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 | 8 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 | 18 Comments

Wild Data-Free Speculation on the SpaceX Landing Attempt

First, before saying anything else–congrats SpaceX! Both on the successful launch, and on coming so close to a successful recovery as well! If SpaceX’s competitors aren’t feeling the heat yet, I don’t know when they will.

As most of you have probably seen, Elon tweeted that while the rocket made it back to the drone ship, it hit at too high of a speed for successful recovery. But as of the time I started this blog post, they haven’t provided any more details.

So, in the grandest tradition of the intertubes, I would like to wildly speculate with almost no data on why they hit too fast. Being a former VTVLer, I have a few theories:

  1. GN&C Failure Modes: This category of failure modes relate to either the rocket not knowing precisely where it was/how fast it was going, or making the wrong decision on how to bring it in for a successful landing.
    1. Navigation Error: In this failure mode, the rocket either thought it was in the wrong place or going at the wrong speed. Ie it thought it was higher up and still had time to decelerate, or thought it was going slower than it really was when it hit. I think these are relatively unlikely–in order to stick a landing with a minimum throttle setting near 2G’s, you need to know very precisely where you are and how fast you were going. SpaceX knew this, so they probably put tons of resources into making sure this was done right. I wouldn’t be surprised if they had some sort of differential GPS “ground station” on the drone ship, combined with accelerometers to back out a very good estimate of GPS errors that could be sent to the rocket. Unless they made some implementation error (I doubt it based on the fact that they got the rocket all the way back to the drone ship), the rocket probably knew where it was to within a couple of cm, and probably knew how fast it was going to within a few cm/s.
    2. Guidance or Control Error: In this failure mode, the rocket knew where it was and how fast it was going, but made some poor decision about how to command the engines in order to bring it to a stop on the pad. For instance, not turning the engine on when it should’ve, or going to gentle on the throttle at first. Once again, I think this one is pretty unlikely, especially with the experience they have with regular F9 flights, previous ocean landings, and F9R dev1 flights.
  2. Engine Issues: This category says that the engine for some reason or other didn’t produce the thrust desired at the time desired.
    1. Relight Failure: In this failure mode, the engine either didn’t relight at all for the final burn, or relit too late (maybe after an unsuccessful first relight attempt). While SpaceX knew this was important, making a complex rocket engine that can relight correctly every single time, on-time, is really hard. That said, knowing this, they probably had some sort of backup plan in case the engine didn’t relight (maybe light two outer engines, and do a faster hover-slam?). This sort of failure mode is why I’ve started gravitating back toward helicopter landing in my rocket philosophizing.
    2. Engine Underperformance: In this failure mode, the engine was behaving sluggishly, underthrottled, or something else. I think this is somewhat unlikely, but possible.
    3. Engine Shut Down Inadvertently by Computer: In this failure mode, the computer saw a sensor reading it didn’t like, and shut the engine down. Knowing that this would doom the vehicle, and that the odds of false-positives is high, if I were SpaceX, I would’ve either disabled this capability entirely, or made it really hard for the vehicle to decide to shut the engine down in this situation. The engine should give its life for the vehicle, not the other way around.
    4. Engine Ate Itself: In this failure mode, the engine had a failure. Either a hard start, or a failure after ignition. Totally possible, and hopefully this is something they’ll have data to easily determine whether or not this happened.
  3. Premature Propellant Depletion: In this category (the most likely one IMO), the rocket ran out of propellant or the engines were starved of propellant before successfully nulling out all of the velocity. I.e. They ran out of gas and hit fast–seeing as how Elon didn’t give a lot of details about how fast the impact was, this is my guess.
    1. Less Landing Reserves Than Planned: In this case, for some reason the F9R first stage used more propellant either during the flight itself (due to off-nominal engine performance or something else–I didn’t get to watch the flight yet), or during the two burns prior to the final landing burn. Basically they got to the burn, but just didn’t have enough gas left.
    2. Too Big of a Divert Burn: This may be a variant on 3A, but it’s possible the grid fins got them only so close to the drone ship, and they had to do a big divert burn in order to get back to the drone ship, resulting in having insufficient fuel to finish the maneuver. This one seems the most likely to me, since getting back to the drone ship always seemed like the hardest part of this mission. The good news is if this is the case they can solve this by refining the grid-fin controls, adding more propellant margin, or some other combination of solutions (maybe an extra divert burn a little higher up where it does more good?). As I said, I think this was the most likely failure mode.

