Tesla Semi is reasonable, part 1

Tesla finally unveiled their semi truck:
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).
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:
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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A Possible LEO Clearing Market

One of the growing concerns is the amount of small debris in LEO. The big stuff can be tracked and mostly avoided, but the small stuff is a more difficult proposition. A hundred gram shard at some LEO closing velocities can impart the kinetic energy of a main tank gun. It is not the new large satellites that are the problem as most of them have deorbit strategies built into their launch vehicle upper stages and their own end of life safeing plans. It is the thousands of much smaller units proposed by all and sundry that concerns some people.

With the quantity of LEO debris existing and tens of thousands of small satellites that may hit orbit in the next decade, the odds of collisions are higher than some people like. Each collision will create large quantities of smaller debris in unpredictable orbits that increase the odds of further collisions in an ever increasing cascade. I personally don’t know the odds of this happening or if it is a rational concern. There are some people that appear well informed that are seriously concerned about a Kessler syndrome that could make LEO uninhabitable by man or unarmored machine.

It would seem that there might be a market developing sometime in the next decade to remove small debris from LEO from simple self interest. Present and future LEO operators along with their insurance companies might decide that the time has come to address the problem. Deciding to address the problem does not necessarily mean that they will feel generous about the solutions. The tragedy of the commons will not disappear like the air and gravity in LEO.

The solution for cleaning out LEO will have to be economical, safe in terms of having near zero chance of making the problem worse, and work in a timely manner. It won’t happen if the proposed solutions are too expensive, risky, or take centuries to operate.

I suggest that a modest satellite could be launched into polar orbit to get a start on the task. It should have excellent detection equipment along with enough on board computing power to calculate intercept trajectories in real time of objects closing at up to 14 km/sec. After action tracking and calculation must be capable of checking the new orbit or deorbit of the target debris.

The mechanism I suggest is laser sails the size of kites that are steered to intercept by the on board laser. The south bound orbit would focus on debris on the northern leg of their orbit while on the north bound portion it would focus on the debris on the southern leg of their orbit. The zigzag of normal west to east orbits to the limits of their inclination would provide high closing velocities with impact resultant sub-orbital if done right.

In this cartoon, the cleaner is heading south with one of the kites in position to impact some debris heading north-east. The dotted line is the possible changed trajectory of the debris as it deorbits. The purple rectangle is a kite that has been used a few times.

The cleaner is heading south and a piece of debris is heading north east with a closing velocity of between 12 and 14 kilometers per second. The laser propelled and steered kite array is a hundred or so kilometers ahead of the cleaner and one of them is off to the side that the debris will pass through. The kite is laser propulsion steered into an intercept which costs the kite a bit of sail and the debris a bit of velocity. Each gram of sacrificial kite material impacts the debris chunk with the kinetic energy of several 50 caliber bullets. Depending on the amount of sacrificial kite mass, debris mass, and debris orbital velocity, a deorbit is likely. Failing that, the debris should have a much lower perigee that will speed up its’ orbital decay.

After the kite has been used several times it will look like Swiss cheese and is steered back aboard while other kites take its’ place. Two or more ventilated kites are mated together for another go in their turn. Repeat until there is nothing left of the stock of kites but tatters. Then the cleaner sat is either replenished or deorbited in its’ turn.

It has often been suggested that the debris should simply be targeted with a laser. The ablation of the larger debris would cause it to deorbit while the smaller ones would be vaporized. It seems to me that it would take a lot more laser and power to get that job done which would create a couple of other problems. One is that it would be far more expensive, and the other is that it would clearly be a space based weapon.

While it would still take a considerable amount of time to significantly reduce the debris field, a 50 kilometer track per orbit would be bandwidth limited rather than hardware limited. Several dozen or hundreds of pieces gone per day would add up over time. Off hand each gram of sacrificial kite could take down a hundred grams of debris. A ton of lost kite for a hundred tons of eliminated debris seems like it would be a good trade.

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Comment Bumping: Venus Electrolysis and Space Settlement Norwegian Perspective

Life has been busy enough lately that I haven’t been able to do many of my own blog posts, but I wanted to bring two recent comments from old Venus threads to the top to get them a little more attention than they’d likely get in an old side thread.

The first was a question about the feasibility of using the lower Venusian atmosphere for electrolytic extraction of metals from the surface:

James Walker wrote:

A question for the more scientifically literate: With a charge of 10 volts and a pressure of 93 bar, is the atmosphere of Venus thick/charged enough to allow electrolysis?

If so, is having cathodes in the atmosphere collecting Potassium, Sodium, Magnesium, and Aluminium from the acid drenched surface an option?

Not being a chemist or electrolysis expert, I don’t know for sure the answer, though my gut suggests that it’s probably no. If the lower atmosphere of Venus can carry a charge like that, that’s usually a sign of it being a dielectric material, not an electrolyte like you’d need for electrolysis. Unless I’m missing something. I mostly brought this up, because there are enough other people on here who could answer better than I, and while I think it’s a long-shot, it would be huge if it was actually true. Thoughts? Comments?

