Author Topic: To the Moon and Beyond–Examining the EELV-L1 Approach v2  (Read 61290 times)

Offline meiza

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #120 on: 12/29/2007 08:36 pm »
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Heavy lift is settled –by Mike Griffin- as the “Big Picture”. Ares is just a “tool” used in that big picture and we believe it is the wrong tool. So we proposed another “tool”; DIRECT.

It's telling that you don't consider the moon the goal and heavy lift just a tool. No, heavy lift is a goal in itself for you.

Offline clongton

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #121 on: 12/29/2007 09:05 pm »
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meiza - 29/12/2007  4:36 PM

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Heavy lift is settled –by Mike Griffin- as the “Big Picture”. Ares is just a “tool” used in that big picture and we believe it is the wrong tool. So we proposed another “tool”; DIRECT.

It's telling that you don't consider the moon the goal and heavy lift just a tool. No, heavy lift is a goal in itself for you.
Incorrect. Heavy lift is not the goal. The VSE is the goal. Heavy lift is the architecture Mike Griffin has chosen to implement the VSE. Heavy Lift is not my choice.  It is the rules I have to play by if I want to play. That's the choice. I get to play by Mike Griffin's rules -or- I don't get to play.

I am not willing to sacrifice my dream of human settlement of the solar system as a protest against the rules. I choose to participate. Life is not a spectator sport. You either play or you wither and die.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline kraisee

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #122 on: 12/29/2007 09:25 pm »
Okay guys, I know I didn't start this thread, but this is now getting so far off-topic that it needs to move to a new thread if its going to continue.   Don't take it to the DIRECT thread either.

Meiza has his own belief in the EELV's, the group of guys involved in the DIRECT Team has a different belief.   But neither has anything that actually relates to this particular thread.

This thread is specifically about how to make a smaller Lunar architecture work with the existing EELV's in the case that VSE money is pulled because Ares-I/V fails.   Its an interesting topic in its own right.

Lets stop boring the majority of the readership and keep to the topic at hand here by moving the DIRECT vs. EELV discussion to a more suitable thread please.   It doesn't belong here.

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

Offline Nathan

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #123 on: 12/29/2007 11:02 pm »
Okay folk - lets assume that either th SpaceX COTS vehicle Dragon will be available for the Command module and that this command module can connect to a reuelable Earth departure stage.

Other options for the comand module include Interorbital sysems CM-1 or a clean sheet design.

Also assume that NASA decides to go the EELV ruoute, regardless of one's opinion on that, so that NASA is an eager customer.
There is no real reason that the EELV-L1 architecture, based on an L1 propellant depot won't work. Is there?
(indeed, LOR-LOR will also work).
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline MKremer

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #124 on: 12/30/2007 12:39 am »
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Nathan - 29/12/2007  6:02 PM
There is no real reason that the EELV-L1 architecture, based on an L1 propellant depot won't work. Is there?
You mean, other than costs and development time (which are pretty intimately interrelated)?

Offline kraisee

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #125 on: 12/30/2007 03:31 am »
I'm not sure who else has been able to crunch any numbers on this, but I'm not getting great performance from the L1 Depot architecture.

I'm getting better results from an LOR Depot architecture because fewer Centaur Stage have to be pushed through TLI.   It results in greater mass in Lunar Orbit in the end.

It should also be noted that I'm not talking about a 23mT CEV, nor a 45mT LSAM - I'm talking about , at best, a 40-42mT of combined CEV and LSAM - which would result in a lander more closely resembling Apollo's 2-person one than ESAS'.

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

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #126 on: 12/30/2007 03:33 am »
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Nathan - 29/12/2007  7:02 PM

Okay folk - lets assume that either th SpaceX COTS vehicle Dragon will be available for the Command module and that this command module can connect to a reuselable Earth departure stage.

Other options for the command module include Interorbital systems CM-1 or a clean sheet design.