There are probably tons of other possible explanations, but those were the ones that popped out to me. Once again, I was doing this as a total fanboy, wanting to speculate about what happened, not in any way a diss on SpaceX or their team. Hopefully once SpaceX has reviewed the data, they can share the conclusions with the rest of us. It’ll be fun to see if any of my guesses were right.

In the other grand tradition of the internet, feel free to speculate in the comments as well!

Posted in SpaceX | 16 Comments

Random Thought: Dragon V2 as an xGRF Platform?

Review: How Much Gravity Do We Need, and Why Do We Care?
One of my hobby horses that I’ve blogged about a few times is the question of how much gravity do humans need to be healthy? As I’ve pointed out in the past, we know microgravity is awful for people long-term, and 1G is fine, but we really don’t know what number between 0 and 1G is the minimum that a typical person needs to avoid unacceptable health degradation.

ReducedGravity

Which Curve is Right? How Much Gravity Do We Need? Is There a Knee In the Curve? If So, Where?

Why do we care? This topic came again today in the context of a twitter conversation about Mars colonization. Obviously, if the magic gravity level people need is higher than 0.38G (Mars gravity), Mars colonization is going to be harder than if it is lower than 0.38G. If the minimum required gravity level is more than Mars levels, you’ll need to come up with some sort of countermeasure on Mars, or face potentially severe health issues over time. This may involved a mix of biochemical countermeasures (drugs), exercise, and even small centrifuges–all of which have large potential drawbacks. If it turns out that the minimum required gravity level is less than 0.38G though, life becomes a lot easier. You might want to do something about the microgravity on the flight out, but wouldn’t have to deal with countermeasures after you landed. And if you went the artificial gravity route on the way out, you wouldn’t need to provide as much of it, which would make the system size a lot smaller and more manageable–for a given max spin rate, the centrifuge radius is inversely proportional to the gravity level required–for lunar gravity you’d only need 8m radius at a 4rpm rotation rate.

But while many in the space community have pointed out the importance of answering this question, and joked about how nice it would be to have a national space program to answer questions like this, no real progress has been lately. Most of the potential solutions have been too expensive to raise the money for. What is needed is a way to start getting the data as cheaply as possible. Hopefully well less than $50M if we want a realistic chance of getting NASA or private donors to fund it.

Dragon V2 as an xGRF Platform
While the idea came to me based on some of the ISS visiting vehicle post-mission reuse ideas we’ve been looking at at Altius, when doing a little research for this blog post, I found that this idea was originally suggested by A. M. Swallow and googaw in comments to my previous post. I usually blow those two off, but they were right a lot sooner than I this time around. The idea is basically using the pressurized volume of a repurposed Dragon V2 as the habitat for a 1-person (and many mouse) version of Kirk Sorensen’s xGRF concept. While there is a lot more info in the previous blog post on xGRF, the high level version is you start with a habitat connected via a variable length tether to a counterweight. As shown below, when the tether is all the way out, the system will settle into a gravity gradient orientation, completing one rotation per orbit. By winching in the cable in the right manner, conservation of angular momentum causes the rotational rate to spin up, creating higher levels of artificial gravity up to a peak level with the tether at its minimum length.

xGRF_spindown

xGRF in a Nutshell

For my Dragon V2 variant, here are some key points in the concept (which is still only partly baked):

