Orbiter Engine Destructiveness

[T.Neo]

Recently I've been wondering on how destructive "torch ship" engines, and the engines of some Orbiter vehicles, can be.

The stock DG for example seems to have an ISP of 39 952 m/s, and a thrust of 320 000 newtons.

Shuttle A has an ISP of 33 000 m/s, and a thrust of 2 129 000 newtons.

The XR2 has an ISP 20 775 m/s, and a thrust of 604 600 newtons.*

The XR5 has an ISP of 20 775 m/s, and a thrust of 8 525 000 newtons.*

The XR1 has an ISP of 20 775 m/s, and a thrust of 384 000 newtons.*

The DGIV has an ISP of 40 000 m/s, and a thrust of 180 000 newtons.*

*default settings

Now, what sort of damage would these craft do to objects behind or near the exhaust stream? Would they really destroy the entire spaceport? Would the craft itself be safe from the effects of the engines on the surface of a planet such as Earth?

Secondly, is there any concept (allowing for varying unobtanium here) that could allow such performance? Or is such performance completely implausible?

 

[Urwumpe]

The thrust/isp combination of the DG is in the range of nuclear fusion engines, but...the size is about 10-30 times too small for it.

You can calculate the exhaust/beam power of a engine as P = F * w

Yes, the Shuttle A has 70 GW power.

 

[Eagle]

Its more the power/m^2. The collimation of the exhaust is important (and usually proportional to the exhaust velocity.) If you're further from a poorly collimated source you'll have much less disruption.

Stand underneath the shuttle during launch and you'll be atomized, point the same engines at yourself from a 10 km away and you'll be fine, even in a vacuum.

However just take a hundred kW laser from a torch ship and have that shine through 100 km of vacuum and you'll likely be crisped.

 

[T.Neo]

The collimation of the exhaust is important (and usually proportional to the exhaust velocity.) If you're further from a poorly collimated source you'll have much less disruption.

That leads to another question: how well collimated is the average exhaust stream?

 

[jarmonik]

The thrust/isp combination of the DG is in the range of nuclear fusion engines, but...the size is about 10-30 times too small for it.

What ? You talk like such thing is already invented.

 

[Sky Captain]

IIRC Saturn V also had ~70 GW of power output. N1 should have ~100 GW because of greater thrust so the effects on spaceport should be similar although the exhaust streams from Shuttle A would be much hotter.

Most dangerous would be the nuclear pulse drive because it would tend to blow up the spaceport and leave some radioactive contamination behind.

 

[Andy44]

Heat effects from a particular drive can be managed by flame ducts and water suppression, etc. Radiaoactive fallout is a different story. If the exhaust leaves readioactive material behind, it's going to do damage which is very hard to clean up. A nuclear pulse drive will leave a lot of fallout unless you take very strict and expensive precautions, such as building a launchpad made of a substance which is immune to neutronic effects and using nuclear charges which are as clean as possible, such as fusion bombs which do not use fission triggers. A nuclear salt water rocket will lay waste to your launch site no matter what you do.

The key to answering this question is to figure out what kind of drive your particular vehicle is using, be it a DG or a Shuttle A or what have you, and then look at what that drive actually does.

 

[T.Neo]

A nuclear pulse drive will leave a lot of fallout unless you take very strict and expensive precautions, such as building a launchpad made of a substance which is immune to neutronic effects and using nuclear charges which are as clean as possible, such as fusion bombs which do not use fission triggers.

I've read that launching an Orion from a concrete tube dowsed with water would reduce fallout. Not sure if this has any relation to constructing the pad out of neutron radiation resistant materials, but doing so makes sense.

such as fusion bombs which do not use fission triggers.

How would that work? Antimatter catalysed fusion, perhaps? I doubt it would be easy.

A nuclear salt water rocket will lay waste to your launch site no matter what you do.

Indeed. The effects of an NSWR seem... unethical...

Even if fallout was avoided with an Orion type drive, or even if it were lofted out of the atmosphere with a chemical rocket, it would likely cause major problems for any satellites within the magnetosphere.

The key to answering this question is to figure out what kind of drive your particular vehicle is using, be it a DG or a Shuttle A or what have you, and then look at what that drive actually does.

Indeed. As Urwumpe suggested, perhaps some sort of fusion engine. And since a lot of the other parameters of the craft do not make sense, their size could be handwaved. :uhh:

Although, I always saw the DG's engines as obtaining thrust by accelerating charged handwavions.

 

[Linguofreak]

Indeed. The effects of an NSWR seem... unethical...

Try "suicidal".

 

[T.Neo]

Try "suicidal".

Hey... the crew might survive...

Then again, if you were in interstellar space, and had the nozzle pointed away from any planets, the exhaust products would eventually leave the solar system due to the exhaust velocity being higher than solar escape velocity- 66000 m/s...

