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Detecting an alien spaceship?


Derek Willis

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I'm writing a science fiction story in which an alien spaceship arrives in Earth orbit - now there's an original plot! To add authenticity I am trying to find out what capability we currently have by way of detecting an alien spaceship. I know there are organisations such as the United States Strategic Command and North American Aerospace Defense Command, which between them have long-range radar systems to detect missiles, satellites and space junk. And of course Europe, Russia and China have similar organisations. But does anyone know the capability of these radar systems? I once read that the Apollo spacecraft were not tracked to the Moon because they were out of range of the radar systems back then. Would that still be the case today? The spaceship in my story is about the size of the International Space Station. Does anyone know what kind of distance this would need to be from Earth if it were to evade radar detection? My thanks to anyone who can help with this.

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48 minutes ago, Derek Willis said:

I'm writing a science fiction story in which an alien spaceship arrives in Earth orbit - now there's an original plot! To add authenticity I am trying to find out what capability we currently have by way of detecting an alien spaceship. I know there are organisations such as the United States Strategic Command and North American Aerospace Defense Command, which between them have long-range radar systems to detect missiles, satellites and space junk. And of course Europe, Russia and China have similar organisations. But does anyone know the capability of these radar systems? I once read that the Apollo spacecraft were not tracked to the Moon because they were out of range of the radar systems back then. Would that still be the case today? The spaceship in my story is about the size of the International Space Station. Does anyone know what kind of distance this would need to be from Earth if it were to evade radar detection? My thanks to anyone who can help with this.

Hi Derek,

Just a quick note. The Apollo missions were tracked all the way except for the time when they were behind the moon (link). For the tracking of ballistic missiles, the NATO main ground radar system is the Ballistic Missile Earl Warning System (BMEWS). However, there are several other systems which are mainly tasked with the tracking of space junk and satellites (link). Admittedly, I am not too familiar with Soviet and later Russian capabilities in this area. Can I ask which era your story is happening in? That would help narrowing down the actual capabilities, although I am sure a good part of the details are classified.

Cheers,
Badeskov  

 

Edited by badeskov
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49 minutes ago, badeskov said:

Hi Derek,

Just a quick note. The Apollo missions were tracked all the way except for the time when they were behind the moon (link). For the tracking of ballistic missiles, the NATO main ground radar system is the Ballistic Missile Earl Warning System (BMEWS). However, there are several other systems which are mainly tasked with the tracking of space junk and satellites (link). Admittedly, I am not too familiar with Soviet and later Russian capabilities in this area. Can I ask which era your story is happening in? That would help narrowing down the actual capabilities, although I am sure a good part of the details are classified.

Cheers,
Badeskov  

 

Hi, the link you give is the document I read. Where it refers to "tracking" I took that to mean the Apollo missions were not tracked by ground based radar but through using the data transmitted from the spacecraft itself (by integrating Doppler, and so on). I know that during Apollo 11, Mission Control had some difficulty in working out where the Eagle had landed, so I again assumed they weren't using ground based radar. The information I found on ballistic missile early warning systems seems to suggest a range of about 3,000 miles, but of course that is with regards to warhead-sized objects, not alien spaceships one hundred meters long. I know that from time to time large radio telescopes are used to bounce radar off Venus and Mars, but they are pretty big! (Actually, I might be able to work back from that). The story is set in the present, and this got me thinking: if aliens did decide to pay us a visit, how near would they get before we realized they were here! Anyway, thanks for your input!

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Hi Derek,

Please see inline.

1 hour ago, Derek Willis said:

Hi, the link you give is the document I read. Where it refers to "tracking" I took that to mean the Apollo missions were not tracked by ground based radar but through using the data transmitted from the spacecraft itself (by integrating Doppler, and so on).

