Before the Crash We had Tempo 3 topic

SpaceNut · 2014-01-04 21:26:51

Mars society was working on a nano sat version of a tether artifical gravity experiment from what I recall.

'TEMPO 3' Artificial Gravity Satellite On Mars Society's To-Do List

The experiment did take place.

French Mars Society Conducts Successful Artificial Gravity Demonstration

Maybe the old thread can be found and repaired.

GW Johnson · 2014-01-05 09:56:01

You can avoid all those difficult start-up dynamics difficulties if you go with a rigid (or at least semi-rigid) baton instead of a "loosey-goosey" cable-type connection. Shapes like that are really easy to build up from docked modules that current rockets can launch.

GW

RobertDyck · 2014-01-05 12:52:01

GW Johnson, you've posted about this many times. How much would that baton mass?

There was one proposal out of NASA to put a fuel tank inside a truss, open on one side so the spent tank could be removed. I'm concerned about the mass, and a short rotation arm has problems. High rotation rate produces dizziness, and difference of force between head and toe. With a total radius from centre of rotation to floor of 10 metres, that means a 2 metre tall man will experience 80% as much gravity at his head vs toes. According to "The Case for Mars" page 123, the maximum rotation rate that humans can withstand is 6 rpm. If you want to achieve Mars level gravity, not Earth level, then rotation rate of 6 rpm requires 10 metres. That's radius, not diameter; you can deduct height of the habitat from roof to floor, but then have to add a length of the arm or truss to the counterweight. And at 6 rpm, rotation is quite noticeable. To make to more tolerable, you want 2 rpm. For Mars level gravity, radius is 86 metres. Again radius, double for total length if the counterweight is the same mass as the hab, increase length further if counterweight is less. If you want Earth level gravity, increase that again. With a baton that long, there will be twisting and bending forces as the craft makes manoeuvres while rotating. There are in-flight manoeuvres required to counter solar wind. Solar wind isn't much, but over a flight of hundreds of millions of kilometres to get to Mars it does affect trajectory. How strong will the baton have to be to withstand that?

So what is the mass of your baton?

GW Johnson · 2014-01-05 15:27:15

The manned vehicle in my chemical powered design was around 600 tons outbound, and a bit over 300 tons inbound to a recovery in LEO, not a free return. It was well under 200 m long, and spun at less than 4 rpm for 1 gee in the lowest deck, about 0.5 gee in the very upper (storage) deck.

Crew of 6, 3 reusable landers, 6 landings plus a Phobos visit, were the features in what amounts to a "cadillac" mission without actually going overboard into the "battlestar galactica" problem. That stuff is posted as "Mars Mission 2013" over at http://exrocketman.blogspot.com.

Sure, there are some not-absolutely-rigid dynamics issues to be resolved with a baton, but nothing anywhere as severe as a completely-nonrigid cable-connected design approach. Simple thrusters can spin it up and down. You put the hab spaces at one end, the engine cluster at the other, and a combined parallel-series stack of docked propellant modules in between.

Every module is small enough to launch with commercial rockets we have, except the landers, which have to be built-up in LEO from smaller components. They're just too fat to ride a Falcon-Heavy, although light enough.

GW

Quaoar · 2014-01-05 16:16:38

GW Johnson wrote:

The manned vehicle in my chemical powered design was around 600 tons outbound, and a bit over 300 tons inbound to a recovery in LEO, not a free return. It was well under 200 m long, and spun at less than 4 rpm for 1 gee in the lowest deck, about 0.5 gee in the very upper (storage) deck.
Crew of 6, 3 reusable landers, 6 landings plus a Phobos visit, were the features in what amounts to a "cadillac" mission without actually going overboard into the "battlestar galactica" problem. That stuff is posted as "Mars Mission 2013" over at http://exrocketman.blogspot.com.
Sure, there are some not-absolutely-rigid dynamics issues to be resolved with a baton, but nothing anywhere as severe as a completely-nonrigid cable-connected design approach. Simple thrusters can spin it up and down. You put the hab spaces at one end, the engine cluster at the other, and a combined parallel-series stack of docked propellant modules in between.
Every module is small enough to launch with commercial rockets we have, except the landers, which have to be built-up in LEO from smaller components. They're just too fat to ride a Falcon-Heavy, although light enough.
GW

Your propellant modules, if I have understud, are not projected to reentry when the ship returns to Earth. So to be reused, every module may have some sort of docking plug to be refueled by some sort of shuttle tanker. It is correct?

