Honeymoon on Mars

Andreas_Firewolf · 2018-08-15 07:40:55

There are a lot of ideas about going to Mars. But most plans have the same weakness.
The trip to Mars takes many months in space.
You can not put a few humans in a metal can and keep them there for half a year or longer.
Perhaps the biggest problem is the absence of gravity: It is detrimental for your health.
But when we reduce the trip to Mars to three days, we can go to Mars, spend a vacation in 'Las Vegas on Mars'
and be back within three weeks. It would be 'the time of your life'.

So the question should not be: How can we go to Mars?
The real question is: How can we reduce the trip to Mars to three days.
And that is quite easy. At least in theory.

First some basic facts. Gravity on earth is about 9.81 m/s2.
If we create a spaceship and we accelerate it with 9.81 m/s2 we have the same pressure on our body as when we are on earth.
What happens when we accelerate a spaceship with say 9 m/s2 for twenty-four hours?
We would reach a speed of 24 * 3600 * 9 meters per second or 2.8 million km/hour.
In that 24 hours we would travel 33.6 million km or 20.1 million miles.
When we decelerate with 9 m/s2 for 24 hours, we travel again 33.6 million km.
So in 48 hours we can travel 67.2 million km. and experience almost the same amount of pressure as Earth's gravity.

The distance between Mars and Earth varies.
When they are very close to each other, the distance is about 60 million km.
With such a 'small' distance we can travel to Mars in only two days.

The average distance is about 401 million km.
When we accelerate with 9 m/s2 for 24 hours
and we keep that speed for 120 hours or five days
and we decelerate with 9 m/s2 for 24 hours
we would travel 403.2 million km.

So in theory it is possible to travel to Mars with acceptable comfort in two to seven days,
depending on the position of Mars and Earth.
How can we do that in practice?

That should be quite easy.
Space is not completely empty, but the resistance of space is not very high compared to the resistance of air on Earth.
We have engines that can give a thrust for 24 hours, that is enough to accelerate with 9 m/s2.
We only have to design engines that can do that in space.
And we have to get fuel in space.
That is also quite easy. In theory.
This is what we should do.

1. We should build two identical space-stations.
When the first is finished, we send it to Mars and bring it in orbit.
The second will be in orbit around Earth.

2. We should build vehicles that can move between Earth and the space-station around Earth.
A vehicle to move people and another vehicle for cargo.

3. We should build vehicles that can move between Mars and the space-station around Mars.
A vehicle to move people and another vehicle for cargo.

4. We should build spaceships that can move between the two space-stations.
They don't have to land on Earth or Mars. They should be build in space and stay in space.
One type of spaceship will be used to move people and should be designed to travel very fast.
Another type of spaceship will be used to move cargo. This should be designed to travel at low cost.
The spaceship for people should have a massive deflector shield.
When you hit a piece of rock with a speed of 3 million km/hour without a deflector shield, your ship will be destroyed in an instant.
The engine of the spaceship for people can run on hydrogen and oxygen.
It must have large tanks with more than enough fuel when something goes wrong.
If you run out of fuel with a speed of 3 million km/hour, you will miss Mars and be out of the solar system within three months.

5. We should create large arrays of solar panels around Earth and around Mars.
The electricity of these panels will be used to split water into hydrogen and oxygen.
This will be the main source of energy for the spaceship for people.

6. We have to get water to the space-stations.
Perhaps this is the most difficult and costly operation.
At first, we can use water from Earth. But we can not continue to do so indefinitely.
Besides, moving water from Earth to the space-station is costly.
So we should explore the asteroid belt and search for asteroids of ice.
If we have solar panels and we can find water in the asteroid belt, we have everything we need to go to Mars.

Note:
I double checked my calculations. But it would not harm to check them again.
If you find errors, please let me know.

Confirming or rebutting Einstein:
Einstein stated, that nothing can go faster than the speed of light.
I do not believe this. See Rebuttal of Einstein.

(I am not allowed to post links. So you have to paste it yourself.
andreasfirewolf.com/index.php?pi=1556&n1=119
).

If we create a probe and we accelerate it with 10 m/s2 for a year, we go faster than the speed of light.
Or not. It would be interesting to see what happens.

If we ever want to travel to other star-systems, we will have to travel much faster than the speed of light.

louis · 2018-08-15 08:15:42

Interesting...

How much fuel/propellant do you need to get a spaceship serving say ten people up to those sorts of speeds? How many tonnes?

A possible solution to the water issue would be to adapt the idea of a space elevator and have a narrow pipe attached to a water source on Earth. Getting the power to pump up the water shouldn't be a problem.

