Rocket engines - from speculations to successful flights

[steve_bank]

Except that to land on an interstellar asteroid requires matching velocities, and doing so without crashing into it requires the same expenditure of rocket fuel as would be necessary without that asteroid. So that method does not get us anything.

There is also the difficulty of finding a suitable asteroid, because once it starts departing, it will not return. Traveling to such an asteroid is also a problem, since one has to reach it before it gets too far away, and one decides to chase it into interstellar space, one has to do what one would do if it was never present.

If such an asteroid was detected sufficiently early, then lassoing it could provide useful acceleration. You might need to use something stretchy, like a bungee-cord, to keep the payload acceleration down to survivable levels; And of course the cord will need to be super strong - perhaps a byproduct of the space elevator research will be a material that is suitable. But predicting its path around the sun, and waiting for it on the other side, shouldn't be too big a task, as long as you detect it (and are able to establish its exact velocity) early enough.

When you speak of survivable levels, you speak of payload. I guess that includes people.

From what I've gathered, two things are remarkable. Humans can both withstand very high acceleration, and humans cannot withstand even moderate acceration. Now that my apparent contradiction is out in the open, let me explain.

Again, from what I've gathered, it's remarkable just how poorly the human body can withstand acceleration. Sure, 2 or 3g's, but beyond that, training is required. Double that, and lots of training and equipment is paramount. 10 g's? Not a chance. Only the elite have a fighting chance.

However, for extremely short periods of time, we can easily withstand 20, 30, 40, 50 or more g's and walk away unscathed. That too is remarkable.

So, for a short moment, high acceration is survivable, but for more than a few seconds, it won't be pretty.

Now, I'm envisioning a whipping action in this bungie cord idea. Maybe there would be a way to harness an object such that tension will be controlled. That's fine, but for how long could we somewhat safely maintain even a 2g acceleration?

I would think we need interim modifications. For instance, 5g's for a period of time with intermittent 1g recuperation breaks.

I think it would be fascinating to solve the problem of surviving high acceleration. Is there (even in science fiction) an idea that teases at this? Altering the space adjacent to us. Something?

The only thing I can think of is for the destination to increase its velocity in our direction.

There is an old idea to use what amounts to a rotating slingshot.

 

[steve_bank]

Fast, we avoid solving the hard problems? Maybe in politics but not sconce. At any point in time we are looking forward into the unknown. The early space program was incredible. Humans did not evolve with any apriori knowledge. It is easy to say in hindsight woulda coulda shoulda.

As Burke pointed out in his 89s series Connections, serendipity and chance unrelated events have been a major part of advance.

All the low hanging fruit has been gotten.

 

[steve_bank]

Propulsion is part of the problem At high velocity stopping or turning is a problem. At .5 C structural forces would be impossibly high. ST invented 'structural integrity fields'. Also space is not empty. Small particles at high speed are catastrophic.

There is a picture of a shuttle window struck by a micrometorite.

 

[fast]

Fast, we avoid solving the hard problems? Maybe in politics but not sconce. At any point in time we are looking forward into the unknown. The early space program was incredible. Humans did not evolve with any apriori knowledge. It is easy to say in hindsight woulda coulda shoulda.

As Burke pointed out in his 89s series Connections, serendipity and chance unrelated events have been a major part of advance.

All the low hanging fruit has been gotten.

It was unfair of me to word it like that. Despite how it sounds, there's no disparaging blame. The choices we make are a function of a number of considerations that lead us down a path of choosing less optimal methods. That was fine, as meeting goals took precedence to solving certain problems.

If we opt for plan B, it's perhaps because of the insurmountable odds of solving the issues that arise from plan A. We're always making goals and finding ways to meet them, and sometimes it's easier to sidestep a barrier to success than it is to divert resources to solving them head on, especially when the solution is unnecessary given other available and viable options are available.

