Author Topic: Artificial Gravity - Why Weight?  (Read 25979 times)

Offline ndevereux

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Artificial Gravity - Why Weight?
« on: 04/30/2016 09:43 PM »
You may enjoy watching this short TEDx talk I gave on Feb 20th, 2016, about the importance of artificial gravity for manned missions to Mars, and beyond.


Offline Elmar Moelzer

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Re: Artificial Gravity - Why Weight?
« Reply #1 on: 05/01/2016 03:43 AM »
I think artificial gravity is cool, but for Mars it might not be necessary.
You would not need artificial gravity if the flight to mars was short enough. I would rather spend the weight (and monetary) budget on more fuel or a better engine that shortens the trip time. For missions beyond mars or for orbital stations, it is a different matter, though. Also, if I may suggest, you could rotate the habitats at the end of the trusses by 90 degrees (using the truss as a rotation axis) and give the inhabitants and longer straight floor. Unless you just rotate the entire spacecraft, you might want to consider counter rotating something (more habitats?) in the other direction?
« Last Edit: 05/01/2016 03:51 AM by Elmar Moelzer »

Offline Coastal Ron

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Re: Artificial Gravity - Why Weight?
« Reply #2 on: 05/01/2016 04:18 AM »
I think artificial gravity is cool, but for Mars it might not be necessary.
You would not need artificial gravity if the flight to mars was short enough. I would rather spend the weight (and monetary) budget on more fuel or a better engine that shortens the trip time.

The availability of fuel for refueling spaceships in space means that over time we can go faster and faster to our destinations, so while artificial gravity would be nice, passengers may be able to make a multi-month trip in 0G without too much physical degradation.  But we will need to ship enough people to Mars so that we can understand what the actual effects are.

Quote
For missions beyond mars or for orbital stations, it is a different matter, though. Also, if I may suggest, you could rotate the habitats at the end of the trusses by 90 degrees (using the truss as a rotation axis) and give the inhabitants and longer straight floor. Unless you just rotate the entire spacecraft, you might want to consider counter rotating something (more habitats?) in the other direction?

Artificial gravity through the use of rotating structures will require more much more mass than we'll be able to push between Mars and Earth in the early years.  That's because mass requires fuel, and fuel requires rockets from Earth (at least for the trip from Earth to Mars).  It's going to be a while until fuel is that cheap that we can build large spaceships with rotating gravity.

But when that time comes I have some ideas...   :D
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Ludus

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Re: Artificial Gravity - Why Weight?
« Reply #3 on: 05/01/2016 07:43 PM »
Zubrin's Mars Direct had this as an element even with a very minimalist approach. He just used a tether between the Hab and the spent upper stage.

I've always been puzzled why so little attention has been paid to this, despite the long history of the idea and the clear data about problems with long stays in microgravity.


Offline mvpel

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Re: Artificial Gravity - Why Weight?
« Reply #4 on: 05/01/2016 11:39 PM »
At a Mars Society convention I attended way back when at UC, there was a really cool presentation about fault-tolerant tether design too.
"Ugly programs are like ugly suspension bridges: they're much more liable to collapse than pretty ones, because the way humans (especially engineer-humans) perceive beauty is intimately related to our ability to process and understand complexity. A language that makes it hard to write elegant code makes it hard to write good code." - Eric S. Raymond

Offline JamesH65

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Re: Artificial Gravity - Why Weight?
« Reply #5 on: 05/09/2016 11:46 AM »
I think artificial gravity is cool, but for Mars it might not be necessary.
You would not need artificial gravity if the flight to mars was short enough. I would rather spend the weight (and monetary) budget on more fuel or a better engine that shortens the trip time. For missions beyond mars or for orbital stations, it is a different matter, though. Also, if I may suggest, you could rotate the habitats at the end of the trusses by 90 degrees (using the truss as a rotation axis) and give the inhabitants and longer straight floor. Unless you just rotate the entire spacecraft, you might want to consider counter rotating something (more habitats?) in the other direction?

Might be worth reading Chris Hadfield's book, to get some idea of the problems he suffered after being in Zero G for his ISS commander mission. I was surprised how badly he was affected. Admittedly, 6 months, so slightly longer than the proposed Mars trips (100 days?), but still very relevant.

