Boeing's plan for Mars

kbd512 · 2015-02-06 15:37:35

I know that chemical, electric, and nuclear thermal propulsion systems all work.

To me, it's a question of what's most suitable for a task, not simply whether or not a particular technology is immediately available.

If you'd have told people 20 years ago that they'd have computers in their pockets that were more powerful than a workstation or server of the times, they'd have told you that that was pure fantasy. Oddly enough, this little technological marvel can be found in the pockets of most working age adults in industrialized countries today.

If we allow the nay-sayers to impede progress because of their short-sightedness, fear, or ego, then technological innovation stagnates and irreplaceable time is lost.

Every study I've seen shows that use of SEP for manned Mars transit vehicles results in the longest transit times, the fewest days spent on Mars, and requires just as many or more launches to implement as NEP or NTR powered transit vehicles. Will improvements in solar panel and thruster technology begin to favor SEP for Mars missions? I certainly hope so, but hope and probability are two entirely different things.

We have another 15 years or so to work on SEP and active radiation shielding to make the transit from LEO to LMO in six months or less or devise a lightweight radiation protection system that permits longer duration flights.

I think nuclear technology provides a redundant and, for certain uses, complementary capability.

Terraformer · 2015-02-06 15:52:29

If you use SEP on your craft, you can send it to EML1 cheaply, send your crew to it fast in a chemically powered capsule, and then use a gravity assist to cut the transit time down to 3 months. Of course, at Mars you don't have to worry about radiation belts, so you can possibly use SEP directly to leave. Or park it in a high orbit and do what you did at Terra.

I don't see why we need to use 6+ month transit times, just because we're not using nuclear...

Impaler · 2015-02-07 01:17:24

kb: As usual everything you say is flat out wrong, you have clearly not even read the material and simply have the idea stuck in your head that Nuclear is superior in every way and in every application to "dirty hippy solar", your rantings on Nuclear power not getting used on Earth (which have zero bearing on in-space use) show that your nothing more then a nuclear ideologue who is trying to re-fight that battle in a new territory, one you haven't done the slightest research in.

And by the way your '20 years ago' was 1994, any one who could not extrapolate Mores law (which had been roaring along for 20 years already) out another 20 years to reach to obvious conclusion that YES your phone would be hugely more powerful then a server would have been a FLIPPING IDIOT. Just as someone today who has ANY doubt that SEP are going to continue the relentless advances they have made in the last 20 years after the technology come to the west. Conversely people who think a dead technology like NTR, aka trend line of ZERO improvement in 30 years is going to suddenly and for no compelling reason take off would be just as foolish. While you TALK about huge progress potential you show your naked bias by saying you 'hope' SEP advances, while having blind-faith in all things Nuclear.

For specifics, as Terraformer points out you DO NOT TIME FROM LEO TO LMO, your repeated attempts to define this a the goal is blatantly dishonest. You send the mission hardware and/or habitat ship to High Earth Orbit first and then send the crew up to it by a taxi capsule crossing the Radiation belt at speed as has always been done. The crew needs that capsule for return to Earth surface ANYWAYS irregardless of the main propulsion system so it is not a disadvantage vs any other main propulsion system. THAT is what Boeing proposed in the mission concept on the FIRST POST, so your apparent ignorance of this indicates you haven't even read that. Second this proposal has SIGNIFICANTLY reduced SLS launches over NTR DRM5 as I already pointed out to you, again you are simply spewing bullshit when you say that SEP doesn't reduce launch mass.

I disagree with Terraformer that gravity assist can reduce transit times to 3 months even from EML1, I think he is confusing gravity assist with oberth-assisted impulsive burns. I've read that three impulsive burns at EM1, Lunar flyby and Earth flyby totaling just 1.2 km/s can send one on a good 6 month transit to Mars, a big savings from doing 4.4 km/s for the same thing from LEO. But 3 months would take considerably more DeltaV then that and I don't think that gravity assists off the Earth itself can be done quickly enough to be useful for human missions (robotic missions needed years of time to do multiple flybys).

Remember HOW LONG YOU TAKE TO REACH EDGE OF EARTH SPHERE OF INFLUENCE IS IRREVERENT TO HELIOCENTRIC TRANSFER TIMES, but climbing the Earth Gravity well is NEARLY ALL OF THE DELTAV of a slowest Holman transfer. We can go slow and efficient inside the Earth Sphere of influence and switch to faster but less efficient propulsion for the Heliocentric transfer once the crew is on board.

Thus the total DeltaV between 6 months and 8 months transit is VERY small, it is only when you try to go below 3 months that DeltaV starts to get really hard. We can do 6 months with SEP with 5k static ISP and a SEP system (solar and thrusters) totaling just 80 W/kg, or using the 'alpha' spec common in SEP system design which is 12.5 kg/kW. And that is COMPLETELY within current technology, our HALL thrusters and power processing units combined are 2 kg/kw which leaves the Solar a full 10 kg/kw, which is a pathetic 100 W/kg, ROSA array already beats that. And both of these numbers are going to keep improving, but basically we can do a transfer of that duration now if were willing to have a SEP hardware mass of around half the total vehicle mass with payload around 25% using these SANDBAGGED numbers and off the shelf components, that's 'ugly' by SEP standards (but normal by rocket standards) and their is so much potential improvement it would be wasteful to do such a mission now, what will happen is that we will do another decade or two of development and end-up sending vehicles that are 10-20% hardware mass and >50% payload. All the other systems like EDL and life-support are at least that far away from being completed anyways.

