The Rivers of Progress

Most if not all people disagreed with my thoughts on bringing in various technologies in the last few posts about the architecture Doug Plata is laying out at spacedevelopment.org. On many blogs, and especially with many of the commenters  on those blogs, I could dismiss their concerns almost out of hand and be right most of the time. On this blog, and with the known high quality of the majority of the commenters disagreeing with me, there is necessarily something else going on. Obviously I could be wrong with them pointing it out. Or there could be misunderstanding as I am not a professional writer that is crystal clear in laying out my ideas.

There is another possibility that came up in the email exchanges with Doug. How many of the disagreements spring from variations in  the ideological base of the individuals involved. Life experiences and historical knowledge of space development does not resolve our differences. It can explain some of them so that we can move forward in developing ideas and eventually hardware.

Our viewpoints on space development could be viewed in the way a river develops. Most rivers in the eastern US grow on their way to the ocean. Rivulets, and creeks, and canals, other rivers, and lakes feed them up as they flow such that the river at the ocean is huge compared to its’ humble origins. In the southwestern US, some rivers have some of their vitality tapped off in so many places that the flow at the ocean is a fraction of the size of some upstream locations. Cities and farms and dams can reduce it to nothing in some cases. There are lawsuits about upstream usage before downstream availability.

Some of the discussion about space development mirrors river development. The question being if a given technology or suggestion is a tributary making the river bigger and stronger. Or is it a city or irrigation system draining the vital juices preventing the full flow to the destination. Much of spaceflight history is that of pet projects and congressional set asides draining the river en route such that the salt water flows upstream into the delta regions poisoning the  freshwater plants that depend on the river. SLS is the current flagship for that view with the funds going to it and its’ precursors being more than sufficient for real progress if it had been properly focused. SLS could be seen as a city in the desert that built a dam that keeps the water from flowing to the downstream drought.

The various ideas I throw out could be tributaries or dams depending on the ideological approach involved. If funds are diverted from the main goals for endless toy  development, potential dam. If they must fund their own way to the river, potential tributary. Whether or not the technology of a concept will work is important. Where the funding comes from, and which strings are pulled to get it is critical.

So in the recent discussions, who is right? There are a lot of variables that could make it either, both, or neither.

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Early Testing and Demonstrations on the Depots and Rotovators

Doug Plata has done some detailed comments on the suggestions, ideas, and differences from his ideas that my posts laid out in minimal form. His comments deserve better than I can do in a little comment window. Probably better than I can do in a post, but I won’t admit that part in public. It is my opinion that these technologies would speed up Lunar development, expand the possible scope of operations, and cut the cost in the process. They do carry risk though, which is Dougs’ objection, along with getting permission to use them in the first place.

I did a post on my views on the Lunar hoverslam landings. This one is how I see the depot and rotovator getting underway. I think initial proof of concepts and bringing the TRL up to snuff should be done on company internal resources without fighting the Federal funding battles.

The only real reason depots are not in use now is that there is no real demand for them. A comment on one post noted that propellant in orbit was as valuable as dirt. A bitingly true statement as long as there are limited missions beyond LEO, and few satellites share orbits that would make depots useful. A constant flow of material to and from Lunar orbit changes the situation with many vehicles taking the same path.

I see the initial depot flights as secondary payload technology demonstrators. Often flights to LEO are at less than payload capacity of the launcher. Either the upper stage carries a small second spacecraft, or it makes a rendezvous with another vehicle. The upper stage docks(berths?) with another vehicle and transfers propellant to it. They separate for a while and then hook up and transfer propellant back. Operating as a secondary payload on a stage that is expendable anyway should have the possibility of being a fairly economical mission. This would give a chance to solve propellant settling and transfer in (off?) the real world. Several missions could be flown for relatively low operating costs until the company is comfortable with the transfer techniques and has the boil off data for a few configurations. Then start flying more ambitious missions that do need some help until it is an accepted practice. There is too much information out there on depots to justify me going long on the subject.

Rotovators are far more risky. The payoff is also very high. The Lunar rotovator alone would offer major savings to a serious development operation. The ability to return material from the Lunar surface to an Earth bound trajectory without propellant, engines, or tanks would make it attractive even without the ability to intercept cargos from Earth for   a soft landing without fuel. The TRL is very low for tethers of any kind in space with rotovators having no test data at all.

I suggest the rotovator  demonstration unit be a secondary payload with the minimum mass that can demonstrate the principles.  This mission would be the rotovator itself, whatever auxiliary equipment is needed to make it work, and a bunch of expendable small spacecraft with the only function being thrown and caught.

The rotovator is lightly spun up when orbit is reached testing deployment and system dynamics. The initial target velocity is that which brings the tip thrown  vehicles to a 15 orbit per day instead of 16 of the base vehicle. This brings the small vehicle back to rendezvous in one day if all the calculations and results work out. It is to be expected that most of the little test spacecraft will be missed and lost early on. Perigee would be kept low enough that missed ships would reenter in a matter of days to avoid creating more orbital debris. It would be a risk that there would not be enough of the little ships to establish success and possibly no captures at all on the first rotovator mission. Further rotovators would be sent out as secondaries  until accurate slinging and reliable captures were expected instead of experimental.

