Lowest Ever Legit Solar Orbit With Evidence?

[Ultimate Steve]

Skipping all the backstory, I'm wondering what the lowest ever legit solar orbit is with the current heating model (or near current). I want to know this so I can maybe have my upcoming space station beat that record.

With the backstory:

Yesterday, a friend of mine, @LittleBitMore challenged me to enter a low polar solar orbit, below 1000 Megameters, about 1/5 of Moho's orbit, for which the prize was one cookie. He offered me 2-3 cookies if I could build a multimodular space station at 1/15 of Moho's distance, or below 333 Megameters, also in polar solar orbit.

I have done a once over of the internet, and the lowest solar orbit I can confirm was by @Foxster back in the 1.0 days in this thread:

The apoapsis was around 271 Megameters. 

However, the heating model may have significantly changed since then.

Recently, I did a test mission in preparation for this challenge, where I was able to obtain a roughly 324x278 Megameter orbit with a probe without exploding before running out of fuel.

After that, I turned on infinite fuel and found I was able to survive until just under 100Mm with that design.

In my testing, I'm reasonably confident I can construct a solar polar space station at 200Mm and still allow the crew to return to Kerbin.

I'm curious as to whether or not this would make it the lowest solar orbit ever achieved legitimately in the game, but I can't find a definitive answer easily on the internet as to what the record is.

 

[Vanamonde]

You'll run into a problem with this. Solar orbits can take a very long time, but if you go into warp, heat gets applied to the craft at an accelerated rate.  You'll have to either fly these runs in real time or be prepared for your ships to explode as soon as you go into warp. 

[QF9E]

For a challenge on this forum I recently did a mission where a probe got to within 100 Mm, but that one was on a highly elliptical orbit. However, I did test the spacecraft I used for that in low circular orbits, and it survived (including at timewarp) to about 80 Mm. Lower than that and even the inflatable heatshield burns up in the heat. You might be able to go lower if you include an extensive thermal control system.

 

[Ultimate Steve]

2 hours ago, Vanamonde said:

You'll run into a problem with this. Solar orbits can take a very long time, but if you go into warp, heat gets applied to the craft at an accelerated rate.  You'll have to either fly these runs in real time or be prepared for your ships to explode as soon as you go into warp. 

I am aware of these issues and have tested and planned around them. As long as I don't go as high as 1000x (or leave to the tracking station for those), I have a design that can survive indefinitely at 200Mm without much hassle.

I intend to have a secondary craft that does go through all the hassle detach from the station and enter an even lower orbit, but the exact altitude is TBD, and it's TBD if I'll circularize or just dip down.

1 hour ago, QF9E said:

For a challenge on this forum I recently did a mission where a probe got to within 100 Mm, but that one was on a highly elliptical orbit. However, I did test the spacecraft I used for that in low circular orbits, and it survived (including at timewarp) to about 80 Mm. Lower than that and even the inflatable heatshield burns up in the heat. You might be able to go lower if you include an extensive thermal control system.

 

Nice job! I'm assuming by test you mean alt f12ing it into an 80Mm orbit? Or did you actually send it there?

[QF9E]

3 hours ago, Ultimate Steve said:

Nice job! I'm assuming by test you mean alt f12ing it into an 80Mm orbit? Or did you actually send it there?

Alt-F12 indeed. Given the orbital speed that close to the Sun it will be a major challenge to circularize your orbit. My craft reached about 74 km/s, and you'll need to lose most of that speed. You could use some gravity assists to your advantage, but that won't bring your apoapse much below Moho's.

[Ultimate Steve]

Well, assuming no counterexamples turn up, I'm tentatively claiming this record.

The only mod installed is better time warp, because without it the ion burns would probably take high single digit or low double digit hours.

The first module of Icarus Station on the launch pad:

The core stage and the nuclear stage push the whole package to an elliptical solar orbit with an apoapsis around Jool so I can do the de orbit and plane change more efficiently (the challenge specified a polar solar orbit). Most of the apoapsis burn was done with the nuclear stage, but I had to do the last 350m/s with ion engines, which was brutal. Even with the 2 Gigantors I had brought in case of this, I could only run 2 of my 8 ion engines at 11.5% thrust. Even at 50x physics warp, it took a long time.

The 20 large xenon tanks are ditched in pairs, except for the last four, which stay with the craft. These give the craft about 28km/s of Delta-V, which is actually a few more km/s than are needed. Right before the first of 3 major Periapsis burns (which are about 2.5 ingame hours each), the gigantors burn up as expected. Power from here on is provided by 2 retractable solar panels placed in mirror mode at an angle so they won't burn up. I've named these solar panels the whiskers, and you can see them in the above picture.

