Starship IUS-Style Upper Stage for Deep Space Probes

[DPRKChlorinePentaflouride]

Would Starship ever use a big, efficient (LH2/LOX) upper stage (like the Exploration Upper Stage or S-IV on steroids) for NASA missions to the solar system? According to Silverbird, a Starship (booster and ship expendable) with a fairing jettison at 363 seconds (assuming 20 tons for the fairing and 100 tons for the ship's empty weight, since I can't find fairing mass numbers), and an upper stage with 6 RL10s (22 tons empty with 180 tons propellant) can send, from an equatorial sea launch (as they will probably start launching from marine platforms within 10-15 years) and a 185km perigee:
-8 tons to Pluto
-12 tons to Saturn/Uranus
-38 tons to Jupiter
-86 tons to Mars (in the least favorable launch window)
-108 tons to TLI
(Note: all interplanetary payloads calculated with Wikipedia info on C3.)
Obviously for Mars/Moon the whole Starship can get there with in-orbit refueling, but would this be a better option for science probes? (Especially since you don't need such a huge number of launches in such a short time and don't have to deal with boiloff.) Imagine a Saturn orbiter using aero capture for an on-orbit mass five times that of Cassini.
I have attached the screenshot of the vehicle configuration, for those interested.

[wannamoonbase]

I've wondered about something similar to this, but I imagined the deep space stage would be refilled in space and maybe only have 1 or 2 RL-10's.

Maybe staging too. 

My gut feel is that the fairing would be less than 20 tons.

Mostly my thought it, I am 51 years old and I want to see a Neptune and Uranus orbiter before I'm too old.

With Starship, just throw all the mass at it.  Maybe a more conventional probe but with enough fuel to get there and enter orbit in less than decades.

If it needs 1000 tons of propellant, so be it.  Lets explore more and faster!

[DanClemmensen]

A methalox non-EDL starship with a hammerhead fairing can still be refuellable. It can carry a huge heavy payload to LEO, refuel, and boost it even further. The payload can include an "IUS-Style" Hydrolox upper stage.

One advantage of this kludge is that this same expendable Starship can be used for any huge payload, not just outer planet missions.

[livingjw]

- Using LH2/LOx engines instead of LCH4/LOx engines will not increase your maximum DeltaV that much. Probably better to stick with LCH4/LOx. LCH4/LOx engine will require more propellant mass but will have about the same maximum DeltaV due to the increased mass fraction when using a LH2/LOx propulsion as compared to a LCH4/LOx.

- For a maximum payload, maximum DeltaV mission and we assume LEO refueling, then LCH4/LOx will be the winner. If the mission is to be done without refueling, then LH2/LOx will make the most sense.

[wannamoonbase]

- Using LH2/LOx engines instead of LCH4/LOx engines will not increase your maximum DeltaV that much. Probably better to stick with LCH4/LOx. LCH4/LOx engine will require more propellant mass but will have about the same maximum DeltaV due to the increased mass fraction when using a LH2/LOx propulsion as compared to a LCH4/LOx.

- For a maximum payload, maximum DeltaV mission and we assume LEO refueling, then LCH4/LOx will be the winner. If the mission is to be done without refueling, then LH2/LOx will make the most sense.

In John I Trust

Thank you, great information.

[Twark_Main]

What about an evolved IUS that can refill its LOX from a Starship tanker?

Launch with empty LOX tanks, maxing out the Starship payload mass with hydrogen and payload. Then refill LOX from a depot in orbit (1 docking) and go.

[DanClemmensen]

What about an evolved IUS that can refill its LOX from a Starship tanker?

Launch with empty LOX tanks, maxing out the Starship payload mass with hydrogen and payload. Then refill LOX from a depot in orbit (1 docking) and go.

That's elegant. Since there are relatively few missions that really need more than a refueled "standard" Starship, this may be the most cost-effective approach.

Yes, the hydrogen is low mass, but it might make sense to go ahead an refill the hydrogen also, to squeeze out just a bit more tonnage. Either build a special-purpose hydrogen tanker or build a specialized depot adjunct that converts CH4 to hydrogen by  methane pyrolysis.

