Thursday, November 10, 2022

A low cost, lightweight lunar lander.

 Copyright 2022 Robert Clark

 In the blog post Possibilities for a single launch architecture of the Artemis missions I discused that a single launch architecture is possible for the SLS rocket if there is a lightweight lunar lander. Such is possible using currently existing space stages. Firstly, a lunar crew module of ca. 2 ton mass is possible based on Orbital Sciences Cygnus capsule, discussed in Budget Moon flights: lightweight crew capsule. The Cygnus is actually build in Italy by Thales Alenia Space. As it is already built, the additional modications for added life support would be comparatively low cost.

 Note Thales Alenia Space is already adding life support sysmtems to a larger version of the Cygnus for the lunar Gateway. Then a lower cost version would simply use the smaller Cygnus itself, at a ~2 ton dry mass for a short term stay on the lunar surface.

 As for the propulsion system, the earlier Ariane 5 EPS storable propellant upper stage prior to the current cryogenic upper stage could be used for the purpose: it had a 1.275 ton dry mass and 9.750 ton propellant mass, for a 11 ton gross mass. Then the crew module and propulsion stage would mass 13 tons.

 An advantage over the SpaceX Starship lunar lander plan is that it is only 3 meters high, the same height as for the Apollo lunar lander descent stage, making it easy for the astronauts to climb down to the lunar surface, compared to the 25 meter height for the Starship.


The delta-v to the lunar surface from low lunar orbit is 1,870 m/s:

 The Aestus engine on the stage has a Isp of 324s. Then the delta-v it could achieve carrying a 2 ton crew module would be:

324*9.81Ln(1 + 9.75/(1.25 + 2)) = 4,400 m/s. Then it could work as single stage to go down to the lunar surface from low lunar orbit and back again.

 It is notable a stage derived from the Space Shuttle OMS pods would also have this capability.

 The specifications for the OMS pods are given here:


The middle size version has a dry mass of 3,955 lbs, 1,800 kg, and propellant load of 25,064 lbs, 11,400 kg. It has an Isp of 316 s. Then with a 2 ton crew module it would have a delta-v of 4,300 m/s:

316*9.81Ln(1 + 11.4/(1.8 +2)) = 4,300 m/s, sufficient for single-stage lunar lander.

  Robert Clark

Saturday, November 5, 2022

Why does the Boeing Exploration Upper Stage(EUS) cost so much?

 Copyright 2022 Robert Clark

 The Boeing Exploration Upper Stage(EUS) is only about 1/10th the size of the SLS core stage. Why couldn't this upper stage be built in the same fashion as the core?

 The SLS core like the shuttle External Tank before it is built by welding together barrel sections:

 Then the upper stage could have been formed in the same fashion simply by using fewer/shorter barrells. Indeed, cost could have cut even further by constructing the upper stage at the same time as the core.

 Being only ~1/10th the size of the core it likely would have fit in the same building during the construction:

 Instead of this simple approach, Boeing chose a more complicated construction that resulted in higher development costs:

  In fairness to Boeing it should be said that they most likely wanted to save on dry mass on the stage. Unlike for lower stages like the core, extra mass on the upper stage results in direct reduction in that mass from the payload.

 However, to accomplish the same payload with a less mass efficient stage they could have just increased the stage propellant size. For instance the Delta IV first stage has a 200 ton propellant load at a 26 dry mass. You would not need the full thrust and high mass of the sea level engine the RS-68 used on the stage for this upper stage use. Smaller thrust and weight engines such as 4 RL-10's or a single J-2X would suffice.

 The mass efficiency for the Delta IV stage without the 6 ton RS-68 engine is also pretty good at a 200 ton propellant load for the 20 ton structural mass sans engine. Note the Delta IV first stage achieves this good mass efficiency without using advanced mass saving methods such as common bulkhead, balloon tanks, or specialty high strength stainless steels as used on the Centaur upper stages.


 The total development and production cost for the Boeing EUS will probably be $10 billion:

More far-out facts: The EUS will probably cost $10 billion and (it's being built by Boeing, recall) won't be completed for at a minimum of five years. Do you think a fully expendable $2.5 billion super heavy lift rocket will have any relevance at that time? 

And the per stage cost likely ~$880 million each:

The story also uses a simple cost estimator model to put a per-unit price on Boeing's Exploration Upper Stage. The result? $880 million. That's just the upper stage, and doesn't include the core stage, SRBs, integration, ground systems, etc. etc.

