De-orbiting from LEO revisited - How to avoid highspeed re-entry

dicktice · 2003-04-17 09:43:35

Thanks, MarsGuy. I'll have a go....

MarsGuy2012 · 2003-04-17 09:45:20

The nonessential she mentioned would be the burnt out upper stage that put you on course to Mars. I think the centrifuge would for one thing be too heavy and take up too much space for Mars Direct. I'd just get a really reliable tether. In case the tether breaks take along some exercise equipment. The current equipment has already been proven to work in zero gravity for extended periods.

dicktice · 2003-04-17 10:44:44

MarsGuy: Since a "burnt out upper stage" counter-mass would have to be accelerated using up rocket fuel, it would be very tempting to load it with spare "essentials" on such long trips. Tether technology holds great promise, what with the new carbon materials being proposed--woven, braided, twisted, redundance.... All I want to know at this early stage is the medical answer to the question: would a sleep-centrifuge work in principle--aren't you (or anyone) even curious?

MarsGuy2012 · 2003-04-17 11:00:35

I would say that it would definitely work better than zero-g. I bet that the larger the radius the better it would work. One of the problems with zero-g is that your body fluids rise to your head. Your body thinks you have a cold or you just have too much fluid, so it starts excreting necessary minerals like calcium. Space doctors have found that calcium supplements don't help because your body thinks it doesn't need the calcium and just gets rid of it.
In the centrifuge, if your head is close to the center (zero-g) then there will still be some of those nasty fluid problems. Correct me if I'm wrong about any of that, I'm no doctor you know.

dicktice · 2003-04-17 11:11:58

Thanks, I wonder ifyou are interested, you might wish to determine if any experiments have been proposed, or carried out, perhaps in miniature, e.g. using plants, or preferably monkeys, along these lines..? I'll try to be on the look-out myself.

soph · 2003-04-17 11:46:33

Ah, but there are drugs being developed that will target activator proteins, that can manufacture, among other things, calcium. These could be very useful.

Shaun Barrett · 2003-04-17 19:44:35

Hi Dicktice!
I can't imagine anyone getting comfortable in the device you mention. When we need to sleep, we do our best to find somewhere flat to lie down. One of the reasons is that during sleep our metabolic rate drops - our pulse slows and blood pressure decreases etc. It's much easier for the body to rest completely if it doesn't have to pump blood against the pull of gravity, so we lie down .. which is the closest we can get on Earth to neutralising gravity's pull on our cardiovascular system.
What you suggest would be almost like sleeping standing up. Blood would try to pool in the lower limbs and the heart would have to work against that. I know that 'working' the heart is a desirable thing in a zero-g environment but trying to sleep through it might prove difficult.

My opinion is essentially biased though, because I'm a 'tether and rotation' man, myself! Your point about the temptation to store stuff in the burnt-out upper stage shouldn't be a problem. All that's in the upper stage, apart from the engine, is fuel - storing stuff in it would be impossible until the fuel is used up and , by then, you're on your way to Mars.

To my way of thinking, unless newly developed nuclear propulsion can reduce the total Mars mission time to something like 400 days, instead of Mars Direct's 860+, we'll be needing good 'centrifugal gravity'.
I've always maintained that humans won't be able to cope with 180 days in zero-g outbound, 500 days in 0.38g at Mars, and another 180 days in zero-g coming home. Nearly 2.5 years away from Earth's gravity would probably make rehabilitation at the end of the trip impossible. Spinning the Hab once a minute, attached via a 1.8 kilometre cable to the burnt-out upper stage mentioned, would give a full 1g of artificial gravity and keep our astronauts strong and healthy.

soph · 2003-04-17 19:46:55

Whoa, whoa, whoa! 180 days? NERVA can cut that in half

The next step in NTR, liquid core, would cut it to 45-60 days. And then gas core NTRs would cut it to 20-30 days.

dicktice · 2003-04-18 09:32:18

Ignoring Soph's nuclear contribution for the moment--since my objective is: surviving imposed weightlessness for an indefinite time, deprived of rotation, due to some unavoidable emergency, say, like in a "space lifeboat." The centrifuge need not be occupied while sleeping. My thought: since sleep I've read is when the body "renews" itself, that should be when the artificial gees would be most efficacious. Myself, I've fallen asleep standing up at work in the lab at 3 a.m.--so, no problemo! I take Melatonin now before bedtime, and within an hour I can't keep my eyes open. But the question of comfort on a sleep centrifuge would be a factor--maybe Swedish "space-mattress" material is called for....
And then ,there's the vibration-method of preventing calcium bone deficiency--announced some months ago. I'll google the internet to bring that to your attention, as well. (No, no ... don't thank me. It's nothing....)

