Refueling for the Secondary Mission

It is fairly obvious that there are many benefits to having refueling capabilities in space. Perhaps not to the monster rocket fanatics with blinders and a few others, but to most of us it approaches no-brainer territory. The problem is getting to the first egg. The first bird we would accept as a chicken came from an egg, but that egg did not have to be laid by a bird we would accept as a chicken. Mules do not have mules for parents. The first refueling capability doesn’t have to have depots in the business plan, perhaps a buddy tank for starters.

The problem with getting refueling capability in space is often called a classic chicken and egg problem. Without a depot there is no refueling capability or reason to build vehicles to use it, and without the vehicles to use it there is no reason to build a depot. Dual launch architectures try to get around this by designing missions around a propellant launch and a mission launch. So far, this hasn’t worked well either as the mission planners try really hard to avoid boxing themselves into a corner where if either launch  fails, the mission fails.

One possibility hinted at in comments a while back is to have the primary mission fully capable of success if the primary launcher works properly. Then have enhanced secondary capability if the propellant launch succeeds and can top off the tanks in the primary. It took me a while to wrap my thoughts around the concept, after which I started working it over to see what I could think of. I can’t give due credit to the original thinker because I didn’t really grasp it until days later, just that it was somewhere in the 40 depot posts by Jon Goff and hundreds of comments associated with them. The originator can chastise me in comments  for not digging back for is name.

So this is my take on the idea. A vehicle arrives in LEO with payload for LEO. It hits the refueling vehicle either before or after placing its’ primary in the correct orbit. It off loads any excess propellant it managed to bring up if it is going to deorbit, or if it simply has excess for the secondary planned mission(s). Alternately it accepts enough more propellant to accomplish other missions that are non-critical to the primary mission.

The secondary missions suggested were along the lines of deorbiting various dead satellites. Surveying satellites with minor issues with the intent to design possible repair missions. Rendezvous with satellites in useless orbits and boosting them to the proper orbits. Creating the capability of the upper stage herding dead GEO sats after a GTO burn for the primary customer. Testing servicing options that would be too expensive for a dedicated launch.

The whole point would be to have some capabilities in place and in use for the cost of one launch that did not have to satisfy any customers other than the company that launched it. It would be replenished with excess propellant in vehicles that didn’t need all they hauled up. It would refuel various company vehicles that were scheduled to do extra work for revenue. The refueling wouldn’t have to be a maximum top off, just a calculated amount for individual missions. By using the capability in house, the problem of selling to and satisfying outside customers goes away. By not putting the capability in the critical path, the primary customers should have very few concerns about endangering their ROI.

It would seem that a capability could be started in the two digit millions. It could be very crude with perhaps LOX only to start, or LOX/Kero, or hypergolics, just as long as it fit that particular companies’ business plan.

Later on it might be possible to put this in the critical path of missions because a solid experience base and track record had been built up. Then after that it should be much simpler to get true multi-propellant depots up and running with whatever the market expresses a need for.

Posted in Uncategorized | 6 Comments

Random Thoughts: The Difference Between a Base and a Settlement (by Doug Plata)

There was an interesting comment by Doug Plata a few days ago that I wanted to repeat as a blog post. Background was discussing the idea of long-term stays on the Moon, similar to my old Lunar One Way to Stay (for a while) concept:

I would also like to point out that extending crew stay really blurs the line between what is a base and what is a settlement. I maintain that the real definition of settlement is when people are settling down. If people are settling down then that is a settlement. Settlements are not necessarily determined by size, economic independence, economic productivity, or the ability to have children. In particular, if retirees are moving away from Earth to stay, their settlement may start with a few people, the money for their settlement comes from their savings not from mining, and they will have no children with them. Yet, as the off-Earth retirement community grows, it will become increasingly obvious that it is a real settlement – Private housing, life support production, growing their own food, community meetings, perhaps it’s own governance structures, etc.

By way of historic analogy, consider a Mormon couple being sent to some distant valley to settle down, build their home, start growing their own food, raising animals, and preparing for the arrival for others. There may be no ore in the area and they may grow food for themselves. Relatives in the city might occasionally send them manufactured items that they couldn’t produce themselves. But they are settling and could rightly be recognized as being the first settlers for that area. Same with settling off Earth.

So, what does it take to do this initial type of settlement off Earth? It takes a habitat, adequate, ongoing life support including maintaining equipment, long-term protection from radiation and insufficient gravity amongst other things. These things are already needed for a permanent base. So, really, the only difference is that a base is a worksite and an initial settlement is a home. And a home is where you have a family. And a family can be as small as a husband and wife.

So, I for one think that the start of settlement doesn’t have to be many decades, trillions of dollars, nor need new, super massive rockets. Additionally, since a base can have a public (government) value and a base could be an initial settlement then a public-private program (e.g. Lunar COTS) could be funded largely by government funds yet also achieve the space advocacy goal of starting settlement.

I believe that this is very doable, I think that we should do it as a priority, and I think that it best that a free country, in particular the US, should do it before someone else finds out that the historic step of starting humanity’s first off-Earth settlement is as much a matter of choosing to do so rather than some huge technical or financial obstacle.