Andreas_Firewolf wrote:

There are a lot of ideas about going to Mars. But most plans have the same weakness.
The trip to Mars takes many months in space.
You can not put a few humans in a metal can and keep them there for half a year or longer.
Perhaps the biggest problem is the absence of gravity: It is detrimental for your health.
But when we reduce the trip to Mars to three days, we can go to Mars, spend a vacation in 'Las Vegas on Mars'
and be back within three weeks. It would be 'the time of your life'.
So the question should not be: How can we go to Mars?
The real question is: How can we reduce the trip to Mars to three days.
And that is quite easy. At least in theory.
First some basic facts. Gravity on earth is about 9.81 m/s2.
If we create a spaceship and we accelerate it with 9.81 m/s2 we have the same pressure on our body as when we are on earth.
What happens when we accelerate a spaceship with say 9 m/s2 for twenty-four hours?
We would reach a speed of 24 * 3600 * 9 meters per second or 2.8 million km/hour.
In that 24 hours we would travel 33.6 million km or 20.1 million miles.
When we decelerate with 9 m/s2 for 24 hours, we travel again 33.6 million km.
So in 48 hours we can travel 67.2 million km. and experience almost the same amount of pressure as Earth's gravity.
The distance between Mars and Earth varies.
When they are very close to each other, the distance is about 60 million km.
With such a 'small' distance we can travel to Mars in only two days.
The average distance is about 401 million km.
When we accelerate with 9 m/s2 for 24 hours
and we keep that speed for 120 hours or five days
and we decelerate with 9 m/s2 for 24 hours
we would travel 403.2 million km.
So in theory it is possible to travel to Mars with acceptable comfort in two to seven days,
depending on the position of Mars and Earth.
How can we do that in practice?
That should be quite easy.
Space is not completely empty, but the resistance of space is not very high compared to the resistance of air on Earth.
We have engines that can give a thrust for 24 hours, that is enough to accelerate with 9 m/s2.
We only have to design engines that can do that in space.
And we have to get fuel in space.
That is also quite easy. In theory.
This is what we should do.
1. We should build two identical space-stations.
When the first is finished, we send it to Mars and bring it in orbit.
The second will be in orbit around Earth.
2. We should build vehicles that can move between Earth and the space-station around Earth.
A vehicle to move people and another vehicle for cargo.
3. We should build vehicles that can move between Mars and the space-station around Mars.
A vehicle to move people and another vehicle for cargo.
4. We should build spaceships that can move between the two space-stations.
They don't have to land on Earth or Mars. They should be build in space and stay in space.
One type of spaceship will be used to move people and should be designed to travel very fast.
Another type of spaceship will be used to move cargo. This should be designed to travel at low cost.
The spaceship for people should have a massive deflector shield.
When you hit a piece of rock with a speed of 3 million km/hour without a deflector shield, your ship will be destroyed in an instant.
The engine of the spaceship for people can run on hydrogen and oxygen.
It must have large tanks with more than enough fuel when something goes wrong.
If you run out of fuel with a speed of 3 million km/hour, you will miss Mars and be out of the solar system within three months.
5. We should create large arrays of solar panels around Earth and around Mars.
The electricity of these panels will be used to split water into hydrogen and oxygen.
This will be the main source of energy for the spaceship for people.
6. We have to get water to the space-stations.
Perhaps this is the most difficult and costly operation.
At first, we can use water from Earth. But we can not continue to do so indefinitely.
Besides, moving water from Earth to the space-station is costly.
So we should explore the asteroid belt and search for asteroids of ice.
If we have solar panels and we can find water in the asteroid belt, we have everything we need to go to Mars.
Note:
I double checked my calculations. But it would not harm to check them again.
If you find errors, please let me know.
Confirming or rebutting Einstein:
Einstein stated, that nothing can go faster than the speed of light.
I do not believe this. See Rebuttal of Einstein.
(I am not allowed to post links. So you have to paste it yourself.
andreasfirewolf.com/index.php?pi=1556&n1=119
).
If we create a probe and we accelerate it with 10 m/s2 for a year, we go faster than the speed of light.
Or not. It would be interesting to see what happens.
If we ever want to travel to other star-systems, we will have to travel much faster than the speed of light.

Andreas_Firewolf · 2018-08-15 08:39:36

The amount of fuel depends on the size of the spaceship, the humans do not add much to the mass. Engineers have to design a deflector shield strong enough to keep the people save. That is a lot of mass. Then you have the mass of the fuel tanks and the fuel. And the mass of the spaceship itself. I would be surprised if the mass of the humans would be more than one percent.
Pumping water from Earth does not appeal to me. But perhaps a modern version of the old fashioned canon? Say you have torpedo-shaped containers filled with water. You put them in a canon and with electro-magnetic force you propel them into space. I am not sure if this would work.
But we can not use water from Earth indefinitely. We have to get it from space.

louis · 2018-08-15 09:19:11

The space cannon might work.

