[FPSPACE] NYTimes reporter Kenneth Chang answers questions about space exploration

Peter Pesavento eagle267@svol.net
Thu, 22 Jan 2004 15:58:50 -0500


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 QUESTIONS FOR . . .=20
Kenneth Chang This week, The Times's science reporter will answer =
readers' questions about the future of human space exploration, the =
current mission to Mars, President Bush's space plan and the allure of =
the moon.=20
Jan. 22=20

What do you think has more potential for scientific discovery: a manned =
mission to Mars or establishing a human colony on Earth's moon? What are =
some of the specific goals of each mission with regard to technological =
advancement? I am an enormous proponent of space exploration and I think =
people would be more supportive of ambitious space programs if they =
understood how much we can learn by actually getting out there.=20
- Lou Antonacci=20

A.Mars certainly has the greater potential. Scientifically, the =
importance of the moon is that it's made of much of the same stuff as =
the Earth, but it's old, older than almost all of the rocks here. =
Geologists would like to examine more moon rocks, because they could =
tell something about what Earth was like in its first billion years. =
Interesting, but not stuff most people would write home about. =
Astronomers think the moon would be a good location for telescopes, but =
space-based ones like Hubble can do many of the same things.=20

Mars, on the other hand, is a whole new world. It has gargantuan =
canyons, the biggest   QUESTIONS FOR . . .=20

Kenneth Chang



            The New York Times
            Kenneth Chang. =20

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                  Submit a Question to Kenneth Chang

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           TIMES NEWS TRACKER
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              Topics =20
            Alerts  =20
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           Space=20


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    =20
    =20
This week, The Times's science reporter will answer readers' questions =
about the future of human space exploration, the current mission to =
Mars, President Bush's space plan and the allure of the moon.=20

Jan. 22=20

What do you think has more potential for scientific discovery: a manned =
mission to Mars or establishing a human colony on Earth's moon? What are =
some of the specific goals of each mission with regard to technological =
advancement? I am an enormous proponent of space exploration and I think =
people would be more supportive of ambitious space programs if they =
understood how much we can learn by actually getting out there.=20
- Lou Antonacci=20

A.Mars certainly has the greater potential. Scientifically, the =
importance of the moon is that it's made of much of the same stuff as =
the Earth, but it's old, older than almost all of the rocks here. =
Geologists would like to examine more moon rocks, because they could =
tell something about what Earth was like in its first billion years. =
Interesting, but not stuff most people would write home about. =
Astronomers think the moon would be a good location for telescopes, but =
space-based ones like Hubble can do many of the same things.=20

Mars, on the other hand, is a whole new world. It has gargantuan =
canyons, the biggest  volcanoes in the solar system and also some of the =
flattest landscapes. For all of these, scientists still have to ask, =
Why? There is still this persistent question of whether Mars was once =
warm and wet with a large ocean for the first billion years in its =
history. If so, then you have conditions suitable for life, and microbes =
could conceivably still live deep underground. (The caveat is that a lot =
of atmospheric scientists don't think Mars was ever warm and wet for =
extended periods of time. Rather, once in a while -- like after a big =
meteor whack -- Mars experienced torrential downpours that carved the =
stuff we see.)=20

            Q. Exposure to zero-G and radiation have been mentioned as =
serious challenges to long-term interplanetary travel. Couldn't =
artificial gravity be used to eliminate the former? As for the latter, =
couldn't a solar "storm shelter" aboard the astronauts' space vehicle =
reduce the risk of brief bursts of intense radiation? I have also heard =
that the exposure to cosmic radiation over the course of a journey to =
Mars would be within acceptable limits. Is that true?
            - Will Cooper=20

            A. Both of these answers are via Robert Zubrin, who =
advocates a 10-year program for getting to Mars that he says would cost =
$50 billion or so:=20

            Yes, artificial gravity would work. Zubrin imagines the crew =
quarters for the trip tethered to the booster rocket and the two would =
twirl around to produce centrifugal force that would keep astronauts in =
a gravity environment.=20

