Stealthy orbital insertion?

[MatterBeam]

39 minutes ago, PB666 said:

liquid hydrogen is extremely difficult to store in long space flights, it needs to be collected from around the storage container, condensed to high pressure, actively cooled and then returned as a liquid back to the tank. This requires energy input and produces energy output in the form of radiation. IN addition the glancing of solar wind produce a 10K temperature on the prograde edge that the vanblack would absorb and emit. While there is very very little matter in space, the matter that is there is extremely energetic (kinetic) and temperature is directly related to the energy gained from collisions. An object that is not absorbing solar and discharging hydrogen would have a noticably cold and hot side, this would clearly identify it as a manmade object. In addition the liquid hydrogen recycler would have a radiator surface that identified it on a cold background, also manmade.

The assumption here is that the target race has a great IR telescope (like J Webb) and could pin point the difference between hot and cold. In addition since SC is intersystemic it would be identified as a local abnormality. Rather than making it less likely man-made, the effforts to hide its radiative heat signature would make it more obvious.

Open-ended cooling means that your heat sink (the liquid hydrogen) is thrown out into space once you're done with it. The liquid hydrogen is a consumable item that grants a number of seconds of stealth for every kilogram you spend. 

Good point about the solar wind. It is not something I have considered.
Solar seems to contain 5 million particles per m^2, mostly protons of mass 1.673e-27kg. At worst, they'll hit the stealth craft at a velocity of 750km/s. That's a kinetic energy of roughly 2.35 nanoWatts per square meter. I don't think it will significantly heat the spacecraft. 

The point of the hydrogen ship is not to have a hot side, and to not be picked up by J.Webb-like telescopes at all. 

[PB666]

1 hour ago, MatterBeam said:

Open-ended cooling means that your heat sink (the liquid hydrogen) is thrown out into space once you're done with it. The liquid hydrogen is a consumable item that grants a number of seconds of stealth for every kilogram you spend. 

Good point about the solar wind. It is not something I have considered.
Solar seems to contain 5 million particles per m^2, mostly protons of mass 1.673e-27kg. At worst, they'll hit the stealth craft at a velocity of 750km/s. That's a kinetic energy of roughly 2.35 nanoWatts per square meter. I don't think it will significantly heat the spacecraft. 

The point of the hydrogen ship is not to have a hot side, and to not be picked up by J.Webb-like telescopes at all. 

The unaddressed 8000 lb elephant is how you kept the liquid hydrogen stable up until the point you went into stealth mode without producing a heat signature.

Aside from that the ejected hydrogen can be detected because of collisions between solar wind and the gas, the collisions are extremely energetic and would emit over hydrogen's entire spectrum.

[MatterBeam]

1 hour ago, PB666 said:

The unaddressed 8000 lb elephant is how you kept the liquid hydrogen stable up until the point you went into stealth mode without producing a heat signature.

Aside from that the ejected hydrogen can be detected because of collisions between solar wind and the gas, the collisions are extremely energetic and would emit over hydrogen's entire spectrum.

In non-stealthy mode, you would handle the liquid hydrogen like any other propellant: insulated tanks. Whatever heat leaks through causes the liquid to evaporate, maintaining a temperature of at most 22K. It is the same reason why boiling water doesn't get hotter: evaporation rate matches heat input at constant temperature. This evaporative cooling creates gas. It can be collected, condensed by a heat pump, and recycled. This consumes power, but like every other system on the ship, it would be handled by conventional radiators. This ESA study describes how cooling down the liquid hydrogen directly allows for long-term Zero BoilOff storage of liquid hydrogen. 

In stealthy mode, the radiators are retracted, the heat pumps switched off and the liquid hydrogen starts circulating through heat exchangers. It cools down the hull, then a trickle of hydrogen is fed to the open-cycle cooling system to match the waste heat from sunlight absorption, habitats and other vital systems such as life support. 

As for the ejected hydrogen colliding with solar wind... I seriously doubt it will create any meaningful signature. 
For one, the hydrogen in vacuum with expand either quickly or very quickly. In the simple hydrogen steamer, hydrogen vapour starts at 22K and expands from a nozzle until it reaches 3K. Even without any expansion (straight pipe), the nozzle would allow the hydrogen to have a velocity of 523m/s (root mean square velocity). The gas would disperse very quickly, and the interaction between that gas and the solar wind would produce even less signature than the spaceship's hull. 

To give you an idea of how faint the signal you are thinking of is, consider a low-frontal-area spacecraft sitting at idle and producing 10kW of waste heat. This is much higher than is strictly necessary, but let's just assume that it is a warship with a large crew. 

