RCgothic

I like short flight times. More seriously, it will allow me to launch spaceplanes into high-latititude orbits uncrewed, or as payload only, and to land science packages in remote locations. My space program is seriously risk-averse, and I figure there's no point sending a kerbal when a probe will do the same job for less mass. And I suppose it's possible I could do the whole thing differently, but this sounded like a nice challenge!

Yeah, I like my polar expeditions so global coverage is kind of mandatory. And although I suppose I could put Communotron 16s in a cargo bay, that feels like cheating! Besides, I'm quite fired up about the challenge now. I'm a little confused how ground stations would be any easier though. You'd have to navigate to and land at, what, 10 different locations? And there'd be massive blind spots near/on the surface caused by the horizon. At least with orbital sats if you get yourself into a terrain blind spot you'll have a sat pass overhead eventually. With a satellite constellation I can get the satellites for each plane deployed in just one launch per each. Then it's just a case of equally spacing the six sats, which is easy. The hardest bit is getting correct phase and inclination to the adjacent plane, but again that's not very difficult with KER. Thanks for the vote of confidence The_Rocketeer! I'll put some pictures up when it's done. Unfortunately my career mode suffered a setback with the off-screen unrecoverable death of Valentina Kerman, which has irritated me to the point of starting again from scratch (No deaths allowed in this Space Program!). I should manage deployment within about a week.

