From: John Frazer [mailto:johnf4303@...]

>-go to the Moon
>
>Yes, in that it is a nearby source of raw materials
>outside of the steepest part of the Earth's gravity well.

Nearby, yes, but NEAs are more accessible (distance doesn't matter
nearly as much as relative velocity), as well as richer sources.

I certainly never meant to imply that the moon necessarily wins hand down
against NEAs. As I recall, asteroids weren't represented on that first
list. It's certainly true that NEAs, as you correctly state, have certain
advantages. But the moon has advantages of its own. I expect we'll do
both.

I think it will turn powerfully on how easy or hard it is to support humans
in space for long durations without resupply in the early days. I can see a
scenario where the technology of telepresence advances only very slowly,
such that you have to send as many people to the moon to mine it as to a
NEA. That, combined with a NEA happening to come along on a particularly
favorable trajectory, might result in us using asteroidal resources first.
I'd expect that afterward we would use lunar resources too, but maybe we
could get by without. Coming back and forth from the moon certainly becomes
orders of magnitude more economical with use of NEA resources in HEO.

But if telepresence advances rapidly, we might have a situation where the
moon could be mined telerobotically from Earth. Such a development might
push us toward use of lunar resources first. But lunar resource use would
most certainly get followed by asteroidal resource use.

Regards,

Mike Combs

From:
John Frazer [mailto:johnf4303@...]
>-go to the Moon
>
>Yes, in that it is a nearby source of raw materials
>outside of the steepest part of the Earth's gravity well.
Nearby, yes, but NEAs are more accessible (distance doesn't matter
nearly as much as relative velocity), as well as richer sources.

I certainly never meant to imply that the moon necessarily wins hand down against NEAs. As I recall, asteroids weren't represented on that first list. It's certainly true that NEAs, as you correctly state, have certain advantages. But the moon has advantages of its own. I expect we'll do both.

I think it will turn powerfully on how easy or hard it is to support humans in space for long durations without resupply in the early days. I can see a scenario where the technology of telepresence advances only very slowly, such that you have to send as many people to the moon to mine it as to a NEA. That, combined with a NEA happening to come along on a particularly favorable trajectory, might result in us using asteroidal resources first. I'd expect that afterward we would use lunar resources too, but maybe we could get by without. Coming back and forth from the moon certainly becomes orders of magnitude more economical with use of NEA resources in HEO.

But if telepresence advances rapidly, we might have a situation where the moon could be mined telerobotically from Earth. Such a development might push us toward use of lunar resources first. But lunar resource use would most certainly get followed by asteroidal resource use.

Regards,
Mike Combs

Hi Mike & All,

Back in the 70s there was quite a bit of research done on this in the
old L5 Society. As I recall, at that time only two or three asteroids
had been discovered that needed less delta V to get to and return than
the Moon. I haven't heard of any new asteroids in that category having
been discovered since, but then delta V is not what the various
reporters report on these days. Perhaps it is time we got that changed
back again? Problem is, most of those who report probably don't know
what delta V is!

Best wishes, Andy.

"Combs, Mike" wrote:

>
> From: John Frazer [mailto:johnf4303@...]
>
> >-go to the Moon
> >
> >Yes, in that it is a nearby source of raw materials
> >outside of the steepest part of the Earth's gravity well.
>
> Nearby, yes, but NEAs are more accessible (distance doesn't
> matter
> nearly as much as relative velocity), as well as richer
> sources.
>
> I certainly never meant to imply that the moon necessarily wins hand
> down against NEAs. As I recall, asteroids weren't represented on that
> first list. It's certainly true that NEAs, as you correctly state,
> have certain advantages. But the moon has advantages of its own. I
> expect we'll do both.I think it will turn powerfully on how easy or
> hard it is to support humans in space for long durations without
> resupply in the early days. I can see a scenario where the technology
> of telepresence advances only very slowly, such that you have to send
> as many people to the moon to mine it as to a NEA. That, combined
> with a NEA happening to come along on a particularly favorable
> trajectory, might result in us using asteroidal resources first. I'd
> expect that afterward we would use lunar resources too, but maybe we
> could get by without. Coming back and forth from the moon certainly
> becomes orders of magnitude more economical with use of NEA resources
> in HEO.But if telepresence advances rapidly, we might have a situation
> where the moon could be mined telerobotically from Earth. Such a
> development might push us toward use of lunar resources first. But
> lunar resource use would most certainly get followed by asteroidal
> resource use.
>
> Regards,
>
> Mike Combs
>
[www.debticated.com]

