SMART-1 vs. Apollo

Okay...I'm thoroughly confused. I've read two articles about the
upcoming SMART-1. In each, they mentioned that SMART-1 is being hailed
as a big step in interplanetary travel. That with the ion thrusters,
it could shave years off such trips.

However, they mention that it will take 18 months to reach the moon.
Didn't the Apollo missions do that in three days? Why is it taking so
long? And why is an 18 month journey going to shave years off of
interplanetary travel when we've made it there in three days before?

In article ,
quilty wrote:
However, they mention that it will take 18 months to reach the moon.
Didn't the Apollo missions do that in three days? Why is it taking so
long? And why is an 18 month journey going to shave years off of
interplanetary travel when we've made it there in three days before?

There are two separate issues: the long-term potential of the technology
for deep-space missions, and what it is capable of in a low-budget
demonstrator mission close to home. Press releases often confuse the two.
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"quilty" wrote in message
om...
Okay...I'm thoroughly confused. I've read two articles about the
upcoming SMART-1. In each, they mentioned that SMART-1 is being hailed
as a big step in interplanetary travel. That with the ion thrusters,
it could shave years off such trips.

However, they mention that it will take 18 months to reach the moon.
Didn't the Apollo missions do that in three days? Why is it taking so
long? And why is an 18 month journey going to shave years off of
interplanetary travel when we've made it there in three days before?

Not sure SMART-1 itself will make a difference, but Ion drives in general
may help us reach places that would have taken too long previously.

With constant but slow acceleration they start off slow, but build up speed
over time.

"Paolo Ulivi" wrote in message
...
|
| ... to test an ion engine that will take it from
| GTO to lunar orbit in 18 months using just a few tens of kg of fuel.

Fuel efficiency isn't the issue. Ion engines are tremendously
fuel-efficient. The problem is the media's claim that the technology being
tested promises to shave months or even years off interplanetary voyages. I
don't yet see how an ion engine would accomplish this. It takes forever to
add energy to an orbit using an ion engine.

--
|
The universe is not required to conform | Jay Windley
to the expectations of the ignorant. | webmaster @ clavius.org

"Jay Windley" wrote:

"Paolo Ulivi" wrote in message
...
|
| ... to test an ion engine that will take it from
| GTO to lunar orbit in 18 months using just a few tens of kg of fuel.

Fuel efficiency isn't the issue. Ion engines are tremendously
fuel-efficient. The problem is the media's claim that the technology being
tested promises to shave months or even years off interplanetary voyages. I
don't yet see how an ion engine would accomplish this. It takes forever to
add energy to an orbit using an ion engine.

And just how long is the cruise phase of a Mars bound craft? Jupiter?
Saturn? Neptune? Uranus? Pluto?

D.
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"Derek Lyons" wrote in message
...
| "Jay Windley" wrote:
|
| It takes forever to
| add energy to an orbit using an ion engine.
|
| And just how long is the cruise phase of a Mars bound craft? Jupiter?
| Saturn? Neptune? Uranus? Pluto?

Obviously very long, but the amount of energy you need to add increases with
the radius of the planet's orbit.

I know what you're getting at, and that might be the key. If the period of
the initial orbit solar orbit of the spacecraft is on the order of a year,
and you have a low-energy transfer orbit with a period of, say, 20-30
months, will a significant portion of that transfer orbit (say 15 months)
provide enough time for the ion engine to have added enough energy to
transform the solar orbit into that transfer orbit? My gut says no, but I
haven't run any numbers to confirm this.

--
|
The universe is not required to conform | Jay Windley
to the expectations of the ignorant. | webmaster @ clavius.org

If the period of
the initial orbit solar orbit of the spacecraft is on the order of a year,
and you have a low-energy transfer orbit with a period of, say, 20-30

Well to cut travel time accelerate half way then turn around and decelerate the
last half.

"Hallerb" wrote in message
...
|
| Well to cut travel time accelerate half way then turn around
| and decelerate the last half.

Orbital mechanics doesn't work that way. That procedure is proposed for
interstellar travel where orbital mechanics is less of a factor.

--
|
The universe is not required to conform | Jay Windley
to the expectations of the ignorant. | webmaster @ clavius.org

"Hallerb" wrote in message
...
Well to cut travel time accelerate half way then turn around and
decelerate the
last half.

How about accelerating an answer to my question?
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"Christopher M. Jones" wrote in message ...


You've got to remember that ESA missions operate in a universe
where NASA doesn't exist. How else could they "pave the way"
in the footsteps of previous NASA missions?

ESA is slowly learning from NASA how to hype a mission. ESA
took much critic during times that they were not selling
their achievments very good - but that's a more general
problem when you compare US and European science.

ESA is very much aware of NASA, there is plenty of cooperation.
And if you consider that ESA is run by 15 governments and
NASA only by one, ESA runs pretty well.