 Note the entire SLS development was in the range of $20 billion, with an expected per lauch cost of $2 billion. Then this EUS stage at ~1/10th the size of the SLS core and without the extra expense of the SLS side boosters or current interim SLS upper stage would amount to half the cost of the entire current SLS.


 While the RS-68 engine(with a vacuum optimized nozzle extension) would be over powered for the upper stage use, it would be significantly cheaper than using 4 RL-10's for example. The RL-10's are estimated to cost $25 million for a total of $100 million for 4. The RS-68 in contrast is estimated to only cost $10 to $20 million. For the J-2X engine, being an engine only developed but not yet used, there are no estimates on its cost, but it's very likely to cost much less than the $100 million for the 4 RL-10's. Another possibility might be the Vulcain engine used on the Ariane 5. It's estimated cost is only $10 million.

 As an estimate on how much the stage aside from the engines might cost if built in the same fashion as the SLS core and shuttle external tank, look at the costs for the shuttle ET built by Lockheed. They were given a contract for 18 External Tanks for a total $3 billion, about $166 million per tank. Note too an SLS upper stage at ~200 ton propellant load would be less than 1/3rd the size of the External Tank. Given this much lower cost Lockheed should be asked how much would be a stage built in the same fashion as the shuttle ET at ~ 200 ton propellant load.

  Robert Clark

Thursday, November 3, 2022

At the new space tourism companies, who should be the smartest people in the room? The launch safety officials.

 Copyright 2016 Robert Clark

(Note: the opinions expressed here are the authors own and should not be interpreted to be those of Widener University.)

 For space advocates the losses of the space shuttles Challenger and Columbia will always rile as accidents that didn't have to be. The decisions that led up to the accidents were made by competent engineers and managers, however in hindsight we realize they were not the correct decisions. A common saying is "hindsight is 20-20" but could it be that the correct decisions could have been made in foresight?

 When someone criticizes your poor decision making after an accident, you could always assert in your defense "hindsight is 20-20". But in many cases we realize the results of bad decisions should have been foreseen. If a man lights a match to a gasoline can, and then after being criticized for that bad decision, he couldn't respond, "Well sure, hindsight is 20-20." In that case it is common knowledge that that would be a foolish thing to do.

 In other cases those with appropriate expertise would have sufficient insight to realize certain actions would have bad results. You also would not say "hindsight is 20-20" then. So the key question is are there people with the right insight to make those right decisions even when those who are experienced in the field would make the wrong ones?

 An example of the type of insight that is required: in the space shuttle Challenger accident it was known that cold temperatures could affect the O rings ability to prevent the breach of hot gases to the outside of the solid rocket boosters. So some of the engineers brought this to the attention of the shuttle managers prior to the launch. But those arguing the other side noted that there had been also cases at warm temperatures that there had been some degree of blow by past the O rings of the hot gases though not enough for complete burn though.

 Unfortunately, the fact that could have decided the issue against launching was not recognized until after the fateful launch. In the post-launch accident review, some shuttle engineers that opposed the launch produced a graph showing that almost all launches at cold temperatures produced blow by and most of the bad cases of blow by were at the colder temperatures. The launches at warm temperatures had relatively few cases of blow by. The Challenger launch was going to be at the coldest temperature ever attempted for the shuttle.

 When presented with that graph after the accident, one shuttle program manager said, "When you look at it that way, it sort of jumps out at you." Unfortunately, that insight to produce that graph only occurred in hindsight, not foresight.

 Another example is provided by the Columbia accident. Shuttle mission managers decided against requesting imaging from more accurate(classified) sources or having the shuttle astronauts do a space walk to examine the wing for damage, because they concluded "nothing could be done anyway". However, could something be done if they HAD to come up with an answer by thinking outside-the-box?

 After the accident, NASA was tasked with coming up with ways the crew could have been saved. The leading proposal was to do a rescue with the space shuttle Atlantis. Part of the reason shuttle managers hadn't thought this feasible before the accident was because Columbia was scheduled to return Feb. 1st, 2003 but Atlantis would not be ready for launch until March 1st.

 Nevertheless, NASA concluded after the accident that the consumables on Columbia could be extended an extra two weeks, and the Atlantis preparation could be speeded up two weeks so that a rescue mission was possible, [1].

