Friday, June 9, 2017

Space Shuttle 2.0

From 1981 to 2011 the United States had access to one partially-reusable launch stack, the Space Shuttle. The stack consisted on two solid-fueled boosters, a large central fuel tank, and the Orbiter Vehicle (the orbital glider that most people associate with the phrase "space shuttle", since it was the part that astronauts flew to orbit and came home in).

The space shuttle was initially supposed to be fully reusable, but eventually settled on partially refurbishable. The boosters crashed into the ocean, the fuel tank was lost each time, and the orbiter required extensive checks of its heat shield between each flight (and it was a failure of this heat shield that caused the loss of Columbia).

In terms of performance and economics the shuttle cost between $450 million and $1.5 billion per launch (depending on how you accrued non-launch program costs) and could put 27,500 kg of payload into Low Earth Orbit. Its launch cadence (per vehicle) was slow; the refurbishment mentioned above took months.

You'll note that even at $450 million per launch, the Shuttle stack was not competitive with even the most expensive expendable rockets operated by Boeing and Lockheed Martin. Compared to the entry-level prices of $60 million for a Falcon 9, the "reusability" of the Space Shuttle created more expenses than savings.

Half way through 2017 however, SpaceX is now well on its way to replacing the capacity of shuttle at significantly lower costs. The base cost of an expendable Falcon 9 is $60 million, and while SpaceX has not provided firm pricing for its reusable variants, their guidance is that the Gen 1 reusability will provide savings between 10% and 30%, while the long term prospects are savings between 90% and 99%. And this is while delivering 22,800 kg of payload to orbit, fully 80% of the performance for 5% of the cost.

I. How have they achieved this price gap?

Vertical Integration
The first question is "How does SpaceX make an expendable vehicle that 1/20th the cost of the Space Shuttle stack on a per flight basis?", and this has been answered may times by Elon Musk in interviews. The starting point is that SpaceX does not use traditional aerospace supply chains (grown fat and inefficient on government contracts) but either buys off the shelf technology or builds tools and systems internally with a focus on low-cost production. By example, in a recent interview SpaceX's Chief Propulsion Office Tom Mueller indicated that the marginal cost of production of the Merlin 1-D engines that power the Falcon 9 booster and upper stage were "within  factor of 5" of the marginal cost of a Tesla Model 3 sedan (which is $30,000). In a field where rocket engines typically cost hundreds-of-thousands to millions of dollars each, this is extraordinary.

II. Then once the lower base cost is achieved, how do they achieve reusability that lowers costs rather than raises them?

Less damage to Boosters, Rapidly Turns Around
The Space Shuttle boosters crashed into the ocean and required extensive safety checks and refurbishment between launches. The Falcon 9 booster flies under power to either a barge in the Atlantic Ocean or back to its launch pad. Despite years of efforts by NASA, the crash landing and immersion in sea water did too much damage to the boosters to ever allow for rapid reusability. By comparison the Block V version of the Falcon 9 booster is designed to have a 24-hour turnaround with minimal maintenance.

The rapid turn-around is a not-to-be-overlooked part of the 90--99% cost savings that Elon Musk is predicting in the long term. A rocket that flies once per year or less (such as the Space Launch System is predicted to have) still has large fixed costs (such as its landing pad and ground crew) that must be maintained in working order all year round for the next flight. A rocket that flies every month, week, or day uses the exact same amount of launch pad, but the costs are spread out over 10-300x more flights.

Non-Reusable Fuel Tank vs. Eventually Reusable Second Stage
The Space Shuttle fuel tank had no ability to land on its own and could not slow or control its descent through the atmosphere, leading to a full loss every time. NASA never attempted to fix this. Currently the Falcon 9 upper stage is also lost every time, but it doesn't have to be this way forever. The upper stage has the necessary engines and guidance systems to propulsively fly back to earth just like the boost stage does, and developing the ability to do so will be necessary to achieve the >90% cost savings mentioned above. This will be easier to achieve once SpaceX is flying the Falcon Heavy, as it will have a larger performance margin to work with.