Offline Elmar Moelzer

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Re: Artificial Gravity - Why Weight?
« Reply #6 on: 05/09/2016 09:57 PM »
I am of course talking about Mars missions with transit times much shorter than 100 days. There are several concepts, using advanced propulsion systems with trip times as short as 30 days.
 Once your trip times get significantly over 30 days, everything starts to get much more complicated and the lack of gravity is only one of those problems. This is why I am saying that it would be a good idea to further investigate those propulsion concepts and invest money and launch weight into those, rather than artificial gravity. This is just my personal opinion of course and I understand that some people might think differently.

Offline JamesH65

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Re: Artificial Gravity - Why Weight?
« Reply #7 on: 05/10/2016 06:15 AM »
I am of course talking about Mars missions with transit times much shorter than 100 days. There are several concepts, using advanced propulsion systems with trip times as short as 30 days.
 Once your trip times get significantly over 30 days, everything starts to get much more complicated and the lack of gravity is only one of those problems. This is why I am saying that it would be a good idea to further investigate those propulsion concepts and invest money and launch weight into those, rather than artificial gravity. This is just my personal opinion of course and I understand that some people might think differently.

Whilst those propulsion systems may be some years/decades away, artificial gravity would still be required for longer trips to the outer planets. So both will be needed I suspect.

Offline Jcc

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Re: Artificial Gravity - Why Weight?
« Reply #8 on: 05/15/2016 03:02 AM »
I think NASA should build a rodent habitat with some male and female mice for the ISS that rotates and can simulate Mars gravity. Maybe put it inside the BEAM if they are short on space. That would be to verify that mammals can reproduce successfully in Mars gravity. They may start with lower animals such as insects or worms first.

Offline Elmar Moelzer

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Re: Artificial Gravity - Why Weight?
« Reply #9 on: 05/15/2016 03:12 AM »
Whilst those propulsion systems may be some years/decades away, artificial gravity would still be required for longer trips to the outer planets. So both will be needed I suspect.
The video is about a trip to Mars. I think for that particular application, trips can be shortened enough to remove the need for artificial gravity. Now for longer trips, this is a different matter all together.

Offline guckyfan

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Re: Artificial Gravity - Why Weight?
« Reply #10 on: 05/15/2016 05:08 AM »
I think NASA should build a rodent habitat with some male and female mice for the ISS that rotates and can simulate Mars gravity. Maybe put it inside the BEAM if they are short on space. That would be to verify that mammals can reproduce successfully in Mars gravity. They may start with lower animals such as insects or worms first.

I think NASA does not want that as it might interfere with microgravity experiments. They would have to shift the entire focus of what is done on the ISS.

I have been thinking for a while they may do that on MCT. I imagine they will want to verify the ECLSS of MCT with a crew in orbit for at least 6-8 months. Time enough to do such an experiment. If they are generous they may do the experiment with moon gravity in parallel, the same centrifuge but nearer to the center. The experiment could run long enough that space born mice can reproduce.

Offline Jcc

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Re: Artificial Gravity - Why Weight?
« Reply #11 on: 05/15/2016 12:54 PM »
I think NASA should build a rodent habitat with some male and female mice for the ISS that rotates and can simulate Mars gravity. Maybe put it inside the BEAM if they are short on space. That would be to verify that mammals can reproduce successfully in Mars gravity. They may start with lower animals such as insects or worms first.

I think NASA does not want that as it might interfere with microgravity experiments. They would have to shift the entire focus of what is done on the ISS.

I have been thinking for a while they may do that on MCT. I imagine they will want to verify the ECLSS of MCT with a crew in orbit for at least 6-8 months. Time enough to do such an experiment. If they are generous they may do the experiment with moon gravity in parallel, the same centrifuge but nearer to the center. The experiment could run long enough that space born mice can reproduce.

SpaceX could do it on an automated DragonLab if NASA or other ISS partners are not interested. NASA does want to go to Mars, so it is relevant, and it could be very interesting basic science. They can call it SpaceSex, that should grab people's attention.
« Last Edit: 05/15/2016 01:28 PM by Jcc »

Offline muomega0

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Re: Artificial Gravity - Why Weight?
« Reply #12 on: 05/15/2016 01:24 PM »
I think artificial gravity is cool, but for Mars it might not be necessary.
You would not need artificial gravity if the flight to mars was short enough. I would rather spend the weight (and monetary) budget on more fuel or a better engine that shortens the trip time.

