sevenperforce

Well it was never intended to be used much. Anything other than the single EM-1 it was originally planned for. Seriously, here's the thought process: "Let's use NASA to make a big jobs program!" "Well, we need a rocket." "Great, let's make one to explore the moon or wherever." "Or wherever?" "Yeah, like, Mars or the moon or asteroids or something." "Well Orion would sorta work for that, but you're gonna need a bigger rocket to actually lobsomething large enough for meaningful BLEO activities. Otherwise Orion just goes and comes back and that's it." "Fine, fine, we'll make a bigger rocket eventually, but in the meantime let's just build a smaller one to send Orion on a test flight." "Okay, working on it." "Actually the bigger rocket is delayed so we'll just use the smaller one for everything for now." The ICPS was only originally intended for EM-1. That's why it's the "Interim Cryogenic Propulsion Stage". But with the EUS hopelessly delayed, the ICPS is going to end up flying on multiple missions, which it wasn't designed for.

Watch us all get trolled when it's a New Glenn grasshopper test.

Needs more thrust if it is to be used for any sort of variable mission profile.

DCSS is a great stage for the Delta IV but it does not have enough thrust to be terribly useful on top of the SLS.

Not disputing.

If you put a 70-tonne payload on top of ICPS, you could just barely get it into LEO. If you put the same payload in place of ICPS, you could just barely get it into LEO. It is a sucky, sucky stage which doesn't actually improve the throw of a launch vehicle to a given orbit (even though ICPS's BLEO performance is obviously better than that of a bare core).

Indeed. ICPS sucks so hard that Block 1's theoretical LEO payload with ICPS is roughly the same as it would be if you took off ICPS entirely and just sent the core all the way to orbit, DIRECT/Jupiter style.

Common bulkhead. Looks like methalox to me.

I know, right? It was hard to believe, but that was the only explanation. I think I posted about it somewhere...not sure if it was this forum. Ah, here it is. Tracked down which rocket body it was, even.

In this context of orbits around a central body the difference is where the zero point is. Altitude is calculated from the surface of the central body while distance from the center of mass. So a satellite in a geostationary orbit is at altitude of 35,786km above the Earth and distance of 42,164 km from Earth, both at the same time. The difference is the Earth's equatorial radius, 6,378km. All numbers copied from the wikipedia article. https://en.m.wikipedia.org/wiki/Geostationary_orbit The reason for this distinction is that when you're discussing objects close to the Earth, it makes a good deal of intuitive sense to talk about their altitude, just as you would with, say, a plane. A small single-engine prop plane like a Cessna 172 flies at up to 4-5 km. A jet airliner flies at 10-11 km. Weather balloons ascend to 30-50 km, and the edge of space is recognized at 100 km. From there, it's natural to say stuff like "the Apollo missions had a parking orbit at 185 km" and "the ISS orbits 400 km above the Earth." However, as you move outward, it gets tricky. The purpose of most MEO and HEO orbits has a lot to do with orbital periods, so you need the semi-major axis, which depends on the distance from the center of the planet rather than the distance from the surface. Thus, for GEO satellites and stuff like the moon, you'd want to report "distance from Earth", so GEO is 42,165 km distance. Yet that gets even more complicated when we are talking about transfer orbits. Suppose you are going from a 200 km parking orbit out to GEO. You'll need to enter a Hohman transfer orbit with a perigee of 200 km altitude and an apogee of 42,165 km distance. That's confusing. So you end up reserving two different values for GEO; 35,786 km altitude and 42,164 km distance. A transfer orbit is thus described in terms of altitude (200km x 35,786km) even though you'd find the semimajor axis (and thus the period) of that ellipse by taking the actual distance of 6,578 km for the perigee with the actual distance of 42,164 km for the apogee and dividing the sum by two.

Yet without a destination BLEO, they are just left repeatedly rebuilding faux destinations around Orion's lack of capabilities. Not that that's something everyone here doesn't already know.

The purpose of Orion is just so vague. Like, it's the Apollo CSM, except the CM is bigger/heavier and the SM is less capable?

Yeah, really no need to bring up BFR. Do we know which engines are selected for EM-1?

I can do a lot of magic with Tweakscale, but it has its limits. You could still do thrust curves using the selectable segments+various nozzles approach if it was coded such that the thrust would drop as segments "burned out". For example, suppose you stack three segments on top of each other: one with 100% fuel, one with 50% fuel, and one with 25% fuel. Then you'd put an appropriately-sized nozzle underneath. Suppose that with the nozzle size you selected, burntime of a single full segment is 20 seconds. The stack would produce 300% the thrust of a single segment for the first 5 seconds, then 200% for the next 5 seconds, then just 100% for the remaining 10 seconds. The nozzle thus serves to thrust-limit all of the connected segments, but each of the segments still acts essentially as its own separate SRB, and stacking segments results in more total thrust rather than greater burntime. To your point -- you could have the following nozzle pack: 0.625m fixed vacuum nozzle (vacuum Isp: 250) 0.625m fixed SL nozzle (vacuum Isp: 180) 1.25m fixed vacuum nozzle (vacuum Isp: 260) 1.25m fixed SL nozzle (vacuum Isp: 200) 2.5m fixed SL nozzle (vacuum Isp: 190) 2.5m TVC SL nozzle (vacuum Isp: 195) 3.5m fixed SL nozzle (vacuum Isp: 180) The nozzles function to limit the thrust of the segments above them. You can freely put an 0.625m nozzle underneath a 2.5m segment, but the thrust will be no greater than if you put it under a 1.25m or 0.625m segment. However, stacking two segments on top of an 0.625m nozzle results in twice as much thrust.