10kW of waste heat must be dealt with by 22grams of liquid hydrogen per second. That is 11 moles of hydrogen. If released out of a straight pipe, the hydrogen would expand into 598926392.5 times its initial volume in one second. If it starts from a liquid density of 70kg/m^3, it would expand from 3.14e-4m^3 to 188234m^3 in one second. So, after one second, the hydrogen forms a gas cloud 523m across, at a density of 1.168e-7kg/m^3. It would interact with 858881m^2 of solar wind, so it would absorb 1.965 milliWatts at most. 

Per square meter, this translates into 5.71e-10W/m^2 across the hydrogen sphere. For comparison, the spaceship's hull is emitting 1.3e-2W/m^2. The hydrogen's signature is ten million times lower. 

[DerekL1963]

9 hours ago, PB666 said:

If you saw and asteroid bleeding off hydrogen gas with hydrogen emission spectrum are you going to think 'pitch black comet' or managed stealth system.

I'm going to think "what?  I need to take a much closer look at this thing that looks like nothing natural and get as many other people to look as possible".   Doubly so if a few days observation shows that it's orbital path comes anywhere near a planet or other body I'm interested in not having something collide with.

[PB666]

1 hour ago, MatterBeam said:

In non-stealthy mode, you would handle the liquid hydrogen like any other propellant: insulated tanks. Whatever heat leaks through causes the liquid to evaporate, maintaining a temperature of at most 22K. It is the same reason why boiling water doesn't get hotter: evaporation rate matches heat input at constant temperature. This evaporative cooling creates gas. It can be collected, condensed by a heat pump, and recycled. This consumes power, but like every other system on the ship, it would be handled by conventional radiators. This ESA study describes how cooling down the liquid hydrogen directly allows for long-term Zero BoilOff storage of liquid hydrogen. 

In stealthy mode, the radiators are retracted, the heat pumps switched off and the liquid hydrogen starts circulating through heat exchangers. It cools down the hull, then a trickle of hydrogen is fed to the open-cycle cooling system to match the waste heat from sunlight absorption, habitats and other vital systems such as life support. 

As for the ejected hydrogen colliding with solar wind... I seriously doubt it will create any meaningful signature. 
For one, the hydrogen in vacuum with expand either quickly or very quickly. In the simple hydrogen steamer, hydrogen vapour starts at 22K and expands from a nozzle until it reaches 3K. Even without any expansion (straight pipe), the nozzle would allow the hydrogen to have a velocity of 523m/s (root mean square velocity). The gas would disperse very quickly, and the interaction between that gas and the solar wind would produce even less signature than the spaceship's hull. 

To give you an idea of how faint the signal you are thinking of is, consider a low-frontal-area spacecraft sitting at idle and producing 10kW of waste heat. This is much higher than is strictly necessary, but let's just assume that it is a warship with a large crew. 

10kW of waste heat must be dealt with by 22grams of liquid hydrogen per second. That is 11 moles of hydrogen. If released out of a straight pipe, the hydrogen would expand into 598926392.5 times its initial volume in one second. If it starts from a liquid density of 70kg/m^3, it would expand from 3.14e-4m^3 to 188234m^3 in one second. So, after one second, the hydrogen forms a gas cloud 523m across, at a density of 1.168e-7kg/m^3. It would interact with 858881m^2 of solar wind, so it would absorb 1.965 milliWatts at most. 

Per square meter, this translates into 5.71e-10W/m^2 across the hydrogen sphere. For comparison, the spaceship's hull is emitting 1.3e-2W/m^2. The hydrogen's signature is ten million times lower. 

HYdrogen is not a normal cryogenic fluid, it leaks from valves, seams in welded metal, just about everything.

In space nothing has a temperature until it collides with something else. Therefore 25K solar gas at collision with hydrogen produces the temperature. The solar wind also does not have a temperature until it collides it basically moving in a laminar fashion away from the sun.

The collisions of gas will emit down to 39 nm emitting in the far UV/X-ray. This covers the entire range of mid and near infrared.

[Hypercosmic]

Don't make your H steamer too large. If it's too large, one can detect the ship from stellar occultation.

[MatterBeam]

On 25/11/2017 at 12:38 AM, PB666 said:

HYdrogen is not a normal cryogenic fluid, it leaks from valves, seams in welded metal, just about everything.

In space nothing has a temperature until it collides with something else. Therefore 25K solar gas at collision with hydrogen produces the temperature. The solar wind also does not have a temperature until it collides it basically moving in a laminar fashion away from the sun.

