RCgothic

Maybe it's true we weren't ready to build bases on the moon immediately post Apollo. But the only reason we're still not ready is because for 40 years we haven't been making any serious effort in that direction. We've flown the same crafts conservatively long past the time we should have been doing something new and boundary breaking, and SLS/Orion is more of the same.

ICPS on top of the falcon second stage looks wrong. And mass to LEO includes fuel residuals, it's not literally how much weight you can have in the payload section. How do ICPS and FUS stack up DV wise? In terms of thrust? Could ICPS be a straight replacement for FUS? That seems a bit more feasible as all the weight is going on top of FS1, which is used to having the weight of stages above it.

I thought he was suggesting using them as an inferometer array. They don't have to go into the far reaches of the solar system, just far apart from each other. A telescope the diameter of Mars orbit?

I am so with tater on this. SLS isn't capable enough to perform any useful mission. It can't fly often enough to do EOR. It can't comanifest enough payload with Orion to perform useful beyond low earth operations. As an architecture it makes no sense. A non-man-rated booster capable of boosting 180 tonnes to LEO 4 times a year with Orion going up separately? Now we're talking.

Does an all up test fire require expending two side boosters? If they don't then the thermal and vibrational environment isn't being tested.

I'm sure this was the plot of a decent episode of Star Trek TNG. The Drumhead.

Well that doesn't sound brilliant.

As has been pointed out, you can't directly use kgf as a stand in for Newtons. There's a hidden factor of g. F=ma 116,000kgf = 5,000kg*a 116,000kg*g = 5000kg*a 1,137,960N = 5000kg*a a = 1,137,960N / 5000kg N= kg*m/s/s So a= 1,137,960 (kg*m/s/s) / 5000kg a = 227.592 m/s/s For constant mass, v=u+at = 0+227.592m/s/s *2s = 455.184m/s

Exactly sh1pman. Dream big. You may not get where you intended to go, but chances are you'll get *somewhere*. SLS is just not ambitious enough - it doesn't acheive anything another booster couldn't manage, nor learn anything new because of its reliance on established tech.

The only way BFR doesn't fly more than SLS after it's been built is if they crash it.

If BFR doesn't beat SLS, it will be New Glenn. SLS is an atrociously managed project from start to finish.

Did someone just use "not-econimical" as an argument against an SLS competitor?

This is a lot (a *lot*) of effort for maybe an extra hundred metres per second, which is at best what drag would afford you. Saturn 5 is over 100m tall. The crush depth of most submarines is under 1000m. So you can go under 10 body lengths deep and in order to do so you have to build your rocket like a submarine. You'd lose any benefit from poor dry mass.

BFR is very much larger than anything else that's ever flown. Perhaps that affords more time for an abort. Cut main engine, deploy grid fins, drag separation sufficient? Doesn't help on the ground, I suppose.

Assuming aerocapture fails, either enough speed has been braked to establish an atmosphere intercepting orbit in which case you'll get a second attempt (although the trajectory may be very harsh on a second attempt or have too long a period), or you're still on an escape course flying off into interplanetary space again.

Falcon Heavy or New Glenn could probably manage about 15t to TLI. That's still less capable than the Apollo lunar lander because it needs to insert into lunar orbit/decent from trans-earth velocity somehow and on Apollo the service module did that. LMFAOROFL at "that low powered SLS"! Pretty much. SLS block 1 has more nominal payload to TLI than that spacex or blue origin, but it can't dual manifest payloads and Orion is a mandatory component so that extra mass amounts to diddly squat. It will never have the launch cadence to support a rendezvous mission with another SLS payload.

So EM2 is probably going not going to meet that target and the ICPS is rubbish but they can't get EUS prepped in time for either of the planned missions that need it. SLS is ever more clearly a booster to nowhere.

Work is force times distance. If you're going faster you apply the force over a greater distance and so do more work.

