Answering questions on vacuum, space, rockets, and space travel

On about September 21, 2017 I received via email some questions/comments related to vacuum and how rockets and spacecraft are able to operate in space.  I replied within about 1 day and my responses are presented below slightly edited.


How can anything be propagated through space if it is a vacuum, nothing?

If space is a vacuum then what does the rocket push off of?

How does the rocket maintain its heading and not spin out of control if there is no air to stabilize off of?

Space travel believers will say that they use special propellant that when ejected out of the thruster nozzle has an equal and opposite reaction.

If that’s the case then wouldn’t the thrusters on let’s say the space shuttle when maneuvering to the ISS have to eject the special propellant faster than 17,500MPH which is the speed they are traveling?

All tests show that rockets don’t work in a vacuum.


I am going to do the best I can to answer these questions as quickly as possible off the top of my head without consulting any sources of information beyond what I currently know.  These are all good questions and certainly more could be learned by studying these things more.


First regarding the question of vacuum, I think that even in space there is not a complete vacuum in the sense that you could find a cubic mile of space that does not contain at least one atom or atomic nuclei.

But even if you could imagine a cubic mile of space without even one atom in it, I believe that other physical phenomena could take place in this space, such as the transmission of light or other electromagnetic waves, and other things possibly (I would have to research this more).

Even if you could have completely empty space, it becomes kind of a philosophical question of what is “nothing.”  I think the view of physics is that even if you could have completely empty space, that is not nothing, but instead a part of reality, known as the space time continuum in physics.  I think this view that even empty space would not be nothing goes back to early philosophers even before Christ.  I would have to double check on this.

I know we have plenty of examples here on earth of physical phenomena taking place in a high vacuum, but we really cannot create a perfect and complete vacuum.

So before we had transistors, we had vacuum tubes.  These accomplished the same sort of electrical tasks that eventually became possible to do with transistors.  When multiple transistors integrated into an electrical circuit were eventually created on a silicon chip, we got computers and relatively shortly thereafter we got computers that ordinary people could buy and use.  But realize that there were digital computers even before transistors, and these computers used vacuum tubes.

But of course, the more common use of vacuum tubes initially was in radio and then eventually television.  So there is a lot going on within the vacuum of a vacuum tube, such as the flow of electrons in the vacuum, and I am remembering how vacuum tubes need a source of heat to operate, and that is done with the filament, which is basically like a separate electrical circuit within the vacuum tube that functions just like a conventional incandescent light bulb.  Also, the screens of the original televisions were cathode ray tubes which were themselves giant vacuum tubes where a fast moving electron beam is used to create the television picture.

Now moving on to the other space questions.  I will paste the questions/comments posed and intersperse my answers/comments.

Question: If space is a vacuum then what does the rocket push off of?

Answer: It pushes off from the mass of propellant reaction products that it expels at high velocity.  I answered this more completely in a separate blog post dated September 20, 2017.

Question: How does the rocket maintain its heading and not spin out of control if there is no air to stabilize off of?

Answer: A physical solid object in space would remain in motion unless acted upon by an external force.  If we were to imagine that it were far enough out in space such that there were no significant gravitational forces acting upon it, then it would continue moving in a straight line for example.  I am using moving in a straight line, because if I said it was at rest, it would raise the question of what is it at rest with respect to, so linear motion is easier to imagine for this thought experiment.  This would be conservation of linear momentum.  The center of mass of the object would continue to move in a straight line.  But if the object had a spin or rotation to it, that spin would also continue indefinitely, unless acted upon by a force to change the rotation.  Just to complicate the example a little for illustration, let’s say it was a spacecraft traveling with a couple of astronauts in it, and the spacecraft was of a long cylindrical shape with one astronaut at one end and the other at the other end, and the spacecraft was tumbling (spinning) end over end.  If the astronauts were to move from the ends to the middle of the spacecraft the rate of the spacecraft’s tumbling would increase.  This would be due to conservation of angular momentum.  By the way, an example of conservation of angular momentum that most people on earth are familiar with is when an ice skater gets to spinning with their arms extended outwards and perhaps even a leg extending outward, and then draws their arms inward as well as their leg, and then they end up spinning noticeably faster.