Premise/Introduction Suppose you have a hypersonic probe aircraft (such as a spaceplane) and are using Remote Tech so that it needs to remain connected to KSC at all times. Aerodynamic forces will rip off any operational antenna other than the Reflectron DP-10, which has a maximum range of 500km. Therefore you need to provide a dense satellite relay network so that there is always an uplink satellite within 500km. This will be a big undertaking, so I'd appreciate someone checking my math before I start building. Sorry for the lack of diagrams, I'll try and update with some later. Walker Star Constellation. Because of the short ranges involved, Kerbin Stationary Orbits are out, as are Molinya orbits. Walker Deltas are a little beyond my understanding (though I'd be very interested if someone could design one!), so I'm going with a Walker Star arrangement. Walker Stars generally consist of a number of polar orbital planes, each of which contains a circle of relay probes. These orbital planes co-rotate, such that all the probes on one side are descending N-S, whilst those on the other side ascend S-N. There is a join between the two where the planes contra-rotate. Each orbital plane provides coverage to a 'street', a parallel band which encircles the planet. The probes within each band are carefully phased with those in the next so as to maximise the width of each street, and to minimise the chance of collision over the poles. The orbital planes are evenly spaced except for the gap between the contra-rotating ones, which provides less consistent coverage because the relays cannot be placed in complementary phases. Satellite Antennas There's a choice to be made here: How do the probes talk to each other? If equipped only with Reflectron DP10s, they need to stay within 500km of each other. This requires a large number of satellites per orbital phase, but as they are closer together they can tolerate a ground receiver more offset from the orbital plane, widening the streets and reducing the number of orbital planes. If equipped with Communotron 16s then they only need to stay within line of sight of each other and within 500km of the surface point midway between. However as they are operating more at the extremity of the ground receiver's range they can tolerate less offset, requiring more orbitals. But they can also operate at higher altitudes, leaving the busy 70-100km zones clear. Reflectron DP10 Taking a guess at sats per orbital n=9 gives: Orbital angle between sats T= 40deg Max in-plane angle between sat-ground SOG = T/2 =20deg Kerbin's Radius R = 600km DP 10 max range r = 500km Orbital altitude (guess) a = 75km Sat separation s = 2(R+a)sin(T/2) = 462km (in range!) Altitude of Line of Sight L = (R+a)cos(T/2)-R = 34km (Tight, but I think I can be this precise) Ground Station max in-plane range g = SQRT((s^2)/4 - L^2) = 233km. These parameters all look good so far, albeit a little tricky. Now we calculate the street widths, beginning with the tolerable offset out-of-plane of a ground station for continuous contact with a particular orbital plane. Chordal ground station offset w = SQRT(r^2 - g^2) = 442km Angle ground station offset GOW = 2*sin^-1((w/2)/R) = 21.6deg (half-chord angle doubled so as to exploit right-angled triangle) This is half the angle fully covered by one orbital plane, and half the maximum angle between contra-rotating planes that cannot beneficially phased. By phasing the satellites in the next plane out of phase (or almost out of phase), the areas of maximum out-of-plane coverage interlock to cover weaknesses in the neighbouring plane. In this case the equatorial sats in neighbouring planes will be out of contact with each other, but the signal can be passed north or south until the planes converge again. The maximum out-of-plane angle is calculated: Max out-of-plane angle GOM = cos^-1(((R+a)^2 + R^2 - r^2)/(2*(R+a)*R)) = 45.7deg (Law of cosines) Therefore the max angle between co-rotating planes is: 89deg And contra-rotating is: 86.5deg The minimum number of planes is 3. With a regular plane angle of 60 degrees, the seam angle is 60. Because the sats are quiteclose together there's little difference between the total coverage offset and the max offset. The total number of sats is 27. With the exception of the LoS altitude, the overlaps are all very comfortable and would look very tidy, though it does clutter 75km band. Now let's try communatrons! Communatron 16s Similar to above: Taking a guess at sats per orbital n=5 gives: Orbital angle between sats T= 72deg Max in-plane angle between sat-ground SOG = T/2 =36deg Kerbin's Radius R = 600km DP 10 max range r = 500km Orbital altitude (guess) a = 190km Sat separation s = 2(R+a)sin(T/2) = 928.7km (range was never going to be a problem here) Altitude of Line of Sight L = (R+a)cos(T/2)-R = 39km (About equivalent difficulty to 4x10 DP10 sats) Ground Station max in-plane range g = SQRT((s^2)/4 - L^2) = 466km. So far so good. Now we calculate the street widths, beginning with the tolerable offset out-of-plane of a ground station for continuous contact with a particular orbital plane. Chordal ground station offset w = SQRT(r^2 - g^2) = 181.2km Angle ground station offset GOW = sin^-1((w/2)/R) = 17.4deg Much narrower than the DP10s. Moving on: Max out-of-plane angle GOM = cos^-1(((R+a)^2 + R^2 - r^2)/(2*(R+a)*R)) = 39.25deg (Law of cosines) Therefore the max angle between co-rotating planes is: 56.6deg And contra-rotating seam is: 34.7deg The minimum number of planes is 4. With a regular plane angle of 50 degrees, the seam angle is 30. The total number of sats is 20. This is better than the DP10 equipped probes in pretty much every respect. The narrowness of the seam angle does imply I can do better though! Refining sats per orbital n=6 gives: Orbital angle between sats T= 60deg Max in-plane angle between sat-ground SOG = T/2 =30deg Kerbin's Radius R = 600km DP 10 max range r = 500km Orbital altitude (refined) a = 150km Sat separation s = 2(R+a)sin(T/2) = 750km Altitude of Line of Sight L = (R+a)cos(T/2)-R = 49.5km (much better) Ground Station max in-plane range g = SQRT((s^2)/4 - L^2) = 378km. So far so better. Now we calculate the street widths, beginning with the tolerable offset out-of-plane of a ground station for continuous contact with a particular orbital plane. Chordal ground station offset w = SQRT(r^2 - g^2) = 327km Angle ground station offset GOW = sin^-1((w/2)/R) = 31.6deg Good. Moving on: Max out-of-plane angle GOM = cos^-1(((R+a)^2 + R^2 - r^2)/(2*(R+a)*R)) = 41.65deg (Law of cosines) Therefore the max angle between co-rotating planes is: 73.3deg And contra-rotating seam is: 63.3deg The minimum number of planes is 3. With a regular plane angle of 60 degrees, the seam angle is also 60. The total number of sats is 18. This solution is chosen. Phase There are 6 satellites in each plane. This gives a phase angle between them of 60 degrees. There are three planes, so each is offset 20 degrees from the adjacent. This ensures they're will only ever be one probe passing through the pole at one time. There is some loss of benefit in coverage through probes in adjacent planes being only 20 deg out of phase instead of the whole 30, but in this instance I'm not actually using the additional angle this effect could generate between co-rotating planes so this doesn't matter. Conclusion I'm going to use a constellation of 18 sats equipped with Communatron 16s in a 150km orbit, in 3 planes 60deg apart. That should give full global coverage and I reckon I can get those all in orbit in three polar launches. And let me tell you how relieved I am this didn't come out as a constellation of 80 or so like I thought it would! (But if my maths is wrong and it actually does, please tell me! ) Can anyone do better? (Walker Delta?) Is there an issue with my maths? Sorry for the lack of diagrams, will try and add some later. I'd be interested to hear people's thoughts, or if anyone has ever done anything similar before. Edit: I made an error related to the tangency of the signal to Kerbin on the street widths, resulting in an over-estimation of the coverage. See page 2 for revised details.

