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Old 5th April 2019, 01:49 AM   #1
3point14
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Mars Sample Return

So, after the rather depressing discussions lately about the utility of human space exploration, I wondered to myself how feasible a Mars sample return mission would be.

Perhaps I should have known already that I'm not the first to think of it (amazing, I know) and that it has budget. Ish - This is Nasa and I've never quite understood how the funding works.


https://www.space.com/nasa-mars-samp...sion-2026.html


How valuable would Mars rocks be?
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Old 5th April 2019, 02:01 AM   #2
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Originally Posted by 3point14 View Post


How valuable would Mars rocks be?

what someone is willing to pay for it.


But scientifically, there isn't that much that earth devices can add to what drone probes can already do.
And, of course, there is the question of how the journey might affect the sample.

That being said, there might be something a rover might find that is so strange that it would make absolutely sense to bring it to earth if that is cheaper than sending a better probe.
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Old 5th April 2019, 07:57 AM   #3
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We can work backwards. We know something has to return to Earth. We know we can reenter, splashdown, and recover stuff at least as big as an Apollo CSM. That's probably more than enough for a useful Mars sample return. So the real limit is what we can lift off the Martian surface.

We know that whatever comes back to Earth, it'll probably have to include:
- a reentry vehicle,
- a deceleration motor, and
- fuel for the deceleration motor.

Basically, a payload and a booster rocket. From this we know that whatever makes it to Mars orbit probably has to include:
- a reentry vehicle,
- a deceleration motor,
- fuel for the deceleration motor,
- an Earth orbit transfer motor, and
- fuel for the Earth orbit transfer motor.

Basically, something to get the return package out of Mars orbit and on its way to Earth. From this we know that whatever we start with on the Martian surface probably has to include:
- a reentry vehicle,
- a deceleration motor,
- fuel for the deceleration motor,
- an Earth orbit transfer motor,
- fuel for the Earth orbit transfer motor,
- a launch motor for all of that to get to Mars orbit, and
- fuel for the launch motor and all of that payload.

Having worked it backwards, we can now turn around and work it forwards: What's the largest launch vehicle we can deliver to the Martian surface? That tells us how much payload we can deliver to Mars orbit, and that tells us how big the return package and transfer vehicle can be. From there, we can derive the upper limits on each component of that system, but that's far, far beyond my capability.
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Old 5th April 2019, 08:30 AM   #4
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That all makes sense. And it's almost certainly technically feasible, I think.

My thoughts were more about the scientific usefulness of bringing rocks back, especially in light of my acceptance of your conclusions regarding manned exploration (damn you ).

Given advances in robotics and AI, is it more worthwhile to send a lab to Mars (as we have done) than it would ever be to bring rocks back.
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Old 5th April 2019, 08:36 AM   #5
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Could it make theoretical sense for the Mars lander to carry with it a much smaller 'ship' that will make the return journey alone, carrying only the samples? That way there's no need to carry fuel enough to relaunch the original lander. The vehicle that does the prospecting, digging etc. is assumed to be expendable and can maybe keep on touring a la current Mars rovers.
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Old 5th April 2019, 08:48 AM   #6
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Originally Posted by GlennB View Post
Could it make theoretical sense for the Mars lander to carry with it a much smaller 'ship' that will make the return journey alone, carrying only the samples? That way there's no need to carry fuel enough to relaunch the original lander. The vehicle that does the prospecting, digging etc. is assumed to be expendable and can maybe keep on touring a la current Mars rovers.
One of the plans is three stage, with a rover collecting samples and leaving them dotted over Mars, a later payload bringing a rover whose sole purpose is to collect the samples and deliver them to a third payload, which is the return rocket.
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Old 5th April 2019, 08:55 AM   #7
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Originally Posted by GlennB View Post
Could it make theoretical sense for the Mars lander to carry with it a much smaller 'ship' that will make the return journey alone, carrying only the samples? That way there's no need to carry fuel enough to relaunch the original lander. The vehicle that does the prospecting, digging etc. is assumed to be expendable and can maybe keep on touring a la current Mars rovers.
My mission profile is based on Apollo, and assumes that the lander would not return. It's purely a question of how much launch vehicle you can get to the surface of Mars, and the upper limit of sample mass such a launch vehicle could lift to Mars orbit along with the necessary return vehicles to get that sample mass all the way home. Everything else from the mission stays on Mars.
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Old 5th April 2019, 08:58 AM   #8
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Automatic rendezvous and docking has been making good progress. Leaving the Earth return vehicle in Mars orbit, so the vehicle taking the samples off Mars surface can be much smaller and lighter is an option. Similar in concept to the LOR (Lunar Orbit Rendezvous) technique that made the Apollo landings possible with a single Saturn V launch, rather than multiple Saturn launches or moving up to the nuclear upper stage, or Nova class launchers.
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Old 5th April 2019, 09:02 AM   #9
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Originally Posted by 3point14 View Post
How valuable would Mars rocks be?
Depends. Can Cydonite stop Superman?
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Old 5th April 2019, 09:05 AM   #10
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ETA: Props to Pope130, who totally ninja'd my "automated shipyard in Mars orbit" proposal.