The collisions of gas will emit down to 39 nm emitting in the far UV/X-ray. This covers the entire range of mid and near infrared.

The leakage rate is negligible compared to the amount you will be using for cooling. 

IR detectors measure the photon hit rate on a Charge-Coupled Device. Once enough photons hit the CCD, the switch is tripped and an electron is let through, corresponding to one pixel lighting up. They have a certain noise rating, which is photons created by the device itself, an uncertainty in measurement and other factors which lead to a minimum amount of 'hits per pixel' to register the presence of a warm object in space, or else it cannot be distinguished from the 'noise floor'. This translates into Watts. For very sensitive cameras, signals as faint at 10e-19W/m^2 can be detected. Using larger collectors allows the IR detector to approach this minimum value, or the 'noise floor'. Trying to obtain a good probability of detection requires a large signal to noise ratio. 

The emissions of the target are subject to the inverse square law: it gets fainter at a rate of 1/distance^2.

For a 10m^2 collector, and a 10e-19W/m^2 noise floor, and a 10:1 Signal-to-Noise ratio, we can detect a 300K object emitting 459W/m^2 at a distance (459*10/(10*10e-19))^0.5: 67.7 million km. 

For hydrogen being blasted by the solar wind, you'll have high temperatures. This shifts the spectrum of the emissions into the lower wavelengths.... but the total energy is very small. Using the above equation, and inputting 5.71e-10W/m^2 instead, we get a detection range of 75.5km.

9 hours ago, Hypercosmic said:

Don't make your H steamer too large. If it's too large, one can detect the ship from stellar occultation.

Quite right! The size of the Hydrogen Steamer will mostly depend on how long you want to hide it. 

[PB666]

8 minutes ago, MatterBeam said:

The leakage rate is negligible compared to the amount you will be using for cooling. 

IR detectors measure the photon hit rate on a Charge-Coupled Device. Once enough photons hit the CCD, the switch is tripped and an electron is let through, corresponding to one pixel lighting up. They have a certain noise rating, which is photons created by the device itself, an uncertainty in measurement and other factors which lead to a minimum amount of 'hits per pixel' to register the presence of a warm object in space, or else it cannot be distinguished from the 'noise floor'. This translates into Watts. For very sensitive cameras, signals as faint at 10e-19W/m^2 can be detected. Using larger collectors allows the IR detector to approach this minimum value, or the 'noise floor'. Trying to obtain a good probability of detection requires a large signal to noise ratio. 

The emissions of the target are subject to the inverse square law: it gets fainter at a rate of 1/distance^2.

For a 10m^2 collector, and a 10e-19W/m^2 noise floor, and a 10:1 Signal-to-Noise ratio, we can detect a 300K object emitting 459W/m^2 at a distance (459*10/(10*10e-19))^0.5: 67.7 million km. 

For hydrogen being blasted by the solar wind, you'll have high temperatures. This shifts the spectrum of the emissions into the lower wavelengths.... but the total energy is very small. Using the above equation, and inputting 5.71e-10W/m^2 instead, we get a detection range of 75.5km.

Quite right! The size of the Hydrogen Steamer will mostly depend on how long you want to hide it. 

You really should read past postings in the group. The topic of hydrogen leakage has been discussed ad nausea. Its the reason when I say x-space craft use RL10b-2 at some great distance from earth I also mention that no provision or some mass provision was give for collection and concentration of hydrogen.

IR detectors are used in Jet craft for targeting surface to ground missiles. They can be (and proabably have already been) made more sensitive for use in space on satellites as they are not quite as surrounded by background radiation. The OP did not make any provision that the target world did not have developed satellites. So now I argue that the world has 50 J. Webb telescopes and 100s of satellites in GTO just looking for aberrant IR signals and peculiar asteriods that have weird hot and cold spots. Just to make a point we detect single photons of red-shifted light that have traveled for 13.8 billion years, detecting something a few 1000 kilometers away is small relative to this.