After initial proficiency is reached at the 15/16 orbits, velocities are increased to 14/16 and 13/16 until the 1,600 m/s target is reached that would validate a Lunar rotovator. Then one is sent to Lunar orbit as a working system. If the 1,600 /s units were successful enough in Earth orbit some would remain to pick up suborbital ships to sling them most of the way to GTO or TLI with the rockets relighting after the rotovator boost.

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Lunar Hoverslam

I suggested in the middle of a couple of recent posts that the hoverslam techniques pioneered by SpaceX with the Falcon9 be used for Lunar landings. It was a kind of throwaway thought along with several other suggestions. As I think about it though, it seems to me that there might be a serious possible schedule and reliability gain from adapting the technique to Lunar development. That’s why I’m putting it up as a separate post.

I didn’t think hoverslam was a viable technique until it had been demonstrated. I was wrong. Now that it has been demonstrated multiple times, it may be time to see if there are more applications in which it might give an advantage. Lunar landings being the application under discussion recently, I want to lay out a few possibilities.

First thing would be a discussion with the team that is already using the technique in operational vehicles. From the outside looking in, it appears that hoverslam is a software solution to landings that was previously considered a hardware development problem. If this thought is accurate, then it may not be necessary to develop engines and control systems that allow an empty tank vehicle to hover in 1/6 gee. It seems that it is a requirement to bring velocity to zero at the instant that altitude is zero with thrust/weight being far less relevant than most of us previously thought possible. It seems that the SpaceX team is landing with thrust/weight levels of well over two on Earth, which would be well over a dozen at the Lunar surface.

If a Lunar lander is at 20 tons at touchdown, then the hovering that most of us consider a requirement would need engines capable of throttling to  3 tons for a gentle descent at very low velocities. The experience of Apollo 11 finding a clear landing area validates this opinion. This is however, not 1969. The Lunar surface is not only far better known now, but any potential landing sites could be imaged to near centimeter precision at relatively low cost. So hovering while making sure of a clear landing zone may not be a requirement. Navigation to the clear areas is also much less of a challenge than a half century ago. So it may be possible to go straight in to a site on near side without even orbiting first. It may be possible to land that 20 ton vehicle with engines that will only throttle down to 50 or 60 tons.

Doug believes that getting funding authorities to sign off on Lunar hoverslam would be a nonstarter. He is right unless the technique is fully validated just as it was on Earth/barge. I suggest the first step would be an RFI to SpaceX to confirm that it would or would not be possible to use the technique in this manner. If the answer is affirmative, then a test mission could be envisioned. For a test mission, perhaps an upper stage of the Falcon9 could be refueled by a Facon9 tanker in Earth orbit to validate tanker technology as well before sending it on to the Lunar surface.

The Falcon9 upper stage with one refueling should be able to place well over 5 tons on the Lunar surface during the test mission if the concept is valid. Depending on the flight backlog and the interest of both NASA and SpaceX, this could fly by Q4 2018. I doubt any other system could land a comparable payload in anything close to that time frame regardless of interest. Cost would be for two Falcon9s plus payload and Lunar operations. 5 tons in useable condition on the Lunar surface would go a long way towards convincing a funding authority to further use the technique for unmanned payloads.

Central to acceptance of the concept would be the failure modes. Obviously a high enough speed impact would destroy the stage and cargo. Hitting a rock with a landing leg and tipping over could be almost eliminated with a good survey and navigation. A sideways vector on landing that tipped the stage over should not be a factor with the current experience level. The most likely failure modes would seem to be engine failure at altitude from fuel depletion, and excess velocity at touchdown from software or navigation error.

Payloads on the first flight(s) should be very robust as well as being useful so that good work can be done even with a less than successful landing. During an excessive velocity landing, the stage propellant tanks provide a crumple zone if done right. An impact at 100 m/s (200 mph) in the vertical orientation could subject the payload to under 10 gees which is survivable to most hardware. It should be expected that the first payload may have to cut its’ way out of the wreckage before deploying solar panels and starting the primary mission. If the stage soft lands but with a side component that tips it over in the 1/6 gee, the payload should also see less than 10 gees.

The spectacular failures we saw from the early Falcon9 barging attempts were almost all from residual propellant exploding. Though technically not detonations, the burns were fast enough that most of us would call it a good boom. The vertical and horizontal vectors on most of the early Falcon9 barging attempts would have been payload survivable without the propellant reactions on impact. In the vacuum at the Lunar surface there would be no reaction from residual propellants in a crash other than fast evaporation and site contamination. All of those spectacular RUDs on the barge would have been stage lost and payload delivered on the Lunar surface.

I suggest that this concept be considered at some low level to see if there is any merit to it. If there is, it could speed up Lunar development by several years and save a few Dirksens.