Originally Posted by 3point14 View Post
That all makes sense. And it's almost certainly technically feasible, I think.

My thoughts were more about the scientific usefulness of bringing rocks back, especially in light of my acceptance of your conclusions regarding manned exploration (damn you ).

Given advances in robotics and AI, is it more worthwhile to send a lab to Mars (as we have done) than it would ever be to bring rocks back.
I think it depends on how much lab we'd send to Mars, and how much value we'd get.

Bringing samples home gives us a lot of flexibility. We can use lab equipment that's already built and working on Earth, and we can use human components in the investigation. We don't have to re-engineer existing equipment to be automated and reliable without human intervention and support on a distant planet.

We can also exploit Earth's existing transportation infrastructure. If one piece of equipment is in one lab, and another piece of equipment is in another lab, we can simply box up samples and drive or fly or rail them around to all the different labs. We don't have to send special Mars versions of all the labs all to the same place somewhere else in the Solar System.

We can also be a lot more flexible, a lot faster. If a researcher comes up with a new test, or preliminary research reveals a novel line of inquiry, it's pretty easy on Earth to put together a new test protocol, design new equipment, and get to work. Even if the new equipment is a buggy prototype, having humans on hand, in a shirtsleeve environment to help out is a huge value that we wouldn't get on Mars.

If we did that in situ, it would take decades from the interesting discovery, to the design of new Mars equipment, to the expensive new mission to Mars to deliver the new lab.

So I think sample return would be a very worthwhile investment.

But then, I also think a manned shipyard in Mars orbit would be a worthwhile investment. That way, you wouldn't have to land the Earth Return Vehicle on Mars, and return it back to orbit from the surface. As long as the sample return vehicle could get off the surface, a crew in orbit could mate it to the ERV there, and send it on its way. But that's a lot of long-duration space stations to construct: One shipyard in Earth orbit, one or more Mars cyclers to rotate crews and resupply consumables, and one shipyard in Mars orbit. Plus redundancy for safety.

The other (probably better) approach would be to use the LEO shipyard as a testbed and proving ground for automated assembly techniques, and then put an automated shipyard in Mars orbit.

I guess the idea is, everyone wants to do missions, but I just want to build infrastructure.

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Old 5th April 2019, 09:42 AM   #11
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I started reading The Case for Mars by Robert Zubrin. In the part I have read (still a work in progress), he explains different ways of accomplishing a Mars sample return. Worth the read.
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Old 6th April 2019, 12:18 AM   #12
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Originally Posted by theprestige View Post
We know that whatever comes back to Earth, it'll probably have to include:
- a reentry vehicle,
- a deceleration motor, and
- fuel for the deceleration motor.
We might not need all of this. I ain't no Rich Purnell, but it seems to me that the returning spacecraft might be able to rendezvous and dock with the ISS. It would need a docking hatch and then be berthed like the Dragon modules, and then brought back to earth as part of the next available cargo or crew return.