Minor correction, the L5 Society did some good lobbying, but they didn't
do any real research.

A lot of asteroids are found these days because of concerns about a
collision with earth. I haven't checked the data for awhile, but I'm
sure many asteroids with very low delta-v have been found. See
http://impact.arc.nasa.gov/index.html.

Anyone know the URL for the minor planet center? They have the
definitive information on what's known.

andy-nimmo wrote:

> Hi Mike & All,
>
> Back in the 70s there was quite a bit of research done on this in the
> old L5 Society. As I recall, at that time only two or three asteroids
> had been discovered that needed less delta V to get to and return than
> the Moon. I haven't heard of any new asteroids in that category having
> been discovered since, but then delta V is not what the various
> reporters report on these days. Perhaps it is time we got that changed
> back again? Problem is, most of those who report probably don't know
> what delta V is!
>
> Best wishes, Andy.
>
> "Combs, Mike" wrote:
>
>>
>>
>> From: John Frazer [mailto:johnf4303@...]
>> >-go to the Moon
>> >
>> >Yes, in that it is a nearby source of raw materials
>> >outside of the steepest part of the Earth's gravity well.
>>
>> Nearby, yes, but NEAs are more accessible (distance
>> doesn't matter
>> nearly as much as relative velocity), as well as richer
>> sources.
>>
>> I certainly never meant to imply that the moon necessarily wins hand
>> down against NEAs. As I recall, asteroids weren't represented on
>> that first list. It's certainly true that NEAs, as you correctly
>> state, have certain advantages. But the moon has advantages of its
>> own. I expect we'll do both.I think it will turn powerfully on how
>> easy or hard it is to support humans in space for long durations
>> without resupply in the early days. I can see a scenario where the
>> technology of telepresence advances only very slowly, such that you
>> have to send as many people to the moon to mine it as to a NEA.
>> That, combined with a NEA happening to come along on a particularly
>> favorable trajectory, might result in us using asteroidal resources
>> first. I'd expect that afterward we would use lunar resources too,
>> but maybe we could get by without. Coming back and forth from the
>> moon certainly becomes orders of magnitude more economical with use
>> of NEA resources in HEO.But if telepresence advances rapidly, we
>> might have a situation where the moon could be mined telerobotically
>> from Earth. Such a development might push us toward use of lunar
>> resources first. But lunar resource use would most certainly get
>> followed by asteroidal resource use.
>>
>> Regards,
>>
>> Mike Combs
>>
>>
>>
>>
>>
>>
>
Al Globus
aglobus@..., (650) 604-4404
http://www.nas.nasa.gov/~globus/home.html

The dinosaurs weren't spacefaring. We are. I don't think that's an
accident.
Maybe we are life's taxi to the stars.

I think we should:

1. Devote half of NASA's budget ($7 billion) to reaching NASA's 2020
goal of
reducing launch costs to Low-Earth-Orbit to $220/kg with a 0.01% failure
rate.
This should enable space tourism. The resulting orbital hotels will need
to
develop efficient orbital life support and other necessary technologies.

2. Build orbital space colonies. The materials in the largest asteroid
are
sufficient for orbital colonies with a combined surface area about 500
times
greater than Earth's. Eros alone could make over ten thousand space
colonies,
each with about about 10 square kilometers of 1g living area.

3. After a few generations of orbital living, people won't need their
colony
to be near Sol. Then small groups of colonies with populations in the
tens-of-thousands can set out on multi-decade journeys to nearby stars.