Also assume that NASA decides to go the EELV route, regardless of one's opinion on that, so that NASA is an eager customer.
There is no real reason that the EELV-L1 architecture, based on an L1 propellant depot won't work. Is there?
(indeed, LOR-LOR will also work).
If we're going to assume that everything NASA has done to date has been thrown out, I think that would also include Orion "as designed". It was deliberately made too big for the Atlas in the first place so I think the first thing to do is to redesign it and create a spacecraft that the Atlas can fly. Begin by redesigning the Orion. This time the CM should be just a taxi, and not include "living space". It should be a 3-module spacecraft, similar to Soyuz, with a mission module and a properly designed SM. SM and MM are expendable, CM is reusable. And don't worry about carrying enough LOX in the SM to get to the moon at launch time, just the LH2 with enough LOX for initial maneuvering to the depot. Fill up in LEO at the depot before departing. For LEO missions, the SM is fully fueled with its LH2 and LOX and the MM is launched with the CSM and the whole stack shouldn't exceed 18mT. For lunar missions, the SM would be lunar sized (larger) with only a partial LOX load and the LSAM is the MM and would be launched separately, with LOX propellant tank empty. They would all meet up at the depot, fill up and go.

Just a note. The depot is a LOX depot. The LH2 required for the mission is very light and would be carried up at launch time in both the SM and the LSAM. That way we don't worry about boiloff issues for the LH2.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline Marsman

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #127 on: 12/30/2007 04:45 pm »
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kraisee - 29/12/2007  11:31 PM I'm not sure who else has been able to crunch any numbers on this, but I'm not getting great performance from the L1 Depot architecture.

I'm getting better results from an LOR Depot architecture because fewer Centaur Stage have to be pushed through TLI. It results in greater mass in Lunar Orbit in the end.

It should also be noted that I'm not talking about a 23mT CEV, nor a 45mT LSAM - I'm talking about , at best, a 40-42mT of combined CEV and LSAM - which would result in a lander more closely resembling Apollo's 2-person one than ESAS'.

Ross.

Wait. The premisis of the archtecture is to refuel on Centaur based stage all of the way through. It is launch full, docks to Orion, flies to L1, is refuled and docked to the lander, and is used as a drop stage for the lander. There should only be one Centaur based stage per flight. The only other ones are the three for propellant transfer...

What are you assuming?


Offline tnphysics

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #128 on: 12/30/2007 07:15 pm »
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clongton - 29/12/2007  11:33 PM

Quote
Nathan - 29/12/2007  7:02 PM

Okay folk - lets assume that either th SpaceX COTS vehicle Dragon will be available for the Command module and that this command module can connect to a reuselable Earth departure stage.

Other options for the command module include Interorbital systems CM-1 or a clean sheet design.

Also assume that NASA decides to go the EELV route, regardless of one's opinion on that, so that NASA is an eager customer.
There is no real reason that the EELV-L1 architecture, based on an L1 propellant depot won't work. Is there?
(indeed, LOR-LOR will also work).
If we're going to assume that everything NASA has done to date has been thrown out, I think that would also include Orion "as designed". It was deliberately made too big for the Atlas in the first place so I think the first thing to do is to redesign it and create a spacecraft that the Atlas can fly. Begin by redesigning the Orion. This time the CM should be just a taxi, and not include "living space". It should be a 3-module spacecraft, similar to Soyuz, with a mission module and a properly designed SM. SM and MM are expendable, CM is reusable. And don't worry about carrying enough LOX in the SM to get to the moon at launch time, just the LH2 with enough LOX for initial maneuvering to the depot. Fill up in LEO at the depot before departing. For LEO missions, the SM is fully fueled with its LH2 and LOX and the MM is launched with the CSM and the whole stack shouldn't exceed 18mT. For lunar missions, the SM would be lunar sized (larger) with only a partial LOX load and the LSAM is the MM and would be launched separately, with LOX propellant tank empty. They would all meet up at the depot, fill up and go.

Just a note. The depot is a LOX depot. The LH2 required for the mission is very light and would be carried up at launch time in both the SM and the LSAM. That way we don't worry about boiloff issues for the LH2.

I assume that all expensive systems (life support, guidance, etc.) would be in the reusable CM.

The LSAM should be a reusable, single stage lander, which would not be available for the translunar and trans-Earth coasts. Even if you launch a new LSAM for each mission, you still need an MM for the trans-Earth coast, since I doubt that you will want to push the LSAM's ascent stage through TEI.

Offline kraisee

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #129 on: 12/30/2007 07:16 pm »
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Marsman - 30/12/2007  12:45 PM
What are you assuming?

