James Webb Space Telescope is a boondoggle

In article ,
Andrew Nowicki wrote:
To reduce unwanted infrared light coming from
the Sun, JWST will be launched into the Sun-Earth
L2 point, which is 1.5 million kilometers away
from the Earth. This far out location was
justified by the shade made by the Earth...

Uh, no, the location was chosen to reduce infrared radiation from the
*Earth*, which is a major problem for infrared telescopes in LEO. The Sun
is a small source and is fairly easy to deal with using a sunshade (which
JWST has). A warm Earth filling half the sky is more of a problem,
especially since it goes around the sky about once every 90 minutes.

...The L2 point is in partial shade called penumbra.

Which would in itself be of some use, *reducing* the solar input, except
that JWST will be in a halo orbit around L2, rather than actually at L2.

...If something goes wrong
with the JWST, the telescope will be difficult to
repair because the L2 point is far away from the
Earth. Worse yet, JWST has a monolithic design
not suitable for telerobotic repair or upgrade.

Correct. As with Chandra and Spitzer, the decision was that manned
servicing capabilities were not worth the added problems of operating in
LEO, and telerobotic servicing was too speculative and imposed too many
design penalties. There will be no repairs or upgrades; JWST will do its
job as designed (they hope) and that will be all.

The astronomers may end up regretting this approach if JWST has deployment
problems -- they often conveniently forget that exactly that happened to
Compton, but since *it* was shuttle-deployed in LEO, the astronauts just
went out and fixed it before turning it loose -- but that aside, it's not
a ridiculous approach, given the current costs and lead times and
uncertainties(*) of servicing visits.

(* The cancellation of the Hubble servicing visit told the astronomers,
loud and clear, that they cannot rely on NASA for telescope servicing. )
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article ,
Andrew Nowicki wrote:
A passive tube-shaped insulation surrounding
the telescope in low Earth orbit could reduce
its temperature to 70 K or so. It seems that
NASA is going to send JWST to L2 because they
cannot design decent thermal insulation.

Hardly. The insulation they designed kept COBE's telescope under 50K in
LEO after its LHe supply ran out.

Trouble is, that requires that the telescope point pretty much directly
away from the Earth. Which is a problem, since as the telescope goes
around Earth, that direction changes constantly. This is workable, pretty
much, for a sky-survey instrument like IRAS or COBE. It's grossly
unsuited to a telescope that wants to point at arbitrary targets, and
preferably stare at them for considerable lengths of time.

Note that when ESA built an infrared observatory, they went to the extra
trouble of putting ISO into a highly elliptical orbit, so it was well away
from Earth most of the time.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

February 19, 2004

Earl Colby Pottinger wrote:

Dear Andrew,
Be very careful. You seem to be going down
the same
road as Brad Guth and Thomas Lee
Elifritz. When they first posted they were just in love with thier
own
ideas/inventions, asking questions to try and improve them. However
once
people started showing a number of faults in thier ideas rather than
admit
they had made some mistakes they just try defending thier same old
ideas more
and more. As they did this over time they drifted into weirder and
weirder
ideas until they became the kooks you see today.


Well, I can't speak for Brad, but ...

So you find the concepts reusable single stage
to orbit launch vehicles and extremophile life
and fossilized microbial mats just to0 weird to
handle, do you? Eh? Uh-huh. Ya sure thing, Ole.

Let me try to explain it to you one last time,
once you accept the idea of iron oxide spherules
as signs of past extremophilic microbial life,
it becomes quite clear that ALL the images contain
evidence of fossilized life on Mars. Mars is covered
with ice insulated by a layer of desiccation slag.
It started out with oceans, and is now covered by
iron oxides and salts. That should be a really big hint.

You just don't get it, because frankly, you are a fool.
I'm making up the subject lines purposely like the Star
because this needs to get out to the public, and NASA
is doing everything they possibly can to slow it down.

The only reason I am pursuing this at all is to
clearly illustrate the need for a real rocket,
a fully cryogenic reusable SSTO launch vehicle.

