Jupiter mission's solar power, a huge mistake?

Notice the article does not address:

What does the increased mechanical complexity of the solar panels
versus the RTG do to the mission’s chances of success?
What are the cost differences (including the launch vehicle
differences needed to accommodate the huge solar arrays), had an RTG
been available?
Why are RTG’s not available, is it because of shortage of plutonium,
or politics?


3 August 2011 Last updated at 21:42 ET
Juno probe goes 'back to Jupiter'
By Jonathan Amos Science correspondent, BBC News

Nasa's $1.1bn (£0.7bn) Juno mission will venture where no solar-
powered spacecraft has dared go before.

The probe, due to launch from Cape Canaveral on Friday, will cruise
beyond Mars to put itself in orbit around the gas giant Jupiter in
2016.

At this distance, where the intensity of sunlight is only 1/25th of
that at Earth, one would normally resort to a plutonium battery.

But Juno will instead travel with three wings coated with 18,000 solar
cells.

At Earth, these 9m-long arrays will produce over 14,000 watts - enough
to power an electric car. At Jupiter, they will muster a little over
400 watts - enough for just a few incandescent lightbulbs.

Of course, it is not lightbulbs Juno's panels must support, but
scientific instruments.

Nonetheless, Scott Bolton, the mission's chief scientist, believes his
spacecraft will cope just fine in the dim outer reaches of the Solar
System.

"As a solar-panelled mission, we have to keep those solar panels
facing the Sun and we never go into Jupiter's shadow," he told BBC
News.

"Those are things we can do and still accomplish our science; it
doesn't hurt us. But it would have been easier if we could have
pointed just any way we wanted. We've had to develop [a strategy], and
in fact we've advanced solar cell technology in doing so."

When Bolton and colleagues submitted their proposal for a Jupiter
mission, a plutonium thermoelectric generator simply was not
available. There were development ideas within Nasa, but the Juno team
thought it less risky to go with solar cells than wait for a nuclear
option to present itself.

Juno's mission is to explain the Solar System by explaining the origin
and evolution of its biggest planetary member.

The spacecraft's remote sensing instruments will look down into the
giant through the many layers and measure their composition,
temperature, motion and other properties.

This should yield some remarkable new insights into the coloured bands
that wrap around the planet, and a new perspective on the famous Great
Red Spot - the colossal storm that has raged on Jupiter for hundreds
of years. Juno will tell us how deep its roots go.

A key quest is to measure the abundance of water in the atmosphere -
an indicator of how much oxygen was present in Jupiter's region of the
Solar System when it formed, and perhaps a tell-tale of any migration
from its original formation location.

The probe will also try to settle old arguments over whether the
planet hosts a rocky core or whether its gases go all the way down to
the centre in an ever more compressed state, under perhaps 40 megabars
of pressure (40 million times the air pressure experienced at sea-
level on Earth).

And it will look for the deep swirling sea of liquid metallic hydrogen
that many suspect is the driver behind Jupiter's strong magnetic
field.

All this information bears down strongly on the competing theories for
how the eight worlds we now call planets came into being.

"Jupiter probably formed first; it's the largest of all the planets.
In fact, it's got more material in it than all the rest of the Solar
System combined," explained Dr Bolton, who is affiliated with the
Southwest Research Institute (SWRI) in San Antonio, Texas.

"So, after the Sun formed, it got the majority of the leftovers. And
that's why it's very interesting to us if we want to go back in time
and understand where we came from. Jupiter holds the secrets. We want
to know the ingredient list - what we're really after is discovering
the recipe for making planets."

Jupiter's immense magnetic field accelerates particles to tremendous
speeds, rendering the local environment the number one hazardous
location in the Solar System for electronics (apart from the Sun's
immediate vicinity).

To prevent these critical systems being scrambled, Juno carries them
inside a titanium vault.

The rocket chosen by Nasa to launch Juno is the Atlas V, the vehicle
recently identified by the space agency as a possible future astronaut
launcher.

Lift-off from the Cape Canaveral Air Force Station on Friday is timed
for a window that opens at 11:34 local time (15:34 GMT; 16:34 BST).

Juno will head out into space but it will come back to Earth briefly
as it looks to pick up the speed it needs to shoot itself out to
Jupiter.

Jan Chodas, the Juno project manager, explained: "We launch from
Earth; we swing out past the orbit of Mars; we fire the engine to do a
couple of deep-space manoeuvres, to target us to come back in by the
Earth. And we do a flyby of the Earth at about 500km in October of
2013, and then we slingshot ourselves out towards Jupiter, arriving in
July 2016."

Juno is the second in Nasa's so called New Frontiers class missions.
The first, New Horizons, was launched towards dwarf planet Pluto in
2006 and should arrive at its target in 2015.

"Juno was confirmed on August 5, 2008, and here we are ready to launch
Juno on August 5, 2011 - three years later," said Jim Green, the
director of planetary science at Nasa. "Juno is on schedule and on
budget."

On 8/4/11 7:55 AM, $27 TRILLION to pay for Kyoto wrote:
Why are RTG’s not available, is it because of shortage of plutonium,
or politics?

See:
http://www.space.com/12548-jupiter-m...t-history.html

Target: Jupiter — Missions to the Solar System's Largest Planet

"NASA is launching its most advanced probe yet to study the planet
Jupiter on Friday (Aug. 5). But the new mission, called Juno, is
standing on the shoulders of giants, its managers said — specifically
the eight robotic spacecraft that visited the gas giant planet previously.

"Each of the missions that we do are providing unique and very important
information," said Juno's principal investigator, Scott Bolton, of the
Southwest Research Institute in San Antonio, during a press conference
Wednesday (Aug. 3). "Some of those earlier missions were reconnaissance,
so we could figure out what are the right questions, and they
essentially led us to ask the questions that we have with Juno."
[Photos: NASA's Juno Mission to Jupiter]

On 04/08/2011 13:55, $27 TRILLION to pay for Kyoto wrote:
Notice the article does not address:

What does the increased mechanical complexity of the solar panels
versus the RTG do to the mission’s chances of success?
What are the cost differences (including the launch vehicle
differences needed to accommodate the huge solar arrays), had an RTG
been available?
Why are RTG’s not available, is it because of shortage of plutonium,
or politics?

RTGs are one answer in the 'where do we get power from' question.

Other questions are 'They cost how much?', 'We need how many?' and 'They
weigh how much?'