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#1 2017-08-07 16:28:52

louis
Member
From: UK
Registered: 2008-03-24
Posts: 2,675

Space X - getting ready for Mars.

http://www.dailymail.co.uk/sciencetech/ … aunch.html

I see no signs of a rethink by Musk from this article.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#2 2017-08-07 18:54:00

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,694
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Re: Space X - getting ready for Mars.

It is still not clear Falcon Heavy has ANYTHING to do with the Mars effort, except for being a step toward building the boosters he really wants. The media often makes a link to the Mars effort that is not accurate.

It appears Musk is redesigning the booster and the MCT, though; apparently the booster will be 9 meters in diameter instead of 12 and therefore a bit more than half as powerful. But a 9 meter booster is more likely to be used for other purposes and thus pay for itself.

Space X has also hinted about going to the moon first. Again, that really does make sense if NASA will pay. Space X's prices are low enough so we could afford both (otherwise, NASA cannot).

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#3 2017-08-07 20:20:01

Oldfart1939
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Registered: 2016-11-26
Posts: 972

Re: Space X - getting ready for Mars.

The Original Post was pretty much a rehash of what's been on the SpaceX website for over a year. Nothing new.

RobS-Where did you get the data about the 9 meter diameter rocket?

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#4 2017-08-08 07:17:45

SpaceNut
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From: New Hampshire
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Re: Space X - getting ready for Mars.

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#5 2017-08-08 07:48:52

Oldfart1939
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Registered: 2016-11-26
Posts: 972

Re: Space X - getting ready for Mars.

OK, in other words, this is a re-run of the older Falcon XX, skipping the Falcon X. Still...a big step forward. I can find no actual reference from Elon in what I read, just some secondary speculations.

Even if this does come to pass, I have my gut feeling that it's too big a jump from Falcon 9, and Falcon X should be an intermediate step for proof of concept. Many of the biggest disasters I've seen in the chemical industry were a result of an overly ambitious scale-up. Any time one works with highly exothermic systems, and rocket motors fit that description, dealing with too much energy without steps taken to mediate the results can have appalling consequences.

On the other hand, the 9 meter concept fits nicely with the Zubrin/Baker model.

Added as an afterthought, in edit: Has anyone calculated how big an explosion would/could result from one of the BFRs would make? The amount of highly energetic material would have a near mini-nuke explosive result! I'm withholding judgment on the proposed 9 meter design. That's roughly a 6x scale up from Falcon 9 v.1.2. The intermediate case will be a Falcon Heavy, a ~3x scale up of Falcon 9. The previously proposed Falcon X was roughly the same level as Falcon Heavy without the separate boosters, and Falcon X Heavy would accomplish roughly the same as Falcon XX.

Last edited by Oldfart1939 (2017-08-08 08:02:46)

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#6 2017-08-08 10:19:09

GW Johnson
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From: McGregor, Texas USA
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Posts: 2,712
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Re: Space X - getting ready for Mars.

Falcon-Heavy supposedly can fling a payload equivalent to a loaded Dragon to Mars for a one-way direct landing.  The "best" way to do this with widest windows for a burn is to stop in LEO before trans-Mars injection. 

So,  why not assemble what you need for Mars in LEO and "launch" it from there?  What do you need a bigger rocket for anyway? 

We already know how to put together 15-ton items.  Falcon-Heavy flown expendibly can put 50-60 ton items to LEO.  Probably 30-40 ton items recoverably. 

Just asking.

GW

Last edited by GW Johnson (2017-08-08 10:20:00)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#7 2017-08-08 10:36:28

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,035
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Re: Space X - getting ready for Mars.