So what's the problem? We're not in a race anymore. We need to back up and punt. Where do we need to prioritize our resources? Go with what works and look for ways to improve? No, we need to scrap the entire system and start fresh. We don't need to have rockets that go off in stages to get someone in outer space. Wouldn't it be quite ludicrous to purchase a new car every time you wanted to go to town?

We need a genuine spacecraft that is capable of repeatedly going to space and back with nothing more than some maintanance. How? Hell, I don't know, but it's a worthy goal of finding out over lassoing passing meteors. That we can get to space is not good enough. Never mind getting into orbit. We need control such that we can go to a specific coordinate and stop (or move nowhere relative to something).

A coordinated effort between an array of technologies is in order. A focus on doing away with the need for huge containers of fuel is a must. We need a breakthrough that will revolutionize space flight. For that to happen, what is required is enormous concerted efforts -- that can be spawned by governments coming together with its people's striving together for a common goal with palatable costs. From the effort alone, there would be technological advances coming out the woodwork benefiting us in ways we weren't even planning for.

In the midst of a sea of nations competing and collaborating to reach some lofty goal (like putting a person on Mars) will unfortunately derail very specific concerted efforts, but a crazier notion like sending someone outside the solar system and back or whatever people can rally behind will pave the way to a new era in planetary travel.

Oh, and something needs to be done about inertia. Repeal the law, galactic reconstruction, something. We need to be able to make maneuvers that the human body cannot withstand with marvel engineering designs that compensate for the effects. It might be easier to locate this unobtainian I keep hearing about, but hey, whatever we do, let's do away with improving the obsolete. The traditional rocket needs to go the way of the Commodore 64.

 

[Treedbear]

...
Oh, and something needs to be done about inertia. Repeal the law, galactic reconstruction, something. We need to be able to make maneuvers that the human body cannot withstand with marvel engineering designs that compensate for the effects. It might be easier to locate this unobtainian I keep hearing about, but hey, whatever we do, let's do away with improving the obsolete. The traditional rocket needs to go the way of the Commodore 64.

You're starting to sound like the pointy-haired boss.

 

[skepticalbip]

...
Oh, and something needs to be done about inertia. Repeal the law, galactic reconstruction, something. We need to be able to make maneuvers that the human body cannot withstand with marvel engineering designs that compensate for the effects. It might be easier to locate this unobtainian I keep hearing about, but hey, whatever we do, let's do away with improving the obsolete. The traditional rocket needs to go the way of the Commodore 64.

You're starting to sound like the pointy-haired boss.

But just think of how great life could be if we really could just ignore the physics of reality and write our own physics to suit our wishes.

Unfortunately, ignoring the physics of reality wastes a hell of a lot of time when trying to solve problems.

 

[Loren Pechtel]

I don't think you and I are considering the same objective here. Why are you jettisoning the tether? Why are you using a long tether, if not to allow you too spool it out from a winch, to translate some (but not all) of the tensile energy into kinetic energy for your spacecraft? In no way am I proposing that the entire energy transferred from the asteroid to the spacecraft needs to be stored in the cable at any one point in time. But even assuming that you DID want to do that - the potential energy stored in the stretched material is proportional to the mass (and therefore to the length) of the bungee cord; Your comparison with chemical explosives is meaningless without some consideration of quantity. A cable massing a hundred tonnes can hold the energy of a tonne of TNT if the material it is made from can hold 1% of the chemical energy stored in TNT, as elastic stress.

You said "bungee". I was working out what would happen--the bungee stretches, absorbing the entire relative velocity of the spacecraft. If the bungee is not vaporized in the process it must then be jettisoned as otherwise it's going to pull the spacecraft back--it impacts the tether point at it's approach velocity.

It appears you actually simply meant a non-stretching cable. You still have the same problems anchoring it, but once you've set the anchor the problem is different. As the tether unwinds from your spool and you slow the energy goes somewhere. Again, several times the TNT equivalent of your spacecraft shows up, but this time as waste heat from your winch. It melts. If it didn't fail the energy liberated would be quite sufficient to vaporize your spacecraft.