All of the propellant deliveries still have to be pushed through TLI even when heading just for EML1 - albeit marginally smaller dV (about 3100m/s as opposed to 3150m/s).

This means every flight you are having to boost ~2.5mT of Centaur Stage (actually closer to 3mT at burnout when you account for residuals and such) for every propellant delivery flight to EML1.   That additional mass then requires a similar amount of propellant to be used for each flight, so you end up with ~6mT of "non-usable" performance on each flight - and that stacks up pretty fast with so many missions being flown.

If you can arrange to send only a single Centaur through TLI (using an LEO Depot) you can get better performance overall.   I have been using a WBC design for this BTW and the results aren't bad.

I'm also working out performance for two Lander options.   Given the premise of the thread - budget cuts forcing a smaller mission - I'm working out performance for both a very expensive reusable lander (waiting in LLO) and also a disposable lander (brought for each mission) which would be a lot less costly to develop.   I feel the latter is the more likely option given the overall premise, but I'm working numbers for both anyway.   Performance is only marginally better with the reusable unit.   It seems to be inefficient because it has to lift the entire deadweight during lunar ascent - which hurts many of its benefits.

One side-note regarding reusable landers is that production costs would be pretty high with only one unit every few years - thus fixed costs can not be shared across many units.   Thus, assuming a very favourable $2bn per year of fixed costs for a lander (ESAS lander is closer to $3.5bn/year fixed costs!), if a new one is used every 4 years (3 missions per year, 12 descents & ascents per unit), each lander would cost $8bn plus the actual cost of production and processing - probably $10bn in total and not including maintenance/repair yet.   I'm personally sitting on the fence as to whether that's workable.

I am not currently accounting for ISRU because of its very high cost and currently extremely long expected schedule (I hear 8-10 years from first return landing).   I am also not accounting for on-orbit or on-surface maintenance/repair of a reusable lander - that's an area I don't even know where to begin working out the full scale of the implications, but it doesn't look at all 'easy' to me.

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

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #130 on: 12/30/2007 08:09 pm »
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tnphysics - 30/12/2007  3:15 PM

I assume that all expensive systems (life support, guidance, etc.) would be in the reusable CM.
Yes, all the expensive things would be in the reusable CM.

You bring up an interesting point about the ascent stage. We'd need to run the numbers, but I wonder if this would work.

Basically, the MM serves a dual purpose: (1) MM for both legs of Orion’s trip and (2) “home” for the LSAM during the lunar phase on the lunar surface. It is designed to dock at both ends – one end to the CM and the other end to the Descent stage.

1. The only part of the LSAM that was reusable is the descent stage, the only part of the LSAM with an engine.
2. The Ascent stage (remember - no engine) functions as the MM for the trip out to L1.
3. At L1, the entire stack docks to the Descent stage.
4. LOX is transferred to the Descent Stage –AND- the SM from the L1 depot.
5. The LH2 for the Descent stage is brought along with Orion and transferred to the Descent stage.
6. The LSAM undocks from Orion and drops to the lunar surface.
7. On the surface, the MM/Ascent stage is “home”.
8. At the end of the mission, the LSAM returns to L1 & re-docks with Orion.
9. The MM/Ascent stage undocks from the Descent stage and now is Orion’s MM for the return trip.
10. Orion does the TEI burn and heads home.
11. Just before re-entry, the MM and SM would both be jettisoned for atmospheric disposal as the CM prepared for re-entry.

LOX is delivered by scheduled EELV flights to the depot, but the LH2 for each mission is brought along each time.

What do you think?
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline kraisee

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #131 on: 12/30/2007 08:36 pm »
Chuck,
Its an interesting idea, but I have absolutely no idea how to accurately calculate the mass breakouts for that, so somebody else is going to have to work that out.


Another idea entirely...   Perhaps this is all wrong.   Perhaps we need a different approach entirely.   Think N**lear Lightbulb powered reusable LEO>LLO taxi module.   Always refuelled in LEO.   Crew Module is the *only* thing launched with crew (on something like an Atlas 401 perhaps?), and the only thing disposed of is the lander (early generation architecture), but even it is replaced ultimately with a reusable unit.

Yes, there is a considerable cost for development of the Prometheus tech, but it does simplify things massively overall with the limited lift capacity.

