# Tag Info

43

There are several compelling engineering and design reasons why a bigger spaceship makes sense and several reasons why making a mini-starship does not make sense for SpaceX specifically (and their vision). First and foremost, Elon Musk has made it clear that his goal for the company and the future isn't to provide cheap satellite launch capabilities, it's ...

38

In my experience, I've noticed that SpaceX uses a lot of temporary components until such temporary components need to actually be tested. Since the legs of MK1, MK2, and most probably MK3 will never see uneven soils rather than concrete landing pads, they will most likely just have simple legs. After a few successes with MK3, we should start seeing much more ...

31

In the question you mention about why Falcon 9 uses four legs to land instead of three, there are multiple great answers. One of them by @David Hammen states that: "Another factor is that the Falcon has nine engines, one in the center and the other eight around it in an octagonal or square-like arrangement. The bottom part of the thruster reflects ...

18

By the time Starship launches for Mars, SpaceX may have changed the number of legs several times. They redesign as quickly as the Haggunenons of Vicissitus Three evolve during lunchtime. Plausible guesses for factors favoring three legs, at the moment: lighter less aerodynamic drag, if the legs also act as fins send a scout beforehand to choose a boulder-...

16

Falcon 9 reentry is only designed for first stages, with a reentry burn that is pretty minor - on the order of a few hundred meters/second. A second stage, reentering with far more velocity than a first stage, can't shed the extra velocity with a cheap burn, because the total delta-v necessary for that would be about as much as the second stage was capable ...

13

There are no published/proposed abort modes for ascent. We can speculate that some incidents can be survived by letting Starship tumble free and light it's own engines to burn to a low orbit or land depending on altitude and velocity, but that capability has not been proposed by SpaceX. Landing redundancy is provided by carrying 7 deep throttling, sea level ...

12

Quick answer is all I have time for now -- if someone wants to do a more detailed and referenced answer, please feel free and I'll delete this: While it's very big, its mass is not that high, and gravity is low. On Mars, for instance, it needs about 150 tons of fuel, plus 100 or so tons of vehicle (mass) to get back to orbit. Under Mars gravity thats only ...

11

According to tweets from Elon, at least part of the decision is due to their design for dealing with the reentry heat: instead of adding ablators to cool the craft on reentry, Starship is going to actively cool the hot side with liquid methane. Steel is better at coping with this than carbon fiber. Tweet 1: Usable strength/weight of full hard stainless ...

8

An answer might be, that three legs will always be able to land on a rough surface with all three legs touching the ground, while with four legs there is the possibility that only three of them will touch the ground. In order for the four legs version to touch the ground with all four legs, those legs should be made telescopic with some sort of dampers, ...

8

Musk's IAC2017 presentation included a "chomper" variant for large cargos: Source: http://spaceflight101.com/spx/wp-content/uploads/sites/113/2017/09/IAC2017-Musk-26.jpg His 2018 announcement included aft cargo holds, around the engines: There's also at least one side hatch. If you're launching a group of small satellites, you could use a carousel or rail ...

8

You can find most of the information you need on the picture below which comes from Reddit. Crucially, if you add up the relevant lines, delta-V from Mars to Earth-Mars transfer is about 5.92 km/s. Assuming they produce the vacuum raptor (not planned for the very first starship missions) Starship will have an $I_{sp}$ around 380s, so by the rocket equation,...

8

Capturing into Mars orbit would consume a fair amount of fuel. You can see this with Mars probes. They usually do one of three things. Propulsive capture into orbit Minimal propulsive capture, but aero breaking for the rest. Direct descent, no real breaking into orbit. Every pound of fuel carried to Mars means lifting it from Earth, so minimizing fuel ...

8

SpaceX has implied that there will be a crew/cargo lift system similar to how skyscraper window washing platforms work (a crane swings the platform out from inside and lowers it to the ground): SpaceX teased it at the end of this video from last year:

8

There was some talk of modifying Falcon 9's second stage to give it full reusability in November of 2018. The idea was that a reusable second stage would be used to test out Starship technologies. This effort was scrapped 10 days later in favor of accelerating development on the current stainless steel design of starship. The superheavy/starship ...