This is Ad-Astra's mission to Mars trajectory plan, applicable to any SEP as they have numbers for fixed and variable ISP
http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf

Here are the numbers on current alpha and ISP values of thrusters
http://enu.kz/repository/2010/AIAA-2010-6771.pdf

Basically where SEP is RIGHT BLOODY NOW, is already competitive with your nonsense Nuclear HIGHEST THEORETICAL POTENTIAL, but SEP has not even scratched the surface of it's theoretical potential. When we start talking highest theoretical potential of SEP the transit times are 1 MONTH, which I pray we don't ever NEED because it's terribly wasteful of payload fraction and we should send more payload to help mitigate radiation and other dangers and in general enhance the surface stay.

Last edited by Impaler (2015-02-07 01:27:25)

Terraformer · 2015-02-07 08:34:43

Ah yes, I meant an Oberth-assist. The figure I saw (I think it was something Hop posted?) was 3.6km/s for the 3 month transit. I think that's manageable, and will possibly allow us to dispense with a centrifuge system. Of course, the solar panels will probably have to be folded in for that, but they'll also have to do that if we use aerocapture...

Everything else will, of course, be sent the slow way. A unused Hab can cope with spending 8 months in transit. Perhaps fuel can be sent as well, allowing the ship to refuel on arrival for it's return?

kbd512 · 2015-02-07 13:32:29

Impaler wrote:

kb: As usual everything you say is flat out wrong, you have clearly not even read the material and simply have the idea stuck in your head that Nuclear is superior in every way and in every application to "dirty hippy solar", your rantings on Nuclear power not getting used on Earth (which have zero bearing on in-space use) show that your nothing more then a nuclear ideologue who is trying to re-fight that battle in a new territory, one you haven't done the slightest research in.

My statements about use of solar technology, made in the context of human space flight only, have nothing to do with whether I like solar panels and everything to do with the limitations of the technology and what use of the technology requires in the context of human space flight.

If I'm a nuclear ideologue then you're most certainly a solar ideologue. Most of your posts in this thread have started with how stupid I am or how wrong I am, but then fail to provide evidence about why what I proposed won't work or how it's inferior to solar electric technology. If you have any cogent arguments about why what I've proposed won't work, I'd love to know. Apart from lots of adolescent insults, which may be all that you have to offer, you've proven spectacularly incapable of providing anything approaching a technical argument about why nuclear technology is inferior to solar electric technology.

Impaler wrote:

And by the way your '20 years ago' was 1994, any one who could not extrapolate Mores law (which had been roaring along for 20 years already) out another 20 years to reach to obvious conclusion that YES your phone would be hugely more powerful then a server would have been a FLIPPING IDIOT. Just as someone today who has ANY doubt that SEP are going to continue the relentless advances they have made in the last 20 years after the technology come to the west. Conversely people who think a dead technology like NTR, aka trend line of ZERO improvement in 30 years is going to suddenly and for no compelling reason take off would be just as foolish. While you TALK about huge progress potential you show your naked bias by saying you 'hope' SEP advances, while having blind-faith in all things Nuclear.

When there's no development of a technology, it doesn't magically improve. Funny that. Whether or not anyone is working on development of a technology has no bearing on its utility.

I'm not advocating for the replacement of your favorite technology, just the development of a complementary technology that doesn't require an external energy source to function. Wouldn't the fact that I kept writing about development funding for SEP tugs for Mars bound cargo indicate this, or did you ignore those parts of what I wrote because it doesn't support your sophomoric argument about my bias against solar technology?

Impaler wrote:

For specifics, as Terraformer points out you DO NOT TIME FROM LEO TO LMO, your repeated attempts to define this a the goal is blatantly dishonest. You send the mission hardware and/or habitat ship to High Earth Orbit first and then send the crew up to it by a taxi capsule crossing the Radiation belt at speed as has always been done. The crew needs that capsule for return to Earth surface ANYWAYS irregardless of the main propulsion system so it is not a disadvantage vs any other main propulsion system. THAT is what Boeing proposed in the mission concept on the FIRST POST, so your apparent ignorance of this indicates you haven't even read that. Second this proposal has SIGNIFICANTLY reduced SLS launches over NTR DRM5 as I already pointed out to you, again you are simply spewing bullshit when you say that SEP doesn't reduce launch mass.

Van Impe, my solevangelist friend, your repeated attempts to ignore what Boeing has in their presentations is what's blatantly dishonest.

The transit times are in Boeing's presentation and are transit times from/to EML2, not LEO.

Boeing wants to put a 130t SEP tug into LEO. There is no launch vehicle capable of putting something that massive into LEO and short of using liquid boosters (redesigning SLS and redesigning the launch facility accommodations) or addition of another RS-25 to SLS (redesigning SLS), there won't be one in the next 10 to 15 years, either. Read the first part of the previous sentence and let that sink in.

Even if this SEP tug that Boeing wants to build to send humans to Mars was available today, it wouldn't matter because there's no rocket capable of launching it.

The SEP tug, less propellant, could be launched on a F9H. The propellant mass is above current SLS capability. It requires SLS Block IA.

Boeing's proposal requires fewer SLS launches than DRM 5 due to the absence of one cargo mission, use of inflatable heat shields, and refueling of the SEP tug at EML2.

