Asteroids as Transportation Hubs

NEOstalk

This is a sketch from a post I did in 2009  about moving asteroids using their own rotational energy to sling ISRU mass  to change their orbit.

http://selenianboondocks.com/2009/09/moving-asteroids/

With Jons’ last post, I got to speculating about other ways of getting mass from an asteroid back to Earth. What if the exploring spacecraft carried a tether to the asteroid that was long enough to serve as a beanstalk. Instead of carting the selected boulder(s) all the way home, the beanstalk is used to sling a number of samples to Cislunar space to be caught by some TBD craft.

Instead of the thousand ton boulders slung in the original post, ten or so tons per throw would send a sizable mass to explore and exploit close to home while leaving the spacecraft in the field for a continuing mission. While as in the previous it would be necessary to wait for launch windows to use the tether,  the time between arrival and window could be spent exploring the body in question and organizing multiple throws. When the window opens, the ten (or one or thirty) ton samples could be sent Earthward every time the asteroid rotates. A four hour asteroid rotational day would give six launches per Earth day. A window a week long could have forty or so samples heading home at once.

If the asteroid is considered explored by that time to the limits of the available craft, it is time to head to the next target. One way of doing that would be for the spacecraft to climb the tether to well past astrosync orbit to a point calculated to sling it to the next body to be explored. At the right time, the tether is cut loose at the asteroid end to send the vehicle and its’ tether to a new little unexplored world. Once there, the cycle is repeated. It would seem that the craft could explore and exploit indefinitely without running out of propellant.

For a second phase of exploitation, tethers are left attached to the asteroids for use by future visitors. Eventually, spacecraft could visit dozens of rocks during an operational lifetime to prospect for different substances or to test new techniques in a variety of locations.

Certain asteroids would be exceptionally useful in a third phase if they proved exceptionally well suited for transportation hubs. Instead of slinging small robotic prospectors to other rocks, long beanstalks could relay humans and cargo to Mars and other points of interest throughout the inner solar system.

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Up in ARMs for No Good Reason

While there has been some slightly more positive discussion about the NASA Asteroid Redirect Mission since my previous blog post and SpaceNews Op-Ed, there have still been a steady stream of criticisms and suggestions of alternatives to the ARM mission being discussed lately. I’ve always been a bit of a knee-jerk defender of the underdog, and I still don’t think ARM is being given a fair shake by many in the space policy community, so I want to take the opportunity to respond to some of these criticisms and alternatives. And by respond, I don’t mean just dismiss–some of the suggestions have real merit, and could lead to ways to improve the existing ARM mission.

Criticisms/Alternatives:

  1. We should be looking for asteroids not trying to redirect them — This criticism is that before sending a mission to an asteroid, we should be making more of an effort to find the vast majority of NEOs that we still haven’t identified. I actually agree that a strong effort at identifying more of the NEO population would be money well spent. As I pointed out in a previous post based on a talk by Josh Hopkins about LM’s Plymouth Rock mission concept, more knowledge of the NEO population and orbits gives us more options and can only make missions like ARM and others better over time. I don’t think this should preclude doing ARM as well, but finding ways to invest more effectively in this area would be useful. Some suggestions for how we could do better here range from traditional approaches such as funding a NASA asteroid hunting mission or  doing a competition for industry provided asteroid finders, to providing matching funds or a free rides for more commercial missions such as what Sentinel and/or the prospecting spacecraft  Planetary Resources and Deep Space Industries are developing, to potentially offering a bounty for detection and verification of new asteroids. It doesn’t have to cost billions, but spending a bit more money in this area is likely to make ARM better, and increase our odds of finding dangerous asteroids with enough time to do something about them.
  2. OSIRIS-REx is already doing this — I’ve heard people criticize ARM because the OSIRIS-REx mission is already going to be returning samples from an asteroid before the ARM mission is flown, and thus we don’t need another mission. I find this argument as silly as Obama dismissing the Moon with his “Buzz has already been there, done that” argument. Just as the Moon is a world the size of Africa, and you can only learn so much from a half-dozen landing missions, how much are we really going to learn about the millions of asteroids in the NEO population from a few hundred grams of materials returned by a handful of sample return missions? How much do we really know about the consistency of material composition even within one single decent-sized asteroid? What are the odds that even two C-type asteroids are going to be identical enough that additional samples wouldn’t be worth it?
  3. We need a large number of samples, not a large sample — I partially agree with this argument–diversity of samples is important, but so is having enough quantity to actually be able to do useful ISRU experimentation. The multi-teaspoon sized samples provided by current missions might provide you with some idea of the chemical composition of at least that part of a given asteroid, but learning how to mine asteroids (and if we can do so in a way that makes economic sense) is going to take larger samples. One possible compromise that could give you the best of both worlds might be a multi-lander/grasper ARM concept. Instead of having one big 4m diameter boulder grasping system, ARM could potentially do 6-7 smaller (~2m) separable grasper/landers, attached to an ESPA-ring like structure, and the spacecraft could also possibly visit more than one asteroid during the mission. As commenters have pointed out previously, there are actually relatively low-delta-V multi-asteroid tours that can be done that go from Earth to several interesting locations along the way before returning to earth. That way you can get sizable samples and variety, maybe 1-2 carbonaceous chondrite boulders, throw in a nickel-iron sample or two, and then one or two samples from another asteroid types. While this may sound a lot more complicated, NASA has already demonstrated multi-asteroid rendezvous with missions like Dawn, and building 6-7 copies of a lander grasper system would actually mean that a lot of the complexity is offset by larger efficiencies of scale–with a Prospector-like Option B grasper mechanism, you’d be making dozens to hundreds of most individual piece parts instead of the one or two that you often see for more traditional science missions. If I get more time, I’d like to flesh this idea out in its own blog post, but I wanted to get it out there publicly in case I can’t find that time.
  4. You shouldn’t pick the boulder just on its pluckability — One concern was that the boulder would be picked entirely from a standpoint of ease of extraction. I agree with this concern wholeheartedly, but NASA has already indicated that they were are planning to include at least a basic sensor suite to help with picking an interesting boulder, not just an easy one.
  5. You should bring the boulder back to Earth Orbit instead of DRO, because that’s just make-work for SLS/Orion — This one also comes up a lot. The fact that ARM is bringing the boulder back to DRO instead of LEO is seen as somehow indicating that this is all just a make-work stunt. But the more you study the problem, the more DRO seems like a reasonable choice. Spiraling in to earth orbit from escape velocity takes >5km/s of delta-V with a low-thrust system, on top of all of the other . This would require either a refueling or two, or a much bigger spacecraft (about 2-3x the size), and would take a really long time. High Thrust-to-Weight SEP stages can take 6 months to 1 yr to spiral out from LEO to escape. But with a 40-80 tonne boulder attached, the T/W ratio for the return spiral would be 5-10x worse, which would mean 3-10 years spiraling through the van Allen Belts. If you use aerocapture/aerobraking instead, with such a large mass, you would need either a large aerobrake, a lot of time, or something like the magnetoshell aerocapture technology we’ve been supporting MSNW on. I’m obviously not opposed to that last option, but this would be a non-trivial additional system development. Plus, even if you could magically snap your fingers and get an asteroid into LEO, there would still be challenges. An asteroid in LEO would be easier to visit but would also be a debris hazard (especially as you try to mine it and accidentally knock dust or rock chunks off or it), would have to deal with a much worse micrometeorite/orbital debris environment than it would in DRO, would be unlikely to have enough T/W to dodge a detected conjunction with other dead space objects in LEO, and would require constant propellant for reboost. It’s not an entirely impossible, but it’s not as much of a slam-dunk as some seem to think.
  6. Grabbing a boulder has nothing to do with planetary defense — This is one of the more ridiculous statements I’ve heard repeated by otherwise very intelligent people. The reality is that unless you’re going to use nukes, the gravity tractor is probably one of your better bets for asteroid deflection. And because the mutual gravitational attraction is proportional to the masses of the two objects multiplied together, there’s a big benefit for being able to increase the mass of the spacecraft using local mass. What better way is there to rapidly increase the mass of your spacecraft via in situ materials than to grab one or more big boulders off the asteroid?
  7. We should do ARM just minus the whole going to an asteroid and bringing a sample back thing — That’s like saying we should go to Mars but without that whole going to Mars thing. I think people are laboring under a false belief that the boulder grasping mechanism is most of the cost of ARM–it probably isn’t. The spacecraft bus and human spaceflight follow-on mission are likely a much bigger chunk, and NASA has already indicated they’d like to do those even if ARM was canceled. Canceling the grasping mechanism is unlikely to save you much at all–maybe the equivalence of a CRS mission or two, or a few months of SLS or Orion development. Spending the vast majority of the cost of the mission but without actually achieving useful exploration or ISRU development would be a waste. Why do people think that play-acting at being astronauts out at DRO without an actual useful mission for them to be performing is somehow more grown-up than doing actual exploration and potential ISRU research?
  8. We should skip the asteroid and go to Phobos instead — This is one of the best alternatives (not surprising considering the source–I have a ton of respect for Wayne Hale), and while I think it’s not the best option, I wouldn’t be heartbroken if ARM was refocused in this way. One of the selling points of ARM was that it is relevant to future Phobos/Deimos missions–the ARM spacecraft can and should be designed so that it can be refueled and “re-clawed” and used for another destination. The marginal cost of a Xenon tank and another copy of the claw is going to be trivial compared to the overall mission development costs, and there are tons of good reasons for an ARM-like mission to go to one or both of those moons. We didn’t explicitly analyze the case of grabbing a boulder from Phobos/Deimos, but a NASA Langley team did, and found that you could get a 1-2m diameter boulder off of them using the existing Option B hardware–notice this is the same size as the multi-lander/grasper concept mentioned above. But by skipping out on the asteroid first, you would lose the ability to test gravity tractor techniques, which could be important, and asteroids are also interesting in their own right. So I’m torn. I’d rather do both.
  9. We shouldn’t do anything that isn’t directly on the quickest path to Mars — I probably won’t convince Zubrinites, but it turns out we have this whole Solar System that doesn’t just consist of Earth and Mars. If manned Mars exploration was something we could do quickly, within NASA’s existing budget, or if there were no other interesting or useful destinations along the way, it might be one thing. But even the committee members who are advocating for this have admitted we don’t have the money to do a manned Mars mission in the next 25 years without significant increases in NASA’s funding. While it has been poorly marketed, Flexible Path wasn’t just about “doing asteroids first” or doing them instead of the Moon or Mars. To me the underlying point was that even if Mars is the long-term goal, we should find ways to do interesting exploration along the way to Mars, even if some of those destinations involve slight detours along the way. When you’re talking about a destination over 25 years out, acting like a 3 month delay is somehow insufferable is flat out ridiculous.
  10. We should just fly an SEP module to Mars and back instead of ARM — While the concept of skipping the asteroid and going straight for a Phobos or Deimos boulder return option actually made some sense–I think the concept of building a big SEP just to fly out to Mars and back is plain ridiculous. We’ve already demonstrated the ability to use SEP systems to do multiple rendezvous with celestial bodies, as mentioned earlier. SEP technology is likely going to shift so much over the next 25 years that the only good reason to spend a lot of money building and flying a demo SEP system now is if we’re using it for something useful like ARM. Building an ARM-class SEP system and just flying it around with no greater purpose seems like a waste to me. And as mentioned previously, you’re not actually saving that much money by ditching the whole grasper thing.

