Part Submarine... All Resuable Scifi SSTO

[Guest]

I should note that turning matter into antimatter is not possible. It would violate the law of baryonic number conservation, among others, so for every bit of antimatter produced, you need to make the same amount of matter. Antimatter is not a means of energy production, but of storage. It can offer an incredible energy density, but you need to pair it with a fusion or fission based energy production.

On 11/27/2019 at 11:05 PM, kerbiloid said:

It does not produce pure photons, how many times was it spoken.

Electron-positron anihilation does. Fun fact: a gamma ray with enough energy will turn into an electron-positron pair at random, and annihilate right back, giving the exact same photon. There's some really fun quantum physics involved in the process. 

Baryon annihilation (such as proton-antiproton) produces all kinds of fun stuff, but nobody says you have to use that. Antihydrogen is more convenient than electron gas, but if you're not using much of it and are big on making this clean, positrons are the way to go.

[kerbiloid]

4 hours ago, Dragon01 said:

Electron-positron anihilation does. Fun fact: a gamma ray with enough energy will turn into an electron-positron pair at random, and annihilate right back, giving the exact same photon. There's some really fun quantum physics involved in the process. 

Baryon annihilation (such as proton-antiproton) produces all kinds of fun stuff, but nobody says you have to use that. Antihydrogen is more convenient than electron gas, but if you're not using much of it and are big on making this clean, positrons are the way to go.

Obviously when somebody is speaking about antimatter used as a fuel, he means a storable and dense form of matter rather than generated particle beams of electron-positron pairs.

Edited November 29, 2019 by kerbiloid

[Guest]

Not so obviously. You're jumping to conclusions, big time. Positrons can be stored perfectly well by themselves (though admittedly, the best way to do it is a particle beam) and are suited to use as fuel. They have poor density and their positive charge complicates things, but these problems are hardly unsolvable, especially with the minute amounts of antimatter that most non-relativistic antimatter rocket designs require. Anti-hydrogen gives you easier storage, but the annihilation is messy, not to mention it produces neutrinos, making it inherently less efficient. Positrons are also somewhat easier to make than antiprotons.

[farmerben]

Future spacecraft designers, recognizing the impossibility of using a gas expansion thrust cycle, decide to develop a gamma ray laser nozzle instead.  Although the wavelength of gamma photons is less than the nucleus of any atom, the distance between two sheets is measurable below that length.  Layers of vacuum and material can create constructive reflections.  

Future astronauts realize it is far to dangerous to aim their engines at their home planet, so they only thrust parallel to the surface.  Unfortunately this is perceived as an act of war by most of the intelligent aliens in the galaxy.  

[kerbiloid]

2 hours ago, farmerben said:

Future astronauts realize it is far to dangerous to aim their engines at their home planet, so they only thrust parallel to the surface.  Unfortunately this is perceived as an act of war by most of the intelligent aliens in the galaxy.  

If start sending fly-by relativistic probes to other worlds, sometimes we can receive an answer from some survivor from a hit planet.

Edited November 30, 2019 by kerbiloid

[sevenperforce]

On 11/27/2019 at 5:05 PM, kerbiloid said:

And no, Orion/pusher plate is not an atmospheric engine. And not an underwater one. It probably can survive an atmospheric launch, but it does not use shockwaves for propulsion, it needs them as much as a car engine needs detonation (see "octane number", etc).
It is propelled with gaseous tungsten flow. The atmosphere doesn't help it, it drags the tungsten jet and dissipates its energy. In exchange it produces shockwaves killing the engine.

Orion is more efficient in atmo.

[kerbiloid]

1 minute ago, sevenperforce said:

Orion is more efficient in atmo.

How?

[sevenperforce]

2 minutes ago, kerbiloid said:

How?

Atmosphere which flows between the pusher plate and the tungsten jet is superheated in the explosion and increases the reaction mass.

[kerbiloid]

38 minutes ago, sevenperforce said:

Atmosphere which flows between the pusher plate and the tungsten jet is superheated in the explosion and increases the reaction mass.