  1. You would use a Dragon V2 after it has launched a crew to the station. All but one member would board the station while the last crew member stayed aboard for the experiment. After successful completion of the mission, the Dragon V2 would return to the station to pick up the crew for return to Earth.
  2. You’d have mice on board as well as the human for two reasons: to give the person something useful to do so they don’t go crazy being by themselves for a few weeks or months at a time, and because you can get a lot more data points in a small volume with mice than you can with humans. While the human data is very useful, the mice might give you a better idea of the variability of the effects.
  3. You’d try to locate the Dragon V2 xGRF experiment as close to the station as you could get while still factoring in the risk of tether breakage–Kirk’s paper shows that at station altitudes a tether break wouldn’t lead to immediate reentry, but you’d want to make sure it also had a negligible probability of hitting the station. But if possible it would be great if you could find a position close enough that you could visibly see the station. Being alone for long periods of time might not be so bad if there are people within easy visual range that you can communicate with with no delay.
  4. You’d probably leave the xGRF kit attached to the Falcon 9 upper stage, but tucked into the trunk volume. This kit would include a dumb docking port, the tether/winch system, any required solar panels (if the solar panels on the trunk of Dragon V2 aren’t enough), and possibly inside the docking port some extra life support equipment/consumables (if you can’t cram enough into Dragon itself). Once the crew going to ISS were offloaded (along with most of the launch couches, and the vehicle configured with the mouse and its one human inhabitant for the experiment), it would leave ISS, re-rendezvous with the upper stage, dock with it, maneuver it to the experiment flight position, and then deploy the xGRF system.
  5. You’d probably want to make sure you had way to do a lot of telepresence, to keep the volunteer from getting too lonely. Two people might be psychologically nicer, but a lot harder to cram into a 10m^3 room for long periods of time. Telepresence coupled with being in visible range of ISS might mitigate the issues with having one person flying solo on a mission like this.
  6. You’d probably want to pick an astronaut who had flown a few times before, so you’d have pre-existing data on how their body responds to microgravity, to use as a comparison point. It’s not perfect–long term you’d want as many human data points as you can get, but at least with someone who has flown a few times already, you wouldn’t be dealing with a completely unknown quantity as far as space physiology reactions. If they weren’t already burned out, having twins like Mark and Scott Kelly do the experiment, with one on ISS and one on the xGRF platform might also be an interesting way of screening-out some potential genetic effects.
  7. The most interesting data is if the minimum required gravity level is less than Martian gravity levels (less than lunar would be even better). If it turns out it’s higher than that, Venus and Earth become the only realistic solar system destinations that you could live at without expensive countermeasures. So it might be worth intentionally designing the system for a maximum of say 0.4G at say a little under the 4RPM max limit that people like to stay under. With the upper stage potentially being a larger chunk of the xGRF mass than Kirk’s original paper suggested, this would greatly reduce the required tether length, making the system lighter and more manageable.

Some potential concerns include:

  1. Is 10m^3 enough volume for one person for long durations? I don’t know for sure, but if I’m not reading it wrong, a quick skim of this reference suggests that 10m^3/person might work for durations up to 3-6 months.
  2. Can the Dragon V2 without structural mods handle the loads in question? I would think so–the docking port is usually resisting a pressure load on the order of 15psi acting on the cross-section of the passageway, which is at lest 30in in diameter–yielding pressure loads of >10,000lbf they’re designed to resist. My guess is the loading would be similar in this situation, so probably something that could be handled without modification.
  3. Can Dragon V2 support 1 person on-board for long durations (>3wks) without expensive modifications? I’m less confident on this one, especially since the life support would be acting in partial gravity instead of zero-gravity. Everything I’ve heard suggests that even a little bit of gravity (for fluid settling and natural convection) can make many things a lot easier, but I’m not sure how much could be done leveraging existing hardware and interfaces, and how much would have to be done semi-custom. The less mods the less development cost. Fortunately, aborts to Earth or aborts to ISS can likely be done quickly enough that if life support stuff starts breaking down, there are plenty of quick rescue options.

The biggest question of all is how much would something like this cost, and would it be cheap enough to cross the line into something that could actually get funded? By reusing a Dragon V2 that’s already going to the ISS, you might only have to pay the delta-cost of operations and of the xGRF module. Could you keep that below $50M? Below $10M?

My guess is you’re almost positively above the $2M-ish limit of what is demonstrably crowd-fundable. But are you too high for a wealthy philantrocapitalist? I’ve heard that part of why Dennis Tito suggested Inspiration Mars was that he wanted a way to invest some of his money into making a lasting difference in the development of humanity in space. Could you get the cost low enough that Dennis, or someone like him, could chip in the money? Could you do this with NASA as a partner without NASA’s safety culture turning this into something so expensive it never flies?