I could go on, and there are other positive suggestions I could provide, like using a COTS model on the SEP module to make something that gets us the experience we want while still being commercially relevant. But I wanted to provide some more thoughts for the ongoing conversation. ARM may not have very good odds of being funded to completion, but it’s not because the arguments against it are actually all that sound.

Posted in NASA, NEOs | 10 Comments

Turbinozzle

Sometimes the ideas I throw out are obscure and hard to communicate, and sometimes they are so blindingly obvious that they have been rehashed many times in the decades past. Since I have no feel for which is which, sometimes I throw an idea to the wolves (that’s you) to see which it might be, and also to see if some of the follow ons are equally obvious, or not as it may be.

In my last post on the small tetherocket, the idea was somewhere in the middle. This is one of the possible follow ons that I have thought about before, but only decided to write out as my reaction to some of the feedback in comments.

turbinozzleOnce again my cartoon may be a bit difficult to read. The black lines at 3,000 m/s are expansion nozzles spinning on a tether complex as in the last post. The small rocket inside the curves is fixed relative to the ship with a suggested exhaust velocity of 4,000 m/s retrograde to the ship. The 4,000 m/s exhaust encounters the spinning nozzles with a closure rate of 7,000 m/s. The exhaust bends nearly 180 degrees in the moving nozzle with the gasses retaining the 7,000 m/s velocity relative to the turbinozzle. The gasses exit the turbinozzle at 7,000 m/s nozzle relative which is 10,000 m/s ship relative.  Net Isp just over 1,000.

I suggested 4,000 m/s exhaust velocity for the H2/O2 rocket as it would likely have a low expansion ratio to fit the envelope. I suggest that the near 180 degree turn in the turbinozzle channels would cause shock losses that would cancel any expansion gains from the nozzles.  I believe that the thrust/weight ratio would remain in the 1 m/s range for the bare engine.

This would retain the capability of using any fluid reaction mass available in the solar system from CO2  to water to impure methane if that is available ISRU. The rocket engine would need changing out to a steam engine using whichever fluid is available for a likely Isp in the 500+ range if I see the reactions correctly.

One of the comments suggested beamed energy and hydrogen only as a superior alternative. Nothing any of us said would preclude using beamed energy to drive the reactions. It would solve a number of problems with onboard power if available. Hydrogen may or may not be the reaction mass of choice. The tankage mass and handling properties may well make it second best even if it happens to be available at a particular location.

On one end of the conceptual capabilities is the possibility that I am pessimistic in the capabilities suggested. A larger envelope for the fixed expansion nozzle may make it  possible to get 4,500 m/s exhaust velocity from the fixed rocket which would add 1,000 m/s to the final exhaust for a total of 11,000 m/s exhaust velocity. It may also be possible to recover the energy from the turbinozzle heating to a higher velocity exhaust which could possibly add another 1,000 m/s to the final gas velocity then totaling about 12,000 m/s.  Hopefully the speculative possibility of Isp=1,200 will have a qualified person of two running a few simulations for the entertainment value.