Food for thought.

Posted in Lunar Commerce, Lunar Exploration and Development | 8 Comments

Lunar Foxhole

Rereading some of the older posts on Lunar exploration, I ran into a lot of discussion on short term vs permanent outposts or bases. The assumption seems to be that short sortie missions will have minimal or even no radiation protection.

A quick thought is that a foxhole approach might be worth looking into for the short sortie or light mobile base concepts. Troops in the field that are likely to get shot at often dig or blast a small hole for shelter. Nothing is assumed to come from below, horizontal incoming is eliminated, and danger is reduced to vertical from above. Then the danger from above is often reduced with logs, sandbags, or even bodies in extreme cases.

With the foxhole model, it seems possible that a small hole can be created in the lower section of a crater to provide radiation protection from 80% of the sky not already covered by the planet. The hab section is lowered into the hole. Then the lander or wheeled vehicle can be parked over the top of the hole to help shield the remaining exposed directions from cosmic radiation. Solar radiation can be almost entirely eliminated from hitting the hab module.

With no high value real estate to destroy, or neighbors to annoy, the hole could be impact from a trans lunar projectile at 2,300 m/s. It could also be explosive, mechanically dug, or pneumatic  as Jon has posted about.

It seems to me that radiation protection for sorties or mobile exploration should be fairly simple except for time in transit.hab

Posted in Uncategorized | 23 Comments

Missing Destination, Missing Opportunity

It looks to be months from the time that SpaceX claimed to have solved the problem that caused the vehicle loss of September 1 until the actual return to flight. There are stories to the effect that the delays are to convince others that the vehicle is safe. One problem is that piles of paperwork and man years of investigation is less convincing than a flying vehicle. I don’t know if SpaceX has solved their problem or not and people far more informed than I am don’t know for sure either.

A convincing argument would be several vehicles flying with no other entity worried about insurance or loss of payload. Production of the Falcon IX is supposedly able to support a flight rate much higher than current practice would suggest. But flying empty vehicles for no revenue is an incredible waste.

An orbital depot would sure be a handy bit of hardware to have in place about now. While many of us have suggested at various times that a rocket under development would be ideal for delivering propellant, relatively few have suggested the same thing as a pure confidence builder after a mishap.

If an upper stage had been modified for use as a propellant depot totally owned by SpaceX, it could have launched after the 2015 vehicle loss as a confidence builder and alternate destination in times of over supply of vehicles. Over supply could be both from over production and reused stages. The modified stage depot would not have to be as sophisticated as the ULA ACES  as long as it was reasonably useful, and more importantly, in use.

It would seem that SpaceX could have launched a couple of tankers by now to build confidence after the September loss and followed it with revenue flights. Revenue flights sooner rather than later could possibly pay for the marginal cost of the confidence builder tankers. Payroll must be met either way, and little more red ink in one month to avoid several months of slightly less red ink per month could be a sound business decision.

I think most of us are already aware of the benefit of having 40-50 tons of propellant in LEO from the last three flights for use in a major mission to the GLAMs. (GEO, Luna, Asteroids, Mars)


Posted in Uncategorized | 23 Comments

Space-based Bitcoin Mining

Preface: if you’re a bitcoin expert, gird your loins because I’m probably going to be making a LOT of technical errors in this post.

So: space based solar power, but instead of beaming the power to Earth, we mine bitcoin with it.

OK. I’m indifferent to Bitcoin. I generally think it’s a dumb idea but that has some interesting technology. But it’s useful conceptually for imagining a straightforward way to turn computing power into money. Or, once progress on mining hardware slows down to the now-slow Moore’s law of 4 year doublings, a way to turn electricity directly into money while only having to transmit a relatively short amount of data.

What it is, very briefly, is a kind of “cryptocurrency” designed to do away with a central ledger, instead using a sort of consensus of many distributed computers as a ledger. Money is added to the money supply by “mining,” which in this case just means doing some pointless but hard and verifiable calculation until you randomly free up a “block” which is a bunch of bitcoins (each bitcoin is like $750 right now… easily subdivided, by the way). Mining difficulty is adjusted to keep the pace of adding to the money supply at a steady but very slowly decreasing rate.

I googled “bitcoin mining hardware,” and this popped up:
The best hardware listed uses about 1200 Watts of electricity (all turned into heat) and produces roughly $4 of BTC per day and costs $400-something (…while consuming about $400 of electricity at 14 cents per kWh…). And weighs about 4 kg, so 300W/kg. So a dollar gets you 3 Watts of useful bitcoin mining, and it takes about 100 days for it to pay for its own hardware cost assuming mining difficulty doesn’t change. (Which is a terrible assumption, as more and more mining hardware comes online, the actual yield of bitcoin mining reduces to compensate.)