Actually, the "tracking" in this context means something else. Excerpt from pp. 1, 2nd paragraph of the document:

Quote

The MSFN will “track” the spacecraft during its entire lunar mission, except for those portions of flight where the Moon occults the spacecraft (approximately for 1 hr during each 2-hr lunar parking orbit). As defined here the word “track” means more than it does in the usual sense; it means the cumbersome “link” between the spacecraft and the Main Control Center at the Manned Spacecraft Center in Houston, Tex. This link consists of the many information, tracking, voice, telemetry, and data channels necessary to keep up with the events of the flight.

The space craft was tracked in the sense of being followed by radar all the way to the moon and back, the "tracking" with the quotation marks simply implied that they lumped other parts in.

Quote

I know that during Apollo 11, Mission Control had some difficulty in working out where the Eagle had landed, so I again assumed they weren't using ground based radar.

They were indeed using ground based radar. The reason why they did not get an exact location is because of ground clutter, which in this case was reflections from the lunar surface. In essence the radar return signal from the lander was buried in false signal returns. Ground clutter is still an issue, although much smaller due to vastly improved signal processing capabilities and more sophisticated radar topologies and signal transmit/receive formats.   

Quote

 The information I found on ballistic missile early warning systems seems to suggest a range of about 3,000 miles, but of course that is with regards to warhead-sized objects, not alien spaceships one hundred meters long.

The range of the BMEWS is indeed around there, however, that range can be deceiving. The BMEWS is not looking much higher than LEO as that is where an incoming nuclear warhead would be. So a giant spaceship in GEO would never be seen. They want to see an incoming warhead as soon as possible, not look for something in GEO where there would be no nuclear warheads lurking. If you look in the notes from the link from before, it states:

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The Thule site J BMEWS station's detection arcs of 200°[45] were a missile warning "fence" created by 4 radars' separate arcs: each AN/FPS-50 created 2 arcs (shown) centered at 3.5° and 7° elevation[7] (exaggerated in illustration.) Each arc was created by a smaller radar beam ~1° wide x 3.5° high at a "horizontal sweep rate…fast enough that a missile or satellite cannot pass through…undetected".[7] Concerns in 1962 of "ERBM's (Extended Range Ballistic Missiles)" were that missile speeds after burnout would be higher than the initially-deployed Soviet ICBMs[46] and prevent the sweeping "Lower Fan" and then the "Upper Fan" (with "revisit time of 2 sec")[47] from detecting the missiles. A missile within the lower arc (~1.75-5.25° elevation) would be detected at a "Lower Fan Q Point" (black dot) and then by the upper fan (black dot with jagged outline), which allowed the impact area to be estimated from "where the object crossed the two fans and the elapsed time interval between fan crossings"[7] (displays showed the uncertain impact point as an elliptical area.) The free flight range of the missile outside the atmosphere (burnout to reentry) depends on the flight path angle and on the missile's parametric value of Q calculated from altitude and speed—additional ballistic range within the atmosphere to an estimated burst altitude was determined from computerized look-up tables in the Missile Impact Predictor.[7]

Emphasis mine.  [7] refers to the following reference:

Bate; Mueller & White (1971) [origyear tbd]. Fundamentals of Astronautics (Google books). Retrieved March 5, 2014. fan-shaped beams, about 1° in width and 3½° in elevation… The horizontal sweep rate is fast enough that a missile or satellite cannot pass through the fans undetected.   

Quote

I know that from time to time large radio telescopes are used to bounce radar off Venus and Mars, but they are pretty big! (Actually, I might be able to work back from that). The story is set in the present, and this got me thinking: if aliens did decide to pay us a visit, how near would they get before we realized they were here! Anyway, thanks for your input!