You really need to recalibrate your irony meter.

Let me guess, you're an AMERICAN, no?

Thomas Lee Elifritz
http://elifritz.members.atlantic.net

Brother, talk about being mainstream status quo or bust, taking
whatever out of context that suits your ulterior motives. There's so
much that's dead wrong about what you've been accusing others
(including myself) about that you can't even flush the bogus
intellectual space-toilet you're using for storing your brains.

If intellectual bigotry is what this forum represents, then lo and
behold you've mastered the necessary talent and supposed first hand
expertise to boot.

"When they first posted they were just in love with their own
ideas/inventions, asking questions to try and improve them. However
once people started showing a number of faults in their ideas rather
than admit they had made some mistakes they just try defending their
same old ideas more and more. As they did this over time they drifted
into weirder and weirder ideas until they became the kooks you see
today."

That's even below LLPOF, as not even worth the usual crapolla/flak
favor returning effort.

Andrew,
if you have even half a brain that's not yet assimilated into the NASA
collective, disregard all of these incest cloned borgs, cold-war incest
lovers of whatever's NASA/Apollo or bust. What's needed is a little
hard science upon the melt/vaporising of ice in space, the rate at
which a m3 of plain old ice remains solid until it's entirely
vaporised. Lo and behold, there's no such hard science on the likes of
any water-ice or even upon dry-ice in space, much less an honest word
as to the extremely harsh radiation environment, other than what an old
Raytheon/TRW Space Data Report offered as 2e3 Sv/year while situated
within the Van Allen expanse and behind 2 g/cm2 worth of aluminum
shielding, and that wasn't anywhere near the L2 point of receiving the
secondary packets of hard-x-rays off the raw solar illuminated moon.

Regards, Brad Guth / GASA-IEIS http://guthvenus.tripod.com/gv-topics.htm

Thomas Lee Elifritz,
I totally agree that once upon a time, actually every 105,000 or so
years, Mars has become wet with open water and a whole lot more
atmosphere, and as for the very same reasons why mother Earth has
cycled through thousands of ice-ages, at least up until humanity
screwed everything environmentally to a fairlywell.

Life upon Mars may not have evolved entirely independently, as per
whatever a little terraforming may have contributed needs to be
seriously considered, and that notion certainly includes the likes of
life upon Earth and Venus.

We are not alone, nor are we humans the one and only smartest DNA
within this universe, and to even think otherwise is proof-positive of
how pathetically ignorant and arrogant of a mutated species we've
become.

I also agree that we'll need a real 3D fly-by-rocket lander, especially
for that of accomplishing almost any expedition task (robotic or
manned) upon the not-so-user-friendly surface of our solar illuminated
moon (via earthshine maybe).

Regards, Brad Guth / GASA-IEIS
http://guthvenus.tripod.com/gv-topics.htm

Henry Spencer wrote:
[ker-snip]
Note that when ESA built an infrared observatory, they went to the extra
trouble of putting ISO into a highly elliptical orbit, so it was well away
from Earth most of the time.

Note also the more recent infrared and longer wavelength
observatories and their designated operating locations:

Launched missions:
WMAP: Earth-Sun L2 Lissajous orbit
Spitzer: Earth-trailing heliocentric orbit

Planned missions:
Herschel: Earth-Sun L2 Lissajous orbit
Planck: Earth-Sun L2 Lissajous orbit
SIM: Earth-trailing heliocentric orbit
SPICA: Earth-Sun L2
JWST: Earth-Sun L2
Darwin: Earth-Sun L2


There are pretty strong trends here.

Henry Spencer wrote:

Uh, no, the location was chosen to reduce infrared radiation from the
*Earth*, which is a major problem for infrared telescopes in LEO. The Sun
is a small source and is fairly easy to deal with using a sunshade (which
JWST has). A warm Earth filling half the sky is more of a problem,
especially since it goes around the sky about once every 90 minutes...

