sevenperforce

"Launch an SLS Block 1B Crew with the DSG Power and Propulsion Module and put it into a Cismunar Near Rectilinear Halo Orbit(DO NOT DOCK THE ORION TO THE SHIP!!!) Station part needs 2 docking ports, one at the front and one at the back.(Station part needs solar panels and ion engines.)"

Upon review, the Power and Propulsion Module of the DSG only needs one docking port, since it has its engines on the other side. Updated info on the PPM: http://www.russianspaceweb.com/imp-ppb.html

Look forward to seeing it! My suggestion would be to start with an SRB and edit the config files to make it throttleable and to accept both solid fuel and monopropellant as a resource. The monopropellant can represent the HTP and can also be used for RCS. I think there's a mod that permits differential throttling for SAS; that might be useful too. Well, we certainly aren't going to be transporting the full rocket post-assembly, so you don't have to load the napalm ahead of time. Napalm loading can be done at the launch site but before assembling the rocket. Then the rocket is assembled and the HTP is loaded once erect. HTP is not hypergolic with hydrocarbons unless it is first catalytically decomposed, so that's not too terrible of a problem. Of course it IS hypergolic with some ordinary materials like leather...but, fortunately, such fires have a low enough temperature that the HTP will not spontaneously decompose. Ah, yes...for some reason I was thinking sugar rockets had higher isp, but they don't. You can't have first-stage use of SRBs, simply because burnout times will vary. If one of the side boosters burns out before the opposite one (and it will), the whole stack starts to cartwheel and then rips itself apart, Challenger-style. The only possible use of a first-stage SRB would be as the core, but that wouldn't help much. Our hybrid rocket will have all the thrust we need.

No; what exactly do you mean by that?

Yeah, combustion of the ammonia would definitely be a non-issue. Right, why would it? You miss the point; I wasn't saying anything about the reaction products of an ammonia-oxygen flame. Rather, I was pointing out that for any airbreathing engine, the majority of the thrust comes not from atmospheric oxygen, but from inert atmospheric nitrogen. For orbital aspirations, a ramrocket is not significantly less efficient than a ramjet, and it's a lot easier to achieve. True isp, perhaps. But effective isp is the reciprocal of thrust-specific fuel consumption, which is where you have to take into account the mass flow at the inlet. Even if you are merely pumping water into your nuclear core and mixing the resultant superheated steam-exhaust with the airflow, with no combustion whatsoever, the increase in thrust is massive. You don't have to worry about fine conditions for supersonic combustion, either. A denser exhaust will mix more effectively with the airflow as well; the only downside is that it may only be useful to a slightly lower Mach number (though honestly body heating is a bigger problem). Water/ammonia/whatever will have better in-atmosphere performance than hydrogen, up to its actual exhaust velocity. Secondary combustion contributes only a very small amount of additional energy. Thrust is linearly proportional to propellant density but only proportional to the square root of energy. Dry mass, not wet mass, is the great determining factor for SSTO concepts, particularly for airbreathing concepts which need to carry a heavy fan to orbit and back. Liquid hydrogen masses 71 kg per cubic meter while liquid ammonia masses over 680 kg per cubic meter. This means that even though a liquid hydrogen SSTO may only need to hold half as much propellant mass, the tanks must be 4.8x larger! Hydrogen's high specific impulse means it has a lot of energy but not very much thrust. Couple that with its very high tankage mass and you've got a uniquely low TWR. Some more on that...

