zaterdag 21 december 2013

Lunar resources and a new Space Race

With the successful landing of Chang'e 3, the attention of the world's spaceflight enthusiasts and experts alike once again turns towards the moon. These things spawn up discussions about why we should go to the moon, whether there is economical benefit to it, or about the "new space race", as well as the usual complaining about NASA's lack of productivity or that those damn commies is taking muh spaceflight.

And to be honest, when these things happen, I can't help but feel a slight annoyance. Many of these things are based upon false premises, or people who live in the 1960's, or general ignorance of spaceflight that results in xenophobia, anti-americanism, armchair experts (I'm being a little bit of a hypocrite here, I'll admit that) schooling others like it's their job and nationalist slapfights. 

Lunar resources

Something I've seen so many times lately is that we can use lunar resources to pay off our debt, make fusion attainable, makes spaceflight more sustainable and many more things. But is this really true? Can lunar resources make the moon an economically viable source for materials needed on Earth? I don't think so. Let me show you this with an example.

Say we assume the cheapest LV in terms of cost/kg currently available in the near future, Falcon heavy. With ~2500 $/kg, this vehicle could get 53 metric tons into LEO with a cost of $135 million. The ∆V needed to return from the lunar surface is 3 km/s. A 53 ton stage with a 0.87 PMF (realistic since there have to be legs and everything attached to the stage) could get about ~35 tonnes back to Earth. This stage would land on the moon, be refueled there, and could be sent back. So how much would this cost?

The cost of this material would be $3900 per kg. But it gets worse. This assumes that the entire payload is nothing but the actual material. If you put it in a container, it becomes more expensive. Something like a Dragon capsule can return 3/4 of it's own mass back down to the surface, or 3/7 of total mass. Suddenly, you're looking at 4 tons returned to Earth, and a cost of $9000/kg. And in the case of a low density material like Helium 3, you get even lower return down to the surface. 

To make things even better, this assumes that the base put there was entirely free and that the stage could be refueled there for free. If you don't assume refueling there's no payload at all, and if you take into account the cost of a lunar mining base, which is on the order of $100 billion, you'll quickly see why lunar mining isn't very economical currently. This also assumed the cheapest vehicle to LEO available in the near future; if you went with Delta IV it would cost 6 times as much.

So, lunar resources are, for the time being, a pie in the sky dream. They are extremely expensive to get back and the ROI would take so long (if there was any profit at all) that it simply isn't worth it for a long, long time. I'm not saying they can't be useful, a prop depot in lunar orbit or a small refueling base could really ease up lunar exploration. I don't think it should be held like a good reason to go there. If lunar resources are to be seriously considered as a reason for lunar exploration, we should first get launch costs down by one or two orders of magnitude before it is a serious argument in favour of lunar resources for use on earth.

And Helium-3... How about we perfect Tritium-Deuterium fusion before we go there to pick it up? And there's always Proton-Boron fusion if neutron-less fusion is so important. It's not really necessary for attainable fusion.

A new Space Race and China's space dominance

By far my favorite. Go on any thread on reddit related to China's space program and you'll find a bunch of people preaching about the new space race, that the US should step up their game because the Chinese are overtaking "us", etc. And I usually just sit there laughing or being slightly frustrated with this.

First, why a new space race? There certainly are no signs of one. China is stepping up their game but neither the US nor Russia show any sign of doing the same. Their plans have changed little regarding exploration; the US still has to work in the direction of an asteroid, and Russia still works in the direction of the moon and Lagrange points. There is no space race going on at the moment.

What surprises me even more are all the people who wish for a new space race. And I flat out don't get it. What happened the last time we had one? The US landed on the moon. The costs, which were so high in part because of time pressure, sent Congress and the administration into shell shock.  Apollo applications was canceled and a "cheaper" LV, the space shuttle, was signed into law. That "cheap" LV got the US stuck into orbit for 30 years. Apollo was expensive, accomplished little and forced NASA into the terrible position it was in for the past few decades, until it was decided to finally axe the shuttle in favor of a conventional rocket with a normal capsule. A safer, more affordable and more flexible vehicle. Alright, Orion and Ares 1 are a bad example. Falcon 9 and Dragon, or Atlas V with CST-100 are better examples. Still, the last space race got us stuck for a long time. 