Except the launch goals, none of this is even a little bit official.

Hi Al,

The L5 Society as such did not sponsor any research that I am aware of,
however many of its members were scientists who most certainly did do
research. They frequently reported on this in L5 News, and there were
many good worthwhile discussions took place in the pages and at meetings
concerned. I myself took part in several such events here in L5 UK
before it died in 1979 - and the Space Settlers' Society was founded to
carry on its traditions in 1980..

The Minor Planets Center is at cfa-www.harvard.edu/iau/mpc.html however,
so far as I am aware they do not have information on required delta V
for reaching the asteroids whose particulars they have. On the other
hand these could probably be worked out from the figures they do supply.
You will find though, that the vast majority require considerably
greater delta V to reach and return from than does our Moon.
Accordingly, to try working this out would involve an enormous quantity
of work for very little useful return.

Best wishes, Andy Nimmo.

Al Globus wrote:

> Minor correction, the L5 Society did some good lobbying, but they
> didn't
> do any real research.
>
> A lot of asteroids are found these days because of concerns about a
> collision with earth. I haven't checked the data for awhile, but I'm
> sure many asteroids with very low delta-v have been found. See
> http://impact.arc.nasa.gov/index.html.
>
> Anyone know the URL for the minor planet center? They have the
> definitive information on what's known.
>
> andy-nimmo wrote:
>
> > Hi Mike & All,
> >
> > Back in the 70s there was quite a bit of research done on this in
> the
> > old L5 Society. As I recall, at that time only two or three
> asteroids
> > had been discovered that needed less delta V to get to and return
> than
> > the Moon. I haven't heard of any new asteroids in that category
> having
> > been discovered since, but then delta V is not what the various
> > reporters report on these days. Perhaps it is time we got that
> changed
> > back again? Problem is, most of those who report probably don't know
>
> > what delta V is!
> >
> > Best wishes, Andy.
> >
> > "Combs, Mike" wrote:
> >
> >>
> >>
> >> From: John Frazer [mailto:johnf4303@...]
> >> >-go to the Moon
> >> >
> >> >Yes, in that it is a nearby source of raw materials
> >> >outside of the steepest part of the Earth's gravity well.
> >>
> >> Nearby, yes, but NEAs are more accessible (distance
> >> doesn't matter
> >> nearly as much as relative velocity), as well as richer
> >> sources.
> >>
> >> I certainly never meant to imply that the moon necessarily wins
> hand
> >> down against NEAs. As I recall, asteroids weren't represented on
> >> that first list. It's certainly true that NEAs, as you correctly
> >> state, have certain advantages. But the moon has advantages of its
>
> >> own. I expect we'll do both.I think it will turn powerfully on how
>
> >> easy or hard it is to support humans in space for long durations
> >> without resupply in the early days. I can see a scenario where the
>
> >> technology of telepresence advances only very slowly, such that you
>
> >> have to send as many people to the moon to mine it as to a NEA.
> >> That, combined with a NEA happening to come along on a particularly
>
> >> favorable trajectory, might result in us using asteroidal resources
>
> >> first. I'd expect that afterward we would use lunar resources too,
>
> >> but maybe we could get by without. Coming back and forth from the
> >> moon certainly becomes orders of magnitude more economical with use
>
> >> of NEA resources in HEO.But if telepresence advances rapidly, we
> >> might have a situation where the moon could be mined
> telerobotically
> >> from Earth. Such a development might push us toward use of lunar
> >> resources first. But lunar resource use would most certainly get
> >> followed by asteroidal resource use.
> >>
> >> Regards,
> >>
> >> Mike Combs
> >>
> >>
> >>
> >>
> >>
> >>
> Service.
> >
> --
> Al Globus
> aglobus@..., (650) 604-4404
> http://www.nas.nasa.gov/~globus/home.html
>
> The dinosaurs weren't spacefaring. We are. I don't think that's an
> accident.
> Maybe we are life's taxi to the stars.
>
> I think we should:
>
> 1. Devote half of NASA's budget ($7 billion) to reaching NASA's 2020
> goal of
> reducing launch costs to Low-Earth-Orbit to $220/kg with a 0.01%
> failure
> rate.
> This should enable space tourism. The resulting orbital hotels will
> need
> to
> develop efficient orbital life support and other necessary
> technologies.
>
> 2. Build orbital space colonies. The materials in the largest asteroid
>
> are
> sufficient for orbital colonies with a combined surface area about 500
>
> times
> greater than Earth's. Eros alone could make over ten thousand space
> colonies,
> each with about about 10 square kilometers of 1g living area.
>
> 3. After a few generations of orbital living, people won't need their
> colony
> to be near Sol. Then small groups of colonies with populations in the
> tens-of-thousands can set out on multi-decade journeys to nearby
> stars.
>
> Except the launch goals, none of this is even a little bit official.
>
[www.newaydirect.com]

