Cost Cuts Kill Climate Satellite

Deep cuts in NASA’s Earth science budget for 2002 have claimed a second casualty. Having mothballed the Triana satellite, which would have provided data on ozone and climate change (see August 2001, page 23), NASA now plans to switch off another Earth-observing satellite, the Upper Atmosphere Research Satellite (UARS). At press time, UARS was scheduled to be turned off on 30 September, despite calls by scientists to keep its $10 million-per-year budget going. They argue, among other things, that NASA is mandated to continually study the ozone layer under the 1976 NASA Authorization Act and the 1990 Clean Air Act. UARS is one of the oldest Earth-observing satellites still in orbit, and has been at risk since August 2000, when NASA decided to exclude it from its budget proposal for 2002. Indeed, this year, an 11.7% cut is anticipated in the Earth science budget (see June 2001, page 24). Mission delays and cost overruns could lead to early termination of four additional missions, according to some NASA employees.The six-and-a-half-ton UARS satellite has been in orbit since 1991, so losing it is a blow to scientists studying long-term atmospheric trends. “No single satellite can currently replace what UARS is measuring,” says Charles Jackman, the project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Mark Schoeberl, the previous project manager, agrees. “The UARS data is critical to the interpretation of changes in the ozone layer,” he says. The gap will be partly filled by Envisat, a European Space Agency satellite, and by the Advanced Earth Observing Satellite-II, a Japanese satellite, both due to be launched in the next several months.But some crucial UARS climate measurements—most notably stratospheric vertical profiles of chlorine compounds and studies of upper tropospheric water vapor and stratospheric trace gases—won’t be revisited anytime soon. The latter two are important contributors to global warming and won’t be measured again until NASA launches EOS Aura in 2003. “The loss of overlap with future data sets is unrecoverable when trends are being studied,” says James Russell from the Center for Atmospheric Science at Hampton University in Virginia.“UARS is providing critical chlorine and fluorine data at a time when chlorine is behaving in a way that is not easy to understand,” says Russell. He points out that, after three years of declining chlorine and changing methane levels in the stratosphere, chlorine levels unexpectedly shot up during 2000. “It suggests that there is some combined atmospheric dynamics mechanism and chemical reaction going on we can’t see,” he says. UARS is also one of the few satellites used to monitor the 1987 Montreal Protocol, which limited the production of ozone-depleting substances.To be sure, mechanical failures have plagued the satellite in recent years. UARS was designed to last just three years. “It’s amazing it’s lasted this long,” says Jackman. “We can still operate up to 7 of the remaining working instruments at the same time, depending on the power available,” he points out, “and 8 of the 10 instruments are still working.”This spring, in a last-minute attempt to save UARS, Goddard submitted a new proposal to NASA’s Earth science division to keep the satellite working. “We only make these recommendations when we’re sure it’s justified,” says Jackman. In late July, the UARS team found out the proposal had failed. “The main issue driving the decision is cost,” argues David Steitz, a press officer at NASA headquarters in Washington, DC. “We have had to make some tough choices over the past several years and we must live within the constraints of the budget.”Now scientists are proposing to wake up UARS for at least two months to help calibrate EOS Aura once it’s in orbit. The stratospheric gases affecting the ozone layer change by a few percent each year. “This is a hard measurement even with the same instrument,” says Schoeberl, “and the best way to do this is with a series of instruments in overlap.” Russell agrees: “It’s better than zero but not by much. You need at least six months to a year of overlapping data to get enough to compare the two satellites.” But, says Steitz, “no decision on that proposal has been made and there is no firm timetable for a decision.”UARS also no longer has enough fuel for a controlled reentry into the atmosphere. Since UARS is a large satellite, not all of it will burn up in the atmosphere; some pieces will impact Earth. If left alone, sometime between 2013 and 2027 it will spin out of control. The three current possibilities, according to NASA, are to boost UARS into a higher “graveyard” orbit, reduce its threat as a navigation risk by pushing it into an early uncontrolled reentry, or pick the satellite up with the space shuttle. There is even talk that such a rescue mission would provide an opportunity to launch Triana.The termination of UARS has caused some bitterness. “Earth science has been hammered in the past couple of years,” says a former NASA employee, “maybe because some people feel Earth science shouldn’t be in NASA.” The decision is “perplexing,” says Russell, who points to President Bush’s call for increased investment in climate research. “It is scientifically unsound to shut down a working satellite that is providing crucial data for climate-change research at a time when this is vitally needed,” he says. But UARS may only be the first of many victims, says Steitz. “We are entering an era when we will have to continue to make tough choices as to which spacecraft we keep in service and which ones we may have to decommission.” Quenching UARS will create a gap in climate data.NASAPPT|High resolution© 2001 American Institute of Physics.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.