Impaler wrote:

I disagree with Terraformer that gravity assist can reduce transit times to 3 months even from EML1, I think he is confusing gravity assist with oberth-assisted impulsive burns. I've read that three impulsive burns at EM1, Lunar flyby and Earth flyby totaling just 1.2 km/s can send one on a good 6 month transit to Mars, a big savings from doing 4.4 km/s for the same thing from LEO. But 3 months would take considerably more DeltaV then that and I don't think that gravity assists off the Earth itself can be done quickly enough to be useful for human missions (robotic missions needed years of time to do multiple flybys).
Remember HOW LONG YOU TAKE TO REACH EDGE OF EARTH SPHERE OF INFLUENCE IS IRREVERENT TO HELIOCENTRIC TRANSFER TIMES, but climbing the Earth Gravity well is NEARLY ALL OF THE DELTAV of a slowest Holman transfer. We can go slow and efficient inside the Earth Sphere of influence and switch to faster but less efficient propulsion for the Heliocentric transfer once the crew is on board.

I would like to get the crew to Mars in six months or less, as I've previously stated, because I want the crew to spend at least as many days on Mars as they spend in transit to/from Mars. I don't care if it can be done in 3 months or 1 month.

Impaler wrote:

Thus the total DeltaV between 6 months and 8 months transit is VERY small, it is only when you try to go below 3 months that DeltaV starts to get really hard. We can do 6 months with SEP with 5k static ISP and a SEP system (solar and thrusters) totaling just 80 W/kg, or using the 'alpha' spec common in SEP system design which is 12.5 kg/kW. And that is COMPLETELY within current technology, our HALL thrusters and power processing units combined are 2 kg/kw which leaves the Solar a full 10 kg/kw, which is a pathetic 100 W/kg, ROSA array already beats that. And both of these numbers are going to keep improving, but basically we can do a transfer of that duration now if were willing to have a SEP hardware mass of around half the total vehicle mass with payload around 25% using these SANDBAGGED numbers and off the shelf components, that's 'ugly' by SEP standards (but normal by rocket standards) and their is so much potential improvement it would be wasteful to do such a mission now, what will happen is that we will do another decade or two of development and end-up sending vehicles that are 10-20% hardware mass and >50% payload. All the other systems like EDL and life-support are at least that far away from being completed anyways.

We can revisit where we're at with solar technology in another decade or two.

Impaler wrote:

This is Ad-Astra's mission to Mars trajectory plan, applicable to any SEP as they have numbers for fixed and variable ISP
http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf

Forgive me, but did you just post a document where the author recommended the development of advanced nuclear power technology?

Impaler wrote:

Here are the numbers on current alpha and ISP values of thrusters
http://enu.kz/repository/2010/AIAA-2010-6771.pdf

Another document that proposes further investigation of advanced nuclear technology?

Impaler wrote:

Basically where SEP is RIGHT BLOODY NOW, is already competitive with your nonsense Nuclear HIGHEST THEORETICAL POTENTIAL, but SEP has not even scratched the surface of it's theoretical potential. When we start talking highest theoretical potential of SEP the transit times are 1 MONTH, which I pray we don't ever NEED because it's terribly wasteful of payload fraction and we should send more payload to help mitigate radiation and other dangers and in general enhance the surface stay.

You're using an argument about the theoretical potential of SEP against the theoretical potential of NEP or NTR.

Impaler · 2015-02-07 22:43:37

kbd512 wrote:

If I'm a nuclear ideologue then you're most certainly a solar ideologue. Most of your posts in this thread have started with how stupid I am or how wrong I am, but then fail to provide evidence about why what I proposed won't work or how it's inferior to solar electric technology. If you have any cogent arguments about why what I've proposed won't work, I'd love to know. Apart from lots of adolescent insults, which may be all that you have to offer, you've proven spectacularly incapable of providing anything approaching a technical argument about why nuclear technology is inferior to solar electric technology.

Every single post I've made has pounded you into the ground on technical details, we have been over Specific Impulse, power density of solar panels, payload mass fractions, initial mass in LEO. To say I haven't provided any technical argument is THE BIGGEST LIE YET from you.

kbd512 wrote:

I'm not advocating for the replacement of your favorite technology, just the development of a complementary technology that doesn't require an external energy source to function. Wouldn't the fact that I kept writing about development funding for SEP tugs for Mars bound cargo indicate this, or did you ignore those parts of what I wrote because it doesn't support your sophomoric argument about my bias against solar technology?

Your arguing for a massive multi-billion dollar research effort that will replace the current NASA program whole-sale. You need to justify that kind of expenditure by showing that it is superior to any alternative and I've shown that it is markedly inferior instead. Thus your arguing for money to be thrown down a rat-hole and I'm going to oppose that no matter who's backside the money is coming out of.

kbd512 wrote:

Van Impe, my solevangelist friend, your repeated attempts to ignore what Boeing has in their presentations is what's blatantly dishonest.
The transit times are in Boeing's presentation and are transit times from/to EML2, not LEO.
Boeing wants to put a 130t SEP tug into LEO. There is no launch vehicle capable of putting something that massive into LEO and short of using liquid boosters (redesigning SLS and redesigning the launch facility accommodations) or addition of another RS-25 to SLS (redesigning SLS), there won't be one in the next 10 to 15 years, either. Read the first part of the previous sentence and let that sink in.
Even if this SEP tug that Boeing wants to build to send humans to Mars was available today, it wouldn't matter because there's no rocket capable of launching it.
The SEP tug, less propellant, could be launched on a F9H. The propellant mass is above current SLS capability. It requires SLS Block IA.
Boeing's proposal requires fewer SLS launches than DRM 5 due to the absence of one cargo mission, use of inflatable heat shields, and refueling of the SEP tug at EML2.

WOW, Boeing actually made a plan on a piece of paper to USE the vehicle that is the current NASA official goal to create. That sure is a lot of unwarranted faith in THEMSELVES to be able to build it don't you think?