They may detect something, but I would honestly doubt it. Again, I think one of the best bets would be the space junk/satellite tracking program. While they are essentially only looking at GEO and not much further out, a spaceship the size that you suggest would most likely produce a significant return signal even though it is much farther out. However, it would most likely not produce a target of significant size due to ambiguity (warning: math in link although I know that isn't a problem for you). Essentially one sets the Pulse Repetition Frequency (PRF) to the maximum range one wants to be able to detect something. If one detects something at double the distance than the maximum range, it would show up as detected at the maximum range. The same if it was detected at a third the distance. So if your space ship decides to park itself a good ways beyond the maximum range, it would only give a small radar return and said radar return would be ranged somewhere within the maximum range due to the aforementioned ambiguity is. So it could easily be categorized as a piece of space junk, albeit newly discovered. However, if your spaceship continues towards Earth then confusion would arise as the target range would still show up as within the maximum range, but the radar return signal would increase fast and naturally incur frowning faces at the radar operator side. And probably a full malfunction check followed by a call to some fellows with an optical telescope to take a gander. If you would like to know more about the above, I can certainly elaborate.  

Another option is the Near Earth Object Program, which is looking for asteroids that could possibly be on a collision course with Earth. Astronomers naturally want to detect those as soon as possible, so they are using some pretty sensitive equipment (RF and optical) to look as far as possible. That may actually be the best bet. From this page:

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Near-Earth Objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood. Composed mostly of water ice with embedded dust particles, comets originally formed in the cold outer planetary system while most of the rocky asteroids formed in the warmer inner solar system between the orbits of Mars and Jupiter. The scientific interest in comets and asteroids is due largely to their status as the relatively unchanged remnant debris from the solar system formation process some 4.6 billion years ago. The giant outer planets (Jupiter, Saturn, Uranus, and Neptune) formed from an agglomeration of billions of comets and the left over bits and pieces from this formation process are the comets we see today. Likewise, today's asteroids are the bits and pieces left over from the initial agglomeration of the inner planets that include Mercury, Venus, Earth, and Mars.\

As the primitive, leftover building blocks of the solar system formation process, comets and asteroids offer clues to the chemical mixture from which the planets formed some 4.6 billion years ago. If we wish to know the composition of the primordial mixture from which the planets formed, then we must determine the chemical constituents of the leftover debris from this formation process - the comets and asteroids.

Finally, I am sure many amateur astronomers may notice something as well, although I am not sure they would be able to recognize it as a spaceship.

My two cents.

Cheers,
Badeskov

Edited by badeskov
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3 hours ago, Derek Willis said:

I'm writing a science fiction story in which an alien spaceship arrives in Earth orbit - now there's an original plot! To add authenticity I am trying to find out what capability we currently have by way of detecting an alien spaceship. I know there are organisations such as the United States Strategic Command and North American Aerospace Defense Command, which between them have long-range radar systems to detect missiles, satellites and space junk. And of course Europe, Russia and China have similar organisations. But does anyone know the capability of these radar systems? I once read that the Apollo spacecraft were not tracked to the Moon because they were out of range of the radar systems back then. Would that still be the case today? The spaceship in my story is about the size of the International Space Station. Does anyone know what kind of distance this would need to be from Earth if it were to evade radar detection? My thanks to anyone who can help with this.

Its an intersting question. Do you have a particular propulsion system in mind ?

If we are talking about a system powerfull enough to drive an interstellar spacecraft, it should give off a lot of infrared radiation, so I think you might think about having the alien spaceship being discovered by an IR system, intead of radar. 

Its a little known problem, but getting rid of excess heat is actually quite difficult in space. The only really feasible method is to carry large heat radiators, which would light up like a christmas three on infrared wavelenghts.

There are several civilian systems, but the military (US and Russia, possibly China too) also have some very sensitive infrared satellites designed to detect the exhaust plume from a rocket launch. 

Here are a few examples: (civilian)

https://en.wikipedia.org/wiki/Spitzer_Space_Telescope

https://en.wikipedia.org/wiki/Wide-field_Infrared_Survey_Explorer

https://en.wikipedia.org/wiki/Stratospheric_Observatory_for_Infrared_Astronomy

https://en.wikipedia.org/wiki/VISTA_(telescope)

Future system:

https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

 

I can highly recommend that you look at this website: http://www.projectrho.com/public_html/rocket/spacewardetect.php#nostealth :tu:

It contains a lot of information if you want to have some realism to your story.