Refurbishable Orbiter vs. Rapidly Reusable Fairing/Dragon
Unlike the Space Shuttle, the Falcon 9 stack cannot fly both a crew and a satellite on the same launch. It can fly either a cargo fairing or the Dragon spacecraft, but not both. Until recently the cargo fairing was always lost, but in March 2017 SpaceX announced that they had recovered the fairing. The fairing included guidance boosters and parachutes that allowed it to descend into the ocean, similar to the old Space Shuttle boosters. Long term it probably makes sense for the fairing to incorporate Draco engines (the same as the Dragon spacecraft) for propulsive landing.

Meanwhile the Dragon spacecraft currently uses a heatshield and parachutes to slow down before landing in the ocean (similar to the Apollo capsules). Using this method SpaceX is able to retrieve and re-fly them, and just for the first time re-flew a Dragon to the International Space Station. Meanwhile the next version of the Dragon (Dragon 2) will have Draco thrusters powerful enough to land propulsively like the Falcon boost stage.

Currently the Dragon spacecraft has only been reused once, so it's hard to gauge just how successful SpaceX will be at beating the Shuttle's reusability record on this part of the stack. But there is one part of the design that bodes well. While the Shuttle had thousands of heat-resistant tiles that hed to be inspected individually between each flight, the PICA-X heat shield on the Dragon is a monolithic part that's designed to withstand a certain number of re-entry burns and then be replaced. As a service schedule this should prove much more efficient than the Shuttle system, and should only delay reuse of the craft every 10-20 flights (however many the shield proves to be good for).

III. Conclusion

The purpose of this essay is not to crow over SpaceX's "victory" over the engineers at NASA. The Space Shuttle design began in 1969 and first flew in 1981. To say that NASA engineers had access to less technology than SpaceX is putting it mildly. They did great considering their political and technological constraints.

The point of this post is to be glad for America. As a nation we are finally within reach of having re-usable rocket stack that can put cargo and crew in orbit once more, with the added benefit of being a fraction of the cost of our old one. Over the next year we should expect Dragon 2 to fly crew to the International Space Station (and possibly beyond) and the Falcon Heavy stack to deliver both larger payloads to Low Earth Orbit than the Space Shuttle and a reusable second stage.

Furthermore the logic of low-cost operations should start to sink into NASA's programming within the next couple years (and hopefully to the private sector as well), and this should deliver a renaissance in terms of space science. When huge chunks of NASA's budget are eaten up trying to develop and maintain a rocket that costs billions to launch and flies once a year, a lot of science gets cut for lack of funding or access to orbit. If the Falcon Heavy can put 20 times a many payloads in orbit for 1/20th the price per kilogram, it suddenly starts making sense to mass produce probes for the asteroid belt, outer solar system, and who knows where else.

The last six months have been a huge boost to the idea that American space has a bright future.

Friday, March 3, 2017

Bezos > Musk

I'm going to lay out a prediction here that will be hard to judge for decades. I think Jeff Bezos will prove to be more important than Elon Musk in the to-be-written history of mankind moving out into the cosmos. I'm a big fan of Musk and SpaceX, but I think Bezos has a better focus. Musk is focused on Mars because he wants to settle humanity off Earth as quickly as possible. However it's too soon for Mars. We need regular cheap access to orbit first, then to develop resources and infrastructure in Cis-Lunar space, then the asteroids, and so on. We are a long, long way from being able to settle Mars in a sustainable manner.

By way of comparison, the Vikings discovered and settled the New World centuries before Columbus, but they couldn't do it sustainably. They didn't have sufficient sea faring technology to make for regular trade between the New World and Europe, or for mass immigration. It took Europe several more centuries to build the technology needed for regular trade with and settlement of the New World. I don't think it will take centuries for us to get where we need to be to settle the rest of the Solar system, but we still need to do a lot of work to get there - and Bezos (and Robert Bigelow, and Made In Space, and Planetary Resources, etc.) are the ones doing that work.