But only 33 cents per watt-used is great! That means we can replace that super expensive laser or microwave transmitter and receiver with cheap computer chips and radiators. And double or quadruple the power is available, too, because we don’t have all those transmission losses. But we do need to radiate all that heat away, so we’ll need a few more radiators, but in principle that’s not too bad. Radiators in this temperature range are like 100W/kg, so if we assume about 200W/kg for the solar power and a little extra for comms and pointing, we’re looking at about 50Wbitcoin/kg launched to orbit.

So at $100/kg to orbit (same price as the mining hardware, by the way!), and another $100/kg for hardware for a total cost of $200/kg, We have about $4/Watt-bitcoin. At 4 year replacement cycles (probably the power and thermal system would last a lot longer, but hardware would need to be updated), that’s about 11 cents per kWh of bitcoin processing, which is competitive (since it includes the mining hardware as well as the power). At longer intervals, even better.

But of course, this assumes bitcoin remains popular WHILE bitcoin mining hardware stagnates. The latter is not a terrible assumption, given that we’ve essentially reached the end of Moore’s Law (we’ll still see large improvements, but over longer timeframes, like 4 years instead of 2 years):

Posted in Uncategorized | 2 Comments


I reread several times Jons’ post on NASA under the next administration that recommends against having NASA focus on anything one finds important. I think he made good points throughout and it should have made for lively discussion. I didn’t comment there as I didn’t have anything useful to add. I felt that I should have had strong opinions to throw out there, but couldn’t find them. A lot of people that used to jump in discussion of that nature were also conspicuous by their silence. Could it be because many of us have become indifferent to the flagship programs of NASA?

All of us know of good work by NASA in various programs. How long has it been since the NASA flagship program was the one that produced the good work? ISS, SLS, Orion and the James Webb telescope seem to be trudging along with the press releases at regular intervals celebrating some milestone or another. It is so hard for someone of my interests to see any of them leading to useful space settlement and development that indifference is probably the best to be hoped for. The alternative is to see them as roadblocks to progress and the enemy. I have enough on my plate without adding gratuitous enemies.

In response to someone calling for one of the flagships to be cancelled, Ed Wright noted that the congressional funding would just be diverted to another similar program by the congressman that kept the first one going. That’s just the way it is as SLS morphed from Aries, which derived from Shuttle, which kept the Saturn/Apollo teams together and so on. Tilting at that windmill will just lead to busted lances and bruises.

So what do I want NASA to do? I don’t know. I accept Jon’s point that it shouldn’t be anything I am passionate about. That is about as far as I can get. Some will no doubt suggest that NASA should put a base on the moon or some other favorite direction. Does anyone believe that ISS on the moon would be any more productive than ISS in LEO?

About half a layer down are the commercial partnerships. I thought it was far more separate than that up until the commercial crew awards. A couple of capsules to go on slightly modified existing launch systems for $6B+ and over half a decade sounds like the same thing only different. Billions for assured safety even as ISS crew transport is dependent on Russia, and Russia has acknowledged QA problems on some of its’ launch systems. Rand Simberg has covered this ground on his blog and in print. If there were a serious push for crew transport, Dragon 1 would have had taxi life support and fast rendezvous capability years ago for a fraction of the money. Boeing and Sierra Nevada could have pushed something through just months later if results rather than process oriented. I think it is sufficient to say that I find the current efforts uninspired.

Stepping a bit farther out, there are the efforts of SpaceX Blue Origin, and ULA among others for reusable orbital systems, or at least some of the components. I guess I am a bit jaded on the various hypes and want to see some gas-n-go operations before I get exited. It is basic math that a weekly turnaround vehicle of 10 ton capacity could put 500+ tons of material in orbit per year per tail number. Basic observation also is that once development is done more vehicles are relatively low cost. Knowing that one company with a handful of such vehicles could launch far more annually than than the whole world does now is also less than inspiring until I see it start happening. It will happen sooner or later, and likely from a direction I don’t expect.

The suborbital companies that I expected to lead the way don’t seem to be forging ahead at the pace I expected. Lynx on hold, Blue Origin is a question, and Space Ship Two seems like it would be better named Bransons’ Braggadocio. For suborbital research flights of RLVs, Masten seems to be the last man standing. I have posted my thoughts that suborbital companies would develop teams, vehicles, and procedures for fast turnaround that would scale into orbital systems with the same characteristics. It’s hard to see that happening right now with the possible exception of New Sheppard.

I don’t see the big idea concepts coming together even by the private players. The Mars Musk plan doesn’t seem credible or well thought out. Monster rockets don’t have a good track record for affordability, or even reliability for that matter.

Space will be developed. It will likely happen in a manner that I don’t expect. That makes my chances of making a useful contribution quite low absent pile$ of luck. So right at the moment I am a bit indifferent to the current state of play in space development, or maybe it’s just holiday blues. Either way, I’m going to try to go to Space Access next year to try to shake this lethargy

Posted in Uncategorized | 7 Comments

Random Thoughts: Throwing the Moon a Bone

[Note: This blog post was originally planned to be something significantly longer, triggered by one of Eric Berger’s recent Ars Technica articles1. But running a bootstrapped startup gave me the choice of waiting until this was totally irrelevant, or saying something less comprehensive now. I went with the latter.]

