Cosmic 1st: European spacecraft lands on comet

"The European Space Agency says it has succeeded in landing a
spacecraft on a comet for the first time in history.

The agency says it has received a signal from the 100-kilogram
(220-pound) Philae lander after it touched down on the icy
surface of the comet named 67P/Churyumov-Gerasimenko.

The landing on the speeding comet marks the highlight of the
decade-long Rosetta spacecraft's mission to study comets and
learn more about the origins of these celestial bodies."

See:

http://hosted.ap.org/dynamic/stories...LATE=DE FAULT


Congratulations ESA!

As a follow-up, apparently the original landing did not go as smoothly as hoped and the probe was unable to anchor itself to the comet on first contact. Subsequently the probe "bounced" back into a position on the comet whereby it's solar arrays* are not longer illuminated hence the probe is relying on limited battery power. The question I have not seen resolved is whether the ESA has decided to try to retrieve as much data as possible with the probe in its current position before the batter power is exhausted vs trying to reposition the probe in a more favorable position on the comet and attempting the anchoring to the comet's surface as was originally intended. Stay tuned.

*For such a distant mission one wonders why a solar array was preferred over an RTG. I'm sure had ESA asked, NASA might have been able to provide, even though I understand the material is in short supply. Or was this yet another case of anti-nuclear bias permeating the scientific community for no real reason?

Le 14/11/2014 17:41, David Spain a écrit :
*For such a distant mission one wonders why a solar array was preferred over an RTG.

I'm sure had ESA asked, NASA might have been able to provide, even
though I understand

the material is in short supply. Or was this yet another case of
anti-nuclear bias

permeating the scientific community for no real reason?


There are real reasons to avoid working with highly radioactive
substances ad the associated hassles. Obviously nobody thought the thing
would rebound, so the choice of solar panels was justified.

Not everything is lost since the comet is approaching the sun and the
sun will become more and more powerful. The machine will just wait for
more solar energy, that's all.

It will enter an hibernation state until the sun is nearer.

On 11/14/2014 4:57 PM, jacob navia wrote:

There are real reasons to avoid working with highly radioactive substances

Define "highly radioactive".

Most RTG's use Plutonium 238, which is mostly an alpha emitter. Alpha
particles take only minimal shielding. Assuming reasonably pure fuel,
the metal case of the unit is probably enough shielding.

Actually, the general policy has been to avoid use of RTG's whenever
solar power will do. Regardless of the ease of shielding, Plutonium is
nasty stuff. A main concern when using it would be the possibility of a
launch accident sprinkling it around the launch area. Remember that
Antares accident just two weeks ago? Imagine it happening with a
payload that included nuclear materials.

Vaughn wrote:
Actually, the general policy has been to avoid use of RTG's whenever
solar power will do. Regardless of the ease of shielding, Plutonium
is nasty stuff. A main concern when using it would be the
possibility of a launch accident sprinkling it around the launch
area. Remember that Antares accident just two weeks ago? Imagine
it happening with a payload that included nuclear materials.

I thought that the RTGs were designed/built with that contingency in
mind? At, I suppose, something of a weight cost.

rick jones
--
a wide gulf separates "what if" from "if only"
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On 11/14/2014 8:49 PM, Rick Jones wrote:
I thought that the RTGs were designed/built with that contingency in
mind? At, I suppose, something of a weight cost.

Conceded, but perhaps more important is the possibility of a
political/public relations "disaster". For a European project, tree
huggers are even a bigger factor.

If you think the public doesn't pay attention to these things, just
search for the Internet tracks from 2004/5 when there was great public
concern over the nuclear payload in the Cassini probe. Such as:
http://www.animatedsoftware.com/cassini/

On 11/14/2014 4:57 PM, jacob navia wrote:
Not everything is lost since the comet is approaching the sun and the
sun will become more and more powerful. The machine will just wait for
more solar energy, that's all.

It will enter an hibernation state until the sun is nearer.



I believe the issue in not proximity but position. The lander is in the
shadow of a surface feature of the comet. I believe the hope is that as
the orbital position changes, the area of the comet which the lander
occupies will become illuminated again, thus recharging the batteries
needed to run the science experiments. Let's hope that happens before
any significant out-gassing occurs, which might easily loft the
un-anchored probe off the comet for good.

Dave

Le 16/11/2014 00:21, David Spain a écrit :
On 11/14/2014 4:57 PM, jacob navia wrote:
Not everything is lost since the comet is approaching the sun and the
sun will become more and more powerful. The machine will just wait for
more solar energy, that's all.

It will enter an hibernation state until the sun is nearer.



I believe the issue in not proximity but position. The lander is in the
shadow of a surface feature of the comet. I believe the hope is that as
the orbital position changes, the area of the comet which the lander
occupies will become illuminated again, thus recharging the batteries
needed to run the science experiments. Let's hope that happens before
any significant out-gassing occurs, which might easily loft the
un-anchored probe off the comet for good.

Dave


It does receive 1.5 hours the sun in its solar panels, as far as I
remember from first reports. It is not enough to recharge at more than 3
AU from the sun, but when it comes nearer it could be enough.

The comet will approach the sun coming to 1.29 AU from it, i.e.
essentially the same solar power of the earth (1.0 AU). That could give
enough solar power to power it up again.

jacob navia wrote:
The comet will approach the sun coming to 1.29 AU from it, i.e.
essentially the same solar power of the earth (1.0 AU). That could
give enough solar power to power it up again.

Of course the ESA folks took distance and inverse square into account
when they sized the solar panels for the initial rendesvouse, but that
is something of a loose definition of essentially isn't it? 1/1
versus 1/1.7 no?

rick jones
--
The computing industry isn't as much a game of "Follow The Leader" as
it is one of "Ring Around the Rosy" or perhaps "Duck Duck Goose."
- Rick Jones
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

In message
David Spain wrote:

*For such a distant mission one wonders why a solar array was preferred over an RTG.

You have looked at how heavy an RTG is? Philae is 100kg with around 25kg
available for instruments. Even allowing for batteries no longer being
required, a suitable RTG is going to eat into the science payload never
mind the extra radiators needed to dump the surplus heat.

Anthony