Friday, November 22, 2013

Getting to Mars With The Reusable Falcon 9

Isn't it a bit odd that the most promising reusable launch vehicle under development today is being build by a company with a proclaimed love for heavy-lift launch vehicles?

As the Falcon 9 Reusable approaches the cusp of operations, with a successful demonstration of first stage reuse expected sometime next year, SpaceX is already moving on to a methane engine - Raptor - four times as big, for a rocket - MCT - with a much larger core size.

This, we're told, is Elon Musk's strategy for going to Mars and it's so much warmed over Bob Zubrin - Mars Direct, Mike Griffin - Apollo On Steroids, cargo cult of the Saturn V, stuck-in-the-1960s thinking.

If you have an operational reusable launch vehicle, as SpaceX says it is their goal to have, then there's much more sensible ways to get to Mars. Come on boffins, get the lead out, let's do the math on this one.


According to the best public numbers I can find, the second stage of the Falcon 9 v1.1 has a dry mass of 4,900 kg and launches with a propellant load of 70,800 kg. This is a very impressive propellant mass fraction of 93.5% and with its single Merlin 1-D engine delivering a specific impulse of 340s it can throw 22 tons on a fast transit (just over 6 months) to Mars (a delta-v of 4.3 km/s).

This alone is probably sufficient to do a great Mars mission. The hitch, of course, is that the second stage gets to orbit empty (well, with some unknown ullage) and must be refueled before it can be sent off to Mars. Also the typical payload to low Earth orbit of the Falcon 9 v1.1 is only about 13 tons, leaving us 9 tons of Mars-bound payload short. As it turns out, this is about the mass I'd estimate for a minimal Dragon-based Earth return capsule, so we'll assume the crew come and dock with the 13 ton Mars transit vehicle later.

The expectation is that the Falcon 9 Reusable will have about 25% less payload to orbit capability as it does acting in expendable mode - that is, about 10 tons, so the crew launch vehicle will not have to be expended. This is what you'd expect, as SpaceX is designing the Falcon 9 Reusable to reduce the cost of ferrying crews to the space station.

Now, about that fuel. We'll need about 70 tons of it, and at 10 tons per Falcon 9 Reusable flight, that's seven flights. However, part of the fuel is cryogenic - the liquid oxygen - and some of it may boil off depending on the length of the launch campaign. So let's say eight Falcon 9 Reusable tanker flights total. Still not enough? Okay, let's say nine flights. What's that? You want more? Okay, let's say ten flights. It's a fully reusable system.

There's some challenges in transferring liquid oxygen in zero-g, but they're minor compared to.. say.. liquid hydrogen. Figure it out.

What if a 13 ton transfer vehicle and a 9 ton crew return vehicle - 22 tons total to Mars transfer orbit - isn't enough? That's okay, just stage together two Falcon 9 v1.1 second stages. Both require 70 tons of fuel, so you're only doubling the total number of Falcon 9 Reusable flights, plus whatever you need to get the massive new payload into low Earth orbit.

Suppose the first stage provides 1463 m/s of delta-v before separating and falling away. The second stage ignites and provides the remaining 2838 m/s of delta-v. How much actual payload is thrown to Mars transfer orbit?

Would you believe, 47,850 kg? Almost 48 tons, surely that's enough!

The Saturn V was an amazing machine, but it was the product of a by-gone era. Fully and rapidly reusable launch vehicles combined with on-orbit refueling will make big boosters obsolete. At least, I sure hope it will.

Thursday, May 30, 2013

Who Would Have Guessed?

It was Stiennon and Hoerr's space-nerd spectacular "The Rocket Company" (now available on Kindle!) that introduced me to Kroemer's lemma:

The last 40 years has seen a lot of futile effort by space enthusiasts to find the one magic product or market that will justify building a truly commercial space industry. Well, it hasn't been found, and we're tired of waiting for it. And if you accept Kroemer's lemma, it can't be done that way anyhow. Even if you guess correctly what it is that won't create a huge growth in demand for launch services so that costs come down, that demand won't -- and can't -- come into being until the cost does come down.

So who is Kroemer and what is his lemma?