One of the space policy ideas that has been getting a lot of air-time recently, particularly with the change in presidential administrations, is that NASA should abandon its Asteroid Redirect Mission and so-called Journey to Mars for a return to the Moon instead. You would think that as someone whose website name more or less means the “lunar back country,” that I would be a huge fan of that idea. But really, I’d rather that Congress and the Trump administration stick with their Journey to Mars, and only “throw the Moon a bone.”

By throwing the Moon a bone, I mean some level of NASA involvement that is greater than benign neglect, but less than being its core focus. Why? Because when NASA picks something as a core focus, it tends to attract all of the NASA centers and their special interests and pet projects out of the woodwork, trying to find some way to be involved, even if it doesn’t make sense. But programs that aren’t core or flagship programs, that get just enough support to actually happen without becoming another “10 healthy centers” make-work project, they sometimes get real things done. I’m thinking of things like COTS, or like the competed SMD missions. So, I’d rather NASA keep its manned spaceflight program focused on an indefinite “Journey to Mars,” with NASA centers fighting over development of some big Mars mission elements like deep space habs, Mars landers, or something else like that, while keeping lunar involvement lower key.

One idea would be to do something like COTS for the Moon, as part of supporting ESA’s Lunar Village concept. Basically do a public/private partnership with 2-3 companies to develop moderate-sized (1-20mT) unmanned cargo landers to the Moon, followed by a modest CRS-like cargo delivery contract. Have that, and possibly the use of a cislunar deep space hab be our contribution to the Lunar Village. If SLS/Orion survive the axe, maybe we could also throw in providing crew transport to the Moon as well. But let ESA develop the crew lander2 and the base facilities. With the commitment of US provided logistics, and possibly crew transport to a cislunar orbital habitat, that should be encouragement enough to ESA and Russia etc to develop the rest. Ironically, that would have the US in a way playing a somewhat similar role for the Lunar Village to what Russia has been doing with Soyuz and Progress for ISS.

In return for us providing cargo deliveries, and possibly some part of the crew deliveries, NASA could ask for one of the crew landing on any given lunar mission be American (much as ESA and JAXA get to send a crew member in exchange for ATV and HTV deliveries), and having some subset of the crew time on the surface dedicated to NASA research and US commercial lunar efforts. Like ISS, they could set aside a useful fraction of the lunar cargo and crew time to be provided to commercial entities trying to prove out lunar ISRU, prospecting, propellantless launch/landing technologies, or other items related to lunar commerce. I’m just thinking about all of the technologies necessary for lunar resources to become useful to humanity–the prospecting, mining, refining, propellantless launching, etc. Imagine how much easier it would be to develop say a lunar ice mining system, if you had access to a little bit of crew support time as needed, without having to cover the full cost of getting the crew there. Without something like lunar village, the cost of having people in the loop would be prohibitive, so you’d be forced to try and do everything robotically. But the mix of robots with a tiny bit of crew time to handle the small subset of tasks that would take the vast majority of the effort to fully automate seems really promising.

My worry is that if the Moon becomes NASA’s core focus again, that NASA will insist on doing core elements in-house, like resurrecting the monstrosity previously known as LSAM to go after a manned lander. If we want to go back to the Moon in a way that doesn’t amount to little more than reheated Apollo leftovers, having the Moon be a secondary priority might actually better than being the main show.

Posted in Commercial Crew, Commercial Space, COTS, Lunar Commerce, Lunar Exploration and Development, Random Thoughts | 9 Comments

What are the Odds?

I wanted to expand on one thought from last night. If you have a launch vehicle that you want a reasonably good chance of reusing 1000x, it actually needs a lot better than a 1:1000 Loss of Vehicle probability for any given mission. With a 1 in 1000 chance of losing the vehicle on any given flight, you actually have a very high chance of losing it long before the 1000th flight. The odds of not losing a vehicle in x consecutive flights with a given reliability rating (probability of a non-LOV flight) is:

Psurvive_all = PnoLOV ^ x

Or solving for the required probability of not losing a vehicle on any given flight (assuming an equal probability on any flight):

PnoLOV = Psurvive_all^(1/x)

So, if you want a 75% chance of surviving 1000 flights in a row, you get:

PnoLOV = 0.75^.001 = .9997 or about 1 in 3500 probability of losing the vehicle on any given mission.

If you’re ok with a 50% chance of surviving 1000 flights in a row, you need more like a 1 in 1500 probability of losing the vehicle on any given flight, and if you want a 90% chance, you’re up to almost one in 10,000.

Long story short, if you want a high probability of amortizing the vehicle over 1000 flights, you’ll need to do much, much, much better than the historical best reliability levels of liquid fueled rockets (98% or so at a 95% confidence interval). This suggests that design for survivability is likely going to be just as important as design for performance or design for cost if you want a lot of flights on an airframe.

Posted in Launch Vehicles | 17 Comments

SpaceX Mars Plans: Jon’s First Take

I’ve had a lot of friends ping me today about my thoughts on Elon’s Mars talk today. I was in a meeting when it happened, and literally was pinged by half a dozen people during the meeting… Now that I’ve had a time to chew and digest things a bit, here’s a bit of a stream of consciousness take on the plan.

