Mission using Pratt and Whitney TRITON engine

[aquitaine]

Using the TRITON engine, assuming it worked, starting from low Earth orbit about how long would it take to get to mars?EDIT: The Triton is a nuclear thermal rocket design, but I can't seem to find too much info about it.

 

[etudiant]

nuclear boost engines have a specific impulse 2-3 times that of conventional rockets. They won't cut the transfer time much at all, just improve your payload materially as well as the launch window size.
Triton is written up here: http://www.pwrengineering.com/dataresources/AIAA-2004-3863.pdf
The new wrinkle is the reactor also drives an electric generator, so there is plenty of power for the mission even during transit or at destination.
Substantial engineering work will be needed to make that work reliably.

 

[aquitaine]

nuclear boost engines have a specific impulse 2-3 times that of conventional rockets. They won't cut the transfer time much at all, just improve your payload materially as well as the launch window size.
Triton is written up here: http://www.pwrengineering.com/dataresources/AIAA-2004-3863.pdf
The new wrinkle is the reactor also drives an electric generator, so there is plenty of power for the mission even during transit or at destination.
Substantial engineering work will be needed to make that work reliably.

So is there anything that would both increase your payload AND greatly improve transit time?

 

[Bob S]

Look up " Project Rover nuclear rocket " on the web. Read http://en.wikipedia.org/wiki/Specific_impulse

Bob S

 

[etudiant]

So is there anything that would both increase your payload AND greatly improve transit time?

In theory, a sufficiently efficient engine could slash transfer times, at the cost of using enormously more energy.
Almost all interplanetary flights are designed to use as little energy as possible, to use barely enough to get out of Earth orbit into a transfer orbit (around the sun) that will eventually intersect the orbit of the target planet at a time that planet is there. Much more complex paths are often used to help boost the spacecraft into a different direction or to hike its speed via a gravitational assist from a planetary fly by or two or many.
If instead a much larger braking burn was possible at the destination, the transit time could be much less, but of course every pound of fuel spent is a pound less payload.
The Triton generates lots of electric power, so it could be combined with a plasma or ion drive to help speed the transit, but the gains would be most evident of long trips, to the outer planets for instance, because these produce little thrust, albeit much more efficiently.
Unfortunately, there is no space equivalent of air, so there we only know to do acceleration or deceleration by throwing away mass, very inefficiently in case of rockets, even nuclear ones.

 

[aquitaine]

Look up " Project Rover nuclear rocket " on the web. Read http://en.wikipedia.org/wiki/Specific_impulse

Good suggestion.

In theory, a sufficiently efficient engine could slash transfer times, at the cost of using enormously more energy.
Almost all interplanetary flights are designed to use as little energy as possible, to use barely enough to get out of Earth orbit into a transfer orbit (around the sun) that will eventually intersect the orbit of the target planet at a time that planet is there. Much more complex paths are often used to help boost the spacecraft into a different direction or to hike its speed via a gravitational assist from a planetary fly by or two or many.
If instead a much larger braking burn was possible at the destination, the transit time could be much less, but of course every pound of fuel spent is a pound less payload.

For probes this doesn't matter as much, but when it comes to actually having people in there (exploring or exploiting the vast riches of our beloved Sol) that quickly becomes a serious issue, after all it's taking new horizons years to get to the asteroid belt, who would want to wait that long?

Actually when I looked up the Rover Project as per Bob's suggestion I ended up running into this, an actual potentially feasible solution to this problem. According to their estimates on page 6 of the pdf that was http://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf a 10 year mission to 550 AU would use 180kg of fuel. Not only would it be able to travel 1 AU every 6.63 days, but do so with relatively cheap energy. With today's Uranium Hexafluoride price at ~160 USD per kilo, that comes out to using only 28,800 USD plus 1.8 million USD to launch that much (assuming $10,000 USD per kilo). Given the insane distance that covers, I would say that's pretty good. Next question, why the heck isn't this thing being seriously pursued?

Unfortunately, there is no space equivalent of air, so there we only know to do acceleration or deceleration by throwing away mass, very inefficiently in case of rockets, even nuclear ones.

Always the warp drive... :)

 

[etudiant]

Good suggestion.



For probes this doesn't matter as much, but when it comes to actually having people in there (exploring or exploiting the vast riches of our beloved Sol) that quickly becomes a serious issue, after all it's taking new horizons years to get to the asteroid belt, who would want to wait that long?