Oh and it's not ready to fly this bloody second either?? Did it ever occur to you that this Boeing plan is perhaps INTENDED FOR THE FUTURE, you know when NASA said they were actually aiming to go to Mars? Now I know your a smoking that Zubrin pipe that says we 'SHOULDA' been on Mars in oh around 1875 or some junk but in the real world things like landing more then 1 ton on Mars and having remotely closed loop life-support are real barriers that can't be glossed over.

Seriously you are absolutely insufferable, it takes decades to develop space vehicles and planning and thinking about how to use them before they are ready to use it the only prudent thing to do, one of the biggest problems with SLS is we DON'T have payloads for it, now you want to rule out even THINKING about payloads of 130 mt until the vehicle is their waiting on the launch pad? That is a guaranteed way to never use the capacity created.

kbd512 wrote:

Forgive me, but did you just post a document where the author recommended the development of advanced nuclear power technology?

No, that would be your desperation speaking, the VASIMIR folks want power at high density, they look at literature on potential solar and nuclear power in terms of theoretical potential and are indifferent as to which ends up providing it. They are not power system experts and can be forgiven for not being well informed about the relative costs to develop these systems or the current state of the art. People who are actually developing Electric propulsion vehicles do not waste time on nuclear fantasies.

kbd512 wrote:

You're using an argument about the theoretical potential of SEP against the theoretical potential of NEP or NTR.

Dose an apples-2-apples comparison frighten you? The fair comparisons are theoretical potentials to theoretical potentials, or current systems to current systems. I've done both and you've been crushed both ways and even the grossly unfair comparison of nuclear theoretical potential to SEP current systems the SEP system is basically tied. I make that intentionally unfair comparison simply to demonstrate how inferior your position is, yet you refuse to see it.

kbd512 · 2015-02-08 01:45:30

Impaler wrote:

Every single post I've made has pounded you into the ground on technical details, we have been over Specific Impulse, power density of solar panels, payload mass fractions, initial mass in LEO. To say I haven't provided any technical argument is THE BIGGEST LIE YET from you.

You've firmly staked your fantasy into the ground, but little else.

The specific impulse numbers that are achievable with SEP are achievable by accelerating V-E-R-Y S-L-O-W-L-Y. So slow that it extends the duration of a manned Mars mission to more than two years and provides for a stay of less than a year on Mars. These numbers come from NASA, Boeing, and every other proposal I've ever seen. Maybe they're all lying because it doesn't support your argument or maybe, just maybe they're trying to tell you something. When higher thrust is utilized to accelerate faster and reduce transit time, the specific impulse drops to numbers that are less than those that would be produced by an advanced NTR.

Impaler wrote:

Your arguing for a massive multi-billion dollar research effort that will replace the current NASA program whole-sale. You need to justify that kind of expenditure by showing that it is superior to any alternative and I've shown that it is markedly inferior instead. Thus your arguing for money to be thrown down a rat-hole and I'm going to oppose that no matter who's backside the money is coming out of.

No, you haven't shown that it's markedly inferior. You've shown that SEP looks better on paper when you use specific impulse numbers that require loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong transit times.

Impaler wrote:

WOW, Boeing actually made a plan on a piece of paper to USE the vehicle that is the current NASA official goal to create. That sure is a lot of unwarranted faith in THEMSELVES to be able to build it don't you think?

It doesn't matter how much faith Boeing has in themselves. Boeing is building a giant gas can for SLS and assembling parts into a rocket. According to ATK, not kbd512 or Impaler or Boeing, 130t without a 5th RS-25 is wishful thinking. If ATK doesn't know how far and how fast their rockets will push the core stage, then I'm going to go way out on a limb and say that no one else does. The SLS core stage doesn't have enough fuel or thrust to put 130t in LEO using current or proposed advanced solid boosters.

The Dynetics liquid boosters would provide enough thrust to put more than 130t in LEO, but according to a NASA engineer working on the redesign of the MLS, there is not room on the pad for the TSM's required for liquid boosters and no facilities have been built to store and pump RP-1 at the pad.

Impaler wrote:

Oh and it's not ready to fly this bloody second either?? Did it ever occur to you that this Boeing plan is perhaps INTENDED FOR THE FUTURE, you know when NASA said they were actually aiming to go to Mars? Now I know your a smoking that Zubrin pipe that says we 'SHOULDA' been on Mars in oh around 1875 or some junk but in the real world things like landing more then 1 ton on Mars and having remotely closed loop life-support are real barriers that can't be glossed over.

You keep throwing that argument in my face about GCNR's, so yeah, I'll throw it back in yours over SLS.

If NASA was permitted to move forward with NTR's and continue use of Saturn V, we'd have been on Mars decades ago. You can call that speculation if you wish, but all of the technology development made it pretty apparent that NASA was serious about the goal.

Let's roll back the clock to 1972 and take stock of where we were more than four decades ago:

* Flight-rated capsule system
* Flight-rated lunar lander, obviously not a Mars lander, but at least it could land somewhere besides Earth
* HLV capable of 130t (150t with F-1A) to LEO
* 1 year out from having a giant Mars transit vehicle, better known as Skylab
* 3 years out from having a flight-rated NTR capable of taking humans to Mars in 6 months or less

Fast forward 45+ years (yes, 45 years because 2 years from now we still won't have a man rated capsule or SLS rocket):

* No flight rated capsule system or manned spacecraft of any kind
* No lander of any kind
* No HLV of any kind
* Russians are nice enough to give us rides to ISS

Impaler wrote:

Seriously you are absolutely insufferable, it takes decades to develop space vehicles and planning and thinking about how to use them before they are ready to use it the only prudent thing to do, one of the biggest problems with SLS is we DON'T have payloads for it, now you want to rule out even THINKING about payloads of 130 mt until the vehicle is their waiting on the launch pad? That is a guaranteed way to never use the capacity created.