 

[Loren Pechtel]

How to stick it to Tsiolkovsky and get anywhere in the solar system:

Lets examine the third item a bit more--the linear motor. Lets go big. Very, very big.

Build one around the moon. The track needs to go above the craft as well as below it so that it doesn't just fly away when you exceed orbital velocity. Since the track is a circle it's effectively of infinite length. G limits still apply but now they show up as centrifugal force. Low lunar orbit is about 1.6km/sec and takes about two hours (interesting tidbit: the period of a low orbit is related only to density. Size is irrelevant.) That's 1/6th g. Lets take this up to 5g--now you're going around in 4 minutes and doing 48 km/sec. That's enough to get you anywhere in the solar system, even an escape orbit.

You still need to be able to stop on arrival but most bodies of interest have an atmosphere for aerobraking. (Even if you're not landing there--you can do an aerocapture on Jupiter and then go to one of it's moons.)

 

[bilby]

I don't think you and I are considering the same objective here. Why are you jettisoning the tether? Why are you using a long tether, if not to allow you too spool it out from a winch, to translate some (but not all) of the tensile energy into kinetic energy for your spacecraft? In no way am I proposing that the entire energy transferred from the asteroid to the spacecraft needs to be stored in the cable at any one point in time. But even assuming that you DID want to do that - the potential energy stored in the stretched material is proportional to the mass (and therefore to the length) of the bungee cord; Your comparison with chemical explosives is meaningless without some consideration of quantity. A cable massing a hundred tonnes can hold the energy of a tonne of TNT if the material it is made from can hold 1% of the chemical energy stored in TNT, as elastic stress.

You said "bungee". I was working out what would happen--the bungee stretches, absorbing the entire relative velocity of the spacecraft. If the bungee is not vaporized in the process it must then be jettisoned as otherwise it's going to pull the spacecraft back--it impacts the tether point at it's approach velocity.

It appears you actually simply meant a non-stretching cable. You still have the same problems anchoring it, but once you've set the anchor the problem is different. As the tether unwinds from your spool and you slow the energy goes somewhere. Again, several times the TNT equivalent of your spacecraft shows up, but this time as waste heat from your winch. It melts. If it didn't fail the energy liberated would be quite sufficient to vaporize your spacecraft.

There is no such thing as a non-stretching cable.

 

[steve_bank]

An insurmountable problem is heat. The shuttle had radiators in the cargo doors. It could not stay up if doors were not opened. The ISS has radiators.

ST never addressed the issue. Even at 99.9% efficient the waste heat of the power source would cook the crew. Place a box filled with air in deep space. Turn on a power source and the temperature will rise if the power exceeds the radiation from the box. It will keep rising until something failed.

 

[steve_bank]

Fast, we avoid solving the hard problems? Maybe in politics but not sconce. At any point in time we are looking forward into the unknown. The early space program was incredible. Humans did not evolve with any apriori knowledge. It is easy to say in hindsight woulda coulda shoulda.

As Burke pointed out in his 89s series Connections, serendipity and chance unrelated events have been a major part of advance.

All the low hanging fruit has been gotten.

It was unfair of me to word it like that. Despite how it sounds, there's no disparaging blame. The choices we make are a function of a number of considerations that lead us down a path of choosing less optimal methods. That was fine, as meeting goals took precedence to solving certain problems.

If we opt for plan B, it's perhaps because of the insurmountable odds of solving the issues that arise from plan A. We're always making goals and finding ways to meet them, and sometimes it's easier to sidestep a barrier to success than it is to divert resources to solving them head on, especially when the solution is unnecessary given other available and viable options are available.

So what's the problem? We're not in a race anymore. We need to back up and punt. Where do we need to prioritize our resources? Go with what works and look for ways to improve? No, we need to scrap the entire system and start fresh. We don't need to have rockets that go off in stages to get someone in outer space. Wouldn't it be quite ludicrous to purchase a new car every time you wanted to go to town?