The star shaped button to the right of 'Blog This Post' under a user's avatar allows you to thank them by boosting their reputation. I use KER and some spreadsheet calcs to set up my satellite constellations. EG, if I'm aiming for an orbit with a period of 1h30m and 3 sats, I'll inject my launcher into a 1h20m elliptical orbit with the correct apoapsis. It's then a case of dropping off a sat at apoapsis every third orbit and burning with the sat's on-board RCS until the orbital period is correct. My most recent constellations are accurate to milliseconds.

Air gathered is proportion to the volume swept by the intake per second (intake area * speed). The ram does provide more intake area per unit mass, but as it's draggier you won't be going as fast. The shock-cone therefore makes up for its reduced area by increased speed. Speed is crucial to SSTOs. Mass is less important. The shock cone is therefore superior.

As Xannari said, it is possible to build a craft that doesn't flame out up to 30km with a little difficulty, and Mach 1 (320m/s) is about a fifth of the speed you should be able to achieve on air-breathers alone. Sounds like you're not going remotely fast enough, which is why you don't get enough air and flame out. You may be too draggy - too many intakes is a negative, not a plus.

Problem was fixed by uninstalling DRE. Something to do with parts heating up in proportion to their mass, so that small parts get hotter than large ones. Anyway, uninstalled and all now behaving as it should.

I think uninstalling DRE fixed the problem. Just survived a Münar re-entry without issue and the heat shield seemed to be ablating properly. I'm not a masochist; I wanted re-entry heat, not ultra-death mode. Now that stock has added that DRE seems to cause more issues for me than it solves. It doesn't work at all like it used to.

Comments on Vertical Ascent vs Direct Ascent noted and edited. The experiment that showed 833 vs 777 ms-1 is a smaller difference than the maths for TWR of 5 would suggest by about 2/3rds. Then I realised that of course TWR increases during a burn, and thus would naturally reduce the difference between the two escape profiles. For a small payload fraction with a high TWR, the difference may not be much. However, an angled burn will still always win, and for a low TWR (optimised) craft it is especially wasteful to burn straight up.

Just draw a force vector diagram. Say your TWR is 2. Vertical Ascent goes up 2 and down 1 due to gravity. Resultant up acceleration is 1. Alternatively, burn at an angle just enough to hover, but pick up horizontal velocity. (Assume launch from a mountain summit with no obstacles to slam into). With a vertical thrust component of 1 and total thrust of 2, by Pythagoras the horizontal thrust is 1.73. Note the vertical component cancels out with gravity, but the horizontal component remains 1.73! So that this is nearly twice as big as the Vertical Ascent case! You'll reach escape velocity on almost half the burn time and therefore half the fuel. Exact figures vary depending on TWR, but at any reasonable TWR burning horizontally will always be significantly more effective than simply fighting gravity.

There were three modes considered for the Apollo mission. Direct Ascent, in which the entire spacecraft goes to the moon and lands before returning to earth. Earth Orbit Rendevous, in which the components of a Direct Ascent are assembled in earth orbit by multiple smaller individual launches. Lunar Orbit Rendezvous, which is the classic Apollo mission. Of these, Direct Ascent was the front-runner because in 1960 nobody had even achieved a rendezvous, let alone a docking. Lunar Orbit Rendezvous was by far the more efficient, but very much less safe conceptually. Once it was chosen, The Gemini program was launched with the main objective of pathfinding these technologies. Earth Orbit Rendezvous was a compromise between the two. Interestingly the Service Module engine was sized for a Direct Ascent (though the module itself would have been bigger), and was massively overpowered for Trans-Lunar Injection burns. They were stuck with the engine developed for Direct Ascent! Note that the Orion engine is much smaller proportionately. Direct Ascent works best in KSP because proportionately the required DV is a lot less and rendezvous is a hassle. Larger missions both in KSP and planned IRL benefit from both Earth/Kerbin Orbit Rendezvous and Target Orbit Rendezvous efficiencies.