            And yes, radiation is not a killer problem. There are two =
sources of radiation. One is a steady stream of cosmic rays from deep =
outer space. The other is energetic particles burped out of the sun in =
solar storms. For the latter, you need a storm shelter, as you say. For =
the former, the anticipated exposure over 2.5 years is about 130 rem. If =
you were irradiated with 130 rem in a day, it'd make you sick, but not =
kill you. Spread over a couple of years, it increases the risk of cancer =
by 1 or 2 percent. Given all the risks that astronauts would face in a =
Mars mission (rocket blowing up, crash landing, stranded on Mars, etc.) =
, that would not seem to be an overwhelming consideration.=20

            Jan. 21=20

            Q. An article and graphic on launch vehicles for a moon =
visit and base referred to "large quantities" of water ice in deep =
craters near the moon's "south pole". Is that confirmed? - Daniel =
Weinstein=20

            A. The Clementine mission in 1996 bounced radar off the =
surface of the moon, and most of the moon looks like, no surprise, dust =
and rock. As it passed over the south pole, the radar reflections looked =
like they were bouncing off something shiny. And the scientists thought, =
hmm, looks like ice.=20

            The Lunar Prospector mission in 1998 and 1999 convincingly =
discovered. hydrogen.=20

            This is a bit complicated, but if you want the details: The =
spacecraft had an instrument that counted neutrons (neutrons and protons =
are the particles found in the nuclei of atoms). On the Moon, =
high-energy cosmic rays from outer space continually knock neutrons from =
atoms on the lunar surface. Cosmic rays are very energetic, so these =
neutrons are really speeding along. But if one of these neutrons runs =
into a hydrogen atom (which is almost the same weight), then neutron =
comes to almost a complete stop, just like a cue ball after it hits =
another billiard ball.=20

            So what Lunar Prospector saw was lots of slow neutrons, and =
the only way you can get lots of slow neutrons is there's a lot of =
hydrogen that they've bounced off of. The most likely molecule to =
contain all that hydrogen is water -- H20 -- although it could still be =
something else like methane (which would still be a very useful resource =
for human explorers).=20

            Q. On Earth we use sea level as the datum for measuring the =
height of physiographic features. Without sea level as a reference, what =
datum is used on Mars? - Dorinda Dallmeyer=20

            A. Zero elevation is arbitrary. (On Earth, sea level makes a =
convenient reference point, but it's still arbitrary. As oceans rise =
with warming temperatures, does that mean Mt. Everest is getting =
shorter?) On Mars, the arbitrary data point that scientists have chosen =
is "the gravitational equipotential surface whose average value at the =
equator is equal to the equatorial radius." I'm still trying to figure =
out myself what exactly that means.=20


            Jan. 20=20

            Q. Why the emphasis on manned flights? An unmanned project =
would be far cheaper and far less hazardous. What great benefits are =
there to a manned project that justify the extra cost and danger? - Mark =
Gromko, Bowling Green, Ohio=20

            A. There's still nothing quite like being there. The =
unmanned probes are wonderful, but limited. In two weeks, the Mars rover =
Spirit has rolled 10 feet and is just now beginning to examine its first =
rock. You could have walked that far in two seconds. People are still =
much more efficient and versatile. (Think of the work that =
archaeologists do in excavating a site and collecting artifacts, and =
imagine how difficult it would be and how much they would miss if they =
tried to do that via remote-control robots.) Scientists, in their search =
for water on Mars and the possibility of life there in the past, would =
also like to do things like drilling a few thousand feet into the ground =
that would be very hard for a robotic mission to do.=20



            Q. Why is the life-span for the Spirit Rover only 90 days? =
Even with degradation in rechargable battery life, shouldn't the solar =
panels keep up power levels for a longer period? - David=20

            A. In a word, dust. Mars is covered with it, and it blows =
around. NASA expects that by the end of the 90 days, the layer of dust =
on the solar panels will cut their power output from 140 watts to 50 =
watts. Since the rover needs 100 watts to work, that's probably the =
point that NASA considers the ratio of time doing science versus time =
recharging batteries too small. There are ways to run longer missions on =
Mars. The two Viking landers in the 1970's used "radioisotope =
thermoelectric generators" -- basically hunks of plutonium that through =
radioactive decay generated heat, which was converted to electricity. =
Viking 1 operated for 6 years, Viking 2 for 4 years.=20



