Jump to content

Project Orion: A discussion of Science and Science Fiction


Spacescifi
 Share

Recommended Posts

11 hours ago, Spacescifi said:

I learned hybrids are thrustier than chemical

Hybrid rocket motors are chemical.

11 hours ago, Spacescifi said:

even though the delta V is less.

Delta-V is a measure of the total velocity change associated with any single stage; it is not a function of propellant type. A better propellant type with a better engine cycle will have a higher specific impulse and therefore a higher dV for a given mass ratio, but that's something else entirely.

11 hours ago, Spacescifi said:

They can also he throttled or cut off unlike solid fuel boosters.

Solid fueled boosters can absolutely be cut off. The ones the US created for ballistic missiles often had blow-out panels near the top to immediately kill the pressure in the combustion chamber and quench thrust instantly.

11 hours ago, Spacescifi said:

So it seems like the only SSTO that could be made right now with a decent cargo load (40 tons) would be an SSTO with hybrid rockets for lift off and orion nuclear pulse propulsion.

Nothing about hybrid rockets or orion nuclear pulse propulsion lends itself in any way to that conclusion. 

11 hours ago, Spacescifi said:

It is unlikely it could land itself safely, but it could at least get up to orbit as an SSTO.

Anything with a T/W ratio greater than 1 can be an SSTO if you can get structural mass fraction low enough or specific impulse high enough.

10 hours ago, Codraroll said:

1) An SSTO needs to be as light as possible for the rocket equation to allow the endeavour.

2) An Orion drive is a monstrously heavy thing. It does not play nice with the rocket equation.

3) The Orion drive has various insane drawbacks that make it a stupidly bad idea overall, and any attempts to improve it will make it obsolete instead.

Slight caveat to 1) -- an SSTO can be as light or as heavy as you want; the issue is that it needs to have a low structural mass fraction.

I know that's what you were getting at, but...yeah.

Link to comment
Share on other sites

Just now, sevenperforce said:

Solid fueled boosters can absolutely be cut off. The ones the US created for ballistic missiles often had blow-out panels near the top to immediately kill the pressure in the combustion chamber and quench thrust instantly.

This only quenches the combustion if you are in a significant atmosphere.  You could also arrange to have net-zero thrust by careful selection of blowout panels in front in vacuum.

 

1 minute ago, sevenperforce said:

Anything with a T/W ratio greater than 1 can be an SSTO if you can get structural mass fraction low enough or specific impulse high enough.

https://what-if.xkcd.com/24/

And the payload small enough.  And even the answer given assumes multiple stages and presumably no structural mass other than the container for the estes rocket engine (which would certainly be more than the payload even if you were just gluing the motors together, thus requiring an even bigger rocket...).

Link to comment
Share on other sites

27 minutes ago, wumpus said:

This only quenches the combustion if you are in a significant atmosphere.  You could also arrange to have net-zero thrust by careful selection of blowout panels in front in vacuum.

It doesn't quench combustion; it just kills thrust. The blow-out panels on US cold war solid-fueled ballistic missiles allowed the pressure in the chamber to vent. Without pressure in the chamber, the choke at the nozzle throat dies and all meaningful thrust stops. And since burn rate in a solid rocket is a function of chamber pressure, this also reduces the propellant burn rate by orders of magnitude.

I don't know whether the blow-out panels created any retrothrust or not.

30 minutes ago, wumpus said:
41 minutes ago, sevenperforce said:

Anything with a T/W ratio greater than 1 can be an SSTO if you can get structural mass fraction low enough or specific impulse high enough.

https://what-if.xkcd.com/24/

And the payload small enough.  And even the answer given assumes multiple stages and presumably no structural mass other than the container for the estes rocket engine (which would certainly be more than the payload even if you were just gluing the motors together, thus requiring an even bigger rocket...).

Well if you COULD make structural mass fraction arbitrarily low, then you could get to orbit with virtually any propellant. But obviously the lower your specific impulse drops, the sillier your mass fractions need to become. For an Estes model rocket engine that has roughly 100 s of specific impulse, you can reach orbit (~9 km/s) with a mass fraction of 0.01%. 

Sadly, model rocket motors typically have a structural mass fraction on the order of 50% in the casing and nozzle alone.

On 6/28/2022 at 5:57 PM, Spacescifi said:

Burn through the atmosphere until air plasma surrounds leading edge of the hull. Activate magnetohydrodynamic fields to deflect and use the air plasma as a source of thrust to cruise out of the atmosphere and into space.