As far as managing time warp, 100x with short bursts of 1000x is the limit at this altitude with this craft. While burns were done with 50x physics warp, and this did lower the temperature, I did leave it at x1 for a while at the lowest point to prove it could survive.

After the first periapsis kick, a short plane change was done to correct our inclination which was like less than 1 degree off of polar, this was about 76m/s.

Second Pe kick went well, but the third one we started too early, which left us in a wonky 185x3xxMm orbit, so we had to withstand the heat all the way down at 185Mm for a while.

Eventually, however, the final orbit is reached, and what fuel remains in the transfer stage is transferred into the station's empty tanks, a last minute addition to facilitate some refueling once I realized I had more Delta-V than I needed.

The whiskers were retracted (that far forward they would melt when facing straight down) and the four rear solar panels are deployed to generate power instead. 

At this orientation, the cupola permanently has a red temperature gauge. That's one of the reasons I chose this altitude, as its the lowest I could reasonably point a Cupola straight down at.

I did run into a bug,  upon loading from the tracking station, the station would always explode due to a heat spike upon loading. Loading the craft from a quicksave doesn't do this. I can get by without tracking station loading it, but if rendezvousing with it has the same effect, I might need to use 5 seconds of ignore max temp to counteract it for future operations.

Ignoring the heat spike upon loading, the station can operate indefinitely at this altitude as long as one doesn't point it in the wrong direction (although most directions are still acceptable). That's another reason I chose this altitude,  it is the lowest I can go without having to maintain a specific orientation behind a heat shield as long as every part there can take 2000K. I did mess up and stuck a 1200K probe core on it, but it is fine because it is in a service bay, although with overzealous time warping, it is often the first part to explode.

Final orbit, just a hair above 199x199 Megameters. Lower is possible even with the same craft, although I'd have to load the save with the engines still attached.

The next step is to somehow rendezvous in this orbit. With no changes, the current tug can get about 9 tons to this orbit with 2 full tanks of xenon remaining. The roadmap is:

1. Science module
2. Crew transfer vehicle
3. Vehicle that will detach from the station and take 1 crew member even lower

That will probably proceed in its own thread in mission reports, however.

[LittleBitMore]

I find it both hilarious and incredible that Steve has:

1: accepted my nigh impossible challenge

2: completed my nigh impossible challenge

3: overachieved my nigh impossible challenge

[Bej Kerman]

21 hours ago, Ultimate Steve said:

The only mod installed is better time warp, because without it the ion burns would probably take high single digit or low double digit hours.

BTW can break sometimes, and lack of precision at high warp factors could have lead to the ship's dV being skewered.

[Ultimate Steve]

Just now, Bej Kerman said:

BTW can break sometimes, and lack of precision at high warp factors could have lead to the ship's dV being skewered.

Thank you, good to know. I did plan out the delta v budget with maneuvers beforehand and added a few km/s extra, and I didn't notice anything too out of the ordinary, but I will keep better track of what is required vs what is expended when I send the crew.

[Ultimate Steve]

1 hour ago, Bej Kerman said:

BTW can break sometimes, and lack of precision at high warp factors could have lead to the ship's dV being skewered.

I did some testing on this, with 2 ships, the first being a very simple ion powered probe with like 5 parts and 10% xenon in the smallest tank, and one being the station core itself. All tests were performed with infinite electricity and the tests near the sun were performed with ignore max temperature on.

I set up the small ship in a very high solar orbit, and then set a maneuver with 0m/s delta-V. I then burned prograde with various time warp levels on. The craft had 291m/s of Delta-V shown by the ingame calculations, and at the end of the burn, these were how much the maneuver registered as having been exerted:

1x - 291.4

4x - 291.5

12x - 237.5

50x - 167.9

50x was the time warp setting I most often used to pilot the station core. I redid that test with the station core itself. The first set of drop tanks held 1755m/s according to the game, and at 50x time warp they did indeed exert 1755m/s.

So given that, I thought it might have something to do with TWR. I redid that test again with the station core, but on its final stage, which held 7861m/s, and sure enough, it exerted 7861m/s. This was the highest TWR that craft could manage, but it was still miniscule compared to the test craft.

So I ran the test again with the small test craft, but at 50% thrust limiter.

12x - 291.5

50x - 189.8

Again with 25% thrust limiter:

50x - 234.0 (I skipped the other tests as they would take forever)

 

So it appears that craft with high TWR underperform with better time warp under those conditions, and the station core is low TWR enough to have no significant deviations under 50x time warp.