A new space race would get NASA to the surface of the moon, maybe Mars, for a few times. We would alienate a potential spaceflight partner, would cause NASA to create an expensive and unsustainable program similar to CxP, only to cause massive budget cuts once the program is over and we'll never go anywhere for many years afterwards. The other option is teaming up with China/Russia/whatever dirty commie country 'Murica is afraid of for no reason/ESA and spread costs and effort over several different nations, allowing large scale exploration for much lower cost in a more sustainable way. Which one do you think will result in more stuff getting done? 

Second thing is, why are people so afraid of China? As reddit user Ambiwlans so eloquently put it, "Since Russia collapsed all the people that need a bad guy to fear seem to have latched on to China." Since there is no big scary red Russia to fear, people start irrationally fearing the other "big scary commie country" out there, which is China. But is China really that big of a danger to the US space "dominance"? Let's compare the two, shall we:

Biggest LV: Long March 2F/G, 11.2 tons into LEO. 25 ton launcher in the works.
One crewed spacecraft, three crew, a few days on orbit life time. No new one in the works.
Budget $1.3 billion

Biggest LV: Delta IV Heavy, 28.8 tons to LEO. 53 and 70 ton launchers in the works.
No crewed spacecraft, but four in the works. One can support crew of four for three weeks.  
Budget $16.8 billion

So yeah. Another big red scare that really isn't that scary. China is not yet capable of doing anything the US hasn't long been able to do, and they don't have the means to do anything significant for the time being. They have a focus, which is a big improvement over what the US has. But should the next administration of the US decide to switch focus, all that has to be done is developing a lunar lander and the US could be back on the moon by 2025. China isn't even trying to land earlier than that. Older articles claim 2017 but these are usually very outdated.

"NASA should get off their arse and do something productive, they don't do anything unlike China"

Let me just answer with a few pictures. 

Curiosity is a lot cooler than Yutu.

Cassini, currently orbiting Saturn
New Horizons spacecraft, currently underway to Pluto
SLS tank barrels being manufactured right now
Dragon spacecraft, funded and co-developed by NASA

zaterdag 14 december 2013

Random Thought: Should we avoid SLS Block 2, or go straight for it?

In previous blogs of mine, I wrote about how I wish NASA would stick with Block 1 instead of continuing development of SLS after EM-1. The reasons for this are simple; development is expensive. If SLS Block 1 was to be NASA's new main launcher, it would save billions in development cost, while at the same time giving a very capable 90 ton launch vehicle that can take whatever we throw at it. However, I changed my mind somewhat. I have given the option of going straight toward Block 2 as our main exploration launcher, instead of sticking with Block 1 or 1A, a chance in my mind. There are many advantages to doing this, and I'll explain myself here.

Advantages of Block 2

#1: Block 2 doesn't have to be so expensive to develop. The current path baselined by NASA is expensive, but it doesn't have to be. The current one has the following order of upgrades:

1. Develop new boosters for SLS, either advanced solid or liquid; increases payload to >105 tons.j
2. Develop an in-space stage for SLS to replace the iCPS. 
3. Wait nine years, fly SLS once every one or two years. 
4. Develop a new, massive J-2X powered upper stage, redesign the core you've been flying for 15 years by adding an extra engine. Increases payload to >130 tons to LEO.