In Should SpaceX consider using SRBs on Falcon 9?, my response was SpaceX should consider upgrading Falcon Heavy by replacing the central core stage with a new stage exactly the same size, but with LCH4/LOX and Raptor engines. And replace the upper stage with one that uses a subscale vacuum Raptor. They already tested a subscale Raptor with 1/3 the thrust of a full-size Raptor. The subscale raptor produced a tiny bit more than double the thrust of Merlin 1D, so this is a major upgrade. I said the core stage could use 9 subscale Raptors using the same octaweb they currently use (8 engines around a central engine), or 3 full-size Raptors.

Falcon 9 v1.2 (aka Full Thrust or FT) uses Merlin 1D+. That means all the upgrades as of now. Merlin 1D produced 650 kN thrust at sea level, or 720 kN in vacuum. Merlin 1D Vacuum produces 934 kN in vacuum. In May 2016 they announced their intention to upgrade Merlin 1D to 845 kN at sea level, and 914 kN in vacuum. I assume this is what they mean by "1D+".

Raptor is supposed to produce 3,285 kN at sea level, or 3,050 kN in vacuum. In August 2016 they tested a subscale engine which produced 1MN thrust (1,000 kN). Obviously that was ground level at McGregor, Texas. Presumably a subscale vacuum engine would produce more in vacuum. Currently Falcon 9 v1.2 produces 9 x 845 kN = 7,605 kN at sea level. Just 2 full-size Raptors would produce 2 x 3,285 kN = 6,570 kN at lift-off. That wouldn't be an upgrade, but 3 full-size Raptors would produce 3 x 3,285 kN = 9,855 kN. That would increase thrust at lift-off by 1.295858 times, round off for significant figures to 1.296 times. Would you say "almost 30% increase" or "29½%"?

But more importantly, Elon Musk said their target for Raptor Vacuum is Isp=382s in vacuum. However, according to Wikipedia, expected performance of regular Raptor is Isp=363s in vacuum. Merlin 1D has Isp=282s at sea level, or 311s in vacuum. Merlin 1D Vacuum has Isp=348s in vacuum. The higher Isp of Raptor would allow thrust for a greater time, accumulating greater delta-V.

I think that should be their next step. Falcon X Heavy would be great! That would have 6 metre core diameter, but able to lift payloads with 10 meter diameter. Falcon X Heavy was said to be able to lift 125,000 kg to LEO, making it perfect for the Zubrin/Baker model. But as GW Johnson said, and RobS said before, why not assemble in LEO using Falcon Heavy?

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#8 2017-08-09 03:16:17

louis
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From: UK
Registered: 2008-03-24
Posts: 2,675

Re: Space X - getting ready for Mars.

Hi GW - My view entirely...LEO assembly has always been my favoured approach with current technology.

I think we also have to build in the politics of all this...I think Musk is savvy enough to understand he has to tread carefully balancing his statements about his Mars vision with others emphasising the current challenges in developing the technology. He has to keep NASA, the US President, Congress, China and the UN all sweet(ish).

I can't personally believe he doesn't understand the scope for putting together a Mars transit vehicle in LEO.

GW Johnson wrote:

Falcon-Heavy supposedly can fling a payload equivalent to a loaded Dragon to Mars for a one-way direct landing.  The "best" way to do this with widest windows for a burn is to stop in LEO before trans-Mars injection. 

So,  why not assemble what you need for Mars in LEO and "launch" it from there?  What do you need a bigger rocket for anyway? 

We already know how to put together 15-ton items.  Falcon-Heavy flown expendibly can put 50-60 ton items to LEO.  Probably 30-40 ton items recoverably. 

Just asking.

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#9 2017-08-09 04:39:53

kbd512
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Registered: 2015-01-02
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Re: Space X - getting ready for Mars.

1. Why not just use Raptor in an upper stage with the same diameter as the payload shroud?

2. If Raptor can actually be built using existing tooling and tech created for Merlin, then why not evolve Falcon Heavy to use full-flow staged combustion for the boosters and the upper stage?

3. If the composite tank technology can really handle LOX and LCH4 without issue, then why not construct Falcon Heavy stages using that new tech first?

