4 ms·

The short answer is: launch costs and crap rockets. Building a big ship, right now, means lifting lots of mass into orbit and assembling it there. That in itse

The short answer is: launch costs and crap rockets. Building a big ship, right now, means lifting lots of mass into orbit and assembling it there. That in itself will be stunningly expensive. But then you want to actually send it to Mars. Earth orbit to Mars orbit costs about 6 km/s (see http://i.imgur.com/SqdzxzF.png http://i.imgur.com/SqdzxzF.png), which is comparable to the 9.4 km/s needed to get from the surface of Earth to low earth orbit. Now, we are in space, which means we can use slow, efficient burns rather than the fuel-belching behemoths you need for a launch... but right now we're limited to inefficient chemical rockets, which means a hell of a lot of fuel. The ISS masses about 400 tonnes. Assuming hydrazine as a fuel, with an isp of about 350, that means that the wet mass of your vehicle has to be (dry mass) * e^(deltav / isp9.8) = 400e3 e^(6000 / 350*9.8) = 2300 tonnes. So you'll need 1900 tonnes of fuel. That's 380 Falcon 9s full of rocket fuel. (Assuming my maths are right.) So you try to make your spacecraft as small as possible. That way you don't need to carry the fuel needed to move the fuel. The rocket equation is a bummer. (Of course, nuclear engines, are vastly more efficient, change all this. Shame we don't have any. If you were willing to wait long enough, an ion thruster with an ISP of 20000 would require only 12 tonnes of fuel. But you wouldn't live that long.)

Balgair 11y ago
Now factor in all the failures on the pad. Lets round to 400 Falcon-9s. And thats just for the ISS. To go to Mars, you also need to get off Mars. Here are some of the challenges to doing that: Constraints are placed on the MAV by the Martian environment and the entry, descent and landing (EDL) system used. The MAV will have to endure daily temperature swings of up to about 100C with an annual maximum of about 24C and minimum of 111C. (These values were calculated using the NASA Ames Global Climate model for Holden Crater, which was the MSL candidate site with the greatest variation in temperature and is assumed to be representative of a MSR landing site.)Current MSR architecture places the MAV in a sky-crane type lander along with a fetch rover to re-trieve the samples. The EDL system constrains both geometric and mass limits on the system. The baseline design is a solid rocket. However, the thrust of solid rockets is dependent on their temperature. Additionally, any cracking of the fuel grain could lead to a cata-strophic failure." http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4342.pdf http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4342.p... Also, and I will have nerd-sniped away any productivity now from you dear reader, all of NASA's papers are public. Here is the whitpaper on a Mars Ascent Vehicle: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110011140.pdf http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2011001... (be warned, this is going to kill any work for the day)
vectorjohn 11y ago
That's "only" 36 falcon heavy launches (with an expected mass to LEO of 53 tonnes). With it being mostly reusable (at least the two boosters), this isn't quite so daunting an idea. I mean, we did build a space station. We've done similar things in scale and complexity. And we did it with the ridiculously inefficient space shuttle.
fredgrott 11y ago
Yes, but realistically one could mine the Moon poles and develop the fuel there... Better yet expand it grow food on moon and refuel and load up on food in moon orbit.
- gizmo686 11y ago
  Does growing food on the moon actually help? Unless you can mine the nutrients for the food, you still need to bring up all of the mass that would go into the food, at which point you might as well just bring up already processed food (which would also be denser in value/weight). The main benefit of growing food in space is that it lets you recycle nutrients. (I am including the atmospheric gasses as nutrients in this).
  - david-given 11y ago
    Yes, you'd have to mine the nutrients there for this to be effective. As you say, there's no point lifting it all from Earth. Organic life is largely made out of carbon, hydrogen, oxygen and nitrogen (the so-called CHON). There's not much carbon or nitrogen. This is one reason why people are so interested in hypothetical ice deposits at the poles. There's a reasonable chance that there'll be stocks of this elements there (in the form of ammonia or hydrocarbons).

Balgair 11y ago

Now factor in all the failures on the pad. Lets round to 400 Falcon-9s. And thats just for the ISS. To go to Mars, you also need to get off Mars. Here are some of the challenges to doing that: Constraints are placed on the MAV by the Martian environment and the entry, descent and landing (EDL) system used. The MAV will have to endure daily temperature swings of up to about 100C with an annual maximum of about 24C and minimum of 111C. (These values were calculated using the NASA Ames Global Climate model for Holden Crater, which was the MSL candidate site with the greatest variation in temperature and is assumed to be representative of a MSR landing site.)Current MSR architecture places the MAV in a sky-crane type lander along with a fetch rover to re-trieve the samples. The EDL system constrains both geometric and mass limits on the system. The baseline design is a solid rocket. However, the thrust of solid rockets is dependent on their temperature. Additionally, any cracking of the fuel grain could lead to a cata-strophic failure." http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4342.pdf http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4342.p... Also, and I will have nerd-sniped away any productivity now from you dear reader, all of NASA's papers are public. Here is the whitpaper on a Mars Ascent Vehicle: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110011140.pdf http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2011001... (be warned, this is going to kill any work for the day)

vectorjohn 11y ago

That's "only" 36 falcon heavy launches (with an expected mass to LEO of 53 tonnes). With it being mostly reusable (at least the two boosters), this isn't quite so daunting an idea. I mean, we did build a space station. We've done similar things in scale and complexity. And we did it with the ridiculously inefficient space shuttle.

fredgrott 11y ago

Yes, but realistically one could mine the Moon poles and develop the fuel there... Better yet expand it grow food on moon and refuel and load up on food in moon orbit.

gizmo686 11y ago
Does growing food on the moon actually help? Unless you can mine the nutrients for the food, you still need to bring up all of the mass that would go into the food, at which point you might as well just bring up already processed food (which would also be denser in value/weight). The main benefit of growing food in space is that it lets you recycle nutrients. (I am including the atmospheric gasses as nutrients in this).
- david-given 11y ago
  Yes, you'd have to mine the nutrients there for this to be effective. As you say, there's no point lifting it all from Earth. Organic life is largely made out of carbon, hydrogen, oxygen and nitrogen (the so-called CHON). There's not much carbon or nitrogen. This is one reason why people are so interested in hypothetical ice deposits at the poles. There's a reasonable chance that there'll be stocks of this elements there (in the form of ammonia or hydrocarbons).