[Black Wolf]

All that matters is that Earth can't talk to them, not that they can't talk to earth.

[jr2]

Ah, right.... so that should work... because by the time they transmit their new coords to Earth, and Earth replies, they'll be there.. almost.

Umm, BTW, I was wondering, how fast does a beam of light/radio wave travel if fired forwards from an object moving quite fast?  (eg, .55c?)  Normal speed, or 1.55c?

[Herra Tohtori]

Umm, BTW, I was wondering, how fast does a beam of light/radio wave travel if fired forwards from an object moving quite fast?  (eg, .55c?)  Normal speed, or 1.55c?

Exactly at c, of course*. In every inertial frame, too. But let's not turn this into a science debate (unless Black Wolf agrees to that); you can ask that question in own thread and I'll provide more physics...


*"of course" here can be derived from two physical principles; the first being the generally accepted assumption that laws of physics must be same to everyone regardless of their inertial co-ordinates, and the second being the fact that the speed of light is a constant at vacuum.

Those two things combined will produce the special theory of relativity, which states that light's vacuum speed is constant to all observers.

[achtung]

Hank 4000

[brandx0]

Maybe the ship was recieving transmissions all the time, and someone was sinisterly throwing them away? (Need a bad guy?)

Could also be a plot device that reveals this conspiracy, where they find logs of all these hundreds of communications that they recieved but never got to read, letters from family, updates on world events?

Of course, motivation for hiding or discarding them would have to tie more into the character and how they fit into the framework of the story.

[jr2]

Exactly at c, of course*. In every inertial frame, too. But let's not turn this into a science debate (unless Black Wolf agrees to that); you can ask that question in own thread and I'll provide more physics...

here is the thread I started.  I still don't understand...

[Mustang19]

It doesn't matter if there are actually humans awake to report what is happening. Every spaceship transmits some kind of signal to its ground control. It's been that way since Sputnik. You want exact coordinates of your ship at all times, and with the near-future tech you're talking about the spaceship would undoubtably be transmitting status reports every second of the day. It doesn't matter if humans are awake to transmit them, that would be redundant.

You're right, it is hard to find a believeable way to do this, although equipment failure may work, as obvious and boring as it sounds. I mean, when you're going at over .5c, there's going to be tons of space dust and space debris in your way. A collision with space dust while going at half the speed of light... not good. So if a spaceship only has 1-2 transmitters, those flimsy things are going to be gone pretty fast unless you have some kind of shields or super-armor.

Alternatively, the crew really doesn't want to talk to Earth in the first place. The captain has always been a rebel against his repressive government, and as soon as they get far away from Earth, he says, "OK, screw them, we're starting our own society here, throw the radios through the airlock". Personally I like jr2's idea the best.

[Colonol Dekker]

Bottany Bay anyopne?

[Maxwell]

Every spaceship transmits some kind of signal to its ground control.

There are a few exceptions.  Current spacecraft on long voyages sometimes have to shut down for extra long periods to conserve energy or defend themselves from solar radiation storms.
Depending on the nature of this spaceships engines and where its traveling, it might also have to turn off its communications gear and be forced to transmitting or receiving the minimal signal needed to maintain operations.
Stuff like news and letters from home would be bumped by more important things like "I am here" and "my systems are still functional".

I also think its a misconception that you could beam a radio wave across the galaxy and still get perfect reception.
Without FTL communication then any signal you get would be years old. Also, without sensitive equipment and big dishes you could expect what comes through will be horribly degraded in quality.

It might make more sense to pack up that gear for now and deploy it after you've made safe orbit at your destination.  Its not like the crew would be able to do anything about events back home.
...and in the nature of those events being controversial, theres a good chance ground control would not want to trouble the crew with any informaiton that could harm the mission.

If a civil war 2 were to break out in the US, the last people to know would likely be ISS or lunar crews. You don't want to spread the chaos there too.

[Mustang19]

The reception would come in fine, I think. Remember that there isn't really anything to block EM waves in space; we can get crystal-clear images of stars and nebulas dozens of LY away. NASA is still getting tracking signals from its Voyager probes, and they've gone beyond our solar system.

There are a few exceptions.  Current spacecraft on long voyages sometimes have to shut down for extra long periods to conserve energy or defend themselves from solar radiation storms.

Huh? What spacecraft? It takes almost no energy to send a radio signal, anyway, relative to all the life support and propulsion functions that the craft is going to be doing. There wouldn't be a need

I also think its a misconception that you could beam a radio wave across the galaxy and still get perfect reception.

True that. But he's talking about "near future" space travel as far as I can tell. Not those kind of extreme voyages.

Regardless, any further replies are practically necros, as the guy who started this thread has obviously stopped looking for help. But it's an interesting chat.

[Black Wolf]

I haven't. I'm not writing this part at the moment - I have my plot nailed down, but I'm still fleshing out the science I want to use and trying to get my head around Post-Voyage human society, as well as trying to pass uni this semester. I'm not even going to start character sketches for my supportings until after exams in a few weeks. So the specifics of this particular detail are still very much up in the air.