Glad you found my post helpful. Note that the TWRs I mentioned are for atmospheric ascent only. One you're in space TWR matters little compared to engine ISP. I once sent a ship to Duna that was hilariously underpowered. I had to make four burns on successive orbits to break free of Kerbin's influence. But it had great ISP, which is what really matters in space. For an early career mode game I'd have a 1st stage of ~1500 DV powered by an LT-30 engine. Great first stage, but had no gimbal so you'll need a few fins at the bottom. 2nd stage should be sufficient to get you into orbit - use an LT-45 as it has better ISP, ~2200DV should give you enough to reach orbit and complete orbital insertion with a little left over. Should be taking over from the first stage after 15km. It has less thrust but by now you've jettisoned some mass and it has a gimbal so you shouldn't need fins anymore. If you want to actually go anywhere from LKO add a third stage powered by an LV909 which has excellent vacuum I SO.

A few starter tips: 1) There are engines you just do not want to use at sea level. The ISP or MPG as you put it just goes through the floor under any sort of atmospheric pressure. This is an easy pitfall. Right-Click on an engine in the parts list for more information and pay attention to it's ISP at sea level (I_ASL) and in a vacuum (I_VAC). 1st stage engines should have I_ASL of 275 or greater at sea level. Later stages should be I_VAC 320 or better. 2) KER is a great mod. To begin with the info you want to pay attention to is TWR (thrust to weight ratio) and DV. You need TWR to get off the pad and DV is how much useful work your built configuration can manage. 3) Accent speed. You want a TWR of 1.1 to 1.3. If you over-engine a craft you're both wasting DV hauling up engines that you don't need and flying too fast in atmosphere that's too thick. The overpowered rocket is also likely to have stability issues. If you're using an engine that can throttle, TWR of up to 1.5 is acceptable as long as you throttle down a bit around Mach1 (~350ms) to about 75-80% until you're above 10km. The key to an efficient accent is to match terminal velocity. Faster and you fight air resistance too much. Slower and you're basically spending some of your fuel hovering by eating time. For this reason Solid rocket boosters are acceptable to get quickly up to speed (TWR ~2) as long as they are discarded before you overspeed (You can also limit their thrust in the VAB to keep TWR down). It's tricky to tell the terminal velocity, but if you get re-entry heating on ascent you're definitely going too fast. 4) Ascent angle. There's a bit of an art to this. I nose-over to 10 deg at about 100ms and try to aim for 45 deg by 15km, 70 deg by 30km and hold that until my apoapsis breaks atmosphere. Then I shut down engines and circularise at Apoapsis of about 75km. 5) Burn efficiency. The most efficient place to change apoapsis is to burn at periapsis. Similarly to change periapsis burn at apoapsis.

Today my hard no-revert career continued. I spent forever trying to find a Mün return re-entry profile that didn't cause key bits of the ship to explode despite having an unexhausted heat shield. Val survived several mach2 bailouts and my program controller was not impressed by the loss of science and funds on each of these failed attempts. That accomplished, I finally have enough tech unlocked to start setting up some satellite relay networks without their batteries going flat, and the Münar surface beckons at last. I'm still very constrained by a 30 part limit, but that should be taken care of with a planned Minmus flyby. Still no Kerbals killed, and one rescued (scientist). Jeb has performed a Münar flyby, and Val has returned from Münar orbit. Neither Bill nor Bob have yet been beyond suborbital. Bill's not impressed to be outranked by a rescued nobody.

Alt-x solved the same problem for me. I also found that retreating to 900m from the craft caused it to stabilize so I could get back aboard.

It also happens with stock chutes. I've also had the KER module blow up inside the service bay on a few occasions.

Amongst others. I'm using Deadly Reentry too, though my understanding is that's basically been reduced to a parts mod. But I was using FAR and Realchutes before I made the switch from 0.9 to 1.02 without issue, so I figure it has something to do with the new version.

Ok, I had another mission go south and got a few pics. This is from a Mun return mission, but it survived the first two passes alright. I suspect the third pass came in too steep, but there wasn't a huge amount I could do about that. In any case I don't think a parachute should be blowing up under these circumstances.

No, the parachutes are very last in the staging and are not deployed when they explode. To clarify, it's the casings that blow up with the chutes still in their boxes. And I am flying heat shield prograde. I'm currently tier 1 science with only all the 45 Science unlocked.