If Elon ends up being more important than Bezos, it will because he realizes this and pivots SpaceX's business model to closer to Bezos' current vision.
"Our ultimate vision is millions of people living and working in space. We have a long way to go." - Jeff Bezos

Blue Moon

Days after Elon Musk announced a tourist trip around the Moon, a paper has been leaked describing Jeff Bezos' pitch to the new Trump Administration for "Blue" Moon missions by 2020.

There's a couple things here which are extraordinary-
  • If Blue Origin plans to be flying to the Moon by 2020, their New Glenn rocket must be closer to flying than we've previously heard of.
  • The paper mentions a "Blue Moon" lunar lander, which we've never heard of before. The paper says it's based on New Shepard, which makes sense if you want to cut down development time.
  • The paper indicates the ability to put 10,000 lbs of mass on the Moon. That's cargo, and doesn't include the mass of the lander itself. That's a lot! If this is based on a single launch architecture (and I assume it must, as we are unlikely to develop on-orbit refueling in three years), this confirms that New Glenn is closer to SLS and Falcon Heavy than the Falcon 9 in terms of performance.
That last bullet is really important. Here's the money-quote from Bezos:
“Blue Moon is all about cost-effective delivery of mass to the surface of the Moon,” Bezos wrote. “Any credible first lunar settlement will require that capability.”
Dollars for kilograms. That's what has been missing from NASA for the last half-century. The Apollo rockets were amazing, and the Shuttle was neat, but what has been holding back space development for the last half century is that the cost to reach orbit stubbornly stayed around $10,000/lb. At those prices, nothing significant is ever going to happen. And SLS was never going to change that.

But finally Musk and Bezos are changing that. And of the two of them, I think Bezos is the more-focused one. So what sort of costs are we talking about?

We don't have pricing for New Glenn, but the Falcon Heavy (before reusability) has a base cost of $90 million per flight (actual flights cost a little more than this, due to integration costs and so forth, but this base is still useful), and Musk has indicated that partial reusability (5 flights per first stage) should reduce costs by 20% and full reusability (at least 20 flights per stage, all stages fly back) would reduce costs 80%. According to those estimates we get the following:

                    LEO/lb  GEO/lb   Mars/lb
Expendable  $90m    $  750  $1,840   $ 3,000
Partial Re  $60m    $  600  $1,470   $ 2,400
Fully Reus  $18m    $  150  $  367   $   600

We don't have exact numbers for the Moon, but the Moon is easier to get to (in terms of delta-v) than Mars. We also don't have cost numbers for the New Glenn yet, but we know that New Glenn will start out with "Partial Reusability" and that Bezos eventually wants to get to full reusability. So look at the second and third lines in the table, and compare those numbers with the $10,000/lb that the Space Shuttle cost to put stuff just in LEO.

NASA has been able to maintain the International Space Station for the last 20 years with $10,000/lb launch costs. If Bezos can put cargo on the Moon for a fraction of that price, there's no reason a manned Moon base is out of the question.

Tuesday, February 28, 2017

To the Moon!

SpaceX is going around the Moon.

The projected date is late 2018, but that's ambitious (as all SpaceX dates are). I believe Elon when he says that Dragon 2 will fly next year, but going from first test cruise to Moon trip in a single year is ... ambitious (there's that word again).

But regardless of whether it's in 2018 or 2019, this is very cool. This is going to be the kind of spectacle that will make a lot of people sit up and take notice. Whoever these paying customers are, they'll go down in history as the first private citizens to fly beyond Earth orbit.

And that's a good thing. NASA has been futzing around for years with their SLS and Orion programs, wasting billions, and they don't have a single rocket to show for it yet. The first planned test launch to LEO is for late 2018 (and then it plans to fly again in 2021 (woo!!)), the same time that SpaceX plans to be flying tourists to the Moon. And from there things don't improve for SLS, as their projected flight tempo is one flight every 2-3 years at a cost of $1-2 billion per flight (depending on how you accrue program development costs). Those sort of costs are great for the cost-plus contractors that fund Congressional campaigns, but if the rest of Congress (who doesn't get kick-back money from SLS contractors) starts paying attention they might start to ask why NASA is paying 10x as much for a rocket that flies 1/20th as often as Falcon Heavy.

