Why is the F-35 slow?

The VTOL variant, F-35B, has the lift fan behind the cockpit. This means weapons bays or the inlet ducts can not be on the centerline, behind the cockpit – instead they are on the sides. This applies to all the variants*. This makes the airplane fatter, more draggy and slower. This is also exacerbated by the fact that the carrier version is length limited. Since it’s a stealth airplane, it needs internal weapons bays. Since it’s multi-role, the bays are large, to be able to fit bombs.

A from-scratch designed airplane with the same engine and other systems as the F-35, but no shared structure, designed for air superiority, would probably have a smaller centerline weapons bay and would be longer and thinner. And yes, it would be faster. Manufacturing the structures would be more expensive (because of no sharing) and it would not be able to carry bombs (or at least not as many) stealthily.

Disclaimer: not an expert on the subject. I just haven’t seen this reasoning mentioned in the complaints about F-35.

*: In the non-lift fan variants, there’s a fuel tank in the lift fan space.


The YF-23 weapons bay was very deep and used a trapeze system. This was changed for the production variant.
The F-23 (never built in production) with a narrow and a relatively deep weapons bay behind the cockpit. From https://yf-23.webs.com/F-23A.html
F-35 with the wide set large weapons bays
F-22. From aerospaceweb.org.

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Mitigating Coronavirus Economic Effects and Finding New Business Opportunities

Currently, governments are taking drastic measures to prevent a large amount of people dying, which is a good thing.

When the lockdown and isolation time extends, the economy will start doing increasingly worse. People are laid off, businesses go bankrupt. While there are certainly some business sectors like cruise ships that are not so essential to society, the effect is large and touches many. Just changing a society a lot at once is very problematic.

Imperial College’s report titled Impact of non-pharmaceutical interventions (NPIs) to reduce COVID19 mortality and healthcare demand from March 16, 2020:


The report contains interesting simulations, how the initial surge of infections can be deflected with drastic isolation methods.

It also contains simulations on what happens after the initial part. Even if the initial peak is flattened in the spring, if the measures are lifted in September, there is a peak later, in December:

This means there needs to be a long term strategy for the after-peak time. The paper presents that as well: having isolation measures on for a while and then off:

The long term strategy is to have isolation measures on 2/3 of the time and off 1/3 of the time. This is better than having them on all the time, but it still have very drastic business effects. We could probably do even better.

Other non-pharmaceutical long term strategies

It’s relatively easy to come up with a lot of improvements. If this slow down the spread, then the proportion of time when strong isolation measures have to be in effect can be smaller. The economy will work a lot better, and people will be healthier.

Here’s a few examples. One could found businesses to do just these.

  • Work shifts, example
    • Divide a company’s workforce into ten groups.
    • Only have one group physically at work at a time
    • Each group has 4 hour time at work
    • It’s much easier to maintain distance this way
    • Risk of infection is a lot lower
  • Improved isolation
    • Move as much as possible interactions to electronic and phone calls
    • Hire much more people to do grocery collection in shops. Have people enter a list electronically and only pick up from a place where distancing is possible (you don’t necessarily need cars for this). With a car, a collector can put the groceries in the trunk.
  • Physical devices
    • Install walls or plexiglass between customers and employees. Also between employees. Even a curtain or space divider is better than nothing. The simplest one is probably a few boards with a fabric stapled on.
    • In a hospital, no door should require hand touching. Install all automatic or button openable doors. The button should be pushed with an elbow or knee. This holds for all businesses with a lot of visitors.
    • Install kits for doors so they can be opened with the arm. Install at businesses where people need to physically visit, and at companies with required physical presence.
    • Contactless payment should be made easier so you need to enter the PIN more rarely.

There is a whole other category of new business regarding “intelligence” businesses around the pandemic: contact tracing, measurement, simulation, isolation observation. This is mostly software.

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A hacker’s guide to climate change

Interesting take on the basics

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USA to Exit Paris Climate Accord

According to some, a letter by 22 republican senators influenced Trump. Here it is as pdf. (It didn’t seem easy to get the plain text. Got it from Inhofe’s senate page.)

The content of the letter is just about the legalities: how the Paris Accord could make USA and companies subject to litigation, via EPA somehow. I’m not entirely clear on it.

Nothing is mentioned if climate change is real or not.

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Against Defamation

CEI accused Michael Mann of various things, and Mann sued for defamation. Now there’s some progress on the case.

“The first line of defense you as a defendant can use in a defamation case, when you’ve done a good job, is that what you’ve said is true. They don’t even attempt to make that argument”


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Life Starts To Resemble A Computer Game


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SpaceX Interplanetary Transport System Architecture Unveiled

They didn’t seem to optimize so feverishly for low trans Mars injection mass. Kudos for orbit refueling and planning for refueling on Mars, Asteroids, Europa, Callisto or what you have!

I’m sure the architecture will still change drastically, it looks like a draft. For example, just look at those huge windows. But it’s a big game opener.

screen-shot-2016-09-27-at-22-36-30 screen-shot-2016-09-27-at-22-26-11

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SpaceX first landing flight: data

SpaceX’s first landing flight’s data at flightclub.io


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SpaceX Did It – What It Should Do Next

Congratulations to SpaceX who landed the first stage intact.
Assuming cost is roughly related to stage mass and engine count, reusing the first stage saves 9/10 of the whole rocket cost.
If they can run the stage ten times, that means on average two new engines per flight as opposed to the original ten, meaning five fold savings.

Now there’s a few very interesting questions.

First is the amount of flights they can get per engine. First, I assume it’s going to be a low count, and experimental at that. Once they inspect and test the engines, they can improve them further.

Second is the ultimate development of the refurbishment process that has to be done to the vehicle between flights. If the turnaround takes a month and 200 people of three shifts each, then it doesn’t save much money, and might even be more expensive than just building a new stage.

If it requires one crane operator to drive some support tower there, place a new second stage, place a new payload, place fuel connections. After refueling they need some air traffic control type permission to fly again in a few hours. Then it has the potential to not only save a lot of money, but to place very large masses to orbit in a relatively short time.

I realize such a vision is still quite far off. Even if all the ground operations were somehow solved, just the winds frequently limit the launch and landing quite a lot at the moment.

Second stage

At the moment the second stage resembles the first one, only with one engine. However it is thrown away after use, as it’s hard to recover.

The first stage is easy to recover because it’s not yet very high or fast when it starts the return trip. On the other end of the stack, the Dragon capsule is relatively easy to recover since it’s so small, so you can make it really sturdy, put a lot of heat shield and parachutes (and RCS rockets on it), and it still doesn’t kill the total weight budget. You can also transport it over sea or land if need be.
One way to get around this would be to combine the second stage and the crew vehicle into one system. It is much more complicated to design though. We don’t want something as heavy as the Space Shuttle, and missions likely won’t need as much cross range anyway.

If a large portion of the flights are tanker flights, one might also not need a separate payload stage at all. Fit the second stage with RCS systems etc and transfer the propellant directly from its tanks. This could save costs a lot. The propellant depot would have most of the complexity, including the robot arm etc as it’s not being thrown away on every flight.

BFR – what do they need it for?

Elon Musk’s BFR plan is for about a 200 ton payload to low earth orbit, with 30 larger LOX-methane Raptor engines in the first stage. He plans to launch three, with two being refueling launches, so the Mars stack will be 600 tons upon leaving Earth orbit.

With Falcon 9 rockets and 10 t per flight, one would need 60 flights for a similar mass – surely hard to reach reliably and with a very long schedule – with last week’s technology!
But now, if the rocket can really be made to work reliably and simply in a Refuel And Go Again fashion, it seems feasible.
If, with some development, a single Falcon 9R flies once per week on average, it can place 500 tons per year to orbit, at relatively little cost. A fleet of twelve rockets might do it in a month! On the side, they would also have a myriad of other uses, revolutionizing spacefaring!

Also, if we can routinely get to Earth orbit relatively cheaply, we can start developing asteroid exploitation technology a lot sooner. Asteroids are the easiest source of materials in space since the delta vee and peak thrust needed to get to them and from them to basically anywhere in space is the lowest. I consider the small moons of Mars pretty much equivalent to asteroids in some senses too.
If you don’t need high peak thrust, you can do everything with high efficiency in space propulsion, and not rockets. Think ion engines or electrostatic sails or what ever. The only downside is the long flight time, but if the raw material hauling is done with robots anyway, I don’t see a problem with that. We just have to plan ahead. Sorry, Space Truckers!
Now, my vision is this:
– Falcon 9R and equivalents flying to low earth orbit frequently with little cost per flight, and
– propellants and raw materials brought from asteroids to Earth or Mars orbit or to the various Lagrange points, or even to cycling orbits (between Earth and Mars for example) with slow unmanned vehicles with high efficiency electric propulsion

With these you got yourself suddenly a potential for actually bringing humans to Mars in a relatively sustainable way.

So, Elon, please don’t build the BFR unless you’re sure it’s absolutely needed.

Posted in Architecture, Depot, Design, engines, industry, Launchers, Lunar, RLV:s, Spacecraft, SpaceX, Transportation | Leave a comment

“Space Is Hard” Is The Wrong Answer

They say “Space is hard

Orbital Sciences crashed a rocket equipped with two 40 year old engines. Physically that old. They were an interim solution and they were working towards new engines. We don’t know at this point if the engines were to blame, but, to me, it is likely: engine brightening and thrust loss points to that. No people were hurt. In may this year, a similar NK-33 engine exploded in a test stand at NASA Stennis.


