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How to propel one's spacecraft

lpetrich

lpetrich

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Wikipedia has a rather comprehensive article on that:  Spacecraft propulsion

I looked in Encyclopedia Britannica (that venerable encyclopedia's online site) and Citizendium (a Wikipedia alternative with expert review of its articles) I could not find anything quite like it.

I looked for the Encyclopedia Americana and Collier's Encyclopedia, but they have no online sites.

That Wikipedia article lists methods by
  • Effective exhaust velocity (specific impulse)
  • Thrust
  • Engine-operation duration
  • Maximum velocity change (delta-v)
  •  Technology readiness level
That last one is a measure of how much R&D will be necessary to get a method to work. From the least ready to the most ready:
  1. Basic principles observed
  2. Technology concept formulated
  3. Experimental proof of concept
  4. Technology validated in laboratory conditions
  5. Technology validated in operational environment (in vacuum)
  6. Prototype demonstrated in laboratory conditions (on the ground)
  7. Prototype demonstrated in operational environment (in space)
  8. Flight qualified
  9. Flight proven
I'd created a previous thread, Rocket engines - from speculations to successful flights but I'd like to go into more detail.
 
I assume Newton's Laws apply. Detaied discusinwuld invole chenistry which I am wek in, thermodynamics, which I know something about same with fluid mechanics, and Newtinia mechanics.


IOW, I am not a rocket scientist. That being said it comes down to f=ma.

http://web.mit.edu/16.00/www/aec/rocket.html

NASA ion engine.
https://www.nasa.gov/centers/glenn/about/fs21grc.html

Historical timeline

https://www.nasa.gov/centers/glenn/about/history/timeline.html

The shuttle engine, it was complex.

https://en.wikipedia.org/wiki/RS-25
https://www.nasa.gov/sites/default/files/files/Space_Shuttle_Main_Engine_Drawings.pdf
 
Last edited:
https://en.wikipedia.org/wiki/Specific_impulse

Looks specific impulse relates to how much fuel energy can be converted to dv. More mass less fuel converted to dv.

s distance
ds/dt velocity
dv/dt aceleration
da/dt jerk rate of chamnge of acceleration

https://en.wikipedia.org/wiki/Jerk_(physics)
https://en.wikipedia.org/wiki/Fourth,_fifth,_and_sixth_derivatives_of_position

Thrust is equal and opposite reaction. For gas particles hitting a surface pressure, Newtons/m^2, is derived using statistical mechanics.
https://en.wikipedia.org/wiki/Thrust


I would think max dv equates to max dE/dt which is watts.

No different than a car. You are are at 1km/hr, what determines how fast you can cahnge to 1.5km/hr.\

A gas car engine is fundamentally the same as a rocket engine. The difference is the gas from combustion in the pistons is contained during combustion.
 
There are plenty of tradeoffs in design.

There are several things that one might want to have:
  • High EEV: that means less propellant for some velocity change (delta-v)
  • High thrust: that means high acceleration, like for departing from a planet
  • High run time: that also helps in getting high delta-V
  • Mechanical simplicity: easier for avoiding maintenance
  • Easy storage of propellants
  • Operational convenience, like the ability to stop and restart

The highest level, 9 (flight proven) has both chemical and electric rocket engines.


The chemical ones are solid-fuel and liquid-fuel engines, which work by combustion, and monopropellant ones, which work by decomposing their propellant, usually hydrazine.

Solid-fuel engines are mechanically simple, and are the oldest kind of rocket engine. They can have an EEV up to 3.0 km/s.

Liquid-fuel engines are mechanically much more complicated, by they can achieve much higher EEV's. Of those that have flown, the champion is H2-O2, at 4.4 km. But H2 has a very low boiling point, 20 K. A common alternative, kerosene-O2 is at 3.3 km/s, but O2 has a boiling point of 90 K. One can use instead of oxygen some oxidizer that is liquid at room temperatures, like fuming nitric acid or nitrogen tetroxide, but such oxidizers tend to be very corrosive. One can get an EEV of 3.1 km/s, however.

Hydrazine decomposition gives an EEV of 2.2 km/s.