The availability of fuel for refueling spaceships in space means that over time we can go faster and faster to our destinations, so while artificial gravity would be nice, passengers may be able to make a multi-month trip in 0G without too much physical degradation.  But we will need to ship enough people to Mars so that we can understand what the actual effects are.

Quote
For missions beyond mars or for orbital stations, it is a different matter, though. Also, if I may suggest, you could rotate the habitats at the end of the trusses by 90 degrees (using the truss as a rotation axis) and give the inhabitants and longer straight floor. Unless you just rotate the entire spacecraft, you might want to consider counter rotating something (more habitats?) in the other direction?

Artificial gravity through the use of rotating structures will require more much more mass than we'll be able to push between Mars and Earth in the early years.  That's because mass requires fuel, and fuel requires rockets from Earth (at least for the trip from Earth to Mars).  It's going to be a while until fuel is that cheap that we can build large spaceships with rotating gravity.

But when that time comes I have some ideas...   :D
While Economic Access to Space is one grand challenge, another is Space Health and Medicine--"Eliminate or mitigate the negative effects of the space environments on human physical and behavioral health"

Studying the solutions in space, say at L2 or LEO, will be way cheaper than sending crew to Mars or the moon and provides parametric data as well.  Avoiding gravity wells saves tremendous cost and asteroid destinations have very low gravity.  Slower trip times result in a substantially cheaper architecture.

Of course, if all of NASA's budget is simply meant to spent on propulsion and capsules, and ignoring the Grand Challenges of the past decades, then by all means continue to spend the next decade spending all the cash on multiple engine, capsule, and LV development efforts.

Online dror

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Re: Artificial Gravity - Why Weight?
« Reply #13 on: 05/15/2016 01:29 PM »
Whilst those propulsion systems may be some years/decades away, artificial gravity would still be required for longer trips to the outer planets. So both will be needed I suspect.
The video is about a trip to Mars. I think for that particular application, trips can be shortened enough to remove the need for artificial gravity. Now for longer trips, this is a different matter all together.

Alternatively, an Earth-Mars cycler with artificial gravity.
Dragons (Orion, Starliners, BFS etc) function as taxi and lifeboats.
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Offline The Amazing Catstronaut

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Re: Artificial Gravity - Why Weight?
« Reply #14 on: 05/15/2016 01:31 PM »

Of course, if all of NASA's budget is simply meant to spent on propulsion and capsules, and ignoring the Grand Challenges of the past decades, then by all means continue to spend the next decade spending all the cash on multiple engine, capsule, and LV development efforts.

Better to have the means to get there and current gen life support, than no means to get there and a significantly better life support.

We have the resources to keep people alive on mars now. The focus (and it's a vital one) is mitigating health risks and making everything cheaper, more sustainable and easier to expand using primarily martian resources - but one fiscal challenge at a time. You don't start fireproofing a building if the basic structure is impossible.

Probably more important than artificial gravity on mars is getting general healthcare fixed. How do I grow basic tissues on a martian environment? If someone gets cancer can we treat that without having to send them back to Earth? Somebody has inhaled martian dust? How do we look after their lungs?
« Last Edit: 05/15/2016 01:34 PM by The Amazing Catstronaut »
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Offline guckyfan

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Re: Artificial Gravity - Why Weight?
« Reply #15 on: 05/15/2016 01:33 PM »
SpaceX could do it on an automated DragonLab if NASA or other ISS partners are not interested. NASA does want to go to Mars, so it is relevant, and it could be very interesting basic science. They can call it SpaceSex, that should grab people's attention.

Probably they could. However it is not that easy to maintain a habitat for mice over many months, keep it clean and feed them without humans. It is also extra expense and funds are limited. Doing it on a MCT test flight brings almost no extra cost assuming they see the need to do a long test flight.

Offline muomega0

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Re: Artificial Gravity - Why Weight?
« Reply #16 on: 05/15/2016 02:03 PM »

Of course, if all of NASA's budget is simply meant to spent on propulsion and capsules, and ignoring the Grand Challenges of the past decades, then by all means continue to spend the next decade spending all the cash on multiple engine, capsule, and LV development efforts.