Or maybe rather than pumping water up, you could have a mini space elevator with robots climbing up line and delivering water...

The moon would be useful as a stop gap before you found your water ice asteroid.

It would still be nice to have an estimate of how fuel is required. Obviously if it was a 3 day trip, then you don't need much in the way of life support supplies, so that reduces mass.

How about, rather than a deflection shield, a series of lasers which would instantly blast any small objects in the way (larger ones could be detected and avoided)? Would that be less mass?

I am just wondering whether we are talking of thousands of tonnes of fuel/propellant, tens of thousands, hundreds of thousands or millions of tonnes of water.

Andreas_Firewolf wrote:

The amount of fuel depends on the size of the spaceship, the humans do not add much to the mass. Engineers have to design a deflector shield strong enough to keep the people save. That is a lot of mass. Then you have the mass of the fuel tanks and the fuel. And the mass of the spaceship itself. I would be surprised if the mass of the humans would be more than one percent.
Pumping water from Earth does not appeal to me. But perhaps a modern version of the old fashioned canon? Say you have torpedo-shaped containers filled with water. You put them in a canon and with electro-magnetic force you propel them into space. I am not sure if this would work.
But we can not use water from Earth indefinitely. We have to get it from space.

louis · 2018-08-15 09:22:52

Just got me thinking - slight diversion but you never know - would it be possible to build a steam rocket for space travel? I am thinking of something with a big PV array that can heat a large body of water to create a steam jet, but which has a condenser unit connected to the main rocket by rigid pipes...the steam jet is captured by the condenser unit and condenses out as water to be pumped back into the steam jet engine. Or does that offend against some principle of rocketry?

GW Johnson · 2018-08-15 13:33:47

Rocketry only works when you expel your jet and just let it go. You cannot recapture it and reuse it. The momentum required to expel the jet in the first place is equal and opposite to the momentum of recapturing the expelled material. That's just Newton's Laws.

Steam rockets have already flown. Evel Knievel's jump attempt across the Snake River Canyon was in a "skycycle" that was really just a steam rocket with a cockpit. It works, but the specific impulse is very unattractively low: a max of about 80 sec for 300 F water at 300 psig expanded through a convergent-divergent nozzle to near-atmospheric pressure.

You won't get near that hot with solar. Maybe 180-190 F water at no more than 10-15 psig. Essentially zero specific impulse Isp.

Super high Isp is required to get a long burn at significant thrust. Exhaust velocity is proportional to Isp: Vex = Isp * gc, where gc is the Earth-normal acceleration of gravity. Your total mission velocity increment required of the rocket is dV. The required rocket mass ratio MR = Wig/Wbo = exp(dV/Vex), where exp denotes base e exponentiation. That's just the "rocket equation" reversed. e^1 ~ 2.72, e^2 ~ 7.39, e^3 ~ 20, etc.

Now, the propellant fraction of your stage or vehicle is Wp/Wig = 1 - 1/MR. There is a burnout fraction comprising payload plus inert structure, which must sum with propellant fraction to unity: Wp/Wig + Winert/Wig + Wpayload/Wig = 1. The best inert fraction I have ever seen is 0.05. Thus, if your propellant fraction exceeds 0.95, then precisely zero or negative is left over for payload: which tells you your design is not feasible. Definitions: Wp = propellant mass, Wig = ignition mass, Wbo = Wpay + Winert = burnout mass, Wpay = payload mass, and Winert = inert structure mass.

If you stage, then your upper stage ignition mass must be the payload mass for your lower stage. This chains exponentially for lowest-stage ignition mass, derived from the payload you want to throw. Each stage provides a portion of the total dV. The simplest split is even: each stage of a 4-stage vehicle provides 1/4 of the total dV. If each of these 4 stages has a .05 payload fraction, then the ultimate payload mass is .05*.05*.05*.05 = .05^4 = 6.25x10^-6 times the lowest stage ignition mass. Daunting, ain't it?

The Isp of hydrogen-oxygen combustion, with vacuum-expansion nozzles, is no more than about 470 sec, even with 3000 psia chamber pressures. You try the numbers, and discover for yourself why the 1-gee accelerating rocket for days at a time was not built long ago. You can get a few km/sec out of a practically-designable stage, not hundreds or thousands of km/sec. That's just the math of it.

The high Isp of ion engines is no solution either: the thrust of these for the mass of the hardware is vanishingly small. Achieving 0.001 gee with them might be possible. Might. Achieving 1 gee with them is impossible, with any currently-imaginable technology. At all.