This is less than the orbit velocity for low Earth orbit, 7.8 km/s, so rockets need sizable mass ratios and more than one stage. But chemical engines have some pluses. They can work in air, and they can produce large thrusts. Here are the champions in initial thrust:
  • US Saturn V first stage, 5 liquid F-1: 35 meganewtons (13 flights, all successful)
  • Soviet N1 first stage, 30 liquid NK-15: 45.4 MN (4 flights, all failed)
  • Soviet Energia initial: 4 solid RD-170, 4 liquid RD-0120: 35 MN (2 flights, all successful)
  • US Space Shuttle initial: 2 solid, 3 liquid RS-25: 30 MN (135 flights, 1 launch failure)
Chemical rocket engines are limited by chemical-bond strengths, and H2-O2 is close to the best case for them. One could do better with fluorine, but it is toxic and corrosive and it does not give much improvement.

-

The electric engines are ion engines, using either electrostatic or Hall-effect propulsion ( Gridded ion thruster ,  Hall-effect thruster).

"As of 2009, Hall-effect thrusters ranged in input power levels from 1.35 to 10 kilowatts and had exhaust velocities of 10–50 kilometers per second, with thrust of 40–600 millinewtons and efficiency in the range of 45–60 percent."

Of the electrostatic ones, the champions:
  • Dawn spacecraft, 3 NSTAR: EEV 30 km/s, each one thrust 90 millinewtons
  • BepiColombo spacecraft, 4 QinetiQ T6: EEV 42 km/s, each one 145 mN
The Dawn spacecraft's engines operated for 5.9 years, 54% of the spacecraft's total mission time, and they achieved a total delta-v of 11.49 km/s.

BepiColombo is on its way to Mercury. It was launched in 2018, and it should go into orbit around that planet in 2025.

-

So we have a choice of:
  • EEV high, thrust low, vacuum-only
  • EEV low, thrust high, air-capable
 
Going to 8 (flight qualified), we find resistojet and arcjet engines. They work by electrically heating a propellant material.

Next down is solar sails. They are listed as 9 and 6, but I'd place them as 7 (prototype demonstrated in space). That is because of  IKAROS is the most successful one, and it achieved a delta-v of 100 m/s over half a year: IKAROS and Extended Solar Power Sail Missions for Outer Planetary Exploration - 2011

Looking at 6 (prototype demonstrated on the ground), I find nuclear-thermal engines like NERVA: heating hydrogen with a nuclear reactor.

Another one is "mass drivers", linear-motor guns.

 Tether propulsion the article lists as 6, but from the looks of it, it seems more like 7.

Also at 6 is an air-augmented rocket, making a rocket that is partially air-breathing at low altitudes, to save on oxidizer mass. Likewise, a liquid-air-cycle engine. That one would get its oxidizer by liquefying air and extracting that air's oxygen. It's intended for airplane-to-space systems.

Going down to 5 (component validated in vacuum), I find some more ion engines, or more precisely plasma engines. These are some more electric engines.

One of them is the variable-specific-impulsemagnetoplasma rocket (VASIMR), designed to switch between high EEV / low thrust and low EEV / high thrust. The first mode would be for interplanetary space and the second one for getting into and out of orbit.

At 4 (component validated in vacuum in the lab) is nuclear reactors for supplying electricity to electric engines.

But the Soviet Union had flown some 35 nuclear reactors in satellites (  List of nuclear power systems in space), 33 of their BES-5 and 2 of their TOPAZ-I. It's not clear how much they were used to power whatever electric rocket engines their satellites may have had. But if they had, that would bump them up to at least 7 and likely 9.

Another lab-demonstrated technology is solar-thermal rocket engines.
 
So far, I have discussed propulsion mechanisms that have had some physical manifestation. So I now turn to those that have only been the subject of theoretical studies.

Here are some that are at 3 (validated proof-of-concept). They are presumably far enough along to be worthy of lab tests.

Project Orion was a proposed nuclear-pulse drive that uses nuclear bombs.

A space elevator is a super tall tower that extends to synchronous-orbit distance or beyond. Extending beyond that distance would be good for providing force to pull it upward. A space elevator would be impractical for the Earth, because it would require some super material that is only borderline feasible. But space elevators are likely feasible for many smaller celestial bodies.

Also electric and magnetic sails. An electric sail is an electrically-charged cable that works by deflecting solar-wind ions. A magnetic sail uses a magnetic field to deflect solar-wind ions.

Also launch loops and orbital rings. A launch loop is a linear-motor track that rises from the ground above the atmosphere and then returns to the ground. It would be used to send spacecraft into orbit aboard sleds on the track. When a sled is at highest point and full speed, it would release its spacecraft. Orbital rings are somewhat similar.

