The Starship "I risk sending a thread off topic" Homeless Posts Thread 2

[aporigine]

IF, big IF, NASA would develop small enough nuclear engines on a payload, then build a mother ship around say 2-3 nuclear engines we could explore without a lot of tanker flights.  A large mother ship that can push a Starship to Mars and back would allow a fully fueled Starship to land and return to the mother ship for the trip back to earth.  A nuclear ship would need less fuel to operate and it could be just a simple tank sway using docking connections to refuel it. 

Private companies would have to jump through the nuclear regulation hurtles just to try to build one.  It takes about 10 years for a private power company to build a nuclear power plant.  But, NASA being a government agency could build the engines starting today and probably have a working model in 5 years.  The did it in the 1960's and developed two nuclear engines, one large one and one small one that was to replace Saturn V's 3rd stage to use for "future" Mars trips.  If the funding stayed and the development continued, we would have been on Mars by 1985.  They could dig up the plans and if I remember correctly one of the engines got over 1,000 ISP on ground testing in the desert. 

Of course it would require more in space assembly, but less tanker trips.  Even a large NEP ship could be built say using argon, because Mars atmosphere is about 6% argon, so refueling could be done at Mars as well as on earth.  But, it would require NASA again to build and launch nuclear engines.

Argon is heavy, and nuclear thermal is limited by temperature. Isp would be back down in the chemical rocket range.

[spacenut]

Problem is Argon can be found in Mars' atmosphere, so refueling in Mars orbit could be done.  Chemical fuels and rockets are even heavier and do require multiple tanker trips to refuel.  Argon would be fewer refueling trips, maybe only one. 

[Vultur]

Let's not confuse nuclear thermal and nuclear-electric.

Argon would be an incredibly terrible propellant for nuclear thermal (high molar weight + since it's monatomic, there's no chance of dissociation helping a bit); specific impulse would be significantly worse than Raptor.

Electric propulsion is vastly more useful, and argon is a good fuel, but solar power is a lot more effective in terms of specific power (watts per kilogram), cheaper, and faces less political/regulatory difficulties. Actually flown space reactors have terrible specific power; unfolding larger solar panels is probably easier to develop than an orders of magnitude better space reactor.
 
Nuclear-electric would be needed in the outer solar system, but that's a long way away.

  Chemical fuels and rockets are even heavier and do require multiple tanker trips to refuel. 

Chemical fuels are heavier than hydrogen fuel for an NTR, sure. But the chemical rocket (hardware) is much lighter than the NTR, for two reasons: the nuclear reactor itself is very heavy, and liquid hydrogen is much lower density & more cryogenic than liquid oxygen+methane, so the tanks are much larger and boiloff prevention more demanding.

Hardware (especially nuclear hardware!) is much more expensive than propellant, so if you are capable of orbital refueling, there's no real advantage to the NTR for this sort of mission. Delta-v from low Earth orbit to Mars is easily attainable by chemical rockets.

Solid-core NTRs, honestly, have extremely marginal use cases in a world with orbital refueling. The Isp isn't high enough for really high delta-V missions, and much of the performance advantage is eaten up by lower mass ratio (because of heavy reactor) and inability to aerobrake (at least at the Earth end) even before you consider cost.

[InterestedEngineer]

Let's not confuse nuclear thermal and nuclear-electric.

Argon would be an incredibly terrible propellant for nuclear thermal (high molar weight + since it's monatomic, there's no chance of dissociation helping a bit); specific impulse would be significantly worse than Raptor.

Electric propulsion is vastly more useful, and argon is a good fuel, but solar power is a lot more effective in terms of specific power (watts per kilogram), cheaper, and faces less political/regulatory difficulties. Actually flown space reactors have terrible specific power; unfolding larger solar panels is probably easier to develop than an orders of magnitude better space reactor.
 
Nuclear-electric would be needed in the outer solar system, but that's a long way away.

  Chemical fuels and rockets are even heavier and do require multiple tanker trips to refuel. 

Chemical fuels are heavier than hydrogen fuel for an NTR, sure. But the chemical rocket (hardware) is much lighter than the NTR, for two reasons: the nuclear reactor itself is very heavy, and liquid hydrogen is much lower density & more cryogenic than liquid oxygen+methane, so the tanks are much larger and boiloff prevention more demanding.

Hardware (especially nuclear hardware!) is much more expensive than propellant, so if you are capable of orbital refueling, there's no real advantage to the NTR for this sort of mission. Delta-v from low Earth orbit to Mars is easily attainable by chemical rockets.

Solid-core NTRs, honestly, have extremely marginal use cases in a world with orbital refueling. The Isp isn't high enough for really high delta-V missions, and much of the performance advantage is eaten up by lower mass ratio (because of heavy reactor) and inability to aerobrake (at least at the Earth end) even before you consider cost.

there are entire threads on nuclear in the advanced concepts forum

https://forum.nasaspaceflight.com/index.php?board=26.0

https://forum.nasaspaceflight.com/index.php?topic=58161.0

https://forum.nasaspaceflight.com/index.php?topic=50188.0

The summary negative argument:  https://forum.nasaspaceflight.com/index.php?topic=50188.msg2529397#msg2529397

I can't find a summary positive argument.