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Small Tetherocket

Some years ago I posted an idea for combining tethers, rockets, and nuclear power to build an engine with very high Isp for orbital transfer operations. 750-850 seconds Isp with LH2/LO2 seemed and still seems possible. I am posting a follow on to that idea with some modifications suggested by commenters and some of my own.

 

The original post is at     http://selenianboondocks.com/2008/10/tetherocket/

spindizzy

In this cartoon, the spiderweb structure is a connected tether complex inside a pressure disk. It is powered up to 3,000 m/s by the onboard nuclear or solar power with the spin maintained by continuous power input.  The little angles on the tether tips are the throatless diverging combustion chambers. The LH2 and LO2  are sprayed into the path of the combustion chambers and both mixed and ignited by the 3,000 m/s impact. The pulse detonation burn will exit the combustion chambers at close to the 4,500 m/s characteristic of an LH2/LO2 engine in vacuum relative to the moving combustion chamber.

The small combustion chamber  expansion ratio is partially compensated by the impact heating and pulse detonation in the initial chamber. The near 4,500 m/s exhaust velocity is relative to the moving combustion chamber though and has a vehicle relative velocity of nearly 7,500 m/s. The exhaust then enters the single fixed high expansion ratio nozzle to finish expanding to as near vacuum as possible. The net exhaust velocity should be in the 8,000-8,500 m/s range.

I still see the T/W as being about 0.1 or 1 m/s acceleration with the bare engine and probably about a tenth of that including  vehicle mass. 100 cm/s would go from LEO to Lunar Transfer Orbit in about half a day using about 1/3 of IMLEO to do it.

Higher T/W than ion engines. No radioactive exhaust as in nuclear thermal and higher propellant densities to boot at similar net Isp. Switch to methane/Lox or any other bi-propellant  by changing two low pressure injector elements. Able to use inert gasses from ISRU anywhere in the solar system for Isp in the 450-500 range using the mechanical drive alone.

Posted in Uncategorized | 35 Comments

Precursor to Station

The comments on the torus station post made it clear that I had skipped steps in suggesting a specific station type. One step is the investigation of exactly how many RPMs are acceptable for a working orbital facility. The acceptable RPMs dictate the length of the station arms to achieve a given gee level. The required arm length or torus diameter needs to be known before design starts, and long before construction starts.

I suggest that an initial investigation on the ground could be a 10 meter radius unit with a 3 meter inclined floor around the circumference. There would be a bit over 190 square meters of available floor area when the unit is spun up. The floor area would be divided into offices, bathrooms, kitchens, bedrooms, and other requirements as needed.

The unit would be spun up to the design RPM for that particular design. There would be one acceptable RPM for any fixed floor angle with several different units for different investigations. This would be terrestrial construction and relatively cheap compared to anything launched which would make multiple units on the ground affordable compared to launching sub-optimal stations.

The unit is spun up to design RPM with the intention that it will spin continually for several months at a time. Several shifts of investigators work in the facility on short and long term ‘missions’. Some works 8 hours plus lunches and go home at night exiting through the hub without stopping the unit. Entry, exit, and transition through the spokes would be part of the experiments. Others stay for 30 days straight, while yet others do business visits of minutes to hours.

The purpose would be to determine whether 10 or more RPM can be adapted to in a working environment. I would see the experimenters as being  perhaps one department of a company or government facility totaling between 20 and 100 people on a near continuous basis plus many visitors. The quality of an individuals work compared to their normal performance in regular environments would be a good baseline to prove/disprove the possibility of very short radius stations for people in high stress and workload environments as during a space mission.

The long term investigators would exit fairly often for family functions and such which would be the  spin equivalent of going to the microgravity sections of the station or an EVA. The ability to conduct the investigation without missing the kids recital or your wedding anniversary would make it possible to get long term volunteers.

After determining the acceptable RPMs for people in a real working environment it wold be much easier to design a real working station. A 5 meter spin radius in orbit is a totally different animal than a 1000 meter radius. If the ability to adapt to high RPMs eliminates 99% of the population, then there would still be about 3 million people in this country to select from plus several times that number world wide.

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YHABFT: MIT MarsOne Analysis — Alternative Solutions to the Excess O2 Problem

A few months ago, a group at MIT did an analysis of the MarsOne mission that was fairly critical of the concept, on technical grounds. This week’s FISO telecon featured an update on the analysis they performed, particularly on the issue of the excess oxygen problem, and I wanted to make a few comments on what I read that were a little too long for twitter.

