warming of the stratosphere, speeding up the chemical reactions that destroy ozone molecules, and they also decrease ozone levels in the tropics by accelerating the upward movement of ozone-poor air. According to the model, their impact is such that HFCs will cause a 0.035 percent decrease in ozone by 2050.
A global representation of the projected impacts of hydrofluorocarbons (HFC) on ozone levels at the various latitudes in 2050.
HFCs’ contribution to ozone depletion is small compared to its predecessors. For example, trichlorofluoromethane, or CFC-11, a once common coolant that is no longer used, causes about 400 times more ozone depletion per unit mass than HFCs.
“We’re not suggesting HFCs are an existential threat to the ozone layer or to ozone hole recovery, but the impact isn’t zero as has been claimed,” said lead author Margaret Hurwitz, an atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. “HFCs are, in fact, weak ozone-depleting substances.”
In the study, scientists also found that HFCs have a nearly linear impact on stratospheric temperature and ozone change. For example, reducing HFC emissions by 50 percent would decrease the ozone change by a comparable amount. Such a direct relationship will prove useful for evaluating the impacts of emerging HFCs, Hurwitz said. “We can provide policy makers with an estimate of the stratospheric impacts of new HFC gases.”
HFCs have been adopted as replacements for chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC) in refrigerators and in home and automobile air conditioners. CFCs were largely responsible for the ozone depletion first observed by scientists in the 1980s, most notably the ozone hole above Antarctica, which continues today. CFC molecules contain chlorine atoms, and each atom can destroy thousands of ozone molecules. Under the auspices of the Montreal Protocol treaty signed in 1987, CFCs were officially phased out of production worldwide in 2010.
While HCFCs contain chlorine atoms, they are less damaging to the ozone layer because they also contain hydrogen atoms, which causes them to break down in the atmosphere faster. HCFCs are currently being phased out in favor of HFCs, which do not contain chlorine.
The study adds nuance to the discussion around HFCs and their full impact on the ozone, according to David Fahey, a research physicist and director of the National Oceanic and Atmospheric Administration’s Earth Systems Research Laboratory, who was not involved in the study.
“What the paper demonstrates is that when you put this much of an infrared radiation-absorbing material in the stratosphere, even though it nominally does not destroy ozone in the same way that mainline ODSs [ozone-depleting substances] do, it’s going to make a difference—it’s going to start changing things,” Fahey said. “It adds a new dimension of thinking that stratospheric scientists need to be aware of as they discuss these matters with policy makers.”
While HFCs are only weak ozone-depleting substances, they are, like CFCs and HCFCs, strong greenhouse gases. If production trends continue, projections show that, by 2050, the amount of global warming by all HFCs could be as large as 20 percent that of carbon dioxide.
Work is also underway to analyze the HFC impacts on surface climate. “We’ve taken a major step towards understanding the effect of HFCs on the stratosphere and the ozone layer,” said Paul Newman, a co-author on the paper and chief scientist for Earth sciences at Goddard. “Our next step is to use a more complex type of model so we can begin to look at the impact of these compounds on land and ocean temperature, rainfall and sea ice.”
Release 15-210 NASA Completes Critical Design Review for Space Launch System
For the first time in almost 40 years, a NASA human-rated rocket has completed all steps needed to clear a critical design review (CDR). The agency’s Space Launch System (SLS) is the first vehicle designed to meet the challenges of the journey to Mars and the first exploration class rocket since the Saturn V.
SLS will be the most powerful rocket ever built and, with the agency’s Orion spacecraft, will launch America into a new era of exploration to destinations beyond Earth’s orbit. The CDR provided a final look at the design and development of the integrated launch vehicle before full-scale fabrication begins.
“We’ve nailed down the design of SLS, we’ve successfully completed the first round of testing of the rocket’s engines and boosters, and all the major components for the first flight are now in production,” said Bill Hill, deputy associate administrator of NASA’s Exploration Systems Development Division. “There have been challenges, and there will be more ahead, but this review gives us confidence that we are on the right track for the first flight of SLS and using it to extend permanent human presence into deep space.”
The CDR examined the first of three configurations planned for the rocket, referred to as SLS Block 1. The Block I configuration will have a minimum 70-metric-ton (77-ton) lift capability and be powered by twin boosters and four RS-25 engines. The next planned upgrade of SLS, Block 1B, would use a more powerful exploration upper stage for more ambitious missions with a 105-metric-ton (115-ton) lift capacity. Block 2 will add a pair of advanced solid or liquid propellant boosters to provide a 130-metric-ton (143-ton) lift capacity. In each configuration, SLS will continue to use the same core stage and four RS-25 engines.
The SLS Program completed the review in July, in conjunction with a separate review by the Standing Review Board, which is composed of seasoned experts from NASA and industry who are independent of the program. Throughout the course of 11 weeks, 13 teams – made up of senior engineers and aerospace experts across the agency and industry – reviewed more than 1,000 SLS documents and more than 150 GB of data as part of the comprehensive assessment process at NASA’s Marshall Space Flight Center in Huntsville, Alabama, where SLS is managed for the agency.
The Standing Review Board reviewed and assessed the program’s readiness and confirmed the technical effort is on track to complete system development and meet performance requirements on budget and on schedule.
The program briefed the results of the review in October to the Agency Program Management Council, led by NASA Associate Administrator Robert Lightfoot, as the final step in the CDR process.
