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If Persephone insists on using those low g limits then actually Starship probably wouldn't be suitable as an alternative launch vehicle.

I would like to see a refueled starship send a 56t probe to the outer planets with a raptor kick stage some day though, that would be rad.

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On 7/9/2020 at 7:23 AM, kerbiloid said:

According to wiki, that's 4 / 153 * 25 ~= 0.65 bln in the Apollo-time prices.

So, if compare it to Saturn V + Apollo, they were probably even more expensive.

Maybe, but political situation was completely different on those days. Apollo was a propaganda project for cold war between superpowers. It had so high share of state's budget that nothing even near is possible in foreseeable future. Unfortunately space exploration is now low cost low interest science project for nerds and budgets compete with tardigrade investigations and ancient languages of disappeared cultures.

SLS could fit in Apollo -like situation but several billions per launch ruin all current scientific space projects immediately. If administration of USA does not give crazy level of funding for example manned moon operations no one is able to buy SLS launch, which cost about as much as whole flagship class planetary mission. And I do not see such funding very realistic.

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On 8/12/2020 at 9:36 PM, RCgothic said:

I would like to see a refueled starship send a 56t probe to the outer planets with a raptor kick stage some day though, that would be rad.

Would using RL-10 on the kick stage be better? Or the TWR would be too low?

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19 minutes ago, Space Nerd said:

Would using RL-10 on the kick stage be better? Or the TWR would be too low?

Depends on the payload mass relative to the stage mass. For a 56t payload, yes, RL10 would be better if you're staging shortly after the main launch vehicle has burned from the parking orbit.

For a 1.3t payload like Persephone, a raptor stage would be better than a Centaur because for small payloads better mass fraction trumps better ISP.

TWR isn't really important to vacuum stages already in orbit.

 

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23 hours ago, Hannu2 said:

SLS could fit in Apollo -like situation but several billions per launch ruin all current scientific space projects immediately.

Can't really do anything Apollo-like, it's the wrong size given Orion.

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maneuvering

On 8/14/2020 at 3:58 AM, RCgothic said:

TWR isn't really important to vacuum stages already in orbit.

TWR isn't completely unimportant in orbit.  First, if your fuel is hydrogen you don't want it to boiloff before being burned.  Second, unless you plan on taking your time and using pressure-fed hypergolics like Mangalyaan (the spacecraft that brought "pe kicking" to real life) you can easily lose out on the Oberth effect.

Scott Manley points out that while the Shuttle maneuvering system may have been fine for the last bit of delta-v needed to circularize the shuttle's orbit, it would have been less effective for achieving escape velocity: https://www.youtube.com/watch?v=5mIRFxYYaC0

That said, the important thing is that this only means that thrust still has advantages in orbit, not that it is absolutely required as in early rocket stages.  If your spacecraft can survive the Van Allan belts, ion engines are more than ready to take you anywhere in the solar system from orbit, even if it takes months to spiral away from Earth.

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  • 2 weeks later...

SLS has their SRB test tomorrow. Full 126 second duration burn.

SRB cost is $485,000,000, so that means the burn costs ~3.85 M$ per second.

It will burn ~4950kg/s of propellant during this time. If the fuel was $1 bills it would only be burning 3850kg/s, though. So it's actually burning money faster than actually burning money.

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1 hour ago, tater said:

SLS has their SRB test tomorrow. Full 126 second duration burn.

SRB cost is $485,000,000, so that means the burn costs ~3.85 M$ per second.

It will burn ~4950kg/s of propellant during this time. If the fuel was $1 bills it would only be burning 3850kg/s, though. So it's actually burning money faster than actually burning money.

But as we all know, this money comes from trees!

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2 hours ago, tater said:

SLS has their SRB test tomorrow. Full 126 second duration burn.

SRB cost is $485,000,000, so that means the burn costs ~3.85 M$ per second.

It will burn ~4950kg/s of propellant during this time. If the fuel was $1 bills it would only be burning 3850kg/s, though. So it's actually burning money faster than actually burning money.

So I make that $778 per kilogram of propellant, rounding up or $354 per pound.

For comparison, Iberico ham, at 2016 prices, comes in at $140 per pound. 

That was the most expensive pork I could find online - but it ain't got nothing on SLS pork!

 

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10 hours ago, tater said:

SRB cost is $485,000,000, so that means the burn costs ~3.85 M$ per second.

Things that KSP doesn’t teach: IRL you can buy several heavy-lift orbital rockets for the price of one SRB

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