Beam power is shooting a laser beam at a spacecraft to heat its propellant.
 
With that kind of thrust, how long does it take to get to say Jupiter?

It seems to me that for a viable commercial application for space travel, we need to be getting to that distance in a matter of say a few months or so. That might make asteroid mining practical. We could send a team out there, get the stuff, and get back in less than six months. Less than an ISS deployment.

Now if only we could adequate radiation shielding. Water?

https://www.newscientist.com/article/dn23230-mars-trip-to-use-astronaut-poo-as-radiation-shield/
 
lpetrich said:
Chemical rocket engines are limited by chemical-bond strengths, and H2-O2 is close to the best case for them. One could do better with fluorine, but it is toxic and corrosive and it does not give much improvement.
Click to expand...

Does it offer any improvement?

From Wikipedia I see the H-F bond energy as 569 kJ/mol and the H-O bond energy as 497 kJ/mol. You get two bonds per water molecule vs one bond per hydrogen fluoride for the same molecular mass. Wouldn't that make the hydrolox engine better?
 
Loren Pechtel said:
From Wikipedia I see the H-F bond energy as 569 kJ/mol and the H-O bond energy as 497 kJ/mol. You get two bonds per water molecule vs one bond per hydrogen fluoride for the same molecular mass. Wouldn't that make the hydrolox engine better?
Click to expand...
You'll also need the H-H, O-O, and F-F bond energies. Or you can look up heats of formation in the NIST WebBook
 
We next go down even further to 2 (technology concept formulated). They presumably need a lot of work before they would be ready for testing.

Nuclear pulse propulsion (Project Daedalus), uses inertial-confinement fusion. It works by focusing pulses of laser light onto small pellets, making the outer layers explode and crushing the inner layers, thus making nuclear fusion. The pellet's expanding gases would then be deflected by magnetic fields, thus transmitting their momentum to the rocket engine.

Though ICF has been researched for several years, it is still far from achieving energy breakeven, and the big lasers it uses don't seem very suitable for spacecraft duty.

Several other types of nuclear-fusion reactor have also been researched, like magnetic confinement (tokamak, etc.). They could either be used for direct drive, like in Project Daedalus, or indirect drive, to power electric rocket engines.

I remember once read the Project Daedalus feasibility study. All of it looked at least halfway plausible except for the stuff on the control computers. That struck me as pure handwaving. It talked about hardware that directly understands high-level programming languages, for instance. The real problem here is the level of AI that an interstellar spacecraft's control computers will need. It may be hard to avoid strong AI.


Also at this level is antimatter. This is not bizarro matter but just like ordinary matter with some properties reversed in sign. This reversal cancels out in what determines its macroscopic properties, so one can use data from the corresponding ordinary matter to get an idea of its properties.

Antimatter is hard to make in quantity. One needs a *lot* of energy to do so. Part of that energy is what's involved in making it: pair-production reactions, where one needs to supply all the energy in the mass of an ordinary particle and its antiparticle. Pair production is a great demonstration of Einstein's famous equation, E = m*c^2. A further problem is the low efficiency of making it, something like 10^(-3) of the particle-beam energy for positrons (antimatter electrons) and 10^(-8) for antiprotons. A further problem is the energy efficiency of the particle accelerators needed to make those beams, and it's hard for me to find good numbers on that. One doesn't need very big accelerators, so one can use some medical linac (linear accelerator) as a reference.

Antimatter is also very hard to store, because it must be kept from reacting with ordinary matter. Their particles annihilate with each other, making energetic photons and pions and the like. Positions electrically repel each other, as electrons do, and likewise for antiprotons, like protons. Antineutrons don't repel each other, but they decay at the same rate as ordinary neutrons. Hydrogen is the simplest combination that is both stable and electrically neutral, so one can consider making antihydrogen. But it will have the same properties that ordinary hydrogen has, meaning that one has to chill it to a few K to keep it from evaporating.

One can try to make heavier elements by irradiating antihydrogen with antineutrons, but there are two stability barriers on the way, at 5 and 8 nucleons. One won't be able to surmount them by adding antineutrons. One must smash together antinuclei, electrostatic repulsion and all. But anticarbon should be refractory enough to easily store, at least by antimatter standards.
 