The combination of composite tanks, a lighter upper stage with a higher Isp Raptor engine, and lighter boosters with higher Isp Merlin engines should permit Falcon Heavy to come quite close to the performance of the initial version of SLS.  If Falcon Heavy can deliver 50t to ISS with reusability, then surely NASA can construct a MTV using a SEP powered habitat module and a NTO/MMH chemical propulsion kick stage to leave LEO.  The spiraling time lost to LMO insertion, TEI orbital transfer, and LEO insertion using the SEP module is of little consequence if there are no other affordable alternatives.

* The testing for the high power SEP thruster, MegaFlex and ROSA PV arrays, and CAMRAS and IWP life support equipment is nearly complete.  There have been no showstopper issues identified with any of these key technologies.  All work well and are significantly better than what NASA currently has.

* AJ-10-190 is thoroughly proven technology, so there's no need to develop an entirely new upper stage engine.  There are no boil-off issues to contend with when using NTO/MMH, either.  LOX/LH2 is obviously better, but the RL-10 engine is not man-rated and Centaur upper stages have had a history of problems.

* The ISS Destiny lab module or MPLM module for habitation is also thoroughly proven technology.

* We don't have any alternatives to SEP at this time.  The spiral times will have to be accepted, otherwise the delivered tonnage is too costly.

As far as SpaceX is concerned, I think Mr. Musk received a lane departure warning from his own engineers regarding ITS.  I thought it was crazy cool, but sometimes engineering reality kinda sucks.

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#10 2017-08-09 08:20:09

Oldfart1939
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Registered: 2016-11-26
Posts: 972

Re: Space X - getting ready for Mars.

IMHO.
I believe that Elon Musk is having an internal struggle--with himself. His dream is HUGE, but it's now being subjected to tempering with a combination of engineering and economic realities. That said, he's a very rational dreamer, so I'm just speculating that he to will see the advantages of  building even a handful of Falcon Xs, if for no other reason than the orbital satellite business, coupled with the return to Moon concepts. Then there is time. Building the BFR (as the ITS was called by the engineers working on it) cannot be done in anything less than 10 years. Musk is still pretty young (at least by comparison with THIS group!). If he wants to go to Mars himself, his aging will encourage his change of plans to something less grandiose and faster to get accomplished.

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#11 2017-08-09 09:13:21

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,035
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Re: Space X - getting ready for Mars.

kbd512 wrote:

* AJ-10-190 is thoroughly proven technology, so there's no need to develop an entirely new upper stage engine.  There are no boil-off issues to contend with when using NTO/MMH, either.  LOX/LH2 is obviously better, but the RL-10 engine is not man-rated and Centaur upper stages have had a history of problems.

Be very careful. I would not make that claim at all. Remember, NASA engine engineers wanted to develop a new engine for Ares V based on SSME but 50% more powerful. NASA executives said no, use the existing engine. Then Boeing sales reps sold them on RS-68; it already provided 50% more thrust, and was optimized to be expendable. They designed it to not have some features of SSME so RS-68 would have lower manufacturing cost, but lower Isp. That required more propellant, but the additional cost of propellant plus tank was less than the cost savings for the engine, so total cost of the stage was minimized. Great! NASA bought it. But the engine guys wanted to develop a new engine, so they made the accusation that RS-68 was not man rated. NASA executives gave them the task of man rating it, but what they did had nothing to do with man rating. What they did is add all those features of SSME that RS-68 was designed without, features that increased Isp and had nothing what so ever to do with man rating. This was their scam to design the new engine they always wanted. That work dramatically slowed development of Ares V, and dramatically increased cost. Again, this meant they were developing a new engine, not man rating an existing one. Delays and cost increases postponed Constellation so long that President George W.'s term was over, and President Obama cancelled Constellation entirely. There was several reasons for delays, but this engine scam was a major one.

kbd512 wrote:

* The ISS Destiny lab module or MPLM module for habitation is also thoroughly proven technology.