[InterestedEngineer]

There is already a well-filled thread full of ideas for this topic

https://forum.nasaspaceflight.com/index.php?topic=55550.0

TL;DR the simplest system was Starship with a GTO refill and Oberth boost, leaving Earth with Vinf of 15 km/sec, which gets you anywhere you want in the solar system and (barely) exceeds escape velocity of the solar system, all with 150t of cargo or braking fuel for the other end.

A benefit is you get to EDL on the other end for any destination with an atmosphere, which saves most of the fuel on the other end.

To get a decent clip out of the solar system, you need to do a gravity slingshot+Oberth burn at Jupiter.

[TomH]

In a word, no. We have already been over this many times. Simply re-propping a stripped down Starship in LEO such that it is completely filled with methalox gives you a more capable EDS than a Hydrolox US. To make it even more capable, take it from LEO to HEO and re-prop it again. Far more robust, more practical, more economical. No real reason to rehash this any more. It has been discussed repeatedly.

[InterestedEngineer]

What about an evolved IUS that can refill its LOX from a Starship tanker?

Launch with empty LOX tanks, maxing out the Starship payload mass with hydrogen and payload. Then refill LOX from a depot in orbit (1 docking) and go.

That's elegant. Since there are relatively few missions that really need more than a refueled "standard" Starship, this may be the most cost-effective approach.

Yes, the hydrogen is low mass, but it might make sense to go ahead an refill the hydrogen also, to squeeze out just a bit more tonnage. Either build a special-purpose hydrogen tanker or build a specialized depot adjunct that converts CH4 to hydrogen by  methane pyrolysis.

Try doing the math to see how much LH2 you can stuff into a Starship3's cargo area.

It's less than half of Starship3's rated cargo mass capacity.

The benefit of 1.22x exhaust velocity can't cover that.  That's a mass ratio of 7 vs 10.8 (for example)  or 1.5x more LCH4 than LH2 to do an LEO burn.  It'd cost 2/1.5 = 1.3x more trips to LEO to refuel your LH2 rocket in LEO.  Simply not worth it.

Now consider that you are completely throwing away the idea of an elliptical orbit burn outboub d from Earth, and the argument for hydrolox gets even worse.

I don't think one could even come up with a hydrolox method of getting Vinf of 15km/sec from Earth with a 100t of cargo.  It's simply not possible, and it'd never be cheaper than Starship doing it.

[Riccardo11]

TL;DR the simplest system was Starship with a GTO refill and Oberth boost, leaving Earth with Vinf of 15 km/sec, which gets you anywhere you want in the solar system and (barely) exceeds escape velocity of the solar system, all with 150t of cargo or braking fuel for the other end.

Would it be possible to combine a fully refueled Starship with an IUS-like fourth stage? Outcome?

[livingjw]

Just to be clear:

- My model is for single stages optimized for in-space DeltaV. I am just pointing out that the maximum achievable DeltaVs for either a LH2/LOx or a LCH4/LOx stage is about the same, the empty masses are about the same. The ratio of propellant mass of LCH4/LOx to LH2/LOx varies with DeltaV as shown below.

- My model does not address orbital mechanics, Oberth effects or multi stage mission designs. Its just straight propulsion system performance. It includes tank mass, engine mass and propellant mass only.

John

[InterestedEngineer]

TL;DR the simplest system was Starship with a GTO refill and Oberth boost, leaving Earth with Vinf of 15 km/sec, which gets you anywhere you want in the solar system and (barely) exceeds escape velocity of the solar system, all with 150t of cargo or braking fuel for the other end.

Would it be possible to combine a fully refueled Starship with an IUS-like fourth stage? Outcome?

Sure, but Oberth burns can only last so long before no more Oberth, and the burn time of a 9 engine Starship with 2000t of fuel is almost too long for Earth.   8 minutes * 15km/sec => 7,200km.  Too lazy to draw the ellipse for that, but it's getting to be away from the low point of Earth's gravity well too long, at an educated guess.

a fourth stage would be handy for a Jupiter Oberth burn, though you can send ~10 fuel-loaded Starships to a Jupiter trajectory on the same Earth Oberth burn and have one full one at arrival to Jupiter too

(the other 9 could slingshot back to Earth through some fancy planetary orbital slingshots/trajectories, though the arrival velocity would be probably too much for EDL at Earth).