--- In spacesettlers@y..., Al Globus wrote:
>
> Anyone know the URL for the minor planet center? They have the
> definitive information on what's known.

Here it is:

http://cfa-www.harvard.edu/cfa/ps/mpc.html

You can also check out NASA's Near-Earth Object Program:

http://neo.jpl.nasa.gov/

Mike Eckardt
mike@...
http://orbitalhabitat.com

andy-nimmo wrote:
(About required delta V for reaching the asteroids)
> You will find though, that the vast majority require considerably
greater delta V to reach and return from than does our Moon.

Which asteroids are you considering? The Main belt? Certainly,
these have high delta-V, but I thought the discussion was
centering on NEAs (Near Earth Asteroids, or the Earth
Crossers). Many of these orbit between .5AU - 1.5AU, and some
even are more nearly circular between .8AU-1.2AU. These have
very near 1 Earth-year orbits, and consequently, they can have
extremely low delta-Vs. Lewis cites at least one with a return to
Earth orbit deltaV of only 60 _meters_/sec.
I'll hazard a guess that nearly a hundred of many types are
known with less delta-V to reach them than our moon. In addition
to their low return velocity, they have surface G of less than
.0001G. Lifting off from them is vastly less demanding than from
our Moon.
Then there is Diemos, the outer moon of Mars (bookmarked
article here)

These offer great leverage, since a mass in LEO from the
ground can send much more equipment to them than to Luna,
many are dead-sure certain to have ices as well as metals of
better concentration than our Moon. Crews can be exchanged
every so often, so even with radio delays of up to 18 minutes,
work can continue, and the _entire big rock_ can be brought
back right to the factory with mass drivers or another rocket
throwing away the slag.
Mining & separating these materials is not difficult to do. See the
relevant articles at permanent.com (the bookmarks link at left)
The fact that the Moon has gravity doesn't make it more
reassuringly familiar to us; gravity hinders many processes, and
the Lunar 14 day night is very bad.

> Al Globus wrote:
>> A lot of asteroids are found these days because of concerns
about a collision with earth. I haven't checked the data for
awhile, but I'm sure many asteroids with very low delta-v have
been found.

I'm fairly sure I wrote this before, but Al is exactly right. The
Earth-crossers include many of those with an elliptical orbit,
some of which take them out to 2.5AU+. The term NEA is more
specific to those which are not so elliptical, and spend more of
their time very near 1AU. The very same fact that they have low
delta-V requirements is what makes them so dangerous: They
would enter our atmosphere with low relative velocity, and they
would not build up a tremendous pressure wave of
super-heated air. The higher the pressure of this bow-wave, the
more likely that it will exceed the crush strength of the body, thus
a lower velocity means it's more likely to hit the ground! Added to
this, is the fact that a metallic or stony body has more mass to be
released as it vaporises after hitting the ground.

>> andy-nimmo wrote:
>>> ...As I recall, (Back in the 70s) only two or three asteroids
had been discovered that needed less delta V to get to and
return than the Moon. I haven't heard of any new asteroids in that
category having been discovered since, but then delta V is not
what the various reporters report on these days. Perhaps it is
time we got that changed back again? Problem is, most of those
who report probably don't know what delta V is!