Since the scoring for this challenge wasn't particularly clear, I just decided to go ahead and launch the relay cloud for as low cost as possible. Here's my launch vehicle: This is with one relay inside. Relay removed, showing relay cost at 2,175 Kerbucks. Fuel drained, showing per-launch propellant cost at 711 Kerbucks. My reusable launch vehicle costs 19,649 Kerbucks. First launch: That's one small relay down (or up, as the case may be), five to go. Second launch: I'll stack the next four relays in a single set: So let's take stock. 19,649 Kerbucks for the launch vehicle (which I still have) and 6 relays up at 2,886 kerbucks each: Costs to date: 36,965 kerbucks. Now to put those two long-distance relays up! Actually used less fuel on this launch because my margins were closer. Final launch cost (subtracting vehicle) was 9317 kerbucks. Slower ascent, heavier payload. Climbing. Used a more careful ascent to maximize dV. Rocket mode. Let's see how high I can get the Ap on the Rapier alone. Rapier burnout! Nose is still toasty. Opening the cargo bay. Deploying the relays. Had to un-hibernate. First set of panels deployed. I've got an Ant for the propulsion bus. Burning prograde with the propulsion bus until my Pe is orbital. Nice shot. All right, I've got orbit! Renamed so I don't get confused. Closing the cargo doors. I'm coming in from a very high suborbital trajectory without power (at least until I get down to airbreathing altitudes) so this might get messy. Tumbling wildly. Will I survive? Made it! Quick kick from the engines so I can make it to land. Landed! Do I get to subtract the cost of my LV since I recovered it? Anyway, back to orbit: Setting up a node. Burning at Pe. Slow going with the Ant. Didn't quite get there, so I'm warping around for another go. Almost there. Lovely! Swinging out to circularize. Kind of a long burn here. Made it! Nice closeup. Throttled the Ant way down to get an exact orbit. Transferring fuel. One relay away! Going to lower my Pe so I can put this relay opposite the other one. After one orbit... And there's my opposite orbit! Both are exactly opposite with identical periods. If I get to subtract the cost of my RLV, then I did this mission for the low-low price of just 26,633 kerbucks; if not, then the cost was 46,282 kerbucks. Either way, it's pretty impressive.

I think we could load the napalm pre-assembly. And I was using White Lightning for the kick motor design, but a sugar rocket would work too. I was going to say, if anyone has RSS and FAR and the know-how to create the hybrid stack, I'd love to see a sim of it. Well, the one saving grace is that we do have a constant chamber volume, so I think it might be possible to do some preliminary engine dimension calculations with these equations.

Problem: this is KSP; there are no halo orbits. Please advise. EDIT: Possible replacements: high polar munar orbit, low polar munar orbit, very high equatorial munar orbit, very high slightly-inclined munar orbit, munosynchronous elliptic Kerbin orbit.

As @DDE pointed out, ammonia burns quite enthusiastically with atmospheric oxygen. But remember that the atmosphere is 70% nitrogen, so for any airbreathing engine, the majority of the thrust is actually coming from the momentum of the ejected nitrogen. That's why even a NTTR using water as a working fluid would be able to have tremendous thrust simply by compressing air, mixing it with nuclear-heated steam, and ejecting it. But it is enough to get the isp of denser propellants up into SSTO territory and overcome hydrogen's low TWR.

Coming up!

The trouble is that at NERVA temperatures, hydrogen is the only fuel that really outperforms chemical hydrolox in terms of isp. Once you boost temperature a good bit higher (my preference is a ceramic-encapsuled molten-uranium pebble-bed), hydrogen is overkill (and very low-thrust).

From this paper:

The only winning move is not to play.

Now that we know a lot of the variables, does anyone have suggestions for modeling drag more accurately, determining volumetric efficiency more concretely, or firming up any of the other "fixed" variables?

I prefer ammonia or just plain water for the working fluid. If you can get the reactor hot enough you can get as much isp as you need, with MUCH better impulse density. A supersonic-flow ramrocket is MUCH easier to get working than a scramjet.

I suppose it's a tossup as to which is more dangerous, LOX or HTP. But HTP is much easier to work with, as far as equipment and handling expenses are concerned.

Obviously. Just a what-if, though. One could suppose that humans evolved faster cell repair mechanisms, or any other defense mechanism.

@DDE I was thinking more of the immediate health impact, as discovered in the early 20th century. If Curie had not died of cancer, if no one ever got radiation poisoning, etc. Nuclear weapons would still be powerful, but there would be no deadly fallout. Nuclear energy would be completely benign. There would be no need for shielding.

Which prompts an interesting alternate universe.... What if humans and other animals had no (none, zilch, 0%) susceptibility to radiation? Where would we be now?