          =20
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    =20
              Copyright 2004 The New York Times Company | Home | Privacy =
Policy | Search | Corrections | Help | Back to Top =20
          =20
          =20


    =20
  volcanoes in the solar system and also some of the flattest =
landscapes. For all of these, scientists still have to ask, Why? There =
is still this persistent question of whether Mars was once warm and wet =
with a large ocean for the first billion years in its history. If so, =
then you have conditions suitable for life, and microbes could =
conceivably still live deep underground. (The caveat is that a lot of =
atmospheric scientists don't think Mars was ever warm and wet for =
extended periods of time. Rather, once in a while -- like after a big =
meteor whack -- Mars experienced torrential downpours that carved the =
stuff we see.)=20

            Q. Exposure to zero-G and radiation have been mentioned as =
serious challenges to long-term interplanetary travel. Couldn't =
artificial gravity be used to eliminate the former? As for the latter, =
couldn't a solar "storm shelter" aboard the astronauts' space vehicle =
reduce the risk of brief bursts of intense radiation? I have also heard =
that the exposure to cosmic radiation over the course of a journey to =
Mars would be within acceptable limits. Is that true?
            - Will Cooper=20

            A. Both of these answers are via Robert Zubrin, who =
advocates a 10-year program for getting to Mars that he says would cost =
$50 billion or so:=20

            Yes, artificial gravity would work. Zubrin imagines the crew =
quarters for the trip tethered to the booster rocket and the two would =
twirl around to produce centrifugal force that would keep astronauts in =
a gravity environment.=20

            And yes, radiation is not a killer problem. There are two =
sources of radiation. One is a steady stream of cosmic rays from deep =
outer space. The other is energetic particles burped out of the sun in =
solar storms. For the latter, you need a storm shelter, as you say. For =
the former, the anticipated exposure over 2.5 years is about 130 rem. If =
you were irradiated with 130 rem in a day, it'd make you sick, but not =
kill you. Spread over a couple of years, it increases the risk of cancer =
by 1 or 2 percent. Given all the risks that astronauts would face in a =
Mars mission (rocket blowing up, crash landing, stranded on Mars, etc.) =
, that would not seem to be an overwhelming consideration.=20

            Jan. 21=20

            Q. An article and graphic on launch vehicles for a moon =
visit and base referred to "large quantities" of water ice in deep =
craters near the moon's "south pole". Is that confirmed? - Daniel =
Weinstein=20

            A. The Clementine mission in 1996 bounced radar off the =
surface of the moon, and most of the moon looks like, no surprise, dust =
and rock. As it passed over the south pole, the radar reflections looked =
like they were bouncing off something shiny. And the scientists thought, =
hmm, looks like ice.=20

            The Lunar Prospector mission in 1998 and 1999 convincingly =
discovered. hydrogen.=20

            This is a bit complicated, but if you want the details: The =
spacecraft had an instrument that counted neutrons (neutrons and protons =
are the particles found in the nuclei of atoms). On the Moon, =
high-energy cosmic rays from outer space continually knock neutrons from =
atoms on the lunar surface. Cosmic rays are very energetic, so these =
neutrons are really speeding along. But if one of these neutrons runs =
into a hydrogen atom (which is almost the same weight), then neutron =
comes to almost a complete stop, just like a cue ball after it hits =
another billiard ball.=20

            So what Lunar Prospector saw was lots of slow neutrons, and =
the only way you can get lots of slow neutrons is there's a lot of =
hydrogen that they've bounced off of. The most likely molecule to =
contain all that hydrogen is water -- H20 -- although it could still be =
something else like methane (which would still be a very useful resource =
for human explorers).=20

            Q. On Earth we use sea level as the datum for measuring the =
height of physiographic features. Without sea level as a reference, what =
datum is used on Mars? - Dorinda Dallmeyer=20

            A. Zero elevation is arbitrary. (On Earth, sea level makes a =
convenient reference point, but it's still arbitrary. As oceans rise =
with warming temperatures, does that mean Mt. Everest is getting =
shorter?) On Mars, the arbitrary data point that scientists have chosen =
is "the gravitational equipotential surface whose average value at the =
equator is equal to the equatorial radius." I'm still trying to figure =
out myself what exactly that means.=20


