Pand5461

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About Pand5461

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  1. Russian Launch and Mission Thread

    So, a reusable aerospike SSTO. Too good to be true?
  2. [1.3] kOS v1.1.3.0 : kOS Scriptable Autopilot System

    @eberkain ON and WHEN ... THEN triggers only work while the main script is running. Are you sure you activate AG while script is running? To make sure, you can always add WAIT UNTIL FALSE to the end of the main script, effectively putting it into an endless loop.
  3. [1.3] kOS v1.1.3.0 : kOS Scriptable Autopilot System

    @scimas, @kcs123 Note on rotations. R(Pt, Yw, Rl) rotates first Pt degrees around global X axis, then Yw degrees around rotated Y axis, then Rl degrees around rotated Z axis. And R(Pt1, Yw1, Rl1) + R(Pt2, Yw2, Rl2) = R(Pt1 + Pt2, Yw1 + Yw2, Rl1 + Rl2). From this, you can readily see that adding R(0,0,Rl) to any rotation induces additional roll angle. In case of R(Pt1, Yw1, Rl1) * R(Pt2, Yw2, Rl2), rotations are done right to left. I will try to explain what happens in this case. Let istar, itop and ifore be the unit vectors of the rotated coordinate system and ix, iy and iz unit vectors of the global coordinate system. Initially, those triplets coincide. After each rotation, starting from rightmost, the whole space rotates to match global (ix, iy, iz) with the unit vectors defining R(Pt, Yw, Rl) rotation. With each rotation, istar, itop and ifore rotate as if they are nailed to the space. So, SHIP:FACING * R(20,0,0) is the orientation of the ship pitched down 20 degrees, where by "pitch" I mean rotation of the ship around its starboard vector. R() + R(0,0,roll) must be the same as R() * R(0,0,roll), at least my kOS terminal tells me so.
  4. [1.3] kOS v1.1.3.0 : kOS Scriptable Autopilot System

    @kcs123, NORMALIZED suffix is redundant for direction components as they already are unit vectors (saves a few bytes in script and some IPU).
  5. UnHohmann transfers

    The problem when you want some deltaV for guaranteed transfer from A to B is there's no upper bound, really. Subway map gives you dV requirements that guarantee that you can in principle travel from A to B with them. However, you may want to have a ridiculously fast travel (say, 1 hour from Kerbin to Duna) and there will be trajectories with that time but they have ridiculous deltaV requirements. You may want to check Transfer Window Planner mod or web-based Launch Window Planner http://alexmoon.github.io/ksp/ to see how timing the launch and time-of-flight affect the mission deltaV requirements.
  6. That is correct. When you know two true anomalies (i.e. angles from Pe direction), you can easily calculate the difference in mean anomalies which easily translates into the time-of-flight. I'm assuming that first burn matches Ap of transfer orbit with the Ap of target orbit. The transfer will take exactly half of the transfer orbit period, which can be calculated from its semimajor axis. And uh-oh, I forgot to say in the previous post that you have to match apoapses by the first burn for fuel-optimal transfer. This also means that, in general case, you have to split the burn at the transfer orbit Ap to match phases, just the same as in the second case.
  7. Why specify the impulse?

    Not true. The best explanation I managed to find so far (from Levantovsky): Specific impulse is, by definition, the impulse produced by burning unit weight of fuel in an engine. Impulse is measured in Force × Time units, so the units for specific impulse should be Force × Time / Weight. Since weight is a kind of force, the unit of specific impulse is the same as the unit of time. With the introduction of SI in 1960, force is measured in Newtons, and someone clever also noted that it's more natural to specify impulse per unit mass of fuel instead of weight, so the specific impulse becomes the same as the effective exhaust velocity (for rockets, not jets) and should be measured in m/s.
  8. Assuming the initial orbit is circular, there are following cases: Orbits are coplanar Orbital planes are different, target orbit semimajor axis lies on the node line Orbital planes are different, target orbit semimajor axis does not lie on the node line I'm also assuming that initial orbit is lower than target orbit. In the first case, you need to time the first burn to arrive at Ap at the same time the target does. To calculate time to apoapsis for arbitrary orbiting object, you have to use the concepts of mean anomaly and mean motion. Mean motion is the average angular speed of an object in orbit (360° / orbital period), and mean anomaly is time since last periapsis divided by the mean motion. Thanks to Kepler's equation, mean anomaly can be expressed as a function of true anomaly, and from it one can easily get time to apoapsis. In the second case, first burn is to match apoapses in the node opposite to AP, second burn at AP ideally combines matching periapses and inclinations. To get the rendezvous, you'l probably need to split the second burn in two. The second burn raises periapsis to get close approach at the next AP pass and partially corrects inclination, the third one finishes matching orbits. In the third case, first burn is on the side opposite to the highest node of the target orbit to raise the AP, then basically the same procedure of split burn to match orbits and phases but with more trigonometry involved. Also, highly recommend Braeunig website. It has lots of useful information on orbital mechanics and calculation of transfers.
  9. Why specify the impulse?

