I was in conversation with someone and the High Frontier came up and
they pooh-poohed it and pointed me to the *definitive debunking*
written by Steven Den Beste. This I had to read, so I went to the URL
and low and behold I come across a strawman stuffed to the limit with
all sorts of assumptions - I immediately thought that Den Beste must
be an alias for Bob Zubrin :)
or "spot the loaded assumption" and compile a comprehensive list of
what's wrong (or right) about the essay.
http://denbeste.nu/entries/00001113.shtml
TangoMan
>http://denbeste.nu/entries/00001113.shtml
"The L5 society originally suggested mining it on the moon and
shooting it towards Lagrange Point 5 with mass accelerators on the
surface of the moon. To mine and refine millions of tons of mass on
the moon would itself require a substantial moon colony. But that
whole concept ignores one basic problem: how do you stop those
capsules when they reach the L5 point? Momentum is always conserved;
you've got to get rid of it some way. For each ton moved to stable
orbit, you're going to require a lot of fuel for rocket engines to
slow the stuff down"
I agree that decelerating masses mined on the moon will need a lot of
energy. But building a habitat has not to depend on masses mined on
the Moon. Masses mined on asteroids will not carry this heavy
gravitation well ballast.
Ideally the habitat would be built near the asteroid which delivers
the most material. This building process would have be done through
robots and remote control.
Men have built the pyramids or the Chinese wall moving masses of
millions of tons, why couldnt engineers build a habitat with robots
which can move hundreds and thousand of tons in an low gravitation
environment?
The hardware needed would get constructed in LEO, for instance using
the ISS as a base for space construction.
The built hardware would than get sent by solar sail or ion propulsion
to the habitat construction site.
To build up an interplanetary communication satellite system for
remote control I would recommend my Solar Sail Launch System :-)
http://solar-thruster-sailor.info/figs/fig19-21d.html which provides
lots of energy for the craft to serve as communication relay.
This craft could carry also landers for first exploration missions on
asteroids.
On the other hand transporting material with solar sail propulsion and
also with ion thruster propulsion were a lot less of fuel is needed
because of the high exhaust velocities made possible through solar
electric acceleration would be a possibility to transport/decellerate
mass driver products of the Moon also.
Frank
> I was in conversation with someone and the High Frontier came up and
> they pooh-poohed it and pointed me to the *definitive debunking*
> written by Steven Den Beste. This I had to read, so I went to the URL
> and low and behold I come across a strawman stuffed to the limit with
> all sorts of assumptions - I immediately thought that Den Beste must
> be an alias for Bob Zubrin :)
regular basis and then just .. stopped when he got email pointing out
where he was wrong on various points.
Brian Dunbar
System Administrator
Liftport - The Space Elevator Company
brian.dunbar@...
aim: bdunbar1967
this email is: [ ] bloggable [x] ask first [ ] private
Remember.
But move forward, too. Light a candle, yes. But also drive a rivet.
~Lileks
It's been my experience that people who rely on
someone else to do their thinking for them are
essentially cannon fodder. Which is why I stubbornly
refuse to even read such rubbish. I've done the
relevant calculations myself, so I know Dr. O'Niell
was right. Enough said,,,
> It's been my experience that people who rely on
> someone else to do their thinking for them are
> essentially cannon fodder. Which is why I stubbornly
> refuse to even read such rubbish. I've done the
> relevant calculations myself, so I know Dr. O'Niell
> was right. Enough said,,,
>
> Gary 7
>
den Beste points out there are more than engineering calculations to
make a good settlement; he outlines some social problems as well.
Brian Dunbar
System Administrator
Liftport - The Space Elevator Company
brian.dunbar@...
aim: bdunbar1967
this email is: [ ] bloggable [x] ask first [ ] private
Remember.
But move forward, too. Light a candle, yes. But also drive a rivet.
~Lileks
I finally looked at it just now.
of handwaving noting that the first colony is going to be difficult --
and likely further in the future than diehard L5 people would like. Why
should it be dominated by a centralized hierarchy? That kind of
structure is very poor at problem solving.
As far as definitive -- don't make me laugh. It's interesting the guy
has sworn off blogging except for anime. Maybe he actually knows
something about that.
