### Author Topic: Stacking the SLS on top of the ITS booster  (Read 984 times)

#### Nilof

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##### Stacking the SLS on top of the ITS booster
« on: 03/05/2017 06:48 PM »
(Disclaimer: this thread may not be too serious.)

So I compared the ITS launcher with the SLS, and noticed that the gross weight of the ITS second stage (tanker) is larger than the gross weight of the entire SLS stack.

So, just for fun, let's compute how much payload to various orbits you could get to various orbits if we stacked an SLS on top of the ITS first stage!
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

#### envy887

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##### Re: Stacking the SLS on top of the ITS booster
« Reply #1 on: 03/06/2017 02:01 AM »
Using the EUS as a 3rd stage and using the solids to get off the pad, this would put 261,159 kg of payload to TLI. It could launch an Altair, three Orions, 36 Centaurs, and the kitchen sink, all to the Moon at once.

But ITS, fully refueled on orbit, would inject 1450 tonnes to TLI. No uberlarge launcher is ever going to match an uberlarger launcher with the ability to refuel in orbit.

#### TomH

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##### Re: Stacking the SLS on top of the ITS booster
« Reply #2 on: 03/06/2017 07:37 AM »

Scroll down the page to see a CGI of it.

Note that you cannot air start RS-25, thus I subbed J-2X.
« Last Edit: 03/06/2017 07:50 AM by TomH »

#### Rei

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##### Re: Stacking the SLS on top of the ITS booster
« Reply #3 on: 03/06/2017 09:30 AM »
But ITS, fully refueled on orbit, would inject 1450 tonnes to TLI. No uberlarge launcher is ever going to match an uberlarger launcher with the ability to refuel in orbit.

This actually raises something I've been wondering.  Why aren't they planning to launch Mars missions from the Earth-Moon L1 or L2?  Their cost figures are predicated on maximizing the use of the boosters and tankers; they have crazy-low cost figures and crazy-high launch rates planned for them, with the primary costs wrapped up in the spaceship itself. So anything that has them using more launches of boosters and tankers, by their figure, costs little.  Two tankers, each filled in LEO, could refuel an ITS spacecraft in L2, with enough remaining for return, landing, and contingency.  The ITS spacecraft can then do an Earth swingby for ~335 (if I remember right) m/s dV to maximize the Oberth effect for interplanetary missions.  You get vastly higher payloads (and/or reduced travel times) launching from L1 or L2 than from LEO.  But by their cost figures it'd only be a marginal increase in cost because their boosters and tankers are so cheap.

Is it a crew loading issue?  They haven't talked about their plans for that, at least anywhere I've seen (correct me if I'm wrong).  And that wouldn't apply to simple cargo deliveries.
« Last Edit: 03/06/2017 09:31 AM by Rei »

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