Prometheus Module performs TLI, MMC, Plane Change & LOI.   Then loiters in LLO for the duration of the mission.   Lander undocks, descends, performs surface mission then later ascends & docks.   Prometheus then performs Plane Change, TEI, MCC and EOI and loiters in 220nm LEO for the next mission.   CM undocks and crew immediately re-enters.

Next mission starts by launching new lander to Prometheus Module, then using Centaur-style stages to perform automated dockings to refuel both Prometheus and Lander with suitable propellant.   They use the same docking adapter as the CM ultimately will.

"Life Support" (a la Apollo 13) for Crew is provided by LSAM habitat.

This basic approach scales up to Mars quite nicely too IMHO.

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

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #132 on: 12/30/2007 09:32 pm »
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kraisee - 30/12/2007  4:36 PM

Chuck,
Its an interesting idea, but I have absolutely no idea how to accurately calculate the mass breakouts for that, so somebody else is going to have to work that out.


Another idea entirely...   Perhaps this is all wrong.   Perhaps we need a different approach entirely.   Think N**lear Lightbulb powered reusable LEO>LLO taxi module.   Always refuelled in LEO.   Crew Module is the *only* thing launched with crew (on something like an Atlas 401 perhaps?), and the only thing disposed of is the lander (early generation architecture), but even it is replaced ultimately with a reusable unit.

Yes, there is a considerable cost for development of the Prometheus tech, but it does simplify things massively overall with the limited lift capacity.

Prometheus Module performs TLI, MMC, Plane Change & LOI.   Then loiters in LLO for the duration of the mission.   Lander undocks, descends, performs surface mission then later ascends & docks.   Prometheus then performs Plane Change, TEI, MCC and EOI and loiters in 220nm LEO for the next mission.   CM undocks and crew immediately re-enters.

Next mission starts by launching new lander to Prometheus Module, then using Centaur-style stages to perform automated dockings to refuel both Prometheus and Lander with suitable propellant.   They use the same docking adapter as the CM ultimately will.

"Life Support" (a la Apollo 13) for Crew is provided by LSAM habitat.

This basic approach scales up to Mars quite nicely too IMHO.

Ross.
Oh Ross
You're pushing ALL my buttons at once!
I had this conversation with vanilla on another thread, and we used a NERVA-style engine for the spacecraft's propulsion.
Basically though, we flew Orion to and from HEO, not LEO, because everyone who participated in the conversation said too many people would be nervous about a nuclear engine approaching the earth after the TEI burn.

But my thought was this:
1. Orion lifts off on an Atlas V 401 and meets a completely reusable NERVA powered, single stage LANDER in HEO which is docked at a propellant depot.
2. Crew transfers to the Lander, fills up Lander for the mission from depot supplies and departs for the lunar surface in the lander, leaving Orion docked at the HEO depot.
3. Lander goes from HEO directly to the lunar surface.
4. At the conclusion of the surface mission, Lander lifts off and departs for HEO.
5. Upon arrival at HEO, crew redocks reusable lander with the HEO depot station, transfers to Orion and departs for re-entry.
6. Lander remains docked at HEO depot for servicing as needed, ready for the next mission.

The question is can we do this with an EELV-only architecture?
It would certainly be easier to keep the depot serviced in HEO rather than L1. The HEO depot would be serviceable by many more launchers from several different counties, plus more alt.space companies as they come on-line. If we are serious about enabling startup commercial launch companies, we could mandate some minimum percentage of supplies to come from them once they become available and prove reliable.

Vanilla's conclusion, after going thru the rocket equations, was that this would certainly work, but that economically (cost of delta-V) the NERVA didn't offer any advantages. My response was that it didn't need to be advantages at this point, because it was just the "beginning" of nuclear use. Basically, by recreating and fielding an updated NERVA, we were committing ourselves to "picking up where we left off", sort of like Griffin is doing with "Apollo on Steroids". Basically, we would be committing to using nuclear power in space for transportation, rather than chemical. We all know that NERVA would represent only the bottom tier of what is possible, but it is a design that was already created, successfully fired many, many times, and was being prepared for actual manned flight test when Apollo was canceled.

My thoughts were that the updated NERVA would only be the precursor of better, more efficient engines that would be gradually developed and fielded as we gained more experience working with nuclear engines. NERVA would simply be opening the door with something that we already know how to do and that we know already works.