Finally, the Bussard ramjet. It works by collecting interstellar hydrogen with a magnetic field, and then fusing it to power itself and to propel itself.

That Wikipedia article has none with level 1 (basic principles observed and reported)
 
Speed comes down to mass and energy density of fuel and conversion efficiency.

To change velocity the equivalent to the change in kinetic energy has to be supplied plus conversion efficiency. Go faster the craft takes on more kinetic energy. Then you have to decelerate at the end of trip to lose kinetic energy.

The first questions for a propulsion method is how much does the fuel weigh and what is the energy density, and what is the conversion efficiency.

The the mundane issues of food, water, and air.
 
NASA went into detail:
NASA's Technology Readiness Level Definitions

I'm quoting here the definition, the hardware description, and the exit criteria. I'm leaving out the software description, because software engineering is a separate issue.
  1. Basic principles observed and reported. - Scientific knowledge generated underpinning hardware technology concepts/applications. - Peer reviewed publication of research underlying the proposed concept/application.
  2. Technology concept and/or application formulated. - Invention begins, practical application is identified but is speculative, no experimental proof or detailed analysis is available to support the conjecture. - Documented description of the application/concept that addresses feasibility and benefit.
  3. Analytical and experimental critical function and/or characteristic proof of concept. - Analytical studies place the technology in an appropriate context and laboratory demonstrations, modeling and simulation validate analytical prediction. - Documented analytical/experi-mental results validating predictions of key parameters.
  4. Component and/or breadboard validation in laboratory environment. - A low fidelity system/component breadboard is built and operated to demonstrate basic functionality and critical test environments, and associated performance predictions are defined relative to the final operating environment. - Documented test performance demonstrating agreement with analytical predictions. Documented definition of relevant environment.
  5. Component and/or breadboard validation in relevant environment. - A medium fidelity system/component brassboard is built and operated to demonstrate overall performance in a simulated operational environment with realistic support elements that demonstrates overall performance in critical areas. Performance predictions are made for subsequent development phases. - Documented test performance demonstrating agreement with analytical predictions. Documented definition of scaling requirements.
  6. System/sub-system model or prototype demonstration in an operational environment. - A high fidelity system/component prototype that adequately addresses all critical scaling issues is built and operated in a relevant environment to demonstrate operations under critical environmental conditions. - Documented test performance demonstrating agreement with analytical predictions.
  7. System prototype demonstration in an operational environment. - A high fidelity engineering unit that adequately addresses all critical scaling issues is built and operated in a relevant environment to demonstrate performance in the actual operational environment and platform (ground, airborne, or space). - Documented test performance demonstrating agreement with analytical predictions.
  8. Actual system completed and "flight qualified" through test and demonstration. - The final product in its final configuration is successfully demonstrated through test and analysis for its intended operational environment and platform (ground, airborne, or space). - Documented test performance verifying analytical predictions.
  9. Actual system flight proven through successful mission operations. - The final product is successfully operated in an actual mission. - Documented mission operational results.
Click to expand...
 
ESA: Technology Readiness Levels for Space Applications
  1. Basic principles observed and reported - Lowest level of technology readiness. Scientific research begins to be translated into applied research and development.
  2. Technology concept and/or application formulated - Once basic principles are observed, practical applications can be invented and R&D started. Applications are speculative and may be unproven.
  3. Analytical and experimental critical function and/or characteristic proof-of- concept - Active research and development is initiated, including analytical / laboratory studies to validate predictions regarding the technology.
  4. Component and/or breadboard validation in laboratory environment - Basic technological components are integrated to establish that they will work together.
  5. Component and/or breadboard validation in relevant environment - The basic technological components are integrated with reasonably realistic supporting elements so it can be tested in a simulated environment.
  6. System/subsystem model or prototype demonstration in a relevant environment (ground or space) - A representative model or prototype system is tested in a relevant environment.
  7. System prototype demonstration in a space environment - A prototype system that is near, or at, the planned operational system.
  8. Actual system completed and “flight qualified” through test and demonstration (ground or space) - In an actual system, the technology has been proven to work in its final form and under expected conditions.
  9. Actual system “flight proven” through successful mission operations - The system incorporating the new technology in its final form has been used under actual mission conditions.
Click to expand...
That document then goes into a lot of detail.

I'm disappointed that no worked examples were provided in either the NASA or the ESA documents that I've found.
 
I see that as basic engineering and technology development and design, but then that is what I did for a living so it is obvious to me.