 

[Hartmann]

IIRC Saturn V also had ~70 GW of power output. N1 should have ~100 GW because of greater thrust so the effects on spaceport should be similar although the exhaust streams from Shuttle A would be much hotter.

Most dangerous would be the nuclear pulse drive because it would tend to blow up the spaceport and leave some radioactive contamination behind.

Yes, i blew up ISS using the first time a orion pulse drive . i was near and when i started the engine it vaporise the station...:lol:

 

[eyu100]

The thrust/isp combination of the DG is in the range of nuclear fusion engines, but...the size is about 10-30 times too small for it.

You can calculate the exhaust/beam power of a engine as P = F * w

Yes, the Shuttle A has 70 GW power.

KE of a small amount of exhaust is

E = 1/2 * dm * v^2 (v is effective exhaust velocity)
= 1/2 * (F dt)/v * v^2
= 1/2 * F * v * dt

P = dE/dt = 1/2 * F * v

Am I missing something?

 

[ikrase]

From Project Rho:

High Thrust or Futuristic engines with ISP in 20,00 to 40,000 range

Antimatter catalyzed fusion

Antimatter Plasma (very small amount of antimatter used to heat much larger exhaust gas) (versitile fuel)

H-B fusion

Mini-MagOrion (a form of fission Orion Drive. Can be made compact.)

Various Orions

D-He3 fusion

Basically any fusion drive.

The bell nozzles are just ridiculous though. The maximum ISP for a bell nozzle engine is around 3,500. Which is pretty damned good. That's for a gas core nuclear thermal rocket. (very small amount of vaporized uranium heats much larger amount of exhaust gas)

Project Rho http://www.projectrho.com/rocket/rocket3c2.html has a section on launchpad destruction under the landing section, but it's for much less energetic nuclear thermal rockets. Basically you ablate whatever you land on. Apollo landers put the engine very close to the surfac without much happening. I would extrapolate that to NTR's not doing terribly much, but my guess is that hover landings on airless planets are going to be tricky.

On the other hand. the engines could be throttled.

 

[T.Neo]

Actually the Project Rho example used an engine with an exhaust velocity of 50 000 m/s, not unlike that of a Deltaglider.

I'd expect launch from a runway to not be too damaging, apart from a bit of ablation. Of course, the runway would not spend much time in the thrust stream. VTOL landings are a different story, but as ikrase said the engines could be throttled.

Recently though I've been wondering about far higher performance engines, like those on my HVIPS. HVIPS has an exhaust velocity of
7 840 000 m/s and each engine has a thrust of 10 meganewtons. Each engine has 39.2 terawatts of thrust power. :focus:

Over the total 9.2 hour burntime, both engines could produce 2.597e18 joules, or about the same amount of energy as 620 megatons of TNT.

However in terms of the damage the craft can cause, both engines are canted 4 degrees outward so it'd be essentially impossible to utilise them both against a target at any acceptable range.

The major wildcard in this situation is the collimation of the thrust stream, and I have absolutely no idea what it would be. I've guessed a divergence angle of 0.285, which means it would be spread over a 10 meter circle at 500 meters.

At 10 kilometers, it is spread over a circle 105 meters wide, which is an area of 8659.015 m^2, or 86590150 cm^2. This is a heat flux of 452707 watts/cm^2, and 4527074 joules/cm^2.

Keep in mind that during 10 seconds of acceleration at 1.5 G, the spacecraft will move 735.5 meters. This means that at the end of 10 seconds, the thrust stream will have a a diameter of 112 meters, and a surface area of 9852.035 m^2, or 98520350 cm^2.

My problem comes in how to calculate what sort of damage that heat flux would do. I've tried the Nuclear Weapons Calculator, but this isn't a nuke- a nuke releases all of it's energy in a tiny period of time, whereas I am leaving my engines burning for 10 seconds. Which could possibly give time for heat to be conducted away, etc.

 

[jedidia]

Keep in mind that during 10 seconds of acceleration at 1.5 G, the spacecraft will move 735.5 meters. This means that the thrust stream will have a a diameter of 112 meters, and a surface area of 9852.035 m^2, or 98520350 cm^2.

I can't quite follow you there... It isn't so important how far the ship moves, since the thrust exhaust has a movement of its own. at that exhaust velocity, it will have travelled 78400 kilometers after ten seconds, which makes the 0.7 kilometers the ship moved a bit moot in the calculation, or not?

My problem comes in how to calculate what sort of damage that heat flux would do.

Well, power is a unit of work per time, so a Watt is Joules per second. So if you know the fraction of your exhaust stream hitting the target, you know the fraction of total power hitting the target, and by this know how many joules hit it every second. It's basically what the nuke calculator gives you if you input the joules released in one second, just that the target gets hit by this amount of energy every freakin' second. I sure wouldn't want to be anywhere near this thing when it lights up...

