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Old 8th April 2019, 02:52 AM   #41
3point14
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Originally Posted by RecoveringYuppy View Post
Let's go back to the start of this tangent. I'll answer the first question better.



No, it can't be "left" in a Mars Cycler orbit. It has to be put in to one. And it's an expensive maneuver. 6 km/s delta-v near Earth. And then anything rendezvousing with it from Mars has to face over 9 km/s of delta-v.

There is no fuel saving here. It's all cost. Cycler orbits aren't about saving fuel. They are about justifying a large fuel cost by recouping the investment over many cycles. Some far term proposals for building cyclers would start with asteroids that are already in near cycler orbits to avoid the fuel cost.

What problem were you trying to solve here?
I wasn't really, just thinking out loud wondering if weight could be saved.
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Old 8th April 2019, 11:56 AM   #42
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Originally Posted by Pope130 View Post
The MOR (Mars Orbit Rendezvous) profile, with the Earth return vehicle parked in Mars orbit, and a separate vehicle to land, collect samples and deliver those to orbit, seems to work out best, with the lowest departure weight from Earth.
Fair enough, but please note that I'm actually interested in the lowest departure weight from Mars. If we can reduce launch weight from Mars by increasing launch weight from Earth, that might be a worthwhile tradeoff in exchange for more payload weight from Mars.

Basically, the idea is to lift as much weight from Mars as possible, and have as much of that weight be actual samples as possible. The more mission components we can keep off the Martian surface, the better. The more mission components we don't even send to Mars in the first place, the better. To a point.
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Old 8th April 2019, 10:52 PM   #43
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Originally Posted by theprestige View Post
Fair enough, but please note that I'm actually interested in the lowest departure weight from Mars. If we can reduce launch weight from Mars by increasing launch weight from Earth, that might be a worthwhile tradeoff in exchange for more payload weight from Mars.
If you're willing to increase the launch weight from Earth, can't you just increase the amount of fuel you carry to Mars and thus the amount of payload you can get from the Martian surface?

There are strategies that can get you more payload for the same launch weight, but if you are going to increase the launch weight then you have to compare that with sending more fuel. If that gets you more payload from Mars than your other option, then that seems like the straightforward way to go.
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Old 11th April 2019, 03:27 AM   #44
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Originally Posted by Roboramma View Post
If you're willing to increase the launch weight from Earth, can't you just increase the amount of fuel you carry to Mars and thus the amount of payload you can get from the Martian surface?



There are strategies that can get you more payload for the same launch weight, but if you are going to increase the launch weight then you have to compare that with sending more fuel. If that gets you more payload from Mars than your other option, then that seems like the straightforward way to go.
I presume folk are thinking about our current and near future maximum payloads from earth so not assuming we can increase the payload by an arbitrary amount and then have to design a new rocket to let us do that?
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Old 11th April 2019, 08:01 AM   #45
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Originally Posted by Roboramma View Post
If you're willing to increase the launch weight from Earth, can't you just increase the amount of fuel you carry to Mars and thus the amount of payload you can get from the Martian surface?



There are strategies that can get you more payload for the same launch weight, but if you are going to increase the launch weight then you have to compare that with sending more fuel. If that gets you more payload from Mars than your other option, then that seems like the straightforward way to go.
Sure. Send down as much fuel as you want. The question is, what do you want lift up with that fuel? Mars rocks? Or an Earth Return Vehicle?

You'll need an ERV at some point in the mission. But you don't need it on Mars, so it may not be the best use of your overall budget to send it down there and bring it back again.
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Old 11th April 2019, 08:02 AM   #46
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Originally Posted by Darat View Post
I presume folk are thinking about our current and near future maximum payloads from earth so not assuming we can increase the payload by an arbitrary amount and then have to design a new rocket to let us do that?
You presume wrong.
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Old 11th April 2019, 11:57 AM   #47
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Originally Posted by theprestige View Post
You presume wrong.
Glad you can speak for everyone.
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Old 11th April 2019, 12:39 PM   #48
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Originally Posted by Darat View Post
Glad you can speak for everyone.
I only need to speak for myself, to falsify your presumption about everyone.
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Old 11th April 2019, 04:55 PM   #49
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Originally Posted by theprestige View Post
Sure. Send down as much fuel as you want. The question is, what do you want lift up with that fuel? Mars rocks? Or an Earth Return Vehicle?

You'll need an ERV at some point in the mission. But you don't need it on Mars, so it may not be the best use of your overall budget to send it down there and bring it back again.
Oh, I think you’re right that it doesn’t make sense to send the ERV down to the Martian surface. I thought we were talking about the choice between taking it to Mars orbit, where it would stay until the lander returned to orbit at which point they rendezvous and return to earth, or if that rendezvous should happen somewhere else.
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Old 11th April 2019, 05:20 PM   #50
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Originally Posted by Roboramma View Post
Oh, I think you’re right that it doesn’t make sense to send the ERV down to the Martian surface. I thought we were talking about the choice between taking it to Mars orbit, where it would stay until the lander returned to orbit at which point they rendezvous and return to earth, or if that rendezvous should happen somewhere else.
Ah, that makes sense. In my concept, the ERV is responsible for making the Trans-Earth injection burn that breaks the payload out of Mars orbit and sends it on its way back to earth. So it would probably have to be in Mars orbit to start.

All of this business makes the simplicity of Elon Musk's unitary BFR seem very attractive.
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