Free your mind, and the rest will follow.

Copyright 2013 Robert Clark 

The story has been told that when the Native Americans first saw the ships of the Europeans they could not grasp what they were seeing because it was so outside their experience. I've always been dubious of that story. But a recent study suggests something of this nature can happen:

Science confirms: Politics wrecks your ability to do math.
By Chris Mooney

Everybody knows that our political views can sometimes get in the way of thinking clearly. But perhaps we don’t realize how bad the problem actually is. According to a new psychology paper, our political passions can even undermine our very basic reasoning skills. More specifically, the study finds that people who are otherwise very good at math may totally flunk a problem that they would otherwise probably be able to solve, simply because giving the right answer goes against their political beliefs.

http://grist.org/politics/science-confirms-politics-wrecks-your-ability-to-do-math/

 So preconceived notions can affect your ability to reason effectively, even among the smartest among us. I'm reminded also of a brain puzzler stated on the "All in the Family" TV show during the '70s. Gloria presented to the family the following:

 A father driving his young son were in an accident and the father was killed, while the son was injured but survived. When the child was brought to the hospital, the surgeon said, "I can't operate on this boy. He's my son."

 That was a puzzler the rest of the family on the show couldn't solve then and neither could I when I first saw the episode back in the '70s. The answer of course is that the surgeon was the boy's mother. 
 With the advance of women in medicine now with most med school graduates being women that probably would not be such a great puzzle to solve now as then. But it indicates how your preconceived ideas can limit your ability to solve really simple problems.
  
 Something like this is currently occurring at NASA. The Constellation program that would have returned us to the Moon has been cancelled due to high cost. However, many space advocates in the public and in Congress would prefer us to return to the Moon rather than the asteroid mission NASA is embarking on. No doubt because of these calls to return to the Moon, NASA released a study on a return to the Moon without Constellation:

Dual SLS launch campaign required for NASA’s Lunar return.
August 21, 2013 by Chris Bergin
http://www.nasaspaceflight.com/2013/08/dual-sls-required-nasas-lunar-landing-option/

 I was surprised to read that the study assumed an Altair-sized lander at the ca. 45 mT range. But the Altair's size was a big reason driving Constellation's large size and therefore great expense. And in fact by using two SLS launches the mission size in this study turns out to be even larger than Constellation. 

 It was as if the study authors had never heard of the Apollo lander that was only one-third the size of Altair. The misperception that a lunar lander has to be as large as the Altair as well as being built from scratch rather than using existing propulsive stages and crew capsules drives the false conclusion that an additional $10 billion expense would be needed for such a lander, and therefore a lunar return is unaffordable. 

  A further misperception is what is the mass that could be transported to LEO by the SLS. The Block 0 version of the SLS was supposed to use three SSME's on the core and use the standard 4-segment SRB's used on the shuttle. This would have a 70 mT payload capacity to LEO.

 However, NASA decided to bypass the Block 0 and go directly to the Block 1. This would stretch the core tank by a third and use a fourth SSME. It would also use a fifth-segment on the SRB's. So the size and thrust of the core would be increased by 33% and the size and thrust of the SRB by 25%.

 Despite these increases in both size and thrust, NASA was still quoting 70 mT capacity for the Block 1 SLS. Logically the payload should have been increased but NASA continued to quote 70 mT. Finally, NASA did release a report that acknowledged the payload to LEO would be 90+ mT:

SLS Dual Use Upper Stage (DUUS).
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130013953_2013013757.pdf


  This is important because at 90+ mT it is much easier to do a manned lunar landing mission using a single launch of the SLS, assuming you use a lander at the Apollo scale not the Altair scale. Indeed it would be possible at the first launch of the SLS in 2017.

 Then it was these preconceived notions that prevented NASA from seeing that we can in fact return to the Moon as early as 2017, and not even at significantly greater expense than that already being spent on the SLS and Orion capsule.