If you are looking for some insight into the process, how does one develop a mathematical proof for something unfamiliar? The

How did Fourier come u with his series or Maxwell EM waves?

To me it is all the same process. Part of it is trial and error, and serendipity.

Look at the rapid development of aircraft from Wright Brothers to Boeing. A long series of experiments and ideas some wokd some dd not.

Aircrft development included catastrophic failures and learning from it.

The first British jet failed in flight due to repeated d pressurization and depressurization leading to metal fatigue.

In the 80s I watched a Boeing fuselage on a giant structure being cyclically pressurized and depressurized while the fuselage is twisted and bent.

Lessons learned. That is how things and knowledge develop. I read an abstract of a NASA relibility study on the shuttle, they predicted catastrophic failure. Nobody ca see all ends as complexity grows.

Today simulations have taken the place of a lot of physical testing.

Theory is part of it but not all of it.
 
You are a mathematician with theoretical knowledge and experience. You are faced with a proof.

Based on knowledge and experience you come up with a first attempt. It fails. You figure out why it failed and formulae a modified approach.

'The Scientific Method'.

Same with computers or rocket engines.
 
If I were off by myself looking at a rocket engine and spaceship the first thing I’d do is bound the problem, look for obvious show stoppers. 1st order paper napkin analysis.

At the top of the list is energy. What woud the peak demand be for the engine. For a change in velocity the total energy is 0.5*m*dv^2. The peak demand is how fast you want to make the change, peak acceleration. You woud want to limit peak acceleration to say 1.5g for comfort and not stressing the ship. You may want an man emergency switch in case yiu have to dodge an asteroid fast....like the Boy Scout saying says, be prepared.

If you are bopping around the solar system y0u want some room. The shuttle empty weight was about 78,000 kg. Changing velocity by say 1000ms , pedal to the metal, 0.5* kg*dv^2. Total energy required .

Next comes engine efficiency and heat. How many m^2 of rasidiators do you need to limit the transient temperaturerise during acceleration to a safe level. Not knowing anything else assume efficiently of 50% as a staring point. 50% of consumed energy goes to heat, 50% to acceleration. Look at the ISS cooling system as a reference point.

Next is how much energy is needed to operate the engine and where does it come from? Nuclear?

Finally fuel. For a given engine what is the mass and energy density. Hw much do you need to carry between fill ups.

If I were doing this kind of thing for real I’d put it into a speread sheet and do what ifs. If it looked possible I’d have a peer review and get inputs, I may have missed something. Then work on a detailed analysis and a written specification.

That’s the general way I worked problems. Sometimes it looks good, sometimes it looks bad. Rerun the numbers sometimes it works out sometimes it doesn’t.

The best way to get around in space is to get rich and start a company to build a rocket and spaceship for you.
 
Who writes the book?

It can be structured. I was out at Boring in Seattle in the 90s. We made avioincs that went on the 777 and a 757 version.

I have been through military and aerospace development programs and qualifications, but that is not what I am talking about. Feasibility comes before proof of concept. Rough order of magnitude to determine feadability.

There is still trial and error as part of development although simulation has replaced a lot of it. In his book Yeager talked about his experience on the X plane program. Incremental increase in speed on the way to supersonic. A problem ocurs. Stop, come up with a fix , test it, and start inching up again. The term X Factor came out of Edwards. It represented unknown variables that could appear and kill a test pilot.

Obviously at Boeing it not not be a lone person, it wooed be a team working to a structured development plan. They have reduced development to a structured process by necessity. Accountability. And recently their system failed miserably.

The OP wanted to talk about development and details.

Regardless of how it is structured development is not always a linear logical step by step process. If it was it would be reduced to an algorithm.

An example of a failure is a fusion reactor. Multiple approaches by competent people and no working solution.
 
Deceleration, at least naively, might be as big a problem as acceleration. Getting to Sirius in 300 years will do little good if we're racing at 30,000 km/sec when we get there and can only wave as we sprint past.

By accurately aiming the spacecraft toward the Star (but not on an exact collision course) can't we do a hair-pin turn, and repeat the manoeuvre a few times to get a less eccentric orbit?

I imagine the motive force for the steering to be provided by some sort of magnetic sail. And with such a sail near a star, can the need for ejecting matter for impulse be avoided? Can't momentum be exchanged with the star via magnetic interaction?
 
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