I will also note that this makes no sense whatsoever. Air turns to plasma in front of a high-hypersonic vehicle because of compression drag. If you are trying to "deflect" drag plasma to create thrust, then you are attempting to create a perpetual motion machine, because whatever energy you can extract from the plasma was put into the plasma by robbing your vehicle of kinetic energy via drag in the first place. That won't work.

If you propose having magnetohydrodynamic fields capable of accelerating the air plasma, so that you actually add energy to it, then that's great and all, but you're going to carry an energy source with you.

Link to comment
Share on other sites

SSTOs won't work just by throwing buzzwords at them.

Solid boosters are exactly the opposite of what you want on an SSTO: they have a high dry mass to withstand the pressures, burn unevenly and unpredictably, suffer from poor residuals (not all the fuel in an SRB burns) and produce residual thrust as leftover scraps of fuel keep burning slowly after the rest has gone out. Their ISP is worse than conventional liquid bipropellants like kerosene/lox (and even kerosene/HTP) and their main strength- high thrust- isn't really that important for a HT/HL SSTO spaceplane but would incur high drag losses as it tried to brute-force its way through the thickest parts of the atmosphere. Trying to conjure usable thrust out of atmospheric plasma is a fallacy and the power supply needed to try and do so would be large, heavy and better used to directly generate thrust in an NTR, even an air-breathing one.

Humans are delicate, squishy things. High g-forces are to be avoided as much as possible to avoid loss of consciousness, thrombosis, strokes and other potentially lethal health issues. The only ways to avoid that are either a) juice them to the gills with drugs (see: The Expanse), b) some form of magic anti-inertia technology to allow extremely high acceleration without turning the crew to puree (see: Honor Harrington) or c) straight-up warp drives.

Link to comment
Share on other sites

It should also be noted that the Sprint missiles didn't achieve their awesome acceleration because they had a "magic" rocket booster. It was more because they placed a dinky little payload atop a honking great booster, and the missile didn't consist of much else to weigh the setup down. If you (somehow) attached a bigger payload to a Sprint missile, the results would be a lot more mundane.

Edited by Codraroll
Link to comment
Share on other sites

9 minutes ago, Codraroll said:

It should also be noted that the Sprint missiles didn't achieve their awesome acceleration because they had a "magic" rocket booster. It was more because they placed a dinky little payload atop a honking great booster, and the missile didn't consist of much else to weigh the setup down. If you (somehow) attached a bigger payload to a Sprint missile, the results would be a lot more mundane.

The Hercules X-265 first-stage booster wasn’t magic, but it was unique; it used zirconium in addition to aluminum as fuel and the base was smokeless gunpowder mixed with nitroglycerin. It had extremely high burn rates as a result. But with high burn rates comes low burn times and low total dV. That’s why the Sprint needed two stages, after all.

The high acceleration was required due to the low intercept window for re-entering Soviet warheads. The high acceleration was, in every other respect, a bug rather than a feature. A high-acceleration solid booster is a terrible idea for creating an SSTO.

Link to comment
Share on other sites

16 hours ago, Codraroll said:

What is wrong with the way we explain things?

Time and time again, various members have made it clear that SSTOs are pretty hopeless endeavours and cannot be combined with Orion in any way, shape or form. Yet barely two days pass, and then your conclusion reverts to "I guess an Orion SSTO is the best answer" again, as if nothing had been said to the opposite.

Why doesn't it sink in? Is anything unclear about the explanations?

To reiterate:

1) An SSTO needs to be as light as possible for the rocket equation to allow the endeavour.

2) An Orion drive is a monstrously heavy thing. It does not play nice with the rocket equation.

3) The Orion drive has various insane drawbacks that make it a stupidly bad idea overall, and any attempts to improve it will make it obsolete instead.

Is it 1), 2), or 3) you have a problem with?

 

I am well aware of the issues, all I was saying was that if the pistons and plate could be made to weigh less than the original orion then a ship could SSTO with it in theory.

 

Would not be very practical or safe I know, I was just saying it could work with a more kerbal mind set (where enviromental concerns go out the window).

Link to comment
Share on other sites

19 minutes ago, Spacescifi said:

I am well aware of the issues, all I was saying was that if the pistons and plate could be made to weigh less than the original orion then a ship could SSTO with it in theory.

If a vehicle driven by nuclear pulses via pressure plate had a less massive pressure plate then it would have a pressure plate that was less massive. I’m not really sure what that is supposed to suggest. Decreasing structural mass is always good for rocket design, of course; every kilogram of reduced structural mass is an extra kilogram of payload. But that doesn’t seem to have any connection to high-acceleration solid rocket boosters.

