sevenperforce

The engines were on the correct side of the CoM, but there was a bigger problem -- the engine plumes were impinging (just barely) on the cargo bay doors. It wasn't enough to overheat them, but it was cutting my effective thrust to almost zero. It's a shame that KSP doesn't allow you to use differential thrust in place of gimbal when you have a large engine cluster or a situation like this. I realize that with the current engine placement, there's virtually no meaningful pitching torque on the ship as a whole. Differential thrust would be much more effective because the horizontal distance from CoM would be an advantage instead of a hindrance. I'll try rearranging the engines, cargo bay, and fuel tanks so that CoM is 100% balanced at all times during the landing burn.

With yaw authority turned off for the Thuds and roll authority turned off for all but the rearmost pair, I can now throttle up gradually without flipping over. I think that attempts to correct minor variations in yaw were misaligning the Thuds and causing it to flip. However, on the landing approach I am telling SAS to hold the internal docking port to retrograde, so that it will try to make the belly face prograde. So constant nose angle isn't the problem. Since nose-down is my main problem right now, I think I'll try turning off pitch authority for the rearmost Thuds and see if that helps. EDIT: Going to try some Grasshopper tests:

Actually, that was happening at about 4 km. Anyway, starting with the canards feathered up for entry and then down for descent solved the nose-down problem completely, if you look at the most recent photo examples. I've got entry and descent licked; the only remaining problem is the actual landing approach. I go from level, stable flight with no control input other than SAS: ...to opening the bay doors, still stable despite a little added drag: ...to throttling up the Thuds slowly, with corresponding instability: ...and then suddenly I roll to one side (which makes no sense; the gimbaled Thuds should have tons of roll authority): ...and dropping like a brick: Maybe the Thuds are trying to control yaw and are throwing everything out of whack. I'll try it again with yaw authority off on all engines and roll authority only on one pair of the tail engines. I'll need to account for the fact that roll is yaw and yaw is roll for this control scheme, incidentally.

A few changes. Going at it with the canards inverted for landing approach.

Yeah, exactly. Although I was thinking it would stay nosed up a little on landing approach; basically, stable at a high angle of attack due to body lift. Hmm, I had been trying to punch the vertical engines, suicide-burn style. I'll try throttling them up more gradually and seeing if I can do a more controlled landing approach. I don't open the main cargo bay on EDL. Though yeah, it's a touch unstable in yaw. Going to more level flight rather than trying to do a straight-down drop has helped with that. I'm intentionally not using any RCS or reaction wheels during the descent or landing approach. If I'm throttling up the aux thrusters slowly, I might kick on the RCS at that point, just to help a bit.

Hmmmm, interesting. What if I try flying it at a very high AOA rather than truly belly-first? E.g., gliding like a brick. That might be able to give me passive stability, and since the Thuds have a decent gimbal range, I can cancel my horizontal velocity pretty easily. Doing some redesign work... Okay, here, this seems to work a bit better. Seems like I'm making progress...

With on-orbit refueling, I have plenty of dV for pretty much anywhere. The Vector's aren't ideal for space, true, but I can replace them with Darts once I get the design perfected; I just need the Vectors to get off the ground. First goal is second stage to LKO and propulsive biconic EDL. The notion of using the same design for executing propulsive EDL followed by SSTO on Duna is secondary.

With the rocket equation. 348 seconds of specific impulse times one gee times natural log of 316 million short tons divided by the mass of the Earth equals 104.6 km/s. https://www.wolframalpha.com/input/?i=(gravity+of+Earth)*(348+seconds)*ln((316+million+short+tons)%2F(mass+of+Earth)) EDIT: 348 seconds was a vacuum specific impulse for kerolox off the top of my head. That's the MVac D. I think the maximum theoretical specific impulse of kerolox is something closer to 358 seconds, which gives you 107.6 km/s. If you want to do something exciting, like going nuclear with a notional specific impulse of 900 seconds, you get a much more impressive 270.5 km/s. To get to galactic escape velocity from our current location and orbital velocity, you'd need to throw your "fuel" at around 1,060 seconds of specific impulse. ANOTHER EDIT: Of course, if you have a perfectly-efficient mass-to-energy conversion engine, you can accelerate Earth to galactic escape velocity for the low, low price of just 0.11% of its mass. Which is 6.33e21 kg, or roughly half the mass of Pluto. Given the influence of relativistic effects at this scale, your mileage (literally) may vary.

I did the same thing. I had my sound muted and so I didn't ever realize it was on a loop.

I've seen the flags-and-footprints-to-Venus video before -- it's awesome to watch. With unlimited funds, how WOULD one do an actual flags-and-footprints on Venus? Kerbals can survive basically anywhere but humans...ehh, not so much. 104 km/s. That's if you count humanity as your payload and dry mass.