The returning spacecraft could then be much lighter as it would not need the re-entry shield or parachutes for landing.

Alternatively, if that is impossible from an orbital mechanics standpoint, then perhaps a lunar gravity assist or aerobraking (which would require some kind of minimal heat shielding) to assist with orbit insertion.
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Old 6th April 2019, 01:16 AM   #13
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Yeah, that sounds like a good idea to me.
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Old 6th April 2019, 03:54 AM   #14
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Originally Posted by smartcooky View Post
We might not need all of this. I ain't no Rich Purnell, but it seems to me that the returning spacecraft might be able to rendezvous and dock with the ISS. It would need a docking hatch and then be berthed like the Dragon modules, and then brought back to earth as part of the next available cargo or crew return.



The returning spacecraft could then be much lighter as it would not need the re-entry shield or parachutes for landing.



Alternatively, if that is impossible from an orbital mechanics standpoint, then perhaps a lunar gravity assist or aerobraking (which would require some kind of minimal heat shielding) to assist with orbit insertion.
Seems like it works out about the same, at our level of discussion.
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Old 6th April 2019, 01:15 PM   #15
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Originally Posted by smartcooky View Post
We might not need all of this. I ain't no Rich Purnell, but it seems to me that the returning spacecraft might be able to rendezvous and dock with the ISS. It would need a docking hatch and then be berthed like the Dragon modules, and then brought back to earth as part of the next available cargo or crew return.

The returning spacecraft could then be much lighter as it would not need the re-entry shield or parachutes for landing.

Alternatively, if that is impossible from an orbital mechanics standpoint, then perhaps a lunar gravity assist or aerobraking (which would require some kind of minimal heat shielding) to assist with orbit insertion.
The propellant for braking into orbit and hardware for rendezvous and berthing would far outmass the heat shield and parachutes for a direct return. You're probably talking about ~6 km/s of delta-v required to enter LEO, more for plane corrections if you aren't perfectly lined up with the ISS's orbital plane. (Stardust had an entry velocity of 12.9 km/s.)
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Old 6th April 2019, 01:22 PM   #16
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Originally Posted by smartcooky View Post
We might not need all of this. I ain't no Rich Purnell, but it seems to me that the returning spacecraft might be able to rendezvous and dock with the ISS. It would need a docking hatch and then be berthed like the Dragon modules, and then brought back to earth as part of the next available cargo or crew return.
Got to agree with cjameshuff. Ablative shield vs. fuel and docking mechanism. Shield has got to be cheaper. Possibly multiple aerobraking maneuvers too.
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Old 6th April 2019, 01:39 PM   #17
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You could get more samples returned if you didn't include any of that reentry hardware, though.

Send a fragile but weighty sample box flashing past Earth at speed, and send up a reentry vehicle to rendezvous with it, slow it down, and bring it home.

The reentry vehicle can be as heavy as you want, since it doesn't have to lift off from the surface of Mars or anything.
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Old 6th April 2019, 02:24 PM   #18
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Originally Posted by theprestige View Post
Send a fragile but weighty sample box flashing past Earth at speed, and send up a reentry vehicle to rendezvous with it, slow it down, and bring it home.

That will likely get more sample back, but the cost of sending up a second vehicle is steep. Hopefully that will change in the future.
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Old 6th April 2019, 02:36 PM   #19
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Originally Posted by RecoveringYuppy View Post
That will likely get more sample back, but the cost of sending up a second vehicle is steep. Hopefully that will change in the future.
"Likely get more sample back"?

How do you get "likely"?

By my estimate, this mission design absolutely gets more sample back.

Besides, what costs more? Sending an entire Earth reentry vehicle to Mars surface and back again? Or sending it to Earth encounter rendezvous and back again?