  Another mental block is operating in regards to how much such BEO missions should cost. NASA's commercial space program has been a great success in producing both launchers and spacecraft at as much as a 90%(!) savings over what NASA would normally have to pay for them. If any other federal agency had managed to reduce costs for normally multi-billion dollar programs to only a few hundred million dollars this would be hailed to the skies as a remarkable success in reducing costs to the American tax payer. Yet NASA was regarding it as if it were something they were only allowed to talk about in hushed tones.

 Finally, NASA has released a report detailing the savings possible under the commercial space approach:

The Commercial Leverage Model and Public/Private Partnerships.
Daniel J. Rasky
Director, Emerging Commercial Space Office
NASA Ames Research Center
Founder & Director, Space Portal
NASA Research Park
Moffett Field, CA 9403
September 11, 2013
https://dl.dropboxusercontent.com/u/47645641/AIAA_2013.pptx 

 Imagine then these cost savings applied also to BEO missions to the Moon or asteroids. This would make these missions much more fiscally feasible. It was NASA not officially acknowledging such cost savings that made it so that they could not study possibilities for returning to the Moon in a low cost fashion.

 For return to the Moon missions conducted by NASA, NASA may initially choose to use the, still expensive, SLS launcher. However, just as NASA has realized commercial space can make flights to the ISS much more cheaply than the shuttle, so also can commercial space make flights to the Moon much more cheaply.

 Indeed, by going small, going commercial, and using preexisting propulsive stages and crew modules, crewed and cargo flights to the Moon can be made for comparable costs to what we are paying the Russians to send a crew of three to the ISS.  

 The conclusion you draw is that a Moon base can be sustained on the Moon for what we are currently paying to sustain the ISS.

 Just free your mind, and the rest will follow.

   Bob Clark

Budget Moon Flights: Ariane 5 as SLS upper stage, page 2.

Copyright 2013 Robert Clark

Artist's rendering of the Space Launch System Block 1 sitting on Launch Pad 39B with the Orion spacecraft at sunrise.

 In the blog post Budget Moon Flights: Ariane 5 as SLS upper stage, I noted that using an Ariane 5 core stage would be a quick and low cost means of getting a higher payload capacity than the 70 mT NASA was giving for the 2017 SLS first launch. This would make it much easier to conduct a manned lunar lander mission using the SLS. However, finally, NASA has acknowledged that the Block 1, first version of the SLS to launch in 2017 will have a 90+ mT payload capacity not the 70 mT always stated by NASA:

SLS Dual Use Upper Stage (DUUS).
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130013953_2013013757.pdf

 This is important since it means we will have the capability to do manned lunar landing missions by the 2017 first launch of the SLS:

SLS for Return to the Moon by the 50th Anniversary of Apollo 11, page 5: A 90+ metric ton first launch of the SLS.
http://exoscientist.blogspot.com/2013/09/sls-for-return-to-moon-by-50th.html

  Still, because of the even higher payload possible using an upper stage, NASA might still want to consider getting a quick and low cost upper stage by using the Ariane 5 core. In that "SLS Dual Use Upper Stage (DUUS)" report are given some specifications for the DUUS. They state they want a highly weight optimized stage, which the Ariane 5 core would certainly fulfill. The Vulcain engine though has thrust size about twice that of the specified 100 - 120K lb range, and the 170 mT of propellant is also larger than the specified 130 mT propellant load. However, these are so much superior to the specified requirements it should result in significantly greater payload delivery than the stated 130 mT to LEO, perhaps to the 150 mT range.
 However, a problem is the 18.3 m specified max height. The Ariane 5 core is at 30.5 m height. Likely the height limitation is coming from limitations on the size and height of the facilities during stage integration. I'll find out if that is a firm limit.
 We could cut down the size of the Ariane 5 core to make it 130 mT in propellant load. Proportionally this would bring the height down to about 20 m, closer to the max. height. It turns out that shortening a stage is rather easy technically so this should still be doable by the 2017 first launch of the SLS.
 Another possibility would be to use the same propellant tank tooling for this DUUS stage as that used by NASA to make the 8 meter wide SLS tank, while using the other components such as the engine of the Ariane 5. However, the idea is to get a low cost upper stage in a short time frame. This might be a costly modification that might also be difficult to manage by the 2017 SLS first launch.
 This possibly though could open up an additional means of lightweighting the stage. We could use aluminum-lithium alloy instead of the standard aluminum used for the Ariane 5. NASA is also planning to use standard aluminum for the SLS core. But as I discuss in SLS for Return to the Moon by the 50th Anniversary of Apollo 11, page 4: further on lightweighting the SLS core, new versions of Al-Li have been developed that could be used for this purpose.
 However, due to the natural inertia of large agencies it might be difficult to change the decision and go with Al-Li for the SLS core. But this decision might be easier to make in regards to the smaller upper stage which wouldn't need as much of the more expensive Al-Li and for which getting a lightweight stage is a much greater priority.