No, this isn't what a gravity slingshot is. A gravity slingshot is when you use a gravity well flyby to borrow velocity from the body at the centre of the gravity well. Relative to the planet you haven't gained or lost any speed, but in the context of the global reference frame you've added or subtracted some velocity due to the motion of the celestial body, accompanied by a course change. ------------------------------------------ What we're discussing is minimising gravity losses on take off. If you have a constant TWR of 5/3 then you can burn upwards but you lose 1g to gravity and so get an acceleration of only 2/3g. If instead you burn sideways you hover at 1g upwards with 5/3g on the hypotenuse and a 4/3g horizontal component. You accelerate twice as fast horizontally as you could vertically and because the earth is a ball the surface will eventually fall away from you so that that horizontal velocity becomes vertical anyway. So for the the same fuel, engine and throttle settings, you'll minimise gravity losses by burning horizontally. In KSP you'll often see players turn horizontally immediately on airless bodies. This is why. As long as they sustain just enough vertical thrust to prevent them from crashing back to the surface the most efficient use of thrust is to burn sideways. Often there are other practical considerations that mean you want to fly a more lofted trajectory - terrain avoidance and atmospheric drag.

Suppose your space vehicle has a TWR of 1.5. It can accelerate straight up at 0.5g as 1g goes into just hovering. Now burn at an angle, with 1g up to cancel gravity and the rest on a horizontal vector sideways. By Pythagoras you accelerate at 1.1g sideways. (1.1g horizontal, 1g vertical, 1.5g hypotenuse). This is *much* better than trying to burn directly upwards!

Some further thoughts - some discussion of the energy required, but not much on the mass requirement. By conservation of momentum: The Earth weighs ~6e24kg. If you flung the entire atmosphere (~8.5e20kg) off at the speed of light that's a DV of 42km/s. The entire oceans (~1.4e21kg) gets you 70km/s. The entire crust (~2.5e22kg) gets you 1250km/s. If you can only manage 0.1c then reduce dv by 10. If you can only manage 0.01c reduce by 100. A very good ion thruster might have an exhaust velocity of 300,000m/s, so reduce by 1000. In the case of a very good ion thruster, throwing the entire mass of the crust gets you just 1.25km/s. That's hardly anything and what's left wouldn't be recognisable as earth. *Effects of relativity ignored (as unlikely exhaust will actually approach c) **Rocket equation not used as in all cases the mass of the earth isn't significantly changed by expending the started fuel quantities.

New sum! It's estimated that there is about 100 trillion tonnes of Uranium in earth's crust. Of that, approx 0.72% is fissionable U235. That's approx 720 trillion kg of fissionable U235. U235 releases 83 trillion joules per kg when fissioned. So all the uranium in earth's crust could produce about 60,000 trillion trillion joules. Earth weighs about 6 trillion trillion kg, therefore we've released about 10,000J/kg. 1kg with a kinetic energy of 10,000J would be travelling at 140m/s, so the velocity of earth powered by uranium fission can't exceed this. Therefore NERVAs can't significantly move the earth. Hydrogen bombs and nuclear fusion is required for anything greater.

A rocket engine requires mass to use as a reaction medium. Simply detonating every nuke in a large combustion chamber would only throw the mass in that chamber. Even accelerated to near light speed that amount would be insignificant compared to the mass of the planet. To change the velocity of the planet by 1km/s, you'd need to throw about 20,000 trillion tonnes of material off at the speed of light. A typical ion thruster has an exhaust velocity in the 20-50km/s range. So let's assume the exhaust leaves Earth's gravity well at 30,000m/s because that's a fraction of the speed of light and makes things easier. The mass required just increased another 10,000 times. 200 quintillion tonnes required. That's about 40 million times the mass of the entire atmosphere by the way. At that scale I'd expect the rocket exhaust to be wide in proportion to the thickness of the atmosphere. Basically the portion of the atmosphere over the rocket exhaust would get blasted off into space and the drag around the exhaust perimeter would be negligible. The energy required would be 1.6e32J. 1 Megaton is roughly 4e15J. 4e16 Megatons of nuke required. We have approximately 6400 Megatons of nuke. Their combined yield of channeled into a perfectly efficient ion thruster could alter the velocity of earth by 0.16nm/s. Or not enough that anyone would notice. I may have misplaced a few factors of a thousand here or there, so it could be worth checking.

Yes, most of Falcon Heavy's theoretical load capacity end up on orbit as Stage 2 propellant. So they have a few options: Direct insertion to GSO. Missions to deep space. Aid recovery of S2.

The best bet is to join TRA and work your way up. I believe they're a little more experimentation friendly than NAR. If you haven't launched an L3 high power hobby rocket chances are you're not going to succeed at anything more ambitious.