sevenperforce
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Everything posted by sevenperforce
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@Kergarin I've got the orbital stack down to 1.807 tonnes and the launch vehicle down to 5.074 tonnes but I'm still having trouble with the ascent profile. I know it has sufficient dV to make orbit but only if every drop of propellant is used to the max. Using only a Whiplash, a Dawn, and Ants. Switching out for Panther was not worth it...the Whiplash can get me more extra dV than switching out the mass savings for extra S2 props. The lander can is just so damn bulky or I would try using Junos and Sparks with a horizontally-climbing spaceplane. -
Nice!! I may need to land at a low altitude and lithobrake off the chute, then roll uphill to a better ascent point. If I do that, I'll need renewable power. Monoprop is not worth it with the command pod, but the lander can has 50% more monoprop and is significantly less massive.
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Fascinating!!!! Did not think of that! Though you need a command module to enter, I assume. I will hazard it falls afoul of the "command pod" restriction. I finally managed it. Doughnut and Oscar, four Ants in 3+1 parallel, lander can monoprop to circularize. 1.363 tonnes, 6200 m to orbit with 179 m/s remaining. Still need to work out power and chutes but that's about as slim as it gets with a real command module.
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Western rim of one of the equatorial craters.
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...........and as it turns out, it is. I came up less than 100 m/s short of orbit. This is promising. Would have been easy enough to get out and push, though I was avoiding that on principle. What's the highest elevation on Duna?
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I tried parallel-staging four Ants and two Oscar-Bs from 6400 m and came up woefully short. I wonder if the drag of the lander can would be less punishing at that altitude.
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What's your liftoff altitude?
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@Kergarin I'm doing everything from SL and I'm doing 2.010 tonnes with 147.7 m/s left in LDO. Way overweight but that's SL for you. If I can manage to land above 3 km then I have good feelings about parallel-staging a Dumpling (with one Ant) with a Doughnut (3 Ants) underneath, using a linear thruster and extra monoprop for circularization and rendezvous. Would only shave down to 1.441 tonnes, though. And that's before the chute.
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Just tested and at 660 m over Dunian SL the Ant already has a higher Isp than the Spider, so there's no reason to use a Spider. Paradoxically, the Spider has a slightly higher TWR ratio at SL because it is closer to its maximum Isp than the Ant, but it's a negligible difference.
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I need to test SL thrust of ant and spider on Duna. I can't remember the scale height curve so I am just doing it manually. If Ants can be used then it's huge for terminal Isp....
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I tried clustering Ants because they have higher Isp than the Spiders but ended up with a really anemic TWR. That approach did allow for parallel mounting, though, which meant I could use the monoprop in parallel and add mono drop tanks. I may revisit.
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Fairing is killer. I have my transfer stage mounted on top of my capsule, to allow my Duna landing spark to do its thing from the time the Whiplash separates, and so my fairing is really long. I have tried the Vostok-style capsules but their fairing problem is as bad as the lander can's, and you need to add a reaction wheel anyway. Some of the tanks could prove useful though. Playing around with a Juno-based first stage but no luck so far.
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It's magic. Magic math goblins come behind your ship and push. In all seriousness, though... The Oberth effect works because of gravity. When a spacecraft swings around a planet, gravity pulls it in, then slingshots it back out. It's easy to think of a hyperbolic trajectory as nothing more than a curved path through space, but it's not. The fabric of space, bent by the planet's gravitational mass, acts like an invisible spring, stretching as you zip around it and then relaxing as you careen away. Basic physics teaches that a compressed spring holds potential energy; the same thing is happening (in reverse) during a hyperbolic flyby. Space is stretchy, and that stretchiness allows us to do some cool things. On a trampoline, you can bounce higher if someone else has just jumped before you, because the surface is already stretched. In the same way, if you burn a small amount of propellant before you approach near another planet, you only get a small amount of dV. You'll hit the gravity well, stretch it, and then be slung out. But if you wait until your momentum has already stretched the fabric of space, and burn the same amount of propellant, then your thrust has something extra to push against and so you emerge going much faster. You can also conceptualize it using the forces acting on the spacecraft. Why do you speed up when you are falling toward a planet, then slow down as you are slung away? Well, gravity is pulling you in as you approach, and then it's trying to pull you back as you escape. It uses the same amount of force pulling you in that it uses to try and pull you back. However, when you burn your engine at closest approach, gravity is no longer just pulling on your ship; part of that total force is now being exerted on the propellant you just dumped. You're now moving faster, meaning that gravity has less time to pull you back, and the propellant is now moving slower (relative to its original speed), meaning gravity has more time to pull on it. So total energy is conserved, but you get a boost because gravity spent more time tugging you in than it did pulling you on your way out.