  Bob Clark

SLS for Return to the Moon by the 50th Anniversary of Apollo 11, page 5: A 90+ metric ton first launch of the SLS.

Copyright 2013 Robert Clark

 Finally someone at NASA acknowledges that the Block 1, first version of the SLS to launch in 2017 will have a 90+ mT payload capacity not the 70 mT always cited by NASA:

SLS Dual Use Upper Stage (DUUS).
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130013953_2013013757.pdf

 This is important since it means we will have the capability to do manned lunar landing missions by the 2017 first launch of the SLS.

 As discussed in the blog post SLS for Return to the Moon by the 50th Anniversary of Apollo 11, page 2: Orion + SEV design, a 90+ metric ton launcher means we can even use the Orion as the crew capsule. This is important for political reasons since the great expense spent on it means there would be a great desire among its supporters to see it be used. 

 There also is a preference at NASA for the departure stages from the lunar surface and from lunar orbit to use hypergolics, which have the surety of igniting on contact. Then another advantage of a 90+ mT SLS is that the heavier hypergolics can be used for these stages rather than the lightweight hydrogen-fueled stages I suggested in that blog post. In an upcoming post I'll show using existing hypergolic stages how we can get a lunar landing mission at less than 90 mT to LEO.

  For any of these methods it is important to use currently existing stages rather than developing them from scratch. A big reason that NASA ruled out a return to the Moon was because of the assumption that it required the development of new Altair-sized lander at a $10 billion development cost. But the need for a 45 mT Altair-sized lander is provably false as shown by the Apollo lander at one-third the size. And simply adapting already existing stages reduces the cost to a fraction of that needed for an Altair.

 So NASA is making expensive policy decisions such that we can't return to the Moon based on provably wrong assumptions. One is that the Block 1 would only have a 70 mT payload capability and so would require an expensive upper stage to increase the payload to do lunar missions, and another is that a lunar lander would require an additional $10 billion development.

 In fact, once you recognize the, obvious, fact that a lunar mission does not require an Altair-sized lander then so many possibilities become apparent. We did not have the great variety of existing launchers back in the Apollo days that we have now. If you allow your lander to be at or smaller than the Apollo lander then there are a variety of launchers that could be used for lunar missions, not just the SLS. And since they are already existing, or will be soon such as the Falcon Heavy, there would be no huge, multi-billion dollar development cost to use them. 

 So likewise also is the case for the in-space stages needed. They are already currently existing and would require relatively minor adaptations to be used for a lunar lander, for example.

 Indeed we could do manned lunar missions for what NASA is currently paying the Russians to send a crew of 3 to the ISS. The implications of that are jarring: we could have regular manned flights to the Moon for the same amount as what we are currently paying to send regular manned flights to the ISS.  And since the cargo flights to the Moon would be similarly low cost and using Bigelow style lightweight habs would allow a habitation module to be sent to the Moon on a single flight, we could have a manned lunar base for the same amount as what we are paying to sustain the ISS.

 All this comes from simply the mental reset that a lunar mission does not require the $10 billion Altair.

 Free your mind, the rest will follow.

    Bob Clark

Note: thanks to M. Moleman for discussing the NASA report "SLS Dual Use Upper Stage (DUUS)" on his blog.

Budget Moon flights: will Canada and Europe take us back to the Moon?