Overall my feelings are mixed. I think the plan has a lot of good points, could probably work given enough money, and would likely be a better use of money than whatever NASA does for its so-called Journey to Mars, but also am really skeptical about a lot of the technical choices made, and the likelihood of hitting the price points SpaceX is predicting.

First, what I liked (some minor, some major):

  • In-Space Refueling: Elon’s plan is built around the idea of refueling his ITS (Interplanetary Transport Ship) in LEO prior to Mars departure. The BFR would have to be a lot bigger, and/or 3STO, to loft a fully-fueled ITS without LEO tanking. This is a point that ULA has been making for over a year now as well–“Distributed Lift” allows you to do a lot more with a given sized booster. As someone running a company trying to develop the rendezvous/capture and propellant transfer technologies needed for Distributed Lift, this was a welcome choice.
  • Mars ISRU: Bob Zubrin has been beating on this drum since I was a teenager, and while I think Elon’s handwaving the challenge of generating 1000s of tonnes of propellant on the Martian surface, not having to haul that all the way from Earth saves a lot of launch mass to LEO, and makes reuse of the lander a ton easier.
  • Lifting, High-Alpha Mars Entry and Supersonic Retropropulsion: By coming in sideways, and doing a somewhat lifting reentry, they’re able to bleed off enough energy early on so that the supersonic retropropulsion delta-V can stay modest even though ballistic coefficients suffer from the square cube law. If they had tried a base-first, low-lift entry, they probably would need a lot more landing propellant.
  • Reusability in General: I’ve always been a fan of both in-space and earth-to-orbit reuse. I think it’s a key to get costs anywhere close to what Elon wants.
  • Depots for Extension Beyond Mars: I also really liked Elon’s point about how his architecture can eventually include depots in various orbits, and that once you do that, you could theoretically use these vehicles for traveling almost anywhere else in the solar system you want. Many of those flights would require more radiation shielding, and possibly some level of artificial gravity to work out, but he’s totally right that once you have depots, the solar system is your oyster. Regular readers of this blog won’t find that too surprising.

Now for what I didn’t like as much (some minor some major):

