Ambitious NASA Probe to Fly Through Sun's Fringe
May 22 2008
By Brian
Berger
WASHINGTON - Spurred to action by
Congress, NASA is finally moving out on an ambitious mission to
send a spacecraft closer to the sun than any has ever gone
before.
Artist's concept of NASA's Solar
Probe spacecraft making its daring pass toward the sun, where it
will study the forces that create solar wind. Credit:
NASA/JHUAPL.
NASA directed the Johns Hopkins
University Applied Physics Laboratory (JHUAPL) to begin
preliminary work on a proposed $750 million Solar
Probe mission last
month, with plans to launch around 2015 to fly through the sun's
corona and study the stream of charged particles it regularly
blasts into space. At its closest approach, the Solar Probe
would fly within 4.3 million miles (7 million km) while being
bombarded by radiation and blasted by withering temperatures.
The Laurel, Md.-based lab will
receive $13.8 million from NASA this year to begin pre-Phase A
development work to address the mission's considerable technical
risks, among them designing a carbon composite heat shield
capable of protecting the roughly 992-pound (450-kg) spacecraft from
temperatures that
will reach as high as 2,552 degrees Fahrenheit (1,400 degrees
Celsius).
And with NASA intending to solicit
instrument proposals for the Solar Probe mission this year, APL
will use part of the $13.8 million to support the instrument
accommodation assessments that must happen before NASA can
select a spacecraft's science payload.
NASA is funding APL's pre-Phase A
work and the upcoming competition to pick the Solar Probe's
science payload with the help of $17 million Congress added to
the space agency's 2008 budget for the mission.
Sen. Barbara Mikulski (D-Md.),
chair of the Senate Appropriations commerce, justice, science
subcommittee told Space News in a written statement she was
pleased NASA tapped APL to begin work on Solar Probe.
"I fought alongside the scientific
community to start Solar Probe because of its importance in
understanding the effects of the sun on the Earth," Mikulski
said in a May 9 statement. "These effects are profound on
everything from the health and safety
of our astronauts,
to civilian and national security satellites, our power grid
system and even international airline flights over the Earth's
poles. I will continue to fight to ensure that there is funding
in the federal checkbook for this important priority."
Mikulski's pledged support could
prove essential to ensuring that the Solar Probe work getting
under way this year continues into 2009. Although NASA intends
to fund Solar Probe instrument proposals starting next year, the
agency has requested no 2009 money for other aspects of the
mission's development.
As a result, after spending nearly
$14 million this year on Solar Probe, expenditures would drop to
zero in 2009 unless Congress again decides to add money. NASA's
five-year budget projection, however, does include $3.4 million
for Solar Probe in 2010, $40.1 million in 2011, $74.2 million in
2012 and $106.3 million in 2013. To keep Solar Probe on track
for a 2015 launch, NASA would need to come up with an additional
$500 million.
Reaching the Sun
The Solar Probe mission concept
has been incubating for more than 30 years, only to be
repeatedly stymied by budget and technical limitations,
according to Walter Faulconer, APL's business area executive for
civilian space programs.
"In the last incarnation, it was a
$1.2 billion mission that required an RTG," he said, referring
to radioisotope thermoelectric generators that transform the
heat from decaying plutonium into electricity. "And that was a
big improvement over a previous version which was a
multi-billion-dollar mission."
In 2007, NASA's associate
administrator for science at the time, Alan Stern, gave APL a
study contract worth $1 million to produce a Solar Probe mission
concept that could be accomplished for around $750 million,
including launch, but not require a nuclear power source.
With NASA uncertain about how much
plutonium-238 it will be able to obtain in the future, the
agency is trying to preserve the current inventory for a
flagship-class mission to the outer planets it intends to launch
in the 2015-2020 timeframe. Previous Solar Probe concepts
entailed sending a fairly massive spacecraft out to Jupiter for
a gravity assist, an indirect route that added several years of
travel time and required a nuclear-power source to compensate
for the dearth of solar energy available so far from the sun.
Faulconer said it was not easy
getting the scientists and engineers to abandon some of their
preconceived notions and take a fresh look at what needed to be
done to send a probe so
close to the sun.
"We had to knock some heads since
a lot of people felt like they had studied this to death," he
said.
By the time the study was
completed in March, the APL-led team, according to Faulconer,
had come up with "a very elegant mission that answered the mail
- it's $750 million, it's non-nuclear and we did not give up any
of the science."
The APL team did, however, relax
two long-established objectives for the mission. As currently
envisioned, Solar Probe would not go as close to the sun and it
would not fly over the sun's poles.
Previous mission concepts called
for flying within 1.8 million miles (3 million km) at closest
approach, closer than the current 4.3 million miles. But even at
9 solar radii, a distance of roughly 4.3 million miles, the
probe still will be well within the sun's outer atmosphere.
"It's still hot but not as hot,"
Faulconer said.
Sending Solar Probe over the sun's
pole also turned out to be "a real cost driver" for the mission,
according to Faulconer. Dropping that requirement "really opened
things up."
"There was a scientific reason why
they wanted to go over the pole," he said. "But it turns out
that the phenomenon scientists once thought occurred only at the
poles we now know thanks to recent discoveries from
our Stereo mission that
the same phenomenon can be observed over other parts of the
sun."
Instead of flying out to Jupiter,
Solar Probe would use seven Venus flybys over nearly seven years
to gradually shrink its orbit, Faulconer said. APL's Mercury
Surface, Space Environment, Geochemistry and Ranging mission is
employing a similar approach, flying past Venus in 2006 and
again in 2007 as it seeks to settle into orbit around the
innermost planet in 2011.
The optimal time to begin the
Solar Probe's seven-year journey would be 2015, Faulconer said,
with less optimal launch opportunities in 2013 and 2018.
Source
http://www.space.com/businesstechnology/080521-nasa-solar-probe.html
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