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Docking ports as decouplers
sevenperforce replied to The_Arcitect's topic in KSP1 Challenges & Mission ideas
The regular docking port actually masses less than a decoupler of equivalent size, so......I actually do this pretty regularly. -
I'll have to go back to that model and look it up later. IIRC, though, it was: Lander can full of monoprop Single linear RCS thruster Two small solar panels Cubic strut and small chute Docking port jr Two tiny-sized decouplers Smallest 1.25m tank Spark Roundified prop tank
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I suppose I could loft the can without any monoprop in it, but it seems a waste to leave that capacity untapped. I also converged to a Whiplash+Spark combo rather than a Rapier, but I managed to use the same spark for Duna ascent that I used for Kerbin. Gotta love those roundified tanks. I think my problem remains aerodynamics during Kerbin ascent.
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For a command pod version, can I leave the command pod in Duna orbit and use a seat for the lander? Or does the pod have to land on the surface of Duna to count? I don't see why not. I used monoprop and a single linear thruster for circularization of the module, since it contains its own monoprop reserves. I'm using the mk1 can rather than the pod for mass reasons but aero problems are keeping me right around 6 tonnes.
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My current version, that lands a capsule on Duna and then returns it to Kerbin by chute, is 6.004 tonnes. I have a version at 5.21 tonnes but can't quite make orbit at Kerbin. I found that using a chute-assisted propulsive landing at Duna took less mass than going pure propulsive, and since I had the chute anyway I might as well repack and use it at Kerbin. I suppose I could attach the chute to one of my ascender's drop tanks and thus save a bit of weight for the Duna LV and transfer stage, but I don't know it would save that much. I assume you are, like me, using an ion transfer stage and leaving it in low Duna orbit, while using (primarily) biprop for the Duna ascent?
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Runway Land Speed Challenge (NO SRB)
sevenperforce replied to Galaxystar Kerman's topic in KSP1 Challenges & Mission ideas
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Question -- if one chooses the command pod version rather than the command seat version, must the pod itself land on Duna, or can you simply use a command seat for the landing and use a pod for the return? Also, if you use a pod, is there a requirement that the pod itself land on Kerbin or can you bail out and chute down?
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You need extra rockets for 0-0 abort. You also need a single-use ablative heat shield underneath the hinged portion. You need a way to break the hinge and blow free of the front end of the ship, because it comes up in a lip. If your entire crew section is the capsule, then you need massive chutes large enough to land it safely; if not, then you need an internal interface to get into the permanent portion of the ship, but ones that can be severed instantly in an abort. All of it is verrrry nontrivial.
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Runway Land Speed Challenge (NO SRB)
sevenperforce replied to Galaxystar Kerman's topic in KSP1 Challenges & Mission ideas
This was my very first approach and I found I could not execute the 180 without tumbling. -
With or without the hinge?
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It is emitted as graviton radiation...energetic ripples in the fabric of spacetime that propagate outward forever. That happens, yes, but that's not related to frame-dragging. It would be interesting to evaluate which has a greater effect on orbital decay: general-relativistic frame-dragging, or local drag. A Fermi estimation says local drag but I have no way of knowing without sitting down and doing the math.