However, gravity wells might affect this, and maybe going retrograde might also affect this. I took the test craft at 100% thrust limiter and put it in very low solar orbit. At 50x time warp, on consecutive prograde and retrograde tests, it exerted 167.9m/s or very close to it whatever I did to it. I also performed this test in the original orbit, both prograde and retrograde, to similar results.

I tested the station core at a 200Mm orbit under 50x time warp, which was listed as having 7861m/s:

Prograde but I forgot to set SAS to prograde so it drifted over the course of the burn - 7686

Prograde - 7519

Retrograde - 7674

An underperformance in all cases, but since the burn took place over at least 1-2 hours, and therefore over a significant angular distance, underperformance is expected for the same reason that people do multiple periapsis kicks. I could do it at 1x time warp to test how much of this is time warp and how much of it is due to duration effects, but I don't want to.

 

The only overperformances ever measured were during the first test, where the ion probe did 0.1m/s better under 4x warp, and during a 50% thrust limiter test where the ion probe also performed 0.1m/s better during 12x warp. However this could easily be due to not performing each test perfectly, and a 0.03% overperformance isn't significant.

 

TLDR, at least in the regimes I tested, higher TWR craft tend to underperform, sometimes very significantly with high time warp. The station core (and therefore probably similar craft based on it) are low TWR enough that no underperformance was measured in high orbit. Tests with a high TWR craft showed no significant difference going prograde or retrograde, deep in a gravity well, or on the edge of a gravity well. Tests with the station core showed no prograde/retrograde difference, but deep in gravity well tests were inconclusive due to other factors causing underperformance (burns took a significant time and angular diameter).

Even shorter TLDR: Higher TWR craft tend to underperform at high time warp. The station core is low TWR enough that no underperformance was measured at the time warp value used most commonly (50x). No statistically significant overperformance was ever measured in any tests.

[Ultimate Steve]

I did some more tests because I was curious:

These are all by that test craft high above the sun.

TWR varies slightly over the burn so this isn't 100% accurate, but it is an 0.7% difference.

Assuming these results hold for all craft, I should be able to use 50x time warp on anything with less than about 0.029 TWR without any underperformance, as that is the "critical TWR" number where the graph changes from something asymptotic into more or less a vertical line. 

However, they don't hold for all craft, because the station core has a peak TWR of about 0.12 and it functions just fine. Odd. While the graph does look very cool, I guess it does not show the whole picture. The critical TWR theory is either wrong or varies based on some other factor.

Part count might have an effect, making the game lag differently, but since the Stratzenblits results showing that fuel flow is to blame for most of the part count lag, it would be hard to make a model for... So I'm probably going to end my analysis here and do this sort of test for every craft I add to the station going forward, to make sure it doesn't over or underperform significantly at the expected time warp levels.

 

[Snark]

On 6/20/2022 at 2:34 AM, Ultimate Steve said:

I'm curious as to whether or not this would make it the lowest solar orbit ever achieved legitimately in the game, but I can't find a definitive answer easily on the internet as to what the record is.

I've done a solar orbit whose Ap was under 1000 meters.

As in, a circular orbit under 1 km from the surface of the sun.

To be clear:  I'm quite sure I'm not the only person who has done this, because the reason I did it was that I was using a mod that involved harvesting a resource that was only available in that very thin zone.  If I did it, then I expect a lot of users of that mod would have done it, too.

The mod in question was Karbonite+, and the resource was Karborundum (which is used to power sci-fi engines with unrealistically high Isp).

There are two reasons why a really low solar orbit would be hard:

1. needing monstrous amounts of dV
2. solar heating

I'll happily grant you that effectively I "cheated" on #1, since to get there, I did in fact use the overpowered modded engines.    I didn't do that using stock engines and fuels.

However regarding #2, that was totally legit.  I didn't have any cheating or mods to deal with heat flow; I just spammed the heck out of deployable radiators and was fine.

[EDIT] Never mind, upon further detective work I was able to deduce that I actually did this in KSP 0.90 before the new heat management, and that I was getting it mixed up in my memory with a different thing.  Sorry, my bad. 

Edited June 29, 2022 by Snark
Oops. :-(

[Ultimate Steve]

7 minutes ago, Snark said:

I've done a solar orbit whose Ap was under 1000 meters.

As in, a circular orbit under 1 km from the surface of the sun.

