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

Suborbital VS Orbital

I did a post on this a few years back, but couldn’t find it to repost.

A commentor in response to one of Rand Simbergs’ articles brought up (again) the old orbital is 8 times the velocity of suborbital and therefore 64 times as hard because energy goes as the square of velocity. Where to begin arguing this again?

The argument was that suborbital is Mach three vs orbital being over Mach twenty-four. Mach three won’t get you to space. 900 meters per second (~Mach 3) vertical velocity will get you 90 seconds of climb at an average of 450 meters per second, or about 40.5 kilometers of altitude. That doesn’t include drag, gravity losses during acceleration or engine back pressure losses. Mach 4 gets you 72 kilometers if you are in vacuum the whole time. It would take nearly Mach 5 to reach the Von Karmin line from sea level if you were in vacuum the whole way. 1,430 meters per second is considerably more than the 900 meters per second implied by the comment.

That was a straight up and down in vacuum from sea level. The flight doesn’t start in vacuum. Back pressure losses on a rocket engine gives 5-20% less performance at sea level than in vacuum. That is a major Isp hit on performance to a vehicle with a finite propellant capacity and facing exponential weight gain for excess mass. That 5-20% more propellant for a given thrust must be lifted by even more propellant. That extra propellant requires a larger airframe and engine capacity. The larger engine and airframe requires more propellant and so on. A suborbital vehicle has just as much back pressure loss as an orbital vehicle .

The vehicle has drag while it is accelerating toward space. The drag costs more propellant equals more engine and airframe, equals even more propellant and so on. If too much acceleration is done too early drag goes up by several more factors which would cost more propellant etc… Another aspect of the drag is heating if too much time is spent at high mach during the climb in the atmosphere. Thermal protection can get up there fast with a poor design. A suborbital vehicle has just as much drag loss in the climb out as an orbital vehicle.

There are gravity losses during the climb out. A suborbital vehicle has just as much drag loss as an orbital vehicle.

Actual mass ratios for suborbital above the Von Karmin line tend to be in the 3 to 4 range. If Mach 3 in vacuum was the whole story, then mass ratios would be in the 1.3 to 1.5 range. Orbital mass ratios tend to be in the 10 to 20 range depending on propellant choices and engine efficiency. The difference in mass ratios is about 4 to 5 with similar propellants. That is undeniably a major difference and order of difficulty. Just not 64 times the difficulty, especially with staging.

Life support is clearly different for manned vehicles. Bottled air for 30 minutes is different than 30 days for one. Food, toilet facilities, and creature comforts are quite different as well. This particular aspect may well be 64 times as hard. I doubt it, but it is possible.

Acceleration couches, controls, and displays will be about the same. More propellant for the RCS with the same number of thrusters is not that much more difficult. Communications will be more complex if the mission requires, though not an order of magnitude, and certainly not 64 times as hard.

Unmanned vehicle payloads have even less need for the 64 times as expensive meme. The energy supply is about the only thing that is clearly in a different league, though solar panels are getting to be quite well known even there.

Look at the historical record for more data. Working backwards from Elons’ billion investment in orbit with the 64 times as hard, any suborbital company spending more than 15 million should have been providing reliable service. Count for yourself the ones that have spent over 15 million and still don’t have an operational vehicle.

Posted in Uncategorized | 12 Comments

Healthy Industries vs. Monocultures

One of the things I’ve believed for a long time is that for the NewSpace industry to be successful and healthy, that we need to see multiple providers and customers for the various goods and services in the industry. One needs look no further than the situation with Aerojet/Rocketdyne and ULA to realize how unhealthy monopoly/monopsony arrangements can be. In an ideal, healthy industry, we’d see several competitive low-cost launch companies offering a range of launch services, multiple companies building in-space facilities like hotels, stations, unmanned free-flyers, and depots, etc.

Having multiple providers and multiple customers is good for many reasons:

  1. Resiliency: If you have multiple providers and customers, problems with one entity don’t necessarily grind the industry to a halt. An example of this was how badly ISS was impacted by the Shuttle fleet stand-down post Columbia. There was also the close-call with Soyuz a year or two ago, where it wasn’t clear if they were going to have to stand-down crew deliveries to the station. On the customer side, technologies and consumer preferences change over time, so having a wide range of customers means that if one particular application stops being as viable, it doesn’t take down the industry with it. In general, more providers and more customers makes any one entity less critical, and makes the industry more robust.
  2. Competition: Having multiple providers to chose from often helps keep an industry innovating, and keeps costs lower than if there were just one provider. Think how good it was for computer users to have both AMD and Intel competing with each other for much of the past 20 years. Would Intel have moved as aggressively at innovating, and would costs have been as low for consumers without them?
  3. Diversity and Specialization: One size doesn’t fit all, and the more firms there are in an industry, the more likely you are to see specialization leading to better solutions for people with different needs.

The interested reader could probably think of other reasons why it’s good to have a range of providers.

Now admittedly, while having a range of providers and a range of customers is ideal, not all industries are large enough to support that level of diversity. Some tend towards “natural monopolies”.  I think at current launch costs, reasonable people can differ on if space launch falls into that category or not. But I think we can all agree we’d like to see a space industry that has a big enough pie to make that sort of healthy diversity possible.

Why am I bringing this all up? Mostly because I’ve been noticing an unhealthy trend towards monoculturalism/”Highlander Syndrome” among many in the NewSpace community. You see this a lot in twitter commenters who seem to think the government should just ditch ULA and give all their flights to SpaceX, or the anger over why NASA picked Boeing as well for a CCtCap award even though they were more expensive than SpaceX. You see this in how people only ever talk about Bigelow Aerospace for in-space habitats. You see this with people badmouthing Masten or Blue Origin and saying that they should give up now because obviously SpaceX is better.Now, I actually like SpaceX and Bigelow a lot, have a ton of respect for what Elon’s team has managed to do over the years, and really genuinely want to see both of those companies wildly successful. But I want to see others successful too. In many cases there isn’t a huge amount I can actively do, since Altius isn’t very involved anymore on the launch side of things, so my support may be limited to trying to cheer on progress by not just SpaceX, but ULA, and Blue Origin as well. I do what I can to put ideas out there that can benefit everyone, and to work on technologies at Altius that can help more than one provider be competitive. I’ve always preferred to run a shop with a reputation for being on friendly terms with everyone as much as possible.Anyhow, I hope others find these thoughts useful.

Posted in Bigelow Aerospace, Commercial Crew, Commercial Space, Launch Vehicles, Space Policy, SpaceX | 17 Comments