WI: Saturn C-5N Launched

The Saturn C-5N was basically a Saturn 5 with a NERVA upper stage. It got cancelled in ‘72 due to both NASA scaling down its ambitions ( it was designed as a key component of a Mars mission) and concern about nuclear anything.

So, lets assume that, at some point before that, at least one C-5N is launched into orbit, and it works without major problems. We’ll still assume that NASA gives up on Mars for the time being, and their budget still drops off sharply (just look up their budget on wikipedia and you’ll see what I’m talking about, the chart is very striking). So, basically, its up there in orbit from when NASA had bigger ambitions, and now they have to find a use for it.

What uses might it have?

How might it change the space programs going forward? Feel free to approach from both the perspective that this is the only nuclear thermal rocket launched to the present, or that its success encourages others.

One idea, depending on just how durable this thing proves to be, is to use it as a tug for various on programs. If it is launched during the moon missions, NASA might use it for one of them (hopefully not 13, though at least if anything went wrong, it wouldn’t have been due to mixing tanks).
 
The essential problem of NERVA is that it is only really useful if NASA is engaged in a large lunar program or a Mars program, and even then there are arguments that other propulsion methods, even conventional chemical, is superior in various respects. The Congressional environment in the late 1960s and early 1970s was extremely anti-large space programs, so neither a large lunar program nor a Mars program is going to happen, especially given that you explicitly specify that NASA's budget still falls. As such, it really doesn't matter whether or not NERVA flies, because no one doubted that it could fly if wanted, it's just that it wasn't wanted, and that's going to be equally true in your scenario.

The only way I can see this happening is that Clinton Anderson (NERVA's main Congressional backer) somehow manages to get one of the Apollo missions canceled in favor of test-launching a NERVA stage. This almost certainly shows that NERVA works, but since the Saturn V would be essentially canceled by the time it could possibly fly and the Saturn IB is going nowhere fast, further stages that would actually be useful for doing anything have no way of getting into space. With no mission, given a very likely NASA refocus to the space shuttle or (much less likely) a space station, the program is canceled as Anderson loses power and influence, as IOTL, and is left as a curious relic that occasionally pops up on news and trivia websites as a "did you know..." sort of thing. Later studies of Mars missions and Moon bases probably use data from the test flight extensively when trading nuclear rockets against other propulsion options, and space advocates will have vicious arguments over whether NERVA ought to be revived or not for Mars missions, slightly enhanced over their vicious OTL arguments because a stage actually flew.

TL;DR: It does nothing except provide fodder for later arguments over how to propel spacecraft beyond low Earth orbit and provide a trivia question for game shows and websites to exploit. Without Saturn it can't fly (given the Astronaut Corps reaction to Centaur, there's going to be an all-out war if someone tries to fly NERVA on Shuttle--besides which I don't think it would fit in the cargo bay), and given your scenario Saturn is dead. Without a bigger mission it's not useful, and given your scenario no bigger mission is possible.
 
I’m not sure NERVA as designed in the 1960s was actually supposed to be refueled—all the plans I’ve seen involve dumping used stages between Earth and Mars. So you’d need to change the NERVA design from the start to make it useful for what you propose—a reusable space tug (just add LH2).

If it’s placed up there, I can imagine it getting use in the 1980s—its presence might butterfly Shuttle-Centaur and IUS entirely, if they can figure out how to transfer propellant to it from STS (presumably involving disposable over-wing drop tanks of LH2–probably too bulky to fit in the payload bay with a useable payload). So you’d see NERVA as the booster for Galileo, Magellan, etc. Maybe TDRSS or some USAF payloads too.

Assuming it was optimized as a tug rather than a Mars stage from the start.

Of course, it’s useful life is not unlimited. If the test flight is in 1973, you’ve then got a live reactor hanging out for 8 years before the first ‘operational’ mission. The whole thing might be radioactive by 1981. It’ll at least be suffering some neutron embrittlement.
 
I’m not sure NERVA as designed in the 1960s was actually supposed to be refueled—all the plans I’ve seen involve dumping used stages between Earth and Mars. So you’d need to change the NERVA design from the start to make it useful for what you propose—a reusable space tug (just add LH2).
No, they were definitely planning on reusing the NERVA stages for non-Mars missions like lunar base resupplies (for Mars missions the delta-V requirements imposed special restrictions). The figure I recall was that they were supposed to go for up to ten restarts, then be disposed through one-way robotic missions. Of course, a test stage is likely to check that capability, so I wouldn't rate it as being reusable.
 
