Valyr ssto; is that even possible?

[king of nowhere]

the spaceplane community keeps getting better and better. nowadays an eve ssto is considered pretty standard, and somebody even managed an eve ssto that can save enough fuel to reach gilly.

can you guys step up and make an ssto for valyr?

valyr is a planet in the whirligig world planetary system. It is significantly bigger than Eve, with a surface gravity of 2.17g and 1100 km of radius. speed of a low orbit is roughly 5 km/s. so a valyr ssto would need to have 1.5 km/s more than an eve ssto, and a greater thrust. seems pretty impossible so far.

but valyr has two saving graces in its favor. first, it rotates fast. on the equator, you already have 600 m/s of lateral speed, reducing quite a tad the deltaV requirement. second, its atmosphere, while denser than eve at sea level, thins more quickly, disappearing at 55 km. this translates in less overall drag and less altitude to climb.

with those two factors reducing the cost, going ssto on valyr may quite barely be possible. I think it's not, but I'm throwing this challenge to the spaceplane community because I may be wrong.

alternatively, i'm declaring the winner of the contest whoever comes closer to orbit in deltaV terms. to take this measure, you have to have an apoapsis outside of the atmosphere, run out of fuel, and create a maneuver node to enter a stable orbit. that would show how much deltaV you're missing.

good luck

 

In case somebody manages to orbit valyr, the next step is derbin. derbin is a moon of mesbin, it's as big as valyr but it does not rotate. so it's basically same as valyr, but with extra 600 m/s required. but while I may be wrong on valyr being impossible to ssto, i feel pretty confident that derbin is completely impossible.

a view of valyr. it's basically a bigger version of laythe. according to the science reports, there's life in the oceans.

valyr is lovely, isn't it?

Edited December 3, 2023 by king of nowhere

[camacju]

What are the rules for drag reduction techniques? It's possible to SSTO on Jupiter with stock parts and all the aero tricks in the book, but I don't think it fits with what you're thinking.

[Lt_Duckweed]

The higher dv requirements along with the higher twr requirements cause me to want to lean on the side of impossible with a "conventional" ssto, ie: limited to standard wings.  Eve already chews through lf/ox mix before you get to a high enough speed to make finishing the burn with nervs viable, and Valyr is going to require even more, with higher twr to boot, as well as more prop mass and wing mass.

The saving grace it might have is that the atmosphere is:

1. Much flatter than Eve, with a more reasonable scale height than Eve.
2. Templated off of Laythe, making heating gentler. (Eve, Duna, and Eve/Duna templated bodies have 20% higher shock heating external temp.  This doesn't necessarily translate to exactly 20% part temps, but it certainly does not help)
3.  A light atmosphere by molar mass, raising the speed of sound.

I still think it's probably impossible, but if it ends up being doable, those three factors will be why.

Edited December 3, 2023 by Lt_Duckweed

[king of nowhere]

11 hours ago, camacju said:

What are the rules for drag reduction techniques? It's possible to SSTO on Jupiter with stock parts and all the aero tricks in the book, but I don't think it fits with what you're thinking.

yeah, right, I forgot to mention.

I'm not the greatest expert in aerodinamics, but I'm aware of a few techniques:

1) magic wings, with lift/weight ratio of hundreds.

2) fairing/cargo bay sheanigans, to make parts dragless

3) placing parts and dragging them inside the ship, to close a node without generating additional drag

 

of those, I suppose 3 is allowed (an open node causing extra drag is a game issue anyway). 1 is definitely not allowed, I've seen stuff way too ridiculous based on it. in a normal challenge I would not allow 2, but what the hell, it's probably impossible without it.

any other aerodinamic trick I didn't mention?

 

EDIT: wait a moment, how is it possible to ssto jupiter? all the stock aero tricks will get you out of the atmosphere, but you still need to provide, like, 20 km/s or so of orbital speed...

45 minutes ago, Lt_Duckweed said:

 

The saving grace it might have is that the atmosphere is:

1. Much flatter than Eve, with a more reasonable scale height than Eve.
2. Templated off of Laythe, making heating gentler. (Eve, Duna, and Eve/Duna templated bodies have 20% higher shock heating external temp.  This doesn't necessarily translate to exactly 20% part temps, but it certainly does not help)
3.  A light atmosphere by molar mass, raising the speed of sound.

I still think it's probably impossible, but if it ends up being doable, those three factors will be why.

1) it is much flatter. it starts at 6 atm, but it reaches 1 atm around 7-8 km and it disappears completely at 55 km. so you have to climb roughly 20 km from the higher point you can reach on propellers to the point where drag becomes low, as opposed to 35 on eve

2) I wasn't considering reentry. i used inflatable thermal shields for my mission there. a spaceplane may actually be unable to land in one piece. however, the objective is to take off and orbit.

3) composition is 65% nitrogen 30% hydrogen 2% helium, so it's definitely a lot lighter than eve.

Edited December 3, 2023 by king of nowhere

[Lt_Duckweed]

1 hour ago, king of nowhere said:

1) it is much flatter. it starts at 6 atm, but it reaches 1 atm around 7-8 km and it disappears completely at 55 km. so you have to climb roughly 20 km from the higher point you can reach on propellers to the point where drag becomes low, as opposed to 35 on eve

2) I wasn't considering reentry. i used inflatable thermal shields for my mission there. a spaceplane may actually be unable to land in one piece. however, the objective is to take off and orbit.

3) composition is 65% nitrogen 30% hydrogen 2% helium, so it's definitely a lot lighter than eve.

Yeah I was saying that those ARE the reasons it could end up possible, I went and looked at the cfg file for Valyr.  My logic behind each:

1. Flatter means lower gravity losses due to ascending at a shallower angle.  Not so much a drag issue as an issue of lift growing with speed.  On Eve lift decays with altitude quite slowly due to the large scale height, so you wing incidence will curve your trajectory quite steeply.  Here, the flat atmosphere means a lift guided ascent will still be quite shallow.
2. Aero heating matters a lot for an efficient ascent.  You want to remain lift supported for as long as possible to reduce twr requirements, but at high enough speeds lift supported flight results in burning up.  An extreme example of lift supported ascent is Jool, where the ascent is lift supported all the way to orbital velocity, due to the 0.5 shock temp multiplier for Jool.
3. This results in a atmospheric molar mass of about 19 g/mole, less than half that of Eve (43 g/mole).  Additionally, Valyr has a higher adiabatic index than Eve does (1.4 vs 1.2).  Since speed of sound goes with the inverse of the square root of molar mass, and linearly  with the adiabatic index, this means that for a given temperature, Valyr will have a speed of sound that is approximately 62% higher than Eve.  Temperatures are a little cooler on Valyr than Eve for the relevant ranges so we can call it probably 50% higher.

[RevanX_LSR]

I have some experience on SSTOs around fairly large bodies:

Revan SSTO - 5100m/s orbital velocity (300 rotation) with oxygen up to 1400m/s, ended up with 600m/s, so there was 4km/s of acceleration with about 700 being closed cycle. Towards the end I experienced a huge amount of shock heating, but it shouldn't be too much worse as the speeds involved are lower. So mainly the mass ratio needs to be improved. (Also, the design was not mine but the piloting completely was, and there was extra ion fuel too)