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Old 6th April 2019, 02:45 PM   #20
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Originally Posted by theprestige View Post
Sending an entire Earth reentry vehicle to Mars surface and back again?
Not sure the reentry vehicle would have to go to the surface of Mars. Could stay in orbit.

Launch costs aren't cheap. Even for a mission like Curiosity which had a very demanding lander launch costs were still 20% of the mission cost. I don't see how this can be an obvious choice right now.
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Old 6th April 2019, 02:54 PM   #21
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Originally Posted by RecoveringYuppy View Post
Not sure the reentry vehicle would have to go to the surface of Mars. Could stay in orbit.

Launch costs aren't cheap. Even for a mission like Curiosity which had a very demanding lander launch costs were still 20% of the mission cost. I don't see how this can be an obvious choice right now.
You're still sending an Earth reentry vehicle all the way to Mars orbit and back again. Which is means both your original Earth launch vehicle and Earth transfer vehicle have to be heavier. And because the ETV has to be heavier, the ELV has to be even heavier.

That's all payload mass you're giving away. Just to send Earth-side mission components to Mars and back again.

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Old 6th April 2019, 03:00 PM   #22
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Originally Posted by theprestige View Post
You're still sending an Earth reentry vehicle all the way to Mars orbit and back again. Which is means both your original Earth launch vehicle and Earth transfer vehicle have to be heavier. And because the ETV has to be heavier, the ELV has to be even heavier.

That's all payload mass you're giving away. Just to send Earth-side mission components to Mars and back again.
The part that comes back from Mars has to go to Mars. The minimum for the "Earth-side mission components" is a heat shield and a parachute.
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Old 6th April 2019, 03:32 PM   #23
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The retriever vehicle sent up to recover the sample return package would have to be sent out far enough for the rendezvous and capture maneuver to occur, and accelerated onto the sample return vehicle's vector. This will entail a separate launch, and a time critical maneuver. It will also require a delta-v for the recovery vehicle similar to sending it along to Mars orbit. For un-manned vehicles cost is not a matter of "how far", but rather a matter of "how fast".
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Old 6th April 2019, 05:51 PM   #24
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Originally Posted by theprestige View Post
You could get more samples returned if you didn't include any of that reentry hardware, though.

Send a fragile but weighty sample box flashing past Earth at speed, and send up a reentry vehicle to rendezvous with it, slow it down, and bring it home.

The reentry vehicle can be as heavy as you want, since it doesn't have to lift off from the surface of Mars or anything.
The return vehicle's going to be on a fast hyperbolic trajectory. Sending a reentry vehicle out to match trajectories with it on its way past Earth would require sending that reentry vehicle years ahead of time on an interplanetary trajectory that makes a fast flyby of Mars as the sample vehicle burns for return to Earth. That reentry vehicle then needs to have the propulsion and mechanisms to rendezvous with the sample return vehicle, transfer the samples, and seal itself up.

If there's any benefit at all, it's very minor, and it's far more complicated. If there's a failure in rendezvous or transfer, you don't get your samples back. If any part of the operation even has a schedule hangup, you don't have a reentry craft in position to handle your samples. A reentry vehicle just isn't anywhere near massive enough to make this worth it.
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Old 7th April 2019, 05:14 AM   #25
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Originally Posted by RecoveringYuppy View Post
Not sure the reentry vehicle would have to go to the surface of Mars. Could stay in orbit.

Could the reentry vehicle be left in an Mars Cycler orbit? Save the fuel for slowing it down and speeding it up again.
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Old 7th April 2019, 08:59 AM   #26
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Originally Posted by 3point14 View Post
Could the reentry vehicle be left in an Mars Cycler orbit? Save the fuel for slowing it down and speeding it up again.
That's essentially what I was describing. It involves adding another schedule-critical launch and rendezvous operation and turning the reentry vehicle into a whole additional spacecraft with its own propulsion system and mechanisms for docking and payload transfer.