I've never used Aero Forces before but I'll activate it and take a look. As for the SPH vs the VAB, I've been playing in Demo for so long that I have no trouble thinking vertically in the VAB. I built Demo shuttles in that thing, haha. I want a multipurpose interplanetary reusable second stage with integrated crew and cargo capability. The idea is to refuel this in orbit and send it pretty much anywhere in the solar system; when needed, I'll send a tanker along with it to refuel at the destination. The aux thrusters will allow me to make propulsive landings on unprepared surfaces. That's easy enough to do on the Mun, etc., but much more challenging on Earth or Duna, where I need to take aerodynamics into account. The purpose of high thrust on the aux thrusters is to be able to lift off vertically on Duna with enough propellant to reach orbit.

Well, slight correction -- I don't need an SSTO; this is a second stage. I've been using it bare as a single suborbital stage for testing purposes, but I would throw it on top of a booster for actual launches. Also, I want nose-first prograde stability going up (which isn't too hard, since I have Vectors on the tail), but I want biconic passive aerodynamic stability coming down. I'm landing on auxiliary thrusters inside downward-facing cargo bays; it lands on its belly like a Star Wars ship. Nose-first on ascent, belly-first on entry, descent, and landing. I'm not actually using RCS Build Aid (I don't have any mods, in fact; I have been playing demo KSP for about a year but I just got the full game a couple of weeks ago), but since I've set the side-mounted tanks to drain last, COM remains constant after the center tanks drain.

Here you go. I replaced the rearmost elevon with a canard that I rotate when I deploy the elevons and airbrakes; that seems to help a little bit. I have control authority turned off for the canards, airbrakes, and elevons, though I'm not sure whether that does more harm than good. Only aerodynamic control authority is the elevons mounted on the side tanks. Should I give the elevons roll authority and give the canards pitch authority? I've edited the advanced tweakables so the center tanks drain first; once they drain, the CoM stays constant since it is right at the center of the side-mounted tanks. The CoT is shown with the rear engines at zero throttle; I've differentially throttled the aux engines to make sure the CoT is right under the CoM.

Yeah, that's what I've been attempting, pretty much. Just not having much luck with the control surfaces working the way I want.

Precisely what I don't want to do, haha. Passive aerodynamic stability is the goal here.

LOL. Yeah, I've got COM/COT down; that's not a problem. The problem is getting center of pressure behind center of mass while dropping belly-first.

I've been wanting to build a reusable manned upper stage that can execute a biconic lifting-body re-entry (like the Shuttle or the ITS proposal), but then come down to land on its belly via auxiliary thrusters. However, no matter how much I try, I can't get passive aerodynamic stability. I can hold pretty well through entry, but it tends to flip or spin during descent, so I can never be anywhere close to the right orientation to stick the retropropulsive landing. Here's the design I've had the most success with so far, albeit without any actual success: I've got a probe core stuck in one of the cargo bays to switch control so I can tell it to stay retrograde, belly-first, but when I try, it ends up spinning wildly. What am I doing wrong?

Anything beyond "it's a Dragon and it's going to land on Mars" is pure speculation at this point. If SpaceX can only do that much with it, it will still be a win. Anything it actually does on the surface beyond saying "I'm here! I made it!" is just icing. Actually, we do have a bit more than pure speculation. There is already NASA-related mission planning regarding spacecraft contact duration with the Deep Space Network; expected post-landing contact lifetime is something like 30 hours. So it will be on internal battery power until it dies. The mission is mostly about testing hypersonic and supersonic retropropulsion with landing on unprepared surfaces.

Pig iron and plutonium, baby.

I'd wanna see the ITS fully funded immediately, with NTR, LANTR, and VASMIR research funded simultaneously. Then, start building some orbital solar arrays for laser-pumped reflector ships. Von Neumman probes next.

You pretty much have to start with the formation of the planet and come up with a way for it to be spinning that fast, and allow the planetary evolution to guide you from there. Because composition, density gradients, and rotation are all interdependent and arise based on planetary formation route. That itself is an interesting question. How could you get a planet spinning ridiculously, ridiculously fast? What mechanisms would produce that result? Conservation of angular momentum is a cold and inflexible mistress.

The supergiant planet Mesklin in Hal Clement's Mission of Gravity is a similar example: it has a solid surface with a very high rotation speed, resulting in roughly 3 gees of gravity at the equator and several hundred gees at the poles. Clement depicts the planet as an extremely oblate spheroid, but in reality it would be almost a flat rotating disc.

I liked this challenge so much that I made another entry. This one had slightly higher scores. Eye of the Needle: +1000 How's the Weather up there?!: +100 Meep Meep: +100 Jet Ski: +100 Wet Nellie: +500 West Koast Kustom: +500 Total: 2300

Lovely orbit, great launch. Excited to see whether there is fairing recovery. Anyone know whether Go Searcher is out there? I haven't been over to NSF in a while so I don't know. I saw they kept the Stage 1 trajectory in view.

Well they got GTO and GEO confused. GTO is a Hohmann Transfer to GEO.