This part of air just slows down the tungsten jet and produces a shockwave compressing the construction from sides.

A fireball radius in lower atmosphere, for midair blast: r,m ~= 59 * yield,kt ^0.4.

So, for a kiloton-class charge it's ~100 m.
So, it's nearly equal to the Orion's reaction distance.

Air density ~1.2 kg/m3.
So, it contains ~120 kg of air per m² of cross-section.

The Orion charge mass is several hundred kg. It's mostly the charge itself and the uranium radiation case.
The thin tungsten membrane (the only part of the charge pushing the plate) is, estimated, ~pi * (0.5 m)² / 4 * 0.01 m * 20 000 kg/m³ ~several tens kilograms of tungsten.

In the lower atmosphere it should pierce the air column of twice greater mass.
So, instead of hitting the plate, it will first dissipate its energy by pushing through the air, will spread and get wider than the plate, so the total energy it can transfer will be probably twice less than in vacuum, where nothing stops it.

Instead, the Xray will in microseconds heat up the air between the charge and the plate, and the waste heat of the blast which is just radiated aside in vacuum will produce a kilokelvins hot fireball right next to the pusher plate.
And if the charge yeld is a little greater (tens-hundreds kt), also around the ship itself.

The fireball will cause:
firstly a shockwave which will crash the pistons and liquify everything inside the ship,
secondly a flow of secondary gamma quants which decreases exponentially every 200..300 m from the blast, which will irradiate everything inside the ship, up to many kSv.

So, the first propulsion blast in the atmosphere will be almost guaranteed the last one.
And just because a super-strong silo can once survive a close contact, we can give the Orion a chance of one survivable ascent to the upper atmosphere.
(If we put a starter nuke in a deep mine and put Orion on top, lol.)

Edited December 4, 2019 by kerbiloid

[wumpus]

5 hours ago, kerbiloid said:

So, the first propulsion blast in the atmosphere will be almost guaranteed the last one.

And just because a super-strong silo can once survive a close contact, we can give the Orion a chance of one survivable ascent to the upper atmosphere.
(If we put a starter nuke in a deep mine and put Orion on top, lol.)

As far as I know, that was why they initially believed that the radiation and various isotopes would not return to Earth: nearly all the explosions happened when it was sufficiently sideways to miss the Earth.  Unfortunately, if you aren't near the poles the magnetosphere can typically grab them and bring them back.

No idea what the initial blasts were supposed to be, I'd just assume they were dialed back to survivable levels.

[farmerben]

15 hours ago, wumpus said:

As far as I know, that was why they initially believed that the radiation and various isotopes would not return to Earth: nearly all the explosions happened when it was sufficiently sideways to miss the Earth.  Unfortunately, if you aren't near the poles the magnetosphere can typically grab them and bring them back.

No idea what the initial blasts were supposed to be, I'd just assume they were dialed back to survivable levels.

They thought it was possible to go from Earth's surface to orbit with about 80 pulse units.  With fission set at the lowest possible levels these 80 units would create about the same fallout as one normal atmospheric test of a megaton weapon with a fissile case.  Or about 1/300 the fission product fallout that humans had already put into the atmosphere around 1960.  Which sounds not that bad.  The EMP effects were barely recognized early on.  

 

21 hours ago, kerbiloid said:

 

The Orion charge mass is several hundred kg. It's mostly the charge itself and the uranium radiation case.
The thin tungsten membrane (the only part of the charge pushing the plate) is, estimated, ~pi * (0.5 m)² / 4 * 0.01 m * 20 000 kg/m³ ~several tens kilograms of tungsten.

In the lower atmosphere it should pierce the air column of twice greater mass.
So, instead of hitting the plate, it will first dissipate its energy by pushing through the air, will spread and get wider than the plate, so the total energy it can transfer will be probably twice less than in vacuum, where nothing stops it.

 

I disagree that only the momentum of the tungsten membrane counts toward thrust.  All the hot plasma striking the pusher plate contributes thrust, as well as ablatives on the plate itself.  Filler material helps capture radiation energy and turn it into plasma heat, atmosphere increases effective filler material.  