[Maxwell]

we can get crystal-clear images of stars and nebulas dozens of LY away.

Thats like comparing a heavy metal band to a mouse fart.
Voyager 2 for example is still inside the heliopause and nearing the end of her reactors useful lifespan.  Thirty years  is a long time for a machine and what power she has left has been dedicated to a few instruments and keeping oriented.
Astronomically speaking she's not even past our doormat and her signal can be easily lost in the background noise if you don't know what your listening for.

For a manned spacecraft based on what we have today, your talking about something that has no payload or amperage to spare.  They wont dedicate tons of equipment and vital juices from a degrading reactor just to get CNN updates. 
"Communications" would likely be a simple ping that goes off during crew rotations or at some set interval. They might suspect somethings up back home if they stopped getting a return ping, but theres nothing you could realistically do about it at that point.

I'd think with a mission that would take so long there would have to be a contingency plan or two for dealing with a loss of guidance from home.

[Mustang19]

Good points. But if we have spaceships that are powerful enough to travel at high percentages of c, then, correct me if I'm wrong, they should have plenty of reactor power.

And aren't there scientists sending radio signals to nearby stars trying to find UFOs? If they assume that their signal can reach these stars, doesn't that mean a spaceship wouldn't have trouble transmitting back over the same distance?

[Ghostavo]

Good points. But if we have spaceships that are powerful enough to travel at high percentages of c, then, correct me if I'm wrong, they should have plenty of reactor power.

And aren't there scientists sending radio signals to nearby stars trying to find UFOs? If they assume that their signal can reach these stars, doesn't that mean a spaceship wouldn't have trouble transmitting back over the same distance?

They're listening to radio signals. Also bear in mind that they listen using massive radio telescopes (or even arrays of them).

[Mustang19]

No, there was one time when a group scientists transmitted a signal, too. Don't remember the details, but it's fairly well known.

With ultrasensitive future recievers, I think that a spaceship could transmit a signal to a ground reciever a good distance away. It all depends on how far said ship travels. But I could easily see your "sleeper ship" traveling 40+ lightyears from Earth and no longer being able to communicate effectively. So no need for a plot device.

[jr2]

For a manned spacecraft based on what we have today, your talking about something that has no payload or amperage to spare.  They wont dedicate tons of equipment and vital juices from a degrading reactor just to get CNN updates. 

Eh... they have reactors that can power a city.  If they decided to colonize someplace, here's betting they'd build one with close to that power output on board, if not more (modern reactor, instead of the current, 30-40 yr old designs).

[Maxwell]

If they had unlimited resources aboard this ship, it wouldn't be putting along at 0.2C. 
I think its safe to assume the designers would have already looked at every possible means to lighten things so they save money and shorten the journey.
Long before they've gotten around to filling the tires with helium, drilling holes in every panel, sawing your crews toothbrushs in half and calculating exactly how many changes of fresh underwear are needed, you can bet they would have chosen the smallest possible reactor that can still feed the needs of the ships basic systems.

The reactor might be putting out some fantastically large number, but you can argue that every drop of that output has been accounted for just to make this mission feasible.

[Herra Tohtori]

The problem with space ships is not power, it's energy.

As in, they can sure make a power output sufficient for a city, not a problem (heck, nuclear submarines are able to do that), but doing that for 60 years or more is a totally different thing. Basically, even if they transformed matter into energy with optimal rate (using anti-matter as storing medium of energy like in Trek) they would want to make their systems as energy efficient as possible, so that they have more margin of error in mission parametres, and can go further with less "fuel".

And you need also to remember that with conventional propulsion, the ship needs lots and lots of propellant in addition to a long life energy source. Even if you have huge amounts of energy at your disposal, you can't go anywhere without propellant to drive your ship, assuming you can't break the conservation of momentum. Most of the gross weight of this kind of space ship would consist of propellant at the beginning of it's journey.

Also, the structural mass (or dry mass) of the ship would need to be as small as possible, as part of making propulsion energy consumption as small as possible. Likely, most part of the structural mass of an interstellar conventional space ship would consist of impact shielding concentrated on the frontside of the ship, but also on sides to some extent - and definitely on propulsion system! Most likely this impact shielding itself would be some lightweight matter (multiple aramid-aerogel-aramid layers might be interesting) but there would sure be a *thick* layer of the stuff. It would probably also be tested for some time with unmanned probes using different methods of protection.

[jr2]

As in, they can sure make a power output sufficient for a city, not a problem (heck, nuclear submarines are able to do that), but doing that for 60 years or more is a totally different thing.

True, nuclear subs have to be refueled... every 20 years!

[Flipside]

Do you even need an excuse? After all, if Earth suddenly stopped talking to them halfway through the voyage, it's not as if they can turn around and go home, since waking all the people early would, as you stated, put too much of a strain on the ship's systems, so having contact suddenly stop for no apparent reason would just add to the eeriness of it. I suppose it depends on 'what happens' and whether it is something that could justify going from 'normal communication' to 'silence' in the space of a single broadcast.