The closest thing to the dream here is the nuclear explosion (pulse) drive. It might not be good enough for a 1-gee trip to Mars. I don't know, I never looked at that particular application. But it is good enough for a two-way trip in a single stage, with one-way travel times on the order of a month or three. It uses tons and tons of fissile material doing that.

It's just math and physics to validate or repudiate these ideas. But it can be a bummer.

GW

Last edited by GW Johnson (2018-08-15 14:31:12)

louis · 2018-08-15 17:32:50

GW,

Well obviously I have no training in rocketry...but (leaving aside whether it would be an efficient rocket...maybe it would be a v. slow one!) it seems to me the difference here is that it is the PV system which would be (a) heating up the water and (b) pumping it back to the "boiler" from the condenser unit - that's where extra energy is coming into the system. The jet itself would not be affected except right at the end of the "tail" where the water molecules would be captured by the condenser unit (so imagine the condenser unit as the base line...the "pipes" run parallel and perpendicular to that baseline, either side of the jet tail and then attach to the rocket-boiler, but are long enough to leave space for the jet tail from the rocket exhaust to do its thing). Surely the "push" to the rocket comes from the steam jet - the equal and opposite action principle, as long as the condenser unit does not interfere with that.

In principle, with this hypothetical spaceship there is no loss of propellant at all - as all the steam is in principle being captured by the condenser and returned to the system.

GW Johnson wrote:

Rocketry only works when you expel your jet and just let it go. You cannot recapture it and reuse it. The momentum required to expel the jet in the first place is equal and opposite to the momentum of recapturing the expelled material. That's just Newton's Laws.
GW

Last edited by louis (2018-08-15 17:33:21)

GW Johnson · 2018-08-15 20:20:23

Louis:

The jet leaving the rocket IS the water in a steam rocket. You cannot capture the water and put it through a condenser without destroying 100% of the thrust you created when you sent the steam jet blasting out in the first place. THAT is Newton's Law. Which has over 3 centuries of verification as accurate.

Another way of saying that is this: yes the condenser DOES interfere with the jet producing thrust. ANYTHING you do to touch that jet after it leaves your nozzle destroys the thrust you worked so hard to produce.

GW

Last edited by GW Johnson (2018-08-15 20:23:50)

Andreas_Firewolf · 2018-08-16 07:22:45

When you accelerate to 2.8 million km/hour or 1 * 10pow13 m per second and then you decelerate to 0
you can use E = mv2/2 to calculate the effective energy you need.
It is just the mass of the vehicle in Newton multiplied by the the velocity squared multiplied by 2 (acceleration and deceleration) divided by 2.
Multiplying by 2 and dividing by 2 cancel each other out.
So you are left with the mass of the vehicle multiplied by the desired velocity squared.
.
I left out the resistance of space. I am not certain that this is right. Space is not completely empty.
On the other hand: The extra thrust you need when accelerating with some resistance should be almost equal to the diminished thrust you need when decelerating.
.
That was the easy and a bit wrong calculation. It is only an approximation.
While you burn and expel hydrogen and oxygen, your spaceship looses mass.
When you leave the space-station you have more mass than when you achieve the highest velocity.
So deceleration would require less energy than acceleration.
I propose the use of hydrogen and oxygen because hydrogen has one of the highest energy densities related to its mass.
.
The spaceship does not have to leave Earth's gravity. It should remain in space and never touch Earth or Mars.
The gravimetric pull of Earth is the gravimetric constant multiplied by the mass of Earth multiplied by the mass of the spaceship divided by the distance squared. If the distance of the space-station to Earth is large, then the gravimetric pull becomes small.
.
I supposed that burning hydrogen and oxygen in a yet would give you a certain amount of thrust related to the energy that is released by burning.
Just like when you burn kerosene in a Boeing.
I am not sure about the efficiency of the conversion of this energy into thrust. I assumed that an efficiency of 20 percent should be possible.
If this is possible, you would need five times the amount of energy that would be needed for the acceleration and deceleration.
.
The question or the challenge is: Can we build an engine that can burn hydrogen and oxygen in space and that has an acceptable efficiency in converting the released energy in thrust.
.
I am under the impression that this is not rocket-science but applying the principles of an ordinary yet in space.
.
When we have water and solar panels in space, we can simply use time to produce hydrogen and oxygen.
The spaceship simply tanks oxygen and hydrogen at the space-station.
If we want more energy, we put more solar panels in space.
.
If I am mistaken about this, I really would like to know what happens to the energy that is released when you burn hydrogen in space.

Andreas_Firewolf · 2018-08-16 07:59:54

After some calculation I believe I found the error in my idea.
A Boeing uses oxygen from air. A spaceship has to carry the mass of its oxygen.