Question: Space travel believers will say that they use special propellant that when ejected out of the thruster nozzle has an equal and opposite reaction.

Answer: I would have to research this for details, but I can say this.  Once you are in space, to make changes or corrections in either linear motion or spinning motion you are going to need more than one thruster pointed in different directions in order to achieve any change that you might want.  Maybe it could be done with just one thruster if you had the ability to change the direction that the thruster points from the spacecraft.  But also, for in space use, the corrections you make are usually going to be relatively small, so you want your thruster to be easy to turn on and off.  So you wouldn’t want to be burning rocket fuel and oxygen for example.  This is where your special propellants come in.  For a propellant to work all it needs to be able to do is expel a mass at a certain velocity, the higher the better, because then you get more effect for the mass that you use.

Question: If that’s the case then wouldn’t the thrusters on let’s say the space shuttle when maneuvering to the ISS have to eject the special propellant faster than 17,500MPH which is the speed they are traveling?

Answer: The unreacted unejected propellant is already going at the same speed as the spacecraft before it is ejected.  To cause a change in the motion of the spacecraft it only has to be ejected at some velocity with respect to the velocity of the spacecraft.  A thorough discussion follows.

Presumably in this example the spacecraft is orbiting the earth in a stable orbit at whatever distance from the earth that would be necessary for orbiting at 17,500 mph.  This could easily be calculated but I am not going to do that now.  I just know from having heard these orbital speeds mentioned before that this would be at a distance from the earth where you would have a very high vacuum, meaning essentially no “air” drag on the vehicle.  This would mean that the spacecraft would keep moving in this orbit unless acted upon by an external force.

The reason it is not moving in a straight line is that gravity is continually exerting a force upon it in a direction perpendicular to its velocity.  This is known as centripetal force and it causes the spacecraft to be continually curving toward the earth.  But it is going fast enough that the curving is the right amount to keep the spacecraft circling or orbiting the earth.

If you wanted to cause the spacecraft to re-enter the atmosphere, all you would need to do is fire a thruster in the opposite direction to the velocity of the spacecraft.  Note that the propellant used would already be travelling at the speed of the spacecraft before it is reacted and released, so it is ejected at high velocity with respect to the spacecraft’s velocity.  In so doing, if it is fired long enough to decrease the velocity enough, and this could all be calculated ahead of time based on the performance characteristics of the thrusters, the slower speed will result in the force of gravity causing it to curve more than the curve required for the orbit, so the spacecraft will start to travel to lower altitudes and eventually start entering the atmosphere.  I have never felt the need to look into the numerical aspects of all of this, but it might be interesting to gather all of this information to see if it all makes sense.  But I suppose, if it is all fake, they could have just made it all calculate out correctly to deceive us all.


Just a little note about how physics works for the equation F=ma in order to help better understand what centripetal force is.  (I am reflecting upon when I first learned about this equation, taking physics for the first time in high school 44 years ago, where I learned how this equation explains why car accidents can kill you, but that’s another story.)  In reality this equation is a vector equation.  A vector has both magnitude and direction.  F is the force vector with both its magnitude and direction.  a is the acceleration vector also with both magnitude and direction.  Acceleration is also by definition the time derivation of the velocity vector.  So in words, F(magnitude&direction) = mass x a(magnitude & direction) or

F(magnitude&direction) = mass x (change in v/change in t)

Where v is the velocity vector also with magnitude and direction.

So if you were in a drag racer, and you got the green light, and you take off, you would feel yourself being pushed from behind by the back of the seat as the car accelerates in a straight line with you in it.  Your velocity would be changing in magnitude (increasing) while its direction stays the same, straight ahead.