7

This has been answered before, but I chose not to just mark it a duplicate because there is one new reason for the header tank unique to Starship. In a Reddit AMA in 2017 where Elon Musk answered questions about the original ITS design, he answered a question about the header tanks: Those are the header tanks that contain the landing propellant. They are ...

7

The amount of energy involved in a take off and landing will be roughly equal to the mass being moved, and approximately the same proportion of energy will be turned into sound given the same engines are involved. Going up a falcon heavy is around 1400 tonnes, coming down the stages have split apart and are almost empty. Have not found authoritative numbers ...

7

Similar to how a small plane can't really carry any people around the world, but a larger plane can, it turns out there are challenges to making really small rockets. These are magnified when you take in to account full reusability. It turns out that Starship is about the smallest spacecraft that makes sense for a fully reusable spacecraft. A few things to ...

6

According to current information Starship is only capable of using one pair of propellants -- liquid methane and liquid oxygen. Some sketches suggest special tankage (a tank inside a tank) to help keep the landing propellants cold on Mars missions.

6

Really this is several questions. Launch abort, and landing abort/recovery questions. Launch abort, there is not yet a lot of good answers, and may have to wait for future information. Landing abort we know they intend to land on at least 3 engines, which they changed from 2 to 3 in the various iterations. This is designed to allow engine out on landing. ...

6

There are 3 possibilities: SpaceX deliberately rolled it It rolled naturally, and SpaceX did not expect / want this It rolled naturally, and SpaceX did expect / want this. Looking at the video, the roll seems to intensify without any use of the rcs thrusters, so it seems likely the roll occured naturally. In this case, the torque that induced the roll ...

6

As @camille-goudeseune writes, we shouldn't draw any conclusions from this "flying water tower" towards the design of the final Starship which will be an order of magnitude larger. Nevertheless, we can have a look why it makes sense to have three legs on Starhopper: It's true that the three legs need to extend 1.4x from the center of the body of the ...

5

Around the 20th of March 2019 various news sources reported that SpaceX had scrapped the majority of its custom-built tooling for BFR. Now switching their focus completely to a stainless steel design. https://www.teslarati.com/spacex-all-in-steel-starship-super-heavy/ In a wholly unforeseen turn of events, SpaceX has taken the extraordinary step of ...

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

No, not from Earth. According to Elon Musk's most recent comments at SpaceX's 2019 Starship Update presentation, Starship cannot reach orbit without the Super Heavy first stage booster, at least on Earth. (Though when launching from the moon or Mars it's no problem.) Previously in 2018 Musk had stated on Twitter that Starship would be technically capable ...

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....

5

The most sensible and specific account I've come across is as follows: RUPTURE UPDATE: Through back channels it has been revealed that MK1 suffered an accidental overpressure to failure. Fuel and oxidizer would typically be loaded to 3 Bar or 43.5 psi— for densification purposes and flightworthy tanks may be tested to 1.5-2x that value for single time ...

4

The design hasn't been confirmed publicly by SpaceX yet, but probably some kind of elevator. One of the mockup drawings showed Starship having a stowed crane for offloading cargo, so it wouldn't be unreasonable to assume they could stick a flat platform with handrails on that. Picture at 33s into the video:

4

I think it’s because they want to use the same pipe work they use for tanking on the ground in orbit. I imagine the Starship will have an LOX inlet/outlet on one side and a Methane inlet/outlet on the other and all Starship will be built in the same way. If you back one Starship onto another with the heatshields pointing in the same direction the LOX pipe ...

3

In the most recent (as of Oct. 2019) SpaceX Starship media event, (SpaceX 29-sep-2019 YouTube video Starship Update) Elon Musk stated after about 21:05 that they were ditching the "transpirational cooling method" which was supposed to pump cryogenic fuel out of "pores" to form a cushion, often described as similar to the " "Leidenfrost effect" . Instead, ...

3

There have been many such. Here's one from way back in 1957 for the Brass Bell vehicle. The primary or load-bearing structure was of aluminum and relied on cooling in a closed-loop arrangement that used water-glycol as the coolant. Wing leading edges had their own closed-loop cooling system that relied on a mix of sodium and potassium metals. Liquid ...

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