Again, you're falling into scams of "Old Space" contractors. Boeing came up with a design for a Deep Space Habitat, intended for the Asteroid Redirect Mission. Their design was simply ISS modules linked together. That DSH would be heavy, clumsy, and require multiple launches. It's just an excuse to create manifest for SLS. But we don't want to arbitrarily increase cost. The goal is to keep cost down so we can do more missions. If each mission required multiple launches of SLS, then we won't get a single mission. Destiny lab was designed to fit in Shuttle's cargo bay, and designed for zero-G. You can use the hull technology, but a complete redesign is necessary for Mars.

kbd512 wrote:

* We don't have any alternatives to SEP at this time.  The spiral times will have to be accepted, otherwise the delivered tonnage is too costly.

SEP could be used for cargo, but not for crew. It's way too slow. Spiral times are not acceptable.

kbd512 wrote:

As far as SpaceX is concerned, I think Mr. Musk received a lane departure warning from his own engineers regarding ITS.  I thought it was crazy cool, but sometimes engineering reality kinda sucks.

That's possible. First stage of the Soviet N1 used 30 engines: 24 in an outer ring, 6 inner engines. They had major problems. Their greatest problem is one Soviet politician who didn't believe in space took away funding for the test stand for that stage, used the money for something that had nothing to do with space. So the first test of the stage was launching the full-stack rocket. First two launch failures were engine failure. Third was a control system failure, uncontrolled roll. The fourth was due to "hammering" propellant feed lines causing rupture when attempting to stage. From Wikipedia...

Wikipedia wrote:

An investigation revealed that the abrupt shutdown of the engines led to fluctuations in the fluid columns of the feeder pipes which ruptured and spilled fuel and oxidizer onto the shut down, but still hot, engines. A failure of the #4 engine turbopump was also suspected. It was believed that the launch could have been salvaged had ground controllers sent a manual command to jettison the first stage and begin second stage burn early.

Cited reference is: Harford, James (1997). Korolev : how one man masterminded the Soviet drive to beat America to the moon. New York; Chichester: Wiley. p. 300. ISBN 9780471327219.

Designing ITS with a similar number of engines risks similar problems.

Last edited by RobertDyck (2017-08-09 16:13:55)

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#12 2017-08-09 09:46:16

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,035
Website

Re: Space X - getting ready for Mars.

Oldfart1939,

I think you're right. But a few of us have come up with plans to send a mission about the size of Mars Direct, but using existing launch vehicles. I read about Energia from Robert Zubrin's book, in the first years of the Mars Society a lot of people were excited about it, so I came up with a plan (a modification of Mars Direct) that used Energia. RobS encouraged me to change the design to use Falcon Heavy, so I did. It's not 100 people at a time, it's only 4, but it's practical.

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#13 2017-08-09 13:39:05

louis
Member
From: UK
Registered: 2008-03-24
Posts: 2,675

Re: Space X - getting ready for Mars.

But didn't he always plan an intermediate rocket/MTV technology before the ITS? That was my understanding...I think it was just never quite clear what was intended...human-rated Red Dragon or something else.

Oldfart1939 wrote:

IMHO.
I believe that Elon Musk is having an internal struggle--with himself. His dream is HUGE, but it's now being subjected to tempering with a combination of engineering and economic realities. That said, he's a very rational dreamer, so I'm just speculating that he to will see the advantages of  building even a handful of Falcon Xs, if for no other reason than the orbital satellite business, coupled with the return to Moon concepts. Then there is time. Building the BFR (as the ITS was called by the engineers working on it) cannot be done in anything less than 10 years. Musk is still pretty young (at least by comparison with THIS group!). If he wants to go to Mars himself, his aging will encourage his change of plans to something less grandiose and faster to get accomplished.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#14 2017-08-09 16:05:24

Oldfart1939
Member
Registered: 2016-11-26
Posts: 972

Re: Space X - getting ready for Mars.