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Tesla Semi is reasonable, part 1

Tesla finally unveiled their semi truck:
tesla.com/semi/
An electric monster with 4 Model 3 motors, one for each drive wheel, with an astounding 500 mile range (beating most people’s expectations). Fully loaded (i.e. 80,000 lbs total), it can accelerate from 0 to 60mph in 20 seconds. Unburdened, it can do 0-60 in 5s. What’s the point of this kind of performance, other than the ability to go up a 5% grade at 65mph fully loaded? In a traditional vehicle, the conventional wisdom is that an over-powered vehicle will kill your efficiency. And how can you make a 500 mile range electric truck without destroying your payload capacity?

In an electric truck, efficiency and power are related in the opposite way you might expect. The truck shaped a bit like a bullet, with a drag coefficient of 0.36 (like a sports car instead of a “barn”) and an efficiency of better than 2kWh/mile. And the insane performance?

Well, by running more motors in parallel, the effective power loss due to resistance in the coils is reduced since Power loss = I^2*R. Torque is proportional to current and number of motors, so if one motor with resistance R1 needs to generate torque T1, it requires a current I1, and thus a power loss: I1^2*R1.

But if you take the same torque requirement and split it among 4 motors, the current for each motor is now just I1/4, and the power loss for each is: (I1/4)^2*R1 = I1^2*R1/16. All 4 motors in total have a resistive power loss of 4*I1^2*R1/16 = I1^2*R1/4, i.e. a quarter of the value of just a single motor. Additionally, the heat generated would be split among 4 motors, reducing the temperature of the windings and further reducing the coil resistance.

However, there are other loss mechanisms, like friction, “windage” (i.e. aerodynamic drag from the spinning of the motor itself), and eddy currents in the windings and the iron of the magnet. However, these loss mechanisms can be reduced by clever and careful engineering of the motor. Resistive losses are more fundamental and at a certain limit, the only way to reduce the resistive loss is to add more copper (or operate at higher RPM through gearing). Anyway, the point is that having more motors can actually increase the efficiency of the powertrain by reducing the effective resistive losses in the windings. (if you’re interested in how all these loss mechanisms play out in the total efficiency of a motor, here’s a brushless motor efficiency map, showing the maximum efficiency of about 98% at relatively low total torque: motor efficiency map and source: motor-engineer.net/products-page/motor-flow-model)

Another instance in which superlative specifications, which would seem to be detrimental to performance, actually improve efficiency is in the battery size. Batteries are not pure voltage sources but contain “internal resistance” which limits performance and reduces efficiency under load. Doubling the capacity of a battery (by, say, adding an identical battery pack in parallel) thus has the effect of halving the internal resistance and thus halving the power losses under a certain load. Therefore, unlike the conventional wisdom which states that you should use the smallest battery possible, under some metrics adding a larger battery will actually improve efficiency. At proportionally low loads, discharge efficiency can be on the order of 99% or higher (source).
https://www.ethz.ch/content/dam/ethz/special-interest/itet/institute-eeh/power-systems-dam/documents/SAMA/2012/Ottaviano-MA-2012.pdf
If on the other hand, the smallest motor and the smallest feasible battery were used, energy efficiency would be lower. Motor efficiency, as the above map showed, can drop to mid-80% efficiency or lower. Discharge efficiency for the battery can also drop to 90% or so. Therefore, using the smallest motor and battery (and then relying on, say, a fuel cell or something) would be a false economy. Tesla claims a sub-2kWh/mile figure for the semi, a figure that other manufacturers (such as Nikola Motors) scoffed at.

And let’s look in detail at the <2kWh/mile efficiency claim, starting with drag.

Tesla gave a drag coefficient of 0.36 for the Semi. A typical semi trailer is 96-104 inches wide and 12.5-13.5ft tall. I will pick the smaller end of this range in an attempt to show the minimum possible energy figure. EDIT: Just kidding, I’ll use 104in and 13.5ft because a poster reminded me I had forgotten a factor of 0.5, which makes such optimistic assumptions unnecessary. I will assume the standard 1.225kg/m^3 sea level air density (higher altitudes offer better efficiency! The Tesla Semi seems perfect for mountain routes…). And to start, 60mph:
.5*0.36*104in*13.5ft*1.225kg/m^3*(60mph)^2 in kWh/mile:
0.770843181 kWh / mile

and for kicks, at 55mph:
0.647722395 kWh / mile

So, already, the 500 mile Tesla semi has to have a battery of 385 or 324kWh assuming perfect drivetrain efficiency and no rolling resistance. Oh, let’s calculate rolling resistance:

Rolling resistance, for our purposes, requires a constant amount of energy per mile to move a certain load. The speed doesn’t matter (much…). Whether 1mph or 30mph, if you neglect air resistance, the rolling resistance will require you to expend energy to move stuff on Earth (although less on other planets like Mars…).

This is basically the same thing as coefficient of friction, if you remember your first physics course in high school or college. Crr, the coefficient of rolling resistance, is technically unitless, although sometimes it’s expressed as kg-f/tonne-f (i.e. Crr times 1000), and sometimes it’s expressed not as a coefficient but as quantity with a unit, such as power in Watts (for a given load and speed) or force (for a given load). Unfortunately, this number seems really hard to find for typical commuter car tires (but I digress).