 One worry about this proposed solution was that speeding up the Atlantis preparation process could lead to errors and would endanger the Atlantis as well. But it is quite likely, with further thinking outside-the-box, it would not have been even necessary to speed up the preparation time for Atlantis.

 In the 2015 film The Martian two instances occurred where unmanned cargo ships were launched to send up supplies to extend the survival time of the crew in the film. This then could have been used to extend the survival time of the crew of the Columbia. The limiting factor for the survival time for Columbia were simply the CO2 scrubbers that removed the carbon dioxide from the air. These canisters were quite lightweight and in fact any of the 5 space faring nations of the world could have sent up these small canisters to rendezvous with Columbia.

 During the proposed 30 day timeframe before Columbia would have run out of air scrubbers with the crew at reduced activity, there were at least 4 launches to orbit, [2].

 The Pegasus rocket that was in this list is especially relevant since being air launched and using all solid stages should have shorter prep time. In fact the Pegasus could be launched within 7 days of notice, assuming the payload was available. The Minotaur 1 rocket also has this capability.

 So what is the quality of having this foresight? Certainly it is intelligence, but it is beyond what is measured in IQ tests. I wish to argue such foresight, which is sometimes inexplicable and perhaps even sometimes cannot even be explained in words, comes from individuals with a unique ability to reason visually.

 Such visual reasoning has been a hallmark of those with great insight. Einstein once said he was led to his theory of special relativity by imagining what it would be like to ride on a beam of light. And he said he was led to his general theory of relativity by the realization that someone falling in freefall would not feel his own weight.

 Richard Feynman's graphical "sum over histories" approach, known as Feynman diagrams, led to a solution of a key problem in quantum electrodynamics, for which he was awarded a Nobel Prize. Feynman is a good example of the point that such visual abilities are beyond what is tested in traditional IQ tests, as Feynman was measured in school to have an IQ of "only" 125, which is under the cutoff considered to be "gifted" of 130.

 The Nobel-prize winning physicists Luis Alvarez and William Shockley, also scored below the "gifted" score on their IQ tests, as did Francis Crick and James Watson, Nobel-prize winning discovers of the double-helix structure of DNA.

 Francis Crick is another example of the importance of visualization. It was said of him that while looking at x-ray diffraction patterns of molecules he could visualize the shape of molecules where other scientists just saw equations, [3].

 Geneticist Barbara McClintock imagined herself down inside the maize she studied with their chromosomes. She won a Nobel for her work describing the workings of the maize chromosomes, [4].

 Einstein's aforementioned "thought experiments " bring to mind another example of a scientist of extraordinary insight, Nikola Tesla. Tesla imagined himself down inside his constructed mechanisms. He said he was able tell where they might fail by visualizing them.

 Another interesting aspect of those with these extraordinary visualization skills is that by using them they knew their ideas were correct. Without being able to explain in words why they knew they were right, they knew it before their mechanisms were built or confirming experiments conducted.

 Such visual reasoning, which may be difficult to describe in words, might be regarded as "mystical" by others. A famous quote of Arthur C. Clarke is "any sufficiently advanced technology is indistinguishable from magic". We might adapt this to the reasoning of the most creative thinkers as, "any sufficiently advanced intellect is indistinguishable from the mystical".

 Such visual reasoning, being able to put yourself down within the mechanism as McClintock and Tesla experienced, is a capability we want to have for those with foresight to diagnose possible problems with our launch vehicles beforehand.

 How do we recognize these individuals? It is now being recognized that visual or spatial ability is a key ability for predicting success in scientific or technological fields [5] and there are tests focusing specifically on this ability. As a first step we could endeavor to promote those who score high on such tests.

 However, Richard Feynman was a skeptic of all intelligence tests. He was proud to note how he was considered below the "gifted" scale when he was tested in school. He argued that a single number could not capture the full variety of human intelligence. I'm inclined to think the same is true even when you have a test focused on a specific kind of intelligence, such as for spatial ability.

 A more inclusive search would be summarized by the idea, "clever is as clever does." Current employees and new hires should be exposed to a wide variety of different problems and issues in the company. Those who have the extensive ability to reason visually, spatially frequently can provide unique insight even outside their fields of specialization. The new hires who have an uncanny ability to diagnose issues or problems that have cropped up or, even more, predict those that will before they actually happen should be encouraged in that ability and promoted within the company.