Louis-

To the best of my knowledge, Musk never actively promoted an intermediate vehicle, since the Red Dragon was something of an outgrowth of the Dragon 2 capsule which is planned to be man-rated. SpaceX DID have a series of design concepts they released a number of years ago; they were available on Spaceflight101.com for some time. That's where the Falcon X and Falcon X Heavy come from, and also the Falcon XX.

Robert-

I'm a strong supporter of orbital assembly using Falcon 9 and Falcon Heavy launches to construct a Mars-capable vehicle. Although I consider a crew of 4 as being too small, I would also support sending it instead of wasting another 10 to 15 years waiting around for NASA to procrastinate further. Maybe the Falcon Heavy and lots of orbital assembly isn't "Ideal," it would at least work.

LET'S GET OUR ASSES TO MARS!

Last edited by Oldfart1939 (2017-08-10 08:23:12)

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#15 2017-08-09 18:02:51

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,637

Re: Space X - getting ready for Mars.

List of current do ables:
1.) capability to launch using what we have for cargo or modules for subassembly and even man once rated.
2.) completed module design for human occupency for a mars duration

Demonstrator needs:
1.) Artificial gravity and course correction while spinning or tumbling end to end
2.) Retro propulsion of larger mass payload to mars surface and relaunch once on the surface back to orbit eother by proven refueling of depot fuels which were delivered or by insitu refueling.

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#16 2017-08-10 09:07:11

Oldfart1939
Member
Registered: 2016-11-26
Posts: 972

Re: Space X - getting ready for Mars.

SpaceNut-
Some thought needs to be applied to use of fuels other than CH4 and RP-1; using Hydrazine type fuels have nearly identical Isp but are better in Id. The Oxygen ratio for combustion is also more favorable. Optimization by refinement of concept.

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#17 2017-08-13 18:55:42

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,637

Re: Space X - getting ready for Mars.

Yes to other fuels as we need to be able to make them early in order to get better performance sooner.

Here is a run down of 40th Falcon 9 mission and 11th rocket this year.Elon Musk Is Getting SpaceX Closer to Mars, One Rocket at a Time

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#18 2017-08-15 12:47:53

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,712
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Re: Space X - getting ready for Mars.

Well,  Spacex was successful again.  Falcon-9 Dragon toward ISS,  first stage landed back at the Cape.  Congrats.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#19 2017-08-16 15:46:37

Oldfart1939
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Registered: 2016-11-26
Posts: 972

Re: Space X - getting ready for Mars.

Capture of the latest Dragon capsule was accomplished earlier this afternoon. This marks successful completion of the first 12 mission contract with SpaceX.

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#20 2017-08-16 17:22:37

louis
Member
From: UK
Registered: 2008-03-24
Posts: 2,675

Re: Space X - getting ready for Mars.

Great news...more cash in the coffers for the Mars effort which remains Musk's prime focus! smile I am buoyed up as well to hear how well the latest Tesla launch went - must translate into more cash available for the Mars effort one way or the other.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#21 2017-08-25 16:39:16

kbd512
Member
Registered: 2015-01-02
Posts: 1,179

Re: Space X - getting ready for Mars.

RobertDyck wrote:

Be very careful. I would not make that claim at all. Remember, NASA engine engineers wanted to develop a new engine for Ares V based on SSME but 50% more powerful. NASA executives said no, use the existing engine. Then Boeing sales reps sold them on RS-68; it already provided 50% more thrust, and was optimized to be expendable. They designed it to not have some features of SSME so RS-68 would have lower manufacturing cost, but lower Isp. That required more propellant, but the additional cost of propellant plus tank was less than the cost savings for the engine, so total cost of the stage was minimized. Great! NASA bought it. But the engine guys wanted to develop a new engine, so they made the accusation that RS-68 was not man rated. NASA executives gave them the task of man rating it, but what they did had nothing to do with man rating. What they did is add all those features of SSME that RS-68 was designed without, features that increased Isp and had nothing what so ever to do with man rating. This was their scam to design the new engine they always wanted. That work dramatically slowed development of Ares V, and dramatically increased cost. Again, this meant they were developing a new engine, not man rating an existing one. Delays and cost increases postponed Constellation so long that President George W.'s term was over, and President Obama cancelled Constellation entirely. There was several reasons for delays, but this engine scam was a major one.