Now if you were traveling in a car at a constant speed and in a straight line, but then you put the car into a turn of a certain radius but at constant speed, you would feel the side of the car pushing against you in the direction that the car is turning.  In this case you are experiencing a constant acceleration, that is, a change in the velocity vector with respect to time, but the velocity vector is changing in direction but not speed or magnitude.  So in this turn the centripetal force is the force being exerted by the ground on the tires of the car perpendicular to its forward motion in order to cause it to turn (with you inside), which is a constant acceleration maneuver.  To make it a little more personal for you in the car, the side of the car is pushing against you causing you to turn, a centripetal force causing the centripetal acceleration of you.

Most people are familiar with the term centrifugal force.  If you are sitting in the turning car, from your point of view as being in the car, known in physics as a rotating reference frame point of view, you feel a force throwing you to the outside of the car, that is indistinguishable from a gravity force from your point of view from inside the car.  This reminds me of the space station in 2001 A Space Odyssey, where it is spinning so as to create an artificial gravity, so the person is able to run around it as if they were running on a surface with a gravitational attraction.

Comment: All tests show that rockets don’t work in a vacuum.

Answer: I would like to review these tests so I can comment upon them.

Rebuttal to Flat Earth argument: Lines of latitude and longitude are distorted to hide the flat earth




PROBLEM STATEMENT AND RESPONSE by T. Mark Hightower 9/19/2017


I cited to a flat earth advocate how the closest distance between Perth Australia and Sydney Australia on the spherical earth model is a little over 2000 miles, whereas the closest distance between these two cities on the flat earth model (azimuthal equidistant map most often cited and shown by flat earth model advocates) is over 5000 miles.  And surely Australians would know that the 2000 mile distance makes sense if they have driven and/or flown between these two cities, whereas the 5000 mile distance is absurd.  How can flat earth advocates explain this?  The explanation I got from the flat earth advocate I posed the question to was that the azimuthal equidistant map is not a correct flat earth map and that they do not yet have a completely correct flat earth map.   Also it was stated that, and here I am doing the best I can to explain how I understood what was said, there is evidence that on land masses on the earth the latitudes and longitudes are distorted and/or stretched to make them come out consistent with the spherical earth model, but out on the oceans where you can’t really know where you are and nobody can check these things, further distortion and/or stretching is done to make it appear that the spherical earth model is correct, when in reality the earth is actually flat.

Although I did not push the point in my conversation with the flat earth advocate, based on the above explanation it seems like flat earth advocates are not able to tell us where well established geographical locations on the earth such as major cities are on their flat earth map.


When I heard the above explanation I thought it seemed to make some sense although I couldn’t quite visualize how this might work.  Later as I have reflected upon this more, I believe that this explanation is convoluted and incoherent.  I find it difficult to explain or to prove that the explanation is convoluted and incoherent.

But if I can bring in some other information that is often seen presented by flat earth theory advocates I think I can clearly show that there is a serious problem here of convolution and incoherence.  Flat earth theory advocates often show the disk shaped flat earth represented by the azimuthal equidistant map and they show the sun and moon circling around the disk in order to explain why those on the earth see what they see and that it is consistent with their flat earth theory.  However, as soon as they claim that the sun and moon are circling around the disk shaped flat earth and that is why we anywhere on the earth see what we see, they have just implied that those on the earth can know where they are on the earth in terms of the flat earth model and its map.

But it was previously said that flat earth advocates do not yet have a flat earth map.  I say if they do not have a flat earth map, they have no business speculating about what is moving around above their undefined flat disk shaped earth.

My challenge to flat earth theory advocates is that they should start locating well know geographical locations on their flat earth map.  May I suggest the following list of cities well distributed on the earth:  Sao Paulo, Brazil; Johannesburg, South Africa; Sydney, Australia; Perth, Australia; San Francisco, United States; New York City, United States; Santiago, Chile; London, England; Berlin, Germany; Moscow, Russia; New Delhi, India; Beijing, China; Tokyo, Japan; Honolulu, Hawaii.

If flat earth theory advocates know how the stars, wandering stars, sun, and moon travel above the flat earth, they should be able to use this knowledge to locate where all of these cities are on the flat disk shaped map of the flat earth, and establish where any other cities or locations are on it as well.