I feel the exact same way about you. Your arguments about forward thinking versus what's available right now apply when it favors your arguments but don't apply when it doesn't favor your arguments.

I want to rule out payloads that simply aren't possible with the current SLS architecture, absent many more billions spent and more years of development that entail redesign of the vehicle and/or launch accommodations. You stated that investment in nuclear technology would be some sort of wholesale diversion of funding. Guess what Orion and SLS are right friggin now!?

Orion can't land anywhere but an ocean, it doesn't have the interior volume to carry the provisions required to take astronauts anywhere into deep space, it has already wasted billions of dollars and will waste many more billions if it's permitted to continue to exist, and all the while NASA lacks funding for those systems that it thinks are critical for deep space operations, like closed loop life support and radiation shielding.

Impaler wrote:

No, that would be your desperation speaking, the VASIMIR folks want power at high density, they look at literature on potential solar and nuclear power in terms of theoretical potential and are indifferent as to which ends up providing it. They are not power system experts and can be forgiven for not being well informed about the relative costs to develop these systems or the current state of the art. People who are actually developing Electric propulsion vehicles do not waste time on nuclear fantasies.

Then I guess the people who are working on these technologies are suffering from the same fantastical thinking as I am, because they all seem to say the same thing and it all seems to run counter to what you're saying. That solar panel on your head is baking your brain.

Impaler wrote:

Dose an apples-2-apples comparison frighten you? The fair comparisons are theoretical potentials to theoretical potentials, or current systems to current systems. I've done both and you've been crushed both ways and even the grossly unfair comparison of nuclear theoretical potential to SEP current systems the SEP system is basically tied. I make that intentionally unfair comparison simply to demonstrate how inferior your position is, yet you refuse to see it.

The theoretical specific impulse of a GCNR starts at 3000s and climbs all the way to 6000s. Whether the former or latter most accurately reflects actual performance, transit time is six months or less. The only way your favorite technology achieves that kind of specific impulse, currently or theoretically, is when transit duration is sacrificed.

Last edited by kbd512 (2015-02-08 01:47:38)

RobertDyck · 2015-02-08 10:21:39

kbd512 wrote:

Let's roll back the clock to 1972 and take stock of where we were more than four decades ago:
...
* HLV capable of 130t (150t with F-1A) to LEO

Saturn C-5 as designed on paper was supposed to lift 127 metric tonnes to LEO, or 45 metric tonnes to trans-Lunar trajectory. Saturn V as built was able to lift 118 metric tonnes to 185km orbit @ 28° inclination, or 47 metric tonnes to trans-Lunar trajectory.

Saturn INT 21 was the first and second stage of a Saturn V, with no third stage. This was used just once to launch Skylab. It was able to lift 115.9 metric tonnes to 185km orbit @ 28° inclination.

SLS: the only configuration able to lift 130t will have 5 SSME, advanced boosters, and an upper stage with a pair of J-2X engines, and fuel tanks with the same diameter as the core stage. They're now talking about only building SLS with 4 SSME, and I don't know if either proposed advanced booster will ever be built, we may only get 5-segment SRBs. All that will significantly reduce lift capacity. And Saturn V as built had reduced lift capacity without compromising number of engines. Be afraid, be very afraid.

kbd512 · 2015-02-08 11:19:16

RobertDyck wrote:

Saturn C-5 as designed on paper was supposed to lift 127 metric tonnes to LEO, or 45 metric tonnes to trans-Lunar trajectory. Saturn V as built was able to lift 118 metric tonnes to 185km orbit @ 28° inclination, or 47 metric tonnes to trans-Lunar trajectory.

Yep, forgot about that. However, with F-1A's it would have been far closer to 150t to LEO than SLS will ever be. Even as-built, it was an improvement over SLS in terms of initial capability.

RobertDyck wrote:

SLS: the only configuration able to lift 130t will have 5 SSME, advanced boosters, and an upper stage with a pair of J-2X engines, and fuel tanks with the same diameter as the core stage. They're now talking about only building SLS with 4 SSME, and I don't know if either proposed advanced booster will ever be built, we may only get 5-segment SRBs. All that will significantly reduce lift capacity. And Saturn V as built had reduced lift capacity without compromising number of engines. Be afraid, be very afraid.

This is speculation on my part, but I think that these factors drove the selection of the number of engines for SLS Block I:

- A 4 RS-25 Block I met the required performance target for IOC
- The RS-25 is an expensive engine and a restart of the production line is required to manufacture additional stock, so with existing stocks a flight test program could be completed

I expect that advanced boosters will eventually be developed, but the only option that NASA actually has infrastructure to support the use of is solid.

The J-2X is currently on hold because the engines didn't meet performance expectations, although I expect that the program will be revived when no suitable replacement exists.

kbd512 · 2015-02-08 11:52:52

To their credit, Boeing is actively looking for ways to reduce the cost and weight of the ET. Robotic FSW and spun domes are part of the initial plan and composite tanks and thrust structures are further down the road. Testing on sub scale test articles was completed last year. If testing on full scale test articles goes well, SLS would come really close to the 130t target with advanced solids and the 4 RS-25 core stage.

I'm crossing my fingers and praying to the rocket gods.