            Jan. 20=20

            Q. Why the emphasis on manned flights? An unmanned project =
would be far cheaper and far less hazardous. What great benefits are =
there to a manned project that justify the extra cost and danger? - Mark =
Gromko, Bowling Green, Ohio=20

            A. There's still nothing quite like being there. The =
unmanned probes are wonderful, but limited. In two weeks, the Mars rover =
Spirit has rolled 10 feet and is just now beginning to examine its first =
rock. You could have walked that far in two seconds. People are still =
much more efficient and versatile. (Think of the work that =
archaeologists do in excavating a site and collecting artifacts, and =
imagine how difficult it would be and how much they would miss if they =
tried to do that via remote-control robots.) Scientists, in their search =
for water on Mars and the possibility of life there in the past, would =
also like to do things like drilling a few thousand feet into the ground =
that would be very hard for a robotic mission to do.=20



            Q. Why is the life-span for the Spirit Rover only 90 days? =
Even with degradation in rechargable battery life, shouldn't the solar =
panels keep up power levels for a longer period? - David=20

            A. In a word, dust. Mars is covered with it, and it blows =
around. NASA expects that by the end of the 90 days, the layer of dust =
on the solar panels will cut their power output from 140 watts to 50 =
watts. Since the rover needs 100 watts to work, that's probably the =
point that NASA considers the ratio of time doing science versus time =
recharging batteries too small. There are ways to run longer missions on =
Mars. The two Viking landers in the 1970's used "radioisotope =
thermoelectric generators" -- basically hunks of plutonium that through =
radioactive decay generated heat, which was converted to electricity. =
Viking 1 operated for 6 years, Viking 2 for 4 years.=20



          =20
          =20

           =20
    =20
              Copyright 2004 The New York Times Company | Home | Privacy =
Policy | Search | Corrections | Help | Back to Top =20
          =20
          =20