I continue to believe that we will never do anything really serious in space until we leave off the irrational fear of all things nuclear. Yes, it is dangerous. So is the gasoline in the tank of the family car. It's all about proper risk mitigation. We've had nuclear powered ships at sea for over 50 years and we have never had a nuclear accident, because the risk mitigation is proper. It is the power source of the future that will open the solar system to us. At some point we are just going to have to get on with it and stop hiding behind the rocks at the opening to our caves.

I'll search out where that thread is and come back and edit this post to provide the link, for anyone who is interested.

Ok, I'll put my soapbox away now. Sorry.

Edit: Adding the Promised Link:
Nuclear Rockets Could Cut the Cost of a Moon Base
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=8605&start=1

An additional thread discussion:
What about a Nuclear Upper Stage?
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=9905&start=1

Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline kraisee

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #133 on: 12/30/2007 10:24 pm »
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clongton - 30/12/2007  5:32 PM
Oh Ross
You're pushing ALL my buttons at once!
I had this conversation with vanilla on another thread, and we used a NERVA-style engine for the spacecraft's propulsion.
Basically though, we flew Orion to and from HEO, not LEO, because everyone who participated in the conversation said too many people would be nervous about a nuclear engine approaching the earth after the TEI burn.

I don't have the same fear.   I'm more concerned about suns radiation effects in HEO.   Approaching Earth you're always in a Hohmann Transfer orbit - a highly eliptical one of course, but the low-point of the orbit (periapsis) would never be targetted below 200-400nm LEO.

An non-catastrophic engine failure would leave the spacecraft in a highly eliptical orbit.

If the engine were to fail spectacularly, you will still never end up lower than that.   The worst case scenario is some fragments of an exploded engine might degrade down towards the atmosphere, but they are going to have to re-enter without protection.   I wouldn't expect anything to reach the surface.

But I would personally want a such an engine to be built to a much higher safety margin than normal engines.   If normal hardware has a 1.4 safety factor, then this thing needs to be 2.0 or better - and designed to handle catestrophic failure in a fashion which does not risk the atmosphere.


As for making the lander go all the way from Earth to the Lunar Surface - I don't think thats workable myself because it makes the Lander awfully big and heavy carrying all that propellant.   It also offers zero lifeboat capability during transit, so I don't think its the right approach myself.

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

Offline meiza

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #134 on: 12/30/2007 10:27 pm »
nukes could be useful for Mars, not the moon.

Offline kraisee

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #135 on: 12/30/2007 10:44 pm »
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meiza - 30/12/2007  6:27 PM

nukes could be useful for Mars, not the moon.

With such high Isp, they're useful anywhere.   NERVA was the next step in Apollo and would have been fielded within two years of Apollo 17 if that program had not been cancelled prematurely.

The only real limitations are the development cost and the schedule impacts.   If they prove not to be a problem, then it is a very good way to go.   That and getting around the general bad public opinion of nuclear.

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

Offline clongton

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #136 on: 12/30/2007 11:11 pm »
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kraisee - 30/12/2007  6:24 PM

I don't have the same fear.   I'm more concerned about suns radiation effects in HEO.   Approaching Earth you're always in a Hohmann Transfer orbit - a highly elliptical one of course, but the low-point of the orbit (periapsis) would never be targeted below 200-400nm LEO. A non-catastrophic engine failure would leave the spacecraft in a highly elliptical orbit.

If the engine were to fail spectacularly, you will still never end up lower than that.   The worst-case scenario is some fragments of an exploded engine might degrade down towards the atmosphere, but they are going to have to re-enter without protection.   I wouldn't expect anything to reach the surface.
I feel the same way. I allowed my original posts to change to HEO however so that I wouldn’t have to argue what was to me a peripheral argument.

Quote
But I would personally want such an engine to be built to a much higher safety margin than normal engines.   If normal hardware has a 1.4 safety factor, then this thing needs to be 2.0 or better - and designed to handle catastrophic failure in a fashion, which does not risk the atmosphere.

As for making the lander go all the way from Earth to the Lunar Surface - I don't think that’s workable myself because it makes the Lander awfully big and heavy carrying all that propellant.   It also offers zero lifeboat capability during transit, so I don't think its the right approach myself.