...The insulation they designed kept COBE's telescope under 50K in
LEO after its LHe supply ran out.

Thanks for correcting me, but I am not yet convinced
that LEO is too hot for infrared telescopes. JWST's
mirror will be kept at the temperature of 50 K or less.

Trouble is, that requires that the [LEO] telescope point pretty much directly
away from the Earth. Which is a problem, since as the telescope goes
around Earth, that direction changes constantly. This is workable, pretty
much, for a sky-survey instrument like IRAS or COBE. It's grossly
unsuited to a telescope that wants to point at arbitrary targets, and
preferably stare at them for considerable lengths of time.

Note that when ESA built an infrared observatory, they went to the extra
trouble of putting ISO into a highly elliptical orbit, so it was well away
from Earth most of the time.

That looks like a more plausible explanation of
the L2 orbit. If JWST is launched far beyond the
LEO, it should have ion thrusters and enough fuel
to return to LEO for repair or upgrade. It seems
possible to run the ion thrusters and take pictures
at the same time -- the ion thrusters would produce
acceleration of less than 0.001 m/s^2.

Andrew Nowicki wrote:

...If something goes wrong
with the JWST, the telescope will be difficult to
repair because the L2 point is far away from the
Earth. Worse yet, JWST has a monolithic design
not suitable for telerobotic repair or upgrade.

Henry Spencer wrote:

Correct. As with Chandra and Spitzer, the decision was that manned
servicing capabilities were not worth the added problems of operating in
LEO, and telerobotic servicing was too speculative and imposed too many
design penalties. There will be no repairs or upgrades; JWST will do its
job as designed (they hope) and that will be all.

The astronomers may end up regretting this approach if JWST has deployment
problems -- they often conveniently forget that exactly that happened to
Compton, but since *it* was shuttle-deployed in LEO, the astronauts just
went out and fixed it before turning it loose -- but that aside, it's not
a ridiculous approach, given the current costs and lead times and
uncertainties(*) of servicing visits.

(* The cancellation of the Hubble servicing visit told the astronomers,
loud and clear, that they cannot rely on NASA for telescope servicing. )

There is not much public discussion about telerobotic
servicing despite the fact that both terrestrial
and space telerobots perform rather well. The telerobot
may be slow and it may need special tools, but I can
hardly imagine any task that a sophisticated telerobot
like Dextre cannot perform. It would be really interesting
to launch Dextre and let it practice its skills on crippled
satellites. From my point of view the technical challenges
of telerobotic servicing are much more interesting than
all the other space programs combined. Telerobotic
servicing is fun! Its partly cerebral (can it be done?)
partly physical (like video games), and safe (humans running
around in uncomfortable space suits and risking their lives
are not needed). Robot competitions are popular among young
people, especially Japanese and MIT students, but space
cadets hate telerobots.

The Lanzerotti panel had 21 members, but only 3 of them
were robotic experts: Rodney A. Brooks, Vijay Kumar,
and Stephen M. Rock. Their final report was propaganda,
rather than science. Goddard Director Edward Weiler and
his engineers still believe that Dextre can repair Hubble.

Sometimes a satellite is crippled because one of its
mechanical parts is stuck. A little knock from a primitive
telemanipulator could fix this problem.

The claim that telerobotic servicing imposes design
penalties is not accurate, because there are both
penalties and advantages. For example, large telescopes
do not fit well into the streamlined bodies of the rocket
launchers, but large, composite mirrors can be, at least
in theory, assembled in orbit by telerobots.

__________________________________________________ _________________________

Here are the official (unconvincing) explanations from
http://www.jwst.nasa.gov/FAQ/FAQans.htm:

9. Why does JWST have to go so much farther away from Earth
than Hubble? What is the second Lagrange point orbit?

Although it makes sense to keep certain satellites near the
Earth for communication considerations or launch weight
considerations (i.e. it's hard to put massive objects far
from Earth because this requires great thrust from the rocket),
JWST requires a distant orbit for several reasons.