[Vultur]

I can't find a summary positive argument.

The summary positive argument is basically "NASA and DARPA are interested in it, they are full of smart people, therefore there must be some advantage".

The problem with that is that they have institutional biases in favor of developing new hardware.

Well, to be fair, from DARPA's perspective... They may not want to rely on refueling, and you can get more delta v in a single stage/non-refueled vehicle from nuclear thermal than from chemical, despite the dry mass disadvantage, if you don't need TWR >1 and are willing to deal with liquid hydrogen. So there may well be some military or military-adjacent applications.

But your delta-V needed has to be significantly more than TMI's 4 km/s or so before even that makes sense. Building a chemical single stage with 4 km/s is really simple.

But dramatic plane changes in Earth orbit can easily have much higher delta-V requirements. So if you could get zero or very low boiloff for liquid hydrogen, so the vehicle could wait in-orbit for long stretches of time, NTR might be useful for some kind of space Coast Guard/rescue vehicle able to access a wide variety of orbits on very short notice.

The other positive argument is that solid-core NTR is a technological step toward much higher performance possible nuclear propulsion systems (like a gas-core NTR that could maybe have electric propulsion competitive Isp of ~3000, or maybe even a nuclear-salt-water rocket or something). That may well be true, but it's not IMO an argument to use it for Mars.

[spacenut]

I know there is nuclear electric for outer solar system. 

I also think nuclear thermal might be faster to get to and from Mars, using maybe hydrogen for fuel.  Maybe not.  Seems like 8-10 tanker flights to fuel up a Starship for Mars, then having to fuel up at Mars is a lot of work.  A large mother ship carrying a Starship or more than one Starship to and from Mars might require less refueling.  NASA would have to build it, then maybe SpaceX could launch to parts and assemble in orbit.  Might be safer than a lot of refueling.  Don't know.  SpaceX chose refueling because of the regulatory hurdles involving Nuclear thermal. 

[Vultur]

I also think nuclear thermal might be faster to get to and from Mars, using maybe hydrogen for fuel.  Maybe not. 

It's not.

A fully refueled Starship could actually do a very aggressive burn to Mars, much beyond the minimum TMI delta-V, to get there faster. The limiting factor may be the heat shield's ability to aerobrake away that velocity, and maybe g forces on the passengers during that aerobraking.

Seems like 8-10 tanker flights to fuel up a Starship for Mars, then having to fuel up at Mars is a lot of work.[\quote]

It's the kind of thing that may be a pain to develop but should be smooth, easy, and reliable once developed.

Also, 8-10 tanker flights may be pessimistic once Starship v4 exists. v4 is supposed to have 200 ton payload, it shouldn't take 1600-2000 tons of propellant to land a Starship on Mars.

TMI is only about 4 km/s ish. Say 1 km/s for the actual landing... 5 km/s for Isp ~370 is only about a mass ratio of 4.

They'll probably use more than that minimum TMI delta-V to get there faster, but still...

SpaceX chose refueling because of the regulatory hurdles involving Nuclear thermal.

Not just that, it's actually better.

[lamontagne]

Standing on it's trusty launch barge.

How do you create these images?

I build the 3D model in Sketchup, then render the color and light in Twinmotion.

[spacenut]

Ok, so nuclear thermal is out.  How big of a solar array need to be to carry a Starship to Mars and back with SEP propulsion.  1 square kilometer?  Less.  I'm thinking carrying a Tanker/fuel depot to Mars orbit using SEP propulsion, same with a tanker/fuel depot Starship to lunar orbit or LL1 or LL2 for topping off ships going to Mars. 

My idea is an easier way to at least get fuel depots in place, even if slow with SEP propulsion so Starships can launch and top off tanks on their way to anywhere, moon or Mars. 

That is why I am asking how big of a SEP tug would have to be built?  Shouldn't the SEP propulsion use a more abundant fuel source that can be found, not only on the moon, but Mars also.  Vasimr I think was one that could even use oxygen for propellant. 

That is why I am asking how big a SEP tug to be able to push a fully loaded Starship to various locations.  Slowly if need be, but at least break Earths gravity well, the moons, and Mars gravity well if necessary. 

[Robotbeat]

The thing about SEP is the Isp is so much higher than chemical you can source it wherever. Both Earth and Mars have lots of Argon, which SpaceX already used in their Starlink electric thruster.

But it probably only makes sense to push propellant around this way. Maybe cargo. Humans take the fast chemical propulsion route, not SEP.

[spacenut]

That is what I was thinking.  Push fuel depots from LEO, to lunar orbit to support Lunar operations.  Then push fuel depots to Mars orbit.  A Starship could escape Mars orbit, refuel say at LL2, then go on to Mars with an almost full Starship.  In Mars orbit at a depot that was brought by a large SEP tug, could refuel, land on Mars, and probably have enough fuel to get back to Mars orbit to refuel for a trip back to earth.  At least early on for a quick trip to Mars without using Robots to build a fuel depot on Mars which may run into problems.