Since then, however, a few new upgrade paths have been drawn up. One of them was put forward in a paper by Boeing named "THE SPACE LAUNCH SYSTEM CAPABILITIES FOR ENABLING CREWED LUNAR AND MARS EXPLORATION" which is available on L2. The paper describes adding a new upper stage to SLS, powered by 2 J-2X engines. This variant, sometimes nicknamed by the community as Block 1C, would use normal boosters, a normal 4x RS-25 core, and a new upper stage. Just by adding a new upper stage, the "70" ton version gets 130 metric tons to LEO. Now, I have to be honest, I'm a little skeptical of this payload. Similar vehicles shown in ESAS couldn't reach the 130 goal, and ATK claimed in their Advanced Booster paper that SLS needs 5 engines to reach 130 tons to LEO. The Boeing paper also renders this "Evolved SLS" as having 5 core engines, despite claiming it has 4 engines. However, it should still be possible to evolve the core design for the follow up to Block 1 to allow for 5 engines. By making such a decision early on, it should save a lot of development cost.

Now, after some time, new boosters will be required. There are sufficient booster casings for ten SLS flights with standard 5-segment boosters, but if we ever get serious with SLS, new ones would become necessary. However, having already reached 130 tons, this would allow for cheaper, affordability focused boosters instead of the big, performance focused advanced boosters using the F-1 engine proposed by Dynetics. In fact, they could be even cheaper than the ATK advanced boosters because they won't have to be as big.

And other possible development path is by adding a 4x RL-10 upper stage to Block 1, then adding advanced boosters. No core redesign required, and although Advanced Boosters will become necessary, the new upper stage would be significantly cheaper than the J-2X upper stage, both to develop and operate.

Either of these paths would probably allow Block 2 to be ready by ~2025 instead of the current 2032.

#2: Block 2 is actually cheaper than sticking with Block 1 in the long run. While it would cost more to develop, Block 2 would cost pretty much the same on a yearly or per-flight basis as Block 1. The rocket shares tooling for the upper stage, costing very little extra. The engines, either RL-10 or J-2X aren't free but don't cost hundreds of millions either. The boosters, whether they're designed to be powerful or affordable, are supposed to be cheaper than the 5-segment ones on Block 1. The fixed costs would be slightly lower, marginal cost slightly higher, but the difference is very small either way. Assuming identical cost, SLS Block 2 costs significantly less at payloads above 70-90 tons, and anything above 140-180 tons because of requiring less flights. The use of advanced boosters compared to normal boosters also allows for lower fixed costs, though the exact costs of this is hard to estimate because of a lack of info. ATK claims a cost reduction of 40% for the boosters, but I don't know how much a booster costs, so the exact difference is hard to pin down.

There's also something I glanced over previously. For sticking with Block 1, you'll eventually need to develop an in-space cryogenic propulsion stage and new boosters too. The cost saved from sticking with Block 1 aren't very significant at all.

#3: Block 2 frees up more money for actual missions. You might be wondering what I'm smoking right now. Believe me, I'm not smoking, this might actually be true. The current plan is to operate Block 1A for nine years to perform all missions to asteroids/the moon and continue developing Block 2 in the background at the same time. By going to Block 2 directly, you save money afterwards because you don't have to keep on developing upgrades for SLS. You might put back missions compared to sticking with Block 1A, but they can be developed quicker afterwards. Considering NASA's dire lack of funding, stopping funding for development of the launcher and flying the final config as soon as possible seems like a more realistic path to other worlds than sticking with a less capable, just as expensive variant that will have to be replaced later anyway. Unless a new NASA Authorization Act is made dropping the 130 ton requirement, Block 1A would require an upgrade sooner and later, and putting it off might only cost more money in the long run.

#4: Unlike Block 1, Block 2 is actually a big improvement over other launchers. Block 1's 70-90 ton LEO payload is very good compared to current rockets, but it's not something cheaper rockets could reach for less. 130 tons to LEO, however, is a different story. I previously estimated that Falcon Heavy with a Raptor upper stage could get ~65 tons to LEO, and Atlas Phase 2 can get 75 tons into LEO according to ULA. Sticking with Block 1 would neuter the point of even having SLS, since these launchers would give similar LEO performance for less. Block 1A would give a decent increase to 105 tons, but 130 tons is sky high above all other launchers and is the only payload capacity that could somewhat justify an expensive Shuttle Derived Architecture over, for example a 70 ton inline kerolox concept combined with in-space refueling. Whether we need that capacity is a bit of a different story, but there certainly are reasons it could be useful.