In vacuum the tungsten plasma projectile has nearly all the useful momentum, but a tiny fraction of the energy from the explosion.  Most of the energy is radiated away without creating a shock wave or fireball, as it does in atmosphere.  

 

 

[kerbiloid]

1 hour ago, farmerben said:

I disagree that only the momentum of the tungsten membrane counts toward thrust.  All the hot plasma striking the pusher plate contributes thrust

The whole idea of Orion is based on the earlier studies of evaporated thin membranes resulting into gas jets. The thinner is the membrane, the longer is the gas jet.
Filler and other parts of the charge are not mentioned as some major part of the Orion propuslion, and they will probably expand spherically, so have a little influence in the pusher plate energetic balance (don't forget it's just 200..300 kg heavy, at ~100 m distance).

1 hour ago, farmerben said:

contributes thrust, as well as ablatives on the plate itself

The liquid ablatives don't contribute anything but the plate protection.

1 hour ago, farmerben said:

Most of the energy is radiated away without creating a shock wave or fireball, as it does in atmosphere.  

Yes, and that's how it should work. All waste energy just misses the ship and doesn't damage it.
The shockwave is the last thing which the Orion needs. It isn't propelled by shockwaves, it is propelled by directed gas flow.
A shockwwave is not a gas flow, it's a front of overpressure.

The tiny test micro-Orions propelled by conventional explosives are not to study a proper Orion dynamics, they just simulate a gas hit on a tiny toy model.

1 hour ago, farmerben said:

atmosphere increases effective filler material.  

The atmosphere can't increase the filler material, first of all because the filler is inside the charge, behind the tungsten membrane.
The atmosphere is all in front of it, right on its way. It can't contribute anything but the air drag slowing the gaseous tungsten jet and dissipating its energy in air.

Even more, the air between the membrane and the plate will be heated by Xray long before the tungsten gas starts moving.
So, the air in between will produce pressure pushing the tungsten jet back and slowing it.

Edited December 5, 2019 by kerbiloid

[sevenperforce]

18 minutes ago, kerbiloid said:

The atmosphere can't increase the filler material, first of all because the filler is inside the charge, behind the tungsten membrane.
The atmosphere is all in front of it, right on its way. It can't contribute anything but the air drag slowing the gaseous tungsten jet and dissipating its energy in air.

Even more, the air between the membrane and the plate will be heated by Xray long before the tungsten gas starts moving.
So, the air in between will produce pressure pushing the tungsten jet back and slowing it.

The atmosphere has to go somewhere. As long as the superheated atmosphere is expanding faster than the airspeed of the spacecraft, a very significant amount of the superheated expanding atmosphere is going to impact the pusher plate. That will provide impulse.

[Terwin]

29 minutes ago, sevenperforce said:

The atmosphere has to go somewhere. As long as the superheated atmosphere is expanding faster than the airspeed of the spacecraft, a very significant amount of the superheated expanding atmosphere is going to impact the pusher plate. That will provide impulse.

It will also engulf the pusher-plate and apply that heat to all of the delicate bits that are protected from the  tungsten spray that it is designed to catch in space.

An atmospheric shock-wave is a very different beast than a spray of tungsten in a vacuum.

[Spacescifi]

18 minutes ago, Terwin said:

It will also engulf the pusher-plate and apply that heat to all of the delicate bits that are protected from the  tungsten spray that it is designed to catch in space.

An atmospheric shock-wave is a very different beast than a spray of tungsten in a vacuum.

 

Are ya saying that project Orion nuke launch to orbit is a no go?

The designers apparently thought it would work... and they know the design better than any of us.

 

Yet there is no solid proof as no real tests of a fully loaded orion have been done.

[sevenperforce]

21 minutes ago, Terwin said:

It will also engulf the pusher-plate and apply that heat to all of the delicate bits that are protected from the  tungsten spray that it is designed to catch in space.

