Five days before Superstorm Sandy hit the East Coast, weather forecasters predicted its infamous "left hook" -- the sharp turn that drove it straight into the New Jersey shore.
That early warning was mostly due to polar-orbiting satellites, the high-tech flecks in the sky that rotate just 600 miles above the Earth's surface. Circling the planet on a north-south orbit, the satellites provide forecasters with high-resolution images and detailed data that their geostationary counterparts miss from a 20,000-mile-high perch.
But soon, some of that data could disappear.
Polar-orbiting satellites are getting old, with the newest among the National Oceanic and Atmospheric Administration's constellation reaching the end of its lifespan in 2016. NOAA won't launch a new satellite until 2017, leaving several months during which the National Weather Service will be relying on several polar satellites that could fail at any time.
The possibility of a "gap" in weather data is well-known on Capitol Hill. Lawmakers have chided NOAA for years over delays in its satellite programs, with Senate appropriators once threatening to hand over all construction responsibility to NASA.
Today, the polar satellite program -- and its geostationary counterpart -- are among the few budget requests that Congress plans to fully fund in fiscal 2015. Lawmakers from both parties don't want to risk the weather forecasts their constituents rely upon.
Indeed, the loss of so much data sounds catastrophic. But is it?
"All is not lost if we lose all of them," said Jeff Masters, founder of the website Weather Underground. "But we're not going to lose all of them. We're going to lose a few."
NOAA now relies on a hodgepodge of polar satellites in an attempt to ensure data for every region of the Earth is no more than six hours old.
Only one "operational," or primary, satellite comes from a NOAA program; it covers the afternoon orbit. Two satellites built through Department of Defense programs and controlled by NOAA cover the early morning and midafternoon orbits, and NOAA also gathers data from a European satellite. A few of NOAA's older satellites provide additional data.
Experts say NOAA's primary satellite is the one most likely to fail, leaving the agency without a fully functioning polar satellite for an afternoon snapshot. But it would still have data from other polar-orbiting satellites -- just not as much and not as frequently. A loss could limit measurements that allow hurricane paths to be predicted earlier and would especially affect forecasts in northern regions, dealing a particular blow to Alaska.
"It's not like we're not going to have forecasts, but the question is: Are they going to be as accurate if we have this gap?" said David Powner, the director of IT management issues at the Government Accountability Office.
Powner has authored several reports on NOAA's satellite programs, and his division continues to keep tabs on the agency's progress. GAO has estimated that a data gap in the afternoon orbit could last anywhere from 17 to 53 months.
But with NOAA on track to launch a new satellite, Powner said the main challenge now is planning for that gap; possibilities range from airplane missions to tweaking computer models. NOAA's primary polar satellite could last years longer -- or fail next year. NOAA must prepare for it all, within its limited budget.
"We just don't want to cross our fingers and hope that something lasts longer than what you built it for," Powner said.
The spacecraft known as Suomi NPP was never intended to last long. Though it is now NOAA's primary polar-orbiting satellite, it was originally designed for a demonstration mission.
But NPP became the only option when a joint military-civilian satellite program dissolved in 2010.
The National Polar-orbiting Operational Environmental Satellite System (NPOESS) had a promising start, bringing together NOAA, the Defense Department and NASA to build satellites that fit all their needs.
It ended in failure with massive cost overruns and yearslong delays. By the time the White House pulled the plug, the program's estimated cost had ballooned to $13.9 billion from a 2002 estimate of $6.5 billion.
In its place, NOAA and the Defense Department each initiated their own programs: the Joint Polar Satellite System (JPSS) and the now-canceled Defense Weather Satellite System. The failure of NPOESS meant their polar satellites would be launched years late. But while the military had backup satellites ready to launch, NOAA had none.
NPP was the stopgap, providing a Band-Aid for the intervening years. Launched in 2011, it has an official lifespan of five years, though NASA engineers have told GAO they fear poor workmanship on the satellite's instruments could mean it lasts as little as three.