First, before I get to some alternative solutions to the excess oxygen problem, I did have one thing I noticed that surprised me–the caloric requirements. On page 19, they talk about a 3040 calorie per day diet per person. That seemed a bit on the high end. The only people I know that consume that many calories without getting fat are people with really active lifestyles (mountain climbers, marathon runners, etc). I wonder if those numbers came from ISS experience, where the effects of microgravity force them into a very strenuous exercise routine in the hopes of not having too bad of bone/muscle loss. This is one of those areas where knowing how much hypogravity we need would be really important. If you didn’t need anywhere near ISS-like exercise requirements to maintain health in a Mars-gravity environment, that would likely cut down significantly on the required calories, and might shift the ratio of carbs/proteins/fats from what was assumed on this page.

Now, moving on to the “excess oxygen problem”. Basically, using plant-based life support, and using the biomass numbers MarsOne estimated would be required to supply the required amounts of carbs/proteins/fats, they found that the plants produce too much oxygen. This leads to venting atmosphere overboard, and trying to make up with other constituents, leading to hypoxia. Their suggested solution was to isolate the plants, and come up with some sort of oxygen scrubber for storing the oxygen elsewhere for later use on EVAs and such.

But I think they may be overthinking this a bit. Here’s a few suggestions of alternative ways of solving the problem:

  1. Small animals (pets or food): The assumption in this analysis is that you only have humans and plants. Plants consume CO2 and produce O2, and humans produce CO2 and consume O2, and some fraction of the plants. What if you brought small animals along? Something that could eat parts of the plants inedible to humans. Could you increase the effective O2 consumption enough that way to counteract the rising O2 levels? If you picked something small that was edible (chickens? Cornish game hens? fish? etc.) it might allow you to replace some of the vegetable biomass dedicated to protein and fat production. I don’t know if this would completely solve the problem, but whether you eat the animals, or keep them as pets, it seems like you might have at least part of a solution there.
  2. Just Burn It: When you have an excess of O2 and a deficit of CO2 it seems like a combustion process might be in order. It would be relatively easy to take some Martian air, split it into CO and O, vent or store the O, and then run the process in reverse to combine CO with excess oxygen inside the habitat. This could be done to provide extra power at night using a solid oxide fuel cell. If this produces too much CO2, that’s easier to scrub using existing technology than O2 is. If you don’t feel safe handling CO in the habitat, turn it into CH4 using a Sabatier reactor, and burn that and recover the excess water from the combustion to put back into the Sabatier reactor.
  3. Mixed Food Sources: It might also be possible to pick some mix of food sources (some of it dehydrated pre-packaged food from earth, some locally grown) so that you optimize what you’re growing locally. For instance, if it turns out that your carbs are taking up the most area and generating the most surplus O2, maybe you can have more of those come in dehydrated ingredients from Earth for a while.

Ultimately, I don’t want to look like I’m ripping on the MIT team. They’ve done a very thorough analysis, and it’s almost always easier to point at potential flaws in an existing analysis than to create one from scratch. I just wanted to suggest some potential solutions. I particularly like #1. The whole idea of space colonist having to go 100% vegetarian always struck me as somewhat nutty. There definitely should be additional research to see if you can strike a balance with primarily biologically-closed life support in this way, but it seems like an obvious angle for further research/development

Posted in ISRU, Space Settlement | 15 Comments

Random Thought: Simulating Mars Speed-of-Light Delays on ISS

[Note: I’m almost positive this isn’t a new idea, but I figured I would share it, just in case.]

One of the many concerns with deep-space human spaceflight missions, is that all of NASA’s experience has been with missions close enough to Earth that mission control could be in direct and nearly instantaneous communication with astronauts. Worst case round-trip speed-of-light delays for the Apollo missions were on the order of 2.5-3s or less. But for missions even to NEOs, let alone Mars, you quickly end up with round-trip speed-of-light delays on the order of tens of minutes, to over 3/4 of an hour worst-case at Mars. It is a legitimate concern that NASA’s practical experience in mission ops has been so used to mission control being able to provide almost instantaneous feedback when problems crop up.

One very cheap way to fix this might be to intentionally start simulating speed-of-light delays between ISS astronauts and mission control (and visa versa). There are very few problems on ISS that really need real-time mission control help, and getting used to dealing even with problems with a built-in time lag would be useful experience for deeper space mission. If NASA can’t stomach the risk of doing this with a big space station like ISS, I can’t imagine they’ll ever have the intestinal fortitude to really do a crewed deep-space mission.

If desired, NASA could theoretically start with only a small delay, and then gradually build to longer times. For instance, once commercial crew starts flying, maybe they intentionally swap the whole USOS team out at once (instead of staggering the replacements like they do right now). Then start initially with no lag, but adding lag little by little, at about the rate that it would build up for a mission to an asteroid or Mars. You might make some exceptions for communication between astronauts performing research on the ISS and the ground subject matter experts they’re working with (since ISS isn’t just about preparing for deep space, but also about performing useful research), but make sure that they’re not allowed to talk with other NASA folks except via the speed-of-light delay simulated communications link. Also keep communication with friends and family on the ground routed through that delayed link as well.