We need a genuine spacecraft that is capable of repeatedly going to space and back with nothing more than some maintanance. How? Hell, I don't know, but it's a worthy goal of finding out over lassoing passing meteors. That we can get to space is not good enough. Never mind getting into orbit. We need control such that we can go to a specific coordinate and stop (or move nowhere relative to something).

A coordinated effort between an array of technologies is in order. A focus on doing away with the need for huge containers of fuel is a must. We need a breakthrough that will revolutionize space flight. For that to happen, what is required is enormous concerted efforts -- that can be spawned by governments coming together with its people's striving together for a common goal with palatable costs. From the effort alone, there would be technological advances coming out the woodwork benefiting us in ways we weren't even planning for.

In the midst of a sea of nations competing and collaborating to reach some lofty goal (like putting a person on Mars) will unfortunately derail very specific concerted efforts, but a crazier notion like sending someone outside the solar system and back or whatever people can rally behind will pave the way to a new era in planetary travel.

Oh, and something needs to be done about inertia. Repeal the law, galactic reconstruction, something. We need to be able to make maneuvers that the human body cannot withstand with marvel engineering designs that compensate for the effects. It might be easier to locate this unobtainian I keep hearing about, but hey, whatever we do, let's do away with improving the obsolete. The traditional rocket needs to go the way of the Commodore 64.

Pie in the sky so to speak. You mean like getting the Russians, Europeans, Chinese, and Americans to deeply collaborate over a long period?

 

[bilby]

An insurmountable problem is heat. The shuttle had radiators in the cargo doors. It could not stay up if doors were not opened. The ISS has radiators.

ST never addressed the issue. Even at 99.9% efficient the waste heat of the power source would cook the crew. Place a box filled with air in deep space. Turn on a power source and the temperature will rise if the power exceeds the radiation from the box. It will keep rising until something failed.

It's a problem that must be accounted for, for sure; But, as the radiators on the ISS and in the shuttle's cargo doors demonstrate, it is not an insurmountable problem.

 

[steve_bank]

An insurmountable problem is heat. The shuttle had radiators in the cargo doors. It could not stay up if doors were not opened. The ISS has radiators.

ST never addressed the issue. Even at 99.9% efficient the waste heat of the power source would cook the crew. Place a box filled with air in deep space. Turn on a power source and the temperature will rise if the power exceeds the radiation from the box. It will keep rising until something failed.

It's a problem that must be accounted for, for sure; But, as the radiators on the ISS and in the shuttle's cargo doors demonstrate, it is not an insurmountable problem.

It depends on how much heat of course. Scaling up to a ST spaceship with a large crew may be a problem.

 

[lpetrich]

The problem is with size scaling: the square-cube law. Small organisms can easily obtain nutrients and excrete wastes by diffusion, but that is impractical for large ones. That is why circulatory systems and similar such systems evolved. Fluid transport is a much more efficient transport mechanism than diffusion, and though these systems still have diffusion, it is over very small distances.

So a large spaceship will need very large radiators.

 

[lpetrich]

We need a genuine spacecraft that is capable of repeatedly going to space and back with nothing more than some maintanance.

The Space Shuttle was an attempt at that, but it failed. It required so much maintenance that it was not very competitive with traditional expendable rockets. But SpaceX has apparently succeeded with its first stages.

We need a breakthrough that will revolutionize space flight.

(proposal of a massive research project)

Looking at my OP's link's table, it is evident that there has already been a lot of research on spacecraft-propulsion technologies. But most of them are (1) rather speculative and/or (2) only suited for outer-space duty.

Oh, and something needs to be done about inertia. Repeal the law, galactic reconstruction, something. We need to be able to make maneuvers that the human body cannot withstand with marvel engineering designs that compensate for the effects. It might be easier to locate this unobtainian I keep hearing about, but hey, whatever we do, let's do away with improving the obsolete. The traditional rocket needs to go the way of the Commodore 64.

I'll believe it when I see it.