Best,
Chuck Divine
excerpt:
"The L5 society originally suggested mining it on the moon and
shooting it towards Lagrange Point 5 with mass accelerators on the
surface of the moon. To mine and refine millions of tons of mass on
the moon would itself require a substantial moon colony. But that
whole concept ignores one basic problem: how do you stop those
capsules when they reach the L5 point? Momentum is always conserved;
you've got to get rid of it some way. For each ton moved to stable
orbit, you're going to require a lot of fuel for rocket engines to
slow the stuff down" You know, there sure isa lot of misunderstanding on this point. When I wrote my Space Settlement FAQ, I made and put up in front of me a sign that said, "K.I.S.S.: Keep It Simple, Stupid". So when it came time to talk about where the lunar ore flyingout the mass-driver goes, I just said, "...to a point in space where it can be easily retrieved". One can get into a multi-page discussion of Lagrange point stabilities and achromatic trajectories. But after seeing so many people either make the above mistake, or mistakenly assume that the mass-driver launches its payloads into low lunar orbit, I finally decided to compromise a little, and at least add the parenthetical "(Earth-moon L-2)". I agree that decelerating masses mined on the moon will need a lot of
energy. But building a habitat has not to depend on masses mined on
the Moon. Masses mined on asteroids will not carry this heavy
gravitation well ballast. There's no need for us to agree with Den Beste's above comment because it's factually wrong. There's also no need for us to give up on the moon for this reason. The originally lunar proposal was just fine; Den Beste's argument derives from a fundamental misunderstanding of the proposal on his part. Ideally the habitat would be built near the asteroid which delivers
the most material.
This would be a fine strategy if the only goal were to build a home in space, and do it as cheaply as possible. But in all likelihood, for the first generation of space habitats the goal will be to provide housing for space workers who are serving an existing market. And at the start of the process, the only market in existence is Earth. I still expect that the first habitat will be built in High Earth Orbit in order to be close by to the market being served. That said, in the long term, I fully expect the vast majority of space habitats will be built as you describe: close by to an asteroid with a wide variety of raw materials.
[mailto:spacesettlers@... On Behalf Of sraj
> throwing bricks to another person at a higher level. When the
> brick reaches the hands of the worker at the higher level it
> has almost zero velocity. It should be possible to launch the
> raw material from the Moon at just the right velocity.
That's pretty much the idea. A payload's journey from the end of the
mass driver to the L-2 point constitutes a long climb up the gravity
well of the moon. The payload's velocity declines from a km/sec regime
to a km/hour one.
And even then, the constant impact of incoming payloads will most
certainly /not/ require a continuous countering thrust from the RCS, as
some seem to think. The vector of the impulse will be along one of the
two stable axes of the L-2 point. The impulses will push the catcher a
certain distance away from L-2, but will not make it leave. When the
impulses cease, the catcher will "spring back" to the L-2 point.
Regards,
Mike Combs
Good analogy Mike that hopefully will bring some reason to this subject Shep
> In India when building houses you will frequently find a worker
> throwing bricks to another person at a higher level. When the
> brick reaches the hands of the worker at the higher level it
> has almost zero velocity. It should be possible to launch the
> raw material from the Moon at just the right velocity.
That's pretty much the idea. A payload's journey from the end of the
mass driver to the L-2 point constitutes a long climb up the gravity
well of the moon. The payload's velocity declines from a km/sec regime
to a km/hour one.
And even then, the constant impact of incoming payloads will most
certainly /not/ require a continuous countering thrust from the RCS, as
some seem to think. The vector of the impulse will be along one of the
two stable axes of the L-2 point. The impulses will push the catcher a
certain distance away from L-2, but will not make it leave. When the
impulses cease, the catcher will "spring back" to the L-2 point.
Regards,
Mike Combs
> You don't know it's rubbish unless you at least skim the article. As
> den Beste points out there are more than engineering calculations to
> make a good settlement; he outlines some social problems as well.
Jon Lennart Beck.
Regards,
Mike Combs
>[mailto:spacesettlers@... On Behalf Of sraj
>
>> In India when building houses you will frequently find a worker
>> throwing bricks to another person at a higher level. When the
>> brick reaches the hands of the worker at the higher level it
>> has almost zero velocity. It should be possible to launch the
>> raw material from the Moon at just the right velocity.