So far, however, NPP appears to be functioning well, providing data from the afternoon orbit with backup assistance from two older polar satellites whose sensors are in various conditions. NOAA and NASA officials have said the positive early performance of NPP bodes well for the future.
Senate and House appropriators have also praised Commerce Secretary Penny Pritzker and NOAA Administrator Kathryn Sullivan for getting the JPSS program more-or-less on track. But some of them have expressed concern over the delay in creating a contingency plan for the potential data gap, along with estimates on the cost.
"The department thus far has failed to present a viable gap mitigation plan, choosing instead to advance nice-to-have satellite projects," Sen. Richard Shelby (R-Ala.), the top Republican on the Senate Appropriations Committee, told Pritzker earlier this year. "I wish you would look closely at that. It concerns a lot of us."
Filling in the blanks
For most Americans, the loss of a polar-orbiting satellite for a few months might go unnoticed. While polar satellites make some forecasting easier -- and more accurate -- geostationary satellites provide the constant image that most forecasters rely on.
"We'd be dead in the water without geostationary satellites. That is our go-to tool," said Eric Christensen, a member of the National Weather Service Employees Organization (NWSEO) and lead forecaster in the Tropical Analysis and Forecast Branch of the National Hurricane Center. "Polar-orbiting satellites fill in the blanks."
For the ocean and northern regions, those blanks become larger -- and polar satellites become more important. The accuracy of the National Weather Service's forecast for Superstorm Sandy was partly thanks to polar satellites that provided detailed data on the storm when it was out at sea.
In particular, a sensor called a scatterometer enables forecasters to spot potential hurricanes and severe storms far in advance. Using microwave energy, the sensor can detect the speed and direction of winds near the ocean's surface -- data that is nearly impossible to obtain any other way.
"We'll get an idea much earlier that there is a very subtle feature out over the ocean that we need to start tracking. It could be many days before anything really develops [but] we're on to these things a lot quicker," Christensen said. "If you go back just 30 years, we would have had almost no information outside of ship observation and what aircraft we could fly out there."
But that capability has already declined. NOAA's celebrated scatterometer QuikScat lost its ability to collect real-time data in 2009, and the agency now uses European equipment to fill the gaps. A replacement -- called RapidScat -- will be launched soon, for a two-year mission on the International Space Station.
Such data is also important in Alaska, where melting sea ice has increased the number of ships traveling through the Bering Strait. The degradation of QuikScat has already left some areas without such detailed wind data.
The loss of polar satellite data would "have a pretty major impact" on the accuracy of Alaska's forecasts, said Jim Brader, the regional chairman of the NWSEO.
The state's high latitude means it's at the far edge of the geostationary satellite's range; each image is taken at a sharp angle, through a long slice of atmosphere. Without computer correction, Alaska is "like a little sliver," said Brader, who is the lead meteorologist at the weather forecasting office in Fairbanks, Alaska.
But polar-orbiting satellites provide high-resolution images six times each day, providing the details missing from the broader geostationary picture. They reveal patches of fog, cumulous clouds, fires and remote floods. When ice jams occur, forecasters can see how much water can accumulate -- and inform public officials of impending floods.
The more polar data lost, the greater the uncertainty.
In 2012, the European Centre for Medium-Range Weather Forecasts used Sandy as an opportunity to calculate the importance of polar satellites. It found that without data from all the 14 polar satellites then in orbit, the five-day forecast would have shown Sandy remaining at sea. With them, forecasters were able to predict that the storm would hit the East Coast.
"If you look at that forecast, it was really kind of spot on," Powner said. "If you didn't have polar data that forecast would have been off."
In short, the polar data enabled forecasters to give the public more warning. Without any polar satellite, most computer models wouldn't have predicted the accurate path until three days before the storm hit.
But that's the worst-case scenario. Losing one or two polar satellites would ostensibly have less of an effect. And tweaked computer models -- along with data borrowed from other countries and through other means -- might be able to partly account for the missing data.
"Without polar orbiters and the information they provide, I think our ability to get things done will be to some extent degraded, but not crippled," Christensen said. "We can still do our job."