 I use the word "promote" with some leeway in its interpretation. Those with the unique ability to reason visually frequently are not the smoothest in their interpersonal relationships. It's a phenomenon now recognized by the term Asperger Syndrome, a form of autism as interpreted as difficulty in interpersonal interaction. It is not uncommon in individuals of highest intelligence. Barbara McClintock's students said of her that she was hard to understand. And Tesla's difficulties in interacting with others have become legendary.

 Those with the high visual reasoning capability likely won't be the best candidates for management positions. It may even be required to hire "intermediaries" between them and management, or lower level employees.

 As mentioned, individuals with this extended capacity of visual reasoning are known to be problem solvers even outside of their fields of specialization. Barbara McClintock's colleagues marveled at her ability to solve a problem they may have been working on for years after only being exposed to it for a short time.

 I'm reminded of one of Isaac Asimov's later novels Foundation and Earth [6] where the main character Golan Trevize had the unique ability to make the right decisions based on insufficient information. While this was in the realm of a science fiction novel, I don't rule out such a capacity exists. It simply might appear to be mysterious, or mystical to us because we don't operate at the level of those with this capacity of super visualization where these objects of the mind's eye are as real and valid as objects we can see directly in front of us.

Robert Clark

Adjunct Professor of Mathematics

Widener University

Chester, PA 19013


1. ) Columbia Accident Investigation Board.

Possibility of rescue or repair.

2.) 2003 in spaceflight.

3.) Francis Crick.

4.) Barbara McClintock: Pioneering Geneticist.

By Ray Spangenburg, Diane Moser

5.) MIND

Recognizing Spatial Intelligence

Our schools, and our society, must do more to recognize spatial reasoning, a key kind of intelligence.

By Gregory Park, David Lubinski, Camilla P. Benbow on November 2, 2010

6.) Home again, home again, in so many ways: Isaac Asimov's Foundation and Earth.

Josh Wimmer and Alasdair Wilkins

5/13/11 6:30pm Filed to: FOUNDATION WEEK

Friday, October 21, 2022

Possibilities for a single launch architecture of the Artemis missions.

 Copyright 2022 Robert Clark

 In the blog post ESA Needs to Save NASA's Moon Plans I noted that the original plan SpaceX submitted to NASA for a lunar lander required 16 launches due to multiple refueling flights, with the refueling flights to orbit requiring a time of 6 months to accomplish. I argued in the blog that if instead NASA used an Ariane 5/6 as the upper stage of the SLS rocket replacing the current Interim Cryogenic Propulsion Stage(ICPS) then it could be done in just a single launch of the SLS, with no launches of the Starship required at all.

 After their proposal was submitted by SpaceX and accepted by NASA, Elon Musk, stung by the criticism it would take so many launches, suggested it probably could be done in only 4 refuelings since a stripped down Starship for a lunar lander mission would weigh much less.

 SpaceX needs to be open about what the mass would be for such a stripped down Starship since that would directly affect how much NASA, and the U.S. taxpayers, would have to pay to SpaceX for refueling launches. See discussion here, 

The nature of the true dry mass of the Starship. 

 My suggestion to use the Ariane 5/6 as an SLS upper stage was critiqued on political acceptability grounds for a such a large contract to be taken from a U.S. company and given to a European company. 

 Here I'll propose a solution using existing, pretty much, American upper stages for the SLS. It's the ULA Centaur V upper stage coming into service next year. I considered using the Delta IV common core stage but at a 40 meter height it might be too tall for this use.


 The Centaur V has a 54 ton propellant load. Following the approx. 10 to 1 gross mass to dry mass ratio of the original Centaur, I'll take the dry mass to be ~5 tons. Then I'll examine  two options: 1.)2 Centaur V's combined into a single stage, and 2.)2 separate Centaur V's.

 The current Block 1 version of the SLS gets about 27 tons to trans-lunar injection(TLI). This is the speed needed to get a spacecraft once in orbit to reach the Moon. The 27 tons is just enough to get the Orion capsule and its service module to TLI

 However, the current approach is not to put the Orion in low lunar orbit around the Moon. Instead, it will be placed in a higher altitude orbit of Earth-lunar space called a near-rectilinear halo orbit(NRHO). The reason is the current version of the SLS did not have enough power to put the Orion in low lunar orbit and for it to be able to escape again.

