How long would it take to catch up to the Voyager probes?
NASA proposes new propulsion to cut Mars voyage to 3 days
31–40 of 105 posts
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#32back-of-envelope: conservation of momentum: 2 (num photons) h/lambda = (100 kg)*(c/3), so 5.9×10^36 photons needed to propel a 100 kg object to 1/3 speed of light. 1.5×10^18 joules of energy, which is 11% of the energy output of the US in 2001 (according to wolfram alpha). That's a 5.8 Tera Watt laser running for 3 days straight. I haven't even gotten into dispersion of a laser beam. The ludicrousness of this proposa…
I like exercise ;-) If we wanted a self-assembling orbital solar array to provide that much power, it would need to be almost half the surface area of the moon. http://www.wolframalpha.com/input/?i=1.5%C3%9710^18+J++%2F+8...
we could use a suitable size black hole to create lensing effect - that way we could capture sizable chunk of the sun's energy
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#33Shooting a 100kg mass off at 30%C wouldn't be taken lightly by whoever it hit!
Planet killer?
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#34Earlier quoted context omitted.
Turn the craft around halfway to your destination and burn to decelerate at the same rate you accelerated. Keeps a nice 1G on the body the entire time.
Propulsion is provided from the earth /LEO/GEO (imagine blowing on a kite with giant fan). turning the kite around will not make it slow down/return to you while you keep blowing on it.
Sail boats are able to sail into the wind. This, however, requires the drag of the keel to work. It might be possible to use a traditional rocket engine to act like a keel to allow using the laser energy to slow down the craft.
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#35Earlier quoted context omitted.
Turn the craft around halfway to your destination and burn to decelerate at the same rate you accelerated. Keeps a nice 1G on the body the entire time.
Propulsion is provided from the earth /LEO/GEO (imagine blowing on a kite with giant fan). turning the kite around will not make it slow down/return to you while you keep blowing on it.
You use 2 kites on board the spacecraft. One gathers the transmitted beam and reflects it to kite #2, which then reflects forward again. Careful design is important to ensure the spacecraft in the middle isn't struck by the photons. And you will have significant losses by the double-reflection, so you have to turn earlier than 50% of the way there.
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#36back-of-envelope: conservation of momentum: 2 (num photons) h/lambda = (100 kg)*(c/3), so 5.9×10^36 photons needed to propel a 100 kg object to 1/3 speed of light. 1.5×10^18 joules of energy, which is 11% of the energy output of the US in 2001 (according to wolfram alpha). That's a 5.8 Tera Watt laser running for 3 days straight. I haven't even gotten into dispersion of a laser beam. The ludicrousness of this proposa…
Another thing to consider: mirrors are never perfect. 100% of the light is not reflected.
If the spaceship uses high quality laser mirror with 0.00001% absorption rate, absorption from 5.8 terawatts is still 5.8 megawatts of power to get rid of in space.
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#37See Larry Niven's Mote in God's Eye (1974) for details..
Did Mars figure prominently in the plot? I read the book exactly six years ago and loved it, but I have no idea why you are quoting it here.
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#38back-of-envelope: conservation of momentum: 2 (num photons) h/lambda = (100 kg)*(c/3), so 5.9×10^36 photons needed to propel a 100 kg object to 1/3 speed of light. 1.5×10^18 joules of energy, which is 11% of the energy output of the US in 2001 (according to wolfram alpha). That's a 5.8 Tera Watt laser running for 3 days straight. I haven't even gotten into dispersion of a laser beam. The ludicrousness of this proposa…
Sounds like fusion and better lasers need to be viable before this is viable.
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#39Earlier quoted context omitted.
Turn the craft around halfway to your destination and burn to decelerate at the same rate you accelerated. Keeps a nice 1G on the body the entire time.
Propulsion is provided from the earth /LEO/GEO (imagine blowing on a kite with giant fan). turning the kite around will not make it slow down/return to you while you keep blowing on it.
Yeah, for this idea to work as transportation, you really need lasers at both ends: one to accelerate the ship, and other to decelerate.
So it doesn't really solve any problems of initial colonization (beyond fly-by surveys), but it could be used for commerce once a colony has already been established.
You'd also probably want the lasers based on the moon: no atmosphere but large enough not to fly off in the opposite direction.
Re: NASA proposes new propulsion to cut Mars voyage to 3 days
#40Earlier quoted context omitted.
Definitely not. Back of the napkin shows that to get to Mars in 3 days would need a speed in excess of 200 km/s. That is an order of magnitude larger than Mars escape velocity. Your only chance of being captured by Mars is by pancaking.
Make the first vehicle nothing but a giant mirror, crash it into Mars and then reflect the laser off the debris to slow down the second vehicle?
The "debris" would a fine dust scattered over millions of square kilometers at that speed.