  • Too Big: Something 3.5x the size of a Saturn V seems like overkill. Doing a BDB-sized launch vehicle but with near-SSTO mass ratios and the highest chamber pressure large propulsion systems to ever fly is a challenge, and I think SpaceX is likely underestimating the challenges with doing an RLV that size, and with that many engines. One thing I wonder about is if they’ve done the acoustics analysis on launching something that big. We’re talking about something several times bigger than Saturn V or Shuttle, and an order of magnitude bigger than the Falcon 9 powered landings they’ve already done. May be a non-issue, but I think both Bezos and Musk are making a mistake with how big of vehicles they’re going after.
  • Swiss-Army Knife ITS: Trying to make the ITS do so much doesn’t bode well to me for keeping it affordable. We’re talking a near-SSTO performance level reusable upper stage, who’s ascent and landing propulsion has to double as a rapid-response launch abort system, with a what amounts to a 100 person space station on top of it. Many SpaceX fans seem to think that slapping more requirements onto the most challenging piece of the overall architecture will somehow save costs compared to developing two or three more optimized system elements, but I’m really, really, really skeptical. This seems like repeating one of the dumbest mistakes from the Space Shuttle.
  • Vertical Mars Landing: I know SpaceX is sticking with what they know, but the crew and payload section on ITS looks like it’s ~30 meters off the ground level. That’s some really long ladders and/or elevators or cranes, which aren’t going to be light. Heck, ITS makes the LSAM look reasonable when it comes to payload accessibility. I know a horizontal powered landing approach ala DTAL/XEUS would require additional engines and potentially landing complexity (depending on what changes you made to the rest of the architecture), but they would probably require less mass than hauling everything down from what amounts to an 8-9 story tall building.
  • Not Refueling In Mars Orbit: I don’t have the exact EDL delta-V requirements for ITS, but it’ll probably take close to 1/3 of the Mars Orbit mass in propellant. Aerocapture/braking first into Mars orbit doesn’t really change the vehicle requirements much, it allows you to cut down on the TMI mass by 1/3. Launching ITS from the surface with only enough prop to get to Mars orbit, and then refueling in Mars orbit, can also dramatically cut down on the overall ITS size. I’m not sure which mission phase is the driver for the ITS propellant tanks and landing engines, but I wouldn’t be surprised if in-space refueling in Mars orbit didn’t cut down both on the overall size of ITS per passenger complement, or if it cut down on the IMLEO of the system. And really, you already have to develop ITS tankers and ISRU on the Mars surface. Just ship a tanker or two along with your original landing group. Use the prop it shipped for refueling the other landers, making sure to leave enough for it to land empty. Even without an actual depot in Mars orbit you can take advantage of that. No new tech, no new elements, but likely a decent savings right from the start. Refuel Early, Refuel Often.
  • Methane Uber Alles: I think Elon oversells his case on how awful Hydrogen is compared to Methane. Sure, for his specific architecture, Methane might make more sense, but I can think of many other architecture where LOX/LH2 could probably be quite competitive for all but maybe Mars Ascent and Landing. Sure, if you insist on having one vehicle do it all, sticking with one propellant makes sense, and sticking with one like Methane probably makes your life easier. But there are so many assumptions baked into that logic chain.
  • Expensive Work In Process Inventory: The major cost driver on the mission is the ITS, because it can only do a Mars trip once per synodic period at best. This is somewhat the nature of the beast for Mars travel–whatever you send to/from Mars is going to take a long time to get there and back, which means you’ll have to amortize its cost over a lot fewer missions. Which is why it would seem like you would want to minimize the cost of the assets that get tied up like that. Having your Swiss Army Knife vehicle be the one that can only fly 12 times in a half century seems like a poor way to optimize for the problem.
  • No Landing Gear on the BFR Stage: I know that my colleagues at Masten also really like the landing-cradle approach, but I’ve never been a fan. Is it doable? Sure. Does it save a lot of cost and time when it works? Sure. But how reliable is it really? I can’t honestly answer this question, but my gut suggests that if your vehicle has a decent chance of surviving landing on an unprepared surface, there are going to be many situations where an abort, a large last second disturbance, or some other error could be survived when a gear-less vehicle is toast. Missing the landing cradle by 10m due to a last-second engine-out scenario probably means loss of vehicle and major pad repairs, where with landing gear it’s a non-event. We could totally build jetliners today without landing gear, using landing trolleys or other things. Or fighter jets landing on sleds on carriers. But we don’t because there’s no way aircraft would be as reliable as they are without having things like landing gear that give them options when something goes off-nominal. Let me put it this way–I don’t think you’re likely to ever see an RLV design that can survive long enough to average 1000 reuses (like SpaceX has baked into their BFR economics) without including landing gear.
  • Crazy Raptor Performance: 4500psi chamber pressure with a LOX-rich preburner sounds like a recipe for fun engine development. This is probably doable, and the Russians eventually tamed RD-180 class engines which have almost as high of chamber pressure, but how reliable will they really be, and how long lived will they really be? I just worry that SpaceX is trying to have its cake and eat it to, by pushing the bleeding edge of performance always, while also trying to push down manufacturing costs and up reusability at the same time. My guess is something is going to give–either the engines will end up being more expensive and finicky, or less reliable than they’ll really want for such a system, or nowhere near as reusable. I just don’t think 4500psi staged combustion seems like a good recipe for a 1000 flight engine. And the failure modes of a 4500psi staged combustion engine when you have 42 of them on your first stage also doesn’t sound likely to be graceful. I could, and genuinely hope I’m wrong. Once again repeating some of the mistakes of the Shuttle by trying to push crazy performance out of their first attempt at a staged-combustion rocket engine.

Ticket Price Economics Thoughts:

  • Per-Vehicle Costs: BFR costs seem to be assuming a per kg cost less than half that of F9 FT. Which seems optimistic to me given the higher performance, more complex engines, and the use of composites for the propellant tanks, and the general scale of the thing. Once again, trying to do a Big Dumb Booster with bleeding-edge performance. But it’s the ITS that I’m really skeptical about. You’re really going to make a spacecraft that has to have all the life support capabilities of ISS, but for 16x the crew, and cram it into a high performance upper stage, a reentry/landing vehicle, and all of that for less than half the cost of a 747-8? Especially given that you’re likely only making a tiny fraction of the number per year. Dragon currently costs probably $30-40M each to produce, and we’re saying that a Dragon designed for 14x the number of people, and 30-50x the duration, with a nearly Saturn V first stage class propulsion system built in is going to only cost 5x as much? Color me extremely skeptical. I think that they’d be lucky to have the production cost of an ITS with all of its subsystems necessary to get 100 people safely to Mars and return reliably down below $1B each anytime in the foreseeable future.
  • BFR Reuse Numbers: I’m also really skeptical they’ll get BFR reliability or engine life high enough to get anywhere near the 1000 reuses they’re claiming. I think they’d be lucky to average 100 flights each once again through the foreseeable future, based on the technology choices they’ve made.

The upshot is that if I’m right on those three items, you’re still talking less than $500M per Mars mission, and a ticket price in the ~$5M per person price range. That’s still three orders of magnitude better than what NASA could realistically do with its architecture. So while I think Elon doesn’t have an architecture that really gets down into the “cost of a median US house” range, he is getting into a range that a lot of people could afford. Having a Mars architecture this affordable would still be absolutely amazing, even if I think it could be done better.