Last edited by Quaoar (2014-01-05 16:19:34)

GW Johnson · 2014-01-05 19:50:31

Assuming nothing goes wrong, the only piece that reenters is the small return capsule. Having one with you enables an emergency free return if the engines both fail before arrival home. But there are two engines.

The propellant modules that come home arrive in LEO essentially empty. To be reused, they would need to be refueled on-orbit from some sort of tanker. The habitat would need to be restocked with supplies from some sort of freighter. Depending upon the nature of the engine design, they might not need refurbishment before re-use. At least, that's the kind of design I would recommend.

Point is, any ship capable of taking men to and from Mars orbit, can take men to near-Earth asteroids (asteroid defense missions), or to orbits about Venus and Mercury. Or it can return to Mars orbit. Why not build it just once to accomplish all those things as the time becomes right for each of them? A different lander would be needed at Mercury, but Venus and the asteroids need no landers at all. You will need more propellant modules, but so what?

GW

SpaceNut · 2014-01-05 20:36:09

Then center of the baton will see at minimal 2g plus forces and if when you start it flipping or stopping it can see even higher transition wave as the balance of thrust might not be perfect and may twist.

Quaoar · 2014-01-06 06:54:25

GW Johnson wrote:

Every module is small enough to launch with commercial rockets we have, except the landers, which have to be built-up in LEO from smaller components. They're just too fat to ride a Falcon-Heavy, although light enough.
GW

On SpaceX's site is written they can also perform launch with custom payload fairings. It's just more expensive, but I think they can find a solution to launch your lander.

An alternative may be to adapt your design to Falcon H: a 5 meters diameter wathever you want long slender body biconic lander, with the rockets nozzle opened in the thermal protected belly and perpendicular to the long axis. This lander may have a docking port in the middle of her back to connect the propellant modules chain, forming a reverse "T".

GW Johnson wrote:

Assuming nothing goes wrong, the only piece that reenters is the small return capsule. Having one with you enables an emergency free return if the engines both fail before arrival home. But there are two engines.
The propellant modules that come home arrive in LEO essentially empty. To be reused, they would need to be refueled on-orbit from some sort of tanker.

An alternative may be some sort of thermal protected belly modules, that reenter slender body, parachute land, be resupplied and send again to LEO. There is a mass penality for thermal protection, but some propellant may be saved performing an aerocapture and/or an aerobraking at the Earth arrival.

GW Johnson wrote:

The habitat would need to be restocked with supplies from some sort of freighter.

In the first times technicians may live in the space-train habitat while working on maintenance. Following, we can imagine a little base in equatorial orbit, with a BA330 or similar habitat for the technicians, some tanks for propellant resupply, a docking hub and a little pressurized hangar for manutencion of modules one-by-one.

GW Johnson wrote:

Depending upon the nature of the engine design, they might not need refurbishment before re-use. At least, that's the kind of design I would recommend.

Something like a very simple pressure feed engine?

GW Johnson wrote:

Point is, any ship capable of taking men to and from Mars orbit, can take men to near-Earth asteroids (asteroid defense missions), or to orbits about Venus and Mercury.

Is your tank module cooling system able to keep liquid hydrogen even in Mercury orbit?

GW Johnson wrote:

Or it can return to Mars orbit. Why not build it just once to accomplish all those things as the time becomes right for each of them? A different lander would be needed at Mercury,

For Mercury we need a lander able to came back to orbit after performing an all propulsive descend. Will it be a two stage lander or is it possible to do it in one stage?

GW Johnson wrote:

but Venus and the asteroids need no landers at all. You will need more propellant modules, but so what?
GW

For Venus we need some sort of unmanned lander with a rover piloted by orbiting astronauts. Is it possible to send your Space-train in Jovian Satellites?

Last edited by Quaoar (2014-01-06 07:35:48)

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#1 2014-01-04 21:26:51

Before the Crash We had Tempo 3 topic

#2 2014-01-05 09:56:01

Re: Before the Crash We had Tempo 3 topic

#3 2014-01-05 12:52:01

Re: Before the Crash We had Tempo 3 topic

#4 2014-01-05 15:27:15

Re: Before the Crash We had Tempo 3 topic

#5 2014-01-05 16:16:38

Re: Before the Crash We had Tempo 3 topic

#6 2014-01-05 19:50:31

Re: Before the Crash We had Tempo 3 topic

#7 2014-01-05 20:36:09

Re: Before the Crash We had Tempo 3 topic

#8 2014-01-06 06:54:25

Re: Before the Crash We had Tempo 3 topic

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