Reentry vehicles aren't that heavy, and it's far from clear that adding another set of avionics and propulsion and equipping everything with what it needs to perform rendezvous and docking would actually result in a net reduction in launch mass. It's a lot more certain that it'd greatly increase the complexity and cost.
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Old 7th April 2019, 09:05 AM   #27
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Originally Posted by 3point14 View Post
Could the reentry vehicle be left in an Mars Cycler orbit? Save the fuel for slowing it down and speeding it up again.
Not sure I'm following what you have in mind. It only saves the fuel if you actually leave it in that orbit. But it has to leave that orbit to be a reentry vehicle.

I would think a cycler orbit has benefit if you plan to bring back (or deliver other stuff) samples multiple times?

Given how expensive launchers and upper stages are for the near future I would think it's fairly simple: Take a minimum energy orbit to get to Mars, take the next minimum energy return back.
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Old 7th April 2019, 09:56 AM   #28
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Originally Posted by RecoveringYuppy View Post
Not sure I'm following what you have in mind. It only saves the fuel if you actually leave it in that orbit. But it has to leave that orbit to be a reentry vehicle.
It also saves the fuel you'd otherwise use to land it on the Martian surface and then lift it up again. And it saves the fuel you'd use to send to Mars the fuel you'd use to land it and lift it up again.
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Old 7th April 2019, 10:04 AM   #29
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Originally Posted by cjameshuff View Post
That's essentially what I was describing. It involves adding another schedule-critical launch and rendezvous operation and turning the reentry vehicle into a whole additional spacecraft with its own propulsion system and mechanisms for docking and payload transfer.

Reentry vehicles aren't that heavy, and it's far from clear that adding another set of avionics and propulsion and equipping everything with what it needs to perform rendezvous and docking would actually result in a net reduction in launch mass. It's a lot more certain that it'd greatly increase the complexity and cost.
Since the ultimate goal is to bring back samples from Mars, mission designs that result in a net reduction in launch mass from the Martian surface are interesting.

If the sample return container can meet the Earth Return Vehicle in Mars orbit, then that's more sample payload that can be lifted from the surface.

As you pointed out, though, the tradeoff is more complexity, cost, and risk; in exchange for more samples per mission. At the very least, it would mean less missions. There's probably a sweet spot somewhere in the middle, where number of missions and payload per mission maximize the total amount of samples returned.
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Old 7th April 2019, 10:33 AM   #30
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Originally Posted by theprestige View Post
It also saves the fuel you'd otherwise use to land it on the Martian surface and then lift it up again. And it saves the fuel you'd use to send to Mars the fuel you'd use to land it and lift it up again.
Land and lift what?
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Old 7th April 2019, 11:20 AM   #31
cjameshuff
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Originally Posted by theprestige View Post
Since the ultimate goal is to bring back samples from Mars, mission designs that result in a net reduction in launch mass from the Martian surface are interesting.

If the sample return container can meet the Earth Return Vehicle in Mars orbit, then that's more sample payload that can be lifted from the surface.

As you pointed out, though, the tradeoff is more complexity, cost, and risk; in exchange for more samples per mission. At the very least, it would mean less missions. There's probably a sweet spot somewhere in the middle, where number of missions and payload per mission maximize the total amount of samples returned.
Every Mars sample return mission concept I've seen (short of those that take advantage of a full blown transport spacecraft like Starship) has a descent stage, ascent stage, and a transport stage that would likely inject itself into orbit separately while the others go directly to the surface. The ascent stage would transfer the payload container and be left behind after the transport stage burned for Earth. Then the transport stage would separate and the reentry capsule would do its thing on arrival.

I've been assuming this is the starting point. Putting the reentry capsule into solar orbit so it can rendezvous with the transport stage on the way back to earth and perform another transfer of the samples would only save the mass needed for propulsion for putting the reentry capsule into Mars orbit, and from there back on the transfer trajectory back to Earth. It'd also greatly increase the risk that you end up with nothing.