    =20
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color=3D#666666=20
size=3D-1><STRONG>QUESTIONS FOR . . .</STRONG></FONT><FONT size=3D3>=20
</NYT_KICKER><NYT_HEADLINE type=3D" " =
version=3D"1.0"></NYT_HEADLINE></FONT></FONT>
<H2>Kenneth Chang<!--StartFragment --> <NYT_TEXT>This week, The Times's =
science=20
reporter will answer readers' questions about the future of human space=20
exploration, the current mission to Mars, President Bush's space plan =
and the=20
allure of the moon. </NYT_TEXT>
<P><STRONG>Jan. 22</STRONG> </P>
<P><IMG alt=3DQ =
src=3D"http://graphics7.nytimes.com/images/dropcap/q.gif" align=3Dleft=20
border=3D0><EM>What do you think has more potential for scientific =
discovery: a=20
manned mission to Mars or establishing a human colony on Earth's moon? =
What are=20
some of the specific goals of each mission with regard to technological=20
advancement? I am an enormous proponent of space exploration and I think =
people=20
would be more supportive of ambitious space programs if they understood =
how much=20
we can learn by actually getting out there. <BR>=97 Lou Antonacci =
</EM></P>
<P>A.Mars certainly has the greater potential. Scientifically, the =
importance of=20
the moon is that it's made of much of the same stuff as the Earth, but =
it's old,=20
older than almost all of the rocks here. Geologists would like to =
examine more=20
moon rocks, because they could tell something about what Earth was like =
in its=20
first billion years. Interesting, but not stuff most people would write =
home=20
about. Astronomers think the moon would be a good location for =
telescopes, but=20
space-based ones like Hubble can do many of the same things. </P>
<P>Mars, on the other hand, is a whole new world. It has gargantuan =
canyons, the=20
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type=3D" " version=3D"1.0"></NYT_HEADLINE></P>
<H2>Kenneth Chang</H2>
<P><NYT_BYLINE type=3D" " =
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            <DIV align=3Dright><FONT size=3D-2>The New York =
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            =
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mp;fdq=3D19960101&amp;td=3Dsysdate&amp;sort=3Dnewest&amp;ac=3DSPACE&amp;r=
t=3D1%2Cdes%2Corg%2Cper%2Cgeo">Space</A></SPAN></TD>
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  <TR>
    <TD width=3D184><!--NYT_INLINE_AD =
AD=3D"Right4"--></TD></TR></TBODY></TABLE><!--inline end =
--><NYT_TEXT>This=20
week, The Times's science reporter will answer readers' questions about =
the=20
future of human space exploration, the current mission to Mars, =
President Bush's=20
space plan and the allure of the moon. </NYT_TEXT></P>
<P><STRONG>Jan. 22</STRONG> </P>
<P><IMG alt=3DQ =
src=3D"http://graphics7.nytimes.com/images/dropcap/q.gif" align=3Dleft=20
border=3D0><EM>What do you think has more potential for scientific =
discovery: a=20
manned mission to Mars or establishing a human colony on Earth's moon? =
What are=20
some of the specific goals of each mission with regard to technological=20
advancement? I am an enormous proponent of space exploration and I think =
people=20
would be more supportive of ambitious space programs if they understood =
how much=20
we can learn by actually getting out there. <BR>=97 Lou Antonacci =
</EM></P>
<P>A.Mars certainly has the greater potential. Scientifically, the =
importance of=20
the moon is that it's made of much of the same stuff as the Earth, but =
it's old,=20
older than almost all of the rocks here. Geologists would like to =
examine more=20
moon rocks, because they could tell something about what Earth was like =
in its=20
first billion years. Interesting, but not stuff most people would write =
home=20
about. Astronomers think the moon would be a good location for =
telescopes, but=20
space-based ones like Hubble can do many of the same things. </P>
<P>Mars, on the other hand, is a whole new world. It has gargantuan =
canyons, the=20
biggest&nbsp;<!--StartFragment -->=20
<TABLE cellSpacing=3D0 cellPadding=3D0 width=3D768 align=3Dleft =
border=3D0 valign=3D"top">
  <TBODY>
  <TR>
    <TD vAlign=3Dtop align=3Dleft width=3D768>
      <TABLE cellSpacing=3D0 cellPadding=3D0 width=3D"100%" align=3Dleft =
border=3D0=20
      valign=3D"top">
        <TBODY>
        <TR>
          <TD vAlign=3Dtop align=3Dleft width=3D"100%">
            <P>volcanoes in the solar system and also some of the =
flattest=20
            landscapes. For all of these, scientists still have to ask, =
Why?=20
            There is still this persistent question of whether Mars was =
once=20
            warm and wet with a large ocean for the first billion years =
in its=20
            history. If so, then you have conditions suitable for life, =
and=20
            microbes could conceivably still live deep underground. (The =
caveat=20
            is that a lot of atmospheric scientists don't think Mars was =
ever=20
            warm and wet for extended periods of time. Rather, once in a =
while=20
            -- like after a big meteor whack -- Mars experienced =
torrential=20
            downpours that carved the stuff we see.) </P>
            <P>Q. <EM>Exposure to zero-G and radiation have been =
mentioned as=20
            serious challenges to long-term interplanetary travel. =