Better to have the means to get there and current gen life support, than no means to get there and a significantly better life support.

We have the resources to keep people alive on mars now. The focus (and it's a vital one) is mitigating health risks and making everything cheaper, more sustainable and easier to expand using primarily martian resources - but one fiscal challenge at a time. You don't start fireproofing a building if the basic structure is impossible.

Probably more important than artificial gravity on mars is getting general healthcare fixed. How do I grow basic tissues on a martian environment? If someone gets cancer can we treat that without having to send them back to Earth? Somebody has inhaled martian dust? How do we look after their lungs?
Gas stations in space with prepositioned supplies and propellant are the fastest way to send crew to Mars, but it appears to be limited to about 3 months one way with existing technology.  EP tugs combined with chemical tugs cycling from near Mars to L2, and likely multiple tugs to reduce LOM/LOC.  A hybrid EP/chemical crew transfer needs more work.   Its N months travel, M months in 1/3rd g, and N back, where M costs a significant amount of dV and IMLEO.

Contrast that cost with a couple of launches of VG hardware and repeated trips to L2--much more data to actually address the challenge, rather than to side step the issue.   Even on a fly by mission to Mars, the crew to pause and 'go out for a spin' so to speak--long term, efficient gathering of data.  They could also spin at 1/3g in preparations for the Mars trip.   The crew would service satellites and gas station at L2 , or perhaps space junk sweepers in preparations for ISRU near zero g sources.  Think multiple purpose missions and 'flight rate'.

Offline Lee Jay

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Re: Artificial Gravity - Why Weight?
« Reply #17 on: 05/15/2016 02:10 PM »
I agree with the OP.

I think sending humans to Mars is a very, very dangerous thing to do.  Having astronauts die on such a mission would result in substantial pain, expense and delay as has been shown in the past.  With a growing culture of risk aversion, it would likely be worse now.

Ways to buy down risk are:

- Artificial gravity
- Radiation shielding
- Larger vehicle
- More people going for more capabilities and more redundancy

I'd like to see an artificial gravity station launched for research.  This could be a simple hab with weight attached by a tether to see what radii and what rotation rates give acceptable and unacceptable human results.  The idea would be to change the tether length and keep gravity the same for Earth, Mars and Moon gravity and see who gets sick and who stays well for each combination.  In this way we could better understand what it would take to build a Mars transport that has the necessary proportions to keep everyone well on a long-duration trip to Mars.

When people say things like, "we can get their really fast", I like to point out that a third of the people who went to the moon on moon landing missions stayed in orbit.  The same makes sense for a Mars mission and those people would potentially be subject to two and a half years in microgravity even with a really fast transport system.  I don't believe this is acceptable.  I also think it would be a lot better if people had time on a mission to the surface of Mars to adapt to Mars gravity on the way.  One could imagine leaving Earth at Earth gravity and transitioning to Mars gravity as the vehicle approached Mars.

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Re: Artificial Gravity - Why Weight?
« Reply #18 on: 05/15/2016 03:32 PM »
I like to point out that a third of the people who went to the moon on moon landing missions stayed in orbit.  The same makes sense for a Mars mission

With modern automated docking maneuvers, is it really necessary to keep somebody on orbit?  I was under the impression that NASA had been planning on this when they were considering new manned lunar missions as part of Constellation before it was cancelled. If separate command and decent modules are used, why not have the orbiting command module run by computer?

Offline Lee Jay

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Re: Artificial Gravity - Why Weight?
« Reply #19 on: 05/15/2016 05:04 PM »
I like to point out that a third of the people who went to the moon on moon landing missions stayed in orbit.  The same makes sense for a Mars mission

With modern automated docking maneuvers, is it really necessary to keep somebody on orbit?  I was under the impression that NASA had been planning on this when they were considering new manned lunar missions as part of Constellation before it was cancelled. If separate command and decent modules are used, why not have the orbiting command module run by computer?

For extra safety, you'd like to have a person or persons on board who could fix things or manually operate things that get persnickety, such as is done during visiting vehicle dockings on ISS.

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