@Hesp Yeah, like @TheEpicSquared said, this is an entirely aboveboard operation. There's no intention of not raising eyebrows. All the intricacies of licensing and permitting would need to be included in our whitepaper. Thankfully I have a legal background (and career) in addition to my physics degree, so I can probably take care of all that research.

In which I outline the plans for a nuclear-thermal ramrocket SSTO:

These are definitely all elements that need to be determined (or at least examined) during the planning phases, because it's something we can figure out and incorporate into whatever we post/publish. From a sampling perspective, virtually everything we need to know can be determined by sampling HTP tank head pressure and napalm column head pressure in conjunction with onboard telemetry to that point. In fact, we could even write the control program now. But there are things that need to be considered: not just throttle fineness, but throttle response time. It's fine if our throttle can't make fine adjustments, because we can just vary the throttle setting in pulses, as long as throttle response time is rapid enough. We don't want to be stuck with a throttle that takes a second or two to move between positions. It would be nice if we could get away from differential throttling entirely, but we simply can't. There will always be slight inconsistencies in burn time, and with any sort of clustering (or parallel staging, as we are using), those inconsistencies make fire-and-forget LVs wholly unrealizable. Not only do we need high-pressure, high-sensitivity valves, but they have to be capable of electronic control. This is an additional research and investigation topic; how do we control the valves? Do they have individual batteries that receive adjustment signals over a small wire, or do they receive power through a larger carrier wire that provides signals? Is the temperature and pressure well within allowances for the valve, the valve control mechanism, and the wiring? What if a valve fails mid-flight? Do we use redundant valves? Is it more likely to fail-open or fail-closed? Are any valve failures recoverable? Oh, 8 km/s is by no means the maximum; that's just the target I was aiming for. Remember that I've already accounted for aerodrag, gravity drag, and isp losses, so 8 km/s should be plenty to get to orbit. And you can simply increase stage diameter to pretty much instantly add as much dV as you need. Of course, that only holds true up to a point; once you go too thick, the drag assessment is no longer valid. I would have tied the drag number to fineness ratio if I had a good way to model the drag coefficient, but I don't, not for a clustered arrangement. Anyway, if you use slightly more generous assumptions then you can push up to nearly 9 km/s with only a 5% increase in stage diameter: This is something else which absolutely must be incorporated into our whitepaper or whatever it is we publish. Ideally, we need to be able to project a reasonably accurate budget for launching an amateur orbital rocket. There are two options for getting HTP: purchasing medical-grade peroxide and concentrating it ourselves with a fairly simple distillation lab setup, or purchasing it at a premium. In either case, there will be some degree of paperwork and permitting, both for handling and the actual launch. Fortunately, HTP isn't actually good for making real bombs, so that's a bit less of a problem. And while napalm is obviously very nasty stuff, precursors are all available without any special permitting (though, again, we'll want to figure out the necessary steps to avoid visits from the BATF). N2O's specific impulse is far, far too poor. Launch clamps shouldn't be a problem. Hydrogen peroxide is synthesis-able using the anthraquinone process. It might be doable at home. Or one could heat hydrogen peroxide (low concentration, from medicine stuff) to 105 degrees Celsius to let the water boil off. This is something we can discuss at length in our whitepaper. One possible route would be to synthesize or distill peroxide "by hand", to a high enough concentration for single-stage flight testing, and then use the positive press from that to help with some of the hurdles in getting large quantities of the high-purity stuff.

Protip: most challenges will not succeed if they require an insane amount of time and energy to complete what are otherwise fairly mundane activities.

If you set minimum throttle at 40% thrust and calculate ascent phase dV based on average isp rather than start isp, then you can get to 7800 m/s at a 13% diameter increase and a naked-stage TWR uprating to 9:1. This does require that you launch with the core at 40% and the second booster pair at 68% thrust, and throttle the latter down to 40% as well after just 8 seconds, though the higher thrust rating means takeoff thrust is still over 4.5:1. Precisely.

Well, linearity of thrust to throttle setting can be handled via software, so that's not a problem. And while I concede your point about deep throttling, the unattainability of the 10% minimum is more a factor of combustion instability in liquid-fueled engines. Hybrids are, by design, able to handle a wider throttle range. But for conservatism, I'll set 40% as the minimum, and see where things go.