    After some googling: Looks like it was introduced by the Germans during V-1 and V-2 development. The original definition was probably "the ratio of thrust to fuel flow" and was applied to V-1's jet engine. So, at the time it wasn't even remotely close to the actual exhaust velocity. The effective exhaust velocity might be a better option when they started developing rocket engine but the tradition was set, and the choice of seconds came in handy when Von Braun started working for the US. And... It's rather convenient for aircraft because "we need X kgf of thrust for Y seconds, so have to load X×Y / Isp kg of fuel" makes total sense.
  10. How to calculate Delta V?

    @Physics Student ah, unit conversion may not really be the cause. It's more about how you measure it and what you need it for. Beside being a characteristics of Delta-V, it's also how much thrust the engine produces when supplied with a certain fuel flow. It's especially useful for throttleable engines such as jets. If thrust T is measured in kgf and fuel flow f in kg/s, then Isp = T/f is in kgf / (kg/s) = kgf×s / kg = s (×g0). The Peenemünde team probably used kgf instead of Newtons for force, so they set the tradition both American and Soviet engineers have been following since.
  11. How to calculate Delta V?

    Presumably, a workaround invented in the US while working with the Von Braun's team. Expressed in seconds×g0, exhaust velocity was the same in SI and imperial units. EDIT: Also, a useful characteristics when you want to calculate the amount of fuel in retrorocket to counteract the afterimpulse after stage separation. So, if the afterimpulse is P kgf×s and the Isp of retrorocket is I seconds, then you need to load P/I kilograms of fuel. The same goes for P in lbf×s and fuel mass in lb.
  12. SSSTS - a legacy, attempting to RTLS

    I could. Thing is, I don't even want to try something that will only work for equatorial launches, and I'm a bit overwhelmed by the complexity of the RTLS / RT-droneship program in the general case. So, it's going to take a while.
  13. Fall and Impact of a CZ-3B Booster

    Of course! I forgot about polymer binder in the SRBs. Thanks for the reminder! The lower estimate of NOx from liquid fuel engines mentioned in the source was ~0.5% of water by moles because this is the typical content of LN2 in LO2 of technical purity. So that would be about half a ton of NO per 65t of water. N2 must obviously be present in the exhaust but it's hard to separate it from the usual air (track isotopes ratio, maybe?).
  14. Fall and Impact of a CZ-3B Booster

    @Starman4308 I've re-read the article on NOx release from different fuel pairs - looks like I've exaggerated the harm from hydrolox a bit. The values there are for rockets, not for pairs. So, Space Shuttle, due to sheer size, released more toxic compounds at launch than a Proton (when it does not somersault, that is). Cloud composition at a Space Shuttle launch: 65 t of water, 72 t of carbon dioxide, 38 t of aluminum oxide, 35 t of hydrogen chloride (!!), 4 t of other chlorine compounds (!), 240 kg of carbon monoxide, 2.3 t of NOx (!). It's hard to tell where the nitrogen oxides come from as it may come as byproduct from hydrolox engines and from ammonia perchlorate in SRBs. The aluminum and chlorine come from solid fuel, so it's probably second worst after UDMH+NTO. And no idea why there's CO2. The shift towards cryogenic fuels is likely due to lower operational costs in the long shot. UDMH is synthetic, hence expensive. Methalox is the cheapest mixture because both components are naturally abundant and don't require much refining. Kerolox needs least measures for personnel safety (being gaseous, methane is potentially more dangerous than kerosene). And the advantage of greater specific impulse with cryogenic fuels matters, of course. There's one relatively safe hypergolic mixture, though, kerosene + HTP. It was used on the UK's Black Arrow and is planned for use on Lin Industrial's Taymyr rocket, which resembles Black Arrow in many ways actually.
  15. KSP Challenge: "Target Practice"

    Here's my estimate. Hitting a 5m target from the distance of 12 Mm (radius of Mun orbit) requires angular precision 5m / (12×106m) = 4.17×10-7 rad = 2.4×10-5°. The slowest angular motion you have is the daily rotation of Kerbin which has the angular speed of 360°/6hrs = 0.0167°/s. So, the desired angular precision requires timing accuracy of 2.4×10-5° / (0.0167°/s) = 0.0014s or better. In-game physics tick is 0.02s, an order of magnitude larger. So, unless you're very lucky or know secret throttling techniques to make time of travel an exact multiple of physics tick duration, it's impossible to hit target precisely.