An atmospheric shock-wave is a very different beast than a spray of tungsten in a vacuum.

It would still work.

[kerbiloid]

1 hour ago, sevenperforce said:

The atmosphere has to go somewhere.

For example, sideways.
The tungsten jet moves at iirc 150 km/s speed, so it has about a millisecond to pass through the air.
It will just burst like a meteorite, and the straight jet will turn into a chaotic cloud, spreading around and dissipating energy. It will not be a direct blast anymore.
So, the increased mass of the propellant will in the same time mean less part of total energy reaching the plate.
Then, the hit will be not as symmetric and of constant distribution as in case of the original charge in vacuum.
Then, the air before the tungsten will be overheated by Xray long before the tungsten flow reaches the plate.
And the air overheated by both Xray and tungsten drag will produce a shockwave of unsymmetric shape close to the plate.

So, instead of precise direct ramming in vacuum, in the air the nukes will randomly smashing the plate making it crash maybe on the very first blast.

Don't forget, a shockwave is a wave of pressure, not a wave of matter, atoms of the matter stay on their places, just get there-and-back a little. You don't want it for the pusher plate.

28 minutes ago, sevenperforce said:

It would still work.

A petrol engine can work on liquid nitroglicerine, too. Just only one stroke.
The Orion drive in the atmosphere is the same. It maybe gets enough efficient, but will be destroyed before it proves its efficiency.

28 minutes ago, Spacescifi said:

The designers apparently thought it would work... and they know the design better than any of us.

The designers apparently thought a neutron bomb would work in Orion even better (they had heard about a "clean bomb", so got interested), but got disappointed after studying.

Also we should remember that in Martian expeditions the Orions were designed to land by chemical rockets.

Edited December 5, 2019 by kerbiloid

[Spacescifi]

18 minutes ago, kerbiloid said:

For example, sideways.
The tungsten jet moves at iirc 150 km/s speed, so it has about a millisecond to pass through the air.
It will just burst like a meteorite, and the straight jet will turn into a chaotic cloud, spreading around and dissipating energy. It will not be a direct blast anymore.
So, the increased mass of the propellant will in the same time mean less part of total energy reaching the plate.
Then, the hit will be not as symmetric and of constant distribution as in case of the original charge in vacuum.
Then, the air before the tungsten will be overheated by Xray long before the tungsten flow reaches the plate.
And the air overheated by both Xray and tungsten drag will produce a shockwave of unsymmetric shape close to the plate.

So, instead of precise direct ramming in vacuum, in the air the nukes will randomly smashing the plate making it crash maybe on the very first blast.

Don't forget, a shockwave is a wave of pressure, not a wave of matter, atoms of the matter stay on their places, just get there-and-back a little. You don't want it for the pusher plate.

A petrol engine can work on liquid nitroglicerine, too. Just only one stroke.
The Orion drive in the atmosphere is the same. It maybe gets enough efficient, but will be destroyed before it proves its efficiency.

The designers apparently thought a neutron bomb would work in Orion even better (they had heard about a "clean bomb", so got interested), but got disappointed after studying.

Also we should remember that in Martian expeditions the Orions were designed to land by chemical rockets.

 

No one in right mind would suggest using nuclear blasts for landing. It's sucidal.

And of the designers thought that about neutrons then it was b4 they understood neutron bombs better.

24 minutes ago, kerbiloid said:

For example, sideways.
The tungsten jet moves at iirc 150 km/s speed, so it has about a millisecond to pass through the air.
It will just burst like a meteorite, and the straight jet will turn into a chaotic cloud, spreading around and dissipating energy. It will not be a direct blast anymore.
So, the increased mass of the propellant will in the same time mean less part of total energy reaching the plate.
Then, the hit will be not as symmetric and of constant distribution as in case of the original charge in vacuum.
Then, the air before the tungsten will be overheated by Xray long before the tungsten flow reaches the plate.
And the air overheated by both Xray and tungsten drag will produce a shockwave of unsymmetric shape close to the plate.

