Cassini a genuine human triumph

Analysis: Cassini a genuine human triumph


By Phil Berardelli
United Press International


Washington, DC, Jul. 1 (UPI) -- NASA's spectacular feat of placing the
Cassini spacecraft in orbit around Saturn, beginning a four-year
mission to explore the giant ringed planet and its 31 known moons,
ranks with the greatest achievements in human history and surpasses
even the stunning successes of the twin Mars rovers.

The spacecraft -- a cooperative project of NASA, the European Space
Agency and the Italian Space Agency -- entered orbit around Saturn at
12:12 a.m. ET Thursday, after traveling nearly 2.2 billion, circuitous
miles (3.5 billion kilometers) since its launch from Cape Canaveral
Air Force Station, Fla., on Oct. 15, 1997.

When flight controllers at NASA's Jet Propulsion Laboratory in
Pasadena, Calif., received a signal that Cassini had completed the
96-minute engine burn needed to place the spacecraft in the correct
orbit, they broke into cheers and tears of relief that their decades
of planning and operations -- and NASA's $3 billion investment -- were
rewarded.

"This is a tribute to the team at NASA and our partners ... to
accomplish this feat taking place 934 million miles (1.5 billion km)
away from Earth," said Ed Weiler, the agency's associate administrator
for space science, at NASA headquarters in Washington. "What
Cassini-Huygens will reveal during its tour of Saturn and its many
moons, including Titan, will astonish scientists and the public."

Robert T. Mitchell, program manager for Cassini-Huygens at JPL, said:
"We didn't expect anything less and couldn't have asked for anything
more from the spacecraft and the team. This speaks volumes to the
tremendous team that made it all happen."

Charles Elachi, JPL director and team leader on the radar instrument
onboard Cassini, said: "It feels awfully good to be in orbit around
the 'Lord of the Rings.' This is the result of 22 years of effort, of
commitment, of ingenuity, and that's what exploration is all about."

David Southwood, director of scientific programs for the European
Space Agency, said: "This was America's night. This was NASA doing it
right. They really gave those of us in Europe a challenge. We've got
six months to go until we land on Titan. We're just praying that
everything will go as well."

Julie Webster, Cassini-Huygens spacecraft team chief, said: "The
spacecraft has been an incredible joy to fly. We stand on the
shoulders of people who had 40 years of experience building and
designing spacecraft."

On rare occasions, the hype by a project's sponsors matches reality.
This is one such occasion.

Though hazards and potential malfunctions always loom whenever
spaceflight is involved, Cassini's successful arrival at Saturn
justifies the risk taken to get it there. Already, the spacecraft has
returned images of unprecedented detail of the planet's cloud tops,
taken from a distance of only about 12,000 miles (20,000 km).

Cassini also captured images of the rings from nearly point-blank
range, revealing incredible detail.

During the most dramatic moments of the mission so far, Cassini
plunged directly through the rings, entering a zone called,
ironically, the Cassini Gap, which scientists had predicted was devoid
of ring material, but no one knew for sure was empty. The tremendous
gamble paid off and Cassini, which as a precaution had turned its dish
antenna away from Earth and toward the ring gap, sent the signal
following the engine burn that it had survived the plunge.

In the coming years, the 6 ton, bus-sized spacecraft is scheduled to
fly close to Saturn 76 times and visit Titan, its largest moon, 45
times. It also will execute 52 close flybys of seven of the other
moons.

At the end of this year, the Huygens probe, which has piggy-backed
aboard Cassini, will attempt the closest view of Titan, the most
distant object from Earth yet contacted by a probe. Titan, which is
bigger than either Mercury or Pluto, possesses an atmosphere that is
denser than Earth's at its surface, and might harbor enough

Everything -- everything -- Cassini does represents humanity reaching
out, literally, across a billion miles of space to probe perhaps the
most spectacular object in the solar system.

Saturn, sixth planet from the sun, is the second largest, after
Jupiter. But its magnificent rings, which stretch 185,000 miles
(300,000 km) in diameter -- or more than two-thirds of the distance
between Earth and the moon -- represent a miniature model of the disc
of gas and dust that surrounded the early sun and eventually formed
the planets. Cassini is designed to accumulate detailed knowledge of
the dynamics of interactions among both those rings and the numerous
moons that scientists think will provide valuable data to help
understand how the solar system and its constituent planets evolved.

Beyond the immediate gains in data, however, Cassini represents a
triumphant revisit to a planetary system that has dazzled earthbound
observers three times before, when Pioneer 11 and Voyagers 1 and 2
flew by on their way to destinations beyond. Each one of those mission
gathered data, but posed many questions for planetary scientists that
could not be answered by transitory probes.

As JPL's Kevin Grazier said, "Now, we go back with a mission to answer
many of those questions."

More than that, Cassini, along with NASA's twin Martian rovers, Spirit
and Opportunity, and its Stardust probe -- which recently captured
samples of the dust of comet Wild 2 -- compose the beginning of what
figures to be a robotic exploration of the solar system that will
continue for many years, to be supplemented -- finally -- by the
return of humans to the moon sometime in the next decade.

--

Phil Berardelli is UPI's Science & Technology Editor. E-mail

I second the sentiment -- well done!