 Our plan then is to first increase the payload capacity of the SLS so that enough additional propellant can be given the Orion service module so the Orion can actually reach and leave low lunar orbit. 

 The Orion with its fully fueled service module has a mass of 26.5 tons. The propellant load of the service module is ~10 tons, with 16.5 total tons dry mass of the Orion and service module. We'll add an additional 10 tons propellant to the service module to bring the total mass to 36.5 tons, including 20 tons of propellant.

 The AJ-10 engine used has a vacuum ISP of 319s. We'll assume a lunar lander of size ~15 tons, comparable in size to the Apollo missions lunar lander. In a following blog post we'll describe it in more detail. So, 16.5 + 15 = 31.5 tons dry mass needs to be put in low lunar orbit.

 For the delta-v calculation, after the SLS places the Orion/Service Module/lunar lander stack in trans-lunar injection(TLI) towards the Moon, we need .9 km/s to put the stack into low lunar orbit. This requires 13 tons of propellant, leaving 7 tons remaining:
319*9.81Ln(1 + 13/(31.5 +7)) = .910 km/s. The lunar lander will then be launched to land on the Moon while the Orion and service module remain in lunar orbit.

 After the lander mission is completed, the lander returns the astronauts to the Orion in lunar orbit, and the lander is then jettisoned. The Orion's service module is then fired to bring the Orion back to Earth. After lander jettison, the dry mass of the Orion and service module will be 16.5 tons. Then the 7 tons of remaining propellant is sufficient to perform the trans-Earth injection(TEI) burn of 900 m/s to escape lunar orbit and place the spacecraft back onto the free return trajectory back to Earth:

319*9.81Ln(1 + 7/16.5) = 1,100 m/s.

Calculations for Earth escape stage to TLI.
 That's the plan if we can upgrade the SLS to carry sufficient payload to give the Orion service module that extra 10 tons of propellant. The total mass that needs to be put into TLI is 36.5 + 15 = 51.5 tons. Here's a calculation for the first approach of two Centaur V's combined into a single stage. I'll use the payload performance calculator of Dr. John Schilling, on The specifications for the 5-segment SRB's are taken by scaling up the numbers from the 4-segment SRB's used on the Space Shuttle system.

 I'll give this stage 4 RL10 engines instead of the Centaur V's 2 because of the larger size, in effect just transferring two of the RL10's from the second Centaur's to the first. The input page looks like this:

 The payload estimator then gives the payload to LEO of ~127 tons:

  And the for the payload to TLI we'll use a C3 of -1.00km2/s2.

 This gives a payload to TLI of about ~52 tons:

  It is notable though the Schilling payload estimator has rather large error bars. These numbers need to be confirmed by more accurate payload estimators.

 The payload can be increased by using instead of the RL10's, a single Blue Origin BE-3U, the vacuum optimized version of the BE-3 engine used on the New Shepard. This engine has a vacuum optimized thrust of 710 kilonewtons. Placing this in for the upper stage thrust gives a payload to LEO of 136 tons, and to TLI of 54.7 tons. Again this needs to be confirmed by more accurate payload calculators.

 The intent here is to find a low cost approach to an upper stage that would allow a single launch architecture for the Artemis lunar lander missions. A combination of adding additional engines and also combining two tanks would ratchet up the costs.

  The second approach would use two separate Centaur V's. However, because of the large mass that needs to be carried by the either Centaur as payload we'll give both Centaurs 4 RL10's. The input screen looks like this on the Schilling calculator:

  And the LEO payload is ~129 tons:

 And the TLI payload is ~54.7 tons:

  Again, these payload estimates would have to be confirmed by more accurate payload estimators.

 This second approach would not incur the extra costs of combining two Centaur V's into a single stage, but it would require 4 additional RL10's. As before though we could get increased payload by replacing the RL10's by the BE-3U, and likely lower cost.

 We still need to come up with that lunar lander of comparable gross mass as the Apollo lander, ~15 tons. In a following blog post I'll show our European partners can come up with such a lander at low cost and at a relatively short time frame.

  Robert Clark


Could ‘Oumuamua be a spent rocket stage?

Copyright 2023 Robert Clark  I was interested to read of a supposed asteroid passing near Earth turning out to be a Centaur upper stage laun...