So, instead of precise direct ramming in vacuum, in the air the nukes will randomly smashing the plate making it crash maybe on the very first blast.

Don't forget, a shockwave is a wave of pressure, not a wave of matter, atoms of the matter stay on their places, just get there-and-back a little. You don't want it for the pusher plate.

 

Again why I suggest an electromagnet pusher plate... an uber one.

That should protect it from the shockwave and even provide some propulstiom from all that plasma and gas.

[kerbiloid]

28 minutes ago, Spacescifi said:

Again why I suggest an electromagnet pusher plate... an uber one.

That should protect it from the shockwave and even provide some propulstiom from all that plasma and gas.

Again you don't need both at once. Either a plate or a magnetic trap.

[wumpus]

1 hour ago, kerbiloid said:

A petrol engine can work on liquid nitroglicerine, too. Just only one stroke.

Detonation of gasoline/oxygen mixtures in cars is not unknown, and common enough to have a name: "knock".  Granted, if your engine starts knocking you pull off, turn the engine off, and have it towed to a mechanic (that much knock may well destroy your engine before it gets there).  So getting the energy the engine was designed for in a shockwave is rarely instantly fatal.  I'm not even sure if nitroglycerin has more energy than properly mixed gas/oxygen (nitromethane does, or at least at mixtures that fit in the same sized engine).  High explosives typically don't have as much energy, just the ability to easily lose it all at once.

And while I haven't worked out the math, at least one thread here was reasonably convincing that the main point of Orion wasn't to capture all the *energy* of the explosion, but the *momentum* of the explosion (well, the momentum of the material hitting the plate).  Momentum is the key to rocketry, and Freeman Dyson and co took advantage of that.

[kerbiloid]

7 minutes ago, wumpus said:

And while I haven't worked out the math, at least one thread here was reasonably convincing that the main point of Orion wasn't to capture all the *energy* of the explosion, but the *momentum* of the explosion (well, the momentum of the material hitting the plate).  Momentum is the key to rocketry, and Freeman Dyson and co took advantage of that.

The materian is a thin (in sense of thickness) membrane which becomes a thin (in sense of density) gas jet which has to pass through a layer of nitrogen plasma (air heated by Xray before the thungsten does) of several times greater mass for 100 meters, when it is designed to form a conical jet in vacuum.

I'm afraid, this would look like a Hindenburg fire cloud but bigger, and both momentum and energy will dissipate long before it reaches the plate.

(That's in addition to the fact that the pusher plate appears to be right at the surface of the nuclear explosion fireball.)

[farmerben]

6 hours ago, kerbiloid said:

 

I'm afraid, this would look like a Hindenburg fire cloud but bigger, and both momentum and energy will dissipate long before it reaches the plate.

(That's in addition to the fact that the pusher plate appears to be right at the surface of the nuclear explosion fireball.)

How much though?  Some of the forward impulse would flow around the ship, resulting in waste, and maybe damage?  It was the observation that steel survived near ground zero and showed fingerprints on it, that convinced the Air Force to pay for it.

The speed of the shockwave front is based on the average velocity of particles squared, so it falls as 1/distance² .  Pretty quickly you'll be surfing one shockwave at a time and outrunning all the previous pulses.  

Energy is not actually a constraint in this case, because boosting yield with tritium is easy. 

The total impulse in the forward direction is greater in atmosphere than in vacuum because the total rearward impulse of stuff other than the ship and the tungsten is greater.

[kerbiloid]

2 hours ago, farmerben said:

How much though?  Some of the forward impulse

Pushing a narrow gas jet through the dense medium means turning the directed blast into an isotropic one, so the whole idea of direct kick into the ship's back looses sense.

2 hours ago, farmerben said:

maybe damage? 

The damage will be caused not by the impulse, but by the shockwave in air next to the ship, which doesn't exist in vacuum, and by the energy emission of the fireball (which also doesn't appear in vacuum).

Don't forget that the very first blasts happen when the ship is almost motionless (stands on ground or moves at < 1 km/s speed), so the shockwave from the kiloton-class nuke explosion at 100 m behind will easily outrun the ship and first break the pistons, then crush it from sides.