Couldn't=20
            artificial gravity be used to eliminate the former? As for =
the=20
            latter, couldn't a solar "storm shelter" aboard the =
astronauts'=20
            space vehicle reduce the risk of brief bursts of intense =
radiation?=20
            I have also heard that the exposure to cosmic radiation over =
the=20
            course of a journey to Mars would be within acceptable =
limits. Is=20
            that true?<BR>- Will Cooper</EM> </P>
            <P>A. Both of these answers are via Robert Zubrin, who =
advocates a=20
            10-year program for getting to Mars that he says would cost =
$50=20
            billion or so: </P>
            <P>Yes, artificial gravity would work. Zubrin imagines the =
crew=20
            quarters for the trip tethered to the booster rocket and the =
two=20
            would twirl around to produce centrifugal force that would =
keep=20
            astronauts in a gravity environment. </P>
            <P>And yes, radiation is not a killer problem. There are two =
sources=20
            of radiation. One is a steady stream of cosmic rays from =
deep outer=20
            space. The other is energetic particles burped out of the =
sun in=20
            solar storms. For the latter, you need a storm shelter, as =
you say.=20
            For the former, the anticipated exposure over 2.5 years is =
about 130=20
            rem. If you were irradiated with 130 rem in a day, it'd make =
you=20
            sick, but not kill you. Spread over a couple of years, it =
increases=20
            the risk of cancer by 1 or 2 percent. Given all the risks =
that=20
            astronauts would face in a Mars mission (rocket blowing up, =
crash=20
            landing, stranded on Mars, etc.) , that would not seem to be =
an=20
            overwhelming consideration. </P>
            <P><STRONG>Jan. 21</STRONG> </P>
            <P>Q. <EM>An article and graphic on launch vehicles for a =
moon visit=20
            and base referred to "large quantities" of water ice in deep =
craters=20
            near the moon's "south pole". Is that confirmed? =97 Daniel=20
            Weinstein</EM> </P>
            <P>A. The Clementine mission in 1996 bounced radar off the =
surface=20
            of the moon, and most of the moon looks like, no surprise, =
dust and=20
            rock. As it passed over the south pole, the radar =
reflections looked=20
            like they were bouncing off something shiny. And the =
scientists=20
            thought, hmm, looks like ice. </P>
            <P>The Lunar Prospector mission in 1998 and 1999 =
convincingly=20
            discovered=85 hydrogen. </P>
            <P>This is a bit complicated, but if you want the details: =
The=20
            spacecraft had an instrument that counted neutrons (neutrons =
and=20
            protons are the particles found in the nuclei of atoms). On =
the=20
            Moon, high-energy cosmic rays from outer space continually =
knock=20
            neutrons from atoms on the lunar surface. Cosmic rays are =
very=20
            energetic, so these neutrons are really speeding along. But =
if one=20
            of these neutrons runs into a hydrogen atom (which is almost =
the=20
            same weight), then neutron comes to almost a complete stop, =
just=20
            like a cue ball after it hits another billiard ball. </P>
            <P>So what Lunar Prospector saw was lots of slow neutrons, =
and the=20
            only way you can get lots of slow neutrons is there's a lot =
of=20
            hydrogen that they've bounced off of. The most likely =
molecule to=20
            contain all that hydrogen is water -- H20 -- although it =
could still=20
            be something else like methane (which would still be a very =
useful=20
            resource for human explorers). </P>
            <P>Q. <EM>On Earth we use sea level as the datum for =
measuring the=20
            height of physiographic features. Without sea level as a =
reference,=20
            what datum is used on Mars? =97 Dorinda Dallmeyer</EM> </P>
            <P>A. Zero elevation is arbitrary. (On Earth, sea level =
makes a=20
            convenient reference point, but it's still arbitrary. As =
oceans rise=20
            with warming temperatures, does that mean Mt. Everest is =
getting=20
            shorter?) On Mars, the arbitrary data point that scientists =
have=20
            chosen is "the gravitational equipotential surface whose =
average=20
            value at the equator is equal to the equatorial radius." I'm =
still=20
            trying to figure out myself what exactly that means. </P>
            <P></P>
            <P><STRONG>Jan. 20</STRONG> </P>
            <P>Q. <EM>Why the emphasis on manned flights? An unmanned =
project=20
            would be far cheaper and far less hazardous. What great =
benefits are=20
            there to a manned project that justify the extra cost and =
danger? =97=20
            Mark Gromko, Bowling Green, Ohio</EM> </P>
            <P>A. There's still nothing quite like being there. The =
unmanned=20
            probes are wonderful, but limited. In two weeks, the Mars =
rover=20
            Spirit has rolled 10 feet and is just now beginning to =