Old data.
SpaceWatch is starting out, with pathetically small funding, but
they're reporting new ones all the time.
Read John Lews: "Rain of Iron & Ice" and "Mining the Sky".
See "Threat or a Promise"
http://www.space-frontier.org/PROJECTS/ASTEROIDS/

"As many as 900 large asteroids (a kilometer or greater) in the
inner solar system... according to a new study published in the
June edition of the journal 'Science'..."

The Delta V for getting to the moon also has to consider the landing and
take-off, when that is considered asteriods like 1982 DB Nereus (return dV is
60 m s-1) become far more attractive.

Asteriods offer better ore bodies, are easier to land on (more like dock with),
have lower dV requirements, much less likelyhood of failure leading to loss of
life as well as not needing a mass driver to launch payloads (technically
possible, but investors may not be too keen on it until proven).

There are also cultural reason for favouring asteriods, for the simple fact
that once you've seen a few you've pretty much seen them all, not many people
would miss it if an asteriod were to become a space colony, but there might be
protests about lunar strip mines.

There is a much better comparison at http://www.permanent.com/ep-a-v-l.htm

--- andy-nimmo wrote:

Hi Ryan,

The asteroid you mention is one of 3 that I have ever heard of that has
a low enough delta V to be economic - if it has resources worth mining.
If you have heard of more asteroids that require low delta V let us know
about them.

However, do please note that I am not against asteroid mining. I'm all
for it, but I suspect the Moon will come first - for both economic and
psychological reasons.

Best wishes, Andy.

Ryan Healey wrote:

> The Delta V for getting to the moon also has to consider the landing
> and
> take-off, when that is considered asteriods like 1982 DB Nereus
> (return dV is
> 60 m s-1) become far more attractive.
>
> Asteriods offer better ore bodies, are easier to land on (more like
> dock with),
> have lower dV requirements, much less likelyhood of failure leading to
> loss of
> life as well as not needing a mass driver to launch payloads
> (technically
> possible, but investors may not be too keen on it until proven).
>
> There are also cultural reason for favouring asteriods, for the simple
> fact
> that once you've seen a few you've pretty much seen them all, not many
> people
> would miss it if an asteriod were to become a space colony, but there
> might be
> protests about lunar strip mines.
>
> There is a much better comparison at
> http://www.permanent.com/ep-a-v-l.htm
>
> --- andy-nimmo wrote:
> > Hi Al,
> >
> > The L5 Society as such did not sponsor any research that I am aware
> of,
> > however many of its members were scientists who most certainly did
> do
> > research. They frequently reported on this in L5 News, and there
> were
> > many good worthwhile discussions took place in the pages and at
> meetings
> > concerned. I myself took part in several such events here in L5 UK
> > before it died in 1979 - and the Space Settlers' Society was founded
> to
> > carry on its traditions in 1980..
> >
> > The Minor Planets Center is at cfa-www.harvard.edu/iau/mpc.html
> however,
> > so far as I am aware they do not have information on required delta
> V
> > for reaching the asteroids whose particulars they have. On the other
>
> > hand these could probably be worked out from the figures they do
> supply.
> > You will find though, that the vast majority require considerably
> > greater delta V to reach and return from than does our Moon.
> > Accordingly, to try working this out would involve an enormous
> quantity
> > of work for very little useful return.
> >
> > Best wishes, Andy Nimmo.
>
[LocalSource.net]

Hi John,

Whether or not a NEA may collide with us is a matter of the relative
trajectories of its orbit and ours. The amount of delta V required to
reach and return from an asteroid is a matter of relative velocity
change required. Accordingly, the fact that an asteroid may or may not
have similar orbital trajectories to Earth does not mean it needs less
delta V than one further away. The fact that any particular NEA might
hit us does not mean it necessarily needs a low delta V to reach it.

Best wishes, Andy.