Copyright 2013 Robert Clark

 Canada and Europe want to send manned missions to the Moon, despite NASA's disinterest:

Canadian on Moon possible under latest space plan.
Roadmap for future missions includes lunar space station and trips to Mars.
The Canadian Press
Posted: Aug 25, 2013 8:39 AM ET
http://www.cbc.ca/news/canada/story/2013/08/25/tech-space-station-canadian-on-moon.html

In the blog post Medium Lift Circumlunar Flights, I noted that current medium lift rockets such as the Atlas V 401, Delta IV Medium, Falcon 9 could launch a Cygnus-sized capsule on a circumlunar flight. Then if the Cygnus were provided with a heat shield and life support this would provide a low cost means of performing a manned circumlunar flight.
 Orbital Sciences is investigating giving the Cygnus a heat shield based on the inflatable ones NASA is developing:

>

  Another possibility for the heat shield would be to give the Cygnus capsule the same degree of small taper as the Dragon capsule. Then you could use the same type of PICA material, which was invented by NASA Ames, as used on the Dragon.
 Still another possibility is suggested by what SpaceX is proposing for the reentry of the upper stage of a reusable Falcon 9. The stage is a cylindrical structure, but according to the images released by SpaceX, heat shield material, presumably their PICA-X material, is applied to the entry end of the upper stage and partially along one side.

 Another possibility would be to use the capsule originally designed by Andy Elson for SpaceX, called "Magic Dragon". This was to be carried by the smaller Falcon 5 and only carry 3 crew. Since the Falcon 5 had half the payload capability to the Falcon 9 and the crew size was half of the current Dragon, this smaller version likely was also half-size, at ca. 2 mT.

 In the blog post Budget Moon Flights I discussed that two cryogenic in-space stages about half-size to the Centaur could take a Cygnus-sized capsule to an actual lunar landing and back. It will actually even be possible to do it with just one of these stages: the Falcon Heavy, according to Elon Musk, will be able to send 35,000 lb, about 16,000 kg to TLI.
 Use the same Ariane 4 H10-3 upper stage used in the "Budget Moon Flights" post. This had a propellant mass of 11.86 mT and dry mass of 1.24 mT. As discussed there, take the round-trip delta-v of 8,650 m/s. The delta-v to TLI is about 3,150 m/s. Then 5,500 m/s would have to be supplied by this single stage. The stage could carry 2.9 mT payload to greater than that delta-v:

445*9.81ln(1 + 11.86/(1.24 +2.9)) = 5,900 m/s.

 Actually, it could take 3.4 mT to a delta-v of 5,500 m/s but we are limited to how much total mass the Falcon Heavy can take to TLI.
 According to the Astronautix page on the Ariane H10-3 the cost of the stage was only $12 million. Then this could serve for a low cost demonstration mission for the Canadian Space Agency (CSA) and ESA to launch as early as the 2014 expected first test flight of the Falcon Heavy.
 It is important that such low cost missions be done to break the mindset that any manned flights to the Moon have to involve super heavy lift rockets such as the Saturn V, Ares V, or SLS.


   Bob Clark

The Coming SSTO's: Page 2.

Copyright 2013 Robert Clark

 In the blog post, The Coming SSTO's I calculated some delta v's that suggested we already have the capability to do SSTO's with significant payload. However, here I'll provide some more accurate estimates by using Dr. John Schilling's Launch Vehicle Performance Calculator page. I'll go back to the Atlas rocket SLV-3 Atlas / Agena B. The specifications are given here:

SLV-3 Atlas / Agena B.
Family: Atlas. Country: USA. Status: Hardware. Department of
Defence Designation: SLV-3.
Standardized Atlas booster with Agena B upper stage.
Specifications
Payload: 600 kg. to a: 19,500 x 103,000 km orbit at 77.5 deg
inclination trajectory.
Stage Number: 0. 1 x Atlas MA-3 Gross Mass: 3,174 kg. Empty Mass:
3,174 kg. Thrust (vac): 167,740 kgf. Isp: 290 sec. Burn time: 120 sec.
Isp(sl): 256 sec. Diameter: 4.9 m. Span: 4.9 m. Length: 0.0 m.
Propellants: Lox/Kerosene No Engines: 2. LR-89-5
Stage Number: 1. 1 x Atlas Agena SLV-3 Gross Mass: 117,026 kg.
Empty Mass: 2,326 kg. Thrust (vac): 39,400 kgf. Isp: 316 sec. Burn
time: 265 sec. Isp(sl): 220 sec. Diameter: 3.1 m. Span: 4.9 m. Length:
20.7 m. Propellants: Lox/Kerosene No Engines: 1. LR-105-5
Stage Number: 2. 1 x Agena B Gross Mass: 7,167 kg. Empty Mass: 867
kg. Thrust (vac): 7,257 kgf. Isp: 285 sec. Burn time: 240 sec. Isp(sl): 0
sec. Diameter: 1.5 m. Span: 1.5 m. Length: 7.1 m. Propellants: Nitric
acid/UDMH No Engines: 1. Bell 8081
http://www.friends-partners.org/partners/mwade/lvs/slvgenab.htm

 We see stage 1 called the sustainer stage has nearly a 50 to 1 mass ratio. However, the Atlas had an unusual "stage and a half" structure where engines needed to lift off from the pad were jettisoned later on in the flight, leaving only a smaller, lower thrust engine behind. This engine which is the one used in stage 1, did not have enough thrust to lift off from the pad. So as in The Coming SSTO's post,  I'll replace it with the NK-33 engine which has now flown successfully on the Orbital Sciences Antares. 

 The propellant load remains 114,700 kg as in the original Atlas but the dry mass increases to 3,086 because of the heavier engine. The vacuum Isp is 331 s for the NK-33, and the vacuum thrust is 1,638 kN. Now input these numbers into Schilling's calculator. Select "No" for the "Restartable Upper Stage?" option and Cape Canaveral for the launch site. For the orbital inclination choose 28.5 degrees to match the latitude of Cape Canaveral. Then the Calculator gives these results:

====================================================

Mission Performance:

Launch Vehicle:	User-Defined Launch Vehicle
Launch Site:	Cape Canaveral / KSC
Destination Orbit:	185 x 185 km, 28 deg
Estimated Payload:	4113 kg
95% Confidence Interval:	2860 - 5625 kg

====================================================

 This value of 4,113 kg is remarkable in being close to that of the payload capability of the full Antares at 5,000 kg, a rocket of twice the gross mass, using two stages and two of the NK-33 engines on the first stage.

 Based on this, this SSTO version could be significantly cheaper than the current Antares. Plus in being only liquid fueled, it could be used as a manned launcher. Note that Orbital already has the Cygnus capsule which with the addition of a heat shield and life support could be a manned capsule.

 The mass ratio of 50 to 1 for the original Atlas is so high it would be interesting to calculate the payload capacity if we used instead the lower Isp Merlin 1D engine. By the SpaceX page, nine Merlin 1D's have total vacuum thrust of 6,672 kN. So one is 741 kN. We will need two to lift off, at 1,482 kN vacuum thrust. The two Merlin 1D's together weigh about 330 kg less than the NK-33 case, so subtract that much from the dry mass of the NK-33 case. However, the Isp is also reduced to 311 s Isp for the Merlin:

 Then Schilling's calculator gives:

====================================================

Mission Performance:

Launch Vehicle:	User-Defined Launch Vehicle
Launch Site:	Cape Canaveral / KSC
Destination Orbit:	185 x 185 km, 28 deg
Estimated Payload:	3025 kg
95% Confidence Interval:	1952 - 4331 kg

====================================================

 It is the quite high mass ratio that leads to these rather high payload capabilities.

 SpaceX might not be inclined to support such an experiment, as they are deeply invested in keeping the Falcon 9 first stage and Merlin 1D engines. However, Orbital Sciences farms out its construction of the Antares first stage to a company in the Ukraine.  So they may be inclined to try a new stage that would at the same time prove to be a revolutionary step of creating an operational SSTO.                                                                                            

   Bob Clark

Medium lift circumlunar flights.