Still, expending 10 Starships at a COGS of $30m/ea is STILL cheaper than designing a custom rocket and building it.

Starship's mass production, reuse, and ability to refuel changes a ton of what we think is correct mission planning.  Most of the traditional methods are obsolete (okay, "soon to be" obsolete).

[meekGee]

TL;DR the simplest system was Starship with a GTO refill and Oberth boost, leaving Earth with Vinf of 15 km/sec, which gets you anywhere you want in the solar system and (barely) exceeds escape velocity of the solar system, all with 150t of cargo or braking fuel for the other end.

Would it be possible to combine a fully refueled Starship with an IUS-like fourth stage? Outcome?

Sure, but Oberth burns can only last so long before no more Oberth, and the burn time of a 9 engine Starship with 2000t of fuel is almost too long for Earth.   8 minutes * 15km/sec => 7,200km.  Too lazy to draw the ellipse for that, but it's getting to be away from the low point of Earth's gravity well too long, at an educated guess.

a fourth stage would be handy for a Jupiter Oberth burn, though you can send ~10 fuel-loaded Starships to a Jupiter trajectory on the same Earth Oberth burn and have one full one at arrival to Jupiter too

(the other 9 could slingshot back to Earth through some fancy planetary orbital slingshots/trajectories, though the arrival velocity would be probably too much for EDL at Earth).

Still, expending 10 Starships at a COGS of $30m/ea is STILL cheaper than designing a custom rocket and building it.

Starship's mass production, reuse, and ability to refuel changes a ton of what we think is correct mission planning.  Most of the traditional methods are obsolete (okay, "soon to be" obsolete).

I'd think you have at least roughly a half circumference, around 20,000 km, before you start to lose significant velocity.  Maybe even more.  (V2 is being traded for 1/r, so whether you're at r=6000 or 8000 can't be super fundamental )

But yes, Oberth is not for slow burns.

[Solarsail]

FWIW, Impulse Space wants to do something pretty close to these ideas on both Starship and the upcoming semi-resuable rockets.  14 ton expendable methalox kick stage, and if I'm interpreting Muller's comments correctly, flying into orbit unfuelled and fueling up off of the Starship after reaching orbit.  Which juxtaposes the cost of Starship tankers  against modest size expendable stages.  There's also the trade off between expending Starships or kick stages.

Also aiming at far less exotic (more common) work than just outer solar system science.

[dabomb6608]

This kind of brings up a potentially interesting usage case for Starship Depots in my mind. It is no secret that Starship and Falcon will likely be the cheapest options for companies to launch their probes/equipment into space. At least for the short-mid term future.

But regardless of how they get to orbit, depots could be use to load propellant into probes that are taken to orbit empty and then they can proceed from there with their mission profiles.

[Jim]

This kind of brings up a potentially interesting usage case for Starship Depots in my mind. It is no secret that Starship and Falcon will likely be the cheapest options for companies to launch their probes/equipment into space. At least for the short-mid term future.

What companies are going to launch probes?

[Jim]

Sure, but Oberth burns can only last so long before no more Oberth, and the burn time of a 9 engine Starship with 2000t of fuel is almost too long for Earth.   8 minutes * 15km/sec => 7,200km.  Too lazy to draw the ellipse for that, but it's getting to be away from the low point of Earth's gravity well too long, at an educated guess.

nah, 8 minute is still short. Apollo burn 5:30, Mars 2020 did 7:30 and Juno was 9:00.  Pluto New Horizons was  10 minutes.

[dabomb6608]

This kind of brings up a potentially interesting usage case for Starship Depots in my mind. It is no secret that Starship and Falcon will likely be the cheapest options for companies to launch their probes/equipment into space. At least for the short-mid term future.

What companies are going to launch probes?

Companies/Entities...Potato/Potahto...the point still stands

Not to mention commercial space is in its infancy, just because it doesn't happen currently doesn't mean it won't in the future.

[Jim]

Companies/Entities...Potato/Potahto...the point still stands

No, it doean't.  There is only one "entity" that does this.  I

Not to mention commercial space is in its infancy, just because it doesn't happen currently doesn't mean it won't in the future.

Commercial?  What is the ROI on a Neptune probe or any?