Ross.
Remember, the amount of fissile material in the engine is extremely small. There is not enough for the mass to go critical enough for an explosion, only enough to get extremely hot. KEY POINT: It cannot explode! It would NOT be difficult to create a fuel container designed to survive re-entry without a tps, intact. That is what I would consider to be a minimum requirement of safety. Nuclear material would never be allowed to contaminate the atmosphere, even in the worst possible case of spacecraft destruction (which btw, could never be caused by the presence of nuclear fuel).

Any nuclear powered reusable spacecraft would be built to such higher standards that the need for a lifeboat would be “unlikely” to say the least. Using throwaway modules, like Apollo did, require that everything be minimized. Switching to the nuclear powered reusable spacecraft is a paradigm shift in attitude toward spacecraft design. It’s like switching from “manufacturing” the mass-produced Dodge Neon to “building” the hand-crafted Lotus Elan. It’s just a different vehicle altogether. It would most likely have “at least” three-fault tolerant systems, if not better, be stronger built, be much more durable and designed from the beginning to recover from almost any conceivable space-based event that would cripple a throw-away module like the Apollo SM. Such an approach opens a world of possibilities. The Orion spacecraft no longer needs to be the be-all, do-all spacecraft. It can be what it always should have been; a taxi that takes its crew up to meet the “real” spaceship. Orion would never be required to leave earth orbit, because that’s where it is designed to go. All the space-based activities would be with real spacecraft that are designed to never taste an atmosphere, so their designs are optimized for space. Orion isn’t optimized for space at all. It’s not even remotely possible. It’s a compromise designed to survive an atmospheric re-entry. Going this route removes that constraint from Orion. It no longer needs to compromise it’s design. It can be made much lighter and more suited to it’s actual role; transport the crew into space where they will transfer to their respective spacecraft, or return them safely and comfortable to their “point of origin” on the earth’s surface. Kinda like taking your car to the train station, parking it there and riding the train across the country to the other side, then riding it back again, right to your car, which takes you right back home again. Each vehicle does what it does best, without compromising it’s real function.

The rocket equations showed that this would actually work. With a NERVA design, it didn’t give us an advantage – it was a wash. But that’s ok because all it does is get us started on the path that would end up paving the way for a true space-faring civilization – powered by nuclear energy. NERVA is the bottom of the nuclear barrel in terms of potential. Even at the bottom it was a wash. It can only get better, whereas we are just about maxed out as far as what we can do with chemicals.

So our best chemicals are a wash with the worst nuclear. I’d say that’s a good transition point.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline meiza

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #137 on: 12/30/2007 11:35 pm »
"It cannot explode"
So how about a failure causing a temperature excursion and core disintegration sending a big portion of the core to free space?

Offline clongton

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #138 on: 12/30/2007 11:39 pm »
Quote
meiza - 30/12/2007  7:35 PM

"It cannot explode"
So how about a failure causing a temperature excursion and core disintegration sending a big portion of the core to free space?
Not enough fissile material on board for that to happen. It would be the way it is designed. If you took all the fissile material out of their jackets and put it all together in a pile, all mixed in real good, all it would do is get extremely hot. It takes a minimum amount to go critical, and that minimum amount would not be on board.

Meiza, that would be the design parameter. That core safety feature would be the very basis of the design and be inviable. Built in to the basic design. Non-explodable. Core non disintegratable. Safety first, middle and last. Basic design feature. Everything else goes from that immutable design point.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline meiza

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Re: To the Moon and Beyond–Examining the EELV-L1 Approach v2
« Reply #139 on: 12/30/2007 11:56 pm »
I'm not a nuclear engineer, but if there is so little material (or it's in a sparse matrix) that it can't even melt itself when made to a pile, (I assume it reaches a steady state where it radiates as much heat as it generates, glowing white hot) what will the hydrogen temperature actually be when it flows through the core. I mean, these seem as pretty opposite design parameters. You want a hot core to make hot hydrogen for high ISP and high thrust but you want a cool core for failure safety. The power is the same in both cases, for an engine that can not explode.

Someone could easily calculate the loss of coolant accident temperature for various size cores with various power ratings with the Beer-Lambert law....

As far as I know, the nerva designs were not safe in this regard (and not in many other regards either). But I could be wrong.

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