Herbert Kroemer is a Nobel Laureate in physics who wrote, in 1995, the Lemma of New Technology:

The principle applications of any sufficiently new and innovative technology always have been -- and will continue to be -- applications created by that technology. Ultimately, progress in applications is not deterministic, but opportunistic, exploiting for new applications whatever new science and technology happen to be coming along.

Around 1999, the Jordi Puig-Suari of California Polytechnic State University and Bob Twiggs of Stanford University decided to work together on a standard that would enable graduate students to design, build, test and operate in space their own spacecraft, with capabilities not much more advanced than the world's first spacecraft, Sputnik. It was called CubeSat. At the time, no-one imagined that commercial aerospace companies would ever be interested in flying such small, limited, even primitive spacecraft. A lot has changed since then, including CubeSats, which have gotten bigger, better communications, propulsion and may even be landing on the Moon soon.

Ten years later, Chen, Strickler and Adler launched Kickstarter. In a perfect example of Kroemer's lemma, The New York Times called it "the people's NEA", comparing Kickstarter to The National Endowment for the Arts, an agency of the United States federal government that offers support and funding for projects exhibiting "artistic excellence". Who would have thought that the most successful project, just two years later, would be "Pebble", an e-paper watch for iPhone and Android devices. Or that Tim DeBenedictis would raise $117,000 for SkyCube, just one of the more famous CubeSats projects that have been funded through the platform.

Which brings us up to today. Next year, Planetary Resources will be flying a 3U CubeSat to prove out many parts of their orbital space telescope hardware, but that's not what has gotten them thousands of backers and over $250,000 on the first day of their Kickstarter project. Aiming for just $1,000,000 by June 30, Planetary Resources is promising to build and fly a space telescope that can be accessed in classrooms around the world, and by the general public.

Who would have guessed that?

Increasingly, I am more interested in people who try to make the future, than predict it.

Thursday, April 18, 2013

In Regards To Secrets

Bob has a secret. His secret is not just something he finds valuable, but something lots of other people would find valuable too. Perhaps it's a new way to make energy, or to dye wool or to build yachts. Perhaps it's just his mother's maiden name. We don't know, because it is Bob's secret.

Does Bob have an obligation to share his secret with us? Can we go to Bob's house and demand he tell us his secret? Can we threaten Bob to get the secret out of him, or promise him payment for his secret and then renege? If not, why not?

Alice would like to know Bob's secret, so she offers him a significant amount of money for Bob to tell her. Bob is worried that Alice will tell others, but she promises not to tell anyone else. Having heard Bob's secret, Alice wishes she had thought of it herself and would prefer no-one else to know the secret, not even Bob. This, of course, is impossible, but Bob offers the next best thing: he'll promise to never tell anyone else the secret for a small fee each month. Alice agrees.

This continues for many years until one day Alice meets Claude. Alice very much wants to tell Claude the secret, but she still has an agreement with Bob promising not to tell anyone else. She talks to Bob and he agrees to let Alice out of her promise, for a small increase in his monthly fee. Alice tells Claude the secret, after swearing him to secrecy.

Shortly after having heard the secret, Claude loses interest in Alice. He floats around the world for a while, visiting various places and eventually meets Desmond, to whom he quickly tells the secret. Claude did not swear Desmond to secrecy. In fact, he didn't even tell Desmond that what was being told was a secret. The idea is no longer a secret. Desmond tells everyone.

The idea sweeps the world and everyone talks about Desmond, the man who told the world. Some people think Desmond actually made up the idea himself, but most people believe Desmond when he says a man named Claude told him the idea. Alice and Bob certainly believe it. Alice is upset because Claude broke her confidence. Bob is upset because Alice doesn't want to continue his monthly payments. They go looking for Claude.

Is Alice right or wrong to be upset with Claude? Is Alice right or wrong to stop paying Bob?

Should anyone be upset with Desmond?

This sort of situation seems to baffle people who don't believe ideas can be "property". They start asking other questions like what laws are applicable (copyright? patents?) and whether those laws are just. If they're honest, they start asking if they really understand the concept of property at all.

Saturday, April 13, 2013

Colonizing the asteroids starts at home!

When I first heard of this proposal I was reminded of the recommendations of the Space Studies Institute to do ore processing experiments on orbit as the first step to building O'Neill colonies. They were talking about using Lunar regolith simulant in low Earth orbit, with the goal of developing the techniques to utilize the products of a future lunar mining operation, but as an asteroid resources advocate I'd always preferred to think about doing the same thing with a captured asteroid.