Actually when I looked up the Rover Project as per Bob's suggestion I ended up running into this, an actual potentially feasible solution to this problem. According to their estimates on page 6 of the pdf that was http://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf a 10 year mission to 550 AU would use 180kg of fuel. Not only would it be able to travel 1 AU every 6.63 days, but do so with relatively cheap energy. With today's Uranium Hexafluoride price at ~160 USD per kilo, that comes out to using only 28,800 USD plus 1.8 million USD to launch that much (assuming $10,000 USD per kilo). Given the insane distance that covers, I would say that's pretty good. Next question, why the heck isn't this thing being seriously pursued?



Always the warp drive... :)

The technical challenges of a fission fragment reactor are severe enough in themselves.
The deal killer however is that the exhaust, much like that of Project Orion, would be seriously dirty.
We are only starting to recognize what a mess we have made of the near Earth environment with all the space junk. Adding a whiff of long lived fissionables to it is a political non starter.
In that context, even Freeman Dyson, the genius behind Project Orion, eventually came to the conclusion that visiting the solar system on a smoke trail of fission products was a bad idea.
Mind that it is possible to dream up deuterium or tritium fusion reactors that only emit charged particles, which abound in space anyways, so there is a potential for super efficient nuclear engines with ISPs in the range of 1,000,000.
Unfortunately, there are a few engineering obstacles...

 

[Bob S]

For probes this doesn't matter as much, but when it comes to actually having people in there (exploring or exploiting the vast riches of our beloved Sol) that quickly becomes a serious issue, after all it's taking new horizons years to get to the asteroid belt, who would want to wait that long?

For serious manned interplanetary travel, first consider the food requirement problem, roughly 1 Kg of food per capita per day. Is it carried on board, or grown (hydroponic?). Do you use natural light, or artificial lighting for photosynthesis? (Photocells are about 20% efficient in converting solar radiation to electricity). Do plants grow well in zero gravity? Do you need insects for fertilization?

Bob S

 

[Bob S]

Mind that it is possible to dream up deuterium or tritium fusion reactors that only emit charged particles, which abound in space anyways, so there is a potential for super efficient nuclear engines with ISPs in the range of 1,000,000.
Unfortunately, there are a few engineering obstacles...

1) If the propellant is charged particles, then the spacecraft charges up. and eventually all the emitted charged particles come back and form a halo around (or stick to) the spacecraft .
2) The density of particles in interplanetary space is less than about 10 per cubic cm. So about 60 million cubic kilometers of interplanetary space contains about 1 gram of hydrogen atoms. Not a good source of matter.
Bob S

 

[etudiant]

1) If the propellant is charged particles, then the spacecraft charges up. and eventually all the emitted charged particles come back and form a halo around (or stick to) the spacecraft .
2) The density of particles in interplanetary space is less than about 10 per cubic cm. So about 60 million cubic kilometers of interplanetary space contains about 1 gram of hydrogen atoms. Not a good source of matter.
Bob S

Not too worried about the charged particle issue. most fusion reactors emit both positive as well as negatively charged nuclear particles, so there is a balance, albeit probably fiendishly difficult to achieve in real life.

The low level of matter in interplanetary space however is a revelation. It means any rocket design will leave a relatively enormous plume. Even a fusion accelerator would greatly upset the environment. Not sure where that leaves space travel, unless someone comes up with a warp drive.

Too bad, another hope busted.

 

[Enthalpy]

http://saposjoint.net/Forum/viewtopic.php?f=66&t=2164
Heat hydrogen by Sunlight, get a significant thrust, as opposed to electric propulsion.
More design subtleties to come when I find time.

http://saposjoint.net/Forum/viewtopic.php?f=21&t=1954
faster transfers: duration, energy. Use my latest Xls tables.
Includes a faster mission with chemical propulsion and aerobraking.

More in the forum there, follow the links or browse, mainly in Technology subforum.

 

[aquitaine]

The deal killer however is that the exhaust, much like that of Project Orion, would be seriously dirty.
We are only starting to recognize what a mess we have made of the near Earth environment with all the space junk. Adding a whiff of long lived fissionables to it is a political non starte

But that also assumes that space is a clean environment, which it isn't. Space is already bathed in radiation of all kinds so ship designs have to take it into account to begin with. It's not like there's any sort of ecosystem out there that's being damaged.

The reason it is a political nonstarter is because people often fail to realize that space is the most hostile environment we've ever encountered, full of radiation, no air what so ever, wild temperature fluctuations. To give some idea as to the extent of the public's ignorance and general idiocy, in the late 90's when the Galileo and Cassini missions were being launched there were all kinds of protests to stop it because they used RTGs. This was obviously in spite of the fact that solar panels are completely useless once you get out to the asteroid belt and beyond.

Bottom line: Gaia love fests have no place there. Until we invent warp drive I'm not seeing a whole lot in the way of viable options for getting us out to the planets in a reasonable amount of time.