This is how your scenario plays out, race Q on Ganymede takes off with a full load of hydrogen. On day 26 it is bombarded by a cosmic ray storm and looses about 1/10th of its hydrogen. As it makes its way to Mars (a trip that takes 1.9 years) it looses about 5% per month. Somewhere around the sixth month the spy realizing that he will not have enough fuel to hide unfolds his solar panels and radiators and begins scavenging all the hydrogen that he can. Just then the target world and its 1000 circumsolar asteroid findng space craft detect a strange signature. They immediately begin panning that area of the sky, now about 10 m Km from the target planet and 8M km min from the telescopes. Sure enough a strange reflection of the solar panels are caught just long enough to plot a course. The course will intercept the target. The target planet then trains all variety of sensors looking for the coincidence of x-ray, uv, visual, and Ir photons from regions of space without sources along the path. Since they are not looking at a single wavelength or a single time but following a path they pick up a very fuzzy signal that suddenly increases as it approaches the world. They train there lasers to the part of space where stars momentarily disappear and blast with many lasers with microwaves that correspond to the frequency absorption of Vanablack, sudddnely a very intense IR signal appears, they keep blasting until the target explodes. No spies were detected, but very stranglely that area of space smells like bar-b-que to death row inmates who get spaced. 

 

 

 

[MatterBeam]

1 hour ago, PB666 said:

You really should read past postings in the group. The topic of hydrogen leakage has been discussed ad nausea. Its the reason when I say x-space craft use RL10b-2 at some great distance from earth I also mention that no provision or some mass provision was give for collection and concentration of hydrogen.

IR detectors are used in Jet craft for targeting surface to ground missiles. They can be (and proabably have already been) made more sensitive for use in space on satellites as they are not quite as surrounded by background radiation. The OP did not make any provision that the target world did not have developed satellites. So now I argue that the world has 50 J. Webb telescopes and 100s of satellites in GTO just looking for aberrant IR signals and peculiar asteriods that have weird hot and cold spots. Just to make a point we detect single photons of red-shifted light that have traveled for 13.8 billion years, detecting something a few 1000 kilometers away is small relative to this.

This is how your scenario plays out, race Q on Ganymede takes off with a full load of hydrogen. On day 26 it is bombarded by a cosmic ray storm and looses about 1/10th of its hydrogen. As it makes its way to Mars (a trip that takes 1.9 years) it looses about 5% per month. Somewhere around the sixth month the spy realizing that he will not have enough fuel to hide unfolds his solar panels and radiators and begins scavenging all the hydrogen that he can. Just then the target world and its 1000 circumsolar asteroid findng space craft detect a strange signature. They immediately begin panning that area of the sky, now about 10 m Km from the target planet and 8M km min from the telescopes. Sure enough a strange reflection of the solar panels are caught just long enough to plot a course. The course will intercept the target. The target planet then trains all variety of sensors looking for the coincidence of x-ray, uv, visual, and Ir photons from regions of space without sources along the path. Since they are not looking at a single wavelength or a single time but following a path they pick up a very fuzzy signal that suddenly increases as it approaches the world. They train there lasers to the part of space where stars momentarily disappear and blast with many lasers with microwaves that correspond to the frequency absorption of Vanablack, sudddnely a very intense IR signal appears, they keep blasting until the target explodes. No spies were detected, but very stranglely that area of space smells like bar-b-que to death row inmates who get spaced. 

I can't follow you into your fantasies anymore. I've disproven every valid point you've raised, but you don't have any of those in here.

[shynung]

5 hours ago, MatterBeam said:

For hydrogen being blasted by the solar wind, you'll have high temperatures. This shifts the spectrum of the emissions into the lower wavelengths.... but the total energy is very small. Using the above equation, and inputting 5.71e-10W/m^2 instead, we get a detection range of 75.5km.

~80-100 km detection range, let's say. Not exactly backstab-range, but definitely a rude surprise.

[MatterBeam]

4 hours ago, shynung said:

~80-100 km detection range, let's say. Not exactly backstab-range, but definitely a rude surprise.

10e-19W/m^2 is for a telescope that sits undisturbed for weeks on end, with its data processed by supercomputers at NASA and pored over by scientists. A more realistic satellite in a combat environment would have much lower sensitivity, due to more noise, random flashes heating the sensor and shorter observation times (closer targets can sweep across the field of view in less than a second). 10e-17 or lower is likely what we'll get. This reduces the detection range of that hydrogen to less than 1km. 

The calculations I did were a simplification too. The hydrogen cloud would actually expand away from the nozzle, forming a sphere with increasing density towards the center. The actual emissions, averaged over the entire expanding volume, will be much lower than what I calculated at the 1 second mark. The low density of the expanding gas cloud also means that only a tiny fraction of the solar wind will actually collide with a hydrogen atom, and I used a worst-case figure of 750km/s when solar wind actually has a range of velocities from 400 to 750km/s.

All in all, if a hydrogen steamer gets detected, it won't be because of the hydrogen gas.