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17

The main issue is one of size. Each engine bell requires space and with 42 that is a lot of space. In order to gimbal there needs to be room for the bell to actually move, which means you need to space the engines further apart. But just allowing the inner ring to gimbal they are the only ones who need the extra space, which you can see in the image cited ...


10

This is a really good question and the answer is probably not 100% known, even by SpaceX at this moment. No doubt they will have some active cooling to minimize boil off. Structurally there are tricks they can play. For example the landing fuel is stored in a smaller tank, which is submerged in the main tank. Thus the surface area to warm up over is ...


9

Completing on Hobbes answer, user sol3tosol4 seems to have nailed my last misunderstanding. A simple edit to Elon's quote, make it a nice gems of information: «It's the first time the [ITS] rocket [... payload to LEO] will [actually] exceed the physical size [dry mass] of the rocket» Sometimes Elon tries to "dumb down" his explanations by using ...


8

We can make a base assumption first about how much $\Delta V$ we need to get to LEO and if you wanna update that the rest of the calculations are super easy to redo. Let's say we need $10km/s$ for now. A stage has a $\Delta V$ given by Tsiolkovsky's Rocket Equation: $\Delta V = g_0 \cdot I_{sp} \cdot ln \Bigl( \frac{m_{dry} + m_{prop} + m_{payload}}{m_{dry}...


8

ITS (to be renamed, I heard) as presented seems to bypass the health threats from microgravity and cosmic/Solar radiation by using a very short travel time to Mars. Nothing was mentioned about simulating gravity by rotation or using massive radiation shields. The further out one goes "naked", the more challenging it gets in these respects simply because of ...


6

It is unclear at this point since everything has been only notional so far. Musk has said that they will try a 9 meter diameter, 21 engine interim ITS first now, (original was 12 meters, 42 engines). This is clearly aimed at maturing the technology and being cheaper to develop and test. Additionally, SpaceX has a 4425 satellite constellation (CommX) they ...


5

It takes 3.8 km/s DV to orbit Mars from the surface, 2.5km/s DV to reach an intercept with Earth, and most likely around 1 km/s to vertically land on Earth as proposed by SpaceX. Altogether the ITS ship would need around 7.3 km/s from the Martian surface to the Earth's surface. The fully fueled ITS ship weighs 2400 tons, and it lands on Mars weighting ...


5

The white bars are payload in kg. They look roughly proportional to me, so in that sense they're accurate. The size of the white bars vs. the dimensions of the rocket is misleading. The performance bar is one-dimensional. The rockets, on the other hand, grow in 3 dimensions. So when you compare a Falcon 9 to a Saturn V, the performance difference is much ...


5

When they were building the pad, there were three big concrete blocks they built fairly deep down. Then the pad was laid atop that. Looks like those are meant to be heavy anchors and then cables are wrapped over the legs and attached to the anchor points. BocaChicaGal caught some great shots of this.


5

I think the most important factor in avoiding boiloff is Not Using Hydrogen. The atmospheric boiling points of the chosen propellants are as follows: Oxygen 90K (-183C, -287F) Methane 111K (-161C, -258F) Compare Hydrogen 20K (-253C, -423F) Space is a place of temperature extremes: roasting in the sun, but pretty cold in the shade. https://en.wikipedia....


3

Ignoring the issue that the refueling mode is expected to be tail to tail, and thus blocking the engines, you are trying to re-invent staging. However, with 6 or 9 (IAC 2016 differed from 2017, and will likely differ from reality when it actually flies) or whatever the current design has in terms of Raptor Vac engines, the booster is quite sufficiently ...


3

Going the other way, NASA has drawn up plans for an inflatable ship to harvest the upper atmosphere of Venus. The first question is, "At this point, how feasible would it be to start exploring the rest of the solar system?" Very feasible. The next question is, "And what would be the potential targets for such missions anyway?" Venus is one planet that is ...


3

Optimally packing the engines, the outer rings would contain 12 and 18 respectively, for a total count of 37 engines. Requiring space around the inner 7 to gimbal them, means adding more engines in the outer rings, allowing the designers to bring the total count up to 42.


3

Besides the points raised, that a cluster of engines would need space to gimbal, and the fact that the outer engines can throttle which can also “turn” your rocket, an engine with the apparatus is slightly heavier and signiicantly more complex than a fixed one. Another thing I have the impression might be true is that “gimballed” engine closer to the sides ...


2

Here's an alternate angle to contemplate (no pun intended). Vectoring engines carries some risk factors the engineers must consider, as with most any sub-system comprising the overall vehicle. In a failure scenario, a hard over gimbal actuator presents a flight emergency that of course they would want to be able to compensate for. Perhaps the central ...


2

No, this is not viable for SpaceX. If they used a booster to do the Trans-Mars orbit insertion burn, so the upper stage can save it's fuel, then the booster would not be recoverable. The booster would be traveling too fast to turnaround and land back on Earth. Elon Musk is all about not throwing away his rockets. He would see this as not being viable.


1

Gimballing has significantly quicker response than throttling so most probably no, differential throttling won't replace gimballed engines. We just did not get to see the "business end" of the first stage because there was nothing "new" compared to last year. Just a different number of engines.


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