The energy needed per unit length is calculated: gravity*Crr*load. g is 9.80665m/s^2, load is 80,000lbs.

Typical semis have about a 0.006 rolling resistance coefficient, so:
https://www.google.com/search?q=9.80665m%2Fs%5E2*.006*80000lb+in+kWh%2Fmile
0.954495836 kWh / mile

Some good semi tires with low rolling resistance have a coefficient of about 0.0045 (so 0.715871877 kWh / mile). But this is not an ultimate limit. A really, really good road bike tire may have a coefficient of about 0.002 (0.318165279 kWh / mile), which is in the range of rail (which has a rolling resistance–metal wheel on metal rail–of about 0.001 to 0.002 in real life conditions… although fundamentally it can be even lower). If you want to compete with rail, you’re going to have to reduce this as much as you can. But, of course, a semi truck is not a road bike.

But there is one way to get even better rolling resistance: a wider tire. Most semi trucks use dual tires on each of the four drive wheels. But it’s also possible to combine the two tires into one. A “super single” tire can have as low as 0.0034 (0.540880974 kWh / mile ), significantly better than the usual low rolling resistance semi tire. Super singles also tend to last longer, and since they have more contact surface with the road, it’s possible they also have better stopping power and even lower road wear. They also can reduce weight (in combination with alloy wheels) by up to 1000 pounds. And 0.0034 is not a fundamental limit. Physics allows you to do better, as road bike tires prove. So this may be an area that Tesla invested in, and according to some rumors, Tesla is planning to use super singles on the Semi.

So, bringing this all together, with a full 80,000 total load, 95% combined motor and battery discharge efficiency (97% may be possible, but not required… and 95% also allows some parasitic load, such as lights, etc), 0.36 Cd at 60mph and 13.5ft tall and 104in wide trailer with a more conservative Crr of 0.0041, I get an energy-per-mile of:
(0.5*0.36*104in*13.5ft*1.225kg/m^3*(60mph)^2 + 9.80665m/s^2*.0041*80000lb)/(.95) in kWh/mile
1.49798105 kWh / mile

That’s consistent with Tesla’s “<2kWh/mile" and with all the data Tesla has given so far and with fairly optimistic assumptions. But if they're using 55mph as a baseline instead and the more efficient tires and drivetrain with the slightly smaller trailer, then the figure could be as low as 1.16kWh/mile (meaning a 600kWh battery may even be realistic). 1.5kWh/mile I think it’s a pretty realistic figure, and so that’s what I’ll use.

That works out to a 750kWh battery for the 500 mile version, which is $180,000 base. The 300 mile version is $30,000 less at $150,000. Does that mean it's 450kWh and thus the cost per kWh is only $100? I'm not so sure that's what it means, although that’s no show-stopper. I DO think Tesla has the ability to make super cheap batteries, but I think there's more to the story.

Tesla announced a 1 million mile guarantee of sorts on the semi drivetrain. I assume that means 1 million miles before the battery degrades by, say, 20%. For a 500 mile battery, that's 2000 cycles. But a 300 mile battery (450kWh?) at 2000 cycles only lasts 600,000 miles until that 20% degradation. Not only that, but since you're loading the battery more relative to its capacity, it might not even last 2000 cycles. So what I think they'll probably do is put a slightly larger battery in there than you might think. Perhaps they increase the battery size to 500kWh to give more margin, thus reducing the depth of discharge slightly and giving room for a little more degradation before your range is reduced too much. That gives a cost of about $120/kWh, which even gives room for profit (imagine that!). But even that kind of number will leave many analysts incredulous. "Breaks the laws of batteries" they'll say: bloomberg…tesla-s-newest-promises-break-the-laws-of-batteries

And I say balooney. Tesla is selling the Semi with initial release in 2019. But they're going to start with the more-expensive, early-adopter $200,000 "founder's edition" semi. So getting to $120/kWh isn't required right away. Ramp-up may be relatively slow, and so let's say they don't start delivering the regular semis until 2020, maybe 2021. Even GM expects to have battery cell prices down to $100/kWh by 2022 (with pack costs estimated by GM at about 20% more). And a cost of $109/kWh for a battery like the one Tesla is using is consistent with Argonne Lab’s modeling BatPaC 3 for 500,000 units per year of 90kWh each: greentechmedia…How-Soon-Can-Tesla-Get-Battery-Cell-Cost-Below-100-per-Kilowatt-Hour
Since Tesla is also going to be selling a bunch of Model 3s and Model S/Xes and PowerPacks and PowerWalls by then in addition to 5 years of chemistry improvements since that analytical model came out, it’s fully realistic that the learning curve will allow a $120/kWh figure to be achieved. Elon Musk has long predicted a $100/kWh figure once the Gigafactory was fully operational. That’s basically why the Gigafactory was and is being built. I think the biggest reason people have a hard time accepting even a $120/kWh figure (let alone $100) is that it breaks a lot of their dearly held notions about energy. At that price (and combined with solar cells at 19 cents per watt at the spot market), anywhere with sun is going to have cheaper energy than fossil fuels (unless you’re right above a gas field or something). But that’s a topic for another post. I will need to address the 7 cents per kWh that Musk promised.

