NASA launches $916 million soil moisture satellite
A United Launch Alliance Delta 2 rocket boosted an innovative NASA satellite into orbit Saturday, kicking off a three-year, $916 million mission to measure the moisture, frozen and liquid, in the top few inches of Earth's soil to improve forecasting, to better understand the causes and impact of droughts, floods and other natural disasters and to improve long-range climate change projections.
"With the launch of this project, decision makers will be better able to understand the water cycle and how soil moisture fits into that," said Christine Bonniksen, NASA program executive of the Soil Moisture Active Passive, or SMAP, mission. "The soil actually gathers the precipitation prior to it entering the rivers and then evaporating back into the atmosphere. As a result, soil moisture impacts many areas of human interest, including flood, drought, disease control and weather."
Running two days late because of high winds aloft Thursday, the long-awaited mission got underway at 9:22 a.m. EST (GMT-5, 6:22 a.m. local time) when the 165-ton Delta 2 booster's first stage engine roared to life, followed by ignition of three strap-on solid fuel boosters.
Lighting up the pre-dawn sky with a torrent of flame, the 127-foot-tall rocket quickly climbed away from Space Launch Complex 2 at Vandenberg Air Force Base, California, arcing away to the south over the Pacific Ocean west of Los Angeles.
The strap-on boosters burned out 65 seconds after liftoff and were jettisoned 35 seconds later. The Aerojet Rocketdyne RS-27A first-stage engine continued to burn another two-and-a-half minutes before shutting down as planned. The first stage then fell away and the second stage's AJ10-118K engine ignited, continuing the boost to orbit.
Ten minutes and 44 seconds after launch, the second stage engine shut down and the booster entered a 41-minute coast phase. Finally, about 55 minutes after takeoff, the second stage engine re-ignited for 12 seconds to put the spacecraft in the desired 426-mile-high orbit around Earth's poles.
Moments later, the 2,000-pound SMAP satellite was released to fly on its own and engineers reported the spacecraft's solar panels unfolded and locked in place as planned. Four small "cubesats" carried aloft on the Delta 2's second stage as part of an educational initiative were scheduled for release about 48 minutes after SMAP's deploy.
It will take two months to check out and calibrate SMAP's two instruments, an L-band microwave radiometer and radar, and to deploy and spin up the unusual 19.7-foot-wide mesh dish-like reflector needed to collect science data. Both instruments share the offset reflector, tuned to detect moisture in the top 5 centimeters -- 2 inches -- of soil around the planet.
The stowed reflector's boom assembly will be commanded to unfold 16 days from now. Then, starting four days later, the satellite's antenna will be commanded to unfurl.
"It starts at 12 inches in diameter," said Kent Kellogg, SMAP project manager at the Jet Propulsion Laboratory. "This is passive release of the strain energy, that'll bloom the antenna out to about seven feet in diameter. Then we'll do the powered deployment, which will deploy the antenna out to its final 20-feet-in-diameter size. That process takes about 30 minutes to complete from start to finish."
To collect the desired soil moisture data, the antenna, which is tilted with respect to the satellite's body, must rotate, sweeping out a circular swath directly below the spacecraft. Starting about 50 days after launch, engineers will spin the antenna up to 4.5 rpm.
"As we begin to spin up, the spacecraft actually counter-rotates in the opposite direction," Kellogg said. "This is by design and is a feature of the fact that we're trying to spin up a very large structure with a relatively small spacecraft. Once the antenna has reached a stable spin rate, the spacecraft attitude system will regain sun pointing very quickly, and we continue on."
After confirming the stability of the satellite with its now-spinning antenna, the spin rate will be gradually increased to 14.6 rpm. The spinning reflector will sweep out a 620-mile-wide swath as the satellite orbits, passing over the equator every day at 6 a.m. and 6 p.m. local time.
Dara Entekhabi, SMAP science team lead at the Massachusetts Institute of Technology, said the radiometer will act somewhat like a camera, using microwaves to "see" in daylight and darkness, penetrating clouds, vegetation and the top few inches of soil to measure water volume. The satellite's radar is not as sensitive, but will provide higher resolution.
"The radar will be providing our high resolution data, and the radiometer provides the high accuracy data," said Bonniksen. "When you put these together, it's very similar to looking through both lenses on a pair of bifocals at the same time. As a result, we will have a highly accurate global map of soil moisture for our scientists to use."
SMAP is unique in that "it has returns in two very distinct areas," Entekhabi said. "One of them is in fundamental understanding of how the environment works. The second is in the arena of applications. SMAP provides data that affect our everyday lives in terms of dealing with some really serious natural hazards."
Soil moisture links the planet's water, energy and carbon cycles, he said, and "if it wasn't for the soil moisture variable, these three processes over land would vary independently, but they don't. They work in concert like gears in a clock. They are linked together through the soil moisture variable."
Understanding the details of those interactions will help scientists improve short- and long-term forecasting.
"As water evaporates from soil water to vapor in the atmosphere, it feeds the water cycle," Entekhabi said. "It takes energy to vaporize water, and water vaporizing cools the surface and maintains the temperature much like humans have evolved sweating to regulate body temperature. The same thing happens with Earth system. And as plants transpire and pick up biomass through absorbing carbon dioxide from the atmosphere and releasing water vapor, they are engaged in the water and energy cycles as well.
"So these three cycles are intimately linked through the water variable. Through measurements SMAP can make, we can test and improve models that we use for atmospheric weather prediction and climate change projections."
SMAP is designed to generate global maps of soil moisture every two to three days, data that will help researchers improve near-term forecasts while building a database that will improve long-range projections, including soil moisture's impact on climate change.
While soil moisture represents less than 1 percent of Earth's water, it plays a critical role "because it's what's interacting with the terrestrial biosphere, with the vegetation, it's what determines how much runoff occurs due to incident precipitation, how much fresh water there is in the rivers and lakes," Entekhabi said.
"It's a tiny amount, but a very important amount. It's not the percentage of the total that's important, but where that soil moisture is and what it's affecting."
This was the 153rd Delta 2 launch since the rocket's debut in 1989 and the booster's 98th straight success dating back to 1997, leaving just two Delta 2's in ULA's inventory. It was the second flight this year for United Launch Alliance and the company's 93rd overall.