examine its=20
            first rock. You could have walked that far in two seconds. =
People=20
            are still much more efficient and versatile. (Think of the =
work that=20
            archaeologists do in excavating a site and collecting =
artifacts, and=20
            imagine how difficult it would be and how much they would =
miss if=20
            they tried to do that via remote-control robots.) =
Scientists, in=20
            their search for water on Mars and the possibility of life =
there in=20
            the past, would also like to do things like drilling a few =
thousand=20
            feet into the ground that would be very hard for a robotic =
mission=20
            to do. </P>
            <P></P>
            <P></P>
            <P>Q. <EM>Why is the life-span for the Spirit Rover only 90 =
days?=20
            Even with degradation in rechargable battery life, shouldn't =
the=20
            solar panels keep up power levels for a longer period? =97 =
David</EM>=20
            </P>
            <P>A. In a word, dust. Mars is covered with it, and it blows =
around.=20
            NASA expects that by the end of the 90 days, the layer of =
dust on=20
            the solar panels will cut their power output from 140 watts =
to 50=20
            watts. Since the rover needs 100 watts to work, that's =
probably the=20
            point that NASA considers the ratio of time doing science =
versus=20
            time recharging batteries too small. There are ways to run =
longer=20
            missions on Mars. The two Viking landers in the 1970's used=20
            "radioisotope thermoelectric generators" -- basically hunks =
of=20
            plutonium that through radioactive decay generated heat, =
which was=20
            converted to electricity. Viking 1 operated for 6 years, =
Viking 2=20
            for 4 years. </P>
            <P><BR></P></TD></TR>
        <TR>
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            <P>volcanoes in the solar system and also some of the =
flattest=20
            landscapes. For all of these, scientists still have to ask, =
Why?=20
            There is still this persistent question of whether Mars was =
once=20
            warm and wet with a large ocean for the first billion years =
in its=20
            history. If so, then you have conditions suitable for life, =
and=20
            microbes could conceivably still live deep underground. (The =
caveat=20
            is that a lot of atmospheric scientists don't think Mars was =
ever=20
            warm and wet for extended periods of time. Rather, once in a =
while=20
            -- like after a big meteor whack -- Mars experienced =
torrential=20
            downpours that carved the stuff we see.) </P>
            <P>Q. <EM>Exposure to zero-G and radiation have been =
mentioned as=20
            serious challenges to long-term interplanetary travel. =
Couldn't=20
            artificial gravity be used to eliminate the former? As for =
the=20
            latter, couldn't a solar "storm shelter" aboard the =
astronauts'=20
            space vehicle reduce the risk of brief bursts of intense =
radiation?=20
            I have also heard that the exposure to cosmic radiation over =
the=20
            course of a journey to Mars would be within acceptable =
limits. Is=20
            that true?<BR>- Will Cooper</EM> </P>
            <P>A. Both of these answers are via Robert Zubrin, who =
advocates a=20
            10-year program for getting to Mars that he says would cost =
$50=20
            billion or so: </P>
            <P>Yes, artificial gravity would work. Zubrin imagines the =
crew=20
            quarters for the trip tethered to the booster rocket and the =
two=20
            would twirl around to produce centrifugal force that would =
keep=20
            astronauts in a gravity environment. </P>
            <P>And yes, radiation is not a killer problem. There are two =
sources=20
            of radiation. One is a steady stream of cosmic rays from =
deep outer=20
            space. The other is energetic particles burped out of the =
sun in=20
            solar storms. For the latter, you need a storm shelter, as =
you say.=20
            For the former, the anticipated exposure over 2.5 years is =
about 130=20
            rem. If you were irradiated with 130 rem in a day, it'd make =
you=20
            sick, but not kill you. Spread over a couple of years, it =
increases=20
            the risk of cancer by 1 or 2 percent. Given all the risks =
that=20
            astronauts would face in a Mars mission (rocket blowing up, =
crash=20
            landing, stranded on Mars, etc.) , that would not seem to be =
an=20
            overwhelming consideration. </P>
            <P><STRONG>Jan. 21</STRONG> </P>
            <P>Q. <EM>An article and graphic on launch vehicles for a =
moon visit=20
            and base referred to "large quantities" of water ice in deep =
craters=20
            near the moon's "south pole". Is that confirmed? =97 Daniel=20
            Weinstein</EM> </P>
            <P>A. The Clementine mission in 1996 bounced radar off the =
surface=20
            of the moon, and most of the moon looks like, no surprise, =
dust and=20