Rebuttal to Flat Earth argument: Space travel impossible since rockets have nothing to push against in space


PROBLEM STATEMENT AND RESPONSE by T. Mark Hightower 9/20/2017


This argument describes physical behavior familiar to most on the earth where it is either clear that motion is achieved by pushing against something or it appears that this is the case.  I will describe two examples.  A car pushes against the road with its drive wheels powered by the car’s engine or motor in a direction opposite to the direction of the car’s motion.  A jet aircraft in motion in the air (atmosphere) appears to be achieving its forward motion by pushing against the air behind it with the thrust of its jet engines.  In space there is no air, but instead a vacuum.  A spacecraft in space firing it rocket engine would have nothing to push against, therefore the firing of its rocket engine would have no effect on its motion. Therefore space travel as commonly believed to be possible is actually impossible.  Therefore the space program and space travel are fake and a complete hoax.


This argument appears to make sense but it does not take into account the proper application of basic principles of physics that are well established by experiments that can be done here on the earth.  The main principle of physics here is known as conservation of momentum.  Linear momentum is the product of mass and velocity.  Let me illustrate this with a simple thought experiment that could easily be demonstrated with an actual experiment.  Let’s say you have two ice skaters who weigh the same and are at rest in the middle of an ice rink facing each other holding hands.  They each weigh 150 lbs.  The skaters then simultaneously push against each other as hard as they can and release their hands, while keeping their skates parallel and in the direction of their pushing.  These are skilled skaters able to maintain their position with skates parallel traveling backwards so that they travel in a straight line in the opposite direction of the mutual push against each other.  What will happen?  They will end up traveling in opposite directions to each other at the same speed.  Eventually they will both slow down to a complete stop due to the slight friction between their skates and the ice as well as slight air drag due to their motion in the air.  But the principle being illustrated depends on looking at their velocities right after they push away from each other, and not how they would eventually slow down.  The total momentum they had before they pushed was zero, (300)(0), because their velocity was zero.  Let’s say the magnitude of their push was enough to give them each the same speed of 5 mph.  So once they pushed off from each other, one had a momentum of (150)(5) and the other had a momentum of (150)(-5), their momentums being equal in magnitude but in opposite directions, which is taken care of mathematically by the negative sign.  So their total momentum is still zero, 750 – 750 = 0.

Let’s imagine a similar experiment.  In this case let’s say one skater weighs twice the weight of the other skater.  Keeping the total weight of the skaters the same, one skater would weigh 100 lbs and the other 200 lbs.  If they then push off from each other in the necessary magnitude of impulse to give the same individual magnitudes of momentum as the previous example, the 100 lb skater would be traveling at 7.5 mph and the 200 lb skater would be traveling at 3.75 mph.  The math works out like this.  (100)(7.5) + (200)(-3.75) = 750 – 750 = 0.  So the skaters are not pushing against the ice or against the air in order to affect their motion.  They are pushing against each other.

So for a spacecraft in space firing its rocket engine you have the mass of the spacecraft and the mass of the reacted rocket fuel that is ejected at high velocity upon firing.  In this case the spacecraft is quite heavy compared to the very light rocket fuel, but the rocket fuel is expelled at such a high velocity that it pushes against the rocket, and the rocket pushes against it as they part ways.  The total momentum of the rocket fuel system looked at as a whole will remain the same, the heavier space craft will go off in one direction at a lower velocity, while the much lighter rocket fuel will go off in the other direction at a much higher velocity.  So this is how rockets work in space so as to change the motion or velocity of the spacecraft.

But as the rocket engine is firing, it is like, if you were on the ice, for the large skater, having a huge number of tiny skaters pushing off from the large skater in rapid succession over a period of time.  The longer this process continues, the faster the large skater will be traveling.  But eventually the tiny skaters will run out, and this would be equivalent to the spacecraft running out of rocket fuel.  There are more details about how you actually calculate the behavior of rocket engines where you get into defining thrust and if I remember right something called specific impulse, but you do not need to get into that level of detail in order to understand the basic principle of how a rocket works in space according to well established laws of physics, as I have illustrated by these simple thought experiments.  Space travel is indeed consistent with the commonly understood and accepted laws of physics.  Therefore, space travel is possible.