John Frazer wrote:

> andy-nimmo wrote:
> (About required delta V for reaching the asteroids)
> > You will find though, that the vast majority require considerably
> greater delta V to reach and return from than does our Moon.
>
> Which asteroids are you considering? The Main belt? Certainly,
> these have high delta-V, but I thought the discussion was
> centering on NEAs (Near Earth Asteroids, or the Earth
> Crossers). Many of these orbit between .5AU - 1.5AU, and some
> even are more nearly circular between .8AU-1.2AU. These have
> very near 1 Earth-year orbits, and consequently, they can have
> extremely low delta-Vs. Lewis cites at least one with a return to
> Earth orbit deltaV of only 60 _meters_/sec.
> I'll hazard a guess that nearly a hundred of many types are
> known with less delta-V to reach them than our moon. In addition
> to their low return velocity, they have surface G of less than
> .0001G. Lifting off from them is vastly less demanding than from
> our Moon.
> Then there is Diemos, the outer moon of Mars (bookmarked
> article here)
>
> These offer great leverage, since a mass in LEO from the
> ground can send much more equipment to them than to Luna,
> many are dead-sure certain to have ices as well as metals of
> better concentration than our Moon. Crews can be exchanged
> every so often, so even with radio delays of up to 18 minutes,
> work can continue, and the _entire big rock_ can be brought
> back right to the factory with mass drivers or another rocket
> throwing away the slag.
> Mining & separating these materials is not difficult to do. See the
> relevant articles at permanent.com (the bookmarks link at left)
> The fact that the Moon has gravity doesn't make it more
> reassuringly familiar to us; gravity hinders many processes, and
> the Lunar 14 day night is very bad.
>
> > Al Globus wrote:
> >> A lot of asteroids are found these days because of concerns
> about a collision with earth. I haven't checked the data for
> awhile, but I'm sure many asteroids with very low delta-v have
> been found.
>
> I'm fairly sure I wrote this before, but Al is exactly right. The
> Earth-crossers include many of those with an elliptical orbit,
> some of which take them out to 2.5AU+. The term NEA is more
> specific to those which are not so elliptical, and spend more of
> their time very near 1AU. The very same fact that they have low
> delta-V requirements is what makes them so dangerous: They
> would enter our atmosphere with low relative velocity, and they
> would not build up a tremendous pressure wave of
> super-heated air. The higher the pressure of this bow-wave, the
> more likely that it will exceed the crush strength of the body, thus
> a lower velocity means it's more likely to hit the ground! Added to
> this, is the fact that a metallic or stony body has more mass to be
> released as it vaporises after hitting the ground.
>
> >> andy-nimmo wrote:
> >>> ...As I recall, (Back in the 70s) only two or three asteroids
> had been discovered that needed less delta V to get to and
> return than the Moon. I haven't heard of any new asteroids in that
> category having been discovered since, but then delta V is not
> what the various reporters report on these days. Perhaps it is
> time we got that changed back again? Problem is, most of those
> who report probably don't know what delta V is!
>
> Old data.
> SpaceWatch is starting out, with pathetically small funding, but
> they're reporting new ones all the time.
> Read John Lews: "Rain of Iron & Ice" and "Mining the Sky".
> See "Threat or a Promise"
> http://www.space-frontier.org/PROJECTS/ASTEROIDS/
>
> "As many as 900 large asteroids (a kilometer or greater) in the
> inner solar system... according to a new study published in the
> June edition of the journal 'Science'..."
>
[www.debticated.com]

Hi John,

Whether or not a NEA may collide with us is a matter of the relative
trajectories of its orbit and ours. The amount of delta V required to
reach and return from an asteroid is a matter of relative velocity
change required. Accordingly, the fact that an asteroid may or may not
have similar orbital trajectories to Earth does not mean it needs less
delta V than one further away. The fact that any particular NEA might
hit us does not mean it necessarily needs a low delta V to reach it.

Best wishes, Andy.

