shynung

Glide back, so the booster can use every last drop of propellant to push the main stack. The wings and landing gear would be sized for an empty booster, and it would have no parachutes or wheel brakes - just a tail hook, to stop it Navy-style.

This, with strap-on kerolox boosters that glide back to the launch site.

Not if you can pulse it like a TRIGA reactor. No, I'm not talking about the infamous Orion.

Yep. It'll be handy if the mission is stuck with low-performance engines like hypergolics, but that's about it. It's basically an extreme form of staging. I'm taking the scenario depicted in your second paragraph, with the added tidbit that the vehicle can be controlled remotely. Hence, the rescue vehicle can launch with empty seats, so we can safely assume there will be enough seats for the rescued crew. Also, I vouch for the practice of keeping a second, unmanned vehicle ready on the pad whenever a crewed launch is underway, especially if abort-to-ISS is unfeasible. If the crewed vehicle cannot return to earth after reaching orbit, the second unmanned vehicle would launch a rescue mission. I'm thinking of a two-type vehicle with a cargo and crew variant, but sharing most of the propulsion hardware. Downmass capability is not something that we have a lot of currently, and it can be useful for dropping massive cargo in Lunar or Mars missions.

Agreed. Although... This is still kind of possible. Barely, but can be a viable choice if payload mass must be conserved at all costs. I'm going under the assumption that the crew cabin ejects only during launch and ascent, so I'd leave most of the ECLSS on the upper stage, leaving just enough oxygen in the cabin for post-abort EDL, and waiting for the rescue crew. The heatshield would then be scaled for, at most, LEO reentry. All that is to shave mass in order to lighten the crew cabin's post-abort landing system (I'm assuming a Soyuz-style parachute-and-landing-solid-rockets), so that the landing system's mass can be minimized. Basically, in an aborted launch before reaching orbit, only the crew cabin returns, the rest of the rocket is written off. If anything bad happens to the upper stage after the vehicle reaches orbit that warrants aborting the mission, a better course of action would be to send an empty, unmanned vehicle, dock the new vehicle with the damaged one, transfer the crew to the new vehicle, use the new vehicle's engine to deorbit both vehicles, then land the new vehicle while dumping the damaged one towards the ocean.

I don't see much advantage in making them reenter together if the upper stage and crew vehicle can reenter independently. The crew cabin can be designed to be detached from the upper stage for emergencies, then have a launch abort tower stuck on top.

Isn't that essentially the Apollo missions' configuration when going from Earth orbit to Lunar orbit? Rocket stage, lander, crew capsule? Not to say this isn't complicated. but it's not that complicated. Though, I tend to agree with the idea that combining the upper stage and the payload/crew module, a la ITS, is a better configuration.

I'm proud to say that I didn't use any guides or YouTube videos to get to orbit. Staging, however, didn't occur to me until much, much later. My earlier rockets were all enormous SSTOs with pitiful mass ratios.

NASA Mars Reconnaissance Orbiter mission used an aerocapture maneuver. This reduced the fuel needed for Mars orbit insertion by half.

I see. Guess we'll need a few more decades for a deflatable module, then. I'd suggest using an aeroshell designed like a wingless Space Shuttle Orbiter, with cargo doors enclosing an unpressurized cargo bay, and a heatshield on the other side. The inflatable/deflatable module is connected to a rigid pressurized module by a swinging joint - to inflate the module, the joint swings the module out of the cargo bay (still attached to the rigid module via a pressurized tunnel/walkway), then inflate after the module is clear of the cargo bay. Stowing the module would be the opposite - deflate, swing-in, the close the cargo bay doors.

You can get around this by having a deflatable expandable module, and a rigid flight deck. Just before aerobraking, the crew goes to the flight deck and strap themselves, while the expandable module retracts (care must be taken to not leave free-floating items that may damage the module). IDK if the BEAM module can be deflated and neatly folded after deployment, though. Might need some more development on that front.

Depends. If both nations have asteroid tugs, and they both are aware of this fact, they may arm the tugs themselves, to ensure the asteroid gets to their target. Whenever a war breaks out, there may be space tug battles to gain control of individual rocks. There would probably also rock vs rock impacts, if the impacting rock trajectories are well known.

Which would trigger all of Soviet's nuclear arsenal to immediately launch all available warheads. The idea is, should anyone destroys the owner nation, their weapons will immediately attack the agressor nation. It's supposed to work as a deterrent rather than an offensive weapon.

On this, I agree. Asteroid tugs are less of a first-strike weapon and more like a retaliatory weapon, much like the Soviet Dead Hand system.

