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It has been announced that SpaceX Starship SuperHeavy will need 16 launches with the tankers to refuel Lunar Starship. Why is the Starship going to be empty after reaching orbit, since the booster is going to exert most if not all of the thrust? In other words, isn't the booster powerful enough to carry a fully loaded Starship into Space?

Thank you

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  • $\begingroup$ The booster exerts precisely zero thrust for the entire portion of the launch that occurs after staging. The Starship's tanks are empty when it reaches orbit because it needed that propellant to reach orbit. What would be the point in carrying all that propellant if it wasn't needed? $\endgroup$ Aug 12 at 20:33
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It has been announced that Starship will need 16x launches to fully refuel the Lunar Starship.

A bunch of accountants have determined that one very specific mission profile under very specific assumptions based on current capabilities of a development prototype will need 16 launches.

Elon Musk has already clarified that it is going to be more like 8, maybe even only 4.

why isn't the Starship already fueled when reaching orbit

Because it burns the fuel to get to orbit.

why will the tankers have fuel whereas the Starships to reach moon or mars will not

Because the Lunar Starship which goes to the Moon has 100 tons of stuff in it that needs to go to the Moon. The Tanker Starship has 100 tons of fuel in it that goes to the Lunar Starship.

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  • $\begingroup$ Accountants source? $\endgroup$ Aug 12 at 16:16
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    $\begingroup$ @Cris: The booster does not get the ship anywhere close to orbital velocity. $\endgroup$ Aug 12 at 18:24
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    $\begingroup$ @BrendanLuke15: There is only one single place where I have seen this extremely high number of 16 launches mentioned. Elon Musk has never talked about 16 launches, SpaceX has never talked about 16 launches, NASA has never talked about 16 launches, Congress has never talked about 16 launches, no space news organization has ever talked about 16 launches, even Blue Origin, when they tried very hard to make SpaceX look as bad, as expensive, as complex as possible, has not claimed a number this high. The only place where this number appears is in a report by the Government Accounting Office. $\endgroup$ Aug 12 at 19:44
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    $\begingroup$ @JörgWMittag there's no evidence that is the case, it is inconsistent with the tone and content of the GAO report, and it's questionable whether they would even perform such an analysis themselves. It is likely SpaceX would have given an upper bound in their proposal, and the 16 launches figure is consistent with an upper bound based on their current prototypes. BO likely wouldn't have any legitimate access to such information (which doesn't exclude the possibility of accidental or intentional leaks), but the GAO would, and the worst case scenario is what they're most interested in. $\endgroup$ Aug 13 at 15:15
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    $\begingroup$ The "16 launches" figure is actually mentioned in the GAO report (page 27, gao.gov/assets/b-419783.pdf) as being part of Blue Origin's protest, it's not something the GAO invented. BO's objection in the protest was that NASA waived a requirement of a flight readiness review for every flight. Of course, the tanker flights are all identical, interchangeable, and replaceable, so a FRR for each one really wouldn't make sense. Probably why they've shifted from "unfair!" to "it's too complicated!" in this...whatever you want to call this little display after their protest failed. $\endgroup$ Aug 14 at 19:20

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