SpaceNut · 2015-02-08 17:14:54

The time from LEO to LMO and back is important it should be kept to a minimum for exposure to radiation plus effects from 0 G.

We have its effect well documented, Outer Space: What are the health effects of staying in outer space for extended periods of time?
•damaging cosmic radiation
•bone structure weakening due to zero g
•muscle weakening and loss due to zero g
•can have psychological impacts as well

Living in Space

Known effects of long-term space flights on the human body

http://www.bio-medicine.org/tag/iss/

Effect of spaceflight on the human body

So lets study the effects on other spieces
A New Purpose for the Pesky Fly

RobertDyck · 2015-02-08 18:03:32

kbd512 wrote:

The J-2X is currently on hold because the engines didn't meet performance expectations, although I expect that the program will be revived when no suitable replacement exists.

J-2: first launch 1966. Used for 2nd & 3rd stages of Saturn V, and upper stage of Saturn 1B.
Engine mass: 1,438kg
Thrust: 1,033.10 kN (232,250 lbf)
Isp (vacuum): 421s, Isp (sea level): 200s
Burn time: 475s

J-2S, Developed 1965-1969, first launch 1967. Proposed Saturn follow-on vehicles
Engine mass: 1,400kg
Thrust: 1,138.50 kN (255,945 lbf)
Isp (vacuum): 436s
Burn time: 475s

J-2X, development 2006-2016, certified for test flight 2012.
Engine mass: 2,430kg
Thrust: 1,310.00 kN (294,490 lbf)
Isp (vacuum): 448s
Burn time: 431s

Aviation Week, Oct 4, 2013: NASA’s J-2X Engine To Be Mothballed After Testing
NASA, June 14: J-2X Engine No. 10002 Tests at Stennis Space Center
NASA fact sheet: The J–2X Engine

The above tests are on the A-1 test stand at Stennis. The Washington Post article is about the A-3 test stand. The difference is A-1 is open air, while A-3 simulates vacuum.

Last edited by RobertDyck (2015-02-08 18:29:37)

Impaler · 2015-02-11 23:31:40

kbd512 wrote:

The specific impulse numbers that are achievable with SEP are achievable by accelerating V-E-R-Y S-L-O-W-L-Y. So slow that it extends the duration of a manned Mars mission to more than two years and provides for a stay of less than a year on Mars. These numbers come from NASA, Boeing, and every other proposal I've ever seen. Maybe they're all lying because it doesn't support your argument or maybe, just maybe they're trying to tell you something. When higher thrust is utilized to accelerate faster and reduce transit time, the specific impulse drops to numbers that are less than those that would be produced by an advanced NTR.

Are you completely incapable of understanding that duration is dependent on THRUST to MASS ratio, not ISP?? We can make a SEP thruster that is ~1.5 kg/kw and Solar is running 3 kg/kW right now (both easily cut in half with future improvement by the way), so for 4.5 kg and 1 kw you get 25-70 mN (5.5 mN/kg - 15.5 mN/kg) depending on ISP choice (remember HALL thrusters are variable now) variable from 1300s to 5000s. The ISP choice determines your propellent FRACTION. The ACCELERATION determines duration.

To get to Mars in 180 days from ESOI you only need ~1 mN per kg providing 1 mm/s acceleration rate and a total DeltaV of 15.5 km/s. Propellent mass fraction would range from 25% - 70% depending on the ISP, so we have PLENTY of room to pile on propellent and payload and still have the desired transit duration. The sweet spot looks to be at the higher end 5k ISP, 5.5 mN/kW, 1 mN/kg, ~25% propellent, ~18% propulsion hardware, 55% payload.

Most SEP designs are going to go either very slow or very fast, because people fall into two camps, "slow-and-lots-of-payload" or "fast-light-avoid-the-radiation" we don't know which solution is the right one yet. SEP can go slow or fast depending on how you size the system so people who are in the slow camp who hope/assume radiation is no problem will go as slow as human factors allow. But if your in the fast camp then you just use a lot of juice and go super fast with SEP, at 10 mm/s acceleration you can go to Mars in 50 days, current systems only barely have that kind of acceleration even without propellent or payload so these uses of SEP are far more speculative. They ARE the fair comparison case to NTR considering that both would need further development of already mid TRL level tech. Their is simply no comparison with GCNTR as it is so much lower TRL.

Last edited by Impaler (2015-02-11 23:37:45)

RobertDyck · 2015-02-12 00:26:44

NASA was founded to develop new technologies. So obsessing about TRL is contra-productive.

GW Johnson · 2015-02-13 14:08:29

RobertDyck wrote:

NASA was founded to develop new technologies. So obsessing about TRL is contra-productive.

I quite agree with Robert about that. When NASA was formed in 1958, it had a front-burner reason-to-be of manned spaceflight (what became the Mercury program), plus technology development issues to address for both spaceflight and aeronautics. Most of the stuff that went into Mercury was not technology development, which is why they were able to pull it off in 3 years. Not much development was needed to fly Gemini, but a fair amount was required for Apollo. And that doesn't even count the launch rocket work.

That being said, technology readiness is quite important, whether or not you use that TRL scale to assess it. If you actually intend to fly something, then all the major bits had better be ready-to-apply technologies. History says if you try to develop a major technology during your vehicle development program, your vehicle will never fly.

The argument I see above about SEP vs nuke stuff seems (1) too vitriolic, and (2) kind of pointless. There are at least two versions of electric thrusters already flying successfully. VASIMR is nowhere near that ready. Neither are the other electric concepts, like arcjet.

