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NASA proposes new propulsion to cut Mars voyage to 3 days

wired.co.uk

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Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#11

Post by arijun »

revicon wrote: post #5
leecarraher wrote: post #2

Jane, Stop this crazy thing! or in other words, how do you decelerate the spacecraft once you near Mars orbit. You'd need either a ton of conventional propulsion fuel , or a mars based laser there too. Worse is that you have a limited energy sources and no one to mine them. Solar might help, but it'd take a helluva alot of planning to install them via some automated system.

Regarding slowing down upon arrival, could they enter a low orbit and skim the atmosphere of Mars to reduce velocity?

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.

Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#13

Post by danjayh »

As much as I love the idea, it is fairly impractical for the reasons that other commentors have noted. Call me greedy, but within the constraints of a balanced budget, I would like to see an increased portion dedicated to science (be it a 'cancer moonshot' or an actual marsshot) vs social programs ... maybe we could find some real solutions to these issues. In my own life I have a tendency to skimp on the 'now' in the name of investing in the future, so this is probably just me applying my own financial philosophies at a larger scale.

Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#14

Post by zelos »

arijun wrote: post #11
revicon wrote: post #5

Earlier quoted context omitted.

Regarding slowing down upon arrival, could they enter a low orbit and skim the atmosphere of Mars to reduce velocity?

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?

Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#15

Post by CapitalistCartr »

To reduce travel time from 9 months to four would be incredibly helpful to sending people. To halve that again to two months even more so. But after that, faster has lessened benefits. One month makes it easier on the human body, less than that is more convenience than anything. We'd be better served putting our money elsewhere. An Earth-Mars cycler would be a great start. https://en.m.wikipedia.org/wiki/Mars_cycler

And for unmanned missions, faster is of marginal benefit.

If I were setting up such a system for planetary flybys and extra-solar missions, I'd put the laser on one of the lunar poles .

Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#16

Post by jobu »

revicon wrote: post #5
leecarraher wrote: post #2

Jane, Stop this crazy thing! or in other words, how do you decelerate the spacecraft once you near Mars orbit. You'd need either a ton of conventional propulsion fuel , or a mars based laser there too. Worse is that you have a limited energy sources and no one to mine them. Solar might help, but it'd take a helluva alot of planning to install them via some automated system.

Regarding slowing down upon arrival, could they enter a low orbit and skim the atmosphere of Mars to reduce velocity?

Mars is actually a pretty bad planet to try landing on. It has just enough atmosphere to burn up a spacecraft that enters too quickly, but not enough to use for air-braking (skimming or parachutes).

Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#18

Post by imglorp »

rubidium wrote: post #9

back-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...

Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#19

Post by Skunkleton »

Kinnard wrote: post #12

Very light on details

Yep, that is wired for you. As far as I can tell, this plan was first proposed in the '80s. The technical challenges of a 1.21 jiggawat laser, and a gigantic sail have led to it never being attempted even though it is probably theoretically feasible.

Re: NASA proposes new propulsion to cut Mars voyage to 3 days

#20

Post by thomasmeeks »

leecarraher wrote: post #2

Jane, Stop this crazy thing! or in other words, how do you decelerate the spacecraft once you near Mars orbit. You'd need either a ton of conventional propulsion fuel , or a mars based laser there too. Worse is that you have a limited energy sources and no one to mine them. Solar might help, but it'd take a helluva alot of planning to install them via some automated system.

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.
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