Copyright 2013 Robert Clark

 In the post  "Golden Spike" circumlunar flights I argued the new Falcon 9 v1.1 would be able to do manned circumlunar flights carrying a Dragon capsule. Note that this could also prove Elon's claims that the Dragon could serve as a lunar mission capsule. Moreover, such a unmanned test could be carried out this year with the first test flight of the Falcon 9 v1.1.

This is important because the original circumlunar flight carrying Apollo 8 used the huge Saturn V rocket. Then the feeling came about that even to do a manned circumlunar flight required a super heavy lift rocket such as the Saturn V. Then showing a much smaller rocket such as the Falcon 9 v1.1 could accomplish such a mission would be important to confirming the idea that lunar landing missions also could be much smaller, and much cheaper, than imagined.

 As further support of that, currently existing medium class launchers such as the Delta IV Medium and Atlas V without side boosters, can also do circumlunar missions by using a capsule half-sized to the Dragon. One such half-sized capsule would be the Orbital Sciences Cygnus, given life support systems and heat shield, as discussed in Budget Moon flights: lightweight crew capsule. 

 Another possibility might be the capsule designed by Andy Elson for SpaceX for the Falcon 5 rocket. Since the Falcon 5 had half the payload capability of the Falcon 9, and this capsule was to carry half the passengers of the Dragon, quite likely it would be about half-size to the Dragon:

Magic Dragon: The UK's first commercially built manned capsule demonstrator.
By Rob Coppinger on April 9, 2008 4:13 PM | 
http://www.flightglobal.com/blogs/hyperbola/2008/04/magic-dragon-the-uks-first-com.html

  The Delta IV Medium and Atlas V without side boosters have a payload capability of about 10 metric tons (mT) to LEO. Page 2 of Boeing's "Delta IV Technical Summary"  gives the translunar injection (TLI) payload capability of the Delta IV Medium as 3 mT, sufficient for the dry mass of the Cygnus. 

 The payload capability to TLI for the Atlas V can be estimated by Dr. John Schilling's Launch Performance Calculator by selecting the escape trajectory option. This gives about 3.4 mT capability to TLI.

 The Ariane 6 is to be a medium class launcher comparable to the Delta IV Medium and Atlas V. Then the liquid-fueled version would not only have the advantage over the solid-fueled version of being able to do manned missions to LEO but manned circumlunar missions as well.


  Bob Clark

Budget Moon Flights: Ariane 5 as SLS upper stage.

Copyright 2013 Robert Clark

Delta IV Heavy Orion Circumlunar Test Flight.

I’m fairly sure looking at the capabilities of the Delta IV Heavy with the upgraded RS-68a engine, about 28 metric tons to LEO, that it could launch the Orion on that 2014 test launch on an actual circumlunar flight, not just to 3,600 miles out as currently planned. A circumlunar flight would result in a much more capable test of the Orion.

The Orion test is planned to only carry a dummy service module, so that will be much lighter. The flight is planned though to carry the launch abort system (LAS) so that detracts from the weight that can be launched.

Without the LAS the DIVH could definitely send the Orion on a circumlunar flight. With the LAS, it makes it a little more difficult to estimate since it is jettisoned before reaching orbit.

This makes the use of the SLS for that unmanned circumlunar test flight in 2017 even more dubious, since the DIVH could do that, even if removing the LAS is required. That is another reason why I argue NASA should be aiming for an actual unmanned lunar landing test with that 2017 SLS flight.

Low Cost Lunar Lander and Crew Module.
ULA has done studies on adapting the Centaur upper stage as a lunar lander stage so you would not need a huge, and hugely expensive, Altair lander. We already even have a crew module that could be used for such a lander in NASA’s SEV, which can be ready by 2017 for test flights:

Inside NASA’s New Spaceship for Asteroid Missions | Space.com.
by Clara Moskowitz, SPACE.com Assistant Managing Editor
Date: 12 November 2012 Time: 02:30 PM ET

If the current schedule holds, NASA could test-drive a version of the SEV at the International Space Station in 2017. http://www.space.com/18443-nasa-asteroid-spacecraft-sev.html

Ariane 5 Core as SLS Upper Stage.
NASA is considering a version of the upper stage to be used with the Block II version of the SLS that uses RL-10 engines instead of the J-2X:

SLS prepares for PDR – Evolution eyes Dual-Use Upper Stage.
June 1, 2013 by Chris Bergin
http://www.nasaspaceflight.com/2013/06/sls-pdr-evolved-rocket-dual-upper-stage/

This is expected to save on costs.