Since coming to 1.02 after a bit of a break from 0.9, I've been having a problem with my parachutes exploding BEFORE deployment (ie at around 30km whereas I'd usually deploy around 10km and <500m/s.) I first noticed that the radial chutes were exploding no matter where I put them, but recently nose cone chutes have been exploding as well. Atmospheric heating is turned up to 1.2x. I figure what's happening is that the pod is heating up to above the endurance limit of the chutes, but I'm at a loss as to how to prevent it. I've got a heat shield, and in other respects it seems to be doing its job. Pod is correctly oriented with heat shield prograde. Any ideas? Luckily Jeb and Val have both survived bailing out several times, but I'd quite like to be able to land properly. Set up is: Mk1 Pod, nose chute, heat shield. Re-entry from 80km apoapsis to 30km periapsis.

Exactly!

Jeb will not come back from space today. And the battery powering his life support has a shelf life of two hours. At least that's how I thought it would go! I'm on an early career mode game (FAR - TAC LS) with no respawns or reverts, and within the 30 part limit I thought 3,900m/s DV should have been enough to get into LKO and back. Turns out my ascent profile on this occasion was... a little less than optimal. I got Jeb into a 150km/71km orbit. It was at this point that I realised that I had zero left in the tank and the game had just auto-saved on achieving orbit. And I hadn't attached any additional batteries because I wasn't expecting to stay up for even one complete orbit. I couldn't even EVA and hope to survive the re-entry and freefall as I haven't yet upgraded the astronaut complex! After thinking things through for a few moments I realised Jeb DID have one remaining source of propulsion! By orientating retrograde and jettisoning his second stage engines at apoapsis I managed to get his periapsis down to 67km! It was now a race against time between aerobraking and hypothermic death! Three orbits later, apoapsis dropped below 70km. Simultaneously the battery expired and I lost manoeuvring control (no RCS). Unsure whether the parachutes would deploy without power,or even whether I'd survive re-entry without having the ability to orient my heat-shield, I armed two of three parachutes in the upper atmosphere just before the battery expired. They were promptly ripped off by Mach 6 winds. Luckily the capsule did manage to orient itself correctly without them. Jeb survived re-entry, even if by now he was twenty minutes without power and getting a little frosty. In any case the manual main chute release must have been working today, and after a fiery re-entry it deployed correctly. Onto a 30' mountainside. After rolling down the mountainside for what felt like 5km and having both radial parachutes detonate under him, Jeb finally climbed from the pod and used his mobile phone to let the recovery crews know he was okay. I don't think I've ever had such a touch and go situation resolve itself positively!

You don't need geostationary sats. You just need at least one visible from KSC at all times, which you get with a 3-sat constellation in equatorial orbit above minimum altitude for line of sight pretty much by default. The other approach you could take is 'How do I enclose maximum volume', which you get by finding the altitude at which the sats are at maximum range from each other, and then minus a small bit.

Yup, if you insert into 600 km altitude you will need to get the spacing and orbital period exactly right or your satellites will drift behind the planet with respect each other and even then you'll often get obscured by mountains. This is a mistake I first made when starting out with remote tech. I put too much trust into the solution of the equations without adjusting for practical experience. 700 km altitude gives you much more phase error to work with, and allows you to spot angular drift over time and correct it before you lose contact between sats.

Ok, the preparations for the Duna mission continue! Some pics from the launch pad: Tallest rocket I've ever launched! Luckily the mk2 cargo bays are quite rigid. Just enough space to fit in an Ike lander and two remote sats. Also contains the main solar arrays and the expedition's primary RCS tankage and all the life support supplies for the mission. And a mobile lab for good measure. I'll be sending six kerbals, so Jeb is currently sitting on more than 5000 days of life support! Two of these! An orange tank and a half to LKO plus docking attachments. The first stage boosters are rescaled S-1Bs to give enough boost. Then a poodle engine to position in accurate LKO. The first one ran out of power before it could dock, but I did manage to align it north before that happened. The second version included a solar pannel and docked successfully: Unfortunately the were orbiting about 120' behind the service module and exhausted their RCS catching up. The service module piloted by Jeb from the Ike lander completed the docking manoeuvre: And so just one more launch to make: This contains the engines and attaches to the front of the service module. It'll also be ferrying Bill, Bob, Merfield, and two others who I forget the names of to the mothership. Merfield's the pilot on this one. Probably a little under-engined, so it may take several burns on successive orbits to complete the transfer burn!