Once a Mars fuel manufacturing base is established, it could send fuel to the fuel depot orbiting Mars. 

Once the Fuel depots are in place the large SEP tug to bring cargo ships to Mars without using a lot of fuel. 

I'm just thinking a big SEP tug built by components brought up by Starships in LEO, maybe could eliminate the need for either refueling or a lot of refueling launches in the long run by being able to transport Starship size payloads to the moon or Mars. 

[lamontagne]

That is what I was thinking.  Push fuel depots from LEO, to lunar orbit to support Lunar operations.  Then push fuel depots to Mars orbit.  A Starship could escape Mars orbit, refuel say at LL2, then go on to Mars with an almost full Starship.  In Mars orbit at a depot that was brought by a large SEP tug, could refuel, land on Mars, and probably have enough fuel to get back to Mars orbit to refuel for a trip back to earth.  At least early on for a quick trip to Mars without using Robots to build a fuel depot on Mars which may run into problems.

Once a Mars fuel manufacturing base is established, it could send fuel to the fuel depot orbiting Mars. 

Once the Fuel depots are in place the large SEP tug to bring cargo ships to Mars without using a lot of fuel. 

I'm just thinking a big SEP tug built by components brought up by Starships in LEO, maybe could eliminate the need for either refueling or a lot of refueling launches in the long run by being able to transport Starship size payloads to the moon or Mars.

They need to be pretty large. The cheapest propellant is oxygen, as long as your system also has a use for iron or titanium. But the efficiency, at this time, is very low.  I'm not certain if this is perfectible or if it is inherent to the energy cost of ionizing the oxygen.

Orbital Transfer Vehicle is in the first tab.
As a bonus the spreadsheet covers a number of other subjects, including my current obsession with Spinlaunch on the Moon.

[spacenut]

With the payload of Starship, a lot of stuff can be built in space.

[Robotbeat]

It’s not that hard to calculate how much power is needed. For Earth or Moon vicinity, you can usually just double the high-thrust delta-v required to get the low-thrust equivalent. You can pick the Isp to be whatever you want, but typically the Isp (in m/s) is optimal when it’s set to sqrt(2*efficiency*specific_power*mission_duration) so if you assume 50% efficiency, 50W/kg specific power (inclusive of the thrusters and solar panels), and two year mission segment duration, you get about 56km/s optimum Isp. https://www.google.com/search?q=sqrt%282*0.50*50W%2Fkg*2year%29

To do like the 6-7km/s to get from LEO to escape, it takes (e^(6/56)-1) times your burnout mass in propellant, so if we’re talking like 3000t burnout mass, 339t of Argon, which at 56km/s exhaust velocity at 50% efficiency and over 2 years requires 17 MW of average power, 337t of SEP hardware at 50W/kg, so your payload would be about 2660t with 337t SEP mass and 339t of Argon.

(.5/.5)*e^(6/56)-1)*3000000kg*(56km/s)^2/(2years)/(50W/kg)

[Nomadd]

 Yous guys are making everything too complicated. In my day, we didn't need all that fancy schmancy computerized gear to build a Starship. Just some spikes and a few landscape timbers.

[catdlr]

New Glen, welcom to the family

https://twitter.com/ScottLikedSLS/status/1990115772077646016

[wes_wilson]

I wish to do a little math for a contribution to one of the threads.  Is there a thread or sticky somewhere that reflects the forums working consensus for dry mass, wet mass, isp, cargo of the starship system, mass to leo, etc?  (understanding it's all a moving target)  I'd like my numbers to be in the ballpark of what others are generally using for inputs to their calculations. 

[rsdavis9]

I wish to do a little math for a contribution to one of the threads.  Is there a thread or sticky somewhere that reflects the forums working consensus for dry mass, wet mass, isp, cargo of the starship system, mass to leo, etc?  (understanding it's all a moving target)  I'd like my numbers to be in the ballpark of what others are generally using for inputs to their calculations.

Maybe this:

https://forum.nasaspaceflight.com/index.php?topic=50049.new;topicseen#new

[wes_wilson]

I wish to do a little math for a contribution to one of the threads.  Is there a thread or sticky somewhere that reflects the forums working consensus for dry mass, wet mass, isp, cargo of the starship system, mass to leo, etc?  (understanding it's all a moving target)  I'd like my numbers to be in the ballpark of what others are generally using for inputs to their calculations.

Maybe this:

https://forum.nasaspaceflight.com/index.php?topic=50049.new;topicseen#new

Exactly what I was seeking, thank you.  And props to xvel and others for that great thread!

[catdlr]

ARSTechina article:

Oh look, yet another Starship clone has popped up in China
Chinese companies are no longer hiding their intent to clone SpaceX. They’re advertising it.

Eric Berger – Dec 15, 2025 8:44 AM


https://twitter.com/AJ_FI/status/2000103853841141986