JWST will observe primarily the infrared light from faint
and very distant objects. But all objects, including
telescopes, also emit infrared light. To avoid swamping
the very faint astronomical signals with radiation from
the telescope, the telescope and its instruments must be
very cold. Therefore, JWST has a large shield that blocks
the light from the Sun, Earth, and Moon, which otherwise
would heat up the telescope, and interfere with the
observations.

To have this work, JWST must be in an orbit where all
three of these objects are in about the same direction.
The most convenient point is the second Lagrange point
(L2) of the Sun-Earth system, a semi-stable point in the
gravitational potential around the Sun and Earth. The L2
point lies outside Earth's orbit while it is going around
the Sun, keeping all three in a line at all times. The combined
gravitational forces of the Sun and the Earth can almost
hold a spacecraft at this point, and it takes relatively
little rocket thrust to keep the spacecraft near L2.
Although the L2 region is nearly 1 million miles
(1.5 million km) from Earth, the JWST can communicate
easily with ground stations on the Earth. The cold and
stable temperature environment of the L2 point will allow
JWST to make the very sensitive infrared observations needed.

10. Why is JWST not serviceable like Hubble?

When JWST is at the second Lagrange point (see previous
question), it will be out of reach of the Space Shuttle
and repairs cannot be made once it has been launched. This
also means that no provisions have to be made to allow
astronauts to make repairs.

The Planck spacecraft is going to be launched into the Earth-Sun
L2 orbit where it will be cooled by refrigerators to 0.1 K!
source: http://www.rssd.esa.int/SA/PLANCK/in...ayl/node8.html

This idea looks like madness to me because these extreme
refrigerators are not reliable. They have mechanical parts
that may be glued by contaminants.

SPICA is almost as ambitious. Its refrigerators are going to
cool it to 1.7 K.

So many vulnerable satellites... so few telerobots to repair them...

Andrew Nowicki wrote:

James Webb Space Telescope (JWST) is going to
take mostly infrared pictures of the universe.
To reduce unwanted infrared light coming from
the Sun, JWST will be launched into the Sun-Earth
L2 point, which is 1.5 million kilometers away
from the Earth. This far out location was
justified by the shade made by the Earth. A quick
calculation proves that the L2 point is *not*
in the Earth's shade! The complete shade, called
umbra, extends only to a distance of 1.39 million
kilometers beyond the Earth, i.e., 110,000 km
short. The L2 point is in partial shade called
penumbra.

If JWST is launched into the L2 point, it will
sizzle in the sunlight almost as much as the
Hubble Space Telescope. If something goes wrong
with the JWST, the telescope will be difficult to
repair because the L2 point is far away from the
Earth. Worse yet, JWST has a monolithic design
not suitable for telerobotic repair or upgrade.
My conclusion: James Webb Space Telescope
should be redesigned to improve its thermal
insulation and compatibility with telerobots,
and then launched into low Earth orbit.

Er, I thought the idea of having it at L2 was to allow it to have a much
wider field of view than if it were close to the earth; it doesn't have a
filthy great lump of rock in front it blocking out much of the view.

As for "compatibility with telerobots", which ones? Another untried
technology. If and when they're used to keep Hubble going (I hope
*SOMETHING* does) then you can start talking about them.

Don't forget Hubble is a real exception in being designed to be
repaired/serviced, and it doesn't look like that will do it any good in the
long term anyway.

So JWST's a throwaway item that can't be repaired... Just like practically
every other space probe. BFD.

--
Malcolm Street
Canberra, Australia
The nation's capital

"Andrew Nowicki" wrote in message
...
The Planck spacecraft is going to be launched into the Earth-Sun
L2 orbit where it will be cooled by refrigerators to 0.1 K!
source: http://www.rssd.esa.int/SA/PLANCK/in...ayl/node8.html

This idea looks like madness to me because these extreme
refrigerators are not reliable. They have mechanical parts
that may be glued by contaminants.


It looks like madness because you either have not done, or cannot do, the
math.

MK