How would I do things differently? Honestly I haven’t put as much thought into it as Elon has, but I have a few high-level thoughts:

  1. Split Things Up More: I’d separate TMI propulsion, the actual transfer habitat, and the Mars to surface and back into three separate elements. If you combine with the next point, the TMI stage can literally just be a normal upper stage like the Falcon 9 upper stage or ACES. The transfer hab would want to aerocapture at Mars, but could do so with a much more modest propulsion, and the Mars landing system can be smaller and higher flight rate. Honestly I think developing three systems that are more optimally split like this will not only cost less to develop than the swiss army knife approach, but will also be lower cost to operate, and open things up more for technology advancements over time.
  2. Go a Bit Smaller: Unless Induced Torpor works out, 100 people in a single vehicle seems really big for the transport stage. Breaking things up into convoys of smaller say 10-20 person vehicles might make more sense. This would mean transfer habitats would be small enough that you could use a TMI stage that is more reasonably sized for use in Cislunar space, so you don’t need a dedicated TMI stage. The transfer habs could be small enough that you have a range of options for aerocapture (inflatable, deployable, in-space assembled, or if it pans out magnetoshell aerocapture). These transfer habs will also have a lot more in common with LEO and cislunar orbital habitats, and possibly early mars surface habitats.
  3. Post TMI or TEI Boostback: I think Dave Masten and I have discussed this in the past, and Robert Zubrin hit on it today in his comments–It probably makes sense to have a separate TMI propulsion system that does the equivalence of a boostback maneuver after the TMI burn is done, to decelerate back into a highly-elliptical Earth orbit, where it can then aerobrake back to LEO. By not sending that along with the transfer hab, you enable it to be reused a lot more, since it’s not tied up for four years now. While not doing transfers to Mars, it can be sending payloads to/from Cislunar space, or to/from GEO. On a similar note, you could send one or two TMI stages along with the transfer habs to serve as TEI stages on the Mars side of things, using a similar post-TEI boostback maneuver and aerobraking to return back to Mars orbit for reuse. The more of your architecture is in the “can get 100+ flights in its lifetime” category vs “synodics mean I can only fly 12x in my lifetime” category, the cheaper things will be overall.
  4. Reusable Horizontal Mars Landers: Having separate landers, possibly smaller than the transit habs makes a lot of sense. The same landers can be used both for hauling people/cargo to/from Mars during arrival season, but also can be used for prepositioning propellant in Mars orbit, and Martian suborbital point-to-point transportation when not being used for Mars arrival landing. Horizontal landing on Mars is trickier than on the Moon, and I’m not totally wedded to the concept, but it seems like a much better way of getting people and heavy cargo onto/off of the surface.
  5. Using LH2 for More of the In-Space Elements: Once you’ve split-up Mars landing/ascent from the TMI/TEI burns, it makes sense to start looking again at LOX/LH2 for those segments. Those are two of the highest delta-V portions of your mission, so the higher performance could help. And LOX/LH2 can be made from Martian, Lunar, NEO, and possibly Phobos/Deimos ISRU sources. I know SpaceX is allergic to LH2, but most of the people I know who’ve worked with it have said “sure it’s a pain, but it’s not as evil as people make it sound”.
  6. Find Ways to Use Transfer Habs for Other Destinations: Say you can only realistically send a reusable Mars transfer hab on every other Mars window. That leaves a decent amount of down-time in-between. If the hab could be used for say taking tourists to/form the Moon or Venus when waiting for the planets to re-align from Mars, you can get much higher utilization out of the transfer hab elements. If you can take the one element in your system that currently can only be amortized over 12 flights (~50 year lifetime), and add in cislunar trips say during the “off-season”, you’re now amortizing it over 100+ flights instead of just 12. If you look at Elon’s architecture, 2/3 of the cost of a Mars ticket is due to the transfer hab’s low number of flights (the same if you make my more pessimistic hardware costs). If you could divide that over 100 flights instead of 12, that would make more of a difference for Mars ticket prices than almost anything else. Could you theoretically do this with the ITS as is? Sure, but without a source of CH4 on the Moon, you’d need to fly a lot more lunar tankers to make that work. Not impossible, but the economics aren’t as good as it would be if ITS could run on LOX/LH2.
  7. Leverage the Moon and NEOs for ISRU More: I still think there are ways that lunar ISRU can eventually beat earth-launched RLV prices for propellants in orbit. Especially if you stage out of a highly-elliptical earth orbit or EML-1 or 2. Investigating if there’s a way to tap into that wouldn’t be a bad idea, and would be a lot easier with the other suggestions I’ve given above.

Anyhow, that’s kind of off-the-cuff, but those are some of how I’d do things differently. As I said above, Elon has a lot of great architecture ideas, but I really don’t think he’s found the “One True Way” to get people to Mars as inexpensively as possible. Worlds better than NASA’s Journey to Mars? Definitely. Technically feasible? Probably. Cheap enough to be interesting? Sure. The best path forward from where we are today? That’s what I’d quibble with.

Posted in Commercial Space, ISRU, Launch Vehicles, Lunar Commerce, Mars, NASA, Propellant Depots, Space Development, Space Exploration, Space Settlement, Space Transportation, SpaceX, ULA, Venus | 60 Comments

I Think I’ve Found a Political Windmill Worth Tilting At

I usually try to keep partisan politics to a tolerable minimum on this blog, and I still intend to. But I had a crazy idea that I wanted to share somewhere other than Twitter.