MarsGuy2012 · 2003-04-18 10:10:49

Here's a thought:

If you want to design an emergency gravity device if the tether fails why don't you just use the ship itself instead of a rotating platform within the ship.

The Mars Direct Hab will be 8 meters in diameter and will have a circular shape. That sounds good enough to just spin up to your desired g. You just have to get used to walking on the walls. Ever want to be like Spiderman? Here's your chance!

Here's the equation for centrifugal force:

F = (0.0011)W^2 * R

F is the centrifugal force measured in Earth gravities,
W is the spin rate in revolutions per minute (rpm),
^2 means squared,
R is the length of the spin arm in meters (radius).

If you want a spin rate of 1g then get ready to puke. You will have to spin at 15 rpm. Studies have shown that humans can function at a spin rate of up to 6 rpm.

So, in an 8 meter diameter hab with 6 rpm as the limit we can produce Lunar gravity in an emergency (0.16g). Not much, but better than zero-g.

dicktice · 2003-04-18 12:02:09

MarsGuy: You've motivated me not to spin-up the ship for another reason ... besides not being able to make observations or perform EVAs. By the way, we're dealing here with centripetal force, right? Anyway, please don't delete your reply for a day or so, until I get access to a printer. Great stuff.

Shaun Barrett · 2003-04-18 20:07:45

Hi again, Dicktice!
For some more discussion of the gravity problem, go to Acheron Labs; Life support systems; 'Catching Some Zs'.
I remember we had other discussions about artificial gravity in other threads here at New Mars last year, too. But I can't locate where just now.

dicktice · 2003-04-19 12:01:28

Okay, Shaun. I just boned up on "Catching some Z's" and it was very interesting. Hard to come to a conclusion, though, wasn't/isn't it? The only phenomenon not discussed was the accelerating rate-of-rotation as you reel-in the two cable separated parts, in order to use the spent booster as a shield from Solar flare events. Just another complication added to the host of other difficulties separated-by-cable gravity simulation introduces, dammit....

MarsGuy2012 · 2003-04-19 12:21:47

dicktice,

To make observations and to perform EVAs on a rotating ship you could do a couple of things:

1. Stop the ship. I know this will need extra fuel, especially if you needed to start it up again.

2. Use a small counter-rotating platform with whatever observation/communication instruments you want on it. And, put an emergency hatch on the top of the Hab at the center. You could go out this hatch and not be flung off into space - You would only be spinning (at 6 rpm). After stopping your spin you could easily fly around and survey the ship to look for damage or whatever. Just don't bump into it or it will push you away. This hatch would be useful on Mars too if the main airlock/hatch was damaged on landing.

Why would you need to perform an EVA anyway. Currently our astronauts stay inside the ISS or Shuttle unless their doing construction or fixing things like Hubble. Even the crew of the Apollo 13 didn't need an EVA. (I know it was a shorter mission, but the point is - they fixed things from the inside.)

As far as I understand centripetal and centrifugal force are just opposites. In a spinning hab the centripetal force is what pushes things away from the center (artificial gravity). The centrifugal force is the force pushing things to the center (leg muscles, the heart). So you can use whatever word you want. When one exists you automatically get the other.