I realize that there are lots of different ways that current propulsion hardware could be "cost-plus" transformed into something that doesn't work because it costs too much or is too complicated.  Presuming we had the same mindset of the Apollo era engineers, in other words "Do we want to go to Mars or do we want to go to Mars?", is there any reason why we can't use what we have or will have in the near term to go to Mars?

AJ-10-190 is about as well proven for in-space propulsion as anything else we have and it's available in the near term.  Is there any reason why the OME needs to be "reinvented" for kick stages or an ascent vehicles?  If not, can we incorporate things that are known to work well into the propulsion elements of the mission architecture and call it a day?

RobertDyck wrote:

Again, you're falling into scams of "Old Space" contractors. Boeing came up with a design for a Deep Space Habitat, intended for the Asteroid Redirect Mission. Their design was simply ISS modules linked together. That DSH would be heavy, clumsy, and require multiple launches. It's just an excuse to create manifest for SLS. But we don't want to arbitrarily increase cost. The goal is to keep cost down so we can do more missions. If each mission required multiple launches of SLS, then we won't get a single mission. Destiny lab was designed to fit in Shuttle's cargo bay, and designed for zero-G. You can use the hull technology, but a complete redesign is necessary for Mars.

ISS hardware is certainly not optimal, but it's available right now and if it really didn't work, then ISS wouldn't still be in operation.  At the end of the day, we need a pressured module with enough volume to store the food and water required, along with decent radiation protection.  Apart from utter reliability, sufficient volume and protection are the only hard requirements.  In this particular case, the "best" has truly become the mortal enemy of the "good" and ISS hardware is "good enough" for the purpose.  I'd like to see humans on Mars before I die and I'd accept pretty much anything that could feasibly work at this point.

RobertDyck wrote:

SEP could be used for cargo, but not for crew. It's way too slow. Spiral times are not acceptable.

Why does anyone care about losing two months of surface exploration time by spiraling in to LMO from TMI or spiraling into LEO from TEI?

It makes the mission affordable as a function of mass and therefore cost.

RobertDyck wrote:

Designing ITS with a similar number of engines risks similar problems.

There are always risks associated with rocketry, but unlike the Soviets we tended to test what we build before we destroy a launch pad with a mini-nuke.  The problems are likely solvable, but at what cost?

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#22 2017-08-25 18:58:35

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,035
Website

Re: Space X - getting ready for Mars.

kbd512 wrote:

is there any reason why we can't use what we have or will have in the near term to go to Mars?

SLS block 2B: core state with 4 SSME (no modification). This is the same core stage as SLS block 1 and block 1B. Exploration Upper Stage (EUS), with 4 RL-10 engines. This is the same upper stage as SLS block 1B (not block 1). And liquid boosters using F-1B engines, 2 engines per booster. This has already been proposed, it isn't new. The alternative is advanced solid boosters, which add RDX and/or HMX to the mix of solid fuel. After Challenger I don't like segmented solids, but the idea of adding the same explosive as C4 to the fuel mix for solids intended for human space flight? I really don't like that. First stage of Saturn V used F-1 engines, the manufacturer developed F-1A in 1969. The only difference between F-1A and F-1B is modern electronics instead of 1969 vintage electronics, and some parts are fabricated using 3D printers.

You could use Mars Direct architecture. Or my mission architecture, which is a modification of Mars Direct.

kbd512 wrote:

Why does anyone care about losing two months of surface exploration time by spiraling in to LMO from TMI or spiraling into LEO from TEI?