What you'll surely here next year though, in defense of SLS, is that Falcon Heavy doesn't have enough power to launch a Moon lander or Mars lander. "We need SLS if we want to actually land anywhere, and not just do fly-bys!" they'll say. And that's true to an extent. The Falcon Heavy doesn't have enough power to land a crewed Dragon 2 on the Moon as long as you have to launch all your fuel at the same time.

The mass of the fuel needed to land on the Moon and return is the limiting factor. As long as we keep sending up the fuel and the crew vehicle on the same rocket, we will need to keep building ever larger and more expensive rockets.

But this is not actually necessary. The current Dragon spacecraft can berth (aka, get close and then be grabbed by the Canadarm) with the International Space Station, and Dragon 2 will be able to dock (aka, mate with a docking port using its own propulsion; no Canadarm necessary) with the International Space Station. A craft that can do this can also dock with an external fuel tank in orbit.

So watch for that, because while circling the Moon will be the big bang of 2018 (or 2019), refueling in orbit will be the prelude to the next one.

Thursday, February 23, 2017

Give me a home where the asteroids roam

Astronomers discover seven Earth-like planets around a nearby star

Or so the headlines tell you. But what does "Earth-like" mean? To give you a sense of what I mean, if we were studying our own solar system from afar, Mercury, Venus, Earth, and Mars would all qualify. And yet, three of the four aren't especially habitable.

Human beings are very clever about adapting to environments on Earth. Populations of humans are found all over, from the equator to above the Arctic circle. But all of those environments have constants which do not change, like gravity and the mix of gasses in the atmosphere. We already know that variations in the air we breathe can be deadly, and variations in the amount of sunlight over a 24-hour period effects long term human health. What if the day was something other than 24 hours? What if the gravity was 90% of Earth?

I'm pessimistic that humans can adapt to environmental factors which are especially different from Earth. Even if there are a dozen planets in every solar system, the odds of any planet being a close-enough match to earth (atmospherically, gravimetrically, and otherwise) to be a good fit for unmodified humans are slim.

However that does not mean I am pessimistic about human settlement of the solar system or the galaxy. It just means we should stop focusing on planets. Planets can be pretty hostile, they exist at the bottom of an gravity well that's very hard to safely enter and exit, and as a percentage of possible habitable real estate they're not even especially large.

Also, if you've read anything about the efforts that would be required to terraform a planet such as Venus, you know that's not a reasonable amount of work for the payoff. Not when there's a better alternative.

Much better than a planet is a small moon or large asteroid belt that can be mined for resources. Ordinary steel from a nickel-iron asteroid could be transformed into an O'Neil Cylinder habitat with an inner surface area of 10,000 square miles. Assuming (within reason I think) that we improve our ability to mass-produce carbon materials such as nanotubes and grapheme, the carbon from an asteroid could be turned into a Bishop Ring with an internal surface area of 1.2 million square miles (about the size of Argentina or India).

And those surface areas are just the top deck where people would probably choose to live, on account of the Mediterranean weather that's maintained year-round. There's no reason you couldn't have multi-level habitats with sub-levels for agriculture, infrastructure, and industry. Fields of rice won't care they only have 50' of headroom. So the upper deck numbers are pure residential land area.

The real benefit of ring habitats is you can produce 1g of gravity for the inhabitants without going down into a gravity well. This is important because if you think about a future where most humans live in space (not on Earth), you want to be closer to the trade networks connecting the many nations. From an energy point-of-view, living at the bottom of a gravity well is sort of like living on a remote mountaintop, whereas living in orbit is like being at a major sea port close to the world's shipping lanes. From earth the only way to get to the shipping lanes is taking a rocket; but from a Bishop Ring you can take an elevator.

So it's nice and all that we found seven planets. That's fine. Science is cool. But from the point of view of whether these planets will ever serve as a home to future humanity, the answer is "Probably not ever". Instead a colonization ship will set up shop in orbit around these worlds and produce 1,000 Earths worth of Mediterranean real estate from their moons, while on the (probably very hostile to human life) surfaces below we will only send robots for mining or scientific inquiry.