Edited by Noteverythingisaconspiracy
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3 hours ago, Derek Willis said:

I'm writing a science fiction story in which an alien spaceship arrives in Earth orbit - now there's an original plot! To add authenticity I am trying to find out what capability we currently have by way of detecting an alien spaceship. I know there are organisations such as the United States Strategic Command and North American Aerospace Defense Command, which between them have long-range radar systems to detect missiles, satellites and space junk. And of course Europe, Russia and China have similar organisations. But does anyone know the capability of these radar systems? I once read that the Apollo spacecraft were not tracked to the Moon because they were out of range of the radar systems back then. Would that still be the case today? The spaceship in my story is about the size of the International Space Station. Does anyone know what kind of distance this would need to be from Earth if it were to evade radar detection? My thanks to anyone who can help with this.

Well, what about displacing/interrupting some satellites?

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4 hours ago, Derek Willis said:

 My thanks to anyone who can help with this.

The Goldstone Solar System Radar , which is also a device used in the NASA/JPL NEO project , has a range that include Mars/Mercury.

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Derek..... the various militaries monitor the skies...for things like enemy aircraft...... so too does EVERY airport...earth is ringed with all kinds of satellites, the space station monitors the space around it....and of course earth....... countless thousands of amateur and pro telescope users monitor the skies....in fact, its these telescope users who tend to spot movement in space while looking for asteroids to be named after them

Then we have god knows how many people with Seti software on their home PC's or phones... tapping into massive observational power....do read

http://setiathome.berkeley.edu/

Then dont forget the probes around and ON Mars....or the Hubble space telescope

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32 minutes ago, seeder said:

Derek..... the various militaries monitor the skies...for things like enemy aircraft...... so too does EVERY airport...

Unfortunately none of the radars looking for aircraft have the range to detect anything in space.

32 minutes ago, seeder said:

earth is ringed with all kinds of satellites,

By far most of those satellites look the wrong way, i.e. towards Earth and not into space. And of those looking into space, only few would have the capability to detect an incoming space ship as they are typically built to look for something much, much larger and further away.

32 minutes ago, seeder said:

the space station monitors the space around it....and of course earth.......

Actually, the ISS has very limited monitoring capabilities of itself with respect to its surroundings. The ISS relies on ground monitoring stations to track space junk and other stuff that could jeopardize it.  

32 minutes ago, seeder said:

countless thousands of amateur and pro telescope users monitor the skies....in fact, its these telescope users who tend to spot movement in space while looking for asteroids to be named after them

The question is if they would recognize it as a spaceship or just see a moving dot and call it an asteroid/comet.

32 minutes ago, seeder said:

Then we have god knows how many people with Seti software on their home PC's or phones... tapping into massive observational power....do read

http://setiathome.berkeley.edu/

SETI wouldn't stand a chance of detecting an incoming spaceship. SETI is a passive listening program and if said spaceship was communicating with it's home world, it would be using some exotic form of communication that we wouldn't know, as ordinary radio wave technology would be way too slow.

32 minutes ago, seeder said:

Then dont forget the probes around and ON Mars....or the Hubble space telescope

The orbiters around Mars look at Mars and not into space and the rovers do not have any radar capabilities, they only have a com link to the orbiters that function as relay stations between the rovers and Earth.

I think the options of detection are actually more limited than one initially imagines, even for a space ship hundreds of meters long. Unless, of course, the incoming spaceship came in blasting Earth with radio signals trying to establish contact.

Cheers,
Badeskov

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15 minutes ago, badeskov said:

Unfortunately none of the radars looking for aircraft have the range to detect anything in space.

 

 

:lol: Yes....agreed mostly.... but he wants ideas for a fanstasy sci fi story...... not REAL facts..... therefore we can suggest whatever.....as in the sci fi book, an alien craft is coming to earth!!!

His first sentence:

Quote

I'm writing a science fiction story in which an alien spaceship arrives in Earth orbit

 

Hey if its earth orbit, we will detect it..... a satellite has been shot at...from earth!!.....they too are in earth orbit

 

 

 

.

.

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Ihteresting info, Badeskov, thanks for that.