(Steve Dufour) wrote in message om...
Analysis: Cassini a genuine human triumph


By Phil Berardelli
United Press International


[snip]

During the most dramatic moments of the mission so far, Cassini
plunged directly through the rings, entering a zone called,
ironically, the Cassini Gap, which scientists had predicted was devoid
of ring material, but no one knew for sure was empty. The tremendous
gamble paid off and Cassini, which as a precaution had turned its dish
antenna away from Earth and toward the ring gap, sent the signal
following the engine burn that it had survived the plunge.

Good thing it didn't really go thru the Cassini Gap or Cassini
Division. (Actually, Gap evokes nicer images, as in Cumberland. Or
maybe not, as in Fulda.)

During the most dramatic moments of the mission so far, Cassini
plunged directly through the rings, entering a zone called,
ironically, the Cassini Gap, which scientists had predicted was devoid
of ring material, but no one knew for sure was empty. The tremendous
gamble paid off and Cassini, which as a precaution had turned its dish
antenna away from Earth and toward the ring gap, sent the signal
following the engine burn that it had survived the plunge.

If Cassini had ion thrusters instead of the
chemical rocket engines (N2O4/MMH and hydrazine),
it would have been able to do much more close
range exploration of the Saturn's rings without
the need for risky maneuvers.

Cassini is far from perfect. One of its reaction
wheels (used to rotate the spacecraft) malfunctioned.

Titan is important because it may have large amount
of nitrogen, which is essential component of safe
atmosphere of orbital greenhouses. Nitrogen is hard
to find beyond the Earth. Although there is plenty
of nitrogen in Jupiter and Saturn, their escape
velocities are too great (60 km/s and 36 km/s) for
mining.

Andrew Nowicki wrote:
snip
Titan is important because it may have large amount
of nitrogen, which is essential component of safe
atmosphere of orbital greenhouses. Nitrogen is hard

Why do greenhouses need any nitrogen?
Do plants have problems with (say) 7PSI O2, and a bit of CO2?
Or do you mean WRT fire.

In article ,
Mike Chan wrote:
Good thing it didn't really go thru the Cassini Gap or Cassini Division.

There was at one time a proposal to send Pioneer 11 through Cassini's
Division, but that wasn't actually done, which is just as well since the
Voyager images revealed that the Division isn't really empty...
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article ,
Ian Stirling wrote:
Why do greenhouses need any nitrogen?
Do plants have problems with (say) 7PSI O2, and a bit of CO2?
Or do you mean WRT fire.

Except for the nitrogen-fixing varieties, I don't think plants care much
about whether there's nitrogen in their air. But the fire concerns are
serious, especially at harvest time when grains in particular are fairly
dry and flammable.

(However, some NEAs are dead comet nuclei, and those are probably more
attractive nitrogen sources than Titan.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Henry Spencer wrote:

(However, some NEAs are dead comet nuclei, and those are probably more
attractive nitrogen sources than Titan.)

Mars is also likely a more attractive source of nitrogen, and lunar
polar deposits may contain nitrogenous organic glop.

Paul

Ian Stirling wrote:

Why do greenhouses need any nitrogen?
Do plants have problems with (say) 7PSI O2,
and a bit of CO2? Or do you mean WRT fire.

Atmosphere of pure oxygen at reduced pressure
is much cheaper than the terrestrial atmosphere
because oxygen is abundant and because low
pressure does not require strong, heavy
greenhouse design.

Fiery death of american astronauts in the Apollo
flight simulator filled with pure oxygen implies
that this atmosphere is not safe for human
habitation. It may also cause respiratory problems.
Living quarters must be filled with terrestrial
atmosphere and shielded against space radiation.
The rest of the greenhouse can be filled with pure
oxygen and devoid of radiation shield. Dense
vegetation is a fire hazard unless it is frequently
drenched with water.

An atmosphere made of oxygen and large amount of
an inert gas would prevent fires. It is highly
probable that Titan abounds with nitrogen, but
Titan is far away.

Carbon dioxide would be an unpleasant choice of
the inert gas since its presence stimulates both
breathing reflexes and the sensation of smothering.

The sun is flinging 1 million tons of matter out
into space every second. The solar wind is made of
hydrogen (95%) and helium (4%) and carbon, nitrogen,
oxygen, neon, magnesium, silicon and iron (~1%).
These atoms are all in the form of positive ions.
http://www.windows.ucar.edu/tour/lin...character.html

Near the Earth the solar wind flux is 14 nanograms
per second per square meter. If we could make a
perfect solar wind collector, it would take 2 years
to capture one kilogram of hydrogen and helium from
the solar wind flux of one square meter.

I do not know how to capture hydrogen and helium
from the solar wind, but if it can be done, they
would be very useful. Helium could be used as inert
part of the atmosphere, while hydrogen could be
used as rocket propellant and chemical ingredient
to make water.

Apollo missions captured solar wind particles in
foils made of aluminum and platinum. The solar wind
particles were firmly trapped at a depth of several
hundred atomic layers. I have no idea if this method
would be feasible on a commercial scale.

"Andrew Nowicki" a écrit dans le message de
...
Ian Stirling wrote:

Near the Earth the solar wind flux is 14 nanograms
per second per square meter. If we could make a
perfect solar wind collector, it would take 2 years
to capture one kilogram of hydrogen and helium from
the solar wind flux of one square meter.

If we make a capturing surface of 100m x 100m we would
collect
14.0e-9 * 3600 * 10 000 = 0.504 gr /hour., 12.096 grams per day.

We would get 1 Kg in 86.67 days, less than 3 months.

Since all those atoms are positively charged, an electric field
would collect them very efficiently without needing any physical support.