As to how to calculate exactly how much it gets hit by, well... Here you'll need to take the aproach velocity between the two vessels into account, either by integration (don't ask me how) or by iteration (shouldn't give you too much trouble). If you have certan features or effects that move energy away from it again, and assuming they are constant, subtract them at every iteration. If these effects are variable (like, the hull can radiate more energy away the hotter it gets), you'll have to calculate the magnitude of the effect every iteration and substract that. I can't think of much other ways to do this...

 

[Izack]

HVIPS has an exhaust velocity of
7 840 000 m/s and each engine has a thrust of 10 meganewtons. Each engine has 39.2 terawatts of thrust power. :focus:

Over the total 9.2 hour burntime, both engines could produce 2.597e18 joules, or about the same amount of energy as 620 megatons of TNT.

Good grief!
I guess the craft's orientation before a burn would have to be factored into the planning of every flight. Could be a pain in the butt for ATCs... (or...STCs?)

As for using them as engines, if they produce 10MN of thrust, wouldn't the displacement caused by firing create a hazard for the HVIPS?

 

[T.Neo]

I can't quite follow you there... It isn't so important how far the ship moves, since the thrust exhaust has a movement of its own. at that exhaust velocity, it will have travelled 78400 kilometers after ten seconds, which makes the 0.7 kilometers the ship moved a bit moot in the calculation, or not?

The ship is moving, which means the thrust is allowed to disperse more, which means the heat flux is reduced.

The Nuke calculator gives 341.2 mm of aluminium vaporised per MJ/cm^2, and I have 4.527074 MJ/cm^2, which going by that would correlate to 1544.6 mm of aluminium vaporised.

Where I'm confused is that this is delivered over a period of 10 seconds, and not instantly. Unless I'm missing something blatantly obvious here...

I guess the craft's orientation before a burn would have to be factored into the planning of every flight. Could be a pain in the butt for ATCs... (or...STCs?)

Well, it shouldn't be too problematic, since space is mostly empty... mostly. But monitoring whatever might be downrange of the thrust stream would be important.

It's a good comparison to a passenger aircraft; they also need their flightplans carefully thought out and monitored, as well as being strictly regulated. Admittedly you'd probably be able to do a good deal more damage with HVIPS than an airliner, but space is emptier than the airspace around a large airport.

As for using them as engines, if they produce 10MN of thrust, wouldn't the displacement caused by firing create a hazard for the HVIPS?

What do you mean by hazard from displacement? In terms of acceleration? Or the thrust streams acting on the structure?

 

[jedidia]

Where I'm confused is that this is delivered over a period of 10 seconds, and not instantly. Unless I'm missing something blatantly obvious here...

Your ship has an energy output of 39.2 e12 Watts. In Explicit, that's 39.2e12 Joules per second. Your 4.25 MW/cm^2 are 39.2e12 / 86590150 cm^2, so no, this is joules per cm^2 PER SECOND (or simply Wats per cm^2, which as explained containes / second within itself). The next second will bring slightly less energy, or much less, or much more, depending on the aproaching speed. To get this absolutly exact, you'll have to integrate it, since the energy is a function of distance and aproach velocity. If aproach velocity isn't too high, iterating by seconds, or miliseconds if it needs be, should give you decent results.

In other words, your ships engines will vaporize any 1 1/2 meter of aluminium per second they will hit at 10 kilometers distance. If there's still something left, they'l vaporize a bit less than that the next second. after 10 seconds, you'll have potentialy something like 14 to 15 meters of vaporized aluminium, no matter how big an area it was that had such a wall around it, as long as it's hit by the exhaust stream.

In short, it's the Kzinti lesson

 

[T.Neo]

I don't see how closing velocity is going to mean much, considering that the maximum velocity of the ship is 6.37% of the exhaust velocity...

I get 1620 millimeters of aluminium vaporised over a period of 10 seconds, accounting for acceleration of the ship during thrust.

There is another aspect though... the engines are angled, which means the exhaust streams will move off of a target, unless the spacecraft is intentionally rotated to compensate.

Another advantage of a "puller" design... :hmm:

 

[jedidia]

I don't see how closing velocity is going to mean much, considering that the maximum velocity of the ship is 6.37% of the exhaust velocity...

Well, the higher the closing velocity between Target and engine, the faster the amount of energy per square centimeter will change. that would still be true even if the ship reached 90% of the exhaust velocity.

the engines are angled, which means the exhaust streams will move off of a target, unless the spacecraft is intentionally rotated to compensate.

Well, they weren't designed as weapons, after all... Most of the time it will be a nuicance because you have to watch out where you point them :lol: