About the "Mars in two weeks" nuclear rocket.

There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two weeks:

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
Date: 2001-01-03
http://www.sciencedaily.com/releases...0103073253.htm

Taking the number 75,000,000 km for the distance at closest approach
for Earth and Mars, we can calculate the acceleration required to reach
the half way point in 7 days, or 608,000 seconds (thereafter the rocket
would turn around and use the engine to decelerate over 7 more days.)
The formula for the distance travelled (s) at constant acceleration (a)
over time (t) is:

s= 1/2 * a * t^2

So:

37.5E9 = 0.5 x a x (608000)^2 = 0.5 x a x 3.7E11 ,
so a = 0.2 m/s^2 .

Then the max velocity is: 0.2 x 608000 = 120960 m/s, about 121 km/s.

I found a report on line that derived some design elements for this
propulsion method:

FISSION FRAGMENTS DIRECT HEATING OF GAS PROPELLANT FOR SPACE ROCKET.
http://www.crs4.it/Areas/cfd/10-IWCP_article.pdf

It gives the Isp as 2500s, maximum.

This page gives the formula for the mass ratio in terms of the velocity
change over the trip, or delta V:

DESIGN-CENTERED INTRODUCTION TO AEROSPACE ENGINEERING.
http://www.adl.gatech.edu/classes/dci/space/dci10.html

The mass ratio is given as: M1/M2 = e^(deltaV/g*Isp)

So in this case: M1/M2 = e^(4.937) = 139. If the ship itself weighed
100 tons the ship plus propellant would weigh 14,000 tons.

This is large, but the "DESIGN-CENTERED INTRODUCTION TO AEROSPACE
ENGINEERING" web page gives the mass ratio to reach Earth escape
velocity for standard chemical rockets, as with the Apollo missions, as
18.7. So this nuclear Mars mission would be less than a factor of 10
higher.
Also, this page on general nuclear propulsion methods suggest some,
gas-core designs, can reach Isp's of 6000s:

Nuclear Propulsion
http://www.astrodigital.org/space/nuclear.html

Since this is only considering plutonium and uranium reactors and the
Am-242m fuel is more efficient, it's likely the Am-242m reactor can
also reach this Isp. Then at 6000s Isp the mass ratio would only be:
e^(120960/9.8*6000) = 7.8 , which is less than the mass ratio for Earth
escape velocity with chemical rockets.
The design shown in the "FISSION FRAGMENTS DIRECT HEATING OF GAS
PROPELLANT FOR SPACE ROCKET" report seems to be intermediate between
the solid core and gas core approach to a nuclear rocket. Perhaps a
fully gas-core approach for using the Am-242m fuel would allow it to
reach Isp's in the 6000s range.

Bob Clark

Robert Clark wrote:
There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two weeks:


What are the G forces involved?

s= 1/2 * a * t^2
The acceleration is given in the calculation:

s= 1/2 * a * t^2,

37.5E9 = 0.5 x a x (608000)^2 = 0.5 x a x 3.7E11 ,
so a = 0.2 m/s^2 .

This is 1/50 of normal Earth gravity of 9.8 m/s^2. So a 200 pound man
would weigh only 4 lbs. This could be a problem over a long mission but
not on a trip of only two weeks duration.

Bob Clark

"Robert Clark" wrote in message
oups.com...
There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two weeks:

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
Date: 2001-01-03
http://www.sciencedaily.com/releases...0103073253.htm

You left out the quotes that indicate that this is far less than a "paper
rocket", more like a theoretical paper rocket.

"There are still many hurtles to overcome before americium-242m
can be used in space," Ronen says. "There is the problem of
producing the fuel in large enough quantities from plutonium-241
and americium-241, which requires several steps and is expensive.
But the material is already available in fairly small amounts.
In addition, actual reactor design, refueling, heat removal, and
safety provisions for manned vehicles have not yet been examined.

So, even the actual design of the reactor has not been examined. At this
point, it's all theory and conjecture.

Jeff
--
Remove icky phrase from email address to get a valid address.

In article .com,
Robert Clark wrote:
There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two weeks:

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
Date: 2001-01-03
http://www.sciencedaily.com/releases...0103073253.htm

Taking the number 75,000,000 km for the distance at closest approach
for Earth and Mars, we can calculate the acceleration required to reach
the half way point in 7 days, or 608,000 seconds (thereafter the rocket
would turn around and use the engine to decelerate over 7 more days.)
The formula for the distance travelled (s) at constant acceleration (a)
over time (t) is:

s= 1/2 * a * t^2

So:

37.5E9 = 0.5 x a x (608000)^2 = 0.5 x a x 3.7E11 ,
so a = 0.2 m/s^2 .

Then the max velocity is: 0.2 x 608000 = 120960 m/s, about 121 km/s.

I found a report on line that derived some design elements for this
propulsion method:

FISSION FRAGMENTS DIRECT HEATING OF GAS PROPELLANT FOR SPACE ROCKET.
http://www.crs4.it/Areas/cfd/10-IWCP_article.pdf

It gives the Isp as 2500s, maximum.

Its great claim to efficiency seems to be directly exposing the propellant
to fission fragments, while the more traditional nuclear rocket needs to
let heat leak out from inside the fuel with the temperature limited by how
well the heat is removed from the fuel and the temperatures that the
engine structure can handle.

For something not requiring americium, consider a more conventional
reactor with an array of cooling tubes running through it, made of uranium
or plutonium or other fissile material of your choice. Forget the thin
films of exotic materials, use bulk material with a switchable neutron
source.

--
"Never argue with a fool. They will drag you down to their level and win
by experience."

Jeff Findley wrote:
"Robert Clark" wrote in message
oups.com...
There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two
weeks:

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
Date: 2001-01-03
http://www.sciencedaily.com/releases...0103073253.htm

You left out the quotes that indicate that this is far less than a
"paper
rocket", more like a theoretical paper rocket.

"There are still many hurtles to overcome before americium-242m
can be used in space," Ronen says. "There is the problem of
producing the fuel in large enough quantities from plutonium-241
and americium-241, which requires several steps and is expensive.
But the material is already available in fairly small amounts.
In addition, actual reactor design, refueling, heat removal, and
safety provisions for manned vehicles have not yet been examined.

So, even the actual design of the reactor has not been examined. At
this
point, it's all theory and conjecture.

Jeff
--
Remove icky phrase from email address to get a valid address.

The purpose of the report:

FISSION FRAGMENTS DIRECT HEATING OF GAS PROPELLANT FOR SPACE ROCKET.
http://www.crs4.it/Areas/cfd/10-IWCP_article.pdf

was to give a preliminary design of such a rocket. It gives a schematic
diagram of the engine and values for the dimensions, thermal
efficiency, exhaust temperature, thrust, and Isp.

There are ways for separating out desired isotopes that are being used
in experimental work that can probably be scaled up to work for
separating out Am-242m in large amounts.


Bob Clark

Gregory L. Hansen wrote:
In article .com,
Robert Clark wrote:
There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two weeks:

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
Date: 2001-01-03
http://www.sciencedaily.com/releases...0103073253.htm

Taking the number 75,000,000 km for the distance at closest approach
for Earth and Mars, we can calculate the acceleration required to
reach
the half way point in 7 days, or 608,000 seconds (thereafter the
rocket
would turn around and use the engine to decelerate over 7 more
days.)
The formula for the distance travelled (s) at constant acceleration
(a)
over time (t) is:

s= 1/2 * a * t^2

So:

37.5E9 = 0.5 x a x (608000)^2 = 0.5 x a x 3.7E11 ,
so a = 0.2 m/s^2 .

Then the max velocity is: 0.2 x 608000 = 120960 m/s, about 121 km/s.

I found a report on line that derived some design elements for this
propulsion method:

FISSION FRAGMENTS DIRECT HEATING OF GAS PROPELLANT FOR SPACE ROCKET.
http://www.crs4.it/Areas/cfd/10-IWCP_article.pdf

It gives the Isp as 2500s, maximum.

Its great claim to efficiency seems to be directly exposing the
propellant
to fission fragments, while the more traditional nuclear rocket needs
to
let heat leak out from inside the fuel with the temperature limited
by how
well the heat is removed from the fuel and the temperatures that the
engine structure can handle.

For something not requiring americium, consider a more conventional
reactor with an array of cooling tubes running through it, made of
uranium
or plutonium or other fissile material of your choice. Forget the
thin
films of exotic materials, use bulk material with a switchable
neutron
source.

--
"Never argue with a fool. They will drag you down to their level and
win
by experience."

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
"To meet the challenge of a light nuclear reactor, Ronen examined one
element of reactor design, the nuclear fuel itself. He found at the
time that of the known fission fuels, Am-242m is the front-runner,
requiring only 1 percent of the mass (or weight) of uranium or
plutonium to reach its critical state."
http://www.sciencedaily.com/releases...0103073253.htm

This seems to be a fundamental improvement in the efficiency over
uranium, plutonium fuels analogous to the efficiency of hydrogen over
kerosene as measured by Isp.


Bob Clark

Robert Clark wrote:

There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two weeks:

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
Date: 2001-01-03
http://www.sciencedaily.com/releases...0103073253.htm

[snip erudition]

So in this case: M1/M2 = e^(4.937) = 139. If the ship itself weighed
100 tons the ship plus propellant would weigh 14,000 tons.

Say there, git, how many kilos of americium were you planning to
snuggle within? Do you have any idea how to manufacture it or how
much it would cost to obtain? Or how to handle it at scale in your
application? Remember how fission was going to generate electricity
so cheap it would not be metered?

Even xenon ion engines are obscenely expensive because isolating 10
tonnes of xenon is no laughing matter - and it's in the air for free.
Volatile metal fuels short out the works (and mercury also dissolves
them). SF6, freons, and the like are horribly corrosive when ionized,
including toward ceramics. Argon does not store densely even as the
cryogenic liquid.

This is large, but the "DESIGN-CENTERED INTRODUCTION TO AEROSPACE
ENGINEERING" web page gives the mass ratio to reach Earth escape
velocity for standard chemical rockets, as with the Apollo missions, as
18.7. So this nuclear Mars mission would be less than a factor of 10
higher.
[snip]

"Less than a factor of 10." Giggle. One Reagan-class aircraft
carrier is ridiculous. Mulitply by eight.

Hey Bob, remember the Enviro-whiner stink about a little Pu-238 in the
Cassini thermal isotope generators? They'll stink on your parade much
more - enriched U, Pu and Am are all fission bomb stuffings.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

Uncle Al wrote:
Robert Clark wrote:

There was a study announced a few years ago on a more efficient
nuclear fuel, Am-242m, that would allow a trip to Mars in two
weeks:

Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
Weeks.
Date: 2001-01-03
http://www.sciencedaily.com/releases...0103073253.htm

[snip erudition]

So in this case: M1/M2 = e^(4.937) = 139. If the ship itself
weighed
100 tons the ship plus propellant would weigh 14,000 tons.

Say there, git, how many kilos of americium were you planning to
snuggle within? Do you have any idea how to manufacture it or how
much it would cost to obtain? Or how to handle it at scale in your
application? Remember how fission was going to generate electricity
so cheap it would not be metered?

Even xenon ion engines are obscenely expensive because isolating 10
tonnes of xenon is no laughing matter - and it's in the air for free.

Volatile metal fuels short out the works (and mercury also dissolves
them). SF6, freons, and the like are horribly corrosive when
ionized,
including toward ceramics. Argon does not store densely even as the
cryogenic liquid.

This is large, but the "DESIGN-CENTERED INTRODUCTION TO AEROSPACE
ENGINEERING" web page gives the mass ratio to reach Earth escape
velocity for standard chemical rockets, as with the Apollo
missions, as
18.7. So this nuclear Mars mission would be less than a factor of
10
higher.
[snip]

"Less than a factor of 10." Giggle. One Reagan-class aircraft
carrier is ridiculous. Mulitply by eight.

Hey Bob, remember the Enviro-whiner stink about a little Pu-238 in
the
Cassini thermal isotope generators? They'll stink on your parade
much
more - enriched U, Pu and Am are all fission bomb stuffings.


Was your purpose in mentioning the Reagan-class carriers a reference
to their weight? They weigh much more than the number I remarked for
the mass of the Mars mission:

USS Ronald Reagan
"Displacement: 77,600 tons light, 98,235 tons full"
http://www.answers.com/topic/uss-ronald-reagan

Or a reference to their cost and size multiplied by the number of
carriers built? In any case, they *were* built. A Mars mission would
likewise require a tremendous investment of national resources.
Actually, my guess is that it will be an international project.

Note also that the ratio of actual liftoff weight of the Apollo
missions to payload was 60 to 1:

Saturn V Rocket.
# Stage m0 mp m1
1. S1C 300.0 4492.0 4792.0
2. S2 95.0 942.0 1037.0
3. SIVB 34.0 228.0 262.0
4. IU 4.5 0.0 4.5
5. payload - - 109.6
"Here m0 is the stage empty weight, mp is the propellant, and m1 is the
stage total, in thousands of pounds."
http://spider.ipac.caltech.edu/staff/waw/mad/mad3.html

Adding up the numbers in the last column you get total weight over
6,200,000 lbs. to the payload of 109.6 lbs. Note also you probably
wouldn't launch from Earth but from space so you wouldn't have to worry
about the gravitational effects on this large mass.
You probably also wouldn't get the fuel, both reaction mass and
radioactive materials, from Earth but from the Moon or near earth
asteroids.
Also, as I said it is *very* likely that a reactor design can be
created for the Am-242m fuel that produces an Isp of 6000s since such
designs already exist for uranium and plutonium and Am-242m is 100
times more efficient. An Isp of 6000s would result in a mass ratio less
than 8.
There are experimental methods now used that can efficiently separate
isotopes in small amounts. These methods very likely would scale up to
larger amounts. The cost of this scaling I estimate would be a small
fraction of the cost of the mission.
I'm sure with your extensive knowledge you could ferret out some of
these methods. I would prefer not to say precisely in a public forum.



Bob Clark

In sci.space.policy Robert Clark wrote:
Also, as I said it is *very* likely that a reactor design can be
created for the Am-242m fuel that produces an Isp of 6000s since such
designs already exist for uranium and plutonium and Am-242m is 100
times more efficient. An Isp of 6000s would result in a mass ratio less
than 8.

It is utterly unimportant how effective Am-242 using nuclear reactors
would be becuase the fact is that you aren't going to get the Am-242.
Because teh total worldwide production of Americum is in kilograms,
only about 5% of that is Am-242 *and* it has a half-life of 150 years.

There are experimental methods now used that can efficiently separate
isotopes in small amounts. These methods very likely would scale up to
larger amounts. The cost of this scaling I estimate would be a small
fraction of the cost of the mission.

You can't extract what isn't there. Am-242 is a short half-life element
that does not occour naturaly at all.


Bob Clark


--
Sander

+++ Out of cheese error +++