There are some new versions of solar electric power that are essentially ready-to-apply. Those combined with the fully-ready electric thrusters are ready enough to fly right now, and we should use them for anything appropriate. The sooner the better. The other concepts need technology development work, which we should be doing.

In contrast, "gas core nuclear thermal" is nowhere near ready for much of anything yet, because almost none of the work was ever done on it. It could have been, and still could be. And I say it should be. There's at least two wildly-different versions of gas core, too.

The nuclear explosion drive was essentially frozen by neglect at its 1959-1965 state of the art. That was essentially ready for its first experimental flights, and so it still is today, if we elect to use obsolete fission device technologies. Better devices could be built, but that's necessary technology development work first. It could have been done, but wasn't. It should be done.

The solid core thermal includes NERVA and several variations of it that were identified as improvements, some experimentally at one level or another. All this died in 1973, with just a snit of work (by CIA I think it was), circa 1990. Basic NERVA was, and still is, about a year away from first experimental flight. The variations that would improve it, are a handful of years away from flying, given normal technology development efforts. These should be happening, but are not.

Biggest problem with any of the nuclear stuff is not technological readiness (which varies considerably), but suitable test sites. Plume capture with any rocket is difficult, this stuff is far worse. So, why don't we test them on the moon, in the open? No neighbors to bother. And you don't need nuclear to take it there for test. We really could bootstrap our way into this.

The electrics as we know them inherently involve high Isp but at extremely low thrust: a few newtons for a ton of hardware to be installed in many tons of vehicle. Accelerations are inherently very low (typically 10^-3 to 10^-5 gee), requiring the slow spiral-out/spiral-in flight plans, if only electric is to be used. And there's the Oberth thing: really that's just gravity loss accumulated over extremely-long burn times.

For cargo long flights and radiation exposures are not objectionable, generally. I think what we have learned says those really are objectionable with human crews. Which in turn says the manned vehicles need high-thrust rockets for arrival and departure burns, and electrics to speed up the long transits. Or, you ferry the crew out to the electric vehicle after it gets clear of the Van Allen belts, which means more launches.

I think a properly-balanced space program would be spending at least something on all of these things, trying to get a wider variety of technologies mature enough to apply to each mission. I haven't really seen that done since the early 1960's.

GW

Last edited by GW Johnson (2015-02-13 14:13:53)

Quaoar · 2015-02-14 07:58:07

GW Johnson wrote:

There's at least two wildly-different versions of gas core, too.

GW

Which are?

Decimator · 2015-02-14 08:06:02

Quaoar wrote:

GW Johnson wrote:
There's at least two wildly-different versions of gas core, too.

GW
Which are?

I can think of three off the top of my head. Nuclear Saltwater, Nuclear Lightbulb, and Coaxial.

kbd512 · 2015-02-14 14:42:55

I think it's reasonable to want to spend half of your mission time on the objective. I think it's reasonable to want half or more of your mission mass to be payload mass rather than power and propulsion mass. A solid core NTR wouldn't permit that kind of payload fraction, but if a gas core NTR proved feasible then we'd have a much more desirable payload fraction.

NASA spends what little money is allocated for nuclear power and propulsion research trying to re-create the fuel rods for solid core NTR's. Using Uranium fissile material and solid core NTR's are technological dead ends for space exploration. We already know that solid core NTR's using Uranium have undesirable mass fractions and that's not going to change. That is why I proposed development of an Americium fueled gas core reactor. The size and mass of the reactor are dramatically reduced by using Americium as the fissile material.

If, through experimentation, NASA determines that gas core NTR's are not technologically feasible then so be it. At least we'll know what is and is not feasible, rather than focusing on what's easy to do with current technology. I would think that this would be a more productive use of the nuclear engineers and scientists. If no quantum leaps in materials science or nuclear engineering are required, then even if it costs real money to develop into flight hardware, I think it's worth the effort and resources required.

With respect to nuclear propulsion technology programs supplanting existing electrical propulsion technology programs, that should only happen if the new technology provides some sort of required capability that existing technology can't provide and aren't likely to provide with further development. This is unlikely. I think of nuclear propulsion as a complementary technology. If the developmental states of these two technologies were reversed and electrical propulsion tech was developmental and nuclear propulsion tech had 40+ years of development and space flight backing it, I would still want funding for development of electrical propulsion.

The notion that we should only use whatever tech is available right now and completely ignore other propulsion options is ridiculous and demonstrates very narrow minded thinking. Every advanced technology has developmental challenges to overcome. Absent a crystal ball to peer into, I think it's prudent to devote some resources to a range of options.

RobertDyck · 2015-02-14 20:15:12

To be fair, if you want established technology, that's chemical. Go to Mars using an upper stage with LH2/LOX. In the 1990s, Russia developed several models of rocket engines using CH4/LOX. And early phase development for Orion paid for two American companies to develop RCS thrusters using CH4/LOX. It would be trivial to expand RCS thrusters to a service module main engine, or TEI stage main engine to return to Earth. Completing NERVA would be fairly easy as well, as GW Johnson stated. Developing Americium gas core NTR would be non-trivial, but it's the kind of work that NASA was established to do. Some have said building a rocket engine test stand that could contain radioactive exhaust would be difficult, but the A-3 test stand at Stennis does that. A-3 simulates vacuum to test the J-2X engine in laboratory grade vacuum. Could we use A-3 itself to test a gas core NTR? You would probably want it located at Jackass Flats, not Stennis.

But using any form of NTR, or VASIMR, or SEP, or NEP, is not the quickest or cheapest way to Mars. Chemical is.