There are also many mission possibilities that could be opened up by Block 2 that would require several launches on other launchers, including other SLS blocks. Assuming 130.0 tons to LEO, a Block 2 with 0.9 PMF CPS optimized for lunar missions and 462 Isp would get the following performances to other orbits:

  • 44.6 metric tons into Low Lunar Orbit
  • 56.3 tons to Trans Lunar Injection
  • 54.2 tons to the nearest Near Earth Asteroids
  • 48.9 tons to Mars ( ~7-9 month travel time, 3700 m/s)
Now assuming these values, there are a few options that open up that Block 1A would require multiple launches for. 

One is a manned lunar landing with 3-4 astronauts for a week down on the surface. A paper with presentation from Spaceworks Enterprises Inc. includes the estimates for lunar landers from L2 with several different propellants. The lander+in space stage combinations show mass estimates for single stage landers that can land from and return to LLO. The mass of a single stage methane lander, including 4 ton habitat, is 20.9 tons, and with hydrogen it's 16.8 metric tons. According to the Boeing paper I referred to earlier, the empty mass of an Orion spacecraft is 14.9 tons; even with a specific impulse of only 316 (STS OMS) and a worst case 1200 m/s ∆V to return, the Orion has a mass of 21.95 tons in LLO. 20.8+21.95= 42.85 tons into Low Lunar Orbit, which fits within the 44.6 ton capability mentioned earlier. A more optimistic case with a hydrolox lander and 900 m/s return ∆V gives a total mass of only 36.8 tons, which fits very well and gives plenty of margin. This Lander uses a habitat that is actually bigger and with more supplies than the Boeing reusable lander, which carries 3 people for 7 days. While the SEI lander is designed for 2 people for 20 days, it could support a crew of 3 or 4 people for a full week, giving the lander similar capability to the Altair lunar lander for much lower mass. A Constellation class mission in a single launch could be possible with SLS Block 2.

Another option could be a mission to a Near Earth Object mission in a single launch. The mass of the notional habitat baselined by NASA has a mass of 23.9 metric tons. It has 72 m^3 of habitable volume and can support a crew of three for a year. Judging from the diameter, this hab would be based on the ISS MPLM module which is built in Italy. Combined with a fully fueled Orion, worst case mass of 24.2 metric tons, the mass of this spacecraft would be 48.1 tons. SLS Block 2 with in-space stage would be able to get this entire stack to a trajectory of 3760 m/s, enough to visit an asteroid. In fact, this is enough to send the crew to visit Mars, though the hab would require some mods to allow for such a mission time, and it wouldn't be able to do anything useful there.

The last option is a Mars Direct type mission. The 48.9 ton capacity to Mars with a C3 of 11 km^2/s^2. According to the NASA trajectory browser this is sufficient to reach Mars in 200-300 days, depending on launch window. That same browser shows plenty of windows to return from Mars with 800 m/s of delta V, or 2.3 km/s total including escape velocity. Assuming aerocapture to reduce MOI delta V to only 100 m/s and 2300 m/s to return, as well as methane/oxygen propulsion to return, a spacecraft of 48.9 tons would have an empty mass of 25.2 tons. This is enough to hold the propellant tanks and propulsion system (2.7 tons), a crew return capsule (8.94 tons) and an inflatable habitat (13.5 tons). That might seem small for such a habitat, but a study from SEI estimated the mass of an inflatable hab for a crew of three with 60m^3 of habitable volume at just 10 tons. Such an ERV, similar to the Mars Semi Direct approach, would be much roomier than the capsule-sized ERV Zubrin proposed in the original Mars Direct, which had a mass of just 7 tons.

All in all, it seems to me that developing Block 2 immediately instead of sticking with Block 1 or 1A has many advantages and it could very well be the right path forward. Unless the 130 ton requirement is dropped, upgrading to it will be necessary, and getting the upgrading out of the way will certainly help. It will all depend on what missions SLS is supposed to perform though. For any case though, getting as much out of SLS as possible certainly seems like the right way to do so.