A stationary orbital attack station would be as visible as an ordinary spy satellite, and just as vulnerable. In a war situation, these will be the first objects to be targeted, destroyed, and rendered useless. Also, having them is equivalent to having a nuclear arsenal; every other nation-state would keep a close watch on its owners. A truly effective orbital weapon would not be an Earth-orbit-based station, but a swarm of SEP tugs around the asteroid belt. When ordered to attack, they'd find a nearby rock of the appropriate size, and nudge them to a collision course towards Earth, ideally towards the enemy nation-state. It'll take a long time to commence such an attack, and it can be spotted well before it hits, but there are almost no effective countermeasures against them that doesn't have a significant collateral damage (spaceborne nuke explosion while in the vicinity of Earth's magnetic field generates EMP, which can fry satellites).

It usually takes a few years for a design to be chosen, because there are usually multiple teams working on competing designs. Even after the final design choice is set, multiple manufacturers design competing production lines (this takes about as much time as the initial part design cycle), and make pricing bids on per-product price they are willing to offer. In between, there are a LOT of tests to ensure that the design will do what it was supposed to do, and even more test to see whether the winning manufacturer's product is up to the standards. And that's for measly little parts such as valves. Every single newly-designed components have to undergo that process, which can be difficult for complicated parts like turbopumps. Then there's an entire software design cycle (more of the same) for every program that's written for every computer-controlled part. Then, there's integration tests (does part A actually work well with part B, which part will bottleneck the others, which will wear out before others, etc) to verify that the assembled design won't run into square-peg-gets-into-round-hole problems. With multiple teams working on competing designs, it can be hard to follow what individual teams are exactly doing, potentially making design compliance with other parts a complicated matter. I'd consider us lucky if we can get something as complicated as a cryogenic propulsion stage from the paper to a manufactured product in half a decade. There's so much things in between.

We need further research into human long-term space habitation systems, medical effects of being in reduced gravity for extended periods of time, closed-system LSS, maybe a medical hibernation system. Basically, anything that can keep us alive out there, far away from home. The "getting there" part, I think we can do by EOR-assembling a multistage expendable methalox transfer vehicle by 6-10 heavy-lifter launches, then stacking a two-stage Mars lander, inflatable hab section, and Earth reentry vehicle on the nose. Crew comes up separately after everything is assembled, then goes off to Mars after everything checks out fine.

Ah, I see. I would suggest an identical stack, though. The original Energia stack is already a powerful machine.

This is Energia II, a reusable booster made by strapping wings and landing gear to the same type of booster that once launched Buran to it's only flight. Most of the engine hardware is the same as the standard Energia and Zenit boosters, just stuck on winged tanks.

Since we're talking about nuclear Earth-based SSTOs, I agree with @KerikBalm at their thread that the nuclear lightbulb is the way to go. Barring a pulsed-solid core rocket, it's one of the few reactors that can run hot enough for a sufficiently torch-like performance on almost all situations.

Yeah, it's basically a whole other game. Not impossible, but pretty tricky. Even the HELIOS program whose picture I posted proposed launching it reeled-in, using a chemical booster. That kind of surprised me. 900 seconds is the typical NTR ISP. I was expecting higher ISP at lower TWR.

Launching, I think. would be fine. It's like a plane towing a glider. Atmo entry, on the other hand, might by tricky; I'm thinking about reeling in the payload section at entry, then reeling it back out during descent and landing. Then, after payload section touches down, the engine section must maneuver to touch down a safe distance away. This is a pretty clever way to end up with an exhaust stream hotter than the reactor. It'd be somewhere between pure NTR and pure nuclear-electric rocket, in terms of ISP, I think.

Well, that's the whole point. A pulsed reactor would try to heat propellant by neutron flux rather than through the reactor structure. Though, you can always tow the payload behind the rocket. Also solves the problem of getting stuff/people on and off the rocket, if using a flexible connector. Also worth considering that if propellant cost is less of a concern than reactor fuel, it's useful to have a nuclear rocket motor than has a variable Isp. This allows a lower-output reactor to have a useful TWR at the cost of propellant fraction, which can ultimately save on nuclear fuel costs.

There's a concept for a pulsed NTR reactor here that can boost effective reactor power output by, obviously, pulsing the reactor. From Atomic Rockets section on it:

I agree, that depends a lot on ship configuration. A winged ship can probably land with the propellant tanks still mostly full, but a Falcon-9-style rocket lander would need more propellant for EDL. Drop tanks would be appropriate for the latter. Also, is the setting's tech levels allow for atmospheric ISRU scoops? This is the kind of device that can take in the surrounding atmosphere and stores what it sucks into a propellant tank, to be used later on. That way, the ship can enter the atmosphere with mostly empty or half-filled tanks, fill them on the way down, and land with a mostly full tank. That same scoop can later top up the propellant tank as the ship ascends to orbit, effectively extending the dV capacity of the tank whenever it is flying in atmosphere.