RobertDyck · 2015-02-14 20:45:34

Anyone who read my rants on this forum, will know I love technology. However, just to throw a "wooden shoe into the gears" of this SEP vs NTR argument, I would like to point something out.

The Davy Crockett was a nuclear weapon developed in the late 1950s. It was a small nuclear bomb propelled by a rocket launched by a tripod. Designed to be carried on the back of a single soldier, who could erect and launch it. The device was issued with an entrenching tool (folding shovel) because before launch the operator would have to dig a fox hole to duck into. The rocket would not throw the nuclear bomb very far, so the operator would be within the bomb's blast radius. The nuclear warhead was sub-kiloton, weight 51 pounds (23kg) with yield between 10 and 20 tons. But imagine how small you could make one with Americium-242m. Could it be built as small as an RPG?
.

Last edited by RobertDyck (2015-02-14 23:31:45)

GW Johnson · 2015-02-15 12:56:50

RobertDyck: it's probably not wise to post things like the last two sentences in the previous post. It gives all sorts of bad guys way too many ideas. But BTW, I actually do remember Davy Crockett. There was another version of the same thing that used a 75 mm gun mounted facing rearward on a speeding jeep. Same problem, too: range < fireball radius. I think it was called Mickey Mouse, but I'm not sure of that after so many decades.

Quaoar: to answer your earlier question to me, I only had in mind two broad categories of gas core thermal engines. Those are open cycle and closed cycle. I'm not familiar at all with something called "saltwater" somewhere just above. I've been outside the industry for 2 decades now (one of those industry "consolidations" got me, where they fire half the workers, keep all the upper level managers, and live off the backlog for about 3 years until they can bail-out with their "golden parachutes"), making it very hard to stay abreast of things.

The closed cycle idea had a "transparent" wall between the uranium plasma and the propellant flow, so it was often called "nuclear light bulb. The open cycle depended critically on some sort of flow scheme that would retain the uranium in preference to the propellant, with a uranium residence time just long enough to achieve effective nuclear burn-up.

There were a great many variations on both ideas. In all of them, greater reactor power levels correspond to both higher and higher Isp, and to greater and greater difficulty dealing with the high temperatures.

The most mature technology available for a Mars mission to be built "today" would be chemical propulsion, although I think you could now add solar electric to that, for speeding up the long transits and sending unmanned cargo. No doubt about the chemical, and solar electric is starting to get used in real probes now. It's ready, too.

I think the real obstacles to having sent a Mars mission as long ago as two decades are institutional, not technical. One that most folks don't think about is the handoff of engineering art from one generation to the next "on the job". It doesn't happen anymore, now that jobs are so fleeting, and employees are like grapes ("a dime a dozen"). That's why we as a people keep reinventing the same wheels over and over (the lousy aluminum tires on Curiosity are but one single example).

This sort of "rocket science" stuff really isn't all science, no matter how loudly management types in and out of government and industry giants claim that it is. It's about 40% science (actually written down somewhere, but often lost anyway during all the "consolidations"), 50% art (never written down because management didn't want to pay for that), and 10% blind dumb luck.

And that's in production work. R&D projects are worse: more art and dumb luck, even less science. Mounting a manned Mars mission is most definitely NOT production work, precisely because we have never done it before. The moon trips just were not in the same league.

GW

Last edited by GW Johnson (2015-02-15 13:04:44)

Impaler · 2015-02-15 15:31:11

I'd say conventional chemical rockets are just 100% plain engineering now as we all the physics involved now, their was hardly any science in rocketry by the Apollo ere, though arguably their was still a lot of 'Art' in it then even that is largely gone.

One last thing anyone who loves NTR should read, this ENTIRE thread from NSF, http://forum.nasaspaceflight.com/index.php?topic=1139.0

Here he have a REAL NASA Nuclear Engineer who went from being an enthusiast for NTR to being highly skeptical after he looked at the numbers.

GW Johnson · 2015-02-15 16:31:59

There aren't any "real NASA NTR engineers", and never were. The actual smarts were (and still are, to whatever extent they haven't died, retired, or gone on to other jobs) in the contractors that NASA hires, in just about any topic area you wish to discuss. Talk to the guys who actually did Project Rover, culminating in NERVA. There's 3 left, all in their 80's now. I did. What you say about NTR simply isn't true. Yep, it has unresolved problems. But it is NO dead end.

As for engineering art in chemical rocket work, yep, it's still there. Still about 40%, even in production work, just like I said. Less to do with the rocket engines themselves now (although Orbital Sciences might disagree with that!!!!), and more to do with successfully flying supersonic vehicles that have to stage.

Ask Spacex; they had real troubles with Falcon-1, until they finally talked to some of us old guys about that. That was somewhat of a humbling experience for them, and it's still a subject they do not like to discuss in public. But they did learn, and well. So far, anyway. But, they do not like to hire anybody over 40-45 years of age. Sooner or later, that art thing will bite them again, precisely because they don't like old, experienced hands on staff.

GW

RobertDyck · 2015-02-15 18:22:49

GW Johnson wrote:

it's probably not wise to post things like the last two sentences in the previous post. It gives all sorts of bad guys way too many ideas.

That's the point. To get them to think twice before continuing their argument. The topic can be twisted the wrong way, so drop it. I had posted how to make nitrate fertilizer for a greenhouse. But after 9/11, it's a really bad idea to post details like that. That discussion did not survive the great crash. Did I shock them enough to halt the argument?

SpaceNut · 2015-02-15 18:34:34

I hope so too....

Back to the first post:

It sure looks very heavy and 2 stage in design.

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