RCgothic

Whilst a miniature black hole in itself is probably relatively benign, wouldn't anything falling into its gravity well release a tremendous amount of energy?

Ariane4 is by far the nicest looking of the Ariane family.

Wikipedia's article on augmented rockets claim they weigh as much as 5x as much as a normal rocket engine when you include the intakes, and that the intakes are not a trivial engineering challenge. I would suggest that's the reason we don't see them on first stages right there.

Basically it's a lot of weight and complication for most rockets that spend very little time in the lower atmosphere. More generally useful for missiles.

Also hydrogen can actually diffuse through solid tank walls, so even a perfectly refrigerated tank is going to lose some.

There's nothing in interplanetary space for anything to back scatter off of. Probably the worst place to be would be the Van Allen belts, but they'll only be passing through those for a short time.

Solar storms only come from one direction. It'd be no big deal to manoeuvre to place the bulk of the fuel tank between sun and passenger compartment. Storms don't hit full intensity instantly, and even if they did they'd need exposure longer than it would take to reorient to do serious damage.

Which way the wheels spin is irrelevant. The winch can tow the car sideways if it wants to. The wheels won't enjoy that, but they don't get a say in the matter. With both the winch and the plane the motive power available far outweighs any conceivable resistance of road, runway or treadmill. And the whole point of freely spinning wheels is that they are resistance reducers. Neither the towed car nor the plane need to push against the runway to move. One can pull on a winch and the other can push on the air. Again, the road is irrelevant.

Now watch me confuse the issue. All previous discussion has assumed that the wheels are massless/inertialess and the wheel hub is frictionless. When this is the case any forces on the wheels are infinitesimal. It takes no force from the belt to rotate the wheels freely or to speed them up or slow them down and there is no resistance from the wheel hub. The wheels spin freely to match whatever speed the belt is moving completely decoupled from the plane. The plane doesn't care what the wheels are doing it sees no force through the wheel hub. Now add wheel mass/inertia. The force of the belt on the wheels is not a couple, or pure torque. It exerts a moment so that when the belt is accelerating it spins up the wheels. But the force at the rim must be matched by a force at the hub in order to hold the wheel stationary relative to the plane (Resolving forces). This force does act as a drag on the plane, but it's tiny relative to the forces the plane's engines are capable of exerting because it takes very little force to spin a wheel compared to moving a plane, so inertialess is a good first approximation. And this force only acts whilst the belt is accelerating relative to the plane. At constant speed no force is required to change the wheels' velocity. Now add wheel hub friction. A resistive torque at the wheel hub is opposed by a force from the belt creating a torque that holds the wheel to the speed of the belt. But as we've previously established, force from the belt is not a pure torque. So the force of the belt on the wheel rim is reacted at the wheel hub. It acts as a constant drag on the plane. But wheel hubs are built to have very low coefficients of friction. This rolling resistance is tiny compared to the force required to accelerate a whole plane. Therefore frictionless wheel hubs are a very good first approximation. The belt is capable of exerting tiny drag forces on the plane. The plane's engines are massively more capable of exerting force on the plane. Therefore for any reasonable speed of belt it doesn't matter what the belt is doing. The plane can just apply thrust to overcome it.

No they don't. It depends on the relative motion of the plane and the belt. If the belt matches the speed of the plane, the plane can take off without the wheels spinning at all and the brakes fully applied. If the belt is stationary, the wheels are turned by friction with the belt as the plane accelerates by the force of the engines. If the belt goes backwards the wheels turn but the plane doesn't move. The wheel hubs are effectively frictionless and can't exert any force on the plane to accelerate it.

Unirradiated uranium isn't all that dangerous. It's only once it's been irradiated in an online reactor that it becomes so (due to neutron activation and fision products). As long as any reactor isn't started until it's on orbit there's nothing particularly nasty on the rocket being launched. The biggest issue is that you'd probably use highly enriched fuel for mass reduction so you'd want to be able to recover it if the spacecraft didn't make orbit, but even if it gets incinerated and disperses into the atmosphere it's no big deal. Of course media and public would probably react hysterically, but that's a separate issue.

ISP and acceleration are not directly linked. ISP = Thrust / Rate of Propellant Expenditure Force released per second? Pretty sure that's not a physical quantity. Closest I can think of is change in force per second, which is a measure of throttle response, not ISP. Agree that ISP isn't always king. A stage with a denser propellant and lower ISP may be smaller than an equivalent stage with higher ISP and less dense propellant. Even between stages with the same propellant density, in a choice between a larger rocket with a Be3 or a smaller rocket (because it doesn't require as much fuel) with an RS25 you might choose the cheaper Be3 because extracting maximum efficiency can be expensive.

ISP is thrust per unit of propellant consumed and is the engine's efficiency. It's one of the most important parameters of a rocket engine when comparing different engines. The units can be written as: N/kg/s or Ns/kg. But N can be broken down into kg m/s2. That gives: Ns/kg = m/s m/s is a speed. What speed? Turns out it's exhaust velocity. The higher your exhaust velocity the higher your specific impulse. To complicate further, this is often "normalised" to change its units by dividing by Earth's gravity. Why? Because some fools get confused by working in meters but everyone agrees what a second is. m/s / m/s2 = s There's also a factor of roughly 10 because earth's gravity has a value, but in terms of units that's the why. ISP in seconds is basically how long an engine can burn for whilst producing 1 unit of thrust from 1 unit of fuel. Longer is better because your end velocity will be higher. So that's what ISP is. Now why does it change in an atmosphere? It's because back pressure on the engine bell slows down the exhaust. Also the engine bell can't be as large because back pressure causes instability that causes turbulent flow separation which is destructive to engine nozzles. Smaller engine nozzles aren't as good at accelerating the exhaust, so that's a second factor in why it ends up slower. The higher atmospheric pressure, the more the exhaust is slowed, the lower your efficiency compared to a vacuum.

If I were planning the moon landings today I would go for earth-lunar orbit rendezvous. We're just so much better at rendezvousing than we used to be. The rocket could be much smaller which would do wonders for launch cadence, and as spacex are discovering quantity is a quality all of its own.

A cutting charge around the nozzle extension wouldn't weigh much, true. Not sure how difficult it would be to change the nozzle afterwards once it's back on earth.

The main problem is that the MVac is too fragile to be exposed to the airflow whether it's doing the final burn or not.

Saturn V. It put us on the moon and looked incredible doing it. Falcon 9/Heavy. You can't watch an orbital class booster land (in tandem even!) and not feel like this is the herald of a new era of space travel. It's been fifty years since the space industry last felt like it was going somewhere, and this is the rocket that defines new space. BFR is going to be a very strong contender for the top spot!

The reactors themselves may all be designed the same company, but they won't be built in the same country by the same people, and there'll end up being substantial local variances. Then there's a very large majority of the station that is not reactor - fuel handling systems, gas supplies, turbines etc that may share no commonality at all.

You would have thought. But nope. My company is preferred bidder for the balance of nuclear island, so HinkleyC has no finalised design yet. Basically we know the reactor and the civil structure, but the populating the mechanical systems around the reactor is what we're bidding for.

As an engineer in the UK nuclear sector, I'm pretty happy that the EPR is working out over there, but it's still going to be a disaster over here. The plant design at Hinkley C is different enough that it's still effectively a first of type. You'd be amazed how different the station around an identical reactor core can change - UK's AGRs 6/7 have identical cores, but even the fuel and control rods are grossly different between station pairs and even those pairs have difference between them. Anyway. Hinkley C is a first of type, in the UK if not worldwide. It's going to be hideously expensive as a result. First of type in a country always are. The other two reactors we're looking at building are different designs. They'll also be first of type. Also hideously expensive. This is because no private entity has the resources to fund more than one reactor, and every private entity wants to build their own design. Nuclear power in the UK is going to get written off as too expensive just when we need it to cover non-carbon baseload to meet environment targets. It doesn't have to be, we're just funding them stupidly. This is a disaster. The UK gov needs to pick one design, and then build a run of ten identical reactors to ammortise the cost of sorting out the issues with the design in the first one. But it won't for two reasons: UKGov flatly refuses to spend on the infrastructure this country needs, insisting the private sector do it. That simply doesn't work when what you need is reactors. Secondly, the NIMBYs have too much right of veto. It's almost impossible to get a new nuclear site approved here.

Edit: NVM, factually incorrect comment.

Large solids don't have any business being on a manned rocket. You can't shut them down. Ullage motors, escape motors and sepratrons are a different matter. Highly reliable in those roles.

It is a cool artist's impression, even if it is unrealistically crowded. :-)

It takes what, an hour to load propellant before launch? There would certainly be collateral damage, but domino effect doubtful.

Black paint in sunlight boils of the liquid oxygen and apparently made the rocket interior miserable to work in for maintenance crews, at least on Apollo.