EDIT: Thanks to comments by James who pointed out I missed the factor of 0.5 in the drag equation. That makes the whole Tesla semi project way easier and should give Tesla a decent profit opportunity. It means only $120/kWh is needed and shrinks the required battery, which reduces the weight considerably and also thus reduces the required charging speed.

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A View on the Alternatives

In the post on the architecture that Doug Plata proposes for the Lunar development, I likely appear as a naysayer as I picked on the sections that I disagreed with or thought that there was a better way forward. Not surprisingly, Doug disagrees with my nitpicking.  There is one point that we will not likely agree on which is government involvement. He believes that a Lunar COTS approach can hold costs to roughly a billion a year. I believe that involving NASA at management level brings in baggage that will blow past a billion a year under any contract method due to congressional involvement. There are a lot of talented people in the agency that answer to political reality. As a single example, commercial crew is $6.8 billion to develop two capsules plus a handful of flights. There is a lot of development for a Lunar program that is far more involved than a couple of capsules. On to the technical stuff that I actually like.

Doug thinks that the technical suggestions that I made would delay Lunar settlement, add risk, and drive up costs. It is a series of reasonable concerns that I will try to address. I suggested Lunar hover slam landings, a rotovator, a low gravity research facility in LEO, and propellant depots. Each of these is questionable without more detail on my meanings, and certainly debatable even after I explain. I will be surprised if one or more of them isn’t honestly trashed in comments.

I was one that didn’t see the hover slam landings working, didn’t expect a high percentage success on the barge, and didn’t believe that landings without deep throttling would be possible. You can probably dig up old posts and comments of mine naysaying on all these things. The fact is that SpaceX has succeeded in reliably landing vehicles vertically with a thrust/weight considerably higher than one. It seems to be a matter of having control systems that can accurately decelerate vertical velocity to zero at a specific altitude. It seems to me that that altitude can be regolith zero just as it can be barge or LZ1 zero. The advantage would be that it would become unnecessary to develop a whole new landing stage for the early equipment and supply deliveries. This would be a way of using the second stage all the way to the Lunar surface. While there is risk, I believe a dedicated Lunar lander will also have some element of risk, just later and more expensive. Later on, dedicated landers will be necessary, especially for human landings.

A rotovator is potentially one of the key pieces for Lunar transportation. A 1,600 m/s unit could catch payloads from TLI and soft land them on the surface. The orbital energy gained could be used to pick up payloads from the surface and sling them to TEI. Dougs’ concern on this one is cost, risk, and schedule. A 1,600 m/s rotovator would seem to have a mass ratio of roughly 25. That is a 25 ton unit could handle 1 ton payloads, in theory. I suggest that the testing and development should take place in LEO. At $2K per kilogram launch costs, a 25 ton rotovator would cost $100M to launch and about a quarter of that for the tether material itself. This would be about an eighth of the first year budget. I would not suggest waiting on it to prove itself before starting the settlement missions. In LEO, the operators train, learn, and develop by picking up payloads from 1,600 m/s below orbital velocity and slinging them to 1,600 m/s above orbital velocity. This would be a long way towards a GTO or TLI. Only after proficiency is reached is a unit sent to Lunar orbit. Assuming it works and survives the clutter of LEO of course. Once in Lunar orbit, it roughly doubles the payload of a vehicle in TLI to the Lunar surface. It also allows material from the Lunar surface to be placed in TEI with no propellant or engines. A third function would be pick up and drop off at various points on the Lunar surface for multi-location prospecting without propellant or engines. The rotovator is a risk, a risk with high payoff. And if it doesn’t work, 1/8 of one years’ budget might be an acceptable loss against the potential benefits.

A low gravity research facility in LEO is another point of disagreement. Doug sees no need for the data until actual settlement generates the information needed. I see it as yet another set of information that should be generated in parallel with development. A 50 ton variable gravity facility could be placed in LEO for a similar cost as the rotovator, as long as feature creep and over engineering is avoided. A simple design that can run unmanned most of the time with occasional visits for maintenance, specimen swap, or clean up. Only after a few generations of rodent and primate trials would it be necessary to send permanent human crew to nail down the data points. It may be that Lunar level gravity is enough to maintain health without centrifuges. Or it may be that it is totally inadequate. It would be good to have some realistic data before shipping large scale equipment to the moon that turns out to be unnecessary on one hand or inadequate on the other. The early animal studies could be started by the time the first humans  are on the surface with the primate studies completed well before adverse reaction might be expected to show up. A possible benefit would be if the settlers could avoid some of the extreme exercise requirements of LEO. This would be another quarter years budget from his program. It just might more than pay for itself in reduced future equipment and exercise requirements.