No, they were definitely planning on reusing the NERVA stages for non-Mars missions like lunar base resupplies (for Mars missions the delta-V requirements imposed special restrictions). The figure I recall was that they were supposed to go for up to ten restarts, then be disposed through one-way robotic missions. Of course, a test stage is likely to check that capability, so I wouldn't rate it as being reusable.
Yeah, most of the plans for cislunar space called for reuse, with 10 starts as the spec. The issue, of course, is that ten starts doesn't go very far once you start reusing a stage. You spend one burn putting the paylaod into lunar transfer orbit, and one getting the stage back into earth orbit for reuse. That's two, which means 5 missions if the payload performs its own lunar orbit insertion maneuver. If it doesn't, then you're up to four--LOI for the payload, and then your own TEI burn back to the lunar transfer orbit. That means only two missions--not much time to ammortize the massively higher cost of a reactor compared to a basic J-2 or RL-10 engine over lower propellant launch requirements.
 
That means only two missions--not much time to ammortize the massively higher cost of a reactor compared to a basic J-2 or RL-10 engine over lower propellant launch requirements.

Was the reactor of a NERVA really that expensive? In terms of complexity, I think it may actually be simpler than the J-2 engine and while there'd be health & safety costs to handling the core dirtside, I would be very surprised if it was more expensive than safely handling hydrazine is. Of course, as an exotic new technology NERVA type stages would be pretty expensive per unit if they're not used much.

Have you ever found an economic analysis of NERVA-derived engines?

The Saturn C-5N was basically a Saturn 5 with a NERVA upper stage. It got cancelled in ‘72 due to both NASA scaling down its ambitions ( it was designed as a key component of a Mars mission) and concern about nuclear anything.

So, lets assume that, at some point before that, at least one C-5N is launched into orbit, and it works without major problems. We’ll still assume that NASA gives up on Mars for the time being, and their budget still drops off sharply (just look up their budget on wikipedia and you’ll see what I’m talking about, the chart is very striking). So, basically, its up there in orbit from when NASA had bigger ambitions, and now they have to find a use for it.

What uses might it have?

How might it change the space programs going forward? Feel free to approach from both the perspective that this is the only nuclear thermal rocket launched to the present, or that its success encourages others.

One idea, depending on just how durable this thing proves to be, is to use it as a tug for various on programs. If it is launched during the moon missions, NASA might use it for one of them (hopefully not 13, though at least if anything went wrong, it wouldn’t have been due to mixing tanks).

Well, it might prove the concept for smaller nuclear stages. The NERVA sized for Mars missions was waaaaaaaaaaaaaaaaaaaaaaaaaaay too big to be practical for any mission Congress would provide money for. Something the size of the RD-0410 the Soviets were working on or the Peewee the US tinkered with would be a real boon for boosting payloads to geosynchronous orbit or across interplanetary space.

A Peewee stage would still not be something you'd want to carry inside the shuttle cargo bay, due to its liquid hydrogen propellant, but it could really boost the payloads of the US Delta, Atlas and Titan rockets.

If you want to see a full sized NERVA stage developed, I think the only way to achieve it is to avoid the Saturn V.

The Saturn V was so absurdly over-capable that for any reasonable mission, there are a dozen cheaper ways to eke out a bit more payload and a bit more Delta V.

By contrast, the Saturn IB first stage, if given a NERVA-derived second stage approaches the Saturn V in performance. With some strap-on boosters, I think a Saturn IB-N vehicle could equal the Saturn V's performance.

Such a Saturn IB-N also doesn't scream "MY ONLY USE IS TO GO TO MARS!" so in an ATL where the US didn't develop the Saturn V, the Saturn IB-N could get funded as a way of boosting heavy space station components, Lunar missions, space weaponry and interplanetary missions.

And one could have a Saturn IB-N with a NERVA-derived second and third stage, either full size or Peewee sized, which would even further extend its interplanetary utility.

fasquardon
 
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