P.S. Why would I delete my reply? My replies are always right. :;):

dicktice · 2003-04-19 14:25:07

MarsGuy: No EVA capability for all those months....! You'd be at each others' throats. EVA, for making antenna repairs (as in: 2001), tether-travelling to the other half of the rotating ship (why not convertable, so both are inhabitable?--I read that once), assembly/replacement/disassembly (e.g. Solar arrays), cleaning windows, for gosh sakes ... I seem to have sidestepped the spinning single ship, haven't I? Well, so be it. Also, I think you'll find that "centrifugal" refers to reaction against the inward-vectoring centripetal force accelerating a body on a string--or while constantly falling in orbit. The deck of the habitat presses your feet up, in other words, not the reverse. (I just wanted you to save the gravity equations for me to copy and print. Still haven't.)

soph · 2003-04-19 15:14:03

:angry:

3 months! Wow! It's not like you wouldn't have anything to do. You could have game rooms stocked with supplies, excercise rooms, etc.

Even if it weren't spinning, EVA's would waste space, time, and expose the crew to radiation they don't need. There's no reason to include EVA's in the mission plan, they'll have plenty of time for Mars walks later.

MarsGuy2012 · 2003-04-19 19:06:30

dicktice,

If I were an astronaut I wouldn't set foot on the darn thing if they told me, "The solar panels are probably gunna break a couple of times in transit and the backups are stored in the cargo bay, unassembled. Plan on the communications dish failing. You'll have to weld that one back together. Oh...and don't forget to go out and clean the windows every week. Now remember, 'Lil Captain Johnny has to go out every other day or he'll start biting and scratching. Oh, one more thing...we haven't tested the heat shield yet but we're 50...I mean...30 percent sure it will work. Good luck!"

Why would you send a billion dollar ship to Mars if it had such unreliable equipment that couldn't even last a few months in space? Why would you send a bunch of lunatics that coudn't get along in a confined space?

But seriously, one of the main reasons for spinning up the whole habitat is that you would be in the artificial gravity 100% of the time. That sounds better than a daily treatment in the centrifuge.

Maybe if you were spending years on the Moon a centrifuge would be a good idea. You can't just spin up the Moon.

sethmckiness · 2003-04-20 02:26:28

There is one problem that has always bugged me about rotating a ship itself. it would work perfectly if it is counterbalanced perfectly, but otherwise I would think that it would be subject to a not so perfect spin.. I may be wrong though..

Algol · 2003-04-26 04:13:52

You are correct, a spinning ship would have significant 'wobble' issues, simply because of its small size (radius) and large rpm. The tether greatly reduces this affect by creating a (technically) large radius and a slower rpm.

Limited EVA would be possible on a tethered ship, but only by exiting the ship from 'top' ie the tethered end. This would probably be in order to access the other end of the tether via a small single person crawler which pulled you up the line (then down the other side) EVA would be possible (yet dangerous - but what isnt in a mars mission) down the sides the hab in an emergency (abseiling?) and would be greatly facilitated if the required induced g were lower than 1.

Mars - i very much doubt they would launch the ship if they werent sure the solar panels/dish would work just fine for the journey, the crew would also be able to handle the conditions without an EVA to 'get some air' , otherwise they simply wouldnt be sent. Oops just re-read your post, think you were joking ???

I also imagine that equipment such as comms dish and possibly solar panels would be located at the centre of the tether in order to minimise problems with keeping them pointed at earth/sun. Also making them acessible on an EVA.

Heres a handy link someone here gave me for working out g equations

http://www.labcentrifuge.com/gforce5.html

nick

dicktice · 2003-04-26 09:44:50

MarsGuy: Regarding unreliability insofar as equipment and crew members, no matter how well thought-out preparatory to this first Mars Expedition ... don't forget the one, uninvited member of the crew... You know, he goes by the name of Murphy?

MarsGuy2012 · 2003-04-26 20:12:38

Algol,

An omnidirectional antenna would work just fine for voice and telemetry. So, if the dish couldn't track the Earth correctly you wouldn't have to worry. I wouldn't put anything important on the tether or on the counterweight (especially not people) just in case the cable breaks. In 'The Case for Mars' Zubrin explains that everything can and should be concentrated on the Hab.

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#32 2003-04-17 19:44:35

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#33 2003-04-17 19:46:55

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#34 2003-04-18 09:32:18

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#35 2003-04-18 10:10:49

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#36 2003-04-18 12:02:09

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#37 2003-04-18 20:07:45

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#40 2003-04-19 14:25:07

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#42 2003-04-19 19:06:30

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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