>
>That's pretty much the idea. A payload's journey from the end of the
>mass driver to the L-2 point constitutes a long climb up the gravity
>well of the moon. The payload's velocity declines from a km/sec regime
>to a km/hour one.
>
>And even then, the constant impact of incoming payloads will most
>certainly /not/ require a continuous countering thrust from the RCS, as
>some seem to think. The vector of the impulse will be along one of the
>two stable axes of the L-2 point. The impulses will push the catcher a
>certain distance away from L-2, but will not make it leave. When the
>impulses cease, the catcher will "spring back" to the L-2 point.
wanted to deliver mass driver payloads, NOT about the L-2 point.
The L5 Lagrange point is 60 grade behind Earth orbit around the Sun.
That means about 150 million km orbital distance, from Moon and Earth
away.
To reach this point in a reasonable time frame you would need a lot of
velocity. The brick analogy would fit for a payload which stays in
Moons gravity well, but L5 is way away of the Moon.
If the Moons gravity would reduce the escape velocity to a km an hour,
that would happen near the Moon and the driver payload would need 150
million hours (about 17123 years) to do those 150 million km above but
I dont think L5 could be reached with a simple straight one time mass
driver shot. I guess at least two accelerations and one with direction
change would be needed.
Frank
>[mailto:spacesettlers@... On Behalf Of sraj
>
>> In India when building houses you will frequently find a worker
>> throwing bricks to another person at a higher level. When the
>> brick reaches the hands of the worker at the higher level it
>> has almost zero velocity. It should be possible to launch the
>> raw material from the Moon at just the right velocity.
>
>That's pretty much the idea. A payload's journey from the end of the
>mass driver to the L-2 point constitutes a long climb up the gravity
>well of the moon. The payload's velocity declines from a km/sec regime
>to a km/hour one.
>
>And even then, the constant impact of incoming payloads will most
>certainly /not/ require a continuous countering thrust from the RCS, as
>some seem to think. The vector of the impulse will be along one of the
>two stable axes of the L-2 point. The impulses will push the catcher a
>certain distance away from L-2, but will not make it leave. When the
>impulses cease, the catcher will "spring back" to the L-2 point.
wanted to deliver mass driver payloads, NOT about the L-2 point.
The L5 Lagrange point is 60 grade behind Earth orbit around the Sun.
That means about 150 million km orbital distance, from Moon and Earth
away.
To reach this point in a reasonable time frame you would need a lot of
velocity. The brick analogy would fit for a payload which stays in
Moons gravity well, but L5 is way away of the Moon.
If the Moons gravity would reduce the escape velocity to a km an hour,
that would happen near the Moon and the driver payload would need 150
million hours (about 17123 years) to do those 150 million km above but
I dont think L5 could be reached with a simple straight one time mass
driver shot. I guess at least two accelerations and one with direction
change would be needed.
Frank
wanted to deliver mass driver payloads, NOT about the L-2 point. I think you misunderstand me. Den Beste was criticizing the High Frontier proposal. That's a very specific proposal with lots of specific points and details. One of them was the mass drivers would be used to deliver lunar ores from the surface up to a "catcher" stationed at the L-2 point. Once the catcher had accumulated a full load of ore, it would then slide off the L-2 point and, using either a rotary pellet launcher or mass driver reaction engine for propulsion, deliver the load to an orbital ore refinery. (At an early point of this research, that refinery would have been at L-5. At a later point, they had decided a circular High Earth Orbit about half thediameter of lunar orbit would be better, but that's irrelevant to my point.) Den Beste got this confused and assumed (or misremembered) that the proposal had been to launch ore straight from the lunar surface to L-5. Thus his argument fit the definition of a straw man since he was criticizing a proposal which was in fact different from the one actually made. If the Moons gravity would reduce the escape velocity to a km an hour,
that would happen near the Moon and the driver payload would need 150
million hours (about 17123 years) to do those 150 million km above but
I dont think L5 could be reached with a simple straight one time mass
driver shot. I guess at least two accelerations and one with direction
change would be needed. You're doing the same thing he was doing, easily trouncing a proposition which is different from the one originally proposed. The mass driver is not intended to deliver the ore to the ore refinery. It only delivers the ore to a catcher at L-2. The catcher in turn uses some small faction of that payload as reaction mass tohaul the ore to the refinery.