Last friday, Scaled Composites’ SpaceShipTwo disintegrated soon after its hybrid rocket engine was started. One of the two pilots was killed.

Many leaders had already quit the organization this year. Scaled had been critizised by some people in the industry for choosing a hybrid motor in the aircraft. Scaled Composites won the X Prize in 2004, ten years ago with the much smaller SpaceShipOne and a hybrid motor built by SpaceDev. The two flights to 100 km were successful. But scaling up to SpaceShipTwo size has taken unexpectedly long. They had a test stand explosion already in 2007, killing three people. The large amount of nitrous oxide (N2O) is dangerous as it is a monopropellant. A chain reaction can occur that will cause an explosion without any propellant mixing. The solid fuel part of the hybrid system can disintegrate and pieces of the solid can block the nozzle. Such things have happened with solid rockets, raising pressure and causing a runaway pressure rise and a catastrophic explosive failure.

I have not followerd Scaled Composites that closely, and I don’t know how many ground tests they have done. There has been talk that they were moving to a new fuel chemistry, but it is unclear if that was on this flight. SpaceshipTwo had already done some successful supersonic flights so the craft was not exploring new flight territory when it was destroyed.


To someone watching from afar, it might seem that failures would actually not be so hard to avoid. Could both of them have been avoided with a simple cure? Just 1) have more ground firings of the engine.

I’m in no position to say so myself for certain, but it seems like quite a simple.

No people were lost on the Orbital Antares flight. The payload was their own Cygnus unmanned space station resupply vehicle. So they can just rebuild the pad and fly again. With no lives at stake, it’s rational to go from engine tests to flight at a much earlier point.

With SpaceShipTwo the situation is much more severe. Two test pilots were flying the vehicle. The design was such that it required large amounts of pressurized monopropellant (N2O) and the engine chamber was large, containing large amounts of hot high pressure gas when operating.

In  a liquid rocket engine, the risks can be mitigated a lot more easily since the chamber is a lot smaller than in a hybrid. The propellants (if ordinary ones are chosen) can not explode by themselves, and only a very small amount of them are mixed at any time in the preburners, pumps and chamber. So one way to avoid accidents like these is to 2) pick a fundamentally less dangerous approach.

There is even a third way to avoid accidents. Make the system resilient to individual component failures. Compared to Antares, in a SpaceX Falcon 9, would a single main engine giving up the ghost a few seconds into the flight resulted in a pad crash? If the stage would have stayed intact and the engine would not have exploded so violently that it would have destroyed other ones (if there were sensors for automatic engine shutdown), the mission would perhaps still have ended in failure but the pad might have been saved. If it had occurred later in flight, even the mission might have been salvageable.

And what about reusable vehicles, like SpaceShipTwo? Its design is like it’s made for tolerating engine problems: after the release in case of any trouble it can just glide to an easy landing, (possibly after venting the oxidizer). There’s no dangerous low altitude zone like with some ground launched vehicles. So the problem is just making really good sensors and having the engine stop at any sign of a problem. And of course making the engine stoppable. Hybrids are stoppable (compared to solids), but the amount of high pressure gas is still so big that it’s not straight forward to sense problems and control the system. The nitrous being a monopropellant can also cause issues.

So Scaled had a dream system. They built a great carrier aircraft, White Knight Two, which had similar avionics and cockpits and systems to SpaceshipTwo, and they test flew that a lot. They had carry and glide tests for SpaceshipTwo, made some changes and ironed out that part. They really knew how to do the aeroplane part, having built multiple record breaking craft before. What really is the tragedy here is that their propulsion seems to have too big failure modes – and just that one bit them now. So 3) Make the system always abortable.


This should apply to software business as well. You should have things like software component testing, regression, internal testing, customer testing. You should also have good software design like for example transactionality and constraints in databases. This stuff is also more than 40 years old, and if done right, categorically prevents a large amount of data corruption problems.

Have fail operational infrastructure design (multiple hard disks, multiple network connections, multiple servers in different physical locations (data centers with redundant power and cooling) with different service providers, backups with restore tests, hot spares, gracefully degraded modes in case of for example data transfer problems).

And then there’s the software development change management process which is another can of worms. I’ll write more about it in a couple of years…


Michael Alsbury was the SpaceshipTwo pilot who was killed in the accident. We should respect his memory and try to publicize ways to make space access safer for all. We should not say “space is hard”. We should say that space requires both a good comprehensive dedication as well as an open attitude towards safety.

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