This year, a significant fraction of the country isn’t happy with either major party candidate. But because of the “first past the post” plurality voting method all states use for selecting their electoral college representatives, it makes it extremely hard for there to be more than two major parties at any given time. You see transitions when one parties goes the way of the Federalists or Whigs, but you never see three major parties stably coexist for very long. There is however no requirement that a state use a plurality voting system to select their electors. For many years, many people have been advocating for alternative voting methodologies such as the Instant Runoff/Preference Voting method (my personal favorite alternative voting method).

For those who don’t want to read the Wikipedia link above, the tl;dr version of Preference Voting is that on the ballot, instead of just making one candidate, you get to rank your order of preference. Ballots are tallied, and if no candidate gets at least 50% of the vote based on everyone’s first choices, the candidate with the least votes gets dropped, and the analysis rerun using the 2nd choices of those voters who picked that candidate. The process is continued until one candidate gets at least 50% of the vote.

The process isn’t perfect, it’s provably impossible to construct a perfect voting system, but if you’re unhappy with the two-party status quo, it’s probably the most practical option out there. It’s currently being used in Australia, New Zealand, Ireland, India, and many municipalities in the US.

The challenge with enacting any alternative election method has always been that how do you get a two party system to enact a law that deliberately limits the power of their two parties?

One fact that helps is that you don’t actually have to do this on the national level to make a difference. A few states have already passed slight variations on the theme of winner-takes-all plurality voting. Nebraska and Maine both have plurality voting by congressional district, with the plurality winner at the state level getting the remaining two electors. But while the Nebraska and Maine approach does make marginal differences around the edges on how many electoral college votes each major party candidate gets, it still stacks the vote against third parties.

What finally got me thinking about an alternative when when I heard about Maine having a ballot initiative this year on whether or not to switch to a “ranked choice” (aka IRV or preference voting) scheme. Unfortunately for some reason they don’t include the presidential election, just governor, their US congressional representatives/senators, and state legislators, but it’s still a step in the right direction.

The nice thing about a ballot initiative is that this provides a potential end-run around the two-party machine in any given state. Admittedly, there are still tons of ways that political parties can oppose such a ballot initiative, but there have been examples of ballot initiatives passing even when strongly opposed by the two major parties.

So, my windmill tilting idea is that I want to figure out if we can get a similar ballot initiative started in Colorado, but this time with the presidential elections included. Here’s several reasons why I think Colorado might be an ideal state for such an initiative:

  1. Colorado has a track record of third party votes already–Ross Perot got nearly 1/4 of the votes in 1992, for instance, and Gary Johnson is currently polling up in the ~15-16% range in the state, and Jill Stein is up around 7% currently, with ~3% undecided.
  2. Colorado is a purple state, which means neither major party has a clear lock on the state. This means that there’s a chance you could get major party voters to vote for this if they thought that their candidate might benefit from more of the 2nd-place votes from 3rd parties.
  3. Colorado requires signatures from 5% of the people who voted for the Secretary of State’s last election in order to become a ballot initiative, but the secretary of state gets elected in non-presidential election years, so the turnout is typically lower–the 98k signatures requirement for a ballot initiative would only be 3.8% of the 2012 voter turnout, for instance.
  4. Colorado has a track record of passing iconoclastic (or at least leading-edge) ballot initiatives like the Taxpayer’s Bill of Rights and the recent initiative that legalized the use of Marijauna.

Here a few thoughts in response to likely questions:

  1. What good will it do if only one state has an IRV voting process for president? First, I think it will likely lead to other states following suit, especially if the experience works out reasonably well. Second, in extremely close presidential elections, even one state going third party could prevent either major party candidate from securing 270 electoral votes, thus throwing the election to the House of Representatives. In the house, each state delegation only gets one vote, and the vote can only be for the three candidates with the highest electoral vote counts. In the case of a close presidential election, I think this would potentially give a benefit to compromise candidates who can appeal to members of both parties.
  2. Wouldn’t Preference Voting be more confusing for voters? According to the Wikipedia article, “In American elections with IRV, more than 99% of voters typically cast a valid ballot1.” This seems like a solvable problem.
  3. Isn’t it too late to get this on the ballot for 2016? I think so. But in some ways it might be better to start pushing for this in the next election. If this year’s presidential election is close, especially if the margin of victory is less than the third party vote, voters for whichever major party loses in Colorado might be swayed to support this initiative if one can make the plausible argument that their candidate would’ve benefited from being the 2nd choice of third party voters. Frankly if you’re a Democrat that thinks Ralph Nader cost Al Gore the election in 2000, isn’t that functionally the same thing as saying you think Al Gore would’ve benefited from a preference voting system? Ralph Nader only cost Al Gore the election if Al Gore was really the second choice of enough Nader voters to have tipped the Florida election to Gore if Nader hadn’t been on the ballot.

It’s still a long-shot, but I think this is a really good idea, especially with the bad taste many people will have in their mouths from this year’s presidential election. I think I’ve found a political windmill well worth tilting at.

Posted in Politics | 28 Comments