Then, don't forget about the ~200 m wide fireball behind the ship. The air gets hot from Xray in a microsecond and will reemit the received energy as visible and gamma photons, irradiating the ship both from back and from sides, causing its overheat and radiation damage.

So the very first nukes will almost surely kill the ship, but we can give an optimistic chance for it just because we are optimists.

2 hours ago, farmerben said:

It was the observation that steel survived near ground zero

Yes, the pusher plate will survive it and will be found several kilometers aside.

(Also don't believe too much in that urban legend about the Plumbob steel cap.
It (?) was seen on just one frame, and you would calculate the total energy of the blast and the cap kinetic energy at the told speed, then compare.)

Quote

During the Pascal-B nuclear test, a 900-kilogram (2,000 lb) steel plate cap (a piece of armor plate) was blasted off the top of a test shaft at a speed of more than 66 km/s 

Pascal-B	August 27, 1957 22:35:00.0	PST (−8 hrs)	NTS Area U3d 37.04903°N 116.0347°W	1,229 m (4,032 ft) - 150 m (490 ft)	underground shaft, safety experiment		300 t		[1][12][13][14][16]	Shaft safety experiment, failed. Sent a 4 in (100 mm) thick steel cap weighing several hundred pounds possibly into solar orbit or burn up in atmosphere, estimated velocity more than 66 km/s (41 mi/s).

1 kt = 4.2*10¹² J.
900 * 66 000² / 2 = 2*10¹² J = 0.5 kt = 500 t.

So, the urbanlegendary 66 km/s speed of the Plumpbob cap exceeds total yield of the charge almost twice, lol.)

2 hours ago, farmerben said:

The speed of the shockwave front is based on the average velocity of particles squared, so it falls as 1/distance² 

While actually it falls as a combination of 1/r, 1/r², and 1/r³ , this doesn't matter.
The shockwave breaks away from the fireball exactly at the fireball surface (because the fireball surface is exactly that place where the hot gas stops expanding, while the wave of pressure keep running).
As during the first blasts the ship stands exactly next to the fireball surface, the shockwave won't decrease, it just starts there.

2 hours ago, farmerben said:

Energy is not actually a constraint in this case, because boosting yield with tritium is easy. 

Tritium does nothing here. You need a tungsten jet of exact energy. It is caused by X-ray vaporizing the filler. It'doesn't matter how you get that X-ray but you need exact value of it.
The only thing will add tritium - it will irradiate the ship and launchpad with neutrons, but will decrease the charge mass (which is not a problem and as is).

2 hours ago, farmerben said:

The total impulse in the forward direction is greater in atmosphere than in vacuum

The total impulse is defined by the charge construction and is the same everywhere.
But in air it will dissipate much faster, by moving forward the air particles aside from the ship.

Edited December 6, 2019 by kerbiloid

[farmerben]

7 hours ago, kerbiloid said:

 

The total impulse is defined by the charge construction and is the same everywhere.
But in air it will dissipate much faster, by moving forward the air particles aside from the ship.

This is the only serious disagreement I have.  I think the total impulse will increase, the more mass is packed around the charge.  For a given amount of energy heavy slow stuff has more momentum than light fast stuff.  

Is the jet going to be effective going through material?  These explosive units are similar to bunker busters, capable of cracking hardened bunkers dozens of meters underground.   They are based on HEAT warheads that move a well shaped jet through armored steel.  That is different than in a gas, and gas is different than plasma.  The nearest thing I can compare it to is ball lightning, and that is not very close.

I would expect the shaped charge plume to work reasonably well in atmosphere.  If it doesn't oscillate the same as in vacuum (pancake-cigar-pancake), it at least goes (pancake-hourglass-broccoli).  Wikipedia currently mentions setting off the charge 25m behind the plate.  So we have some room to tune that variable.  

Can we get useful thrust?  That is the question.  How much potential thrust is wasted?  Doesn't matter within wide margins.  

