From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Jul 06 2005 - 08:49:00 PDT
http://space.com/businesstechnology/050706_star_voyage.html
Voyage to the Stars: NASA Study Mulls Options
By Leonard David
posted: 06 July 2005
06:41 am ET
To send a spacecraft where none has gone before is a dream assignment for
any space scientist and engineer.
The idea of dispatching a dedicated robotic probe on an interstellar trek
has been seriously advocated for nearly 30 years. A recently finished
appraisal of how to build such a craft shows that it is within reach -- but
nonetheless remains a challenging task.
A NASA-sponsored study team has blueprinted an Innovative Interstellar
Explorer (IIE).
Goal of the IIE would be to plunge outward some 200 Astronomical Units. An
astronomical unit (AU) is the mean distance between the center of the Earth
and the center of the Sun - approximately 93 million miles (150 million
kilometers).
Put that in your cosmic calculator and you'll get: 18,591,186,595 miles
(29,919,614,600 kilometers).
No matter how you figure it, that's a lot of infrequent flyer miles to
travel.
Pull out all the stops
"I think we're converging on something that's doable," said Ralph McNutt,
the principal investigator for the Innovative Interstellar Explorer study.
He is a space scientist at The Johns Hopkins University Applied Physics
Laboratory (APL) in Laurel, Maryland, and also the project scientist for
APL's Messenger mission to Mercury.
If launched in 2014, the probe would arrive at the 200 AU distance in about
2044.
Clearly, along with doses of technology and a requisite high velocity, IIE
demands a good deal of patience from awaiting scientists here on Earth.
McNutt said the IIE concept has moved forward over the last several years as
a NASA Vision Mission project, through a Team X study group at Jet
Propulsion Laboratory (JPL), and by way of NASA Institute for Advanced
Concepts study grants.
"There is always interest in keeping an interstellar probe going through
various studies. But the problem that we've always run up against is
propulsion. That's because you're trying to pull out all the stops and get
out of the Solar System as fast as you can," McNutt told SPACE.com.
Continuous acceleration
In sketching out IIE, McNutt said the relatively small spacecraft would use
radioisotope power sources that energize small electric thrusters. "You need
to make a spacecraft that is Ômassless' as possible," he said, something
akin to "unobtanium".
Still, in taking a hard look at conjuring up an interstellar probe -- and
the kind of science that could be done by the craft -- things do look
promising.
"We can start building them tomorrow, if we had the money," McNutt said.
Efficient, lightweight electric propulsion and power systems are part of the
key.
The Innovative Interstellar Explorer would carry a compact science payload
weighing all of 66 pounds (30 kilograms). It would be boosted from Earth
atop a Delta 4 heavy launcher. A custom upper stage is also required.
That initial launch energy in 2014 would push IIE to an arrival at Jupiter
two years later where the probe would acquire a gravity assist from the
massive planet. Long-term, low-thrust, continuous acceleration of the probe
would be provided by a kilowatt-class ion thruster running off electricity
provided by advanced Stirling radioisotope generators.
Burnout speed
The interstellar probe would cruise out of the solar system at about 7.8 AU
per year. It would accelerate to a "burnout" speed of 9.5 AU per year at 103
AU in November 2029.
In contrast, Voyager 1 is speeding about 3.6 AU per year. Its twin, Voyager
2, is a slow poke at about 3.3 AU per year.
"The IIE would end up being at 200 AU in about 2044," McNutt noted. "Yes, I
know that sounds like a long time from now. But you have to keep this into
perspective. When we started out with the Voyagers, none would have believed
they'd still be going," he said.
In fact, the dual Voyager spacecraft launched in 1977 are now dubbed the
Voyager Interstellar Mission (VIM), investigating the outermost edge of the
Sun's domain ... and beyond. The Voyager probes are expected to go dead
around 2025 as their plutonium-fueled generators are fully discharged.
Decades of lifetime
The 30-year mission by IIE to address fundamental scientific questions about
the interaction of the Sun with the interstellar medium, McNutt said, can
only be answered via on-the-spot measurements that such a mission would
provide.
"The idea here is to try to get as close to true interstellar space as
possible ... past the heliopause and past what we think is an external bow
shock," McNutt pointed out.
But traveling for three decades to do so is tough going.
"Designing something that's going to be good for 30 years ... that scares
the daylights out of people," McNutt admitted. "How to qualify all the parts
for decades of lifetime is a hard problem. But it's something that we're
going to eventually come to terms with. We'll figure out how to deal with
it."
Receiver farms
Pumping back science data from afar is also a challenge. And Earth will also
have to keep up its end of the bargain.
Already in the works is a hoped for upgrade of NASA's Deep Space Network,
turning huge antenna dish complexes into "receiver farms" -- that is,
multiple numbers of smaller antennas. That could enable reception of
downlink signal from IIE of about five kilobytes per second out at 200 AU,
McNutt said.
At some point, as IIE keeps moving onward and outward, it will increasingly
become more difficult for ground controllers on Earth to reprogram the
spacecraft's onboard data processing unit. "The probe will then have to
decide for itself when to phone home. It's not going to be you asking for
the call," McNutt said.
Pulling the plug on the Voyagers
The recent chorus of disapproval about turning off the long-distance Voyager
craft may be a good sign of support for interstellar probe development. The
very idea of shutting down the venerable Voyager probes to save a few
million dollars per year sparked public and Congressional comment.
"I can't answer why there was an outcry," McNutt said, "but I'm certainly
glad there was one."
Indeed, Voyager 1 relayed in May evidence that it reached the heliosheath -
an area just where the solar wind crashes into the thin interstellar gas of
the galaxy.
In a House of Representatives hearing last month, Congressman Vernon Ehlers
of Michigan implored NASA chief, Michael Griffin, to keep a scientific ear
attuned to Voyager. "It seems foolish to wait all these years to reach the
heliosheath and then suddenly pull the plug," Ehlers told Griffin.
"I assure you that I also think it's rather dumb to be turning off Voyagers
1 and 2," Griffin responded. Nonetheless, a NASA assessment on what
spacecraft will be kept in operation and which ones will not is to be
wrapped up later this year, he added.
Step to the stars
While the Innovative Interstellar Explorer is a real study, not real
hardware, McNutt said the reviews are favorable for such a probe to be
lofted within a reasonable period of time.
"This would be a stepping stone. A lot of people resonate with the science
fiction side about taking the first step to the stars," McNutt said.
Given a go-ahead, McNutt senses that the Innovative Interstellar Explorer
could be done for less than $2 billion. While some might consider that
inexpensive, there would also likely be a debate about whether the first
dedicated step to the stars is worth it, he said.
"Basically, it's kind of like throwing a note out in a bottle ... throwing
it out to sea and seeing what comes back," McNutt said. "If we really want
to understand the world around us, we ought to be out there making those
measurements."
Interstellar Travelers Will Have to Watch Their Language
Sailing to the Stars: Sex and Society Aboard the First Starships
The Closest Star System: Alpha Centauri
NASA's Vision: Probes At Stars by 2100
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