My guess is that if they started performing this experiment on a regular basis, they’d likely learn all sorts of new things. Some things they’ve done in the past may translate fairly well to a delayed environment, while large parts of how they do things now may have to change. But really, if NASA wants to prepare for deep-space missions, why not start now when the risks are low? Not only would the mission control people learn better how to interact with crews at long distances, but those crews will also be gaining experience with interacting with mission control at long distances. My guess is even if a commercial deep space mission isn’t done exactly as NASA would (fairly likely), that there’ll still be all sorts of useful lessons learned that could be passed on.

And really this experiment wouldn’t cost hardly to add to the ISS manifest.

Does anyone know if NASA has thought of doing something like this? Any suggestions on how to run the experiment better?

Posted in Lunar Exploration and Development, NASA, NEOs, Space Exploration | 16 Comments

Launching a Torus Station

A torus space station is one of the staples of future thinking. Launching it in one piece from the ground is not. It has however, been occasionally mentioned in various comments. Here are a few numbers on the idea a few of us have kicked around from time to time.

Assume a 100 meter torus with a 10 meter minor diameter. 23,000 net cubic meters of internal volume should do for a start. A 50 meter radius that is not enough for an Earth gravity at under 4 rpm is sufficient for lower levels of artificial gravity that may mitigate some of microgravities’ harmful effects. It is getting it up there that seems to be a bit of a problem.

10,000 square meters of station surface would mass 540 tons if we assume the skin has the equivalent mass of 2 centimeters of aluminum including insulation, braces and such. Internal structure and furnishings would have to go up in subsequent flights. 540 tons in orbit would require something over 10,000 tons GLOW. This is heavy launcher country. Fortunately the internal volume of the torus is sufficient for fuel tanks.

Bladder fuel tanks inside the station could mass under half a percent of fuel mass, while LOX could be carried with simple bulkheads in the appropriate sections. Sooner or later an F1 equivalent will become operational at reasonable prices. 15 of them could push the torus edge on with a sled take off to avoid building launch towers and such. This would be a near SSTO with just engines dropped off for recovery at designated velocities when they are no longer required. Final push to LEO could be with just one engine with all the others recovered from various suborbital velocities.

How the station would be equipped and used would be up to the parties that paid for it.

Posted in Uncategorized | 30 Comments

PhD Dissertation Idea: NEO Trade Network Analysis

Frequently I wish I could afford to have a personal orbital dynamics minion that I could have run analyses for me whenever I have a complex orbital dynamics question and would like to test my intuition. Unfortunately, Altius isn’t successful enough yet for me to afford that luxury, and while we have friends and advisors with the relative skills, I don’t have enough money to have them run every analysis I’m interested in. So I figured maybe I could toss this out as a potentially useful topic for someone’s PhD dissertation instead.

Short version: I’d like to do an analysis to see how hard it is (in delta-V, travel time, and launch window frequency) to get from one NEO to another, versus going from a NEO to a planet and back.

I’ve got a lot of friends (bless their hearts) who like to turn up their nose at poor benighted planetary chauvinists, and who go on and on about “once you’re out of a gravity well, why would you want to go back into one?” My intuition suggests they may be wrong, but I’d like to see numbers to either back up my opinion, or shoot it down. My intuition suggests that without atmospheres or the Oberth effect, you’re going to pay big delta-V penalties at each end of the trip, unless the synodic periods are really really long.

My thoughts on how to run the analysis:

  1. Before you start, pick some subset of the NEO population above a certain size (say 100m diameter, or maybe 1km depending on available computing resources). Gather ephemeri for all of them.
  2. Pick a random NEO in that group.
  3. Depending on computing resources pick some specific number of other asteroids to analyze (say 50 or 100 or 1000), and randomly select them from the population.
  4. Calculate pork-chop plots for travel from the initial asteroid to the other asteroid, and then back again.
  5. Automatically extract from the pork-chop plots say the minimum delta-V for both legs of the trip, and the associated trip times, stay times, and estimated revisit frequency.
  6. Run steps 4 and 5 using the Earth, Mars, and Venus as destinations, both with and without aerocapture/aerobraking at the planet end.
  7. Repeat steps 3-6 a bunch of times (say 100 or 1000 times depending on how much parallel computing capability you have, and how thorough you want to be).
  8. Analyze the data.

My hunch says that especially if you have aerocapture, you’re going to find that most of the time it’s easier for a given NEO to regularly “trade” with planets than it is with other NEOs, because you can both take advantage of the Oberth effect on departures from the planets, and you can take advantage of aerocapture on the way in. But I’d love to see someone run the numbers–I could be completely wrong.

