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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

#21

Post by tehbeard »

thomasmeeks wrote: post #20
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.

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.

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

#22

Post by melling »

danjayh wrote: post #13

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 th…

"Preaching to the choir". Since the government is not going to spend significantly more on science because most citizens don't want it, can you come up with a different solution that might work? For example, a Kickstarter for science that actually works. Crowdfunding X-Prizes, YC (incubator) for basic science companies, etc.

The US economy is $15 trillion. How to redirect some of that into more research?

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

#23

Post by mahranch »

> Lubin supposes that the system could propel crafts to an "unheard of" 30 percent the speed of light.

> "There is no known reason why we could not do this"

Yeah, no. There is a known reason. What do you think happens to a spaceship hitting something at 30% c? What do you think happens to the front of a spaceship or craft hitting something the size of bead or pebble at 30% c? The ship will disintegrate.

Granted, the ship could be shielded or employ some sort of plasma/magnetic deflector technology (still in proof of concept stages of development), but now you're talking technology that's just as far away, if not further than the propulsion system they're talking about using. It's also why things like project Orion really never got off the ground or are feasible in their current forms. Sure, we can get up to those speeds, it's surviving at those speeds that's the challenge.

Also, they talk about the weight of a ship being ultra light. If you had to shield it to survive the impact of tiny particles and other space debris you'll inevitably encounter on your trip, it's no longer going to be ultra light.

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

#24

Post by tehbeard »

wjnc wrote: post #4
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.

I had the same question. One thing that crossed my mind is that if speeds like these are possible, you could let the spaceship fly a gigantic loop and slow it down on the way back to earth. Same laser for acceleration and deceleration. (Things I've learned from the Martian #1.)

Did Hermes use a solar(laser) sail?

I know the ISV Venture Star from Avatar did (with antimatter engines for the Pandora side of the trip.)

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

#25

Post by tomswartz07 »

zelos wrote: post #14
arijun wrote: post #11

Earlier 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?

I think you're having trouble grasping exactly how fast 200km/s actually is.

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

#28

Post by ygra »

tehbeard wrote: post #24
wjnc wrote: post #4

Earlier quoted context omitted.

I had the same question. One thing that crossed my mind is that if speeds like these are possible, you could let the spaceship fly a gigantic loop and slow it down on the way back to earth. Same laser for acceleration and deceleration. (Things I've learned from the Martian #1.)

Did Hermes use a solar(laser) sail? I know the ISV Venture Star from Avatar did (with antimatter engines for the Pandora side of the trip.)

Hermes used an ion engine, so no sailing, just steady (but slow) acceleration.

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

#29

Post by mikeash »

jobu wrote: post #16
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?

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).

Given that aerocapture and parachutes have been successfully used for Mars probes in the past, that seems unlikely to be true.

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

#30

Post by [deleted] »

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…

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