In reality the jet engine is based on the same principle of conservation of momentum as the rocket engine in space.  It creates its thrust by expelling mass behind it at high velocity.  Here’s the difference.  The jet engine brings air in at the front to provide oxygen for the combustion of the jet fuel, so a portion of the mass the jet engine ejects at high velocity comes from the air.  The rocket engine carries its own oxygen in addition to its fuel, so the mass that it ejects comes entirely from on board fuel and oxygen tanks.

The jet engine is pushing against the exhaust gases that it is expelling at high velocity, some of which comes from the air.  The expelled exhaust gases are pushing against the engine.  Forces always occur in pairs.  Every action has an equal and opposite reaction.

In the case of the car, it is definitely pushing against the road in the direction opposite its motion with its drive wheels.  Any exhaust it expels is not contributing to its motion.


Rebuttal to Flat Earth argument: Vacuum bottle sucking up water implies atmosphere should be gone

Kelvinsong, Earth’s atmosphere, CC BY-SA 3.0


PROBLEM STATEMENT AND RESPONSE by T. Mark Hightower 9/17/2017


First pull some significant level of vacuum in a rigid bottle.  Place the bottom of the bottle into a body of water.  Create a hole in the bottom of the bottle.  A significant amount of water will be sucked up into the bottle above the level of the body of water.  Since this vacuum sucked up water, a liquid, it would be even easier to suck up air (a gas) which is what makes up the atmosphere according to spherical earth theory.  Since the atmosphere does not get sucked up into space, the spherical earth theory fails this simple thought experiment.


This argument appears to make sense in a qualitative sense, but it is far off the mark in a quantitative sense, and does not bring to bear upon the problem enough conventional physics theory to allow any meaningful conclusion to be reached.  Since it is assuming conventional physics in order to show that it gives a result contrary to common observation, I will show that a complete and correct application of conventional physics to this problem will actually give a result in keeping with the observation that pressure gets lower the higher you go in the atmosphere.  I am going to describe a more rigorous thought experiment that will illustrate what we would really expect to happen based upon conventional physics theory.

Suppose you had a rigid bottle 500 miles tall and you could evacuate it to a perfect vacuum and then stick its bottom in a body of water and introduce an opening in the bottom so the vacuum would start sucking water up into the bottle.  What would happen?  The water would get sucked up into the bottle until it reached a level of about 34 feet (atmospheric pressure is equal to roughly 34 feet of water) above the level of the water that it is sitting it.  The water at the level in the bottle would start to vaporize and begin filling the bottle from that point upwards with water vapor, that is, water in the gas phase.  The reason this vaporization takes place is that the vapor pressure of water at room temperature is about 20 mm Hg, so it vaporizes into the lower pressure of the vacuum in the bottle.  Standard atmospheric pressure is 760 mm Hg just for comparison.  Eventually the entire bottle will be filled with water vapor above the 34 foot level where the liquid water had risen to.  The water vapor in the bottle will not all be at the same pressure.  It will be highest at the liquid vapor interface, and decrease to its lowest value at the very top of the bottle.  Calculations could easily be done to determine what this pressure would be at the top, but it is not necessary to go to that level of detail to make the point of this thought experiment.  It would certainly be a very very low pressure, much like the very very low pressures (i.e. high vacuum) of space.

So this shows that the simple experiment of sucking water up into a vacuum bottle does not imply that the entire atmosphere would be sucked up or out into space according to the conventional physics model, of which the spherical earth model is a part.

Now realize that what I have just illustrated is not a final answer.  Nothing ever is.  Things can always be looked into in more detail.  I would pose this question.  Is the atmosphere losing any of its gases to space with time?  The answer may be that it is.  But the rate may be very slow.  But this would certainly be a question worth looking into further.  I have not done so yet, but I will.  Perhaps this is something all Earth Model researchers should pursue further.