            rock. As it passed over the south pole, the radar =
reflections looked=20
            like they were bouncing off something shiny. And the =
scientists=20
            thought, hmm, looks like ice. </P>
            <P>The Lunar Prospector mission in 1998 and 1999 =
convincingly=20
            discovered=85 hydrogen. </P>
            <P>This is a bit complicated, but if you want the details: =
The=20
            spacecraft had an instrument that counted neutrons (neutrons =
and=20
            protons are the particles found in the nuclei of atoms). On =
the=20
            Moon, high-energy cosmic rays from outer space continually =
knock=20
            neutrons from atoms on the lunar surface. Cosmic rays are =
very=20
            energetic, so these neutrons are really speeding along. But =
if one=20
            of these neutrons runs into a hydrogen atom (which is almost =
the=20
            same weight), then neutron comes to almost a complete stop, =
just=20
            like a cue ball after it hits another billiard ball. </P>
            <P>So what Lunar Prospector saw was lots of slow neutrons, =
and the=20
            only way you can get lots of slow neutrons is there's a lot =
of=20
            hydrogen that they've bounced off of. The most likely =
molecule to=20
            contain all that hydrogen is water -- H20 -- although it =
could still=20
            be something else like methane (which would still be a very =
useful=20
            resource for human explorers). </P>
            <P>Q. <EM>On Earth we use sea level as the datum for =
measuring the=20
            height of physiographic features. Without sea level as a =
reference,=20
            what datum is used on Mars? =97 Dorinda Dallmeyer</EM> </P>
            <P>A. Zero elevation is arbitrary. (On Earth, sea level =
makes a=20
            convenient reference point, but it's still arbitrary. As =
oceans rise=20
            with warming temperatures, does that mean Mt. Everest is =
getting=20
            shorter?) On Mars, the arbitrary data point that scientists =
have=20
            chosen is "the gravitational equipotential surface whose =
average=20
            value at the equator is equal to the equatorial radius." I'm =
still=20
            trying to figure out myself what exactly that means. </P>
            <P></P>
            <P><STRONG>Jan. 20</STRONG> </P>
            <P>Q. <EM>Why the emphasis on manned flights? An unmanned =
project=20
            would be far cheaper and far less hazardous. What great =
benefits are=20
            there to a manned project that justify the extra cost and =
danger? =97=20
            Mark Gromko, Bowling Green, Ohio</EM> </P>
            <P>A. There's still nothing quite like being there. The =
unmanned=20
            probes are wonderful, but limited. In two weeks, the Mars =
rover=20
            Spirit has rolled 10 feet and is just now beginning to =
examine its=20
            first rock. You could have walked that far in two seconds. =
People=20
            are still much more efficient and versatile. (Think of the =
work that=20
            archaeologists do in excavating a site and collecting =
artifacts, and=20
            imagine how difficult it would be and how much they would =
miss if=20
            they tried to do that via remote-control robots.) =
Scientists, in=20
            their search for water on Mars and the possibility of life =
there in=20
            the past, would also like to do things like drilling a few =
thousand=20
            feet into the ground that would be very hard for a robotic =
mission=20
            to do. </P>
            <P></P>
            <P></P>
            <P>Q. <EM>Why is the life-span for the Spirit Rover only 90 =
days?=20
            Even with degradation in rechargable battery life, shouldn't =
the=20
            solar panels keep up power levels for a longer period? =97 =
David</EM>=20
            </P>
            <P>A. In a word, dust. Mars is covered with it, and it blows =
around.=20
            NASA expects that by the end of the 90 days, the layer of =
dust on=20
            the solar panels will cut their power output from 140 watts =
to 50=20
            watts. Since the rover needs 100 watts to work, that's =
probably the=20
            point that NASA considers the ratio of time doing science =
versus=20
            time recharging batteries too small. There are ways to run =
longer=20
            missions on Mars. The two Viking landers in the 1970's used=20
            "radioisotope thermoelectric generators" -- basically hunks =
of=20
            plutonium that through radioactive decay generated heat, =
which was=20
            converted to electricity. Viking 1 operated for 6 years, =
Viking 2=20
            for 4 years. </P>
            <P><BR></P></TD></TR>
        <TR>
          <TD width=3D5><IMG height=3D1 alt=3D""=20
            src=3D"http://graphics7.nytimes.com/images/misc/spacer.gif"=20
width=3D5></TD>
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width=3D"100%"><NYT_DYNAMIC_RELATED_ARTICLES=20
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            =
instance=3D"sitesearch"></NYT_DYNAMIC_RELATED_ARTICLES><BR><BR></TD>
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