An analysis like this would be really useful for figuring out what trade networks might look like in the future between NEOs and other solar system entities. If it turns out it’s much harder to get from one NEO to another on a regular basis, as my intuition suggests, it would suggest planets may remain the trade hubs with NEOs being more mining bases. If my hunch is wrong, maybe I owe my NEO-chauvinist friends an apology. :-)

Bonus points if you can run the analysis using both high-thrust impulsive maneuvers as well as low-thrust, high-Isp maneuvers (like Solar Electric Propulsion systems can provide), to see if SEPs noticeably change the equation–I really have no intuition on how realistic SEPs change or don’t change the equation for NEO transportation.

Posted in NEOs, PhD Dissertation Ideas | 11 Comments

Top 10 Reasons Why Something ARM-like Is Worth Doing

[Up-front Disclaimer: My space startup is being paid under the Asteroid Redirect Mission BAA to do a study contract on one possible way to do the Option B mission. Even though we’re not dependent on follow-on work, I figured it was worth stating up front my potential biases.]

I’m not sure I’ve ever seen a major NASA program as nearly-universally disliked as the Asteroid Redirect Mission. Some people hate it for ad hominem reasons like the fact that the Obama Administration has been pushing it, or the supposition that Darth Garver (as they see her) came up with the idea. I’ve also heard a few anti-SLS/Orion people refer to it as a “pathetic attempt to reengineer the Solar System to make it handicapped-accessible for SLS and Orion”, or to come up with something for SLS and Orion to do that is more inspiring for them than endless Apollo-8 rehashes (but without the subsequent Apollo missions to follow). Ironically, I think some of the pro-SLS/Orion fanboys on the internet who hate it are afraid that ARM doesn’t really need SLS or Orion (which is true to some extent–in a NASA where Human Spaceflight was done more with PI-led, competitively selected, not-overly-politically-driven missions, I bet few PI’s would be suggesting SLS or Orion for this mission). Some of the Small Bodies scientists seem to hate it because they see it coming from the human spaceflight side, and think the whole thing could be done better without humans involved, and it wasn’t invented there anyway. All told, lots of people find lots of reasons to hate this mission.

But I wanted to provide 10 reasons why a mission like ARM might be actually be worthwhile:

  1. Adding a new, even more accessible moon to the Earth-Moon System: A lot of people fixate on the fact that we’re going to spend all of this money for a couple of astronauts to go out to a rock in lunar orbit, climb over it for a few days, and bring some samples back. What they conveniently ignore is that >99.5% of the material brought back will still be there, orbiting the moon for the next several hundred to several thousand years, in a fashion that is easily revisitable for a long time (docking adapter pre-attached, and at least for a while still attitude stabilized). And this new moon would be about as hard to get to as L1/L2. Which means that yes, future missions to it using a lightly modified CC vehicle are totally possible.
  2. Providing an ideal testbed for Asteroid ISRU development: Many people, including many of my friends, see the asteroids as the premier source of vast quantities of off-world resources. But while there are no shortage of low-TRL concepts for how to extract resources from asteroids, actually testing those out isn’t going to be easy. I think testing will be much easier when you have the ability to send people and robots, when you’re close enough that teleoperation of robotics is an option, and when you have frequent repeat visit opportunities where you can try new approaches, and where you can do your testing in a microgravity or near microgravity environment, like you would have at an asteroid.  I’m sure prospective asteroid miners like DSI or Planetary Resources wouldn’t complain about having one or more easy-to-access testbeds to work with.
  3. Providing a much larger sample quantity to work with than other existing or proposed missions: While scientists may be happy spending $800M to return 60g of material from an asteroid (OSIRIS-REx), and can likely tease out all sorts of information from that two Tablespoons worth of material, ISRU development needs a lot more material to work with. Even the smallest of Option B concepts I’ve seen brings back tens of tonnes of material, both rocky and regolith, which should be plenty to work with for ISRU development.
  4. Providing a good way of testing out a man-tended deep space habitat: As was reported by Jeff Foust at SpaceNews, one of the ideas NASA is looking at incorporating into ARM is attaching a prototype deep space habitat (possibly commercially derived if the NextSTEP BAA leads somewhere useful). This would allow visits of up to 60 day duration by crews of up to 4. While there are other ways you could test something like this (such as L1/L2 gateways), testing it in an operational environment would be useful. As would demonstrating the ability to do long-term habitation in close proximity to an asteroid.
  5. Demonstrating large-scale Solar Electric Propulsion (SEP) systems: This is one of NASA’s main interests in the ARM mission–in the land of expensive launch vehicles, very high Isp propulsion like you can get with SEPs can make many missions a lot more affordable. Even with low-cost earth-to-orbit transportation, SEPs probably make sense for a wide range of missions. Demonstrating the ability to use large-scale SEPs for tugging huge objects in heliocentric space, and performing precision injection maneuvers, etc. might be very useful. We already have a fair deal of experience with small SEP systems, but doing these sort of missions with 100kW+ class SEP systems can be pretty useful.
  6. Demonstrating Planetary Defense Techniques: If something like “Option B” (the grab a boulder option) is selected, NASA is interested in demonstrating the Enhanced Gravity Tractor method for deflecting the parent asteroid (see slides 27-29 of this presentation on Option B). Learning how to deflect potentially hazardous asteroids is probably one of the more worthwhile things NASA could be spending money on right now, and providing a way of getting real hands-on experience applying those techniques would be very useful. We have lots of theory on how this would work, but getting experience with a real, lumpy, non-idealized asteroid of significant (>100m) size would be really useful. And contra some of their critics, using a “Rube Goldberg arcade claw” to pick up a boulder and increase your spacecraft mass by 5-10x is a great way of allowing you to get measurable results in a reasonable amount of time.
  7. Developing Technologies for a Phobos/Deimos Large Sample Return: One of the keys to affordable exploration and settlement of Mars will be determining if Phobos and/or Deimos have water in them, and if so, figuring out how to extract it efficiently. Having a large source of propellant feedstocks available in Mars orbit (for supersonic retropropulsion on landing, hydrogen feedstock for surface ISRU, and earth-return propellant) could significantly reduce the amount of propellant needed for both round-trip and one-way Mars missions. If Option B is selected, and if it designed properly, it would be possible to use the same hardware (with slightly modified CONOPS) to capture and return a decent sized (>1 tonne) sample to lunar DRO for evaluation and hopefully ISRU process development/debugging. A manned Phobos and/or Deimos mission is something I strongly support in the future, but if they had enough info that they could be setting up a propellant extraction facility while they’re there (that we’ve already pilot-tested in cislunar space so we know it has a high probability of working), that would just be awesome.
  8. Providing the Beginnings of a Lunar Gateway?: It turns out that getting to and from Lunar DRO, and getting to/from the lunar surface from a Lunar DRO aren’t massively different from getting to/from Earth-Moon L1 or L2. The orbital dynamics is a bit more complex, but the propellant and travel times are relatively similar. And some lunar DROs can be long-term (centuries or millennia) stable without active stationkeeping. While if we were ready for going straight to the Moon (I’m actually a bit of a Moon-Firster believe-it-or-not), L1 or L2 might be slightly preferable to a lunar DRO as a location for a lunar gateway, if we did something like ARM, with the habitat module, you’d already have a de-facto start to a lunar gateway. One that will likely be setup (by NASA or follow-on efforts) with ISRU hardware, which would likely include at least rudimentary LOX/LH2 and/or LOX/Methane storage and handling capabilities (after all, if they’re going for a carbonaceous chondrite sample, extracting water will be a key part of what they’d be trying to prove). While this wouldn’t likely provide anywhere near enough fuel storage for a Constellation-class mission, it might provide enough propellant to refuel a “Golden Spike” class lander. And even if the asteroid itself only yields a mission or two or three worth of propellant, the tanks and handling equipment would be there and it could make shift as a miniature depot for earth-launched and eventually lunar-derived propellants. Lots of details have to be done right to make this feasible, but it’s possible that ARM could be done in a way that make future lunar missions easier.
  9. Providing More Experience with On-Asteroid Operations: If the Rosetta/Philae mission should tell us anything, it’s that there’s still a ton to learn, from an engineering standpoint, about how to operate successfully on the surface of large, low-gravity objects like asteroids or comets. While we’ll continue to get some small-scale experience using other robotic missions, and while a manned mission to a free-range asteroid will also provide a good way to get more data, ARM will likely extend our knowledge about how to do operations like these safely with large objects, and would likely provide good data increasing the likelihood of success of future manned missions to free-range asteroids.
  10. Leaving Something Permanent: One of the saddest things about the Apollo missions is that they didn’t leave anything permanent that made future missions any easier. When they were canceled all that was left was museum pieces, pictures, and a few hundred kg of rocks. But the nice thing about ARM is that once the asteroid sample has returned to lunar DRO, it’s there. It doesn’t require continued expenditures from NASA for it to stay there. Until we’ve mined every last kg of it, it’s going to be there orbiting the moon, close enough that almost any spacefaring country or business in the world can reach if it wants to. It doesn’t need an ongoing standing army that can be defunded. It doesn’t need a mission control to watch over it 24×7. It doesn’t need some sustaining engineering contract that’s going to suck up significant portions of NASA’s limited human spaceflight budget on an ongoing basis. It’s just there. Ok, if there’s a hab there or a more sophisticated node, it could require ongoing mission support when being used. But if for some reason they decided to stop visiting that node for a while, it would still be there, waiting to be restarted whenever someone cares again, or ready to be handed off to private companies or international partners once NASA is done with it. At least for a few centuries. Having something that accessible and that permanent out there is worth something, at least to me.
Posted in Commercial Crew, International Space Collaboration, ISRU, Lunar Exploration and Development, NASA, NEOs, Space Development, Space Exploration | 23 Comments