NASA also wants to encourage European participation in the proposed asteroid retrieval mission:

NASA Pitches Asteroid Capture To International Partners.
By Frank Morring, Jr.
Source: Aerospace Daily & Defense Report
June 28, 2013
http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_06_28_2013_p01-01-592208.xml

Then a way to save further on development costs and to get European involvement would be to use the Ariane 5 core as the upper stage. It’s of common-bulkhead design to save mass. I recently learned it also uses the pressure-stabilized, “balloon tank”, method a la the Centaur to further save on tank mass.

The ESA also believes its Vulcain II engine can be made air-startable since this was planned for the Liberty rocket. The Vulcain uses a rather short nozzle since it is meant for ground launch, giving it a 432 s Isp. But simply giving it a nozzle extension would give it the ca. 462 s ISP of the RL-10.

Another key advantage is that because little additional development would be needed it might even be ready by the 2017 first launch of the SLS. Then this first 2017 launch of what was only to be a 70 mT interim version could have the 100+ mT capability of the later versions of the SLS. Such a version would clearly have the capability to do manned lunar lander missions.

You could also give this stage the RL-10 engines, instead of the Vulcain. The Vulcain weighs about 1,800 kg. Four RL-10′s would weigh 1,200 kg. So this would save 600 kg off the stage dry mass.

The NasaSpaceFlight.com article mentions the advantage of having different diameters for the hydrogen and oxygen tanks to maintain commonality with tooling of existing stages, and that is the reason for not having both tanks the same diameter. That would not be a problem of course with using the Ariane 5 core at a common 5.4 meter diamter. And someone noted on the Nasaspaceflight forum thread on this topic that for a uniform 8.4 m diameter, NASA could just use the same tooling for both that is used for the 8.4 meter SLS core stage tank.

For any of these possibilities it would be very good if NASA could use the composite tanks Boeing is investigating. Aerospace engineer Jon Goff on his blog noted ULA estimated their ACES proposed upgrade of the Centaur could get a 20 to 1 mass ratio by switching to aluminum-lithium for the tanks. And according to Boeing, an additional 40% can be saved off the Al-Li tank mass by using composites, resulting in an even larger mass ratio than 20 to 1:


NASA Sees Potential In Composite Cryotank.
By Frank Morring, Jr. morring@aviationweek.com
Source: AWIN First
July 01, 2013
http://www.aviationweek.com/Article.aspx?id=/article-xml/awx_07_01_2013_p0-592975.xml


Scaling up your stage mass, such as to the DUUS size, is also known to be able to improve your mass ratio. Imagine then all these mass ratio improving factors being applied. How high could the mass ratio get, perhaps to the 25 to 1, or even 30 to 1 range???

Imagine what you could do with a hydrolox stage with an ISP as high as ca. 462 s with a mass ratio as high as 30 to 1. (*)

Bob Clark


(*) By rocket equation, the delta-v is:  462*9.81ln(30) = 15,400 m/s.


Update, Sept. 28, 2013:

 Finally, NASA has acknowledged that the Block 1, first version of the SLS to launch in 2017 will have a 90+ mT payload capacity not the 70 mT always stated by NASA:

SLS Dual Use Upper Stage (DUUS).
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130013953_2013013757.pdf

 This is important since it means we will have the capability to do manned lunar landing missions by the 2017 first launch of the SLS:

SLS for Return to the Moon by the 50th Anniversary of Apollo 11, page 5: A 90+ metric ton first launch of the SLS.
http://exoscientist.blogspot.com/2013/09/sls-for-return-to-moon-by-50th.html