The added cost and risk of additional long-duration spacecraft compared to launch costs is such that if you need more capacity, you're better off doing a few launches to assemble a larger but simpler vehicle in LEO. And doing it more than a couple times is probably going to cost more than just developing a far more capable launch and transport system (as long as you're not paying Boeing to do it, anyway). Really, pursuing this scheme is pretty much betting that SpaceX will fail with Starship, to the point that they cease to exist and nobody else tries something similar.
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Old 7th April 2019, 11:28 AM   #32
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Originally Posted by RecoveringYuppy View Post
Land and lift what?
The Earth Return Vehicle, comprising the motors and fuel to get into an Earth transfer orbit, the motors and fuel to get into an Earth reentry orbit, and the reentry vehicle itself. The less of that you send along on each step of the way, the less you have to bring back, at the expense of more samples.
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Old 7th April 2019, 11:32 AM   #33
RecoveringYuppy
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Originally Posted by theprestige View Post
The Earth Return Vehicle,

You were replying to a message that was about a cycler.
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Old 7th April 2019, 12:04 PM   #34
theprestige
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Originally Posted by RecoveringYuppy View Post
You were replying to a message that was about a cycler.
A message about a reentry vehicle, left in a cycler orbit, and whether that represents a weight savings compared to the "default" mission design.

My thinking is that it adds weight to the overall mission, but reduces weight from the Martian surface.

Since the ultimate value of the missions is the weight of samples returned, and since that's capped by the total amount of weight we can lift from Martian surface (the payload as such), adding weight to other parts of the mission means we can lift more payload, which is interesting.
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Old 7th April 2019, 12:33 PM   #35
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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.

Except for the use of robot, rather than manned, vehicles, this is the same profile put forward by Von Braun in "The Mars Project" back in the late '40s.
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Old 7th April 2019, 12:52 PM   #36
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What's the advantage of a cycler orbit if you aren't cycling?
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Old 7th April 2019, 01:49 PM   #37
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Originally Posted by RecoveringYuppy View Post
What's the advantage of a cycler orbit if you aren't cycling?
Well it cycles at least once, but yeah, a cycler is useful when you have a lot of mass that can be left in permanent transit. A reentry pod is not going to be more than a small fraction of the overall transport vehicle mass injected into Mars orbit. This is a really minor mass optimization, if you can turn it into an optimization at all.

There's only so much you can economically get from a given amount of launched mass, and doing more tends to have an extremely steep penalty in increased cost and risk. I think you're way into the territory where you're better off just sending two missions if you want more samples. Or having someone build a transport system that's actually capable of doing what you want.
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Old 7th April 2019, 04:09 PM   #38
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Originally Posted by cjameshuff View Post
Well it cycles at least once, but yeah, a cycler is useful when you have a lot of mass that can be left in permanent transit. A reentry pod is not going to be more than a small fraction of the overall transport vehicle mass injected into Mars orbit. This is a really minor mass optimization, if you can turn it into an optimization at all.

There's only so much you can economically get from a given amount of launched mass, and doing more tends to have an extremely steep penalty in increased cost and risk. I think you're way into the territory where you're better off just sending two missions if you want more samples. Or having someone build a transport system that's actually capable of doing what you want.

Yeah, I was thinking you don't have to slow down the earth reentry vehicle at mars or speed it up again for the way home. The complexity would outweigh the advantages.
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Old 7th April 2019, 04:47 PM   #39
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Originally Posted by 3point14 View Post
Yeah, I was thinking you don't have to slow down the earth reentry vehicle at mars or speed it up again for the way home.

How does it do anything useful then?
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Old 7th April 2019, 07:16 PM   #40
RecoveringYuppy
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Let's go back to the start of this tangent. I'll answer the first question better.

Originally Posted by 3point14 View Post
Could the reentry vehicle be left in an Mars Cycler orbit? Save the fuel for slowing it down and speeding it up again.
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?
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