To me, propellant depots are almost a no brainer. Not everyone shares my opinion. The way I see it, Lunar development would almost require depot type facilities. The first depot could simply be a repurposed upper stage combined with high sortie rates. A relatively high boil off rate could be acceptable if it means being able to launch the large pieces with the equipment you have instead of the equipment you hope will be available eventually. Refuel the upper stage of the FH and send a 60 ton payload to the Lunar surface in one shot. Propellant can be bought from any delivery including from excess capacity in a given launcher. If a vehicle has  the capability of placing 20 tons in LEO and the volume restricted payload is 10 tons, then 10 tons of propellant can be bonus payload. The same applies in Lunar orbit where it would make almost as little sense to send a half loaded vehicle to the surface as it would to send one with insufficient margins. There should be no reason for depots to slow down Lunar development,  and the efficiencies should make the system self funding almost from the start. As long as the over specified and over designed techniques of the past are avoided of course.

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An Opinion on an Architecture

Doug Plata has a new website at spacedevelopment.org with a concept for sustainable Lunar development. He sent me the link and suggested I look it over. I read it through the first time as a plan and promptly (in my mind) picked it apart. I went over it again as a conceptual approach coming away with considerably more positive feelings about it. I am quite opinionated about various approaches to getting things done with a normal reaction that I could do this or that better after someone else has done the heavy lifting of the initial approach. Anyone interested in developing the moon would benefit from a reading of his website including all the specific links.

My take on it is that it contains many desirable features and has missed a few critical points. One of the main ones is the knock on effect that the drop in launch prices will bring. I can see prices to LEO dropping to under $500.00 a kilogram within the timeframe he is suggesting. FH, New Glenn, BFR, etc in the near future. At that rate, a billion dollars launches 2,000 tons into LEO.  This is the main basis for the criticisms I see. I will use that number in this post.

Doug suggests that a small percentage of the NASA budget could implement his scenario. A billion a year being 6-7% of the normal budget would be sufficient if used intelligently, mostly with COTS type applications. I don’t see any NASA managed project of this magnitude being immune to the various congressional feature creeps for the long term. Major NASA programs  tend to multiples of that, which then tend to political rather than effectiveness direction. He makes a few mentions of international participation which to me has the same effect multiplied. IMO, his scenario needs to be a private venture ramrodded by a hardheaded businessman with a solid technical team in order to remain in reasonable cost territory.

I can see a variation of his vision being done possibly faster than his website suggests. One example is that of the partial gravity research that has been left fallow for so many decades. He suggests the partial gee research takes place on the moon after the early human landings. I suggest that a 50 ton partial gravity research facility in LEO will be possible for $25M in launch costs and  less than $10M in hardware costs. $200.00 a kilogram for hardware is in line with terrestrial computers and electronics, and well above most hardware. With low launch costs, much of the over engineering of current spacecraft can be eliminated. The partial gravity research could start year one with results starting to be well characterized before the first human landings on the Lunar surface. It could be known whether a fetus could develop at 1/6 gravity by the time the first couple headed that way. It may not even be necessary to have a centrifuge on the moon, or it may be desirable to have a much larger one. That knowledge is necessary and long overdue.

The focus on finding and mining water dominates much of Dougs’ concept. I think the results of inexpensive launch has not been well factored in. With methane/LOX a mass ratio of about 5 from LEO to the Lunar surface puts a ton in place for about $2.5M for launch costs.  A hundred tons of water for a quarter billion FOB moon seems like a good early supply. Four hundred tons of equipment and supplies delivered to the moon for a billion dollars seems like a good year two operation. By exploring and prospecting for all potential valuables instead of a water dedicated mining operation, it seems possible that better and easier sources of almost everything will be found. It would be most unfortunate if a massive effort were made to extract water from the polar regolith only to find that nearly pure sources were available in many locations. It would be bad as well to hope that better sources would be found only to find that the polar regolith was indeed the only reasonable source. I suggest a lot of exploration and prospecting before major mining investments.

Doug puts a lot of emphasis on communicating the excitement to Earth in as many languages as possible even if by naturalized Americans with all early crew members multilingual. I personally place less value in talking to people than getting them there in the first place. If a person can be delivered to the Lunar surface alive and healthy with a ton of gear, launch costs of $2.5M per person are down to the point that any interested nation should be able to pay their own way. The six person international teams that he suggests could get there, stay a while, and back for under $40M. Any nation group that can’t or won’t supply that level of support shouldn’t expect much sympathy from those that do pay. International pride would come from self sufficient groups paying their own way instead of being dependent on the charity/political connections of others.

The gymnastics and dance routines that he suggests be practiced with tethers on Earth could instead be developed and learned properly in the Lunar environment. Artists need some freedom to be artists. Earth control and choreography is unlikely to give the best results  compared to the experimentation on location by the artists themselves. Again, $40M for a gymnastics or dance troupe to spend a month or so on the moon seems a quite reasonable cost. It also doesn’t require your geologist to be selected for athletic abilities.

The suggestion is that crew should have very long stays of several years or perhaps indefinitely due to costs and transport risks. I suggest that that attitude is caused by the ridiculous prices of crew transport that exist now, and not those that will exist in the near future. At the $2.5M that I suggest will be possible to get someone to the Lunar surface, and about that much more for a year of supplies, crew rotations could resemble those of the ISS currently. While some could stay longer and would be encouraged to do so, I don’t see it being the bottleneck to Lunar development.