 

[lpetrich]

I checked, and  100 Year Starship is for research into interstellar spaceflight.

Under  Nuclear pulse propulsion is  Project Orion (nuclear propulsion) and  Project Daedalus and  Icarus Interstellar and  Project Longshot.

The Orion drive involves shooting nuclear-fission bombs backward and then being pushed forward by the bombs' explosions' blasts. Some of its researchers considered launching from the Earth's surface, but that seems like an awful idea to me. It may be possible to assemble an Orion-drive spacecraft in low Earth orbit, but exploding nuclear bombs there might create some nasty Electromagnetic Pulse. So I suspect that an Orion drive will only be started well away from the Earth.

The other three involve nuclear fusion, doing inertial confinement fusion on small pellets. This involves focusing some high-power laser pulses on a pellet, something that makes it implode and cause fusion in it. I'll call that the Daedalus drive, after where it was first proposed: Project Daedalus – Interstellar Mission. Icarus Interstellar is a successor project. Inertial confinement fusion has been worked on, and while one can get more nuclear-fusion energy out of a pellet than the laser energy put into it, the whole system has yet to demonstrate that it can power itself, and its lasers and other apparatus do not seem as rugged as some nuclear-fission reactors can be. So we are a long way from a workable Daedalus drive.

 

[lpetrich]

The British Interplanetary Society | From imagination to reality
Tau Zero Foundation - Pioneering Interstellar Flight
Icarus Interstellar

From Methods of Interstellar Propulsion | Tau Zero Foundation:

Technology Based on Accrued Physics

• Sails
  • Solar
  • Laser
  • Maser
  • Magnetic
  • Antimatter ablated (hBar)
• Rockets requiring onboard propellant
  • Chemical
  • Electric
    • Electrostatic
    • Electromagnetic
  • Nuclear
    • External Nuclear pulse (Orion)
    • Nuclear Fission
    • Nuclear Fusion (Daedalus/Icarus)
    • Antimatter Catalyzed Fusion (AIM Star)
    • Antimatter-Matter
• Rockets without onboard propellant
  • Bussard interstellar (fusion) ramjet
  • Bussard Buzz-Bomb [J. Kare]

These include everything listed in the big table in  Spacecraft propulsion: existing ones (chemical, some electric), under-development ones (solar sails, some electric), and subjects of feasibility studies (Orion, Daedalus, Bussard).

It must be noted that the electric engines must be powered by something -- solar panels or nuclear reactors. The electromagnetic ones include:

• Hall effect: crossed electric and magnetic field generate an ion current.
• Plasma engines: something similar, with some of them having more thrust.

Goals that Require Physics Advancements

• Non-propellant Space Drives, by approach discipline:
  • Idea Zombies – Bad ideas that won’t stay in their graves – and Common Misinterpretations to Avoid
  • Coupling of Fundamental Forces
  • Inertial Frame Kinematics
  • Tachyon Rocket [J. Cramer]
  • Quantum Physics
  • General Relativity using Riemannian Geometry
• Faster-Than-Light Flight
  • Brute Fast (Analogous to Cerenkov radiation)
  • Tachyonic conversions
  • Quantum Nonlocality
    • Entangled & Teleported States
    • Tunneling
    • Infinite Improbability Drive (fiction)
    • Translocation (fiction)
  • Hyperlightspeed Hypomatter (Analogous to how Light breaks the sound barrier)
  • Hyperspace (fictional version of that term)
  • Spacetime Engineering with General Relativity using Riemannian Geometry
    • Traversable Wormholes
    • Warp Drives
      • Alcubierre, Warp Drive (Expansion/Contraction)
      • Van Den Brock, Thin wall Alcubierre
      • Krasnikov, Warp Tunnel
      • Natario, Slipping

None of these are in that Wikipedia article's big table, though some of them are mentioned below that table.