A few years ago I wrote about colonizing a near-Earth asteroid (without moving it), with a focus on artificial gravity issues. The reality is that we don't yet know enough about the composition of any asteroids to have a decent shot at making water, oxygen, plant nutrients, or any of the other things you'd need for a space colony. We need to learn it before the colonists are sent, and having a captured asteroid to experiment on is a great way to do it.

Ultimately, though, the largest asteroids you can capture won't be big enough for a colony. Designing a mission to take a few hundreds of people out to (at least) 20 lunar distances is quite a challenge if you want to get them there healthy and ready to build a new world. Most problems can be solved by throwing mass at it, but typically that means more launches. Having material that is already in orbit, especially high lunar orbit or the Lagrange points, which you can use for shielding, know how to process into consumables or even structural components, would be of great help.

How likely is survival of that first colony? Mostly, they'd be cut off from resupply - close approaches to Earth of the same asteroid only happen infrequently. If they are to survive and thrive they'll have to be independent and stubborn. They'll need to see what they're doing as important and have a forward looking motivation.

After just a generation, they may be ready to expand. If their home is an Apollo asteroid, they might have the option of hopping over to the asteroid belt. Their well-honed technology will come in handy there. Eventually they may pull apart entire asteroids to make O'Neill type colonies, or just very large spaceships.

Visiting Earth will be easier for the asteroid dwellers than visiting the asteroids is for the Earthicans.

Sunday, March 17, 2013

Jon Goff's Lunar Patent

On a recent edition of The Space Show, Jon Goff discussed a lunar analogy to the 10 year patent grant awarded to Columbus on trade with any of the lands he discovered. This follows on from the great work done by Mike Mealling at dispelling myths about Columbus' funding which, I believe, he was inspired to do after watching one of my videos. Unfortunately, I think Jon fails to convey his analogy in a convincing way. Being somewhat libertarian, Jon is a little too concerned with where the tax revenue comes from and too specific with who will receive the incentives. This may also simply be a result of the origin of the idea - the analogy to Columbus - and the attempt to describe it as such.

Talking about who will be taxed to fund a government program is never popular. Even "let's tax the rich" is too specific not to leave a bad taste in the voter's mouth. Politicians have learnt that the subject is completely avoidable anyway. Talking about who will receive the bulk of government funding, even in the abstract, is rarely popular. It suggests that the purpose of the program is just to reward cronies or enrich one group over another. Politicians like to talk about having "free and open competition" to select contractors, or however they are handing out taxpayer money. Keeping these elements of modern statecraft in mind, how could the lunar patent concept be sold in today's terms?

I imagine something like this:

"To encourage greater commerce on the Moon, the federal government is offering to pay the majority of lunar launch costs and lunar facility leases for lunar operations. This offer will be valid for the first 10 years of lunar commercialization, which is defined as starting with the establishment of a permanent lunar base by any US non-goverment entity."

More detail could be added as to what exactly the government is subsidizing, but the initiative is sold as a means to reduce the cost of lunar commerce.. not as rewarding first movers. The first movers are required to get the kickoff to happen but it’s up to them to ensure that the government kickbacks come to them and not some latecomer. Thankfully, that's how markets tend to work anyway.

Eventually, someone will inevitably ask how the government is going to pay for this lunar development.. especially if the assumption is that launch costs are going to remain high and lunar facility leases will be in high demand. Assuming you can get a politician to give you a straight answer, the truth may be that they expect taxes collected on lunar commerce will cover the subsidies. They'll trot out an economist who is willing to testify to such and the public will swallow it because, hey, the guy has charts and graphs and stuff.

Friday, February 15, 2013

Imagining Mars Colonization

Recently, Ken Anthony invited me to critique his work over at Planet Plots. Although I've only scratched the surface of his blog, there's not much I disagree with, and recommend the visit. The only problem, as I see it, is a lack of depth.. and a lot of hand waving. Just about anything can be explained away with "free people will figure it out". I very much agree with that sentiment, as Ken knows, but aren't we free people? Can't we figure it out?