A lot of these questions generate tautological answers.  What happens if you decrease the structural mass of a rocket? Well, if you decrease the structural mass of the rocket, then you get more payload, regardless of what kind of rocket it is or what propulsion system it uses.  What happens if you had a  spaceship that could accelerate at three gees for three hours? Well, you would have a spaceship that could accelerate for three hours at three gees.  What if you had a special drive that could turn off gravity? Well, I suppose you wouldn’t have to worry about gravity.

I’m not trying to discourage you from learning about these things; I’m just very confused because you don’t seem to be.

19 minutes ago, Spacescifi said:

Would not be very practical or safe I know, I was just saying it could work with a more kerbal mind set (where enviromental concerns go out the window).

The United States government found the Nike Sprint missile to be very practical, until they decided it wasn’t.

Link to comment
Share on other sites

Posted (edited)
7 minutes ago, sevenperforce said:

If a vehicle driven by nuclear pulses via pressure plate had a less massive pressure plate then it would have a pressure plate that was less massive. I’m not really sure what that is supposed to suggest. Decreasing structural mass is always good for rocket design, of course; every kilogram of reduced structural mass is an extra kilogram of payload. But that doesn’t seem to have any connection to high-acceleration solid rocket boosters.

A lot of these questions generate tautological answers.  What happens if you decrease the structural mass of a rocket? Well, if you decrease the structural mass of the rocket, then you get more payload, regardless of what kind of rocket it is or what propulsion system it uses.  What happens if you had a  spaceship that could accelerate at three gees for three hours? Well, you would have a spaceship that could accelerate for three hours at three gees.  What if you had a special drive that could turn off gravity? Well, I suppose you wouldn’t have to worry about gravity.

I’m not trying to discourage you from learning about these things; I’m just very confused because you don’t seem to be.

The United States government found the Nike Sprint missile to be very practical, until they decided it wasn’t.

 

My point is that a lighterweight orion would cause hard g-force but a prepared crew could survive it.

So it is not impossible... just wildly unsafe and impractical.

 

It just illustrates how impractical SSTO's are unless you have an airbreathing spaceplane and even then it would be lightweight with minimal cargo.

 

Trying to build a heavy SSTO seems to be a foolish endeavor when 2 staging is superior.

 

Only way around it is outright scifi make believe and accepting the consequences of it.

Edited by Spacescifi
Link to comment
Share on other sites

4 hours ago, Spacescifi said:

if the pistons and plate could be made to weigh less than the original orion then a ship

would have five piston stages instead of two (because the pusher plate would jump up at much higher acceleration), and still lost the pusher plate because of its overheat and mechanical damage.

Link to comment
Share on other sites

15 hours ago, Spacescifi said:

 

I am well aware of the issues, all I was saying was that if the pistons and plate could be made to weigh less than the original orion then a ship could SSTO with it in theory.

 

Would not be very practical or safe I know, I was just saying it could work with a more kerbal mind set (where enviromental concerns go out the window).

How exactly is a low-mass piston & plate supposed to work?  The whole point is to absorb the momentum from the shock wave and slowly transfer the momentum to the ship.  It entirely relies on mass for that.

Link to comment
Share on other sites

9 hours ago, wumpus said:

How exactly is a low-mass piston & plate supposed to work?  The whole point is to absorb the momentum from the shock wave and slowly transfer the momentum to the ship.  It entirely relies on mass for that.

 

Okay what if we omitted the pistons and just put an oiled plate in the back before detonating the nuke?

How much g-force are we talking for say.... a spaceship on par with the second stage SpaceX starship for weight? I would to think that with liquud breathing the crew could still survive the extreme gees, since have not tests shown that humans can survive tens of gees (like 40-60g) under liquid breathing? At least someone claimed as much online once.  

 

Link to comment
Share on other sites

Posted (edited)
On 7/2/2022 at 4:16 AM, Spacescifi said:

Okay what if we omitted the pistons and just put an oiled plate in the back before detonating the nuke?

Then we get a crew smoothie.

Spoiler

4502820.jpg

That's why the two-stage pistons were added.

On 7/2/2022 at 4:16 AM, Spacescifi said:

How much g-force are we talking for say.... a spaceship on par with the second stage SpaceX starship for weight? I would to think that with liquud breathing the crew could still survive the extreme gees, since have not tests shown that humans can survive tens of gees (like 40-60g) under liquid breathing? At least someone claimed as much online once.  

The liquid breathing doesn't play a role when the brain is liquided against the skull wall.

The Orion plate jumps at 10 000 g.

It's mass is several tons. The ship mass is ~100 t. So, ~ 1000 g, like a cannon shell.

