NTR spacecraft for Asteroid visits/Deep space missions

[Valcan]

I was reading this

http://www.aviationweek.com/aw/generic/ ... r%20Routes

And one particular part really made me kinda happy :lol:

"With the exploration emphasis also focused on interim missions to near Earth objects (NEO), the study includes options for one-year round trips to specific asteroids. ”Because the NTR operational lifetime at full thrust and temperature is around 6 hr., multiple missions to various destinations (other NEOs, Moon, Mars) are possible,” the study finds"
Maybe we should invest in a large Deep space transport and exploration vehicle. Use bigelow moduals and other such components. As the technology matures we could eventually have the ability to send a expadition like was originaly wanted by Vonbraun.

 

[MeteorWayne]

You should at least explain the acronym NTR in your OP.

 

[Valcan]

You should at least explain the acronym NTR in your OP.

Oops my bad.

http://en.wikipedia.org/wiki/Nuclear_thermal_rocket

Nuclear Thermal Rocket.

 

[EarthlingX]

For start, i'm not impressed with 'twice as good as chemical rockets'. There are many types of propulsion which have Isp higher than 3000s.

Nuclear-electric propulsion is better, because there is no radioactive exhaust, it can use different techologies for propulsion with the same generator, and have much better Isp.

Not so good Wiki article : Nuclear electric rocket

 

[pleed]

I don't under stand why some people are against using nuclear fission based technology for the applications of space. I mean are they afraid that it will pollute the vacuum of space?

 

[DarkenedOne]

For start, i'm not impressed with 'twice as good as chemical rockets'. There are many types of propulsion which have Isp higher than 3000s.

Nuclear-electric propulsion is better, because there is no radioactive exhaust, it can use different techologies for propulsion with the same generator, and have much better Isp.

Not so good Wiki article : Nuclear electric rocket

Yes there are thrusters that have ISPs in the 10000s, however the problem with these thrusters is mainly that they have very low thrust. They have the thrust of essentially the weight of a piece of paper. This essentially limits them to deep space applications and station keeping because for nearby objects like the moon using these propulsion forms will result in much longer travel times.

What makes nuclear thermal so appealing is that it has 2-3 times the ISP without the tradeoff in thrust. They can be just as powerful as chemical rockets.

 

[EarthlingX]

Once in space, there is no need for thrust, since everything, but Moon, is so far away that thrust doesn't matter. What matters is mass of propellant which you need to get to LEO, therefore Isp.

A lot of thrust is needed only for launching from gravity wells, to minimize gravity losses. It makes sense for Moon-only solution, but for everything else is too costly comparing to other solutions.

Isp of 1000s (NTP) is not good enough to make any really big difference comparing to chemical propulsion.

 

[Boris_Badenov]

A 1960's designed NERVA had a burn time of 20 minutes with multiple restarts. Pratt & Whitney Rocketdyne says they can build a Nuc upper stage that could have burn time in the 6 hour range with up to 20 restarts. A SSME has a burn time of about 8 minutes with limited restarts. A Bimodal Nuc could provide electrical power far in excess of what a Solar Array could provide as well. The benefits of Nuclear Power in space are immense. We only need the political will to start using it.

 

[DarkenedOne]

Once in space, there is no need for thrust, since everything, but Moon, is so far away that thrust doesn't matter. What matters is mass of propellant which you need to get to LEO, therefore Isp.

A lot of thrust is needed only for launching from gravity wells, to minimize gravity losses. It makes sense for Moon-only solution, but for everything else is too costly comparing to other solutions.

Isp of 1000s (NTP) is not good enough to make any really big difference comparing to chemical propulsion.

LOL. Clearly you are not fimilar with the laws of physics that goven rocket propulsion my friend. You need to look up the ideal rocket equation to understand the effect that almost tripling the ISP has on a rocket ship.

However that is not the main benefit of the high thrust. It is true that low thrust, high ISP will dominate interplanetary travel and even interorbital travel when speed is not an important factor, however what about when you make it to your destination. Both places like the moon and mars have gravity, which means that you will need a high thrust system in order to travel to and from the surface just like we need high thrust to make it off of Earth.

In fact getting out of Earth's gravity well is where most of the delta-V of any space mission gets spent anyway. It takes about 8km/s to make it into LEO.

 

[EarthlingX]

However that is not the main benefit of the high thrust. It is true that low thrust, high ISP will dominate interplanetary travel and even interorbital travel when speed is not an important factor, however what about when you make it to your destination. Both places like the moon and mars have gravity, which means that you will need a high thrust system in order to travel to and from the surface just like we need high thrust to make it off of Earth.

That's what lander is for, which will be rather different for places with atmosphere from the one used for where there is no atmosphere.

In fact getting out of Earth's gravity well is where most of the delta-V of any space mission gets spent anyway. It takes about 8km/s to make it into LEO.

It takes a bit over 9 km/s to get to 7.7 km/s orbit (ISS).

As for tripling Isp, 850s (NERVA) is not three times 450s (SSME).