Author Topic: Nuclear propulsion systems for DIRECT  (Read 21152 times)

Offline kraisee

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RE: Nuclear propulsion systems for DIRECT
« Reply #40 on: 12/24/2006 03:39 AM »
Didn't NERVA also suffer from similar problems during it's development?   My understanding was those problems were ultimately resolved before that program got canceled.

I would thus have to ask whether, with appropriate research and development, these problems with Timberwind could not also likely be resolvable?

Ross.
"The meek shall inherit the Earth -- the rest of us will go to the stars"
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Offline kraisee

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Re: Nuclear propulsion systems for DIRECT
« Reply #41 on: 12/24/2006 06:23 AM »
Here's a question for y'all...

Given that there are different preferences regarding the NTR/NEP/SEP propulsion systems, can anyone briefly summarize (for all of us) what the advantages/disadvantages are for each, specifically in the context of the 15 year synodic period (where every 15 years Earth and Mars are in the most 'advantageous' orbital positions relative to each other).

I know that there a great opportunities around 2018 and 2032 for Mars missions, but I'd like to better understand how advantageous this alignment is for each of the propulsion alternatives?

And actually, I just realized that DIRECT opens up the opportunity around 2018, but Ares can not.   Anyone think that could be a selling point?

Ross.
"The meek shall inherit the Earth -- the rest of us will go to the stars"
-Robert A. Heinlein

Offline Jim

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Re: Nuclear propulsion systems for DIRECT
« Reply #42 on: 12/24/2006 01:08 PM »
just less performance is required.  The MER missions of 2003 could not have flown on Delta II's on any other opportunity

Offline tnphysics

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Re: Nuclear propulsion systems for DIRECT
« Reply #43 on: 04/03/2008 12:17 AM »
What about an NTR on a Jupiter Core, making it a Jupiter 231-N ("N" for "nuclear").

Offline tnphysics

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Re: Nuclear propulsion systems for DIRECT
« Reply #44 on: 04/03/2008 12:17 AM »
What about an NTR on a Jupiter Core, making it a Jupiter 231-N ("N" for "nuclear").

Offline Lampyridae

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Re: Nuclear propulsion systems for DIRECT
« Reply #45 on: 04/03/2008 01:15 AM »
Here's my take on the pros and cons of each:

NTR:
Pros: high Isp, high thrust
Cons: nuclear safe orbits, radiation shielding, difficult environmental issues for testing, HEU may wind up in Obama's lap, radioactive exhaust plume
DIRECT compatibility: low LOM makes for safer nuclear launch

NEP:
Pros: high power density, high isp, lots of power available for hab
Cons: low thrust, even more Van Allen belt passes, large radiator required (larger set required for reactor heat engine loss), heavy power conversion equipment, rectifier losses, HEU may wind up in Obama's lap
DIRECT com

SEP:
Pros: high Isp, constant power (with variable solar concentrators), direct drive DC power supply, robust system, rapidly advancing photovoltaic tech
Cons: artificial gravity difficult with SEP, cannot thrust while in Earth's shadow

All in all, I'd say NEP was the more effective but SEP is easiest... hundreds of examples have flown and engine. Using NTR in the Jupiter core stage is absolutely bananas and it would never fly politically. Foreign voters will not be happy with (slightly) radioactive exhaust plumes over their territory or fishing waters. Look at the reaction to something like BSE in British beef.

I'm not sure which grade of fuel is used but I assume HEU ~20% for a nice hot core (the guys who actually worked on NERVA may know better but I'm working backwards from commercial reactor temps and refinements). That's OK when in a solid slug but powdered it causes problems. Even mill tailing have significant associated cancer risks but not so much they are carted away in barrels and stored in nuclear waste facilities. An intact fuel case landing in someone's backyard will kill noone unless it hits them in the head, but a cracked case with powdered HEU will result in a spate of cancer cases in the area some 10 years down the line and NASA will be in for a lot of bad press. Bottom line with this stuff is, as long as you don't take it into your body it's OK. Partially or fully burnt fuel is another matter. A hot unshielded core can still kill somebody even if it's intact if they hang around it long enough.

That being said, the fuel could be carried up in the same crew CEV in somebody's lap. I think that would be the safest way to do it.
SKYLON... The League of Extraordinary Gentlemen's preferred surface-to-orbit conveyance.

Offline kttopdad

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RE: Nuclear propulsion systems for DIRECT
« Reply #46 on: 04/24/2008 01:08 AM »
A quick search on this thread didn't turn up anything on Dr. Bussard's work.  Are y'all familiar with it?  There has been a lot of work done in that context regarding applying an IEC fusion reactor (assuming they work, which we will know in the next couple of months) to space travel.  

http://www.askmar.com/Fusion.html

Online Lee Jay

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RE: Nuclear propulsion systems for DIRECT
« Reply #47 on: 04/24/2008 01:30 AM »
Quote
kttopdad - 23/4/2008  7:08 PM

A quick search on this thread didn't turn up anything on Dr. Bussard's work.  Are y'all familiar with it?

Yup.

http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=5367&posts=2068&start=1

Offline kttopdad

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RE: Nuclear propulsion systems for DIRECT
« Reply #48 on: 04/24/2008 12:38 PM »
Quote
Lee Jay - 23/4/2008  8:30 PM

Quote
kttopdad - 23/4/2008  7:08 PM

A quick search on this thread didn't turn up anything on Dr. Bussard's work.  Are y'all familiar with it?

Yup.

http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=5367&posts=2068&start=1

Doh!  Thanks.  The funny thing is I've been following that thread as well.  Juggling too many threads makes it difficult to keep track of where one saw what.

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