Some of the hardware in the scenario seems to be missing a few tricks. The lander based on the  Masten Space Systems work with ULA seems like a future manned transportation system to the Lunar surface. For early hardware delivery, a variation of the Falcon 9 hover slam seems to have something to offer. A stage that hits hard or tips over is not going to explode as seen in footage of some early barge landings. The propellant will evaporate in the vacuum faster than it could sustain ignition. So the cargo could be saved even in the early learning curve landings. An upright stage that landed properly could unload with an onboard gantry crane in the 1/6 gravity. Several companies could learn by doing rather than learn by designing and simulating and then learning the hard way anyway.

A Lunar rotovator has been proposed many times and a development scenario like Dougs’ could afford to learn to operate it. A 1,600 m/s rotovator could pick up as well as deliver which would eliminate much of the need for mining or delivering water. A 25 ton unit could pick up and deliver ton packages, though not people at first.  That would be about a $100M investment that would pay off in operational knowledge that could apply to LEO, Mars and asteroids just a few years on.

A depot scenario would benefit this development. A delivery to LEO that had extra mass capacity could deliver propellant as a secondary payload for nearly free. A refueled upper stage would make a dedicated transfer stage unnecessary. Refueling or off loading extra propellant in Lunar orbit could also make the trips more cost effective. Storage facilities in Lunar orbit and on the surface would definitely enhance the value of Lunar propellant when it did start becoming available.

Doug mentions saving the capability of the SLS for Mars missions. I say why bother if 4,000 tons can be placed in LEO for the price of one SLS launch. I also disagree that a manned Mars flyby is a useful mission. Phobos and Demos mission, maybe, though I’m not sold on those either. Of course, not being a Mars enthusiast, I probably would be a hard sell for a surface mission as well.

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A Flat Earther

I had a new experience tonight. A woman I went out with a few times a year or so back got in touch and we went out for dinner. Somewhere in the middle of the dinner she mentioned that she had looked into the flat Earth claims that some people are making. I waited for the punch line.

She said there are no pictures of the Earth from space as a round ball. The cameras take a bunch of pictures that are spliced together to make it look that way. Spacecraft couldn’t get through the Van Allen belts anyway so that is why there are no pictures of the whole Earth. The dozen or so pictures on my phone were obviously photo shopped because every picture was different and if they were real they would all be the same. I waited for the punch line.

We obviously didn’t go the the moon and it was all done on sound stages and such with CGI. Frank Bormans’ Earth rise picture  was made from a dozen pictures spliced together and wasn’t real. She knows because she saw an interview with the guy that made the picture and he told how he did it. And then there was the interview with three astronauts just back from the moon. They should have been pumped up but instead they were somber because they knew they were lying to everybody. I waited for the punch line.

The Earth couldn’t be rolling around like they said because at a thousand miles an hour the wind would destroy everything. The proof being that a helicopter that went straight up for an hour and came straight down would come down somewhere else because the Earth would have rotated out from under it if it was really rotating. I started doubting that there was a punch line.

Further proof that the Earth wasn’t round came from some photographers that took some pictures of the Chicago skyline from across Lake Michigan. If the Earth was round they wouldn’t have been able to see it. There was more evidence gathered by people with the same type special camera that could see ships that should have been hidden by the curvature. I realized that there wasn’t a punch line.

Gravity is an illusion because density and mass are the same thing. Several time she mentioned that she was intelligent and not gullible. At somewhere around this point I quit trying to answer seriously and got annoyed. It is possible that me calling her opinions stupid is not conducive to further interaction. I remember thinking that she made Gary Church sound rational. The punch line was me as I had forgotten why we quit going out a year ago.

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The Fate of the Falcons

At some point it seems that SpaceX plans to retire the Falcon series in favor of the BFR (series?). For a fully developed and productive launch system to be retired due to improvements within the company line there must be compelling reason. If it comes to pass of course.

The Falcons seem to have reached one of their goals with 16 successful landings in a row. So are the accumulating first stages of a reusable vehicle to be left to rot when the new kid takes over? Seems quite odd to me. If the BFR series ends up as cheap to operate as projected, it’s just possible that the Falcons cannot be profitably flown by SpaceX when development becomes operations.

What about other launch providers. By the time BFR is fully operational there could be dozens of flight proven Falcon cores available. How many providers would jump at the chance of buying a first stage that could be flown repeatedly after some modifications of their own upper stages. It still wouldn’t let them compete with BFR. It would however, allow them to operate a national or corporate proprietary launch system for substantial savings without having to buy launches externally.

This could provide revenue from the vehicle sales to SpaceX just when it is trying to recover financially from multiple development efforts. There would be a steady revenue stream from parts and technical assistance. It may be one of the reasons for proving the recovery of the vehicle in the first place.

I could see ATK buying a couple of cores to fly out their manifest without have to deal directly with a competitor. Ariane could probably use a few. I wonder how the economics would trade for India.