As for protecting the sides of the ship.  We need mass for mechanical reasons, more than we need armor.  Preferably attaching as much mass as possible to the plate, rather than the payload.

 

 

 

[KerikBalm]

On 11/28/2019 at 2:27 AM, Spacescifi said:

Still... the real reason I consider this is basically how to find a way to beat gravity and get massive payloads up without cheating make believe.

...

lifting off a planet like Earth can be done several ways, one way among them being an MHD... which strangely enough, if powered via antimatter and it rocket engines too,  it could do a air rocket/air MHD combo to orbit.

...

any somewhat more grounded approach to the challenges of SSTO flight is a composite solution

A launch loop? Orbital rings? a spacegun?

Antimatter "catalysed" P-B11 fusion?

Heck, U233 pebble bed reactors wouldn't be so bad. Sure you'd have neutron radiation, but half lives of resulting products are much much less, waste material is safe in centuries, not several millenia.

Also, why is a SSTO needed, why not a re-usable first stage? SSTO would only really be needed if you're landing on an un-colonized earth like planet with no infrastructure to help boost your ship to orbit (such as a reusable booster, orbital ring, launch loop, space gun, etc).

Quote

In space I don't mind making up stuff, as it is required to go anywhere interesting in a reasonable amount of time.

 When making sh!t up, less is more. Similar to what KSK says (quoted below), its better to just say what your craft is capable of doing, and not describing how it does it... especially if your description of how it does it is just making sh!t up.

 

On 11/27/2019 at 11:06 PM, KSK said:

Yeah, that's kind of my point. You're writing a setting where access to space is so safe and commonplace that interstellar trade is a thing. ...

But then you throw in a load of detail which gives the exact opposite impression. The weight of your spacecraft is a factor. Engine running temperature is a factor. Propellant quantity is a factor. These are all things that suggest that spaceflight is still hard and risky and, speaking as a reader, it jars.

Put another way, if I was writing a story set in the present day, I might have one of my characters cross the Atlantic in an airliner. Unless anything of note happened along the way, there wouldn't be much to say about it. My character buys a ticket, goes to the airport, ... The next paragraph he's debarking, checking his coat pocket for his passport and resigning himself to more security checks.

The design and technical details of the airliner wouldn't get a moment of page time. They're normal, they're routine, my character in all probability doesn't know much about them and if he did he wouldn't care enough for them to warrant a mention. He certainly wouldn't spend his flight wondering about the make, model and ISP of whatever turbofan was pushing him through the sky, still less fret about the operating temperature of the turbine at the core of that turbofan.

Yes... this... but good science fiction has what the airliner can do be within the limits of what is known to be scientifically plausible, and extrapolates from that. Pre-flight sci fi would have been good if it predicted the security checks, because of the dangers involved if someone deliberately tries to disrupt the function, and if they saw post 9/11 security, bravo to them... after all, a 747 for instance would be hundreds of tons of fuel and metal travelling close to the speed of sound... these aren't things society an allow to be used by any person for joyrides.... for instance.

If there was a sci-fi setting written before commercial air travel, describing airliners and security, because they though about the dangers involved, they'd have done a good job... the question is... if the reader doesn't understand why all that security is there, do you explain it or leave the reader to try and figure out on their own why all that security is there (when the reader isn't used to that security on a train)? do you explain it with only a subtle hint or two? or do you hit them over the head with some announcement: "Attention, as there is a pressure difference of X pascals at our cruising altitude, the aircraft much be pressurized for crew safety and hull breaches would be a serious concern. If structural damage occurs, or the pilots are incapacitated, or the plane is caused to deliberately crash, it will strike there ground with X joules of energy according to 1/2mv², since it has a mass of X and flies at X m/s, therefore strict security controls are needed". That is clearly jarring, and bad writing (even if the science is good).

On the other hand, all those calculations may be good, if the story is told from the point of view of someone with a technical background encountering advanced technology and trying to understand what it is capable of.

Edited December 10, 2019 by KerikBalm