 

[lpetrich]

Icarus Interstellar - Projects

• Project Icarus: To Design a Theoretical Interstellar Spacecraft
• Project Hyperion: Manned Interstellar Flight
• Project Bifrost: Nuclear Space Technologies
• Project Forward: Beamed Propulsion
• Project Persephone: Living Architectures
• Project Tin Tin: Interstellar nano mission to Alpha Centauri
• Project XP4: X-Physics Propulsion and Power Project
• Project Astrolabe: Navigating the Future of Civilization
• Project Voyager: Mapping a Path to the Stars

Beamed propulsion?  Breakthrough Starshot proposes a version of that: spacecraft with sails that would be illuminated by laser beams coming from here on the Earth. That proposal has serious problems, like aiming the lasers and keeping their beams from spreading out too much. Another sort of beamed propulsion is for a laser beam to power rocket engines, and it also has those problems.

 

[lpetrich]

I remember once reading the British Interplanetary Society's report on Project Daedalus. All of it seemed straightforward except for the part about the control software. It seemed very hand-wavy to me, with its mentioning computers that run high-level languages directly. The idea of a  High-level language computer architecture was popular in the 1960's and 1970's, but fell out of favor in the 1980's.

It expands on  Microcode, a common CPU-design practice, where instructions received by a CPU make it run short programs inside of it.

An automated interstellar spacecraft would likely need some very good AI to do maintenance and repairs and the like.


Now something about the effective exhaust velocity. It is (backward momentum emitted) / (mass emitted). The mass includes the mass of radiation from heat-rejection radiators, using E = m*c². Thus, imagine that one has a laser drive. One might expect its EEV to be c, but the laser must be powered, and if its powerplant rejects heat by radiating infrared light in all directions, then its EEV will be (fraction of energy in laser light) * c.

One can get a bit of momentum from the waste heat by making one side of the radiators face rearward, with the other side having insulation on it. The radiators will then radiate much more rearward than forward, though if they radiate isotropically (same in all directions) rearward and not forward, they will make an EEV of (1/2)*c.


Here are some rocket equations. They were derived ignoring gravity and environment friction like air resistance. They find the velocity change v as functions of the exhaust velocity ve, the initial mass mi, and the final mass mf. The logarithm is the natural one.

Tsiolkovsky's rocket equation (Newtonian): v = ve*log(mi/mf)

Ackeret's rocket equation (relativistic): v = c * tanh( (ve/c)*log(mi/mf) ) = c * ( (mi/mf)^(2ve/c) - 1 ) / ( (mi/mf)^(2ve/c) + 1 )

 

[Loren Pechtel]

I don't think you and I are considering the same objective here. Why are you jettisoning the tether? Why are you using a long tether, if not to allow you too spool it out from a winch, to translate some (but not all) of the tensile energy into kinetic energy for your spacecraft? In no way am I proposing that the entire energy transferred from the asteroid to the spacecraft needs to be stored in the cable at any one point in time. But even assuming that you DID want to do that - the potential energy stored in the stretched material is proportional to the mass (and therefore to the length) of the bungee cord; Your comparison with chemical explosives is meaningless without some consideration of quantity. A cable massing a hundred tonnes can hold the energy of a tonne of TNT if the material it is made from can hold 1% of the chemical energy stored in TNT, as elastic stress.

You said "bungee". I was working out what would happen--the bungee stretches, absorbing the entire relative velocity of the spacecraft. If the bungee is not vaporized in the process it must then be jettisoned as otherwise it's going to pull the spacecraft back--it impacts the tether point at it's approach velocity.

It appears you actually simply meant a non-stretching cable. You still have the same problems anchoring it, but once you've set the anchor the problem is different. As the tether unwinds from your spool and you slow the energy goes somewhere. Again, several times the TNT equivalent of your spacecraft shows up, but this time as waste heat from your winch. It melts. If it didn't fail the energy liberated would be quite sufficient to vaporize your spacecraft.

There is no such thing as a non-stretching cable.

Of course every cable stretches. I meant "non-stretching" as in the stretching isn't enough to be of practical value. You wouldn't use a steel wire for a bungee jump!