Mike Combs
>the brick may appear to have reached 0 velocity, but only because the worker "catches' the brick so that the gravity doesnt pull it back down, and if it was going faster than the gravity ability to recover, then it keeps going at same velocity, wouldn't it?
brick out of Earths gravity well, once the well is overcome the brick
keeps the same velocity.
If that is one km an hour it is to slow to reach L5 in a reasonable
time frame. If it would be 30 km a second, (which is incredible fast,
since ion drives output velocities are about the same) 150 million km
would be made in about 58 days (if my calculation is correct) but you
would have to stop this mass with this incredible speed and inertia.
Frank
since ion drives output velocities are about the same) Even lunar escape velocity is only 2.4 km/sec. 150 million km
would be made in about 58 days (if my calculation is correct) but you
would have to stop this mass with this incredible speed and inertia. That's the beauty of exploiting one of the two stable axes of the L-2 point; there's no need to counter the inertia of the incoming payloads.
Mike Combs
>
> The Den Beste article was about the L5 point were the L5 society
> wanted to deliver mass driver payloads, NOT about the L-2 point.
>
>I think you misunderstand me. Den Beste was criticizing the High Frontier proposal.
I have only what Den Beste wrote on his article, I post it once more:
"The L5 society originally suggested mining it on the moon and
shooting it towards Lagrange Point 5 with mass accelerators on the
surface of the moon. To mine and refine millions of tons of mass on
the moon would itself require a substantial moon colony. But that
whole concept ignores one basic problem: how do you stop those
capsules when they reach the L5 point? Momentum is always conserved;
you've got to get rid of it some way. For each ton moved to stable
orbit, you're going to require a lot of fuel for rocket engines to
slow the stuff down"
If the article did criticize the High Frontier proposal which as you
write did not propose to shoot the mass directly to the L5 point, then
Ben Beste seems to be wrong.
>"That's a very specific proposal with lots of specific points and details. One of them was the mass drivers would be used to deliver lunar ores from the surface up to a "catcher" stationed at the L-2 point. Once the catcher had accumulated a full load of ore, it would then slide off the L-2 point and, using either a rotary pellet launcher or mass driver reaction engine for propulsion, deliver the load to an orbital ore refinery. (At an early point of this research, that refinery would have been at L-5. At a later point, they had decided a circular High Earth Orbit about half the diameter of lunar orbit would be better, but that's irrelevant to my point.) Den Beste got this confused and assumed (or misremembered) that the proposal had been to launch ore straight from the lunar surface to L-5. Thus his argument fit the definition of a straw man since he was criticizing a proposal which was in
>fact different from the one actually made.
>
> If the Moons gravity would reduce the escape velocity to a km an hour,
> that would happen near the Moon and the driver payload would need 150
> million hours (about 17123 years) to do those 150 million km above but
> I dont think L5 could be reached with a simple straight one time mass
> driver shot. I guess at least two accelerations and one with direction
> change would be needed.
>
>You're doing the same thing he was doing, easily trouncing a proposition which is different from the one originally proposed.
I did only write my opinion about that what Ben Beste wrote. That I
think, he is right when he states that the momentum is conserved when
the mass is shooted directly toward the L5 point.
I did not even know the originally proposed proposition, how could I
trounce it than?
>The mass driver is not intended to deliver the ore to the ore refinery. It only delivers the ore to a catcher at L-2.
>The catcher in turn uses some small faction of that payload as reaction mass to haul the ore to the refinery.
Sounds better to me.
Frank
write did not propose to shoot the mass directly to the L5 point, then
Ben Beste seems to be wrong. Yeah, he just left a step out of the process. Like I said, there seems to be lots of confusion on this score, and even people who were paying attention at the time seem to be getting kind of hazy about the details of what was proposed back in the days of disco. I did not even know the originally proposed proposition, how could I
trounce it than? Oh, I highly recommend getting Gerard O'Neill's "The High Frontier". It's simply the definitive work on the subject of use of space resources, space industrialization, and space settlement.
http://www.space-frontier.org/HighFrontier/ Also, the Summer Study is online at http://space.alglobus.net/75SummerStudy/Design.html
Mike Combs
>Behalf Of Frank
>
> If the article did criticize the High Frontier proposal which as
>you
> write did not propose to shoot the mass directly to the L5
>point, then
> Ben Beste seems to be wrong.