Energy in hydrogen 120 MJ/kg
Energy in hydrogen plus oxygen: 120/9 Mj/kg = 13.3 MJ/kg
Most energy would be used to accelerate the fuel, which is not very useful.

GW Johnson, am I right if I assume that we need to tame nuclear fusion energy before we can seriously explore space?

Andreas_Firewolf · 2018-08-16 08:36:08

If an acceleration of 1 G is impossible, space-exploration seems almost impossible.

Suppose we can get a velocity of 0.01 c and we want to go to a planet at a distance of 50 light-years, it would take 5.000 years to get there.
I doubt if humans can survive in empty space for three generations. And now I am not referring to physical problems, which would be enormous.
I am referring to psychological problems as a result of cultural stagnation and boredom.

Spending half a year or longer in a metal can towards Mars seems horrible to me, but might be doable for some people.
But surviving 200 generations in empty space and remaining sane?

GW Johnson · 2018-08-16 10:33:05

Well, I think 1-gee travel of the sort you dreamed of is technologically very much beyond humanity's reach at this time, and likely for some time to come. Some very major breakthroughs in physics, and engineering, are necessary to make such travel possible.

Given what we can do with chemical rocketry, the plans dreamed up over the last half century or so to reach Mars all relied on minimum-energy "Hohmann" transfer orbits. At average orbital conditions, the one-way transfer time was 8.5 months. There was a considerable rocket burn to leave the Earth onto this trajectory, and another to capture into Mars orbit. Today, we know we can travel a bit faster, if we sacrifice payload for extra propellant. 6 months one way appears feasible, and not too impractical in terms of payload.

You will find two schools of thought in the debates on these forms. The majority want to do what is called direct landing upon Mars without stopping in Mars orbit, using aerobraking in the Martian atmosphere to substitute for most of the arrival burn otherwise required. To reduce the sizes of payloads sent to Mars, they want to produce the return propellant on Mars. The arrival at Earth is also a free-return aerobraking event, which in most but not all cases precludes re-using any of the return trip hardware.

The technology for propellant production on Mars works in small scale in the laboratory (at Earthly conditions). It has never been scaled up or field-tested at harsh conditions. The technology and infrastructure to land more than one vehicle at the same site on Mars does not yet exist there. We know what to do, we have not yet done it. It does need to be in place before men make the trip.

A minority (myself included) think the older proposal for an orbit-to-orbit spaceship with separate landers (likely sent ahead for rendezvous later in orbit) makes more sense from practicality and safety standpoints, despite the much higher propellant demand. Very much more mass must be launched from Earth to do this. When you separate the transport function from the landing function, into two separate designs, you can optimize each one.

The orbit-to-orbit transport approach can accommodate radiation shielding and artificial spin gravity, plus a whole lot more volume in which to live for months at a time, plus if you recover it in Earth orbit, you can use it again. If you insist on traveling in the thing that makes the landing, there is no room for any of those 3 essentials. And essential they are. Plus, there is no re-use at all.

With launch costs coming down dramatically (by significantly more than a factor of 10 compared to the Space Shuttle), the objection to high launched mass is disappearing. The direct-landing majority do not yet recognize this, however.

A part of the debates here revolve around the giant vehicle Spacex wants to build for travel to Mars. It lies sort-of in-between the two extremes. It is a direct-landing approach, but it is a two-way trip and recoverable, if refuelling on Mars can actually be achieved. I think it can, but probably not in the stay time of just one mission. So there is a danger with that plan.

Anyhow, that's the sort of things humanity actually could do at this time in history. Right now, even the outer planets are too far a trip for us with men, much less men traveling to the stars. Some day, but not yet.

GW

Last edited by GW Johnson (2018-08-16 10:35:11)

Oldfart1939 · 2018-08-16 12:17:43

Back in 1989-90, when the original Mars Direct plan was constructed, the concept of orbital assembly was known but not yet accomplished. In light of the construction of ISS, the objections to building a deep space vessel in orbit have diminished, but not to the vanishing point. GW is correct, however, that many of the features required to make Mars travel a safe reality are not yet in place. Provision of some form of spin induced gravity--in my mind--ranks as number one requirement. Provision of some radiation shielding using stored foodstuffs in addition to water supply and wastes would work to offset solar flare damage, but not for Galactic Cosmic Radiation. The answer here is to use OLD GUYS, beyond the age of reproduction as the crews. And also, the likelihood of dying from cancer in old age would be a joke to those lucky enough to make the trip. I also like GW's twirling baton approach to spin gravity production.

louis · 2018-08-16 14:14:15

Sorry to test your patience but in my theoretical steam rocket, I don't think the condenser unit is interfering with the thrust...

