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Damburger
2007-Sep-19, 08:19 PM
How much mass could be shaved off an apollo-style moon mission, if all the equipment for the landing and return journey were sent to the moon as a separate mission?

The cargo component of the mission isn't under a time constraint, so could get to the moon using the same technique as SMART-1, saving a lot of delta-v and therefore money.

Nicolas
2007-Sep-19, 11:34 PM
nitpick: you need the same delta-v whether you send a butterfly or an elephant to the moon. The latter requires a bit more thrust to achieve that delta-v though.

What you suggest is done more or less in the ares 1/V concept, only the parts are assembled already in LEO in this concept. I think you don't gain impressively much by waiting until LO for docking. Only a smart1 ion engine approach wouldn't work that way. On the other hand, I don't think current ion engines are very suitable for heavy loads anyway.

Bob B.
2007-Sep-20, 03:13 PM
nitpick: you need the same delta-v whether you send a butterfly or an elephant to the moon. The latter requires a bit more thrust to achieve that delta-v though.

Nitpicking your nitpick...

Thrust is irrelevant in determining delta-v. Applying 1 pound of thrust for 1,000 seconds is the same as applying 1,000 pounds of thrust for 1 second; both produce the same impulse and thus the same delta-v.



On the other hand, I don't think current ion engines are very suitable for heavy loads anyway.

They are not.

The advantage of ion propulsion is not that it requires less delta-v (it doesn't), but that it is more efficient and can provide a specific amount of delta-v using less propellant. Despite being very fuel efficient, ion propulsion required a tremendous amount of power in the form of electricity. Because a spacecraft's power supply is limited, ion propulsion can be provided in very low thrusts only. Achieving a large delta-v therefore requires a very long period of time -- SMART-1 took about a year to get to the Moon and it weighing only a few hundred kilograms. Transfering a large payload to the Moon via current ion propulsion could take many years or even decades. I don't think this is a practical thing to do.

Nicolas
2007-Sep-20, 04:08 PM
Thanks for the nitpickČ, now we're getting dangerously close to being completely correct ;).

mugaliens
2007-Sep-21, 04:07 PM
Transfering a large payload to the Moon via current ion propulsion could take many years or even decades. I don't think this is a practical thing to do.

Ok, so, put a hundred ion thrusters on the back and reduce it by a factor of 100.

Add solar panels for the electricity, or give it a nuclear system instead.

What's the issue? Ion propulsion does have a theoretical limit, which involves the weight of the propulsion unit(s), the electrical generating equipmentn which drives those units, and whatever payload we're trying to push wherever.

They make good sense for deep space stuff. The don't make very good sense for Moon stuff, given the fact that chemical propulsion gets all equipment 90% of the way there just to escape Earth's orbit, and that it's required for Lunar landing, so why not just keep it 100% chemical?

Ok, so I've just answered my own question...

It might be more efficient, but it's far less practical, all things considered, to move stuff to lunar orbit via ion rocket.

Karl
2007-Sep-21, 08:28 PM
One problem is that a slow spiral up results in a large radiation dose as you make multiple passes through the radiation belts. Any cargo you send has to be able to handle that.

Damburger
2007-Sep-21, 08:51 PM
One problem is that a slow spiral up results in a large radiation dose as you make multiple passes through the radiation belts. Any cargo you send has to be able to handle that.

Is that such a problem? SMART-1 managed it, and that had fairly delicate telemetry equipment on board. What I'm talking about sending is pretty much just a couple of rocket engines.

Regarding how long it takes, does it matter? If you want a sustained series of landings, you can afford to take a year to send your lunar module/lunar departure stage as long as you launch them regularly

KaiYeves
2007-Sep-21, 11:27 PM
Can I come with?