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3 hours ago, Habitat said:

Ihteresting info, Badeskov, thanks for that.

You are most welcome!

Cheers,
Badeskov

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3 hours ago, seeder said:

:lol: Yes....agreed mostly.... but he wants ideas for a fanstasy sci fi story...... not REAL facts..... therefore we can suggest whatever.....as in the sci fi book, an alien craft is coming to earth!!!

His first sentence:

Very, very true. It is a story. But as is listed under my avatar:

Get your facts first, and then you can distort them as much as you please - Mark Twain

I kind like to know what I have to work with and then figure out where best to apply some artistic freedom. :lol:

Quote

Hey if its earth orbit, we will detect it..... a satellite has been shot at...from earth!!.....they too are in earth orbit

Well, in Earth orbit is a rather relative term. The moon is also in Earth orbit and that is at an average distance of ~384500 km (238,917 mi). And one could envision an orbit even further out, severely limiting the available detection options. Or they could enter an orbit between LEO and GEO, in which said spaceship would most certainly be detected by a multitude of different sensor platforms. :)

Cheers,
Badeskov 

Edited by badeskov
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7 hours ago, badeskov said:

Actually, the "tracking" in this context means something else. Excerpt from pp. 1, 2nd paragraph of the document:

Another option is the Near Earth Object Program, which is looking for asteroids that could possibly be on a collision course with Earth. Astronomers naturally want to detect those as soon as possible, so they are using some pretty sensitive equipment (RF and optical) to look as far as possible. That may actually be the best bet. From this page:

Finally, I am sure many amateur astronomers may notice something as well, although I am not sure they would be able to recognize it as a spaceship.

My two cents.

Cheers,
Badeskov

Ah, I see. When I read the definition of "tracking", I couldn't find any mention of radar and so assumed radar wasn't used because in the vicinity of the Moon the Apollo spacecraft would be too small to be detected. However, the definition basically means "radar, plus other methods such as Doppler". Do you have any idea which radar systems were used? Were they using the same antennae as were used for the telemetry and voice - i.e. the dishes of the Deep Space Tracking Network (Goldstone etc.).

If you have time I would be grateful if you could elaborate with regards to range detection. My basic assumption was that if an object is big enough to be detected, then its range is determined by the round-time of the signal. However, I can see there is more to it than that!

And regarding your comment (and those of others) on optical tracking, I had wondered if that would actually be the most likely means - accidental or deliberate - of detecting an alien spaceship.

Cheers!   

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7 hours ago, Noteverythingisaconspiracy said:

Its an intersting question. Do you have a particular propulsion system in mind ?

If we are talking about a system powerfull enough to drive an interstellar spacecraft, it should give off a lot of infrared radiation, so I think you might think about having the alien spaceship being discovered by an IR system, intead of radar. 

There are several civilian systems, but the military (US and Russia, possibly China too) also have some very sensitive infrared satellites designed to detect the exhaust plume from a rocket launch. 

 

The issue of detecting the propulsion system is very valid. I haven't yet thought about it in detail, but whatever it is - probably nuclear fusion - it is bound to produce a great deal of IR. And of course, the engine would have to be used to slow the spaceship into Earth orbit. However, a big chunk of the IR spectrum is absorbed by the Earth's atmosphere, so detection might not be straight forward. There are, as you say, satellites designed to detect rocket plumes - but they would surely be looking down and not up. And there are IR telescopes in orbit, but as far as I know they don't scan the skies like radar, so it would be "luck" if they happened to be pointing in the right direction when the spaceship fired its engine.

My basic premise is that the aliens are not all that advanced compared to we humans. Hence, they are not able to arrive at Earth with the sure knowledge that they can zap the entire planet if we try to attack them. So, they want to hedge their bets and keep out of range of our current detection systems before announcing their arrival. And that - in the interests of accuracy for the story - led me to wonder how well we would be able to detect an alien spaceship if one were ever to arrive. Of course, I may add a twist in that the aliens are pretty sure they haven't been detected, but our governments have detected them - e.g. by the spaceship's IR output - but don't want them to know we know!