On the segmented boosters... A more expansive way of doing it would be to create a single solid-segment part with a selector similar to the node-count selector on the thrust plates, that cycles size through 0.625m up through 3.5m. Thus that single part would be able to be used to build multisegment boosters of multiple sizes, and you'd only need the nozzle part for each individual size. You could have vacuum or SL nozzles, TVC or fixed nozzles, etc. But then you'd have to have your thrust limiter on your nozzle, which means you can't very easily build the same de facto thrust curves.

Enabling the "grab" option if you're close enough to another kerbal, perhaps? It would also be cool (but hacked) if Kerbals could fire their RCS from within a command seat.

[snip] Those are 5-meter tanks from Making History. Unfortunately they are skinned identically with the old 3.5-meter tanks so it is tricky to figure out which are which, except by trial and error.

I've seen this bandied about here and there, but I thought I'd pull several different ideas into one discussion thread for simplicity. KSP would benefit greatly from the addition of improved solids. It would only take a very small part pack to open up virtually infinite possibilities. Upper-stage solids Upper-stage solid kick motors are hugely used across the spaceflight industry, but the form factor and Isp of KSP's small solids just don't fit. Proposal: add one surface-attachable vacuum-optimized kick motor. It would have the same size as the new R-4 Dumpling tank (and could even use the same model, albeit recolored) with a large, protruding nozzle. Vacuum isp of 260, low empty vacuum TWR (~10:1), and very good mass fraction (6:1). So its Isp is comparable to the Puff engine, its TWR is slightly poorer than a Kickback, but its mass fraction is comparable to a Separatron. In-atmo Isp of 100. Might be worth it to make an 0.625m and 1.25m variant. Probably not worth it to make a larger variant because you can just cluster the smaller ones. Segmented boosters Larger boosters with more customization options are sorely needed. To that end, I propose a total of three new parts: a 2.5m solid-fuel segment, a 2.5m Fixed Nozzle, and a 2.5m TVC Nozzle. Each 2.5m solid segment would function like a separate solid booster and could have its thrust and fuel load adjusted. In order to be fired, however, they'd have to be stacked vertically on top of a nozzle. When stacked on top of a nozzle and fired simultaneously, they'd all have their own individual thrust levels and fuel depletion, but their thrust vectors would be located in the nozzle they were stacked on. You could create complex thrust curves by varying the thrust level (and/or fuel load) in each segment. The nozzle part would serve as the location of the staging option for the stack (so you can put solid segments into your rocket without a nozzle, but you have no way to stage them). Nozzles have no bottom node. The TVC nozzle has some vectoring ability and is twice the mass of the fixed nozzle. In theory, you can rotate the nozzle to do deflected thrust, though with 2.5m parts this wouldn't be as useful as with smaller SRBs.

How's Germany this time of year? Unfortunately Heavens-Above doesn't really calculate during the day, so a sunset case like this just doesn't show up because passes start later. Here's a list of all Molnya sats -- if you plug each of them into Heavens-Above individually, you can chart whether any of them passed overhead with the "all passes" option: https://www.n2yo.com/satellites/?c=14

Yeah, I wasn't aware that they had fabricated the core yet, let alone attached the SSMEs.

Try using http://www.heavens-above.com/ to get a picture of your sky at that point. I can do it for you but I would need your lat/long and time zone.

Something in a Molinya orbit near apogee would likely appear to be fixed if you only saw it for about 3 minutes.

Could be a chance alignment of light off a stationary comsat. EDIT: Change alignments of light can do crazy things. I once saw the image of the moon literally projected onto a low, diffuse cloud bank, larger than life, 180 degrees opposite the actual location of the moon. Only, the projected image was moving. Turns out it was a shiny rocket stage from an old US launch passing at perigee, and it just happened to be lined up so that the image of the moon was flipped and showed up in the clouds above my head. The projection became smaller and smaller until it met with the actual spot of light that was the rocket body itself.

Read this. So Mars is right out, then.

That's certainly possible. A cutting charge would probably be unnecessary, actually. An MVac engine bell probably couldn't handle more than one re-use anyway so it would likely be replaced as a matter of course. However, even if you used a charge to cut the engine bell, it still has far too much thrust to be used for retropropulsive landing. EDIT: Crazy idea... The Merlin is a GG engine. Could they use it for retropropulsive landing by simply not lighting the engine? If they could vent the gas generator straight into the combustion chamber, it should produce SOME degree of thrust. Actually, now that I recall, the GG vent is outside of the engine, so that won't work. I was thinking of the preburners on Raptor. You could, in theory, run just a single preburner in Raptor (or both and not light it) and you'd have low engine thrust. Merlin uses pintle injectors that cannot easily have their mixture ratios varied. You'd have to use GG pressure to push propellant through without lighting it. Don't know what kind of pressure thrust that would give.