This review is the last of four reviews that examine concepts and designs. The next step for the program is design certification, which will take place in 2017 after manufacturing, integration and testing is complete. The design certification will compare the actual final product to the rocket’s design. The final review, the flight readiness review, will take place just prior to the 2018 flight readiness date.
“This is a major step in the design and readiness of SLS,” said John Honeycutt, SLS program manager. “Our team has worked extremely hard, and we are moving forward with building this rocket. We are qualifying hardware, building structural test articles, and making real progress.”
Critical design reviews for the individual SLS elements of the core stage, boosters and engines were completed successfully as part of this milestone. Also as part of the CDR, the program concluded the core stage of the rocket and Launch Vehicle Stage Adapter will remain orange, the natural color of the insulation that will cover those elements, instead of painted white. The core stage, towering more than 200 feet tall and with a diameter of 27.6 feet, will carry cryogenic liquid hydrogen and liquid oxygen fuel for the rocket’s four RS-25 engines.
The integrated spacecraft and payloads are nearing completion on their CDR. Flight hardware currently is in production for every element. NASA is preparing for a second qualification test for the SLS boosters, and structural test articles for the core and upper stages of the rocket are either completed or currently in production. NASA also recently completed the first developmental test series on the RS-25 engines. Release M15-155 NASA Teleconference to Preview Historic Flyby of Icy Saturn Moon
NASA's Cassini spacecraft will sample an extraterrestrial ocean on Wednesday, Oct. 28, when it flies directly through a plume of icy spray coming from Saturn's moon Enceladus. The agency will hold a news teleconference at 2 p.m. EDT on Monday, Oct. 26, to discuss plans for and anticipated science results from the historic flyby.
The teleconference participants are:
- Curt Niebur, Cassini program scientist at NASA Headquarters in Washington
- Earl Maize, Cassini project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California
- Linda Spilker, Cassini project scientist at JPL
To participate in the briefing, media must contact Laurie Cantillo at 202-358-1077 or laura.l.cantillo@nasa.gov no later than noon on Oct. 26. Questions also can be submitted during the briefing via social media using the hashtag #askNASA.
Audio of the event will stream live on the NASA website, where visitors also can find accompanying visuals. Event audio also will stream live online, with visuals, on Ustream.
The spacecraft will make its closest approach to Enceladus at 11:22 a.m. Wednesday at an altitude of 30 miles (49 kilometers) above the moon's south polar region. The encounter will be Cassini's deepest-ever dive through the Enceladus plume, and is expected to provide valuable data about activity in the global ocean stirring beneath the moon's frozen surface.
Cassini scientists are hopeful the flyby will provide insights into how much hydrothermal activity is occurring within Enceladus, and how this hot-water chemistry might impact the ocean’s potential habitability for simple forms of life. If the spacecraft’s ion and neutral mass spectrometer instrument (INMS) detects molecular hydrogen as it travels through the plume, scientists may get the measurements they need to answers these questions.
"Confirmation of molecular hydrogen in the plume would be an independent line of evidence that hydrothermal activity is taking place in the Enceladus ocean, on the seafloor," said Hunter Waite, INMS team lead at Southwest Research Institute in San Antonio. "The amount of hydrogen would reveal how much hydrothermal activity is going on."
Using Cassini's cosmic dust analyzer (CDA) instrument, scientists expect the flyby will lead to a better understanding of the chemistry of the plume. The low altitude of the encounter is, in part, intended to increase the spacecraft’s access to heavier, more massive molecules -- including organics -- than the spacecraft has observed during previous, higher altitude passes through the plume. The CDA instrument, which is capable of detecting up to 10,000 particles per second from the plume, also is expected to reveal how much material the plume is spraying from the moon's ocean into the space around Saturn.
"There's really no room for ambiguity," said Sascha Kempf, a CDA team co-investigator at the University of Colorado at Boulder. "The data will either match what our models are telling us about the rate at which the plume is producing material, or our concept of how the plume works needs additional thought."
Scientists also hope the flyby will help solve the mystery of whether the plume is comprised of column-like, individual jets, or sinuous, icy curtain eruptions -- or a combination of both.
Given the important astrobiology implications of these observations, the scientists caution that it will be several months before they are ready to present their detailed findings.
Cassini will acquire images of Enceladus both before and after the encounter. For the time of closest approach, the cameras' fields of view will drag across the surface. These observations are expected to capture some of the highest-resolution views ever of the icy south polar terrain, lit by reflected light from Saturn. Post-flyby processing will be used to remove blurring caused by the spacecraft's movement during exposure.
"Cassini truly has been a discovery machine for more than a decade," said Curt Niebur, Cassini program scientist at NASA Headquarters in Washington. "This incredible plunge through the Enceladus plume is an amazing opportunity for NASA and its international partners on the Cassini mission to ask, 'Can an icy ocean world host the ingredients for life?'"
The last of Cassini's three final close flybys of this icy moon, targeted at an altitude of 3,106 miles (4,999 kilometers) on Dec. 19, will examine how much heat is coming from the moon's interior. The closest-ever Enceladus flyby took place in October 2008 at an altitude of 16 miles (25 kilometers). Cassini flew closer to the moon's icy surface during that encounter, but passed through the plume at a much higher altitude than it will during the Oct. 28 flyby.
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate in Washington.
