PDA

View Full Version : SOL question



J Riff
2010-Jan-27, 01:08 PM
I'm a newbie non-scientist here... but...The speed of light... how long, or how much power would be needed to get close to the SOL, assuming steady acceleration in vacuum ?
Would such a spacecraft have to be a probe, and could it be sent out and back, perhaps circling a nearby system like Alpha Centauri... How long before something like this is possible ?
Maybe half the SOL ?

antoniseb
2010-Jan-27, 02:13 PM
Hi J Riff, welcome to the BAUT forum.

The short answer to your question is "it depends".
- it depends on the mass you are planning to accelerate.
- power depends on how rapidly you want to accelerate.
- it depends on how close to the speed of light you want to go (half).

Perhaps if the question were "how much energy would it ideally take to get a 10 ton space craft up to half the speed of light?" we could give a concrete answer. Heck, I bet there are calculators on the web that will give your answer with just a few clicks.

Also, in the short answer is the fact that such a craft is impractical right now, and will be for the foreseeable future.

Hopefully someone with a link to such a calculator will post a followup here.

PhillipJFry
2010-Jan-27, 02:59 PM
Did a little searching on the interwebz and found this...

http://www.1728.com/reltivty.htm

http://www.ksc.nasa.gov/facts/faq04.html

http://www.stardestroyer.net/Empire/Science/Relativity.html

http://home.att.net/~srschmitt/script_starship.html

Hope it helps.

J Riff
2010-Jan-28, 11:52 PM
Dandy. Thats some serious numbers. I know most people have trouble with time dilation and relativity in general... an unmanned ship would seem to have fewer issues as the SOL is approached///so why not send one off towards a nearby star system ? Even at a decent percentage of the SOL it would be a beacon for our Alien pals out there.

antoniseb
2010-Jan-29, 12:10 AM
... so why not send one off towards a nearby star system ?...

Did you calculate how much energy it would take? Figure out how many years worth of all the energy generated in the US it would take to get a ten ton probe up to 50% the speed of light. We aren't close to the technology to do this yet.

01101001
2010-Jan-29, 12:18 AM
Spacecraft Speed Records (http://www.aerospaceweb.org/question/spacecraft/q0260.shtml)


Fastest Manmade Object: Helios 2 in orbit around the Sun ~ 150,000 mph (241,350 km/h)

About 0.00022 c.

J Riff
2010-Feb-01, 08:31 AM
Well that answers THAT. 150,000 mph. That's the best we can do ? What about solar panels on a spaceship ? Would that not supply constant acceleration ? At least we'd know it was out there, beeping away if anyone is looking.
Man. 150,00 mph... that's slow !

Jens
2010-Feb-01, 08:42 AM
Even at a decent percentage of the SOL it would be a beacon for our Alien pals out there.

Why would it be a beacon? The heat from the exhaust? It wouldn't be much on a galactic scale.

Plus, are you sure you would want our "pals" out there to see us? Like the ones in Starship Trooper? :)

NEOWatcher
2010-Feb-01, 01:11 PM
What about solar panels on a spaceship ? Would that not supply constant acceleration ?
No;
If you're talking about the electricity from some kind of fusion drive or something, then as you distance yourself from any star, you're not going to be getting much energy.

If you're talking about solar sails, then you will not only get this reduction as you move away, but you will also run into a problem at the heliopause.

Hungry4info
2010-Feb-01, 02:05 PM
Well that answers THAT. 150,000 mph. That's the best we can do ?

I'm sure we could do much better if we truly wanted. There's just not much of a reason. If you speed way up, you'll have to slow way down to get to your destination, so there's no need for excessive speed.

noncryptic
2010-Feb-01, 02:12 PM
Not to mention that due to time dilation there's probably not that much of a point in sending a probe at a speed that comes anywhere near the speed of light:

Such a trip would not take all that long in the probe's frame of reference, but it will take a long long time in our frame of reference, so we'd have to wait a long long time for any signal from the probe to get back to us on Earth (assuming we want to know what the probe finds).

I didn't do any calculations on this (if only because i can't) but i'd venture to guess there's not that much difference in the total wait time for us, between on the one the above scenario and on the other hand the probe moving at a much lower speed that doesn't introduce significant time dilation.

In other words:

1. probe moving at significant fraction of speed of light:
our wait time = not very long probe trip time + a whole lot of time dilation + signal trip time

2. probe moving at very small fraction of speed of light:
our wait time = very very long probe trip time + very little time dilation + signal trip time

I figure that in both cases the 'probe trip time' + 'time dilation' is more or less in the same ball park. Signal trip time being the same in both cases.

Since staying well below the speed of light requires far less energy, that might be the more realistic option if we're ever going to send such a probe.

I see some practical problems in managing such a project that spans many decades, and in building a probe that will last that long.

J Riff
2010-Feb-02, 12:37 AM
Thanks for the excellent answers. I can't do the math, but I have training in logic, and I now see the difficulties...I DO think that if it becomes possible, such a probe or beacon should be out there... roll the dice on Aliens being non-aggressive. That's a whole other argument though. Thanks again.

Dragonchild
2010-Feb-02, 02:50 AM
Since staying well below the speed of light requires far less energy, that might be the more realistic option if we're ever going to send such a probe.

I see some practical problems in managing such a project that spans many decades, and in building a probe that will last that long.

Well, this isn't a matter of absolutes. Keep the payload down, get something up to a decent speed, slingshot it past the Sun (if feasible) and Jupiter and try to get the speed up to, say, 0.1c? Hardly relativistic, but at 18,600 miles per second that's a dandy clip.

As for having a probe last that long, New Horizons will be a bit of a trial balloon, methinks. Main limiting factors seem to be the deterioration of the RTG power supply (can't exactly rely on solar panels in the middle of nowhere) and on-board hydrazine for maneuvering. Basically, the problem with sending a probe halfway to another star is that there's no energy out there. WYBIWYG (what you bring is what you get), and for perspective, New Horizons' power supply is a meagre 200W. That's smaller than the power supply of a Playstation 3!

Noclevername
2010-Feb-03, 08:54 PM
I'm partial to the old-school approach (http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)), myself.

grav
2010-Feb-04, 03:36 PM
I'm a newbie non-scientist here... but...The speed of light... how long, or how much power would be needed to get close to the SOL, assuming steady acceleration in vacuum ?That would depend upon how close to the SOL one is trying to get, as the work required climbs very rapidly upon approaching it from their initial frame. As for anyone actually trying to reach the SOL itself, well they are just SOL.

macaw
2010-Feb-06, 05:02 PM
Did you calculate how much energy it would take? Figure out how many years worth of all the energy generated in the US it would take to get a ten ton probe up to 50% the speed of light. We aren't close to the technology to do this yet.

E=Integral_0_to_x{Fdx}
F=dp/dt
dx=vdt
p=m_0*v/sqrt(1-(v/c)^2)

so:

E=m_0*Integral_0_to_v{v*d(v/sqrt(1-(v/c)^2)=
=m_0*c^2*(1/sqrt(1-(v/c)^2)-1)

For v=0.5 and m_0=10T, the number for E is gigantic, especially due to the factor m_0*c^2..

J Riff
2010-Feb-09, 09:29 AM
Looking at that equation, though, makes me think that maybe WE are the advanced race here )..and just the minute someone discovers a new energy source,
ET will have visitors. What does E end up being, in terms comprehensible to a human brain ?