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7 hours ago, Lord Fedorable said:

Well, what about displacing/interrupting some satellites?

That is a possibility, though I had in mind that the alien spaceship would be - initially at least - in an orbit way beyond our satellites, at least 100,000 miles out.

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7 hours ago, toast said:

The Goldstone Solar System Radar , which is also a device used in the NASA/JPL NEO project , has a range that include Mars/Mercury.

Thanks for that excellent link. The asteroid is about a kilometer in diameter and so has an area roughly one hundred times greater than that of the spaceship in my story. However, the asteroid is 3.6 million kilometers away. The radar image taken by the Goldstone radio telescope certainly suggests the spaceship could be detected if it were in an orbit, say, within the Moon's orbit. But as far as I know, the large radio telescopes don't regularly scan the skies like radar, so as with IR or optical methods, detection would be more a case of luck.

What I am trying to do is to inject some realism into the story whereby the aliens - who are not significantly more advanced than we humans - know that we may well be able to detect their spaceship, but are able to calculate the odds that we actually will. Hopefully that will add a bit of tension.

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Thanks for everyone's input. My general conclusion is that at some point the alien spaceship in my story would be detected, but most probably by accident. For example, the third stage of the Apollo 12 Saturn V was randomly discovered by an amateur astronomer. At first it was thought to be an asteroid, but after mapping a segment of its orbit, and analyzing its spectrum, it was identified for what it is. As has been mentioned, there are lot of amateur astronomers out there, so even if the authorities aren't actively looking for alien spaceships, someone would spot it. Of course, their initial reaction won't be "I've spotted an alien spaceship!". They will think they have discovered a near-Earth object such as an asteroid. Perhaps only when professional astronomers get on to it - as is what happened with the Saturn V third stage - would an alien spaceship be identified. The key to making this part of the story realistic is to take a stab at how long an alien spaceship could remain undetected. Again, thank you all for your input!

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9 hours ago, badeskov said:

The space craft was tracked in the sense of being followed by radar all the way to the moon and back ...

Hi, I am still having trouble pinning down whether or not the Apollo spacecraft were tracked by ground-based radar. Here is a quote from A Man on the Moon (Andrew Chaikin, 1994, page 105) regarding Apollo 8:

"For all Borman's worries about whether Apollo 8 was staying on the free-return trajectory, there was absolutely no way for him to find out except to ask Mission Control. Kraft's trajectory specialists were able to detect tiny changes in Apollo 8's path by measuring the Doppler shift in its radio signals."

There is no mention of radar here in determining Apollo 8's trajectory. This was done using Doppler shift data in the radio signals from the craft itself. The book later describes how by using the Doppler shift data, Mission Control could even plot the tiny wiggles in the trajectory caused by Apollo 8 rotating in "barbecue mode". Earlier in the book it says that the only way Apollo 8's lunar orbit could be accurately determined was by the astronauts making optical measurements of craters and other features. I haven't found any mention of ground-based radar, but I will have another look.

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6 hours ago, Derek Willis said:

Hi, I am still having trouble pinning down whether or not the Apollo spacecraft were tracked by ground-based radar. Here is a quote from A Man on the Moon (Andrew Chaikin, 1994, page 105) regarding Apollo 8:

"For all Borman's worries about whether Apollo 8 was staying on the free-return trajectory, there was absolutely no way for him to find out except to ask Mission Control. Kraft's trajectory specialists were able to detect tiny changes in Apollo 8's path by measuring the Doppler shift in its radio signals."

There is no mention of radar here in determining Apollo 8's trajectory. This was done using Doppler shift data in the radio signals from the craft itself. The book later describes how by using the Doppler shift data, Mission Control could even plot the tiny wiggles in the trajectory caused by Apollo 8 rotating in "barbecue mode". Earlier in the book it says that the only way Apollo 8's lunar orbit could be accurately determined was by the astronauts making optical measurements of craters and other features. I haven't found any mention of ground-based radar, but I will have another look.