John Frazer wrote:

> andy-nimmo wrote:
> (About required delta V for reaching the asteroids)
> > You will find though, that the vast majority require considerably
> greater delta V to reach and return from than does our Moon.
>
> Which asteroids are you considering? The Main belt? Certainly,
> these have high delta-V, but I thought the discussion was
> centering on NEAs (Near Earth Asteroids, or the Earth
> Crossers). Many of these orbit between .5AU - 1.5AU, and some
> even are more nearly circular between .8AU-1.2AU. These have
> very near 1 Earth-year orbits, and consequently, they can have
> extremely low delta-Vs. Lewis cites at least one with a return to
> Earth orbit deltaV of only 60 _meters_/sec.
> I'll hazard a guess that nearly a hundred of many types are
> known with less delta-V to reach them than our moon. In addition
> to their low return velocity, they have surface G of less than
> .0001G. Lifting off from them is vastly less demanding than from
> our Moon.
> Then there is Diemos, the outer moon of Mars (bookmarked
> article here)
>
> These offer great leverage, since a mass in LEO from the
> ground can send much more equipment to them than to Luna,
> many are dead-sure certain to have ices as well as metals of
> better concentration than our Moon. Crews can be exchanged
> every so often, so even with radio delays of up to 18 minutes,
> work can continue, and the _entire big rock_ can be brought
> back right to the factory with mass drivers or another rocket
> throwing away the slag.
> Mining & separating these materials is not difficult to do. See the
> relevant articles at permanent.com (the bookmarks link at left)
> The fact that the Moon has gravity doesn't make it more
> reassuringly familiar to us; gravity hinders many processes, and
> the Lunar 14 day night is very bad.
>
> > Al Globus wrote:
> >> A lot of asteroids are found these days because of concerns
> about a collision with earth. I haven't checked the data for
> awhile, but I'm sure many asteroids with very low delta-v have
> been found.
>
> I'm fairly sure I wrote this before, but Al is exactly right. The
> Earth-crossers include many of those with an elliptical orbit,
> some of which take them out to 2.5AU+. The term NEA is more
> specific to those which are not so elliptical, and spend more of
> their time very near 1AU. The very same fact that they have low
> delta-V requirements is what makes them so dangerous: They
> would enter our atmosphere with low relative velocity, and they
> would not build up a tremendous pressure wave of
> super-heated air. The higher the pressure of this bow-wave, the
> more likely that it will exceed the crush strength of the body, thus
> a lower velocity means it's more likely to hit the ground! Added to
> this, is the fact that a metallic or stony body has more mass to be
> released as it vaporises after hitting the ground.
>
> >> andy-nimmo wrote:
> >>> ...As I recall, (Back in the 70s) only two or three asteroids
> had been discovered that needed less delta V to get to and
> return than the Moon. I haven't heard of any new asteroids in that
> category having been discovered since, but then delta V is not
> what the various reporters report on these days. Perhaps it is
> time we got that changed back again? Problem is, most of those
> who report probably don't know what delta V is!
>
> Old data.
> SpaceWatch is starting out, with pathetically small funding, but
> they're reporting new ones all the time.
> Read John Lews: "Rain of Iron & Ice" and "Mining the Sky".
> See "Threat or a Promise"
> http://www.space-frontier.org/PROJECTS/ASTEROIDS/
>
> "As many as 900 large asteroids (a kilometer or greater) in the
> inner solar system... according to a new study published in the
> June edition of the journal 'Science'..."
>
[www.debticated.com]

For the moment that rock is good enough for our needs.

We wouldn't have much trouble finding others if we wanted them, there are
probably hundreads with comparable dV to Nereus.

I would suspect that the lower cost and high ore quality of asteriods would
make them the ones that are mined first, the moon can only get parity with
rocks if a mass driver or simliar device is used.

Except for the lack of certain volitiles (which may be present at the poles)
the moon would meet all our needs, whether it it will do it better or worse
then asteriods and which will come first or be used to a greater extent is
something we will probably find out later.

--- andy-nimmo wrote: