RCgothic

We're through Max Q!

Falcon 9 is in start up!

Go for launch at 27m past the hour! Engines are in chilldown!

SES-10 is on internal power!

As a European I really don't get why Americans do that. :-P Looking forward to the launch!

Yup, fizzle at best (worst?). If a core is not detonated precisely right, the heat of assymmetric fission will scatter the core, leaving the vast majority unfissioned and all that potential energy unreleased. And that's if any fission at all is achieved. Maybe you get none at all and the implosion charges just scatter uranium all over the place. The trick of keeping a mass sub-critical and then making it go prompt super-critical on demand is exceptionally difficult.

At those speeds the difference between hitting a solid and a gas is negligible. Might help if there's time enough for the generated gas to diffuse out of the path, but see again the ridiculously fast speeds involved.

I estimate ~300m/s extra required to get to 1000km and then to a lunar intercept vs starting from 100km and going straight to TMI. Perhaps it's not much. For the moon. It is an extra ~500m/s required for every craft trying to get to the space station from earth though, particularly over the multiple supply runs required.

That was apparently a result of searching for the engine size that maximised thrust to weight ratio. (Or for the very important scientific number 42).

My mistake indeed. It's tricky to keep all these different payload figures straight! Guess that puts New Glenn squarely in SLS block 1 territory.

Motokid600 already picked up two of my first thoughts on that vid: grid fins and moving landing platform. My other thought was that that is an excessive amount of cowling around those engines. As a two stage launcher it doesn't quite compare to falcon heavy to LEO or GTO, yet is much bigger. I guess the difference comes if they can stick a third stage on it'll have greater potential beyond earth orbit (Falcon is pretty much at structural limits). Certainly interested in seeing how they do though, and a second launcher in the 45t to LEO range makes it more likely the full payload of falcon heavy will be used, as sat operators like redundant options.

How do they get a crew of four aboard if the space suit hogs the airlock? Other than that, the casualness of the whole thing is what struck me. The degree of autonomy of the ship, how easily things are constructed on orbit (and then we install the nuclear reactor!), the aggressive manoeuvres close to other vessels/structures, and the way a repair was made by just piloting a space suit into a jet of venting nitric acid at however many atmospheres and casually plug that right up. And our mars mission is under constriction even as we flyby the moon for the first time. No incorporating lessons learned for us! Oh, and the space station was at an altitude of 1000 miles, nicely within the inner Van Allen belt and squandering the oberth effect for moon missions.

The big stuff is just a source for the little stuff, which is the real threat. The big stuff can be tracked and avoided. A cloud of little stuff is lethal. Big stuff spawns little stuff whenever it is struck by anything. Enforce an 'everything must be de-orbited at end of life' regulation. That takes away new debris sources. Lasers are the means to get rid of the smaller stuff, but it requires very good tracking and an exceptional power source.

Is Dragon 2 even rated beyond LEO?

Why would they change?

Latest I'm hearing is NET 12th March for Echostar 23.

I think people would fall from a height much greater than 60m. Centripetal acceleration alone may put people that high, but remember that at the point gravity turns off everything on Earth's surface is pushing down with enough force to generate 1g. That force doesn't stop just because gravity does. Assuming that it takes 5cm for the average person to lose contact with the ground, they'd gain an additional m/s just through this spring force. That's an additional 60m height over a minute for anyone not inside, even at the poles. Snark is also right about the guidance issues for a shuttle due to the lack of inertics. It's not going to know it has an extra accelerating except by atmospheric wind speed. Possibly not fatal to a mission depending on what stage of the launch you're at, but it could make max Q very dicey. Over 60s the maximum possible dv gain is about 600m/s, which is not an enormous amount. And you'd actually gain less speed due to additional wind resistance and the fact that once you've turned you aren't directly fighting gravity.

Actually I think there were two flights of Columbia with ejector seats and a crew of more than two. For ethical reasons the mission commander requested they be disabled so that the two on the flight deck would share the fate of the rest of the crew. They would have been of questionable use anyway. Pre SRB burnout there would be a high risk of passing through the fire trail. Post burnout you're going four times the speed of sound at sea level and ejection starts getting dicey.

Getting a little off-topic, but I believe the OV-0 series were never intended for flight, and the OV-1 series were supposed to be the operational vehicles. Except it was more cost effective to rebuild STA-099 (Challenger) into a proper orbiter than OV-101 (Enterprise), which then never flew to orbit and wasn't retroactively renumbered, but Columbia was upgraded to OV-99.