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Falcon Heavy Skepticism

The long anticipated Falcon Heavy should fly towards the end of this year. Many people seem to believe that this launcher is going to be the answer to the PorkLauncher, big private payloads, launch costs, reliability, and all the other competition. I tend to think it can be a good launch vehicle without being any of those things.

Up until recently, I thought bolting three or more first stages together for larger payloads was close to a no brainer, especially if those stages are getting reused. I saw little problem with using up to seven stages bolted together. A few recent articles have made me question my previous opinion. One about Elon Musk discussing the difficulties of  making three stages work together brought up a few interesting issues on the problem. Another by Rand Simberg going into some detail on dispatch reliability and complexity issues that I have not previously considered.

I have been skeptical of some of the claims made by people from outside the company since they started posting them. There are some that insist that the F9H is going to get costs per pound down to $50.00 or less. I still believe it is too early in the game to confidently predict such prices. It should be possible to be a fan of the SpaceX accomplishments without being a wild eyed fanboy that thinks Elon walks on water in the liquid phase. There are some more debatable points I have met relatively recently.

The F9H will be the death of SLS/Orion as soon as it flies seems to be fairly popular. This would seem to be against the history of government procurement programs. The logical arguments against developing the SLS/Orion system were as valid a decade ago as they will be when F9H flies. If it was about logic, a crew capsule would have been flying on an EELV before the Shuttle was retired. An orbital depot would have enabled any mission the SLS/Orion is purported to have. The SLS/Orion may go out with a whimper in the next decade. It is politically nearly impossible that it will be in direct response to the early flights of the F9H. A politician has a primary job of getting elected, and the SLS/Orion systems will last as long as they contribute to that primary job.

There seems to be a lot of belief that huge private payloads will be ready to go as soon as the LV is available. I don’t think this matches payload history on current launch vehicles. Ariane5 and Delta Heavy don’t seem to have a backlog of full weight payloads. It is common for there to be two or more full size satellites in an Ariane launch. For that matter, F9 doesn’t seem to have payloads that come close to the advertised capability. I believe that the F9H will be an infrequent launcher of specialty payloads that are just a bit more than the F9 and competitors can handle. Once proven, it is likely that the F9H will have single digit flights per year. Elon has mentioned that one of the reasons for the delays in getting the F9H on line is that there is little demand for it. Plenty of others have mentioned that the steadily increasing capability of the stock F9 also cuts into the demand for the heavy.

Launch costs are the choke point on space development and always have been. Many people believe that the F9H is going to solve this problem. The advertised prices seem to support their opinions. The normal method of figuring launch costs use dollars per pound as the metric of affordability. Dividing maximum payload by launch price supports  the belief in the F9H as the frontier enabler. My skepticism comes from some recent articles discussing technical issues I hadn’t previously considered. When the rubber hits the road, all three of the first stages in the F9H have to go through the same level of processing as in a normal F9 flight, plus be integrated into a complete F9H. The additional level of work required to make three stages into one makes it likely that the actual launch prices per pound will end up being higher for the F9H than for the stock F9.

I expect the F9H to be a fairly reliable launch vehicle. I can’t see it matching the parent vehicle in that respect. There will be some risk associated with three cores working together with aerodynamics, vibration, and structural loads that don’t apply to the F9. There will be the additional risk of individual reliability of four stages instead of two in the F9. Very low probability events per stage will have twice as many chances to manifest in the larger vehicle. There is also the likelihood IMO that the F9H will have a much lower flight rate than the stock F9 which could lead to a bit less proficiency in catching the minor issues. Bottom line is that unless the F9H flies a lot, there will always be some question as to its’ reliability relative its’ parent vehicle.

I find the opinions often expressed that the F9H will sweep the competition to be less well thought out than they should be. As long as there are many reasons to launch a variety of sizes and orbital inclinations, there will be a variety of launch vehicles to serve the various niches. From national launchers to smaller proprietary payloads to personal animosities, there will always be reasons to have other launchers by other countries and companies.

At the end of the day, I expect the Falcon 9 Heavy to be a good launcher with fair reliability. I don’t expect it to be the greatest or the cheapest, just a good machine for the intended purpose.

 

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Roton as Booster/LES/Shroud Recovery

This idea has been kicked around in pieces before, though I think this particular combination may be unique.

Mount a Roton blade system on top of the shroud of a standard launch vehicle. Power it up before launch such that it is supplying perhaps 20% of the total thrust at sea level. At the 10/1 Isp gain early on, this would be a serious enhancement to the vehicle performance.

If there is a launch vehicle problem, the payload and shroud are detached to be accelerated out of harms way by the already thrusting Roton unit using it as an LES system.

The Isp gain will fade as it climbs out until in vacuum the tip rockets are at perhaps Isp 300 which is less performance than the main propulsion system. When the shroud is ready for detachment, it is separated from the launch vehicle and pulled away by the Roton unit.

The Roton unit is used to control the shroud reentry and to guide it to a recovery vessel where it auto rotates to a landing.

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