To be clear:  I'm quite sure I'm not the only person who has done this, because the reason I did it was that I was using a mod that involved harvesting a resource that was only available in that very thin zone.  If I did it, then I expect a lot of users of that mod would have done it, too.

The mod in question was Karbonite+, and the resource was Karborundum (which is used to power sci-fi engines with unrealistically high Isp).

There are two reasons why a really low solar orbit would be hard:

1. needing monstrous amounts of dV
2. solar heating

I'll happily grant you that effectively I "cheated" on #1, since to get there, I did in fact use the overpowered modded engines.    I didn't do that using stock engines and fuels.

However regarding #2, that was totally legit.  I didn't have any cheating or mods to deal with heat flow; I just spammed the heck out of deployable radiators and was fine.

1km above the atmosphere that starts at ~600km or 1km above the surface? If the surface, how did you deal with the atmosphere? In my experience radiator spam stops working for me below about 40 megameters, I'd love to see your design.

[Snark]

1 hour ago, Ultimate Steve said:

1km above the atmosphere that starts at ~600km or 1km above the surface? If the surface, how did you deal with the atmosphere? In my experience radiator spam stops working for me below about 40 megameters, I'd love to see your design.

That, unfortunately, I don't remember.  It's been a few years.  I remember that I didn't have to deal with an atmosphere, but the wiki tells me that the sun got an atmosphere in KSP 1.0, and I'm pretty sure this was after 1.0.  For one thing, I'm pretty sure I was running Scatterer, mainly because I remember being wowed by the stark "whiteout / black shadow" effect it gives under super-intense sunlight; and that means it would have been after 2016 when I did this.

[UPDATE]  Ah, nuts.  Never mind.    Turns out that my memory was conflating different things.  I found this old post of mine, which dates my sun-skimming expedition to KSP 0.90, which is before the new heat management.

...and it was PlanetShine, not scatterer, that was giving the cool lighting effects.

So, sorry for the false alarm, I was mis-remembering.  It was in the "easy" days. 

(The thing I was conflating it with, in my memory, was playing with the New Horizons mod, which includes a planet that orbits at 1300 Mm, and the sun has about 2.4x the luminosity of stock, so heat management becomes pretty important.)

[Ultimate Steve]

While I'm here, I may as well post an update. The station has 3 modules now, the core, a science module, and a single use craft that will take one crew down to a 40-50x50Mm orbit. No pictures right now as I'm away from my computer.

I was keeping the next craft a secret until now because I thought I was the first person to do so, but at least two people have done it so there's no point now. The third craft will utilize a oversight in the thermodynamics model to obtain atmospheric science from the sun. This will not be a super low orbit, just a low periapsis, the orbit will be 199x0.6Mm.

This was previously done with an exploit involving fairings, but I independently discovered a similar exploit involving service bays.

Then the next craft will take the crew. They will take the two sundivers out, and then they will head home.

 

[imcute]

does kal overclocking count?if so,----------------------------------------my craft got an eliptical orbit at apoasis 1/5 moho and then melted on that point

[Beamer]

'Legit' in the sense that no cheats or part mods were used (not even better timewarp, basically only MechJeb and KerbalEngineer), I have this station in my career game, it got to 99,999 km periapsis, but with an apoapsis at Kerbin orbit:

IIRC I tried 80 Gm but that was too low, so the minimum for this build is between 80 and 100 Gm. The problem with circular orbits is that you have to turn away from the ever important 'radial in' to get out of the orbit again, which limits your minimum distance unless you shield the sides too. Since this is meant as a permanent station with rotating crew I did not want to do that. Also, at this high eccentricity the time you actually spend close enough to Kerbol to vaporize if you aim the shield wrong is limited to about 2 hours, which is just about manageable for my playing schedule. I only did a few passes at this distance, after which I raised the periapsis to around 1.5 Gm for 'unattended orbiting'.

4 medium and 6 small TCSes and about 20 assorted large and edge radiator panels, all tucked behind a single inflatable heat shield keep it just cool enough. The shield got up to around 92% of maximum temperature before it went down again. It has a Lab, all science equipment, room for 12 Kerbals and is driven by 19 Ion engines and has 28 large Xenon tanks. Done in a single launch. Check the second pic in this post to see it unfolded with the engines running:

 

 

Edited August 25, 2022 by Beamer

[Bej Kerman]

On 7/5/2022 at 6:01 AM, imcute said:

does kal overclocking count?if so,----------------------------------------my craft got an eliptical orbit at apoasis 1/5 moho and then melted on that point

Kal overclocking is a cheat, exploiting a massive hole in the game that the devs left. Open-and-shut.