The second comment I wanted to bump was from a discussion about what the governments would need to be like in isolated settlements in harsh environments. One poster had speculated that the harsh environments would make Venusian cloud colonies, asteroid mines, and other such places fairly totalitarian. Povel Vieregg from Norway had an interesting competing perspective (the part that stood out to me starts five paragraphs in):

I thought I’d add my two cents about the politics and types of society that a Venus colony would be. A lot of people here related to the American experience, but I think there are many other cultural experiences to draw from to say something about this.

As a Norwegian, I also come from a country which had its own flavor of rugged individualism. Norwegians also settled Iceland and went on many polar expeditions. All cases which involved extreme climates and environments.

I personally think people have a tendency to overstate the influence of nature on the culture of a people. For instance the Dutch as surprisingly similar to Norwegians in ways of thinking and organizing society, yet their country could be no more different from Norway. Shared germanic roots and similarities in way of life (both maritime nations) probably led to many similarities.

Americans should not forget that a large part of their national character derives from the British and Irish.

I don’t think it follows that great dependency on each other leads to a totalitarian style regime. I think individualism exists in different forms than just the anglo-saxon style libertarianism. The Vikings were quite democratic minded, or perhaps a better description would be that they were used to seeking and making compromises and find consensus. That was a natural result of weak central power. The dutch are similar. Many lived historically in polders (farm land surrounded by dikes keeping the sea out). If anyone living in the polder failed to maintain their part of the dike, it would spell disaster for everybody.

Neither case led to totalitarianism. Quite the opposite, both Norway and the Netherlands are very consensus oriented democracies. You see similar on Iceland which also lived through pretty rough times when it got settled with a lot of bloody conflicts. That kind of hardship teach people that there is no alternative but to cooperate.

If you read about the polar expeditions by the British and Norwegians, you’ll see very big difference in the approach and culture involved. The British had strict power hierarchies, were commoners and officers were clearly separated. Norwegians had much flatter hierarchies, and was more based on cooperation and consensus that some top leader acting as dictator.

You can see this among any primitive people. Look at Inuits e.g. who live under harsh climates. These groups don’t function as totalitarian regimes. They are not fully democratic either, but there are more marked by cooperation and consensus than by master-servant relationships.

I think likewise a Venus culture will develop with a basis in the culture of the original inhabitants. But I do think that over time it will develop in the direction of Dutch/Norwegian experience. Nobody will have a natural power base to just be a dictatorial ruler. There will be too strong interdependency among people for anybody to assume too much power. You will have to listen to what everybody says.

I don’t think you can necessarily classify such societies as we do countries today, because they will be much smaller and will thus be based far more on informal structures as we see in smaller human societies.

When societies are smaller they can function primarily on trust. As societies get much larger and you can’t know everybody in it or trust them, one will have to rely much more on formal structures and rules.

Anyhow, I know that just reposting peoples comments instead of creating new content of my own is kind of cheating, but a) I thought they were both very interesting, and b) it’s going to be a while before I have the bandwidth to write anything of my own, and I can’t let John have all the fun on this blog.

Posted in Comments, ISRU, Space Settlement, Venus | 16 Comments

Failed Visions (mine)

I just read that XCOR laid off its’ remaining employees with a few core people kept on contract. This is another shot against the vision that I have blogged and commented about many times. The concept being that sub-orbital RLVs would create companies and teams with experience creating RLVs. This is where orbital RLVs would come from. It appears that I was off so badly as to defy excuses.

XCOR seems to have joined a number of other sub-orbital efforts that have folded, or gone into stealth mode at least. Armadillo and TGV being a couple of the best known along with a dozen or so of varying credibility around X-Prize time. I don’t think Virgin Galactic should be considered a validation for my vision even if they are eventually successful.

SpaceX is coming at RLV from the other direction, backing into it from an expendable. I’m sure I’ve posted or at least commented on several occasions that this was a bad idea with little chance of working. Blue Origin  seems to be using its’ sub-orbital RLV as an X-vehicle for its’ orbital class RLV. It would be a stretch to suggest this is similar to my vision as it seems to be a parallel effort rather than serial as I suggested might be necessary. The other orbital companies talking RLV seem to be dragging their heels on any changes so I discount them for this post at least.

It does seem to validate one argument I’ve made from time to time about the difficulty of sub-orbital vs orbital flight. The argument by some others was that orbital flight was 8 times the velocity of sub-orbital flight and difficulty rises as the square of velocity so that made it 64 times as hard. The ones making that argument didn’t believe my calculation that it was more like 4-5 times the difficulty. Maybe they can note that several attemptees have had far more than 1/64 of the funding of SpaceX or Blue Origin with no flying hardware.

There is a bright spot or two though. Masten is still going, and a few others are still in the game. Come on guys, you are the last hope to make me right on this one.

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