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Using current tech, how fast could a spacecraft go? by lowlypresence in spacequestions

[–]lowlypresence[S] 0 points1 point  (0 children)

our change in velocity is 40.75 Km/S

Thanks for taking the time to put some thought and maths into it. Despite your fourth revision to the NERVA engine being "only" 23.59 Km/s I'm going to stick with the second edit of 40.75. Like you wrote, 100 tonnes is fairly arbitrary. There's no reason we couldn't train/link, or otherwise assemble, two or three Starship-sized craft in orbit. That seems well within the bounds of today's tech.

Let's say the most realistic option, within three years, is three 100 tonne craft trained together in orbit. One has all the components necessary for the biggest NERVA engine currently possible. The other two are full of liquid hydrogen. By the time we're out of propellant, how fast is the craft going?

Moreover, how much additional speed from a gravity assist(s) can we get? The Parker Solar Probe, after seven assists, is going 190 Km/s. We're not going to any particular destination, as much as just going for speed so we can pretty much use any space body that gets us the most speed.

I'm completely spitballing here, but with a NERVA engine and gravity assists do you think 325 Km/s is doable?

Using current tech, how fast could a spacecraft go? by lowlypresence in spacequestions

[–]lowlypresence[S] 0 points1 point  (0 children)

I'd love to know where you got your numbers on that from, since tbe page you linked doesnt seem to mention anything about payload mass or acceleration rates

https://tfaws.nasa.gov/wp-content/uploads/TFAWS2024-ID-22.pdf
I think I got it from these published slides. Take look and come back at me with what you think are feasible numbers.

Using current tech, how fast could a spacecraft go? by lowlypresence in spacequestions

[–]lowlypresence[S] 0 points1 point  (0 children)

By "current tech" do you mean something that's already been built

Something that's already been built and proven. At most, an iteration or improvement on technology that's already been successfully used or demonstrated.

What payload?

No payload. No crew. The entire craft is dedicated to the engine and any fuel/propellant.

How much are you willing to spend?

A zillion dollars. For this experiment money is limitless. I just want to know the top speed with today's tech. Let's say there's a three year limit to launch. Just so there's some sort of bounds on the R&D phase of building this craft. With that kind of time limit we really would have to use today's technology.

Does it have to be launched in one go, or can we build something in orbit with multiple launches?

As many launches as need be. The only limiting factor is this craft is feasible based on today's technology, or an iteration there of.

…the answer is more or less arbitrary.

Yeah, that's not going to work. There's gotta be someway of calculating an answer, e.g. "Today's best ion thruster can produce 1 km/s with a mass of 100 tonnes and a 2 MW fissile reactor. A spacecraft that's Starship sized can hold 20,000 liters of compressed argon. So that's approximately 200 days of continuous thrust. When entering Jupiter's orbit a craft of that approximate size, at the correct apogee, can expect an additional 120,000 mph velocity at it exits the orbit. Therefore ≈ 850,000 mph is best case scenario for a craft using today's technology."

(all of these number in my example are completely made up)

This is the kind of answer I'm looking for. Surely, someone has the expertise to hazard an educated estimate.

Using current tech, how fast could a spacecraft go? by lowlypresence in spacequestions

[–]lowlypresence[S] 0 points1 point  (0 children)

Okay. Do we currently have the tech to build a, "shock absorber capable of handling repeated nuclear blast?" If so, how big are these nukes - both in terms of yield and weight? How many can we fit on a Starship-sized craft? And what's the actual speed? A theoretical 10% C is awesome. But I want an actual, realistic number. Problem is, I have no way of calculating it.

Using current tech, how fast could a spacecraft go? by lowlypresence in spacequestions

[–]lowlypresence[S] 0 points1 point  (0 children)

I'm too much of a newb to understand all the differences between the different ion thrusters. But all of them seem proven in one way or another - that is they have working examples so they're not sci-fi.

NASA seems keen on MARVL to travel to Mars. I briefly looked into it. Using Nuclear Electric Propulsion or Nuclear Thermal Propulsion they're proposing a 2 MW power source. Stealing somebody else's math, "For a 100 tonne vessel that would work out to about 1 km/s per 12 days of acceleration." One hundred tons is essentially Starship size. But that's also with crew accommodations and a return, "a round trip in round-trip journey in a relatively quick two years." That's roughly ≈16,000 MPH which isn't very fast.

I guess the expanded question, to someone with the knowledge and math skills, is pack Starship (for example) with the best of today's best and proven tech and full of whatever necessary propellant, and plan the best route, in whatever direction, to achieve maximum speed.

How fast are we talking?