There must be an end to the exhaust plume deriving from the (controlled) explosion in the reaction chamber (it's the explosion that propels the rocket forward, isn't it?)...I think that as long as the condenser unit is positioned so it catches the plume at its boundary, thus ensuring it does not create a reverse pressure wave, but rather sucks in the water particles at the tail end of the exhaust, then - theoretically - it would simply be recycling water particles that would otherwise radiate through space...the trick would be catch the exhaust while it's still in an organised state, just on the edge of the plume boundary.

GW Johnson wrote:

Louis:
The jet leaving the rocket IS the water in a steam rocket. You cannot capture the water and put it through a condenser without destroying 100% of the thrust you created when you sent the steam jet blasting out in the first place. THAT is Newton's Law. Which has over 3 centuries of verification as accurate.
Another way of saying that is this: yes the condenser DOES interfere with the jet producing thrust. ANYTHING you do to touch that jet after it leaves your nozzle destroys the thrust you worked so hard to produce.
GW

GW Johnson · 2018-08-16 16:22:24

Louis:

I'm sorry, but you are very wrong. There is no "boundary" to the expelled plume. In theory (and practice) it extends to infinity. If you touch it in any way, you kill its thrust. Newton says so, plus 3 centuries' experience applying Newton.

GW

louis · 2018-08-16 17:13:07

Plenty of experts in the field refer to plume boundaries...such as this one.

https://aip.scitation.org/doi/10.1063/1.1407640

I accept what you say about in theory and practice the "plume" extending to infinity, but me walking under a rocket's thrust when it's ten miles high isn't going to bring it falling down, so there must - it seems to me - be some point at which the exhaust becomes disorganised and no longer part of what you might call "the rocket system".

Also isn't the equal and opposite action thing happening in the reaction chamber...so disrupting the plume/exhaust will only affect the rocket's progress if that disruption in turn disrupts the reaction chamber process?

Also, for the purpose of this discussion, I would stress this theoretical steam rocket has been assembled in space, it's not launching from Earth. So it's operating in the vaccuum of space.

Just to get the design right...think of a three rung ladder. Between the top rung and the middle rung is the body of the rocket with the steam boiler. Attached to the body of the rocket either side would be large PV arrays providing the energy for heating the boiler and pumping the water from the condenser unit to the boiler. The bottom rung is the condenser unit. The condenser unit would capture the water molecules from the rocket plume at it's tail end.

Maybe it's quite a modest steam rocket...not providing much thrust but enough to move the thing through space.

GW Johnson wrote:

Louis:
I'm sorry, but you are very wrong. There is no "boundary" to the expelled plume. In theory (and practice) it extends to infinity. If you touch it in any way, you kill its thrust. Newton says so, plus 3 centuries' experience applying Newton.
GW

SpaceNut · 2018-08-16 17:55:56

Anything that is in the exit direction of the nozzle will block the ability to produce thrust based on the materials burnt or steam coming out of the nozzle...even trying to collect what would hit a small target still means a small loss and then an increase of power required to cool it back down in order to heat it back up...all these are just adding mass that will not aid in getting it to where you want to be any faster and will not make the rocket have less mass based on reusing the collected as it requires more mass to be able to achieve it....

louis · 2018-08-17 02:41:41

To emphasise again - the design would not interfere with the integrity of the rocket plume...the condenser unit would simply be collecting the water particles otherwise heading out in all directions to space at the point where the plume becomes "disorganised" as I put it.

The PV arrays are providing the power to pump the water back to the boiler and reheat. Assume ultralightweight arrays for the purpose of this exercise.

I'm not arguing here for efficiency or great speed, just theoretical feasibility. Unless I've misunderstood the physics, even a very small jet impulse will move a very large mass in the frictionless vacuum of space. So don't think 100 metre plume for the moment, think perhaps 10 metres or less.

If there was a loss of thrust, of say 5%, resulting from collecting water particles, that would not prove lethal to the design.

The interesting thing about this theoretical concept is that of course you are recycling your propellant. The power to recycle it comes from the PV source, not rocket fuel. Indeed the PV power is the "fuel" for the propellant.

SpaceNut wrote:

Anything that is in the exit direction of the nozzle will block the ability to produce thrust based on the materials burnt or steam coming out of the nozzle...even trying to collect what would hit a small target still means a small loss and then an increase of power required to cool it back down in order to heat it back up...all these are just adding mass that will not aid in getting it to where you want to be any faster and will not make the rocket have less mass based on reusing the collected as it requires more mass to be able to achieve it....