So CRS-8 first stage is due to be reflown as SES-10. How do we refer to reflown stages? CRS-8/SES-10 could get a bit unwieldy after a few flights.

For those in the UK, it should be noted that manufacturing solid rocket motors is an offence under the 1875 Explosives Act, the 1883 Amendment, and later Prevention of Terrorism acts, since these are classed as an explosive.

Log10(y) =x for the same values as y = 10^x Loge(y) = ln(y) = x for the same values as y = e^x Similarly there are log#(y) functions for arbitrary values of #^x, but they're rare. I think the most common non-10 non-e values are 2 (binary) and 16 (hexadecimal).

Or, if you want to calculate the DV required for a particular manoeuvre between orbits, that's an orbital mechanics question, rather than a rocket equation question. Generally manoeuvres are either Hohmann manoeuvres, which go circular to elliptical to circular in two manoeuvres, plane change, which is negating velocity in one direction and adding it in another by pythagoras, or launch/landing. Don't try and calculate launch/landing unless you are going advanced. Just look it up. Plane change DV is easy. How much do you want to change your angular inclination by, and how fast are you going? By the rearranging the cosine rule: DV = SQRT(2 * v^2 [1-cos(angle)]) Thus for zero inclination change cos(0) is 1 and the DV required is 0. For a 180, the DV required is 2*v, because you have to negate all of v and add it again in the other direction. For a 90deg change you need 1.414*v. And of course any other angle can be calculated in the same way. Hohmann transfers are a little involved and I'm out of time. Maybe someone else can explain, or I'll be back later.

DV = Isp * g0 * ln(m0/mf) I'll unpack that a bit. DV is change in velocity. It can be calculated for a specific manoeuvre or more generally as the total ability of a vehicle or rocket to change its velocity by. Isp is specific impulse. It is a measure of engine efficiency - basically how long in seconds an engine takes to exhaust a weight of fuel equal to its thrust. Longer is better because it means you get to burn longer for the same quantity of fuel. It's directly proportional to exhaust velocity, and you'll often find the rocket equation written in terms of exhaust velocity instead of Isp. g0 is the acceleration due to Earth's gravity, and is required for the conversion between exhaust velocity and Isp. It may seem weird that we use Earth's gravity no matter where the rocket is, but that's because we're implicitly converting from kilograms to Newtons and Newtons are defined in terms of Earth's gravity. m0 is the mass before the burn. mf is the mass of the rocket after the burn. m0/mf is therefore a measure of the mass ratio, or how much of the rocket you've used as fuel. The more fuel you've used, the greater this number, the faster you go. ln(m0/mf) is the natural logarithm of the mass ratio. It's a non-linear function, but any calculator or spreadsheet can work it out. The reason it's necessary is because the fuel you burn first also has to accelerate the fuel you burn later before that can be used, reducing its efficiency. Burning the 1st kg of a 1000kg spacecraft changes the velocity by less than 1/600th of the amount the 999th kg will get you. Where m0 is the total mass of a spacecraft topped full of fuel and mf is the dry mass after all fuel has been exhausted, the rocket equation gives you the total ability of the rocket to change its velocity. If you have the DV required for a manoeuvre, and the Isp of the engines, then the equation can be rearranged to tell you either how much fuel you need to bring along on top of dry mass in order to perform it, or if you have current mass, what your end mass will be after the manoeuvre (And therefore fuel required - but better hope end mass is higher than dry mass or the manoeuvre is impossible). The rearranged form is: m0/mf = e ^ (DV / [Isp *g0]) Where e is the exponential function (opposite of natural logarithm) and ^ means "to the power of" And that's basically all you need to know. Any questions?

It's a good point that recovering the centre core of a Falcon Heavy is going to be harder than recovering a Falcon 9. The second stage isn't changing but the payload is getting bigger, meaning stage 2 has less DV so Stage 1 has to be going faster at separation, faster even than Falcon 9 on GTO. This problem gets worse with crossfeed, which I saw someone on Reddit mention is still being studied. (Pinch of salt duely taken). But perhaps on Falcon Heavy there can be more fuel saved to leave greater allowance for the entry burn or even return to launch site! It's difficult to guess what their plans are.