(10 000 / (100 / ( 10- * (~2 do to the ship elasticity, when the bottom jumps up before the nose)))

P.S.
The liquid breathing just prevents suffocation from the high pressure, but has nothing to do with inertial damage.

The condition of brain trauma conditional prevention:  
Overload2.5 * Duration,s < 500..1000

Edited by kerbiloid
Link to comment
Share on other sites

I just skipped to the last page, so this has probably already been brought up. However...

The fact they considered using NUKES (correct me if I'm wrong and they were just supersized explosive charges) on a SPACECRAFT unsettles me. Plus, who's to say the plate couldn't get slightly dented in a previous detonation, throw the kinetic energy from the blast in the wrong direction and detonate the entire "fuel" reserve? That'd be catastrophic because... well, it's a truckload of nukes, for goodness sake! The explosion would vaporize the ship. Even if it didn't the crew would probably be stranded in space without any means of getting back.

This is just one heck of a can of worms...

Link to comment
Share on other sites

1 hour ago, Second Hand Rocket Science said:

Plus, who's to say the plate couldn't get slightly dented in a previous detonation, throw the kinetic energy from the blast in the wrong direction and detonate the entire "fuel" reserve?

The non-central hit had been studied, too, among other misexplosion cases.

1 hour ago, Second Hand Rocket Science said:

well, it's a truckload of nukes

It's a  big truck.
200+ nukes if not additionally count the standard 200 x 1.5 Mt warheads onboard. (Let alone the small Casaba nuke shells).

Looks not that many, when you plan to use Davy Crocketts.

1 hour ago, Second Hand Rocket Science said:

The fact they considered using NUKES (correct me if I'm wrong and they were just supersized explosive charges) on a SPACECRAFT unsettles me.

The charm of atompunk is charming.

1950s are for heroes.

Link to comment
Share on other sites

Posted (edited)
2 hours ago, Second Hand Rocket Science said:

The fact they considered using NUKES (correct me if I'm wrong and they were just supersized explosive charges) on a SPACECRAFT unsettles me.

You're correct, the plan was nukes. Supersized explosive charges won't work; if you're going to use explosive chemicals then you put them into an engine in small amounts, after all. The reason to use nukes was that nukes have a spectacularly high energy density.

2 hours ago, Second Hand Rocket Science said:

and detonate the entire "fuel" reserve?

One element of good news here: nukes are notoriously tricky things that do not want to go off. Shock or nearby explosions or whatever won't trigger them; they have to be commanded to explode or they won't.

Edited by sevenperforce
darn typo
Link to comment
Share on other sites

An Orion drive is cool, but would these nuclear pules give less orbital control than a chemical engine? I feel that you wouldn't be able to do anything precise because every pulse is the same amount of power, so precise travel wouldn't be possible. For example, say you need 20ms of dv for a maneuver, but the Orion drive puts out 40 every pulse. Wouldn't that make those maneuvers impossible?

Link to comment
Share on other sites

Posted (edited)
15 hours ago, Rutabaga22 said:

An Orion drive is cool, but would these nuclear pules give less orbital control than a chemical engine? I feel that you wouldn't be able to do anything precise because every pulse is the same amount of power, so precise travel wouldn't be possible. For example, say you need 20ms of dv for a maneuver, but the Orion drive puts out 40 every pulse. Wouldn't that make those maneuvers impossible?

Why not let the charge drift further away before detonation?

Edited by HebaruSan
Link to comment
Share on other sites

1 hour ago, Rutabaga22 said:

Wouldn't that make those maneuvers impossible?

I would guess that you would probably have a few chemically powered dedicated OMS engines, or perhaps small space tugs to maneuver the Orion for precise maneuvers.

Link to comment
Share on other sites

  • 3 weeks later...

Would it be possible to recycle military nuclear bombs into the very small yield devices needed for an Orion?

Carl Sagan made what appears to have been a very casual proposal (off hand comment level) that if the world were to do nuclear disarmament, instead of simply destroying the weapons it would make sense to utilize them in Orions to transport supplies for colony construction.

Link to comment
Share on other sites

They were of the normal tactical yield range, 0.1 .. 100 kt.

And the yield gets higher by adding the secondary fusion charge, which in the Orion propelling nuke is replaced with the nozzle chamber.

So, nothing to recycle, just cut off the half and replace the body,


Just the colony requires many times more nukes than actually exist, as the Orion project is from atompunk era, when you could just take another thousand of nukes for the next Martian flight.

So, to follow the Sagan's suggestion, the humanity should first significally increase the nuclear weapon production rate.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...