>
>Yeah, he just left a step out of the process. Like I said, there seems
>to be lots of confusion on this score, and even people who were paying
>attention at the time seem to be getting kind of hazy about the details
>of what was proposed back in the days of disco.
>
> I did not even know the originally proposed proposition, how
>could I
> trounce it than?
>
>Oh, I highly recommend getting Gerard O'Neill's "The High Frontier".
>It's simply the definitive work on the subject of use of space
>resources, space industrialization, and space settlement.
>
>http://www.space-frontier.org/HighFrontier/
once tried an order.
What worked good that was charging the credit card account.
What did not work so good was getting what I payd.
The books and articles I ordered never arrived. More than 100 dollars
payd for nothing.
Frank
> The L5 Lagrange point is 60 grade behind Earth orbit around the Sun.
> That means about 150 million km orbital distance, from Moon and Earth
> away.
earth-moon L5 point, not the earth-sun L5 point. Earth-moon L5 is 0.3
million km from the moon.
For this distance, at a pedestrian speed of 500 m/s, the transit time
is 7 hours.
-Phil
You are correct about the Earth-Moon L5 being the target and not the
mistaken Sun-Earth L5.
However, I calculated 8.89 days. But I'm kinda new to trying on
armchair rocket science:
(* I might be off by as much as the Earth's radius if I've looked that
up wrong)
384,400,000(m) / 500(m/s) = 768,800 seconds
= 12,813 minutes
= 213.5 hours
= 8.89 days
I'm writing a scifi/astronautics series, sticking firmly to known
science. In it, I answer the stopped momentum problem by using "catcher
ships," like fishing vessels of olde, which use leveraged braking tech,
as found in electric car brakes, to convert kinetic energy into
rotational/turbine potential stores. It cannot be 100% efficient, but
it brings it into the realm of the feasible.
- Joel 'Twisty' Nye
the OTHER science guy
> You are correct about the Earth-Moon L5 being the target and not the
> mistaken Sun-Earth L5.
> However, I calculated 8.89 days. But I'm kinda new to trying on
> armchair rocket science:
>
> Dist(Earth_Luna)=Dist(Earth_L5)=Dist(Luna_L5) = 384,400km*
> (* I might be off by as much as the Earth's radius if I've looked that
> up wrong)
>
> 384,400,000(m) / 500(m/s) = 768,800 seconds
> = 12,813 minutes
> = 213.5 hours
> = 8.89 days
> I'm writing a scifi/astronautics series, sticking firmly to known
> science. In it, I answer the stopped momentum problem by using
> "catcher
> ships," like fishing vessels of olde, which use leveraged braking tech,
> as found in electric car brakes, to convert kinetic energy into
> rotational/turbine potential stores. It cannot be 100% efficient, but
> it brings it into the realm of the feasible.
I have a related idea for a variation of the SSI catcher. Its purpose
is not to reclaim residual kinetic energy in a projectile, but to drag
a projectile up to orbital speed, avoiding using a rocket to
circularize an orbit.
My catcher variation is based on a science demo that you might have
seen: In the demo, a strong magnet is dropped down a copper tube, and
the currents that are induced in the tube slow the magnet's fall. My
catcher idea works the same way. The (large, probably superconducting)
magnets are in orbit, and the projectile carries a conductive ring that
plays the same role as the copper tube. Launches are timed so that, as
a projectile reaches its apogee, the magnets in orbit intercept it and
drag it up to speed. The payload experiences a large acceleration, but
no impact.
You can read a white paper on the idea here:
http://keyuke.me.uh.edu/~phil/ssilist/
If you like the idea, feel free to use it in your fiction. If anyone
else has thoughts or criticisms, I would appreciate hearing those, too.
-Phil
Hey Mike, I haven't received any SSI reports for the
last dozen days. Is everyone on vacation???
last dozen days. Is everyone on vacation??? Nowadays, I'm not a very good contact for finding out about the inner workings of SSI (if indeed I ever was). Since I'm no longer involved with the website, right now managing the maillist is my only SSI work. Every rare once in a while I might get an E-mail from Lee Valentine, and I haven't heard from Bettie in years.
Mike Combs