Mars Direct was designed in 1990 to use ADEPT for Mars atmospheric entry. That's the carbon fibre fabric heat shield that unfolds like an umbrella. My mission architecture would still use ADEPT for the lander, but for planetary orbit insertion at each planet (Mars and Earth) use aerocapture with a heat shield that unfolds like an umbrella, the same as ADEPT, but instead using Nextel 440 fabric. That's a synthetic ceramic fibre, more durable for reuse. Carbon fibre can handle more heat, but tends to degrade. That makes carbon fibre more applicable for single-use applications, such as the lander. NASA's Ames Reserach Centre developed DurAFRSI as the new thermal blanket to replace AFRSI.

The last thermal blanket used by Shuttle was AFRSI: a quilt of 99% pure silica fibre cloth on the outside, normal fibreglass on the side toward the Shuttle's aluminum alloy skin, and fibre fill is more 99% pure silica fibre. DurAFRSI uses Nextel 440 as the fabric, with Nextel 440 threads to quilt it, and Saffil fibre for batting. DurAFRSI has a wire screen mesh of Inconel 617 sewn on with the quilting threads, then a foil of Inconel 617 is brazed to the screen mesh. DurAFRSI can withstand more heat than AFRSI, and has a smooth metal skin to the air stream. My idea was to use the fabric from this heat shield for aerocapture.

Aerocapture means entering orbit quickly. However, aerocapture would typically leave you in highly eliptical high orbit. For Mars you would leave the vehicle in that orbit, because it's easy to depart. However, for Earth you would then use repeated aerobraking to drop to the orbit of ISS. My mission architecture would rendezvous with ISS, where the interplanetary vehicle can be serviced, prepared for the next mission. So if you really want to spiral down, at Earth you would, just with aerobraking instead of SEP.

kbd512 wrote:

There are always risks associated with rocketry, but unlike the Soviets we tended to test what we build before we destroy a launch pad with a mini-nuke.  The problems are likely solvable, but at what cost?

To be fair, Soviet engineers insisted on a static test stand for the first stage of N1. It was a Soviet politician who had no interest in space who took away funding for that.

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#23 2017-08-25 19:54:16

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,637

Re: Space X - getting ready for Mars.

The only thing I see stopping man is a demonstrator mission for the Mars lander in the loaded mass range we are looking to have for mars. I do not care if its got real cargo or rocks just have it prove out the ADEPT heat shield and landing accuracy and then lets get going....

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#24 2017-08-26 12:52:50

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,712
Website

Re: Space X - getting ready for Mars.

What I see is forgotten (unaddressed) issues in many mission architecture proposals.  One has to remember to address all the risks,  not just most of them,  and in the best ways available.  While min thrown mass may be the lowest cost,  it is not usually the lowest risk,  so “bottom-line” thinking is the wrong way to go.  It has killed many folks in all sorts of endeavors here at home. 

The loss of a crew is so catastrophically expensive in both direct and indirect ways,  that multiplying probability times loss is an unacceptable (although incorrectly “standard”) way of treating risk assessment.  The error is in figuring it that way for rare events.  They either do or do not occur,  there is no “fractional event”.  That is the true nature of the error.

An example relates to using electric propulsion.  Generalizing,  I see two camps on these forums:  those who want to fly everything electrically,  and those who want nothing-to-do with electric propulsion.  The truth lies in between.  Anything sent to Mars not manned and which is “proof” against radiation damage should be sent with electric propulsion to minimize thrown mass and costs.  Equipment and components do not care how long the spiraling departure is,  or whether spiraling-in or aerocapture is used to arrive. 

You cannot do that with the human crew:  life support mass is very sensitive to travel time,  as are crew health effects,  whether from microgravity,  or radiation,  or confinement,  or any combination of those.  Shorter is better for both those issues (life support mass or health).  Plus,  and this is the real “killer”,  spiraling-out at departure exposes the crew to van Allen belt radiation for months,  which would be rather lethal. 