Anyway, it’s some food for thought.

Posted in Commercial Crew, Commercial Space, NASA, Space Development, Space Settlement, Space Tethers, SpaceX, Variable Gravity | 30 Comments

ULA Stage Recovery

George had a thought in comments on the last post that could easily be relevant. If SpaceX starts reusing the Falcon9 cores, which are the cheapest cores in current production, then how much more financial sense would it make to reuse the SLS cores? The success of SpaceX could put pressure on NASA via the taxpayer to save the hundreds of millions of dollars per launch of the SLS system.

NASA may be the wrong target. ULA has quite expensive Atlas and Delta cores that they should have a financial interest in recovering. The Atlas could use some fairly small kerosene/LOX engines from in-house or any number of suppliers, including XCOR and Masten. Any number of small firms now have in-house expertise on vertical landing systems. Adding a small number of pressure fed engines for the landing sequence would add weight and complexity, with these engines optimized for sea level operation could also be used to increase allowable GLOW.

After main engine cutoff of the booster, residual propellant could be pumped into one of the empty helium spheres. There will be time in between main engine cutoff to compress helium from the main tanks into the new repurposed landing tanks. It seems possible that a minimal amount of hardware would but need to be added to the stage.

The Delta system could use the RL 10 and Delta Clipper software so as to use the same hydrogen propellant as the RS 68. This could use known systems to recover quite expensive hardware.

Posted in Uncategorized | 19 Comments

Pressure On SpaceX

Sometimes seemingly unconnected events can have an effect out of proportion to what seems rational. In this case SpaceX, having no connection to Orbital or Virgin Galactic, will have its next flight partially judged on the misfortune that fell on the other two companies. While there is no rational connection, in much of the public eye they are all commercial companies that stand in opposition to NASA. The negative tweets and comments that have accompanied the two failures have already affected some people’s minds on the viability of independent companies performing critical launch services.

The near worship of NASA by people with less information than most of the people reading this blog as the agency that got us to the moon, casts doubts on the ability of any other organization in the country to do the same job. The upcoming SpaceX flight will be performed in the limelight of both a critical and a hopeful public. The barge landing, whether it succeeds or fails, will be measured against the hundred plus Shuttle flights.

The SLS and Orion crowd will be using the previous two accidents to highlight any problem SpaceX may experience on this mission. They see themselves threatened and backed into a corner even though their budget has consistently been far in excess of anything SpaceX has used.They believe a failure will prove  SpaceX cannot do the job and cannot be trusted anymore than any other company, while a success will highlight their inability to provide reusable hardware. Even a failure to land on the barge would be used to insult all commercial companies, with the Anteres and SpaceShipTwo mishaps used to help make their points.

So I would suggest you be prepared to see a far more critical take on this mission than any reasonable person would use.For the next couple of missions a tendency to overpromise or under deliver by SpaceX or its fans will be used as ammunition to attack the company. And it should be remembered that some of these fairly low information people have a tendency to write their congressman.

Posted in Uncategorized | 14 Comments

Humble Arrogance For an Inspiring Mission

The Orion flew today for the first time.

The hype and hoopla surrounding this flight was about what you would expect from an agency that is spent so many years and billions getting to this point. If you listen to the media releases it would seem that this is the start of our expansion into the entire solar system with the development of science and exploration to follow.

Those of us that have followed the development and cost of this program, question the value of this flight, especially in relation to the price tag and excessively long schedule. It will be at least 8 to 10 years before astronauts will fly on this vehicle to any destination worthwhile or not, totaling decades from concept to manned test flight.

It would be interesting if SpaceX could do a little trick to upstage the hype and hoopla of the flight of the Orion. If one of the Dragon capsules could be sent around the moon and reenter from there, that would capture the imagination of people that know where the moon is but have no concept of how far 3600 miles from Earth is. I suggest they do this with one of the Dragon One capsules that has already been to the international space station. Demonstration of reusability would be clearly demonstrated in a most spectacular manner.

Justification for this flight could be as simple as Elon Musk claiming, without attribution, that his detractors in Congress are questioning the ability of his vehicles to safely carry humans, especially to the distances expected of Orion. Properly done, he might even get NASA to pay for it. By doing it in a humble manner to address the issues that people claim that his vehicles have, he could actually pretend to be in a very defensive position about the flight, which afterwards would stand in stark contrast to a vehicle that only went 3600 miles into space after 10 years and as many billion dollars.

The cargo Dragon would obviously be unmanned, as was the Orion flew today. For the general public it could easily be a distinction without a difference that the Dragon One is not a human rated capsule after you clearly show people from the International Space Station inside it loading and unloading cargo. The Dragon One is clearly capable of housing humans in space as witnessed by the international space station astronauts. It can be shown to have astronauts inside it in space, which the Orion cannot do.

A Dragon capsule which had been to the international space station and back, which afterwards flew to the moon and back, would demonstrate reusability, deep space capability, and a willingness to take risks. This would stand in stark contrast to the Orion that flew today, and the organizations that were responsible for that flight.

The time to do this for flight would be after NASA, Lockheed, and Boeing, have had enough time to emphasize their superiority in space flight based on the Orion test flight.Then do a simple series of press releases which emphasizes that the Lunar flight was simply a test flight to prove the equipment. Now we know the heat shield will work, and that our navigation is sufficient unto the task. Them very humbly refuse to compare it publicly to the Orion, and let the voting public do that for themselves.

If it is possible to fly a Dragon Two on this mission with a simple Falcon Nine, an argument could be made that SpaceX has surpassed NASA on its own turf. Especially a Dragon Two with crash test dummies inside including the one from MythBusters if possible. The recovery of the dummies from the ocean after they had been around the moon could well be the private enterprise spaceflight Kennedy moment.

Posted in Uncategorized | 29 Comments

YHABFT: Perspective and Probability Estimation (SpaceX Edition)

I had a quick thought about SpaceX that I wanted to blog about instead of doing a bunch of tweets. Basically, I think that how you judge SpaceX’s probability of success probably should depend strongly on whether you’re thinking as a competitor or as a customer.

If you’re one of SpaceX’s other competitors, you should probably take your expectations of SpaceX’s probability of success or failure (for reusability, Falcon Heavy working, etc), and bias them a bit more towards the success side. Underestimating your competition is a great way to obsolete yourself. So, if you’re a SpaceX competitor, and you’re being wise, you should probably base your plans on SpaceX being at least moderately successful at reusability, and eventually getting Falcon Heavy flying. You probably don’t need to assume that every word that cometh out of the mouth of the Elon is the veritable word of God or anything, but you should be really careful about making sure you’re being conservative–which in this case means assuming that they’re going to be somewhat successful at continuing to disrupt the industry. Anything less is setting yourself up for failure.

On the other hand, if you’re either a potential SpaceX customer, or a fanboy whose dreams are impacted one way or another based on SpaceX’s successes, you should probably bias your expectations more towards the failure side. You should assume that reuse is going to be harder than it looks (because unless you’ve actually done anything with flight vehicles it probably is harder than you think), take longer to work out, and be not quite as amazingly awesome as it theoretically ought to be. You should probably assume that while FH will probably fly, it probably won’t have the full performance expected initially, will have its own set of teething pains, and won’t be as amazing as you hope–at least at first. Overestimating your suppliers is just as stupid as underestimating your competitors. I’m not saying you should be gloom and doom on SpaceX, just temper your enthusiasm enough that you end up pleasantly surprised occasionally instead of disappointed if things don’t go perfectly. I’ve been watching commercial space since I was 16, and us commercial space fans are almost never under-optimistic.

Do I think SpaceX is going to make a huge difference in the industry? Of course. Do I think they’ll make reusability work at least for their first stage? Of course. I think it’ll take longer than fanboys expect, and be faster than competitors are hoping. I’m not entirely convinced they’ve figured out a way to scale up to the kinds of flight rates they’d need to hit their more ambitious cost targets, but even if they only get down to $1000/lb with a semi-reusable F9R, that’ll be awesome enough.

So to recap: Never underestimate your competitors, and never over-estimate your suppliers.

Posted in SpaceX, YHABFT | 7 Comments

Random Thought: Venus Really-Balloon Rockets

I haven’t run the numbers on this yet, but I was thinking about how to do reusable transportation on Venus recently. My previous Venusian Rocket Floaties blog post showed that existing upper stages, sealed off, could float at altitudes high enough not to melt their seals (though still roasty-toasty). My thought was that you could drop down to that altitude, deploy a balloon, and float back up to a safe altitude for recovery by another vehicle. But I got thinking about the reliability and risks of that approach, and it gave me a crazier idea (which as I said above I haven’t run the numbers on yet):

What if you designed a rocket with one of its tanks (the fuel most likely) actually a balloon with the fuel in gas form? Make the balloon big enough so that when the propellant tank is “empty” (and just some sort of buffer gas is in there to fill it), the whole stage is buoyant at a safe altitude. Leave the engine and oxidizer tanks at the bottom “normal”, but have a big balloon tank attached to them via some sort of truss structure.

Some considerations:

  • You’d most likely have to attach payloads to the side not the top of the balloon because you probably want the balloon at as low a pressure as possible when it reaches orbit.
  • However you’d want it at around 1atm pressure of something when you come back in, so it won’t collapse at the 1atm pressure level.
  • You’d have to parallel stage bimese style instead of the more traditional vertical stacking you do on earth, for similar reasons to those mentioned above.
  • While a spherical balloon would be most mass efficient, to keep air drag down you’d probably want a cylindrical balloon.
  • It might be best to pick a fuel gas that liquifies when chilled (methane or propane?). Then you could theoretically have a fan pull gas from the balloon, and run it through a heat exchanger with the LOX to liquify it before running it into the engine?
  • Likewise, you probably want the gas in the balloon on reentry to be something light like GH2 or GHe…not sure the best way to transition between the fuel filling the balloon and this filling the balloon. Could be something carried in an onboard reinflation tank, or it could be something you do at an orbiting station?
  • Due to the very large diameter you could get even with a cylindrical real ballon tank, I wonder if you could use that large diameter to wrap a fixed MAC coil around for both initial aerocapture, and maybe magnetoshell assisted aeroentry. Could you get the velocity low enough that your balloon can take the remaining heating without any special TPS on it?
  • You probably don’t want to make the thing have to float when fully-fueled–you probably want the carrier blimp to support it until it is launched. That way your balloon volume is determined by the mass of the system at recovery, and you just fill the balloon to whatever density of fuel gas makes the most sense to provide the right amount of fuel for the stage.

I won’t have time to run the numbers on this for a week or more, but I wanted to toss this out there. It’s crazy, but if you could pull it off, it would enable fully-reusable Venus rockets with passively safe recovery. You’d still need a carrier vehicle to come out and fetch it, much like ocean recovery of capsules, but without flat, non-moving platforms to land on, this may be the best way of doing things.

Posted in Launch Vehicles, Space Transportation, Venus | 10 Comments

Integral Payload Fairing Habitats

In the spirit of my previous post promoting healthy, competitive industries, I wanted to toss out an idea I’ve had for several years about an alternative to inflatable structures for providing large volume pressurized space facilities. The idea is a derivative of one of the concepts I discussed for dual fluid depots in my paper I did with ULA back in 2009–to make the pressure vessel be integral with the payload fairing walls.

Normally payloads fit inside the fairings, and have to have a sufficiently large gap between them and the fairing that they don’t accidentally vibrate into the fairing during launch. This “dynamic envelope” often cuts the diameter of objects inside a notionally 5m diameter fairing to ~4.5m or less. Building your structure so its cylindrical section is the fairing structure can increase the effective cross-section of your module significantly (~35% more cross sectional area for a 5.1m vs. the 4.39m cross section used for ISS).

Here’s an illustration lifted from that paper I referenced earlier:

Integral Payload Fairing Depot Concept provides ~200m^3 of volume fitting within existing Atlas V payload fairings

Integral Payload Fairing Depot Concept provides ~200m^3 of tank volume fitting within existing Atlas V payload fairings

As you can see, by building a tank that effectively replaces part of the fairing wall, you can fit over 200m^3 of pressurized volume into an existing Atlas fairing (actually closer to 250m^3 once you include that gas buffer tank shown in light blue between the big tank and the Centaur, and add in a docking node fitting into the nosecone area). I haven’t run the numbers on versions flying on Delta-IV or Falcon 9, but figure they’re likely similar since all have ~5m diameter fairings.