For example, take what the Mars Starter Kit page has on it. There's many links to the Open Source Ecology wiki, which is a fantastic resource, but ultimately it's still just geeks in front of the computer screen.. where's the meat? Elon Musk made a comment the other day that has stuck with me:

"Making standard efficiency solar panels is about as hard as making dry wall. It's really easy. In fact, I'd say dry wall's probably harder."

The context indicates that he's talking about making solar cells (not panels from cells). I'd love to see someone back this up in a graphic way. Make a few hundred solar panels in a carpark somewhere.

Why solar cells? Why not just demonstrate that you can make glass or bioplastic? You're probably going to want one of them for your solar panel, anyway. Well, because solar panels still represent, to many people, a level of technology that is mystical and impressive. Proof: if I say a kid in Africa has a solar panel to charge his cell phone, you might still imagine that African kid living in a grass hut, but you'll appreciate his access to "high technology".

I'm also more than a little concerned with Ken's acceptance that colonizing Mars will cost billions. I don't doubt that it will - actually, I expect his estimates are low. The concern comes from the fatalistic implication that there's nothing we can do to get it started. It reminds me of the recent announcement of Planetary Resources and Golden Spike, both of whom claim to have received an outpouring of emails and other communication from members of the public asking how they can help - "send money" has been their only response.

What I think Ken fails to recognize in his pages describing how people can live on Mars is that it doesn't fit into anyone's mental model of How People Live. The words "self sufficiency" conjure up in people's minds an agrarian lifestyle. We think of hippie communes, at best, and starving African villages, at worst. We certainly don't think about extracting aluminum from clay to cast into machine parts. Nor do we think about running our own nuclear power plant.

There is no word for a small self-sufficient high-technology society because none exist. As far as I'm aware, no-one has ever even tried to make one. The idea itself is fantastical to us - even if we're talking about right here on Earth. If we can't get people to imagine a small group of people going out into the wilderness or the desert to build a high-technology society, then how are we ever going to get them to imagine the first colonists doing it on Mars?

I think the best way is just to show them. Let's get started.

Monday, December 10, 2012

Dragon-LP



Sending humans in a SpaceX Dragon v2 capsule to EML-1 or 2 is a worthwhile possible step in a 100% commercial return to the Moon. The SuperDraco thrusters to be included in the sidewalls of the crew Dragon capsule are more than capable of performing the trans-lunar injection burn, as well as station keeping at the Lagrange point, rendezvous with any preemplaced assets - such as a lander - and returning the crew to Earth.

The total delta-v for such a bare bones mission to EML-2 is a mere 4835 m/s. EML-1 is similar. This is a "quick transit" 4-day trip up to EML-2, so the crew spends less time in the radiation belts. A good estimate of the dry mass of the Dragon v2 is 8000 kg. Using an isp of 320s, the initial mass in LEO is just 37344 kg, or 68% of the maximum payload mass of a Falcon Heavy.

Just going to a Lagrange point with a crew on Dragon would be a momentous achievement and could be done for a mere $150M. However, it is just the first step.

If we fill the remaining Falcon Heavy payload mass with fuel, the total delta-v available to the Dragon becomes 6050 m/s. This is sufficient to go from LEO to EML-2 to low lunar orbit and back to Earth, with significant margin for maneuvering and rendezvous, if required.

What might the crew in the Dragon rendezvous with at EML-1, EML-2 or low lunar orbit? Using the same SuperDraco thrusters to take the slower 9-day transit - a delta-v of just 3470 m/s - 18.2 tons of payload can be delivered to EML-2. This payload can loiter for months waiting for the crew to arrive. Up to 14.8 tons can be deployed from EML-2 to low lunar orbit when required. Up to 6.2 tons can be landed on the surface if the lander is taken via low lunar orbit, or up to 8.1 tons if taken directly from EML-1 or 2.

This is all possible because I have avoided two pitfalls of lunar return architectures that have become very common in recent years.

Firstly, I have ignored the possibility of using the second stage of the Falcon Heavy to perform any part of the trans-lunar injection burn. A simple trade study shows that it is not advantageous when you have sufficient thrust on the payload - which you must have to do later maneuvers - so I'm baffled as to why people keep considering it.

Secondly, I have not used any high isp propulsion such as LH2/LOX or CH4/LOX. Although this may become preferable in future lunar architectures (especially if propellant made on the Moon becomes available), it is currently an additional expense which does not provide significant advantage to justify its cost.