The way around that last problem is to spiral the transit vehicle by electric propulsion outside the van Allen belts unmanned,  and then send the crew on a high-energy trajectory to it.  The cost of that high energy crew delivery offsets part of the gain you made sending the transit vehicle by electric spiral-out,  but only part,  since the crew capsule is smaller than the transit vehicle.  It does add the risks of rendezvous (and how to recover from a missed rendezvous !!!) on an orbit that is nearly an escape trajectory.  Addressing those risks does make the high-energy crew launch into a rather large and expensive rocket and payload. 

Mars has no van Allen belts,  so the choice of spiral-in electric or use aerocapture for a crewed vehicle is open.  Both take time.  We haven’t done enough aerocapture unmanned yet to trust it with a crew.  We have never done electric spiraling,  crewed or not.  Both therefore require some very serious demonstrations before we risk a crew.

That last is why I tend to favor sending the crew in the transit vehicle direct from LEO with conventional rocket propulsion.  The trip is shorter,  so the transit vehicle is slightly lighter,  and (most important) there are no new technologies requiring demonstration before you risk lives with them.  You can freeze the design and start-to-go “now”.  (My own preference is to spin this vehicle for artificial gravity,  to maximize crew health.)

That last consideration (basically technological readiness) does also apply to the ADEPT and HIAD soft entry shield technologies.  They will need some serious demonstrations before we risk lives on them.  If neither of them pans out,  then you don’t get to go.  Retropropulsion is actually further along in the demonstrations needed,  because of the recent work by Spacex and Blue Origin.  It also resembles in some ways what we did at the moon with Apollo,  although Mars arrival is quite different due to the “air”.  But there is heritage there.

I’d be more inclined to bet on the landing technology that is further along (retropropulsion),  although I certainly would invest serious effort in the soft heat shields,  too.  If they work well enough,  then use them,  too,  and just make the landing easier and even safer. 

Note that I have not at all discussed whether to arrive in Mars orbit or direct to the surface.  That’s a choice still to be made.  And that choice need not be the same choice,  for all the items sent to Mars before sending the crew.  But I think the most practical choice for the crewed transit vehicle is parking in Mars orbit.  It can be refueled there with propellant flung earlier from Earth,  and then convey the crew safely home from there.  You just jettison the empties,  and dock the refills,  and connect them up,  the very same way we built the ISS.  That’s just the choice I would make,  others differ.

As for landing accuracy,  remember there is no on-board radio or radar capability while enveloped in the plasma sheath during entry hypersonics.  Precise timing,  direction,  and amount of the deorbit burn is the critical element,  until entry hypersonics is over. 

Dangling from a drifting chute is not the path to landing accuracy,  nor the way to a survivable touchdown in that near-vacuum of an atmosphere on Mars.  Terminal retropulsion is the path to accuracy,  and the only means for a survivable touchdown anyway. 

Whether it starts at Mach 3-ish speeds or after-subsonic,  you still have to do it.  A homing beacon helps for that terminal descent’s accuracy.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#25 2017-08-26 16:33:10

louis
Member
From: UK
Registered: 2008-03-24
Posts: 2,675

Re: Space X - getting ready for Mars.

I feel some are overcomplicating the problem.

Space - especially interplanetary space - is basically a very benign environment. You're very unlikely to encounter any external threat on the journey from Earth to Mars. Compared with the sea on Earth (hurricanes, hidden rocks and all the rest) or land (earthquakes, landslides and floods) it's a doddle.

The only problems are getting your stuff to LEO and then landing the stuff on Mars really.

We have the rocket technology - chemical rockets. No need to go beyond that technology at this stage.

Yes, we need a focus on failsafe life support, radiation protection and so on but these are v. manageable problems in my view. The greatest problem we face I think is the medical effects of humans operating in low or no gravity - but I think that challenge is often exaggerated.


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