Last edited by louis (2018-08-17 02:43:55)

Andreas_Firewolf · 2018-08-17 07:11:01

While meditating on the problem, I came up with some insane ideas.
I do not know if they are already proposed.
And I do not know if they will be useful.
In any case, it was fun and educational writing them down.

Imagine an elevator shaft (or rather accelerator shaft) that accelerates an elevator (or container) with electro-magnetic force.
I will call the shaft EMA (short for Electro Magnetic Accelerator).
The EMA accelerates a container with in this container a space-ship.
The EMA is open at the end. The container will leave the EMA with the space-ship.
The space-ship then starts a little yet to push itself out of the container.
Once it is clear of the container, it can start the main propulsion system (if it has one)
to bring it to the desired or possible speed.
Since the space-ship does not have to carry fuel for its initial acceleration, it can reach higher speed.
Or it can carry more cargo.

Imagine two identical space-stations, one around Mars, the other around Earth.
They are massive, at least 100 times more mass than the space-ships they have to launch.
They have plenty of water, plenty of solar cells and plenty of fuel cells to reduce hydrogen and oxygen to water.
And both have an extremely long EMA.
You can use the solar panels to produce hydrogen and oxygen.
You reduce this fuel to water and produce the necessary electricity.
This is in essence an endless recycling of water.

It should be obvious, that the space-stations must have much more mass than the space-ship.
Otherwise, the space-station would be pushed away from the space-ship.

s = at2/2 (s = distance, a = acceleration, t = time)

If we accelerate with 10 m/s2 for 10 seconds we travel a distance of 500 meters.
To get a velocity of 100 m/s we need an EMA with a length of 500 meters.
But that is not much for a trip to Mars.
If we want to accelerate the spaceship to 40,000 km/hour or 11.1 km/s we need a longer EMA.

We 'only' have to build an EMA with a length of 620 km to get to that speed.
The previous sentence is written 'with tongue in cheek', that should be obvious.
I do not believe that such a construction is possible.
But engineers have surprised us again and again during the last century.

If we can build very large EMA's in space,
we can either reduce the duration of the trip to Mars or we could send more cargo.
It is up to engineers to come up with a reasonable design.
If this idea is worth pursuing.

Earth - moon traffic
====================
How about using EMA's for exploring the moon?
And how about using EMA's when launching vehicles from Earth into space?
If you have an EMA on Earth with a height of 2000 meters, you can accelerate a vehicle to 200 meters per second.

a = 10 m/s2
t = 20 seconds
v := 200 m/s
s := 2000 m

That would mean, that the vehicle can reach the required speed with less fuel.
The weight reduction of the fuel can be used for extra cargo.

If we would build a very large EMA on the moon, it can launch space-vehicles from the moon without fuel.
The space-vehicles only need small jets and a small amount of fuel to move towards a space-station around the moon.

The distance between the moon and Earth is about 384,400 km.
If you want to travel this distance in 72 hours, you need a velocity of 1483 m/s.
You would need an EMA of 102 km to get this velocity.
Perhaps this is possible.
An EMA of 10 km would give us a velocity of 447 m/s.
With that speed it would take 239 hours or 10 days to travel between the space-stations.
That might be acceptable for transporting humans. It certainly is acceptable for moving cargo.

With this technology it should be possible to build moon-bases and to travel at reasonable costs between Earth and the moon.
We can experiment with building moon-bases and then use the technology on Mars.
That seems better to me than to start with building a permanent base on Mars.

Exploring the Milky Way.
========================
Imagine that the space-station around Earth has an EMA that can be rotated
360 degrees in one plane and
20 degrees in another plane
in a right angle with the first plane.
Then you can propel a space-ship in any direction.
You can use the EMA for travelling between the Earth and the moon.
And you can 'point it at Mars' and reduce the duration of the Mars trip a little.
And you can use it to send out probes to every direction.

Currently we are like Europeans in the 14th century.
Europeans in the 14th century sailed the coastal waters around Europe, but never left the coastal waters.
At the end of the 14th century Columbus boldly sailed were no one did sail before.
(This is not entirely true. The people from Iceland had colonies on Greenland around the year 1.000 AD.)
We are the same. We are just leaving the solar system with the two Voyagers.

Suppose we are going to explore the Milky Way more seriously.
You can point the EMA on the space-station around Earth to any point in the Milky Way.
With it you can launch a rocket. At some point the rocket starts its jets and accelerates to its maximum velocity.
Then it propels a probe directed to some direction of the Milky Way.
Once the probe is clear from the rocket, it starts its tiny jets and accelerates further.
This could be a way to send out a few dozen probes with high resolution camera's
and enough energy to transmit the images to the rocket that helped launching it.
The rocket should be able to act as a relay station to transmit the images to Earth.