In many ways this concept is pretty similar to what was done for Skylab. While NASA originally intended to use a “wet workshop” design for Skylab–where the habitable space would actually be filled with propellant during launch and only converted to warm living space after reaching orbit–in the end they ended up going with a dry-lab that was pre-fitted-out with internal structures, wiring, and a lot of the hardware that would be used on-orbit.

For an Atlas V-launched version, the 5.4m OD of the fairing would work well with the 5.1m OD LH2 tank tooling used for the DCSS upper stage, leaving about 15cm on each side for a variant of Quest Thermal’s  MMOD-MLI that could include a thin aeroshell over the outside similar to the LV-MLI. With a tank stretched to fill the available length in the long Atlas V fairing, you’d have somewhere in the 210-220m^3 in the main cylinder, with a pressure vessel and MMOD/MLI dry mass under 4 tonnes.

Quest Thermal MMOD-MLI Test Article

Is this revolutionary? Not really. But I think it’s a reasonable competitor to inflatable modules for a similar job. Some of the benefits of this approach, compared to inflatables:

  • Much simpler, lower-risk design, analysis, and fabrication. You’re basically just doing a stretched propellant tank for your pressure vessel. Most of the complexity in a useful hab isn’t in the pressure vessel itself, so making that as simple as possible might not be a bad idea.
  • Similar overall volumes. The BA330 would only be about 30-50% bigger (220-250m^3 vs 330m^3 for Bigelow), in spite of the benefits of inflation. This would also be significantly (~50%) bigger than the largest ISS module–Kibo.
  • More efficient internal volume utilization. Unlike an inflatable you wouldn’t have a rigid core structure taking up prime real estate down the center of the module, and you also wouldn’t need to have all the volume associated with the inflation pressurization system, as you could launch the module pre-pressurized. If you wanted to have a wide open space for some reason, this would provide it a lot easier than you could get with a comparable inflatable structure.
  • If you went with an isogrid aluminum construction like the DCSS tank, you can probably put threaded/helicoiled holes at the repeating nodes where the 6 rib elements come together. This would make it very easy to attach structures or other systems in a reconfigurable manner, whereever you want. With some work, you might even be able to have some set of the node holes done as blind (not thru) tapped holes on the outside for externally mounting hardware.
  • Since the structure is rigid, it’s possible to mount items like solar arrays or radiators to the outside of the structure a lot easier than it is with a soft-walled structure. These pieces would have to be stowed somewhere else for launch (maybe back in the gap between the centaur stage and the bottom part of the fairing), and then moved into place using a robot arm, and attached to some form of separable interface. There are some definite details that would need to be sorted out there, but nothing that seems to hard. Plus you wanted a robot arm anyway for delivery vehicle capture/berthing. This may not seem like that big of a deal, but one of the real challenges with a Bigelow module is all of those external pieces have to attach to two fairly narrow pieces of real estate at either end. Being able to attach to the cylinder section gives you a lot less crowded of a space to deal with.
  • Adding windows or other local stress points is also a lot easier to do with a rigid structure, as is adding vacuum electrical or fluid pass thrus along the cylinder section if desired.

Now, I didn’t mean this post as bashing on Bigelow or inflatable structures. I’m a big fan of what Bigelow is trying to do, and have nothing but respect for a guy willing to put that much of his own money on the line to make a dream happen. That’s balsy. I’m not even necessarily saying that my approach actually is better overall once all factors are taken into consideration. I’m just saying it’s another approach to solving the “large amounts of pressurized volume” problem that’s not particularly high-tech or high barrier-to-entry.

While I definitely want to see Bigelow successful, I’d also love to see him have some successful competition as well, and I just wanted to point out there are other legitimate approaches for solving this problem that I hope someone will try out.

Posted in Bigelow Aerospace, Commercial Space, Space Development | 12 Comments