Hi Derek,

I will get back to you later today, as this morning is Christmas decoration morning with the daughter, and it would be frowned upon if I just sat in front of the computer :P But in short, the three main stations were Goldstone (US), Honeysuckle Creek (AU) and a station in Spain (the name eludes me and I don't have time to look it up right now).

Cheers,
Badeskov

 

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With all of the orbiters out there, maybe the spaceship is discovered by accident in your story. It might appear as a new star, but there is no such supernova visible from Earth leading to a mystery.

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First contact stories are a dime-a-dozen. It's hard to find one without the same old tired plot devices and shop-worn clichés. The ones by people soft on science are the worst. Even the latest first contact movie is reminiscent of one a few years back, right up to the alien ship hanging suspended, nose down, almost touching the ground.

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9 hours ago, Derek Willis said:

The issue of detecting the propulsion system is very valid. I haven't yet thought about it in detail, but whatever it is - probably nuclear fusion - it is bound to produce a great deal of IR. And of course, the engine would have to be used to slow the spaceship into Earth orbit.

Fusion does look like a good candidate for your story. Its not very far beyond what we can do now, not to mention scientifically possible, so a good fit for aliens that aren't super advanced.

9 hours ago, Derek Willis said:

 However, a big chunk of the IR spectrum is absorbed by the Earth's atmosphere, so detection might not be straight forward. There are, as you say, satellites designed to detect rocket plumes - but they would surely be looking down and not up. And there are IR telescopes in orbit, but as far as I know they don't scan the skies like radar, so it would be "luck" if they happened to be pointing in the right direction when the spaceship fired its engine.

I was thinking along the lines of a civilian satellite detecting an anomaly and then using the military system to get more detail. You are ofcourse right that the military IR satellites look down on Earth, not into space, but if something really interesting turns up they might be redirected. 

9 hours ago, Derek Willis said:

My basic premise is that the aliens are not all that advanced compared to we humans. Hence, they are not able to arrive at Earth with the sure knowledge that they can zap the entire planet if we try to attack them. So, they want to hedge their bets and keep out of range of our current detection systems before announcing their arrival. And that - in the interests of accuracy for the story - led me to wonder how well we would be able to detect an alien spaceship if one were ever to arrive. Of course, I may add a twist in that the aliens are pretty sure they haven't been detected, but our governments have detected them - e.g. by the spaceship's IR output - but don't want them to know we know!

Don't know if you read the link I gave you, but the basic premise is that there is no such thing as stealth in space, so having the spaceship detected in advance is actually very realistic.

Adding a bit of government conspiracy to a story about aliens can't go wrong, can it ?  (But please don't publish it as a true story :P)

Best of luck to you.

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2 minutes ago, Hammerclaw said:

First contact stories are a dime-a-dozen. It's hard to find one without the same old tired plot devices and shop-worn clichés. The ones by people soft on science are the worst. Even the latest first contact movie is reminiscent of one a few years back, right up to the alien ship hanging suspended, nose down, almost touching the ground.

Thats why I like Dereks idea. He is trying to make it as realistic as possible.

Not that there is anything wrong with bending the laws of physics for a piece of fiction, it's just that, as you rightly said, its been done so many times allready.

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42 minutes ago, Hammerclaw said:

First contact stories are a dime-a-dozen. It's hard to find one without the same old tired plot devices and shop-worn clichés. The ones by people soft on science are the worst. Even the latest first contact movie is reminiscent of one a few years back, right up to the alien ship hanging suspended, nose down, almost touching the ground.

You are correct in this regard. However, the "contact" aspect is only incidental to my story - I'm not going to be so silly as to give away the plot! However, as there is "contact" I wanted opinions on how likely we are, with our current technology, to detect a fairly large alien spaceship if it is a fairly long way from Earth. It is interesting in that we would most certainly detect such a spaceship, but most likely because of random but regular searches of the sky by amateur astronomers or satellites (e.g. IR telescopes) that were looking for something else.

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