GW Johnson · 2018-08-17 08:25:20

Louis:

Your 3 rung ladder out in space is a high-school physics error.

To create thrust, you expel matter with momentum from your vehicle. Once expelled, out in space it continues to move with exactly that momentum, forever. Only down here in the atmosphere does atmospheric drag on the expelled matter slow it down, so that far enough from the rocket nozzle, you feel no effect.

If you now reach out from your vehicle (out in space) to catch the matter you expelled as your propulsive plume, BY DEFINITION you just had to kill all the momentum you previously gave it. That is an equal and opposite reverse thrust. Your vehicle's net thrust is now exactly zero. Lots of energy expended to expel the plume, but by catching it, you waste 100% of that energy.

Ask any high school student who actually passed basic physics.

GW

louis · 2018-08-17 11:05:40

Well I'm not the only one to come out with this idea:

Etaila:

"Yes you can use steam effectively, whatever steam comes out will instantly freeze. This frozen water can be collected in a device like a solid parachute at the back and then recycled again and again. Nuclear fission can be used for heating the water, and as space is already super cold the necessary cooling effect for the nuclear device can be regulated. Solar energy can be stored for other things. This way you have a cheap and endless supply of fuel to make you move in any direction."

https://worldbuilding.stackexchange.com … eam-engine

Obviously nuclear or PV can work with this theoretical craft.

GW Johnson wrote:

Louis:
Your 3 rung ladder out in space is a high-school physics error.
To create thrust, you expel matter with momentum from your vehicle. Once expelled, out in space it continues to move with exactly that momentum, forever. Only down here in the atmosphere does atmospheric drag on the expelled matter slow it down, so that far enough from the rocket nozzle, you feel no effect.
If you now reach out from your vehicle (out in space) to catch the matter you expelled as your propulsive plume, BY DEFINITION you just had to kill all the momentum you previously gave it. That is an equal and opposite reverse thrust. Your vehicle's net thrust is now exactly zero. Lots of energy expended to expel the plume, but by catching it, you waste 100% of that energy.
Ask any high school student who actually passed basic physics.
GW

SpaceNut · 2018-08-17 16:39:26

The ice when it strikes the hard parachute collection causes a slowing of the rocket as it counter the the motion of the rocket via its attachment point. The ever increasing mass of collection changes the rockets forward motion as the drag of the materials collected offsets the very light steam ejected from the nozzle. This means mass change is zero for thrust and so will the motion in time rather than the rocket getting lighter which is what thrust will be an effect of for the forward motion.

https://spaceflightsystems.grc.nasa.gov … ktpow.html

So the change in mass is not happening for the equation but is staying nearly at the same value which means not change in speed or motion....

louis · 2018-08-17 17:19:29

Hmmm... If it's sucked into the condenser unit at a speed slightly at or above the speed of the exhaust stream, I don't see how you get that effect. Put it another way, as I did to GW: why don't rockets fall out of the sky when you walk under their exhaust stream? There must be some limit to disruptive effects...my suspicion is the limit is what experts refer to as the plume boundary.

The material collected in the condenser unit isn't held there - it's immediately pumped back into the boiler system. I could accept that you might be reducing the rocket's efficiency by some small percentage, but that doesn't affect the great merit of the theoretical PV/nuclear-steam-condenser rocket, which would be that you don't have to seek out new propellant, it's being recycled all the time...of course you can't achieve 100% recycling but even if you are getting 95%, it's a huge advantage in the vaccuum of space, allowing you 20 cycles of acceleration.

SpaceNut wrote:

The ice when it strikes the hard parachute collection causes a slowing of the rocket as it counter the the motion of the rocket via its attachment point. The ever increasing mass of collection changes the rockets forward motion as the drag of the materials collected offsets the very light steam ejected from the nozzle. This means mass change is zero for thrust and so will the motion in time rather than the rocket getting lighter which is what thrust will be an effect of for the forward motion.
https://i.pinimg.com/564x/0c/72/70/0c72 … 8935b8.jpg
https://www.grc.nasa.gov/WWW/k-12/Virtu … rktalo.gif
http://68.media.tumblr.com/01fed62476be … t90qmt.png
https://spaceflightsystems.grc.nasa.gov … ktpow.html
So the change in mass is not happening for the equation but is staying nearly at the same value which means not change in speed or motion....

SpaceNut · 2018-08-17 17:34:33

The mass of the earth is not attached to the rocket... add a chain between both and you do not move.

louis · 2018-08-17 18:27:48

The Earth has nothing to do with this hypothetical steam rocket. It's operating in the vacuum of space so don't know what you mean by the Earth reference.

SpaceNut wrote:

The mass of the earth is not attached to the rocket... add a chain between both and you do not move.

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